Patent Description:
A battery electrode generally comprises an electrode current collector made of metal and an active material layer provided on a surface of the electrode current collector. The electrode current collector has a based portion in which the electrode current collector surface is covered by the active material layer, and a tab portion projecting from the based portion. Patent Literature <NUM> discloses a battery electrode with cutouts formed in a root of a tab portion of an electrode current collector and a vicinity thereof. Also, Patent Literature <NUM> discloses that cracking of the electrode current collector can effectively be curbed by compressing an active material layer after provision of the cutouts in the root of the tab portion and the vicinity of the root. Further, Patent Literature <NUM> discloses an electrode assembly having indented portion formed on electrode plate and secondary battery including same.

A volumetric energy density of a battery can be enhanced by an increase in packing density of each active material layer via compression of the active material layer with a strong force. However, strong compression of the active material layer may cause cracking in a root of a tab portion of a relevant electrode current collector and a vicinity thereof. Also, cracking may occur in the root of the tab portion of the electrode current collector and the vicinity thereof due to expansion and contraction of the active material layer along with charging and discharging of the battery. The electrode disclosed in Patent Literature <NUM> can be expected to exert an effect of curbing such cracking; however, as a result of the present inventors' study, it has turned out that there is still room for improvement.

A battery electrode according to an aspect of the present invention is a battery as defined by independent claim <NUM>.

The present invention is also a battery according to claim <NUM> comprising the battery electrode (<NUM>, <NUM>) according to any one of claims <NUM> to <NUM>.

The present invention is also a method for manufacturing a battery electrode according to independent claim <NUM>. Preferred embodiments are as defined in the dependent claims.

The battery electrode according to an aspect of the present invention enables sufficiently curbing cracking of a root of a tab portion of an electrode current collector and a vicinity thereof.

In recent years, secondary batteries such as lithium ion batteries have been used as drive power sources for, e.g., electric vehicles (EV) and hybrid electric vehicles (HEV, PHEV), and thus, there is an increasing demand for enhancement in volumetric energy density of batteries. As mentioned above, a method in which an active material layer is compressed with a strong force to increase a packing density of the active material layer is conceivable as a method for increasing a volumetric energy density of a battery. However, in this case, cracking may occur in a root of a tab portion of an electrode current collector and a vicinity thereof.

When the active material layer is compressed with a strong force, not only the active material layer but also the electrode current collector is strongly compressed, and thus, the electrode current collector is rolled out. At this time, although a part with the active material layer provided thereon (based portion) of the electrode current collector is rolled out, an electrode current collector exposed part (tab portion) is smaller in thickness than the part with the active material layer thereon and thus is not rolled out because of no load of the compression being applied to the electrode current collector exposed part. Therefore, in the electrode current collector, a difference in length occurs between the part with the active material layer provided thereon and the electrode current collector exposed part with the active material layer not provided thereon, which causes cracking in the root of the tab portion of the electrode current collector and the vicinity thereof. Also, cracking may occur in the root of the tab portion of the electrode current collector and the vicinity thereof due to expansion and contraction of the active material layer along with charging and discharging of the battery.

As a result of diligent study to curb such cracking, the present inventors have finally created an electrode structure having a cutout defined by a first curve formed of a first arc and a straight line from a root of a tab portion to a based portion or in a part of the based portion, the part being adjacent to the tab portion. As described in detail below, cracking is specifically curbed by the cutout.

An example of an embodiment of the present disclosure will be described in detail below. Note that a battery electrode, a battery, and a battery electrode manufacturing method according to the present disclosure are not limited to the below-described embodiment. Since the drawings referred to in the description of the embodiment are schematic ones, e.g., dimensional ratios between components drawn in the drawings should be determined taking the below description into consideration. In <FIG>, a z-direction is a direction of stacking of electrodes forming an electrode assembly <NUM> (thickness direction of the electrodes), an x-direction is a direction in which a positive electrode terminal <NUM> and a negative electrode terminal <NUM> are arranged side by side and a y-direction is a direction orthogonal to the x-and z-directions. For convenience of description, the x-direction may be referred to as "transverse direction" and the y-direction may be referred to as "up-down direction".

<FIG> is a sectional view of a battery <NUM> that is an example of an embodiment. As illustrated in <FIG>, the battery <NUM> comprises an outer covering body <NUM> that is bottomed and has an opening, and a sealing plate <NUM> that closes the opening. The outer covering body <NUM> is a bottomed rectangular tubular container, and in the outer covering body <NUM>, a stack-type electrode assembly <NUM> is housed together with an electrolyte (not illustrated). The sealing plate <NUM> is a lid body that closes the opening of the outer covering body <NUM>, and in the sealing plate <NUM>, a positive electrode terminal <NUM>, a negative electrode terminal <NUM>, a gas discharge valve <NUM>, an electrolytic solution injection hole <NUM> for injecting an electrolytic solution and a sealing plug <NUM> for sealing the electrolytic solution injection hole <NUM> are provided. The gas discharge valve <NUM> has a function that when pressure inside the battery reaches a predetermined value or more, breaks and discharges gas inside the battery to the outside of the battery.

The electrolyte may be either an aqueous electrolyte or a non-aqueous electrolyte. In the present embodiment, a non-aqueous electrolyte is used. The battery <NUM> is a non-aqueous electrolyte secondary battery, for example, a lithium ion battery. The non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. For the non-aqueous solvent, for example, any of esters, ethers, nitriles, amides and solvents of mixtures of two or more thereof may be used. The non-aqueous solvent may contain a halogen substitution product resulting from substitution of at least a part of hydrogens in any of these solvents with a halogen atom such as fluorine. Note that the non-aqueous electrolyte is not limited to a liquid electrolyte but may be a solid electrolyte. For the electrolyte salt, for example, a lithium salt such as LiPF<NUM> is used.

The positive electrode terminal <NUM> has a function that electrically connects an external element and positive electrodes. The negative electrode terminal <NUM> has a function that electrically connects the external element and negative electrodes. The positive electrode terminal <NUM> is attached to the sealing plate <NUM> in a positive electrode terminal attachment hole 5a provided in the sealing plate <NUM> in such a manner that the positive electrode terminal <NUM> is electrically insulated from the sealing plate <NUM> by insulating members <NUM>, <NUM>. Also, the negative electrode terminal <NUM> is attached to the sealing plate <NUM> in a negative electrode terminal attachment hole 5b provided in the sealing plate <NUM> in such a manner that the negative electrode terminal <NUM> is electrically insulated from the sealing plate <NUM> by insulating members <NUM>, <NUM>.

The electrode assembly <NUM> is housed in the outer covering body <NUM> in such a manner that side surfaces and a bottom surface are covered by an insulating sheet <NUM>. For the insulating sheet <NUM>, for example, one folded in a box shape so as to extend along inner walls of the outer covering body <NUM> or a pouch-shaped one covering the electrode assembly <NUM> can be used. Although in the present embodiment, the stack-type electrode assembly <NUM> is housed in the rectangular outer covering body <NUM> made of metal, the electrode assembly may be of a wound type and the outer covering body may be formed of a laminating film.

The electrode assembly <NUM> is disposed inside the outer covering body <NUM> in such a manner that positive-electