Current collector for non-aqueous secondary battery, electrode plate for non-aqueous secondary battery using the same, and non-aqueous secondary battery

An object of the invention is to provide a current collector for a non-aqueous secondary battery in which the strength of the current collector is sufficient in forming an electrode plate and an active material can be efficiently disposed on the protrusions of the current collector, and to provide an electrode plate for a non-aqueous secondary battery and a non-aqueous secondary battery using the same. The invention relates to a current collector for a non-aqueous secondary battery, including a metal foil for carrying at least a positive electrode active material or negative electrode active material. Protrusions are formed in a predetermined arrangement pattern on at least one face of the metal foil and at least tops of the protrusions are not compressed. The arrangement pattern includes: a row direction in which the protrusions are aligned linearly at an equal pitch; and a column direction in which row units comprising a group of the protrusions aligned in the row direction are aligned in parallel at a predetermined interval. The respective protrusions of any one of the row units are displaced in the row direction from the protrusions of another row unit that is adjacent in the column direction. The invention also pertains to an electrode plate for a non-aqueous secondary battery and a non-aqueous secondary battery using the same.

RELATED APPLICATIONS

This application is the U.S. National Phase under 35 U.S.C. §371 of International Application No. PCT/JP2007/072220, filed on Nov. 15, 2007, which in turn claims the benefit of Japanese Application No. 2006-308773, filed on Nov. 15, 2006, Japanese Application No. 2006-312600, filed on Nov. 20, 2006, Japanese Application No. 2006-313790, filed on Nov. 21, 2006, Japanese Application No. 2007-059444, filed on Mar. 9, 2007, and Japanese Application No. 2007-296871, filed on Nov. 15, 2007, the disclosures of which Applications are incorporated by reference herein.

TECHNICAL FIELD

The invention relates to a current collector for a non-aqueous secondary battery such as a lithium ion secondary battery, and to an electrode plate for a non-aqueous secondary battery and a non-aqueous secondary battery using the same.

BACKGROUND ART

Recently, lithium ion secondary batteries (hereinafter referred to as simply “lithium secondary batteries”) have been increasingly used as the power source for portable electronic devices. They use, for example, a carbonaceous material capable of absorbing and desorbing lithium as the negative electrode active material, and use a composite oxide containing transition metal and lithium, such as LiCoO2 (lithium cobaltate), as the positive electrode active material. By this, secondary batteries with high potential and high discharge capacity are realized.

However, with the recent increase in functionality of electronic devices and communications devices, it is desired to further improve the performance of lithium secondary batteries, in particular, to reduce performance degradation due to charge/discharge cycles.

Generally, an electrode plate, which is a power generating element of a lithium secondary battery, is produced by mixing and dispersing a positive electrode active material or negative electrode active material, a binder as a binding agent, and optionally a conductive agent in a dispersion medium, applying the resulting paint mixture onto one face or both faces of a current collector, drying it, and pressing it to form a positive electrode mixture layer or negative electrode mixture layer.

One cause of performance degradation due to charge/discharge cycles is a decrease in the adhesion between the positive electrode mixture layer or negative electrode mixture layer applied onto the current collector and the current collector. This occurs because the expansion and contraction of the electrode plate due to charge/discharge decreases the adhesion of the positive electrode mixture layer or negative electrode mixture layer at the interface of the current collector, thereby causing it to separate therefrom.

To increase the adhesion between the positive electrode mixture layer or negative electrode mixture layer and the current collector, attempts have been made to increase the interfacial contact area of the current collector. In this case, the surface of a current collector is usually roughened by a method of etching the surface of a current collector by electrolysis or a method of depositing constituent metal on the surface by electrodeposition.

As another method to roughen the surface of a current collector, there has been proposed, for example, a method of causing fine particles to collide with the surface of a rolled copper foil, which is the material to be processed, at a high speed to form minute protrusions and depressions on the surface (see, for example, Patent Document 1). There has also been proposed a method of irradiating a metal foil with a laser beam to form protrusions and depressions whose surface roughness is 0.5 to 10 μm in 10-point average roughness (see, for example, Patent Document 2).

Also, reducing the thickness of the applied electrode mixture layer to enhance power density results in a decrease in energy density. To avoid this dilemma, it has been proposed to increase the surface area of a current collector in order to increase the contact area of the electrode mixture layer and the current collector, as illustrated inFIG. 27. In the example illustrated in this figure, a metal foil current collector61is sandwiched between a pair of guide rollers62and63to form protrusions and depressions on the surface thereof (see, for example, Patent Document 3).

Also, to obtain a current collector for a lithium secondary battery that can firmly retain an active material and has good electrical conductivity, it has been proposed, for example, to form a metal foil into the shape of a corrugated sheet having ridges and grooves, so that one face of the metal foil is recessed while the other face is raised, as illustrated inFIG. 28(see, for example, Patent Document 4).

Further, to obtain an inexpensive, long-life lithium secondary battery having good power characteristics and little variations in capacity, power, etc., there has been proposed a method of forming depressions and protrusions by embossing, filling the depressions with an active material, and making the surfaces of the protrusions exposed or covered with the active material, as illustrated inFIG. 29(see, for example, Patent Document 5).

Another known method for producing an electrode plate for a lithium secondary battery is a method of forming a thin film of an active material on a current collector by electrolytic plating, vacuum deposition, or the like. In this method, the adhesion between the current collector and the active material is also essential to obtaining a stable battery. For example, with the aim of obtaining an electrode plate for a lithium secondary battery having a large discharge capacity and excellent charge/discharge cycle characteristics, a method of forming an active material thin film on a current collector made of a metal not alloyable with lithium has been proposed. In this method, the value: (the surface roughness Ra of the active material thin film)−(the surface roughness Ra of the current collector) is set to 0.1 μm or less (see, for example, Patent Document 6).Patent Document 1: Japanese Laid-Open Patent Publication No. 2002-79466Patent Document 2: Japanese Laid-Open Patent Publication No. 2003-258182Patent Document 3: Japanese Laid-Open Patent Publication No. Hei 8-195202Patent Document 4: Japanese Laid-Open Patent Publication No. 2002-270186Patent Document 5: Japanese Laid-Open Patent Publication No. 2005-32642Patent Document 6: Japanese Laid-Open Patent Publication No. 2002-279972

DISCLOSURE OF THE INVENTION

Problem to be Solved by the Invention

According to the surface roughening method described in Patent Document 1, a current collector having random protrusions and depressions locally can be formed. However, it is difficult to form uniform protrusions and depressions in the width direction and longitudinal direction of the current collector, since there are variations in the speed of the fine particles sprayed from the nozzle.

According to the metal foil roughening method described in Patent Document 2, depressions can be formed by irradiating the metal foil with a laser beam to locally heat and evaporate the metal, and protrusions and depressions can be formed throughout the metal foil by continuous irradiation. However, since the laser is applied linearly, the metal foil is locally subjected to heat equal to or higher than the melting point of the metal. It is thus difficult to prevent the metal foil from becoming corrugated, wrinkled, or warped due to the heat. Further, when a metal foil with a thickness of 20 μm or less such as a current collector for a lithium secondary battery is subjected to a laser process, the metal foil may be undesirably perforated due to laser power variation.

In the case of the current collector production methods of Patent Document 3 and Patent Document 4, the metal foil is so structured that the backside of a depression on the surface side is inevitably a protrusion, and it is thus difficult to prevent the metal foil from becoming corrugated, wrinkled, warped, etc., during the formation of the protrusions and depressions.

According to the electrode production method described in Patent Document 5, since a punched metal with an open area ratio of 20% or less is embossed to form protrusions and depressions, the strength of the current collector lowers, which may cause a problem of breakage of the electrode plate.

In the case of the electrode for a secondary battery described in Patent Document 6, the value: (the surface roughness Ra of the active material thin film)−(the surface roughness Ra of the current collector) is set to 0.1 μm or less. As a result, the adhesion between the current collector and the active material thin film becomes stable. However, if the active material thin film contains a metal which expands significantly upon lithium intercalation, the adhesion between the current collector and the active material thin film becomes weak. Thus, the electrode plate may become wrinkled and a problem of degradation of charge/discharge cycle characteristics may occur.

Also, Patent Documents 1 to 6 are silent as to any problem which may arise when electrode plates (a positive electrode plate and a negative electrode plate) are prepared by using current collectors with protrusions formed thereon and these electrode plates are wound with separators interposed therebetween to form an electrode assembly. However, as illustrated inFIG. 30, a positive electrode plate70and a negative electrode plate72are spirally wound with separators74and75interposed therebetween to form an electrode assembly. Between the inner side and the outer side of this electrode assembly, there is a difference in the curvatures of the positive electrode plate70and the negative electrode plate72. Thus, when protrusions are formed on the surface of a positive electrode current collector69or a negative electrode current collector71at an equal pitch, the pitch at the end of the protrusions is wide on the inner side and narrow on the outer side.

Further, in an electrode assembly formed as described above, the positive electrode plate and the negative electrode plate are curved, and the pitch at the end of protrusions76is wide on the outer face of a current collector75and narrow on the inner face, as illustrated inFIG. 31.

The invention has been made in view of the problems described above, and an object of the invention is to provide a current collector for a non-aqueous secondary battery in which the strength of the current collector is sufficient in forming an electrode plate and an active material can be efficiently disposed on the protrusions of the current collector, and to provide an electrode plate for a non-aqueous secondary battery and a non-aqueous secondary battery using the same.

Also, another object of the invention is to provide a current collector for a non-aqueous secondary battery in which the strength of the current collector is not adversely affected by the difference in curvature between the outer side and the inner side of an electrode assembly and the difference in curvature between the outer face and the inner face of the electrode plate when the electrode assembly is formed by spirally winding positive and negative electrode plates, and in which an active material can be efficiently disposed on the current collector, and to provide an electrode plate for a non-aqueous secondary battery and a non-aqueous secondary battery using the same.

Also, still another object of the invention is to provide a highly reliable current collector for a non-aqueous secondary battery in which when protrusions are formed on both faces of a metal foil current collector, the arrangement of the protrusions at corresponding positions can be adjusted so that the current collector is prevented from becoming corrugated, wrinkled, warped, etc., during the formation of the protrusions thereon, and to provide an electrode plate for a non-aqueous secondary battery and a non-aqueous secondary battery using the same.

Means for Solving the Problem

In order to achieve the aforementioned objects, a current collector for a non-aqueous secondary battery of the invention includes a metal foil for carrying at least a positive electrode active material or negative electrode active material. Protrusions are formed in a predetermined arrangement pattern on at least one face of the metal foil, and at least tops of the protrusions are not compressed. The arrangement pattern includes: a row direction in which the protrusions are aligned linearly at an equal pitch; and a column direction in which row units comprising a group of the protrusions aligned in the row direction are aligned in parallel at a predetermined interval. The respective protrusions of any one of the row units are displaced in the row direction from the protrusions of another row unit that is adjacent in the column direction.

Also, a current collector for a non-aqueous secondary battery of the invention includes a metal foil for carrying at least a positive electrode active material or negative electrode active material. Protrusions are formed in a predetermined arrangement pattern on at least one face of the metal foil, and at least tops of the protrusions are not compressed. The arrangement pattern includes: a row direction in which the protrusions are aligned in a zigzag at an equal pitch; and a column direction in which row units comprising a group of the protrusions aligned in the row direction are aligned in parallel at a predetermined interval. The intervals between each of the protrusions and all the protrusions adjacent to each of the protrusions are equal.

Preferably, the current collector is shaped like a long strip, the longitudinal direction of the current collector agrees with the column direction while the width direction of the current collector agrees with the row direction, and the interval at which the row units are aligned decreases gradually from one end of the current collector in the longitudinal direction thereof toward the other end.

Also, preferably, the protrusions are formed on both faces of the metal foil, and the protrusions on one face of the metal foil are out of phase with the protrusions on the other face of the metal foil in the row direction.

Preferably, the protrusions are formed on both faces of the metal foil, and the interval at which the row units are aligned in the column direction on one face of the metal foil is greater than the interval at which the row units are aligned on the other face of the metal foil.

Preferably, one face of the metal foil has the protrusions in the arrangement pattern while the other face is a flat surface, and the flat surfaces of two or more such metal foils are bonded together.

Preferably, one face of the metal foil has the protrusions in the arrangement pattern while the other face is a flat surface, the metal foil is folded at a predetermined position, and the flat surfaces of the folded metal foil are bonded together.

Effect of the Invention

According to the current collector for a non-aqueous secondary battery of the invention, protrusions are formed in a predetermined arrangement pattern in such a manner that at least the tops thereof are not compressed. Thus, produced current collector is highly durable. Also, in the step of forming the protrusions on the surface of the current collector and the step of disposing an active material on the protrusions, the current collector is prevented from becoming locally deformed or distorted. At the same time, in the step of disposing an active material on the protrusions of the current collector and the subsequent step such as slitting to a predetermined width, the separation of the active material can be suppressed. Therefore, by using this, it is possible to produce a highly reliable non-aqueous secondary battery.

Also, according to the non-aqueous secondary battery of the invention, when an electrode assembly of a non-aqueous secondary battery is produced, it is possible to reduce the difference in bending stress exerted on the electrode plate resulting from the difference in curvature of the electrode plate between the inner side and the outer side of the electrode assembly. It is also possible to reduce the difference in bending stress exerted on the electrode plate resulting from the difference in curvature of the electrode plate between the outer face and the inner face of the electrode plate. By this, in the step of spirally winding the electrode plates to form an electrode assembly, the misalignment of the wound electrode plates and separation of the active material can be suppressed. Therefore, by using such electrode plates, it is possible to produce a highly reliable non-aqueous secondary battery.

Also, according to the electrode plate for a non-aqueous secondary battery of the invention, a current collector, which is a constituent element of the electrode plate, is produced by forming a large number of uncompressed protrusions on one face of the current collector while making the other face a flat surface, and bonding the flat surfaces together. By this, the phase of the protrusions on one face and the other face of the current collector can be freely adjusted. It is therefore possible to match the strength characteristics of the electrode plate to the characteristics of the active material. Also, by making the protrusions on one face and the other face of the current collector out of phase with one another, a large resistance to stress can be obtained. Hence, in the step of forming the protrusions on the surface side of the current collector and the step of disposing an active material on the protrusions of the current collector, it is possible to prevent the current collector from becoming locally corrugated, wrinkled, warped, etc. Also, by making the protrusions on one face and the other face of the current collector in phase with one another, the flexibility of the electrode plate can be heightened. Thus, when such electrode plates are wound to form a battery assembly, the separation of an active material can be prevented.

BEST MODE FOR CARRYING OUT THE INVENTION

The invention is directed to a current collector for a non-aqueous secondary battery, including a metal foil for carrying at least a positive electrode active material or negative electrode active material. Protrusions are formed in a predetermined arrangement pattern on at least one face of the metal foil, and at least tops of the protrusions are not compressed. The arrangement pattern includes: a row direction in which the protrusions are aligned linearly at an equal pitch; and a column direction in which row units comprising a group of the protrusions aligned in the row direction are aligned in parallel at a predetermined interval. The respective protrusions of any one of the row units are displaced in the row direction from the protrusions of another row unit that is adjacent in the column direction. With respect to the shape of the protrusions, at least the tops thereof can be substantially circular.

Also, as described later, the protrusions are formed by applying a compression process to a metal foil by using a roller or die having corresponding depressions. At this time, the portion of the metal foil facing the portion having no depressions is compressed, so that the portions of the metal foil facing the portions having the depressions are raised. In this way, plastic deformation occurs. As a result, the protrusions are formed. It should be noted that when the protrusions are formed, their edges (tops) are not in contact with the bottom faces of the depressions, and thus at least their tops are not compressed.

The aforementioned arrangement pattern of the protrusions exhibits a large resistance to stress. Thus, in the step of forming the protrusions on the surface of the current collector and the step of disposing the electrode active material on the protrusions of the current collector, it is possible to prevent the current collector from becoming locally deformed or distorted. At the same time, in the step of disposing the electrode active material on the protrusions of the current collector and the subsequent step such as slitting to a predetermined width, it is also possible to suppress separation of the electrode active material.

The current collector can be shaped like a long strip, and the longitudinal direction of the current collector can agree with the column direction while the width direction of the current collector can agree with the row direction. The tops of the protrusions can be in the shape of a substantial oval, and the major axis of the oval can agree with the width direction of the current collector. As a result, the arrangement pattern of the protrusions exhibits a large resistance to stress. Thus, in the step of forming the protrusions on the surface of the current collector and the step of disposing the electrode active material on the protrusions of the current collector, it is possible to prevent the current collector from becoming locally deformed or distorted. Also, the major axis of the oval is caused to agree with the width direction of the current collector. Thus, when the electrode active material is disposed on the protrusions of the current collector toward the longitudinal direction of the current collector, it can be efficiently disposed. Further, in the step of disposing the electrode active material on the protrusions of the current collector and the subsequent step such as slitting to a predetermined width, it is also possible to suppress separation of the electrode active material.

Also, the current collector can be shaped like a long strip, and the longitudinal direction of the current collector can agree with the column direction while the width direction of the current collector can agree with the row direction. The tops of the protrusions can be in the shape of a substantial rectangle, and the longitudinal direction of the rectangle can agree with the width direction of the current collector. As a result, the arrangement pattern of the protrusions exhibits a large resistance to stress. Thus, in the step of forming the protrusions on the surface of the current collector and the step of disposing the electrode active material on the protrusions of the current collector, it is possible to prevent the current collector from becoming locally deformed or distorted. At the same time, the longitudinal direction of the rectangle is caused to agree with the width direction of the current collector. Thus, when the electrode active material is disposed on the protrusions of the current collector toward the longitudinal direction of the current collector, it can be efficiently disposed. Further, in the step of disposing the electrode active material on the protrusions of the current collector and the subsequent step such as slitting to a predetermined width, it is also possible to suppress separation of the electrode active material.

Also, the current collector can be shaped like a long strip, and the longitudinal direction of the current collector can agree with the column direction while the width direction of the current collector can agree with the row direction. The tops of the protrusions can be in the shape of a substantial rhombus, and the direction of the longer diagonal line of the rhombus can agree with the width direction of the current collector. As a result, the arrangement pattern of the protrusions exhibits a large resistance to stress. Thus, in the step of forming the protrusions on the surface of the current collector and the step of disposing the electrode active material on the protrusions of the current collector, it is possible to prevent the current collector from becoming locally deformed or distorted. At the same time, the direction of the major axis of the rhombus is caused to agree with the width direction of the current collector. Thus, when the electrode active material is disposed on the protrusions of the current collector toward the longitudinal direction of the current collector, it can be efficiently disposed. Further, in the step of disposing the electrode active material on the protrusions of the current collector and the subsequent step such as slitting to a predetermined width, it is also possible to suppress separation of the electrode active material.

Also, the current collector can be shaped like a long strip, and the longitudinal direction of the current collector can agree with the column direction while the width direction of the current collector can agree with the row direction. The tops of the protrusions can be in the shape of a substantial square, and the direction of one diagonal line of the square can agree with the width direction of the current collector. As a result, the arrangement pattern of the protrusions exhibits a large resistance to stress. Thus, in the step of forming the protrusions on the surface of the current collector and the step of disposing the electrode active material on the protrusions of the current collector, it is possible to prevent the current collector from becoming locally deformed or distorted. At the same time, the direction of one diagonal line of the square is caused to agree with the width direction of the current collector. Thus, when the electrode active material is disposed on the protrusions of the current collector toward the longitudinal direction of the current collector, it can be efficiently disposed. Further, in the step of disposing the electrode active material on the protrusions of the current collector and the subsequent step such as slitting to a predetermined width, it is also possible to suppress separation of the electrode active material.

Also, the current collector can be shaped like a long strip, and the longitudinal direction of the current collector can agree with the column direction while the width direction of the current collector can agree with the row direction. The tops of the protrusions can be in the shape of a substantial equilateral hexagon, and a pair of opposite sides of the equilateral hexagon can be perpendicular to the width direction of the current collector. As a result, the arrangement pattern of the protrusions becomes a honeycomb arrangement in which substantially equilateral hexagons are closely packed. Hence, the strength of the current collector can be improved, and the current collector can exhibit a large resistance to deformation. Thus, in the step of forming the protrusions on the surface of the current collector and the step of depositing an active material thin film on the protrusions of the current collector, it is possible to prevent the current collector from becoming locally deformed or distorted. At the same time, the direction of one diagonal line of the square is caused to agree with the width direction of the current collector. Thus, when the electrode active material is disposed on the protrusions of the current collector toward the longitudinal direction of the current collector, it can be efficiently disposed. Further, in the step of disposing the electrode active material on the protrusions of the current collector and the subsequent step such as slitting to a predetermined width, it is also possible to suppress separation of the electrode active material.

Also, the invention relates to an electrode plate for a non-aqueous secondary battery including at least a positive electrode active material or negative electrode active material disposed on the above-described current collectors for a non-aqueous secondary battery. With this configuration, the arrangement pattern of the protrusions exhibits a large resistance to stress. Thus, in the step of disposing the electrode active material on the protrusions of the current collector, it is possible to prevent the current collector from becoming locally deformed or distorted. At the same time, in the step of disposing the electrode active material on the protrusions of the current collector and the subsequent step such as slitting to a predetermined width, it is also possible to suppress separation of the electrode active material.

Also, the invention pertains to a current collector for a non-aqueous secondary battery, including a metal foil for carrying at least a positive electrode active material or negative electrode active material. Protrusions are formed in a predetermined arrangement pattern on at least one face of the metal foil, and at least the tops of the protrusions are not compressed. The arrangement pattern includes: a row direction in which the protrusions are aligned in a zigzag at an equal pitch; and a column direction in which row units comprising a group of the protrusions aligned in the row direction are aligned in parallel at a predetermined interval. The intervals between each of the protrusions and all the protrusions adjacent to each of the protrusions are equal. With respect to the shape of the protrusions, at least the tops thereof can be substantially circular.

Due to the aforementioned arrangement pattern of the protrusions, when a tensile stress is applied in the column direction, the stress is exerted on the respective protrusions aligned in a zigzag. Also, since the distances between each of the protrusions and all the adjacent protrusions are equal, an equal stress is exerted on the respective protrusions. Hence, for example, when the current collector is shaped like a long strip and is produced so that the longitudinal direction thereof and the column direction agree with each other, the shearing force exerted on the current collector is reduced and the strength of the current collector can be improved. Thus, in the step of forming the protrusions on the surface of the current collector and the step of disposing the electrode active material on the protrusions of the current collector, it is possible to prevent the current collector from becoming locally deformed or distorted. At the same time, in the step of disposing the electrode active material on the protrusions of the current collector and the subsequent step such as slitting to a predetermined width, it is also possible to suppress separation of the electrode active material.

Also, the current collector can be shaped like a long strip, and the longitudinal direction of the current collector can agree with the column direction while the width direction of the current collector can agree with the row direction. The tops of the protrusions can be in the shape of a substantial square, and a pair of opposite sides of the square can be perpendicular to the width direction of the current collector. As a result, when a tensile stress is applied to the longitudinal direction of the current collector, the stress is exerted on the respective protrusions aligned in a zigzag, and the stress exerted on the respective protrusions is scattered in comparison with the arrangement in which the protrusions are aligned in a row in the width direction of the current collector. Hence, the shearing force exerted on the current collector is reduced and the strength of the current collector can be improved. Thus, in the step of forming the protrusions on the surface of the current collector and the step of disposing the electrode active material on the protrusions of the current collector, it is possible to prevent the current collector from becoming locally deformed or distorted. At the same time, in the step of disposing the electrode active material on the protrusions of the current collector and the subsequent step such as slitting to a predetermined width, it is also possible to suppress separation of the electrode active material.

Also, the current collector can be shaped like a long strip, and the longitudinal direction of the current collector can agree with the column direction while the width direction of the current collector can agree with the row direction. The tops of the protrusions can be in the shape of a substantial square, and the direction of one diagonal line of the square can agree with the width direction of the current collector. As a result, when a tensile stress is applied to the longitudinal direction of the current collector, the stress is exerted on the respective protrusions aligned in a zigzag, and the stress exerted on the respective protrusions is scattered in comparison with the arrangement in which the protrusions are aligned in a row in the width direction of the current collector. Hence, the shearing force exerted on the current collector is reduced and the strength of the current collector can be improved. Thus, in the step of forming the protrusions on the surfaces of the current collector and the step of disposing the electrode active material on the protrusions of the current collector, it is possible to prevent the current collector from becoming locally deformed or distorted. At the same time, in the step of disposing the electrode active material on the protrusions of the current collector and the subsequent step such as slitting to a predetermined width, it is also possible to suppress separation of the electrode active material.

Also, the current collector can be shaped like a long strip, and the longitudinal direction of the current collector can agree with the column direction while the width direction of the current collector can agree with the row direction. The tops of the protrusions can be in the shape of a substantially equilateral hexagon, and the direction of one of the longest diagonal lines of the equilateral hexagon can agree with the width direction of the current collector. Also, the current collector can be shaped like a long strip, and the longitudinal direction of the current collector can agree with the column direction while the width direction of the current collector can agree with the row direction. The tops of the protrusions can be in the shape of a substantially equilateral polygon having an even number of eight or more angles, and the direction of one of the longest diagonal lines of the equilateral polygon can agree with the width direction of the current collector.

With this configuration, when a tensile stress is applied in the longitudinal direction of the current collector, the stress is exerted on the respective protrusions aligned in a zigzag. Also, since the distances between each of the protrusions and all the adjacent protrusions are equal, an equal stress is exerted on the respective protrusions. Hence, the shearing force exerted on the current collector is reduced and the strength of the current collector can be improved. Thus, in the step of forming the protrusions on the surface of the current collector and the step of disposing the electrode active material on the protrusions of the current collector, it is possible to prevent the current collector from becoming locally deformed or distorted. At the same time, in the step of disposing the electrode active material on the protrusions of the current collector and the subsequent step such as slitting to a predetermined width, it is also possible to suppress separation of the electrode active material.

Also, the current collector can be shaped like a long strip, and the longitudinal direction of the current collector can agree with the column direction while the width direction of the current collector can agree with the row direction. The tops of the protrusions can be in the shape of a substantially equilateral hexagon, and a pair of opposite sides of the equilateral hexagon can be perpendicular to the width direction of the current collector. Also, the current collector can be shaped like a long strip, and the longitudinal direction of the current collector can agree with the column direction while the width direction of the current collector can agree with the row direction. At least the tops of the protrusions can be in the shape of a substantially equilateral polygon having an even number of eight or more angles, and a pair of opposite sides of the equilateral polygon can be perpendicular to the width direction of the current collector.

With this configuration, when a tensile stress is applied in the longitudinal direction of the current collector, the stress is exerted on the respective protrusions aligned in a zigzag. Also, since the distances between each of the protrusions and all the adjacent protrusions are equal, an equal stress is exerted on the respective protrusions. Hence, the shearing force exerted on the current collector is reduced and the strength of the current collector can be improved. Thus, in the step of forming the protrusions on the surface of the current collector and the step of disposing the electrode active material on the protrusions of the current collector, it is possible to prevent the current collector from becoming locally deformed or distorted. At the same time, in the step of disposing the electrode active material on the protrusions of the current collector and the subsequent step such as slitting to a predetermined width, it is also possible to suppress separation of the electrode active material.

Also, the invention relates to an electrode plate for a non-aqueous secondary battery including at least a positive electrode active material or negative electrode active material disposed on any one of the above-described current collectors for a non-aqueous secondary battery. With this configuration, the arrangement pattern of the protrusions exhibits a large resistance to stress. Thus, in the step of disposing the electrode active material on the protrusions of the current collector, it is possible to prevent the current collector from becoming locally deformed or distorted. At the same time, in the step of disposing the electrode active material on the protrusions of the current collector and the subsequent step such as slitting to a predetermined width, it is also possible to suppress separation of the electrode active material.

Also, the invention relates to a non-aqueous secondary battery that is produced by winding or laminating a positive electrode plate and a negative electrode plate according to the above-described electrode plate for a non-aqueous secondary battery with a separator interposed therebetween to obtain an electrode assembly, and sealing the electrode assembly and a non-aqueous type electrolyte into a battery case. With this configuration, when the non-aqueous secondary battery is charged and discharged, the volume change due to expansion of the electrode active material upon lithium absorption and shrinkage of the electrode active material upon lithium desorption can be reduced. It is thus possible to obtain a high-capacity, high-reliability non-aqueous secondary battery that does not suffer such a problem as breakage of the electrode plate due to charge/discharge and separation of the electrode active material layer.

Also, the current collector can be shaped like a long strip, and the longitudinal direction of the current collector can agree with the column direction while the width direction of the current collector can agree with the row direction. The interval at which the row units are aligned can decrease gradually from one end of the current collector in the longitudinal direction thereof toward the other end. As a result, by spirally winding an electrode plate using the above-described current collector in such a manner that the interval of the row units is larger on the inner side, it is possible to reduce the adverse influence of the difference in curvature between the inner side and the outer side. That is, when the pitch of the tops of the protrusions is narrow on the inner side and wide on the outer side, there is a difference in bending stress exerted on the electrode plate, but such difference can be reduced. Thus, in the step of producing an electrode assembly from an electrode plate using the above-described current collector, the misalignment of the wound electrode plate and separation of the electrode active material can be suppressed.

Also, the protrusions can be formed on both faces of the metal foil, and the protrusions on one face of the metal foil can be in phase with the protrusions on the other face of the metal foil. As a result, the flexibility of this current collector can be heightened compared with a current collector of the same total thickness having protrusions on both faces. Thus, when an electrode plate using this current collector is wound to form an electrode assembly, a problem such as the misalignment of the wound electrode plate does not occur, and a uniform electrode assembly can be produced.

Also, the protrusions can be formed on both faces of the metal foil, and the protrusions on one face of the metal foil can be out of phase with the protrusions on the other face of the metal foil in the row direction. As a result, the strength of this current collector can be improved compared with a current collector of the same total thickness in which the protrusions on both faces are in phase with one another. In the step of forming the protrusions on the surface of the current collector and the step of disposing the electrode active material on the protrusions of the current collector, it is possible to more effectively prevent the current collector from becoming locally deformed or distorted.

Also, the protrusions can be formed on both faces of the metal foil, and the interval at which the row units are aligned in the column direction on one face of the metal foil can be greater than the interval at which the row units are aligned on the other face of the metal foil. As a result, when an electrode plate using this current collector is spirally wound to form an electrode assembly, it is possible to reduce the adverse influence of the difference in curvature between the inner face and the outer face of the electrode plate. That is, when the pitch of the tops of the protrusions is wide on the outer face and narrow on the inner face, there is a difference in bending stress exerted on the electrode plate, but such difference can be reduced. Thus, when the electrode plate is wound to form an electrode assembly, the misalignment of the wound electrode plate and separation of the electrode active material can be suppressed in a more reliable manner.

Also, one face of the metal foil can have the protrusions in the aforementioned arrangement pattern while the other face can be a flat surface, and the flat surfaces of two or more such metal foils can be bonded together to form a current collector. As a result, the protrusions on one face of the current collector and the protrusions on the other face can be provided so as to have a desired phase difference therebetween. When an electrode plate using the above-described current collector is wound with other battery components to form an electrode assembly, it is bent at various curvatures, but the stress created by bending at various curvatures can be easily addressed. That is, by adjusting the phase according to the curvature, the electrode plate can have a desired function while having strength characteristics and flexibility as the current collector. Also, the phase can be partially adjusted in one electrode assembly, and the portions of the current collector with a large curvature and under a large stress can be reinforced. Further, since the protrusions are formed on only one face of the metal foil, higher protrusions can be formed on a thinner metal foil, compared with the case where the protrusions are formed on both faces of the metal foil. Also, in an electrode plate for a non-aqueous secondary battery using the above-described current collector, the volume ratio of the positive electrode active material or negative electrode active material can be changed freely. When such electrode plates are wound to form an electrode assembly, the efficiency of the electrochemical reaction on the outer side and the inner side of the electrode assembly can be heightened, and the battery capacity can be increased.

Also, when two or more such metal foils are bonded together in such a manner that the protrusions on one face of the current collector are out of phase with the protrusions on the other face, the portions where the widths of the protrusions on both faces partially overlap can receive stress due to winding of the electrode plate while reducing it. On the other hand, when the portions where no protrusions are formed on both faces receive stress, they bend flexibly. Thus, the balance between stress resistance and flexibility can be changed freely. It is therefore possible to prevent the electrode plate and current collector from becoming cracked.

Also, when two or more such metal foils are bonded together in such a manner that the protrusions on one face of the current collector are in phase with the protrusions on the other face, the portions where the protrusions are formed on both faces can receive stress due to winding. On the other hand, when the portions where no protrusions are formed on both faces receive stress, they bend flexibly. Thus, in a battery having an electrode assembly whose electrode plate partially has a large curvature, such as a prismatic battery, the excellent flexibility of the electrode plate permits prevention of separation of the active material.

Also, since this current collector is produced by bonding the flat surfaces of two or more such metal foils together, the phase of the protrusions on one face and the protrusions on the other face can be freely adjusted. Also, the production process can also be simplified.

Also, one face of the metal foil can have the protrusions in the aforementioned arrangement pattern while the other face can be a flat surface. The metal foil can be folded at a predetermined position, and the flat surfaces of the folded metal foil can be bonded together to form a current collector. As a result, there is no need to cut the current collector, and occurrence of burrs due to cutting can be prevented. Also, by changing the folding position of one metal foil, the phase of the protrusions on both faces of the metal foil can be adjusted, and it is thus possible to simplify the process of cutting and adjusting the bonding position necessary when two or more metal foils are used. This makes it possible to reduce the production cost of the position adjustment process, increase the yield of the current collector, and improve the production capability.

Also, by winding or laminating the above-described positive electrode plate and negative electrode plate with a separator interposed therebetween to form an electrode assembly, and sealing the electrode assembly and a non-aqueous type electrolyte into a battery case to produce a non-aqueous secondary battery, the aforementioned arrangement pattern of the protrusions exhibits a large resistance to stress. Thus, in the step of forming the protrusions on the current collector surface and the step of disposing the electrode active material on the protrusions of the current collector, it is possible to prevent the current collector from becoming locally deformed or distorted. The following Embodiments and Examples will be described with reference to the application of the invention to current collectors for non-aqueous type secondary batteries, and electrode plates for secondary batteries and secondary batteries using the same, but they are not to be construed as limiting the invention. For example, the invention is applicable to current collectors for non-aqueous type primary batteries or other primary batteries than non-aqueous type, and electrode plates for primary batteries and primary batteries using the same. The invention is also applicable to current collectors for other secondary batteries than the non-aqueous type, and electrode plates for secondary batteries and secondary batteries using the same.

Referring now toFIG. 1toFIG. 4, Embodiment 1 of the invention is described.FIG. 1is a plane view schematically showing the structure of a current collector for a non-aqueous secondary battery according to Embodiment 1 of the invention.

InFIG. 1, a current collector10is a current collector for use in an electrode plate of a lithium ion secondary battery (hereinafter also referred to as simply a lithium secondary battery), which is an exemplary non-aqueous secondary battery. The current collector10is formed of a metal foil1at least one surface of which has a large number of columnar protrusions2in a predetermined arrangement pattern, and the tops and cross-sections of the columnar protrusions2are substantially circular. It should be noted that at least the tops of the protrusions2are not compressed.

In the arrangement pattern ofFIG. 1, the protrusions2are aligned at an equal pitch P1in the row direction X in such a manner that the centers of the respective protrusions2are positioned on a straight line represented by a broken line3. A group of these protrusions2aligned in the row direction X constitute a row unit4. The row units4are aligned in parallel at an equal pitch P2in the column direction Y, which is a direction perpendicular to the row direction X. Also, the respective protrusions2of such a row unit4are displaced in the row direction X from the protrusions2of another row unit4that is adjacent in the column direction Y, and the amount of displacement is a pitch P3which is ½ of the pitch P1. The amount of the pitch displaced is not limited to ½ of the pitch P1and can be increased or decreased if necessary.

InFIG. 2, (a) is a perspective view of a roller used to form the protrusions2on the current collector10, and (b) is an enlarged perspective view of the surface of this roller.

A roller20ofFIG. 2is prepared by coating a surface6of a metal roller material5with a ceramic such as CrO, WC, or TiN and then forming depressions7corresponding to the protrusions2in an arrangement pattern corresponding to the aforementioned arrangement pattern by laser machining or the like.

That is, the depressions7are aligned linearly in the axial direction of the roller20at a pitch P1′ which is equal to the pitch P1, thereby forming a row unit, and such row units are aligned in parallel in the circumferential direction of the roller20at a pitch P2′ which is equal to the pitch P2.

Also, the respective depressions7of the row units that are adjacent to one another in the circumferential direction of the roller20are displaced in the axial direction of the roller20, and the amount of displacement is a pitch P3′ which is equal to the pitch P3. The amount of the pitch displaced is not limited to ½ of the pitch P1′ and can be increased or decreased if necessary.

FIG. 3shows an example of a processing method for forming the protrusions2on the surfaces of the current collector10using the rollers20.

In the example shown in the figure, a pair of the rollers20are disposed with a predetermined space therebetween, and the long metal foil1is passed through the space to press both faces of the metal foil1with the rollers20, so that a large number of the protrusions2are formed on both faces of the metal foil1in the aforementioned arrangement pattern. By this, the portion of the metal foil1facing the portion of the surface of each of the rollers20having no depressions7is compressed, so that the portions of the metal foil1facing the portions having the depressions7are raised by plastic deformation. As a result, the protrusions2are formed. As shown in Examples that will be described later, when the protrusions2are formed, their edges (tops) are not in contact with the bottom faces of the depressions7, and thus at least their tops are not compressed.

It should be noted that the method of forming the protrusions2on the surfaces of the metal foil1is not limited to the method described above. For example, dies may be used in place of the rollers20, and the metal foil1may be sandwiched and compressed between an upper die and a lower die in order to form the protrusions2on both faces of the metal foil1.

In the following, an electrode plate (which is the general term for a positive electrode plate and a negative electrode plate) using the current collector10is described. A positive electrode plate and a negative electrode plate are prepared by disposing an electrode active material (which is the general term for a positive electrode active material and a negative electrode active material and is hereinafter referred to as simply an active material) on the surface of the current collector10with the protrusions2formed thereon.

One method for disposing an active material on the surface of the current collector10is a method of applying a paint containing an active material (positive electrode mixture paint or negative electrode mixture paint) onto the current collector.

The positive electrode mixture paint is prepared by placing a positive electrode active material, a conductive agent, and a binder into a suitable dispersion medium, mixing and dispersing them with a dispersing device such as a planetary mixer, and kneading the mixture while adjusting its viscosity so that it becomes suited for application to the current collector10.

Examples of the positive electrode active material which can be used include composite oxides, such as lithium cobaltate and modified materials thereof (e.g., solid solution of lithium cobaltate containing aluminum or magnesium), lithium nickelate and modified materials thereof (e.g., materials in which part of the nickel is replaced with cobalt), and lithium manganate and modified materials thereof.

Examples of the conductive agent for the positive electrode include carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black, and various graphites, and they can be used singly or in combination.

Examples of the binder which can be used for the positive electrode include polyvinylidene difluoride (PolyVinylidene DiFluoride, PVDF), modified PVDF, polytetrafluoroethylene (Poly Tetra Fluoro Ethylene, PTFE), and rubber particle binders having an acrylate unit. It is also possible to mix an acrylate monomer or acrylate oligomer containing a reactive functional group in the binder.

The positive electrode mixture paint prepared in the above manner is applied onto the metal foil1made of, for example, aluminum foil with a die coater, followed by drying. This is pressed to a predetermined thickness and then slit to a predetermined width and length to obtain a long-strip like positive electrode plate. The slitting is made so that the column direction Y agrees with the longitudinal direction of the long-strip like positive electrode plate.

Also, the negative electrode mixture paint is prepared by placing a negative electrode active material and a binder into a suitable dispersion medium, mixing and dispersing them with a dispersing device such as a planetary mixer, and kneading the mixture while adjusting its viscosity so that it becomes suited for application to the current collector10.

Examples of the active material which can be used for the negative electrode include various natural graphites and artificial graphites, silicon-based composite materials such as silicide, and various alloy composition materials.

As the binder for the negative electrode, polyvinylidene difluoride and modified materials thereof can be used. However, in terms of improving lithium ion acceptance, it is preferable to use a particulate styrene-butadiene copolymer rubber (SBR) or a modified material thereof and a cellulose-type resin such as carboxymethylcellulose (CMC) in combination, or to use a mixture of particulate SBR or a modified material thereof and a small amount of such a cellulose type resin.

The negative electrode mixture paint prepared in the above manner is applied onto the metal foil1made of, for example, copper foil with a die coater, followed by drying. This is pressed to a predetermined thickness and then slit to a predetermined width and length to obtain a long-strip like negative electrode plate. The slitting is made so that the column direction Y agrees with the longitudinal direction of the long-strip like negative electrode plate.

Also, another method for disposing the positive electrode active material or negative electrode active material on the current collector10is a vacuum process in which the positive electrode active material or negative electrode active material can be selectively disposed on a specific position of the current collector. In the case of vacuum process, it is preferable to dispose the positive electrode active material or negative electrode active material mainly on the uncompressed tops of the protrusions2in columnar form.

This is for the following reason. Since the tops of the protrusions2are not compressed, they maintain the initial plane precision without being affected by processing strain or the like. Thus, an active material thin film can be formed thereon with good accuracy. In addition, when the active material is disposed on the tops of the respective protrusions2in columnar form in such a manner that these columnar active materials align continuously in a lateral direction to form a thin film, it is expected that the volume expansion of the active material thin film upon lithium absorption can be reduced. At this time, although the thickness of the active material thin film differs according to the characteristics the intended non-aqueous secondary battery is required to provide, it is preferably in the range of about 5 to 30 μm, and more preferably in the range of 10 to 25 μm, in terms of obtaining the greatest effect of reducing the volume expansion.

As the vacuum process, a dry process such as deposition, sputtering, or CVD (Chemical Vapor Deposition) can be used. In the case of a dry process, examples of the negative electrode active material which can be used include Si, Sn, Ge, and Al and alloys thereof, oxides such as SiOx and SnOx, and SiSx and SnS. Also, in the case of a dry process, the negative electrode active material is preferably amorphous or low crystalline.

In the following, a non-aqueous secondary battery using the positive electrode plate and negative electrode plate is described.FIG. 4is a longitudinal perspective view of a lithium secondary battery as an exemplary non-aqueous secondary battery.

In a lithium secondary battery30illustrated inFIG. 4, a positive electrode plate31including a composite lithium oxide as the active material and a negative electrode plate32including a material capable of retaining lithium as the active material are spirally wound with a separator33interposed therebetween, to form an electrode assembly34.

The electrode assembly34is housed in a cylindrical battery case35with a bottom while being insulated from the battery case35by an insulator plate36. Also, a negative electrode lead37attached to the lower part of the electrode assembly34is connected to the bottom of the battery case35, while a positive electrode lead38attached to the upper part of the electrode assembly34is connected to a seal plate39.

Also, after a predetermined amount of an electrolyte (not shown) comprising a non-aqueous solvent is injected into the battery case35, the seal plate39the circumference of which is fitted with a seal gasket40is inserted in the opening of the battery case35, and the opening of the battery case35is bent inward and crimped for sealing.

The separator33can be composed of any materials if only they have a composition capable of withstanding the use in the non-aqueous secondary battery. In particular, it is preferable to use microporous films made of an olefin resin such as polyethylene and polypropylene as single agent or in combination. The thickness of the separator is desirably 10 to 25 μm.

As for the electrolyte, various lithium compounds such as LiPF6 and LIBF4 can be used as the electrolyte salts. Also, as the solvent, ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and methyl ethyl carbonate (MEC) can be used singly or in combination. In order to form a good coating film on the positive electrode plate or negative electrode plate and ensure stability under overcharged conditions, it is preferable to use vinylene carbonate (VC) and cyclohexyl benzene (CHB), and modified materials thereof.

Referring now toFIG. 5, Embodiment 2 of the invention is described.FIG. 5is a plane view schematically showing the structure of a current collector for a non-aqueous secondary battery according to Embodiment 2 of the invention.

As illustrated inFIG. 5, a current collector10A of Embodiment 2 is different from that of Embodiment 1 in the shape of protrusions2A formed on a metal foil1, and the tops and cross-sections thereof are substantially oval. The arrangement pattern of the protrusions2A formed on the surface of the metal foil1is the same as that of Embodiment 1.

Specifically, the protrusions2A are aligned linearly at an equal pitch P4in the row direction X. A group of the protrusions2A aligned in the row direction X constitute a row unit, and such row units are aligned in parallel at an equal pitch P5in the column direction Y. Also, the respective protrusions2A of such a row unit are displaced in the row direction X from the protrusions2A of another row unit that is adjacent in the column direction Y, and the amount of displacement is a pitch P6which is ½ of the pitch P4. The amount of the pitch displaced is not limited to ½ of the pitch P4and can be increased or decreased if necessary.

In addition, in the arrangement pattern of this embodiment, the protrusions2A whose tops and cross-sections are substantially oval are disposed so that the major axis of the oval agrees with the row direction X.

The processing method of forming the protrusions2A on the surfaces of the current collector10A is the same as that of Embodiment 1 shown inFIG. 3. Also, the protrusions2A can be formed by using dies, etc. in place of the rollers in the same manner. The method of producing an electrode plate by using the current collector10A is also the same as that of Embodiment 1. Further, the method of producing a non-aqueous secondary battery by using the electrode plate prepared in the above manner is also the same as that of Embodiment 1 shown inFIG. 4.

Referring now toFIG. 6, Embodiment 3 of the invention is described.FIG. 6is a plane view schematically showing the structure of a current collector for a non-aqueous secondary battery according to Embodiment 3 of the invention.

As illustrated inFIG. 6, a current collector10B of Embodiment 3 is different from that of Embodiment 1 in the shape of protrusions2B formed on a metal foil1, and the tops and cross-sections thereof are substantially rectangular. The arrangement pattern of the protrusions2B formed on the surface of the metal foil1is the same as that of Embodiment 1.

Specifically, the protrusions2B are aligned linearly at an equal pitch P7in the row direction X. A group of the protrusions2B aligned in the row direction X constitute a row unit, and such row units are aligned in parallel at an equal pitch P8in the column direction Y. Also, the respective protrusions2B of such a row unit are displaced in the row direction X from the protrusions2B of another row unit that is adjacent in the column direction Y, and the amount of displacement is a pitch P9which is ½ of the pitch P7. The amount of the pitch displaced is not limited to ½ of the pitch P7and can be increased or decreased if necessary.

In addition, in the arrangement pattern of this embodiment, the protrusions2B whose tops and cross-sections are substantially rectangular are disposed so that the longitudinal direction of the rectangle agrees with the row direction X.

The processing method of forming the protrusions2B on the surfaces of the current collector10B is the same as that of Embodiment 1 shown inFIG. 3. Also, the protrusions2B can be formed by using dies, etc. in place of the rollers in the same manner. The method of producing an electrode plate by using the current collector10B is also the same as that of Embodiment 1. Further, the method of producing a non-aqueous secondary battery by using the electrode plate prepared in the above manner is also the same as that of Embodiment 1 shown inFIG. 4.

Referring now toFIG. 7, Embodiment 4 of the invention is described.FIG. 7is a plane view schematically showing the structure of a current collector for a non-aqueous secondary battery according to Embodiment 4 of the invention.

As illustrated inFIG. 7, a current collector10C of Embodiment 4 is different from that of Embodiment 1 in the shape of protrusions2C formed on a metal foil1, and the tops and cross-sections thereof are substantially rhombic. The arrangement pattern of the protrusions2C formed on the surface of the metal foil1is the same as that of Embodiment 1.

Specifically, the protrusions2C are aligned linearly at an equal pitch P10in the row direction X. A group of the protrusions2C aligned in the row direction X constitute a row unit, and such row units are aligned in parallel at an equal pitch P11in the column direction Y. Also, the respective protrusions2C of such a row unit are displaced in the row direction X from the protrusions2C of another row unit that is adjacent in the column direction Y, and the amount of displacement is a pitch P12which is ½ of the pitch P10. The amount of the pitch displaced is not limited to ½ of the pitch P10and can be increased or decreased if necessary.

In addition, in the arrangement pattern of this embodiment, the protrusions2C whose tops and cross-sections are substantially rhombic are disposed so that the longer diagonal line of the rhombus agrees with the row direction X.

The processing method of forming the protrusions2C on the surfaces of the current collector10C is the same as that of Embodiment 1 shown inFIG. 3. Also, the protrusions2C can be formed by using dies, etc. in place of the rollers in the same manner. The method of producing an electrode plate by using the current collector10C is also the same as that of Embodiment 1. Further, the method of producing a non-aqueous secondary battery by using the electrode plate prepared in the above manner is also the same as that of Embodiment 1 shown inFIG. 4.

Referring now toFIG. 8, Embodiment 5 of the invention is described.FIG. 8is a plane view schematically showing the structure of a current collector for a non-aqueous secondary battery according to Embodiment 5 of the invention.

As illustrated inFIG. 8, a current collector10D of Embodiment 5 is different from that of Embodiment 1 in the shape of protrusions2D formed on a metal foil1, and the tops and cross-sections thereof are substantially square. The arrangement pattern of the protrusions2D formed on the surface of the metal foil1is the same as that of Embodiment 1.

Specifically, the protrusions2D are aligned linearly at an equal pitch P13in the row direction X. A group of the protrusions2D aligned in the row direction X constitute a row unit, and such row units are aligned in parallel at an equal pitch P14in the column direction Y. Also, the respective protrusions2D of such a row unit are displaced in the row direction X from the protrusions2D of another row unit that is adjacent in the column direction Y, and the amount of displacement is a pitch P15which is ½ of the pitch P13. The amount of the pitch displaced is not limited to ½ of the pitch P13and can be increased or decreased if necessary.

In addition, in the arrangement pattern of this embodiment, the protrusions2D whose tops and cross-sections are substantially square are disposed so that the direction of one diagonal line of the square agrees with the row direction X.

The processing method of forming the protrusions2D on the surfaces of the current collector10D is the same as that of Embodiment 1 shown inFIG. 3. Also, the protrusions2D can be formed by using dies, etc. in place of the rollers in the same manner. The method of producing an electrode plate by using the current collector10D is also the same as that of Embodiment 1. Further, the method of producing a non-aqueous secondary battery by using the electrode plate prepared in the above manner is also the same as that of Embodiment 1 shown inFIG. 4.

Referring now toFIG. 9, Embodiment 6 of the invention is described.FIG. 9is a plane view schematically showing the structure of a current collector for a non-aqueous secondary battery according to Embodiment 6 of the invention.

As illustrated inFIG. 9, a current collector10E of Embodiment 6 is different from that of Embodiment 1 in the shape of protrusions2E formed on a metal foil1, and the tops and cross-sections thereof are substantially equilateral hexagonal. The arrangement pattern of the protrusions2E formed on the surface of the metal foil1is the same as that of Embodiment 1.

Specifically, the protrusions2E are aligned linearly at an equal pitch P16in the row direction X. A group of the protrusions2E aligned in the row direction X constitute a row unit, and such row units are aligned in parallel at an equal pitch P17in the column direction Y. Also, the respective protrusions2E of such a row unit are displaced in the row direction X from the protrusions2E of another row unit that is adjacent in the column direction Y, and the amount of displacement is a pitch P18which is ½ of the pitch P16. The amount of the pitch displaced is not limited to ½ of the pitch P16and can be increased or decreased if necessary.

In addition, in the arrangement pattern of this embodiment, the protrusions2E whose tops and cross-sections are substantially equilateral hexagonal are disposed so that a straight line perpendicular to a pair of opposite sides of the equilateral hexagon agrees with the row direction X.

Also, the shape of the protrusions is not limited to the substantially equilateral hexagon, and it is possible to form protrusions that are in the shape of a substantially equilateral polygon having an even number of eight or more angles on the current collector in the same arrangement pattern as that of this embodiment.

The processing method of forming the protrusions2E on the surfaces of the current collector10E is the same as that of Embodiment 1 shown inFIG. 3. Also, the protrusions2E can be formed by using dies, etc. in place of the rollers in the same manner. The method of producing an electrode plate by using the current collector10E is also the same as that of Embodiment 1. Further, the method of producing a non-aqueous secondary battery by using the electrode plate prepared in the above manner is also the same as that of Embodiment 1 shown inFIG. 4.

Examples of the invention are hereinafter described. Examples 1 to 6 show examples of electrode plates of the invention, and Example 7 shows an example of a non-aqueous secondary battery of the invention.

A 15-μm thick aluminum foil was used as a current collector for a positive electrode plate of the invention. A pair of rollers (ceramic rollers) were produced in order to form a large number of protrusions whose tops and cross-sections are substantially circular, as illustrated inFIG. 1of Embodiment 1, on the surfaces of this aluminum foil in the aforementioned arrangement pattern. On the surface of each roller, depressions (depth 4 μm) having a shape corresponding to that of the protrusions were formed in the aforementioned arrangement pattern. The pitch P3was ½ of the pitch P1. The aluminum foil was passed between the pair of rollers while being pressed. In this way, a current collector for a positive electrode plate having 3-μm-high protrusions on both faces and having a total thickness of 18 μm was produced.

Subsequently, a positive electrode mixture paint was prepared by stirring and kneading 100 parts by weight of lithium cobaltate in which part of the cobalt was replaced with nickel and manganese, serving as a positive electrode active material, 2 parts by weight of an acetylene black conductive agent per 100 parts by weight of the active material, 2 parts by weight of a polyvinylidene difluoride binder per 100 parts by weight of the active material, and a suitable amount of N-methyl-2-pyrrolidone with a double-arm kneader. This positive electrode mixture paint was applied onto both faces of the current collector prepared in the above manner, dried, and pressed. The current collector was then slit to a predetermined width and length to produce a long-strip like positive electrode plate. At this time, the slitting was made so that the column direction Y agreed with the longitudinal direction of the positive electrode plate and that the row direction X agreed with the width direction of the positive electrode plate.

In the current collector thus produced, the substantially circular protrusions are formed in a close-packed arrangement pattern. Thus, it exhibits a large resistance to the tensile stress exerted on the longitudinal direction (the column direction Y) of the current collector or positive electrode plate during the production of the current collector and positive electrode plate. Hence, when the positive electrode mixture layers were formed on the current collector to produce the positive electrode plate, or when the positive electrode plate was slit in the above manner, it was possible to prevent the current collector from becoming locally deformed or warped and prevent the positive electrode mixture layers from separating therefrom.

A 20-μm thick copper foil was used as a current collector for a negative electrode plate of the invention. A pair of rollers (ceramic rollers) were produced in order to form a large number of protrusions whose tops and cross-sections are substantially oval, as illustrated inFIG. 5of Embodiment 2, on the surfaces of this copper foil in the aforementioned arrangement pattern. On the surface of each roller, depressions (depth 13 μm) having a shape corresponding to that of the protrusions were formed in the aforementioned arrangement pattern. The pitch P6was ½ of the pitch P4. The copper foil was passed between the pair of rollers while being pressed. In this way, a current collector for a negative electrode plate having 9-μm-high protrusions on both faces and having a total thickness of 29 μm was produced.

Subsequently, using purity 99.9999% silicon (negative electrode active material) as the sputtering target, a deposition process was performed on both faces of the current collector prepared in the above manner by means of a deposition device equipped with an electron beam heating means while purity 99.7% oxygen was being introduced, so that a SiO0.5 film with a thickness of 23 μm was formed on each of the protrusions. This was then slit to a predetermined width and length to obtain a long-strip like negative electrode plate. At this time, the slitting was made so that the column direction Y agreed with the longitudinal direction of the negative electrode plate and that the row direction X agreed with the width direction of the negative electrode plate.

The current collector prepared in the above manner is formed so that the major axis of the substantially oval protrusions agrees with the width direction (row direction X) of the current collector, as described in Embodiment 2. Thus, when the negative electrode active material is deposited toward the longitudinal direction (column direction Y) of the current collector, the active material can be efficiently attached onto the protrusions and, in addition, the current collector can exhibit a large resistance to the tensile stress exerted on the longitudinal direction of the current collector. Hence, when the negative electrode mixture layers were deposited on the current collector to produce the negative electrode plate, or when the negative electrode plate was slit in the above manner, it was possible to prevent the current collector from becoming locally deformed or warped and prevent the negative electrode mixture layers from separating therefrom.

A 15-μm thick copper foil was used as a current collector for a negative electrode plate of the invention. A pair of rollers (ceramic rollers) were produced in order to form a large number of protrusions whose tops and cross-sections are substantially rectangular, as illustrated inFIG. 6of Embodiment 3, on the surfaces of this copper foil in the aforementioned arrangement pattern. On the surface of each roller, depressions (depth 7 μm) having a shape corresponding to that of the protrusions were formed in the aforementioned arrangement pattern. The pitch P9was ½ of the pitch P7. The copper foil was passed between the pair of rollers while being pressed. In this way, a current collector for a negative electrode plate having 5-μm-high protrusions on both faces and having a total thickness of 20 μm was produced.

Subsequently, using purity 99.9999% silicon (negative electrode active material) as the sputtering target, a deposition process was performed on both faces of the current collector prepared in the above manner by means of a deposition device equipped with an electron beam heating means while purity 99.7% oxygen was being introduced, so that a SiO0.5 film with a thickness of 15 μm was formed on each of the protrusions. This was then slit to a predetermined width and length to obtain a long-strip like negative electrode plate. At this time, the slitting was made so that the column direction Y agreed with the longitudinal direction of the negative electrode plate and that the row direction X agreed with the width direction of the negative electrode plate.

The current collector prepared in the above manner is formed so that the longitudinal direction of the substantially rectangular protrusions agrees with the width direction (row direction X) of the current collector, as described in Embodiment 3. Thus, when the negative electrode active material is deposited toward the longitudinal direction (column direction Y) of the current collector, the active material can be efficiently attached onto the protrusions and, in addition, the current collector can exhibit a large resistance to the tensile stress exerted on the longitudinal direction of the current collector. Hence, when the negative electrode mixture layers were deposited on the current collector to produce the negative electrode plate, or when the negative electrode plate was slit in the above manner, it was possible to prevent the current collector from becoming locally deformed or warped and prevent the negative electrode mixture layers from separating therefrom.

A 18-μm thick copper foil was used as a current collector for a negative electrode plate of the invention. A pair of rollers (ceramic rollers) were produced in order to form a large number of protrusions whose tops and cross-sections are substantially rhombic, as illustrated inFIG. 7of Embodiment 4, on the surfaces of this copper foil in the aforementioned arrangement pattern. On the surface of each roller, depressions (depth 10 μm) having a shape corresponding to that of the protrusions were formed in the aforementioned arrangement pattern. The pitch P12was ½ of the pitch P10. The copper foil was passed between the pair of rollers while being pressed. In this way, a current collector for a negative electrode plate having 8-μm-high protrusions on both faces and having a total thickness of 26 μm was produced.

Subsequently, using purity 99.9999% silicon (negative electrode active material) as the sputtering target, a deposition process was performed on both faces of the current collector prepared in the above manner by means of a deposition device equipped with an electron beam heating means while purity 99.7% oxygen was being introduced, so that a SiO0.5 film with a thickness of 20 μm was formed on each of the protrusions. This was then slit to a predetermined width and length to obtain a long-strip like negative electrode plate. At this time, the slitting was made so that the column direction Y agreed with the longitudinal direction of the negative electrode plate and that the row direction X agreed with the width direction of the negative electrode plate.

The current collector prepared in the above manner is formed so that the direction of the longer diagonal line of the substantially rhombic protrusions agrees with the width direction (row direction X) of the current collector, as described in Embodiment 4. Thus, when the negative electrode active material is deposited toward the longitudinal direction (column direction Y) of the current collector, the active material can be efficiently attached onto the protrusions and, in addition, the current collector can exhibit a large resistance to the tensile stress exerted on the longitudinal direction of the current collector. Hence, when the negative electrode mixture layers were deposited on the current collector to produce the negative electrode plate, or when the negative electrode plate was slit in the above manner, it was possible to prevent the current collector from becoming locally deformed or warped and prevent the negative electrode mixture layers from separating therefrom.

A 10-μm thick copper foil was used as a current collector for a negative electrode plate of the invention. A pair of rollers (ceramic rollers) were produced in order to form a large number of protrusions whose tops and cross-sections are substantially square, as illustrated inFIG. 8of Embodiment 5, on the surfaces of this copper foil in the aforementioned arrangement pattern. On the surface of each roller, depressions (depth 3 μm) having a shape corresponding to that of the protrusions were formed in the aforementioned arrangement pattern. The pitch P15was ½ of the pitch P13. The copper foil was passed between the pair of rollers while being pressed. In this way, a current collector for a negative electrode plate having 2-μm-high protrusions on both faces and having a total thickness of 12 μm was produced.

Subsequently, a negative electrode mixture paint was prepared by stirring 100 parts by weight of artificial graphite, serving as a negative electrode active material, 2.5 parts by weight (1 part by weight when converted to the solid content of the binder) of a dispersion of styrene-butadiene copolymer rubber particles (solid content 40% by weight), serving as a binder, per 100 parts by weight of the active material, 1 part by weight of carboxymethylcellulose, serving as a thickener, per 100 parts by weight of the active material, and a suitable amount of water with a double-arm kneader. This negative electrode mixture paint was applied onto both faces of the current collector prepared in the above manner, dried, and pressed. The current collector was then slit to a predetermined width and length to produce a long-strip like negative electrode plate. At this time, the slitting was made so that the column direction Y agreed with the longitudinal direction of the negative electrode plate and that the row direction X agreed with the width direction of the negative electrode plate.

In the current collector produced in the above manner, the substantially square protrusions are formed in a close-packed arrangement pattern. Thus, it exhibits a large resistance to the tensile stress exerted on the longitudinal direction (the column direction Y) of the current collector or negative electrode plate during the production of the current collector and negative electrode plate. Hence, when the negative electrode mixture layers were formed on the current collector to produce the negative electrode plate, or when the negative electrode plate was slit in the above manner, it was possible to prevent the current collector from becoming locally deformed or warped and prevent the negative electrode mixture layers from separating therefrom.

A 12-μm thick aluminum foil was used as a current collector for a positive electrode plate of the invention. A pair of rollers (ceramic rollers) were produced in order to form a large number of protrusions whose tops and cross-sections are substantially equilateral hexagonal, as illustrated inFIG. 9of Embodiment 6, on the surfaces of this aluminum foil in the aforementioned arrangement pattern. On the surface of each roller, depressions (depth 3 μm) having a shape corresponding to that of the protrusions were formed in the aforementioned arrangement pattern. The pitch P18was ½ of the pitch P16. The aluminum foil was passed between the pair of rollers while being pressed. In this way, a current collector for a positive electrode plate having 2-μm-high protrusions on both faces and having a total thickness of 14 μm was produced.

Subsequently, a positive electrode mixture paint was prepared by stirring and kneading 100 parts by weight of lithium cobaltate, serving as a positive electrode active material, 2 parts by weight of an acetylene black conductive agent per 100 parts by weight of the active material, 2 parts by weight of a polyvinylidene difluoride binder per 100 parts by weight of the active material, and a suitable amount of N-methyl-2-pyrrolidone with a double-arm kneader. This positive electrode mixture paint was applied onto both faces of the current collector prepared in the above manner, dried, and pressed. The current collector was then slit to a predetermined width and length to produce a long-strip like positive electrode plate. At this time, the slitting was made so that the column direction Y agreed with the longitudinal direction of the positive electrode plate and that the row direction X agreed with the width direction of the positive electrode plate.

In the current collector produced in the above manner, the substantially equilateral hexagonal protrusions are formed in the shape of a honeycomb in a close-packed arrangement pattern. Thus, it exhibits a large resistance to the tensile stress exerted on the longitudinal direction (the column direction Y) of the current collector or positive electrode plate during the production of the current collector and positive electrode plate. Hence, when the positive electrode mixture layers were formed on the current collector to produce the positive electrode plate, or when the positive electrode plate was slit in the above manner, it was possible to prevent the current collector from becoming locally deformed or warped and prevent the positive electrode mixture layers from separating therefrom.

To produce a non-aqueous secondary battery of the invention, a positive electrode current collector having 3-μm-high protrusions on both faces in the aforementioned arrangement pattern and having a total thickness of 18 μm was produced in the same manner as in Example 1.

Subsequently, a positive electrode mixture paint was prepared by stirring and kneading 100 parts by weight of lithium cobaltate in which part of the cobalt was replaced with nickel and manganese, serving as a positive electrode active material, 2 parts by weight of an acetylene black conductive agent per 100 parts by weight of the active material, 2 parts by weight of a polyvinylidene difluoride binder per 100 parts by weight of the active material, and a suitable amount of N-methyl-2-pyrrolidone with a double-arm kneader. This positive electrode mixture paint was applied onto both faces of the current collector prepared in the above manner, dried, and pressed. The current collector was then slit to a predetermined width and length to produce a long-strip like positive electrode plate. At this time, the slitting was made so that the column direction Y agreed with the longitudinal direction of the positive electrode plate and that the row direction X agreed with the width direction of the positive electrode plate. In this way, a 57-μm-thick positive electrode mixture layer was formed on each face of the positive electrode current collector, and a positive electrode plate having a total thickness of 126 μm was produced.

Also, in the same manner as in Example 4, a negative electrode current collector having 8-μm-high protrusions on both faces thereof in the aforementioned arrangement pattern and having a total thickness of 26 μm was produced.

Subsequently, using purity 99.9999% silicon (negative electrode active material) as the sputtering target, a deposition process was performed on both faces of the current collector prepared in the above manner by means of a deposition device equipped with an electron beam heating means while purity 99.7% oxygen was being introduced. Herein, the negative electrode active material was deposited in columnar form on the tops of the protrusions so that they aligned continuously in a lateral direction to form a 25-μm-thick thin film of SiO0.5. This was then slit to a predetermined width and length to obtain a long-strip like negative electrode plate. At this time, the slitting was made so that the column direction Y agreed with the longitudinal direction of the negative electrode plate and that the row direction X agreed with the width direction of the negative electrode plate.

Using the positive electrode plate and the negative electrode plate prepared in the above manner, a lithium ion secondary battery illustrated inFIG. 4was produced. More specifically, the positive electrode plate and the negative electrode plate were spirally wound with a separator interposed therebetween, to form an electrode assembly. This electrode assembly was housed in a cylindrical battery case with a bottom together with an insulator plate. A negative electrode lead attached to the lower part of the electrode assembly was connected to the bottom of the battery case. Subsequently, a positive electrode lead attached to the upper part of the electrode assembly was connected to a seal plate, and a predetermined amount of an electrolyte (not shown) comprising a non-aqueous solvent was injected into the battery case. Thereafter, the seal plate the circumference of which was fitted with a seal gasket was inserted in the opening of the battery case, and the opening of the battery case was bent inward and crimped for sealing. In this way, a lithium ion secondary battery was produced.

In the lithium ion secondary battery, after the production of the spirally wound electrode assembly, the electrode assembly was disassembled and observed. As a result, both the positive electrode plate and the negative electrode plate were found to have no problem such as breakage of the electrode plate or separation of the active material layer. Further, when the charge/discharge of this lithium ion secondary battery was repeated 300 cycles, no cycle deterioration occurred. Also, after the repetition of 300 charge/discharge cycles, the lithium ion secondary battery and the electrode assembly were disassembled. As a result, they were found to have no problem such as deposition of lithium or separation of the active material layer. This is probably because the formation of the thin film comprising the columnar active material on the uncompressed tops of the protrusions enabled a reduction in volume change due to expansion of the active material thin film upon lithium absorption and shrinkage of the active material thin film upon lithium desorption, so that good battery performance could be maintained.

As shown in the foregoing Examples 1 to 6, in the electrode plate for a non-aqueous secondary battery of the invention, protrusions at least the tops of which were not compressed were formed on the surfaces of a current collector in the aforementioned arrangement pattern, so that the arrangement pattern of the protrusions exhibits a large resistance to stress. Therefore, in the step of forming the protrusions on the surfaces of the current collector and the step of disposing the active material on the protrusions of the current collector, it is possible to prevent the current collector from becoming locally deformed or distorted. At the same time, in the step of disposing the active material on the protrusions of the current collector and the subsequent step such as slitting to a predetermined width and length, it is also possible to suppress separation of the active material.

Further, since the tops of the protrusions of the current collector are not compressed, no processing strain due to compression process remains thereon and the surface accuracy of the top of the protrusions is good, and it is thus possible to form an even thin film thereon. Also, since the surface roughness is not reduced by compression process and the original surface roughness is maintained, it is possible to heighten the adhesion between the protrusions and the active material thin film. In this respect, in order to further heighten the adhesion between the surface of the protrusions and the active material, it is very effective to roughen the current collector surface in advance before subjecting it to a process. The arrangement pattern of the protrusions in Examples 1 to 6 is such that the respective protrusions of the row units that are adjacent to one another in the column direction are displaced by ½ of the pitch of the row unit, but the invention is not limited to this, and the amount of displacement of the protrusions can be set freely.

Also, as shown in Example 7, it is preferable to dispose the active material mainly on the uncompressed tops of the protrusions in columnar form. In this case, when the non-aqueous secondary battery is charged and discharged, the volume change due to expansion of the active material upon lithium absorption and shrinkage of the active material upon lithium desorption is reduced. It is thus possible to obtain a high-capacity, high-reliability non-aqueous secondary battery that does not suffer such a problem as breakage of the electrode plate due to charge/discharge and separation of the active material layer.

Referring now toFIG. 10andFIG. 11, Embodiment 7 of the invention is described.FIG. 10is a plane view schematically showing the structure of a current collector for a non-aqueous secondary battery according to Embodiment 7 of the invention.

InFIG. 10, a current collector10F is a current collector for use in an electrode plate of a lithium ion secondary battery (hereinafter also referred to as simply a lithium secondary battery), which is an exemplary non-aqueous secondary battery. The current collector10F is formed of a metal foil1at least one surface of which has a large number of columnar protrusions2F in a predetermined arrangement pattern, and the tops and cross-sections of the columnar protrusions2F are substantially circular. It should be noted that at least the tops of the protrusions2F are not compressed.

In the arrangement pattern ofFIG. 10, the protrusions2F are aligned in the row direction X at an equal pitch in a zigzag, as shown by a polygonal broken line9. A group of these protrusions2F aligned in the row direction X in a zigzag constitute a row unit4. The row units4are aligned in parallel at an equal pitch in the column direction Y, which is a direction perpendicular to the row direction X. Also, the respective protrusions2F of such a row unit4are at the same positions in the row direction X with those of the protrusions2F of another row unit4that is adjacent in the column direction Y. Also, a given protrusion2F is disposed so that the intervals L11, L12, L13, L14, L15, and L16between itself and all the adjacent protrusions2F are equal.

FIG. 11is an enlarged perspective view of the surface of a roller used to form protrusions on the current collector.

The roller ofFIG. 11is prepared by coating the surface of a metal roller material with a ceramic such as CrO, WC, or TiN and then forming depressions7A corresponding to the protrusions2F in an arrangement pattern corresponding to the aforementioned arrangement pattern by laser machining or the like.

That is, the depressions7A are aligned in the axial direction of the roller at an equal pitch in a zigzag, as shown by a polygonal broken line9A, thereby forming a row unit, and such row units are aligned in parallel in the circumferential direction of the roller at an equal pitch.

Also, the respective depressions7A of the row units that are adjacent to one another in the circumferential direction of the roller are at the same positions in the axial direction of the roller. Also, a given depression7A is disposed so that the intervals between itself and all the adjacent depressions7A are equal.

The processing method of forming the protrusions2F on the surfaces of the current collector10F by using the rollers ofFIG. 11is the same as that of Embodiment 1 shown inFIG. 3. Also, the protrusions2F can be formed by using dies, etc. in place of the rollers in the same manner. The method of producing an electrode plate by using the current collector10F is also the same as that of Embodiment 1. Further, the method of producing a non-aqueous secondary battery by using the electrode plate prepared in the above manner is also the same as that of Embodiment 1 shown inFIG. 4.

Referring now toFIG. 12, Embodiment 8 of the invention is described.FIG. 12is a plane view schematically showing the structure of a current collector for a non-aqueous secondary battery according to Embodiment 8 of the invention.

As shown inFIG. 12, in a current collector10G of Embodiment 8, the arrangement pattern of protrusions2G formed on a metal foil1is the same as that of Embodiment 7, but the shape of the protrusions2G is different from that of Embodiment 7, and their tops and cross-sections are substantially square.

That is, the protrusions2G are aligned in the row direction X at an equal pitch in a zigzag, as shown by a polygonal line9B. A group of these protrusions2G aligned in the row direction X in a zigzag constitute a row unit, and such row units are aligned in parallel at an equal pitch in the column direction Y. Also, the respective protrusions2G of such a row unit are at the same positions in the row direction X with those of the protrusions2G of another row unit that is adjacent in the column direction Y, and a given protrusion2G is disposed so that the intervals between itself and all the adjacent protrusions2G are equal.

In addition, in the arrangement pattern of this embodiment, the protrusions2G whose tops and cross-sections are substantially square are disposed so that a straight line perpendicular to a pair of opposite sides of the square agrees with the row direction X.

The processing method of forming the protrusions2G on the surfaces of the current collector10G is the same as that of Embodiment 1 shown inFIG. 3. Also, the protrusions2G can be formed by using dies, etc. in place of the rollers in the same manner. The method of producing an electrode plate by using the current collector10G is also the same as that of Embodiment 1. Further, the method of producing a non-aqueous secondary battery by using the electrode plate prepared in the above manner is also the same as that of Embodiment 1 shown inFIG. 4.

Referring now toFIG. 13, Embodiment 9 of the invention is described.FIG. 13is a plane view schematically showing the structure of a current collector for a non-aqueous secondary battery according to Embodiment 9 of the invention.

As shown inFIG. 13, in a current collector10H of Embodiment 9, the arrangement pattern of protrusions2H formed on a metal foil1is the same as that of Embodiment 7 and the shape of the protrusions2H is substantially square in the same manner as in Embodiment 8, but the orientation of the protrusions2H is different from that in Embodiment 8.

That is, the protrusions2H are aligned in the row direction X at an equal pitch in a zigzag, as shown by a polygonal line9C. A group of these protrusions2H aligned in the row direction X in a zigzag constitute a row unit, and such row units are aligned in parallel at an equal pitch in the column direction Y. Also, the respective protrusions2H of such a row unit are at the same positions in the row direction X with those of the protrusions2H of another row unit that is adjacent in the column direction Y, and a given protrusion2H is disposed so that the intervals between itself and all the adjacent protrusions2H are equal.

In addition, in the arrangement pattern of this embodiment, the protrusions2G whose tops and cross-sections are substantially square are disposed so that the direction of one diagonal line of the square agrees with the row direction X.

The processing method of forming the protrusions2H on the surfaces of the current collector10H is the same as that of Embodiment 1 shown inFIG. 3. Also, the protrusions2H can be formed by using dies, etc. in place of the rollers in the same manner. The method of producing an electrode plate by using the current collector10H is also the same as that of Embodiment 1. Further, the method of producing a non-aqueous secondary battery by using the electrode plate prepared in the above manner is also the same as that of Embodiment 1 shown inFIG. 4.

Referring now toFIG. 14, Embodiment 10 of the invention is described.FIG. 14is a plane view schematically showing the structure of a current collector for a non-aqueous secondary battery according to Embodiment 10 of the invention.

As shown inFIG. 14, in a current collector10I of Embodiment 10, the arrangement pattern of protrusions2I formed on a metal foil1is the same as that of Embodiment 7, but the shape of the protrusions2I is different from that of Embodiment 7, and their tops and cross-sections are substantially equilateral hexagonal.

That is, the protrusions2I are aligned in the row direction X at an equal pitch in a zigzag, as shown by a polygonal line9D. A group of these protrusions2I aligned in the row direction X in a zigzag constitute a row unit, and such row units are aligned in parallel at an equal pitch in the column direction Y. Also, the respective protrusions2I of such a row unit are at the same positions in the row direction X with those of the protrusions2I of another row unit that is adjacent in the column direction Y, and a given protrusion2I is disposed so that the intervals between itself and all the adjacent protrusions2I are equal.

In addition, in the arrangement pattern of this embodiment, the protrusions2I whose tops and cross-sections are substantially equilateral hexagonal are disposed so that the direction of one diagonal line of the equilateral hexagon agrees with the row direction X.

The processing method of forming the protrusions2I on the surfaces of the current collector10I is the same as that of Embodiment 1 shown inFIG. 3. Also, the protrusions2I can be formed by using dies, etc. in place of the rollers in the same manner. The method of producing an electrode plate by using the current collector10I is also the same as that of Embodiment 1. Further, the method of producing a non-aqueous secondary battery by using the electrode plate prepared in the above manner is also the same as that of Embodiment 1 shown inFIG. 4.

InFIG. 14, the protrusions2I are substantially equilateral hexagonal, but their shape is not limited to this; the shape of the protrusions can be a substantially equilateral polygon with N angles (N: N is an even number of 6 or more). In this case, also, the protrusions are formed so that one of the longest diagonal lines of the equilateral polygon with N angles agrees with the row direction X and that the intervals between a given protrusion and all the adjacent protrusions are equal.

Referring now toFIG. 15, Embodiment 11 of the invention is described.FIG. 15is a plane view schematically showing the structure of a current collector for a non-aqueous secondary battery according to Embodiment 11 of the invention.

As shown inFIG. 15, in a current collector10J of Embodiment 11, the arrangement pattern of protrusions2J formed on a metal foil1is the same as that of Embodiment 7 and the shape of the protrusions2J is equilateral hexagonal in the same manner as in Embodiment 10, but the orientation of the protrusions2J is different from that in Embodiment 10.

That is, the protrusions2J are aligned in the row direction X at an equal pitch in a zigzag, as shown by a polygonal line9E. A group of these protrusions2J aligned in the row direction X in a zigzag constitute a row unit, and such row units are aligned in parallel at an equal pitch in the column direction Y. Also, the respective protrusions2J of such a row unit are at the same positions in the row direction X with those of the protrusions2J of another row unit that is adjacent in the column direction Y, and a given protrusion2J is disposed so that the intervals between itself and all the adjacent protrusions2J are equal.

In addition, in the arrangement pattern of this embodiment, the protrusions2J whose tops and cross-sections are substantially equilateral hexagonal are disposed so that a straight line perpendicular to a pair of opposite sides of the equilateral hexagon agrees with the row direction X.

The processing method of forming the protrusions2J on the surfaces of the current collector10J is the same as that of Embodiment 1 shown inFIG. 3. Also, the protrusions2J can be formed by using dies, etc. in place of the rollers in the same manner. The method of producing an electrode plate by using the current collector10J is also the same as that of Embodiment 1. Further, the method of producing a non-aqueous secondary battery by using the electrode plate prepared in the above manner is also the same as that of Embodiment 1 shown inFIG. 4.

InFIG. 15, the protrusions2J are substantially equilateral hexagonal, but their shape is not limited to this; the shape of the protrusions can be a substantially equilateral polygon with N angles (N: N is an even number of 6 or more). In this case, also, the protrusions are formed so that the direction of a straight line perpendicular to a pair of opposite sides of the equilateral polygon with N angles agrees with the row direction X and that the intervals between a given protrusion and the adjacent protrusions are equal.

A 20-μm thick copper foil was used as a current collector for a negative electrode plate. A pair of rollers (ceramic rollers) were produced in order to form a large number of protrusions whose tops and cross-sections are substantially circular, as illustrated inFIG. 10of Embodiment 7, on the surfaces of this copper foil in the aforementioned arrangement pattern. On the surface of each roller, depressions (depth 13 μm) having a shape corresponding to that of the protrusions were formed in the aforementioned arrangement pattern. The copper foil was passed between the pair of rollers while being pressed. In this way, a current collector for a negative electrode plate having 9-μm-high protrusions on both faces and having a total thickness of 29 μm was produced.

Subsequently, using purity 99.9999% silicon (negative electrode active material) as the sputtering target, a deposition process was performed on both faces of the current collector prepared in the above manner by means of a deposition device equipped with an electron beam heating means while purity 99.7% oxygen was being introduced, so that a SiO0.5 film with a thickness of 23 μm was formed on each of the protrusions. This was then slit to a predetermined width and length to obtain a long-strip like negative electrode plate. At this time, the slitting was made so that the column direction Y agreed with the longitudinal direction of the negative electrode plate or the current collector and that the row direction X agreed with the width direction of the negative electrode plate.

In the current collector produced in the above manner, the protrusions are aligned in the width direction (row direction X) at an equal pitch in a zigzag to form a row unit, and the intervals between a given protrusion and all the adjacent protrusions are equal. Thus, when the negative electrode active material is deposited toward the longitudinal direction (column direction Y) of the current collector, the negative electrode active material can be efficiently attached onto the protrusions and, in addition, the current collector can exhibit a large resistance to the tensile stress exerted on the longitudinal direction of the current collector. Hence, when the negative electrode mixture layers were deposited on the current collector to produce the negative electrode plate, or when the negative electrode plate was slit in the above manner, it was possible to prevent the current collector from becoming locally deformed or warped and prevent the negative electrode mixture layers from separating therefrom.

A 15-μm thick copper foil was used as a current collector for a negative electrode plate. A pair of rollers (ceramic rollers) were produced in order to form a large number of protrusions whose tops and cross-sections are substantially square, as illustrated inFIG. 12of Embodiment 8, on the surfaces of this copper foil in the aforementioned arrangement pattern. On the surface of each roller, depressions (depth 7 μm) having a shape corresponding to that of the protrusions were formed in the aforementioned arrangement pattern. The copper foil was passed between the pair of rollers while being pressed. In this way, a current collector for a negative electrode plate having 5-μm-high protrusions on both faces and having a total thickness of 20 μm was produced.

Subsequently, using purity 99.9999% silicon (negative electrode active material) as the sputtering target, a deposition process was performed on both faces of the current collector prepared in the above manner by means of a deposition device equipped with an electron beam heating means while purity 99.7% oxygen was being introduced, so that a SiO0.5 film with a thickness of 15 μm was formed on each of the protrusions. This was then slit to a predetermined width and length to obtain a long-strip like negative electrode plate. At this time, the slitting was made so that the column direction Y agreed with the longitudinal direction of the negative electrode plate or the current collector and that the row direction X agreed with the width direction of the negative electrode plate.

In the current collector produced in the above manner, the protrusions are aligned in the width direction (row direction X) at an equal pitch in a zigzag to form a row unit, and the intervals between a given protrusion and all the adjacent protrusions are equal. Thus, when the negative electrode active material is deposited toward the longitudinal direction (column direction Y) of the current collector, the negative electrode active material can be efficiently attached onto the protrusions and, in addition, the current collector can exhibit a large resistance to the tensile stress exerted on the longitudinal direction of the current collector. Hence, when the negative electrode mixture layers were deposited on the current collector to produce the negative electrode plate, or when the negative electrode plate was slit in the above manner, it was possible to prevent the current collector from becoming locally deformed or warped and prevent the negative electrode mixture layers from separating therefrom.

A 18-μm thick copper foil was used as a current collector for a negative electrode plate. A pair of rollers (ceramic rollers) were produced in order to form a large number of protrusions whose tops and cross-sections are substantially square, as illustrated inFIG. 13of Embodiment 9, on the surfaces of this copper foil in the aforementioned arrangement pattern. On the surface of each roller, depressions (depth 10 μm) having a shape corresponding to that of the protrusions were formed in the aforementioned arrangement pattern. The copper foil was passed between the pair of rollers while being pressed. In this way, a current collector for a negative electrode plate having 8-μm-high protrusions on both faces and having a total thickness of 26 μm was produced.

Subsequently, using purity 99.9999% silicon (negative electrode active material) as the sputtering target, a deposition process was performed on both faces of the current collector prepared in the above manner by means of a deposition device equipped with an electron beam heating means while purity 99.7% oxygen was being introduced, so that a SiO0.5 film with a thickness of 20 μm was formed on each of the protrusions. This was then slit to a predetermined width and length to obtain a long-strip like negative electrode plate. At this time, the slitting was made so that the column direction Y agreed with the longitudinal direction of the negative electrode plate or the current collector and that the row direction X agreed with the width direction of the negative electrode plate.

In the current collector produced in the above manner, the substantially square protrusions are formed so that the direction of a diagonal line agrees with the width direction (row direction X) of the current collector. Thus, when the negative electrode active material is deposited toward the longitudinal direction (column direction Y) of the current collector, the active material can be efficiently attached onto the protrusions and, in addition, the current collector can exhibit a large resistance to the tensile stress exerted on the longitudinal direction of the current collector. Hence, when the negative electrode mixture layers were deposited on the current collector to produce the negative electrode plate, or when the negative electrode plate was slit in the above manner, it was possible to prevent the current collector from becoming locally deformed or warped and prevent the negative electrode mixture layers from separating therefrom.

A 10-μm thick copper foil was used as a current collector for a negative electrode plate. A pair of rollers (ceramic rollers) were produced in order to form a large number of protrusions whose tops and cross-sections are substantially equilateral hexagonal, as illustrated inFIG. 14of Embodiment 10, on the surfaces of this copper foil in the aforementioned arrangement pattern. On the surface of each roller, depressions (depth 3 μm) having a shape corresponding to that of the protrusions were formed in the aforementioned arrangement pattern. The copper foil was passed between the pair of rollers while being pressed. In this way, a current collector for a negative electrode plate having 2-μm-high protrusions on both faces and having a total thickness of 12 μm was produced.

Subsequently, a negative electrode mixture paint was prepared by stirring 100 parts by weight of artificial graphite, serving as a negative electrode active material, 2.5 parts by weight (1 part by weight when converted to the solid content of the binder) of a dispersion of styrene-butadiene copolymer rubber particles (solid content 40% by weight), serving as a binder, per 100 parts by weight of the active material, 1 part by weight of carboxymethylcellulose, serving as a thickener, per 100 parts by weight of the active material, and a suitable amount of water with a double-arm kneader. This negative electrode mixture paint was applied onto both faces of the current collector prepared in the above manner, dried, and pressed. The current collector was then slit to a predetermined width and length to produce a long-strip like negative electrode plate. At this time, the slitting was made so that the column direction Y agreed with the longitudinal direction of the negative electrode plate and that the row direction X agreed with the width direction of the negative electrode plate.

In the current collector produced in the above manner, the substantially equilateral hexagonal protrusions are formed so that the direction of one of the longest diagonal lines agrees with the width direction (row direction X) of the current collector. Thus, the current collector can exhibit a large resistance to the tensile stress exerted on the longitudinal direction of the current collector during the production of the current collector and the negative electrode plate. Hence, when the negative electrode mixture layers were deposited on the current collector to produce the negative electrode plate, or when the negative electrode plate was slit in the above manner, it was possible to prevent the current collector from becoming locally deformed or warped and prevent the negative electrode mixture layers from separating therefrom.

A 12-μm thick aluminum foil was used as a current collector for a positive electrode plate. A pair of rollers (ceramic rollers) were produced in order to form a large number of protrusions whose tops and cross-sections are substantially equilateral hexagonal, as illustrated inFIG. 15of Embodiment 11, on the surfaces of this aluminum foil in the aforementioned arrangement pattern. On the surface of each roller, depressions (depth 3 μm) having a shape corresponding to that of the protrusions were formed in the aforementioned arrangement pattern. The aluminum foil was passed between the pair of rollers while being pressed. In this way, a current collector for a positive electrode plate having 2-μm-high protrusions on both faces and having a total thickness of 14 μm was produced.

Subsequently, a positive electrode mixture paint was prepared by stirring and kneading 100 parts by weight of lithium cobaltate, serving as a positive electrode active material, 2 parts by weight of an acetylene black conductive agent per 100 parts by weight of the active material, 2 parts by weight of a polyvinylidene difluoride binder per 100 parts by weight of the active material, and a suitable amount of N-methyl-2-pyrrolidone with a double-arm kneader. This positive electrode mixture paint was applied onto both faces of the current collector prepared in the above manner, dried, and pressed. The current collector was then slit to a predetermined width and length to produce a long-strip like positive electrode plate. At this time, the slitting was made so that the column direction Y agreed with the longitudinal direction of the positive electrode plate and that the row direction X agreed with the width direction of the positive electrode plate.

In the current collector produced in the above manner, the direction of a straight line perpendicular to a pair of opposite sides of the substantially equilateral hexagon agrees with the width direction (row direction X) of the current collector. Thus, the current collector can exhibit a large resistance to the tensile stress exerted on the longitudinal direction of the current collector during the production of the current collector and positive electrode plate. Hence, when the positive electrode mixture layers were formed on the current collector to produce the positive electrode plate, or when the positive electrode plate was slit in the above manner, it was possible to prevent the current collector from becoming locally deformed or warped and prevent the positive electrode mixture layers from separating therefrom.

To produce a non-aqueous secondary battery of the invention, a positive electrode current collector having 3-μm-high protrusions on both faces in the aforementioned arrangement pattern and having a total thickness of 18 μm was produced in the same manner as in Example 1.

Subsequently, a positive electrode mixture paint was prepared by stirring and kneading 100 parts by weight of lithium cobaltate in which part of the cobalt was replaced with nickel and manganese, serving as a positive electrode active material, 2 parts by weight of an acetylene black conductive agent per 100 parts by weight of the active material, 2 parts by weight of a polyvinylidene difluoride binder per 100 parts by weight of the active material, and a suitable amount of N-methyl-2-pyrrolidone with a double-arm kneader. This positive electrode mixture paint was applied onto both faces of the current collector prepared in the above manner, dried, and pressed. The current collector was then slit to a predetermined width and length to produce a long-strip like positive electrode plate. At this time, the slitting was made so that the column direction Y agreed with the longitudinal direction of the positive electrode plate and that the row direction X agreed with the width direction of the positive electrode plate. In this way, a 57-μm-thick positive electrode mixture layer was formed on each face of the positive electrode current collector, and a positive electrode plate having a total thickness of 126 μm was produced.

Also, in the same manner as in Example 4, a negative electrode current collector having 8-μm-high protrusions on both faces thereof in the aforementioned arrangement pattern and having a total thickness of 26 μm was produced.

Subsequently, using purity 99.9999% silicon (negative electrode active material) as the sputtering target, a deposition process was performed on both faces of the current collector prepared in the above manner by means of a deposition device equipped with an electron beam heating means while purity 99.7% oxygen was being introduced. Herein, the active material was deposited in columnar form on the tops of the protrusions so that they aligned continuously in a lateral direction to form a 25-μm-thick thin film of SiO0.5. This was then slit to a predetermined width and length to obtain a long-strip like negative electrode plate. At this time, the slitting was made so that the column direction Y agreed with the longitudinal direction of the negative electrode plate and that the row direction X agreed with the width direction of the negative electrode plate.

Using the positive electrode plate and the negative electrode plate prepared in the above manner, a lithium ion secondary battery illustrated inFIG. 4was produced. More specifically, the positive electrode plate and the negative electrode plate were spirally wound with a separator interposed therebetween, to form an electrode assembly. This electrode assembly was housed in a cylindrical battery case with a bottom together with an insulator plate. A negative electrode lead attached to the lower part of the electrode assembly was connected to the bottom of the battery case. Subsequently, a positive electrode lead attached to the upper part of the electrode assembly was connected to a seal plate, and a predetermined amount of an electrolyte (not shown) comprising a non-aqueous solvent was injected into the battery case. Thereafter, the seal plate the circumference of which was fitted with a seal gasket was inserted in the opening of the battery case, and the opening of the battery case was bent inward and crimped for sealing. In this way, a lithium ion secondary battery was produced.

In the lithium ion secondary battery, after the production of the spirally wound electrode assembly, the electrode assembly was disassembled and observed. As a result, both the positive electrode plate and the negative electrode plate were found to have no problem such as breakage of the electrode plate or separation of the active material layer. Further, when the charge/discharge of this lithium ion secondary battery was repeated 300 cycles, no cycle deterioration occurred. Also, after the repetition of 300 charge/discharge cycles, the lithium ion secondary battery and the electrode assembly were disassembled. As a result, they were found to have no problem such as deposition of lithium or separation of the active material layer. This is probably because the formation of the thin film comprising the columnar active material on the uncompressed tops of the protrusions enabled a reduction in volume change due to expansion of the active material thin film upon lithium absorption and shrinkage of the active material thin film upon lithium desorption, so that good battery performance could be maintained.

As shown in the foregoing Examples 8 to 12, in the electrode plate for a non-aqueous secondary battery of the invention, protrusions at least the tops of which were not compressed were formed on the surfaces of a current collector in the aforementioned arrangement pattern, so that the arrangement pattern of the protrusions exhibits a large resistance to stress. Therefore, in the step of forming the protrusions on the surfaces of the current collector and the step of disposing the active material on the protrusions of the current collector, it is possible to prevent the current collector from becoming locally deformed or distorted. At the same time, in the step of disposing the active material on the protrusions of the current collector and the subsequent step such as slitting to a predetermined width and length, it is also possible to suppress separation of the active material.

Further, since the tops of the protrusions of the current collector are not compressed, no processing strain due to compression process remains thereon and the surface accuracy of the protrusions is good, and it is thus possible to form an even thin film thereon. Also, since the surface roughness is not reduced by compression process and the original surface roughness is maintained, it is possible to heighten the adhesion between the protrusions and the active material thin film. In this respect, in order to further heighten the adhesion between the surface of the protrusions and the active material, it is very effective to roughen the current collector surface in advance before subjecting it to a process.

Also, as shown in Example 13, it is preferable to dispose the active material mainly on the uncompressed tops of the protrusions in columnar form. In this case, when the non-aqueous secondary battery is charged and discharged, the volume change due to expansion of the active material upon lithium absorption and shrinkage of the active material upon lithium desorption is reduced. It is thus possible to obtain a high-capacity, high-reliability non-aqueous secondary battery that does not suffer such a problem as breakage of the electrode plate due to charge/discharge and separation of the active material layer.

Referring now toFIG. 16andFIG. 17, Embodiment 12 of the invention is described. InFIG. 16, (a) is a plane view schematically showing the structure of a current collector for a non-aqueous secondary battery according to Embodiment 12 of the invention and (b) is a Z-Z cross-sectional view thereof.

InFIG. 16, a current collector10K is a current collector for use in an electrode plate of a lithium ion secondary battery (hereinafter also referred to as simply a lithium secondary battery), which is an exemplary non-aqueous secondary battery. The current collector10K is formed of a metal foil1at least one surface of which has a large number of columnar protrusions2K in a predetermined arrangement pattern, and the tops and cross-sections of the columnar protrusions2K are substantially circular. It should be noted that at least the tops of the protrusions2K are not compressed. Also, the protrusions2K do not need to be substantially circular, and their shape may be, for example, substantially oval, substantially rectangular, substantially rhombic, substantially square, and substantially equilateral polygonal with N angles (N: N is an even number of 6 or more).

In the arrangement pattern ofFIG. 16, the protrusions2K are aligned linearly at an equal pitch P19in the row direction X, and a group of these protrusions2K aligned in the row direction X constitute a row unit. Such row units are aligned in parallel in the column direction Y, which is a direction perpendicular to the row direction X, at predetermined pitches P20, P21, P22, P23, P24, . . . . Also, the respective protrusions2K of such a row unit are displaced in the row direction X from the protrusions2K of another row unit that is adjacent in the column direction Y, and the amount of displacement is a pitch that is ½ of the pitch P19. The amount of the pitch displaced is not limited to ½ of the pitch P19and can be increased or decreased if necessary.

Also, as illustrated inFIG. 16(b), the protrusions2K formed on one face of the current collector10K are in phase with those on the other face in the row direction X.

It should be noted that the pitches P20, P21, . . . at which the row units are aligned in the column direction Y are set, for example, so as to satisfy the following inequality 1. That is, in the arrangement pattern of the protrusions2K of the current collector10K, the pitches in the column direction Y are changed, and the column direction Y corresponds to the longitudinal direction of the long-strip like positive electrode plate31and negative electrode plate32that are spirally wound to form the electrode assembly34as illustrated inFIG. 4. The positive electrode plate31, the negative electrode plate32, and the electrode assembly34are produced so that the largest pitch P20is positioned at the innermost part of the electrode assembly34and that the pitch gradually decreases and becomes smallest at the outermost part of the electrode assembly34.
P20>P21>P22>P23>P24>  (1)

FIG. 17is an enlarged perspective view of the surface of a roller used to form the protrusions2K on the current collector10K.

The roller ofFIG. 17is prepared by coating the surface of a metal roller material with a ceramic such as CrO, WC, or TiN and then forming depressions7B corresponding to the protrusions2K in an arrangement pattern corresponding to the aforementioned arrangement pattern by laser machining or the like.

That is, the depressions7B are aligned linearly in the axial direction of the roller at a pitch P19′, which is equal to the pitch P19, thereby forming a row unit, and such row units are aligned in parallel in the circumferential direction of the roller at pitches P20′, P21′, . . . , which are equal to the predetermined pitches P20, P21, . . . .

Also, the respective depressions7B of the row units that are adjacent in the circumferential direction of the roller are displaced from one another in the axial direction of the roller, and the amount of displacement is a pitch that is ½ of the pitch P19′. The amount of the pitch displaced is not limited to ½ of the pitch P19′ and can be increased or decreased if necessary.

The processing method of forming the protrusions2K on the surfaces of the current collector10K by using the rollers ofFIG. 17is the same as that of Embodiment 1 shown inFIG. 3. Also, the protrusions2K can be formed by using dies, etc. in place of the rollers in the same manner. The method of producing an electrode plate by using the current collector10K is also the same as that of Embodiment 1. Further, the method of producing a non-aqueous secondary battery by using the electrode plate prepared in the above manner is also the same as that of Embodiment 1 shown inFIG. 4.

Referring now toFIG. 18, Embodiment 13 of the invention is described.FIG. 18has a plane view (a) schematically showing the structure of a current collector for a non-aqueous secondary battery according to Embodiment 13 of the invention and a Z1-Z1cross-sectional view thereof.

As illustrated inFIG. 18, in a current collector10L of Embodiment 13, protrusions2L are formed on both faces in the same arrangement pattern as that of Embodiment 12, but Embodiment 13 is different from Embodiment 12 in that the protrusions2L formed on one face of the current collector10L are out of phase with those on the other face.

That is, in the current collector10L ofFIG. 18, the substantially circular protrusions2L are aligned linearly in the row direction X at an equal pitch P25, thereby forming a row unit, and such row units are aligned in parallel in the column direction Y at predetermined pitches P26, P27, . . . , which decrease gradually. Also, the respective protrusions2L of such row units that are adjacent in the column direction Y are displaced from one another in the row direction X, and the amount of displacement is a pitch that is ½ of the pitch P25. The protrusions2L do not need to be substantially circular, and their shape may be, for example, substantially oval, substantially rectangular, substantially rhombic, substantially square, and substantially equilateral polygonal with N angles (N: N is an even number of 6 or more). Also, the amount of the pitch of the protrusions2L displaced in the row direction X is not limited to ½ of the pitch P25and can be increased or decreased if necessary.

In the current collector10L, the protrusions2L formed on one face are out of phase with those on the other face in the row direction X by 180°. The phase difference does not need to be 180° and can be increased or decreased if necessary.

The processing method of forming the protrusions2L on the surfaces of the current collector10L is the same as that of Embodiment 1 shown inFIG. 3. Also, the protrusions2L can be formed by using dies, etc. in place of the rollers in the same manner. The method of producing an electrode plate by using the current collector10L is also the same as that of Embodiment 1. Further, the method of producing a non-aqueous secondary battery by using the electrode plate prepared in the above manner is also the same as that of Embodiment 1 shown inFIG. 4.

Referring now toFIG. 19, Embodiment 14 of the invention is described.FIG. 19has a plane view (a) schematically showing the structure of a current collector for a non-aqueous secondary battery according to Embodiment 14 of the invention and a Z2-Z2cross-sectional view thereof.

As illustrated inFIG. 19, in a current collector10M of Embodiment 14, protrusions2M are formed on both faces in the same arrangement pattern as that of Embodiment 12, but Embodiment 14 is different from Embodiment 12 in that the pitch of the protrusions2M on one face of the current collector10M is different from that on the other face.

That is, on each face of the current collector10M ofFIG. 19, the substantially circular protrusions2M are aligned linearly in the row direction X at an equal pitch P61, thereby forming a row unit, and such row units are aligned in parallel in the column direction Y at predetermined pitches P62, P63, . . . , which decrease gradually. Also, the respective protrusions2M of such row units that are adjacent in the column direction Y are displaced from one another in the row direction X, and the amount of displacement is a pitch that is ½ of the pitch P61. The protrusions2M do not need to be substantially circular, and their shape may be, for example, substantially oval, substantially rectangular, substantially rhombic, substantially square, and substantially equilateral polygonal with N angles (N: N is an even number of 6 or more). Also, the amount of the pitch of the protrusions2M displaced in the row direction X is not limited to ½ of the pitch P61and can be increased or decreased if necessary.

In the current collector10M, pitches P32, P33, P34, P35, and P36of the row units on one face (the face on the upper side in the figure) in the column direction Y are different from pitches P37, P38, P39, P40, and P41of the row units on the other face (the face on the lower side in the figure) in the column direction Y. That is, as shown in the following inequalities 2, the pitches on “the other face” are greater than those on “one face”. It should be noted that “one face” corresponds to the face positioned on the outer side of the electrode assembly34ofFIG. 4, while “the other face” corresponds to the face positioned on the inner side of the electrode assembly34. This can reduce the influence of the difference in curvature between the faces on the outer and inner sides of the electrode assembly34.
P41>P36, P40>P35, P39>P34, P38>P33, P37>P32  (2)

The processing method of forming the protrusions2M on the surfaces of the current collector10M is the same as that of Embodiment 1 shown inFIG. 3. Also, the protrusions2M can be formed by using dies, etc. in place of the rollers in the same manner. The method of producing an electrode plate by using the current collector10M is also the same as that of Embodiment 1. Further, the method of producing a non-aqueous secondary battery by using the electrode plate prepared in the above manner is also the same as that of Embodiment 1 shown inFIG. 4.

Referring now toFIG. 20, Embodiment 15 of the invention is described.FIG. 20has a plane view (a) schematically showing the structure of a current collector for a non-aqueous secondary battery according to Embodiment 15 of the invention and a Z3-Z3cross-sectional view thereof.

As illustrated inFIG. 20, in a current collector10N of Embodiment 15, protrusions2N are formed on both faces in the same arrangement pattern as that of Embodiment 14, but Embodiment 15 is different from Embodiment 14 in the shape of the protrusions.

That is, on each face of the current collector10N ofFIG. 20, the substantially rhombic protrusions2N are aligned linearly in the row direction X at an equal pitch P42, thereby forming a row unit, and such row units are aligned in parallel in the column direction Y at predetermined pitches P43, P44, . . . , which decrease gradually. Also, the respective protrusions2N of such row units that are adjacent in the column direction Y are displaced from one another in the row direction X, and the amount of displacement is a pitch that is ½ of the pitch P42. The amount of the pitch of the protrusions2N displaced in the row direction X is not limited to ½ of the pitch P42and can be increased or decreased if necessary.

In the current collector10N, pitches P48, P49, P50, P51, and P52of the row units on one face (the face on the upper side in the figure) in the column direction Y are different from pitches P53, P54, P55, P56, and P57of the row units on the other face (the face on the lower side in the figure) in the column direction Y. That is, as shown in the following inequalities 3, the pitches on “the other face” are greater than those on “one face”. It should be noted that “one face” corresponds to the face positioned on the outer side of the electrode assembly34ofFIG. 4, while “the other face” corresponds to the face positioned on the inner side of the electrode assembly34. This can reduce the influence of the difference in curvature between the faces on the outer and inner sides of the electrode assembly34.
P57>P52, P56>P51, P55>P50, P54>P49, P53>P48  (3)

The processing method of forming the protrusions2N on the surfaces of the current collector10N is the same as that of Embodiment 1 shown inFIG. 3. Also, the protrusions2N can be formed by using dies, etc. in place of the rollers in the same manner. The method of producing an electrode plate by using the current collector10N is also the same as that of Embodiment 1. Further, the method of producing a non-aqueous secondary battery by using the electrode plate prepared in the above manner is also the same as that of Embodiment 1 shown inFIG. 4.

A 15-μm thick aluminum foil was used as a current collector for a positive electrode plate. A pair of rollers (ceramic rollers) were produced in order to form a large number of protrusions whose tops and cross-sections are substantially circular, as illustrated inFIG. 16of Embodiment 12, on the surfaces of this aluminum foil in the aforementioned arrangement pattern. On the surface of each roller, depressions (depth 4 μm) having a shape corresponding to that of the protrusions were formed in the aforementioned arrangement pattern. The aluminum foil was passed between the pair of rollers while being pressed. In this way, a current collector for a positive electrode plate having 3-μm-high protrusions on both faces and having a total thickness of 18 μm was produced.

Subsequently, a positive electrode mixture paint was prepared by stirring and kneading 100 parts by weight of lithium cobaltate, serving as a positive electrode active material, 2 parts by weight of an acetylene black conductive agent per 100 parts by weight of the active material, 2 parts by weight of a polyvinylidene difluoride binder per 100 parts by weight of the active material, and a suitable amount of N-methyl-2-pyrrolidone with a double-arm kneader. This positive electrode mixture paint was applied onto both faces of the current collector prepared in the above manner, dried, and pressed. The current collector was then slit to a predetermined width and length to produce a long-strip like positive electrode plate. At this time, the slitting was made so that the column direction Y agreed with the longitudinal direction of the positive electrode plate and that the row direction X agreed with the width direction of the positive electrode plate.

In the current collector produced in the above manner, the substantially circular protrusions are formed in a close-packed arrangement pattern. Thus, it exhibits a large resistance to the tensile stress exerted on the longitudinal direction (the column direction Y) of the current collector or positive electrode plate during the production of the current collector and positive electrode plate. Hence, when the positive electrode mixture layers were formed on the current collector to produce the positive electrode plate, or when the positive electrode plate was slit in the above manner, it was possible to prevent the current collector from becoming locally deformed or warped and prevent the positive electrode mixture layers from separating therefrom.

A 10-μm thick copper foil was used as a current collector for a negative electrode plate. A pair of rollers (ceramic rollers) were produced in order to form a large number of protrusions whose tops and cross-sections are substantially circular, as illustrated inFIG. 18of Embodiment 13, on the surfaces of this copper foil in the aforementioned arrangement pattern. On the surface of each roller, depressions (depth 3 μm) having a shape corresponding to that of the protrusions were formed in the aforementioned arrangement pattern. The copper foil was passed between the pair of rollers while being pressed. In this way, a current collector for a negative electrode plate having 2-μm-high protrusions on both faces and having a total thickness of 12 μm was produced.

Subsequently, a negative electrode mixture paint was prepared by stirring 100 parts by weight of artificial graphite, serving as a negative electrode active material, 2.5 parts by weight (1 part by weight when converted to the solid content of the binder) of a dispersion of styrene-butadiene copolymer rubber particles (solid content 40% by weight), serving as a binder, per 100 parts by weight of the active material, 1 part by weight of carboxymethylcellulose, serving as a thickener, per 100 parts by weight of the active material, and a suitable amount of water with a double-arm kneader. This negative electrode mixture paint was applied onto both faces of the current collector prepared in the above manner, dried, and pressed. The current collector was then slit to a predetermined width and length to produce a long-strip like negative electrode plate. At this time, the slitting was made so that the column direction Y agreed with the longitudinal direction of the negative electrode plate and that the row direction X agreed with the width direction of the negative electrode plate.

In the current collector produced in the above manner, the substantially circular protrusions are formed in a close-packed arrangement pattern. Thus, the current collector exhibits a large resistance to the tensile stress exerted on the longitudinal direction (the column direction Y) of the current collector or negative electrode plate during the production of the current collector and the negative electrode plate. Hence, when the negative electrode mixture layers were formed on the current collector to produce the negative electrode plate, or when the negative electrode plate was slit in the above manner, it was possible to prevent the current collector from becoming locally deformed or warped and prevent the negative electrode mixture layers from separating therefrom.

A 15-μm thick copper foil was used as a current collector for a negative electrode plate. A pair of rollers (ceramic rollers) were produced in order to form a large number of protrusions whose tops and cross-sections are substantially circular, as illustrated inFIG. 19of Embodiment 14, on the surfaces of this copper foil in the aforementioned arrangement pattern. On the surface of each roller, depressions (depth 8 μm) having a shape corresponding to that of the protrusions were formed in the aforementioned arrangement pattern. The copper foil was passed between the pair of rollers while being pressed. In this way, a current collector for a negative electrode plate having 6-μm-high protrusions on both faces and having a total thickness of 21 μm was produced.

Subsequently, using purity 99.9999% silicon (negative electrode active material) as the sputtering target, a deposition process was performed on both faces of the current collector prepared in the above manner by means of a deposition device equipped with an electron beam heating means while purity 99.7% oxygen was being introduced, so that a SiO0.5 film with a thickness of 18 μm was formed on each of the protrusions. This was then slit to a predetermined width and length to obtain a long-strip like negative electrode plate. At this time, the slitting was made so that the column direction Y agreed with the longitudinal direction of the negative electrode plate or the current collector and that the row direction X agreed with the width direction of the negative electrode plate.

In the current collector produced in the above manner, the substantially circular protrusions are formed in a close-packed arrangement pattern. Thus, when the negative electrode active material is deposited toward the longitudinal direction (column direction Y) of the current collector, the active material can be efficiently attached onto the protrusions and, in addition, the current collector can exhibit a large resistance to the tensile stress exerted on the longitudinal direction of the current collector. Hence, when the negative electrode mixture layers were deposited on the current collector to produce the negative electrode plate, or when the negative electrode plate was slit in the above manner, it was possible to prevent the current collector from becoming locally deformed or warped and prevent the negative electrode mixture layers from separating therefrom.

To produce a non-aqueous secondary battery of the invention, a positive electrode current collector having 3-μm-high protrusions on both faces in the aforementioned arrangement pattern and having a total thickness of 18 μm was produced in the same manner as in Example 14 as shown inFIG. 16.

Subsequently, a positive electrode mixture paint was prepared by stirring and kneading 100 parts by weight of lithium cobaltate, serving as a positive electrode active material, 2 parts by weight of an acetylene black conductive agent per 100 parts by weight of the active material, 2 parts by weight of a polyvinylidene difluoride binder per 100 parts by weight of the active material, and a suitable amount of N-methyl-2-pyrrolidone with a double-arm kneader. This positive electrode mixture paint was applied onto both faces of the current collector prepared in the above manner, dried, and pressed. The current collector was then slit to a predetermined width and length to produce a long-strip like positive electrode plate. At this time, the slitting was made so that the column direction Y agreed with the longitudinal direction of the positive electrode plate and that the row direction X agreed with the width direction of the positive electrode plate.

Also, in the same manner as in Example 16 shown inFIG. 19, a negative electrode current collector having 6-μm-high protrusions on both faces thereof in the aforementioned arrangement pattern and having a total thickness of 21 μm was produced.

Subsequently, using purity 99.9999% silicon (negative electrode active material) as the sputtering target, a deposition process was performed on both faces of the current collector prepared in the above manner by means of a deposition device equipped with an electron beam heating means while purity 99.7% oxygen was being introduced. Herein, the negative electrode active material was deposited in columnar form on the tops of the protrusions so that they aligned continuously in a lateral direction to form a 25-μm-thick thin film of SiO0.5. This was then slit to a predetermined width and length to obtain a long-strip like negative electrode plate. At this time, the slitting was made so that the column direction Y agreed with the longitudinal direction of the negative electrode plate and that the row direction X agreed with the width direction of the negative electrode plate.

Using the positive electrode plate and the negative electrode plate prepared in the above manner, an electrode assembly34illustrated inFIG. 4was produced (also seeFIG. 28). More specifically, the positive electrode plate and the negative electrode plate were spirally wound with a separator interposed therebetween, to form a cylindrical electrode assembly. At this time, the two electrode plates were wound so that the side of each current collector with a larger pitch (upper side in the figure) in the longitudinal direction (column direction Y) was positioned on the inner side of the electrode assembly and that the side with a smaller pitch (lower side in the figure) was positioned on the outer side of the electrode assembly.

The electrode assembly prepared in the above manner was found to have no displacement in the wound electrode assembly or no separation of the positive electrode active material and the negative electrode active material in the process of winding the electrode assembly. Also, after the preparation of the electrode assembly, this electrode assembly was disassembled and the positive electrode plate and the negative electrode plate were observed. As a result, they were found to have no problem such as separation of the positive electrode mixture layer and negative electrode mixture layer.

Further, as illustrated inFIG. 4, this electrode assembly was housed in a cylindrical battery case with a bottom together with an insulator plate. A negative electrode lead attached to the lower part of the electrode assembly was connected to the bottom of the battery case. Subsequently, a positive electrode lead attached to the upper part of the electrode assembly was connected to a seal plate, and a predetermined amount of an electrolyte (not shown) comprising a non-aqueous solvent was injected into the battery case. Thereafter, the seal plate the circumference of which was fitted with a seal gasket was inserted in the opening of the battery case80, and the opening of the battery case was bent inward and crimped for sealing. In this way, a lithium secondary battery was produced as a non-aqueous secondary battery.

After the charge/discharge of this lithium secondary battery was repeated 500 cycles, the electrode assembly was taken out and disassembled. As a result, it was found to have no problem such as deposition of lithium and separation of the positive electrode mixture layer and negative electrode mixture layer.

A 18-μm thick copper foil was used as a current collector for a negative electrode plate. A pair of rollers (ceramic rollers) were produced in order to form a large number of protrusions whose tops and cross-sections are substantially rhombic, as illustrated inFIG. 20of Embodiment 15, on the surfaces of this copper foil in the aforementioned arrangement pattern. On the surface of each roller, depressions (depth 10 μm) having a shape corresponding to that of the protrusions were formed in the aforementioned arrangement pattern. The copper foil was passed between the pair of rollers while being pressed. In this way, a current collector for a negative electrode plate having 8-μm-high protrusions on both faces and having a total thickness of 26 μm was produced.

Subsequently, using purity 99.9999% silicon (negative electrode active material) as the sputtering target, a deposition process was performed on both faces of the current collector prepared in the above manner by means of a deposition device equipped with an electron beam heating means while purity 99.7% oxygen was being introduced, so that a SiO0.5 film with a thickness of 25 μm was formed on each of the protrusions. This was then slit to a predetermined width and length to obtain a long-strip like negative electrode plate. At this time, the slitting was made so that the column direction Y agreed with the longitudinal direction of the negative electrode plate or the current collector and that the row direction X agreed with the width direction of the negative electrode plate.

In the current collector produced in the above manner, the substantially circular protrusions are formed in a close-packed arrangement pattern. Thus, when the negative electrode active material is deposited toward the longitudinal direction (column direction Y) of the current collector, the active material can be efficiently attached onto the protrusions and, in addition, the current collector can exhibit a large resistance to the tensile stress exerted on the longitudinal direction of the current collector. Hence, when the negative electrode mixture layers were deposited on the current collector to produce the negative electrode plate, or when the negative electrode plate was slit in the above manner, it was possible to prevent the current collector from becoming locally deformed or warped and prevent the negative electrode mixture layers from separating therefrom.

To produce a non-aqueous secondary battery of the invention, a positive electrode current collector having 3-μm-high protrusions on both faces in the aforementioned arrangement pattern and having a total thickness of 18 μm was produced in the same manner as in Example 14 as shown inFIG. 16.

Subsequently, a positive electrode mixture paint was prepared by stirring and kneading 100 parts by weight of lithium cobaltate, serving as a positive electrode active material, 2 parts by weight of an acetylene black conductive agent per 100 parts by weight of the active material, 2 parts by weight of a polyvinylidene difluoride binder per 100 parts by weight of the active material, and a suitable amount of N-methyl-2-pyrrolidone with a double-arm kneader. This positive electrode mixture paint was applied onto both faces of the current collector prepared in the above manner, dried, and pressed. The current collector was then slit to a predetermined width and length to produce a long-strip like positive electrode plate. At this time, the slitting was made so that the column direction Y agreed with the longitudinal direction of the positive electrode plate and that the row direction X agreed with the width direction of the positive electrode plate.

Also, in the same manner as in Example 18 shown inFIG. 20, a negative electrode current collector having 8-μm-high protrusions on both faces thereof in the aforementioned arrangement pattern and having a total thickness of 26 μm was produced.

Subsequently, using purity 99.9999% silicon (negative electrode active material) as the sputtering target, a deposition process was performed on both faces of the current collector prepared in the above manner by means of a deposition device equipped with an electron beam heating means while purity 99.7% oxygen was being introduced. Herein, the active material was deposited in columnar form on the tops of the protrusions so that they aligned continuously in a lateral direction to form a 25-μm-thick thin film of SiO0.5. This was then slit to a predetermined width and length to obtain a long-strip like negative electrode plate. At this time, the slitting was made so that the column direction Y agreed with the longitudinal direction of the negative electrode plate and that the row direction X agreed with the width direction of the negative electrode plate.

Using the positive electrode plate and the negative electrode plate prepared in the above manner, an electrode assembly34illustrated inFIG. 4was produced (also seeFIG. 28). More specifically, the positive electrode plate and the negative electrode plate were spirally wound with a separator interposed therebetween, to form a cylindrical electrode assembly. At this time, the two electrode plates were wound so that the side of each current collector with a larger pitch (upper side in the figure) in the longitudinal direction (column direction Y) was positioned on the inner side of the electrode assembly and that the side with a smaller pitch (lower side in the figure) was positioned on the outer side of the electrode assembly.

The electrode assembly prepared in the above manner was found to have no displacement in the wound electrode assembly or no separation of the positive electrode mixture layer and the negative electrode mixture layer in the process of winding the electrode assembly. Also, after the preparation of the electrode assembly, this electrode assembly was disassembled and the positive electrode plate and the negative electrode plate were observed. As a result, they were found to have no problem such as separation of the positive electrode mixture layer and negative electrode mixture layer.

Further, as illustrated inFIG. 4, this electrode assembly was housed in a cylindrical battery case with a bottom together with an insulator plate. A negative electrode lead attached to the lower part of the electrode assembly was connected to the bottom of the battery case. Subsequently, a positive electrode lead attached to the upper part of the electrode assembly was connected to a seal plate, and a predetermined amount of an electrolyte (not shown) comprising a non-aqueous solvent was injected into the battery case. Thereafter, the seal plate the circumference of which was fitted with a seal gasket was inserted in the opening of the battery case80, and the opening of the battery case was bent inward and crimped for sealing. In this way, a lithium secondary battery was produced as a non-aqueous secondary battery.

After the charge/discharge of this lithium secondary battery was repeated 500 cycles, the electrode assembly was taken out and disassembled. As a result, it was found to have no problem such as deposition of lithium and separation of the positive electrode mixture layer and negative electrode mixture layer.

As shown in the foregoing Examples 14 to 16 and 18, in the electrode plate for a non-aqueous secondary battery of the invention, protrusions at least the tops of which were not compressed were formed on the surfaces of a current collector in the aforementioned arrangement pattern, so that the arrangement pattern of the protrusions exhibits a large resistance to stress. Therefore, in the step of forming the protrusions on the surfaces of the current collector and the step of disposing the active material on the protrusions of the current collector, it is possible to prevent the current collector from becoming locally deformed or distorted. At the same time, in the step of disposing the active material on the protrusions of the current collector and the subsequent step such as slitting to a predetermined width and length, it is also possible to suppress separation of the active material.

Also, as shown in Examples 17 and 19, it is possible to reduce the difference in bending stress exerted on the electrode plate resulting from the difference in curvature between the inner side and the outer side of the electrode assembly and the difference in curvature between the face positioned on the inner side and the face positioned on the outer side. Also, when the non-aqueous secondary battery is charged and discharged, the volume change due to expansion of the active material upon lithium absorption and shrinkage of the active material upon lithium desorption is reduced. It is thus possible to obtain a high-capacity, high-reliability non-aqueous secondary battery that does not suffer such a problem as breakage of the electrode plate due to charge/discharge and separation of the active material layer.

Referring now toFIG. 21andFIG. 22, Embodiment 16 of the invention is described. InFIG. 21, (a), (b), and (c) are three sectional views schematically showing the structures of a current collector for a non-aqueous secondary battery according to Embodiment 16 of the invention, and (d) is a plan view.

InFIG. 21, a current collector10P is a current collector for use in an electrode plate of a lithium ion secondary battery (hereinafter also referred to as simply a lithium secondary battery), which is an exemplary non-aqueous secondary battery. The current collector10P is prepared by forming a large number of columnar protrusions2P, the tops and cross-sections of which are substantially circular and at least the tops of which are not compressed, on one surface of a metal foil1in a predetermined arrangement pattern, making the other surface of the metal foil1a flat surface, and bonding the flat surfaces of two metal foils1together.

In the arrangement pattern ofFIG. 21(d), the protrusions2P are aligned linearly in the row direction X at an equal pitch, and a group of the protrusions2P aligned in the row direction X constitute a row unit. Such row units are aligned in parallel at an equal pitch in the column direction Y, which is a direction perpendicular to the row direction X. Also, the respective protrusions2P of such a row unit are displaced in the row direction X from the protrusions2P of another row unit that is adjacent in the column direction Y.

As shown inFIGS. 21(a), (b), and (c), the current collector10P is formed by bonding the flat surfaces of two metal foils1in such a manner that the phase of the protrusions2P is varied. That is, inFIG. 21(a), the protrusions2P are out of phase in the row direction X or column direction Y by a length L1, which is ½ of the diameter of the protrusions2P. InFIG. 21(b), the protrusions2P are out of phase by a length L2, which is ⅓ of the diameter of the protrusions2P. InFIG. 21(c), the protrusions2P are out of phase by a length L3, which is ¼ of the diameter of the protrusions2P.

FIG. 22is an enlarged perspective view of the surface of a roller used to form protrusions on the current collector.

The roller ofFIG. 22is prepared by coating the surface of a metal roller material with a ceramic such as CrO, WC, or TiN and then forming depressions7D corresponding to the protrusions2P in an arrangement pattern corresponding to the aforementioned arrangement pattern by laser machining or the like.

That is, the depressions7D are aligned linearly in the axial direction of the roller at an equal pitch P58to form a row unit, and such row units are aligned in parallel in the circumferential direction of the roller at an equal pitch P59.

Also, the respective depressions7D of the row units that are adjacent in the circumferential direction of the roller are displaced from one another in the axial direction of the roller, and the amount of displacement is a pitch P60, which is ½ of the pitch P58. The amount of the pitch displaced is not limited to ½ of the pitch P58and can be increased or decreased if necessary.

The roller with the depressions7D formed on the surface in the arrangement pattern ofFIG. 22and a flat roller with a surface roughness Ra (center line average roughness) of 25 μm or less are disposed with a predetermined space therebetween, and the long metal foil1is passed through the space to press both faces of the metal foil1with the two rollers. By this, a large number of the protrusions2P are formed on one face of the metal foil1in the aforementioned arrangement pattern, while the other face of the metal foil1is made a flat surface. In this way, the current collector10P is produced.

The method of producing the current collector10P is not limited to the method described above. For example, instead of the rollers, dies etc. can be used, and the current collector10P can also be produced by placing the metal foil1between an upper die with the depressions7D formed in the aforementioned arrangement pattern and a lower die with a flat surface, and compressing it. Also, the flat surfaces of the two metal foils1can be bonded together by high temperature roll pressure welding, ultrasonic welding, diffusion bonding, brazing, conductive bonding, etc. At this time, with the temperature of the metal foils1set to 350° C., a plane pressure of 400 Mpa or higher is applied for bonding.

The method of producing an electrode plate by using the current collector10P is the same as that of Embodiment 1. Also, the method of producing a non-aqueous secondary battery by using the electrode plate prepared in the above manner is also the same as that of Embodiment 1 shown inFIG. 4.

Referring now toFIG. 23, Embodiment 17 of the invention is described. InFIG. 23, (a) is a sectional view schematically showing the structure of a current collector for a non-aqueous secondary battery according to Embodiment 17 of the invention, and (b) is a plane view.

As illustrated inFIG. 23, a current collector10Q of Embodiment 17 is produced in the same manner as the current collector10P of Embodiment 16, but is different from that of Embodiment 16 in that protrusions2Q formed on both faces of the current collector10Q are in phase with one another.

The method of bonding the flat surfaces of metal foils1together is the same as that of Embodiment 16. The processing method of forming the protrusions2Q on the surface of the current collector10Q is also the same as that of Embodiment 16. Also, the protrusions2Q can be formed by using dies, etc. in place of the rollers in the same manner. The method of producing an electrode plate by using the current collector10Q is also the same as that of Embodiment 1. Further, the method of producing a non-aqueous secondary battery by using the electrode plate prepared in the above manner is also the same as that of Embodiment 1 shown inFIG. 4.

Referring now toFIG. 24, Embodiment 18 of the invention is described.FIG. 24schematically shows the structure of a current collector for a non-aqueous secondary battery according to Embodiment 18 of the invention; (a) is a sectional view in a process of production and (b) is a sectional view upon completion of the production.

As illustrated inFIG. 24, a current collector10R of Embodiment 18 is the same as that of Embodiment 16 in that it is composed of a metal foil1one face of which has protrusions and the other face of which is a flat surface, but is different from that of Embodiment 16 in that it is produced by folding one metal foil1and bonding the flat surfaces thereof.

In the example illustrated in the figure, protrusions2R on both faces of the current collector10R are in phase with one another; however, by adjusting the folding position of the metal foil1, the protrusions2R on both faces of the current collector10R can be made out of phase with one another, as inFIGS. 21(a), (b), and (c) of Embodiment 16.

However, as illustrated inFIG. 24, by causing the protrusion2R to be positioned at the folded end of the metal foil1, it is possible to prevent the folded end from becoming cracked and enhance the strength of the current collector10R.

The method of bonding the flat surfaces of the metal foil1together is the same as that of Embodiment 16. The processing method of forming the protrusions2Q on a surface of the current collector10Q is also the same as that of Embodiment 16. Also, the protrusions2Q can be formed by using dies, etc. in place of the rollers in the same manner. The method of producing an electrode plate by using the current collector10Q is also the same as that of Embodiment 1. Further, the method of producing a non-aqueous secondary battery by using the electrode plate prepared in the above manner is also the same as that of Embodiment 1 shown inFIG. 4.

A 7.5-μm thick aluminum foil was used as a current collector for a positive electrode plate. A roller (ceramic roller) was produced in order to form a large number of protrusions whose tops and cross-sections are substantially circular, as illustrated inFIG. 21(d) of Embodiment 16, on a surface of this aluminum foil in the aforementioned arrangement pattern. On the surface of the roller, depressions (depth 4 μm) having a shape corresponding to that of the protrusions were formed in the aforementioned arrangement pattern. The aluminum foil was passed between the roller with the protrusions on the surface and a flat roller with a surface roughness Ra (center line average roughness) of 25 μm or less while being pressed. As a result, 3-μm high protrusions were formed on one face of a metal foil1. The metal foil1was folded at a predetermined position, and the flat surfaces of the metal foil1were bonded together. In this way, three kinds of current collectors for positive electrode plates corresponding toFIGS. 21(a), (b), and (c) and having 3-μm-high protrusions on both faces and a total thickness of 18 μm were produced.

Subsequently, a positive electrode mixture paint was prepared by stirring and kneading 100 parts by weight of lithium cobaltate, serving as an active material, 2 parts by weight of an acetylene black conductive agent per 100 parts by weight of the active material, 2 parts by weight of a polyvinylidene difluoride binder per 100 parts by weight of the active material, and a suitable amount of N-methyl-2-pyrrolidone with a double-arm kneader. This positive electrode mixture paint was applied onto both faces of the current collector prepared in the above manner, dried, and pressed. The current collector was then slit to a predetermined width and length to produce a long-strip like positive electrode plate. At this time, the slitting was made so that the column direction Y agreed with the longitudinal direction of the positive electrode plate and that the row direction X agreed with the width direction of the positive electrode plate.

Using the current collectors produced in Example 20, electrode assemblies were produced. As a result, the portions with large cross sectional areas where the protrusions on one face and the other face overlapped one another received the stress created by the winding of the electrode plate and the other portions bent flexibly. It was thus possible to prevent these current collectors from becoming corrugated, wrinkled or warped.

To evaluate the positive electrode plates using these current collectors, rollers20A were arranged so as to cause a positive electrode plate31A to meander, as illustrated inFIG. 25(a), and a transport test was conducted to simulate winding onto rollers in a production process of a positive electrode plate. With the positive electrode plate31A wound onto the eight rollers20A, it was transported at a speed of 20 m/min. As illustrated inFIG. 25(b), by the weight of a positive electrode mixture layer80that fell off from positive electrode mixture layers79carried on the current collector10P, the state of falling-off of the positive electrode mixture layers was compared.

As a result, when the positive electrode plates using the current collectors produced in Example 20 were compared with a positive electrode plate composed of a flat current collector with a surface roughness of 100 μm or less (both faces) and positive electrode mixture layers carried thereon, the amount of the positive electrode mixture layers that fell off was 5% or less. This indicates that the adhesion between the current collector and the positive electrode mixture layers is good.

Also, in the step of forming protrusions2P on the surface of the current collector, the step of disposing the active material on the protrusions2P of the current collector, and the subsequent step such as slitting to a predetermined width, due to sufficient resistance to stress, it was possible to reduce local deformation or distortion by 30% or more, reduce falling-off of the positive electrode mixture layers, and reduce the amount of the positive electrode mixture layers that fell off to not more than 8% of that for the conventional positive electrode plate. This is because work hardening involving recrystallization occurred 2 to 4 μm from the protrusion surface and the size of the crystal grains in the surface of the current collector became very small.

Also, according to the method in which an electrode plate was produced by forming rhombic protrusions on both faces of a current collector at a pitch of 30 μm and depositing active material layers on the tops of the protrusions, by executing a deposition process at an angle relative to the surface of the current collector, the active material layers can be partially deposited. Because, the active material layers were not deposited on areas of the surface under the shadow of the protrusions. Due to the not-deposited areas created intentionally, a contact between the adjacent active material layers could be avoided. Even when the active material expanded and contracted due to repeated charge/discharge, a contact between the adjacent active materials and deformation or distortion of the current collector could be prevented. It was thus possible to reduce the amount of the positive electrode mixture layers that fell off to 12% or less.

Further, the relation between the electrode plates using the above-described current collectors and the sizes to which they were wound was examined. When these electrode plates were used in cylindrical secondary batteries with diameters of 18 mm and less, the electrode plate using the current collector illustrated inFIG. 21(a), in which the phase displacement is ½, was most effective in reducing the amount of the positive electrode mixture layers that fell off. In the case of cylindrical secondary batteries with diameters of 18 mm to 32 mm, the electrode plate using the current collector illustrated inFIG. 21(b), in which the phase displacement is ⅓, was most effective in reducing the amount of the positive electrode mixture layers that fell off. When these electrode plates were used in cylindrical secondary batteries with diameters of 32 mm and more, the electrode plate using the current collector illustrated inFIG. 21(c), in which the phase displacement is ¼, was most effective in reducing the amount of the positive electrode mixture layers that fell off.

Also, as illustrated inFIG. 26, an electrode assembly34B of a prismatic battery has two ends81and82at which the electrode plates have a large curvature. In prismatic batteries of every size, the amount of falling-off of the positive electrode mixture layers is greatest at the ends81and82. Thus, the use of a highly flexible current collector43illustrated inFIG. 23, in which the protrusions on both faces are in phase with one another, permitted a reduction in the amount of falling-off of the positive electrode mixture layers, and enabled an approximately 26% reduction in the amount of falling-off of the positive electrode mixture layers in comparison with the current collector ofFIG. 21(a), in which the phase displacement is ½.

A 10-μm thick copper foil was used as a current collector for a negative electrode plate. A roller (ceramic roller) was produced in order to form a large number of protrusions whose tops and cross-sections are substantially circular, as illustrated inFIG. 21(d) of Embodiment 16, on a surface of this copper foil in the aforementioned arrangement pattern. On the surface of the roller, depressions (depth 13 μm) having a shape corresponding to that of the protrusions were formed in the aforementioned arrangement pattern. The copper foil was passed between the roller with the protrusions on the surface and a roller with a flat surface while being pressed. As a result, 9-μm high protrusions were formed on one face of a metal foil1. The metal foil1was folded at a predetermined position, and the flat surfaces of the metal foil1were bonded together to obtain a current collector for a negative electrode plate having 9-μm-high protrusions on both faces and having a total thickness of 29 μm, which corresponds toFIG. 23in which the protrusions are not out of phase.

Subsequently, using purity 99.9999% silicon (negative electrode active material) as the sputtering target, a deposition process was performed on both faces of the current collector prepared in the above manner by means of a deposition device equipped with an electron beam heating means while purity 99.7% oxygen was being introduced, so that a SiO0.5 film with a thickness of 23 μm was formed on each of the protrusions. This was then slit to a predetermined width and length to obtain a long-strip like negative electrode plate. At this time, the slitting was made so that the column direction Y agreed with the longitudinal direction of the negative electrode plate or the current collector and that the row direction X agreed with the width direction of the negative electrode plate.

In the current collector produced in the above manner, the substantially circular protrusions are formed in a close-packed arrangement pattern. Thus, when the negative electrode active material was deposited toward the longitudinal direction (column direction Y) of the current collector, the active material could be efficiently attached onto the protrusions.

Also, in the compressed base plane1aof the metal foil1and the surface (2 to 4 μm) of the protrusions11, work hardening occurs at symmetrical positions on the surface side and the back side. Hence, both faces of the metal foil1could exhibit an equal resistance to the tensile stress exerted on the longitudinal direction (column direction Y) of the current collector. Thus, when the negative electrode mixture layers were deposited on the current collector to form the negative electrode plate, or when the negative electrode plate was slit to a predetermined width, it was possible to prevent the current collector from becoming locally deformed or distorted and to suppress separation of the negative electrode mixture layers.

Also, as illustrated inFIG. 26, the electrode assembly34B of the prismatic battery has straight portions83. After this battery was charged and discharged 500 times, the electrode assembly34B was taken out from the battery case, and the electrode plates were unwound to stretch the electrode plates.

As a result, even when the straight portions83of the negative electrode plate receive the tensile stress exerted on the longitudinal direction (column direction Y), the current collector of the negative electrode plate stretches mainly at the areas of the thin compressed base planes1a. Thus, the shearing stress created by the stretching of the current collector at the interface between the current collector and the negative electrode mixture layer could be exerted only on the compressed base planes1a. This is effective for reducing the shearing stress at the interface between the protrusions of the current collector and the negative electrode mixture layer. As a result, the shearing stress in approximately half of the whole area of the negative electrode plate could be reduced, and the separation at the interface between the current collector and the negative electrode mixture layer could be suppressed.

Also, the current collector could exhibit a sufficient resistance to the tensile stress exerted on the longitudinal direction (column direction Y) of the current collector. In the step of forming the protrusions11on the surface of the current collector, the step of disposing the negative electrode active material on the protrusions11of the current collector, and the subsequent step such as slitting to a predetermined width, it was also possible to prevent deformation or distortion such as local corrugation, wrinkles or warpage.

In order to produce a non-aqueous secondary battery of the invention, a 8-μm thick copper foil was used as a current collector for a negative electrode plate. A roller (ceramic roller) was produced in order to form a large number of protrusions whose tops and cross-sections are substantially circular, as illustrated inFIG. 21(d), on a surface of this copper foil in the aforementioned arrangement pattern. On the surface of the roller, depressions (depth 13 μm) having a shape corresponding to that of the protrusions were formed in the aforementioned arrangement pattern. The copper foil was passed between the roller with the protrusions on the surface and a flat roller with a surface roughness Ra (center line average roughness) of 25 μm or less while being pressed. As a result, 4-μm high protrusions were formed on one face of a metal foil1, and the surface roughness Ra of the other face was made 6.3 μm. The metal foil1was folded at a predetermined position, and the flat surfaces of the metal foil1were bonded together to obtain a current collector for a negative electrode plate having 4-μm-high protrusions on both faces and having a total thickness of 18 μm, which corresponds toFIG. 21(a) in which the phase displacement of the protrusions is ½.

Subsequently, using purity 99.9999% silicon (negative electrode active material) as the sputtering target, a deposition process was performed on both faces of the current collector prepared in the above manner by means of a deposition device equipped with an electron beam heating means while purity 99.7% oxygen was being introduced, so that a SiO0.5 film with a thickness of 23 μm was formed on each of the protrusions. This was then slit to a predetermined width and length to obtain a long-strip like negative electrode plate. At this time, the slitting was made so that the column direction Y agreed with the longitudinal direction of the negative electrode plate or the current collector and that the row direction X agreed with the width direction of the negative electrode plate.

Also, a positive electrode current collector having 3-μm-high protrusions on both faces in the aforementioned arrangement pattern and having a total thickness of 18 μm was produced in the same manner as in Example 1 as a current collector for a positive electrode plate.

Subsequently, a positive electrode mixture paint was prepared by stirring and kneading 100 parts by weight of lithium cobaltate in which part of the cobalt was replaced with nickel and manganese, serving as a positive electrode active material, 2 parts by weight of an acetylene black conductive agent per 100 parts by weight of the active material, 2 parts by weight of a polyvinylidene difluoride binder per 100 parts by weight of the active material, and a suitable amount of N-methyl-2-pyrrolidone with a double-arm kneader. This positive electrode mixture paint was applied onto both faces of the current collector prepared in the above manner, dried, and pressed. The current collector was then slit to a predetermined width and length to produce a long-strip like positive electrode plate. At this time, the slitting was made so that the column direction Y agreed with the longitudinal direction of the positive electrode plate and that the row direction X agreed with the width direction of the positive electrode plate. In this way, a 57-μm-thick positive electrode mixture layer was formed on each face of the positive electrode current collector, and a positive electrode plate having a total thickness of 126 μm was produced.

Using the positive electrode plate and the negative electrode plate prepared in the above manner, a lithium ion secondary battery illustrated inFIG. 4was produced. More specifically, the positive electrode plate and the negative electrode plate were spirally wound with a separator interposed therebetween, to form an electrode assembly. This electrode assembly was housed in a cylindrical battery case with a bottom together with an insulator plate. A negative electrode lead attached to the lower part of the electrode assembly was connected to the bottom of the battery case. Subsequently, a positive electrode lead attached to the upper part of the electrode assembly was connected to a seal plate, and a predetermined amount of an electrolyte (not shown) comprising a non-aqueous solvent was injected into the battery case. Thereafter, the seal plate the circumference of which was fitted with a seal gasket was inserted in the opening of the battery case, and the opening of the battery case was bent inward and crimped for sealing. In this way, a lithium ion secondary battery was produced.

In the lithium ion secondary battery, after the production of the spirally wound electrode assembly, the electrode assembly was disassembled and observed. As a result, both the positive electrode plate and the negative electrode plate were found to have no problem such as breakage of the electrode plate or separation of the active material layer. Further, when the charge/discharge of this lithium ion secondary battery was repeated 300 cycles, no cycle deterioration occurred. Also, after the repetition of 300 charge/discharge cycles, the lithium ion secondary battery and the electrode assembly were disassembled. As a result, they were found to have no problem such as deposition of lithium or separation of the active material layer. This is probably because the formation of the thin film comprising the columnar active material on the protrusions at least the tops of which were not compressed enabled a reduction in volume change due to expansion of the active material thin film upon lithium absorption and shrinkage of the active material thin film upon lithium desorption, so that good battery performance could be maintained.

As shown in the foregoing Examples 22 to 23, in the electrode plate for a non-aqueous secondary battery of the invention, protrusions at least the tops of which were not compressed were formed on the surfaces of a current collector in the aforementioned arrangement pattern, so that the arrangement pattern of the protrusions exhibits a large resistance to stress. Therefore, in the step of forming the protrusions on the surface of the current collector and the step of disposing the active material on the protrusions of the current collector, it is possible to prevent the current collector from becoming locally deformed or distorted. At the same time, in the step of disposing the active material on the protrusions of the current collector and the subsequent step such as slitting to a predetermined width and length, it is also possible to suppress separation of the active material.

Further, since the tops of the protrusions of the current collector are not compressed, no processing strain due to compression process remains thereon and the surface accuracy of the protrusions is good, and it is thus possible to form an even thin film thereon. Also, since the surface roughness is not reduced by compression process and the original surface roughness is maintained, it is possible to heighten the adhesion between the protrusions and the active material thin film. In this respect, in order to further heighten the adhesion between the surface of the protrusions and the active material, it is very effective to roughen the current collector surface in advance before subjecting it to a process. The arrangement pattern of the protrusions in Examples 1 to 6 is such that the respective protrusions of the row units that are adjacent to one another in the column direction are displaced by ½ of the pitch of the row unit, but the invention is not limited to this, and the amount of displacement of the protrusions can be set freely.

Also, as shown in Example 23, it is preferable to dispose the active material mainly on the uncompressed tops of the protrusions in columnar form. In this case, when the non-aqueous secondary battery is charged and discharged, the volume change due to expansion of the active material upon lithium absorption and shrinkage of the active material upon lithium desorption is reduced. It is thus possible to obtain a high-capacity, high-reliability non-aqueous secondary battery that does not suffer such a problem as breakage of the electrode plate due to charge/discharge and separation of the active material layer.

INDUSTRIAL APPLICABILITY

The current collector for a non-aqueous secondary battery according to the invention, and the electrode plate for a non-aqueous secondary battery and the non-aqueous secondary battery using the same are useful, for example, as a portable power source that is required to provide higher capacity due to the increase in functionality of electronic devices and communications devices.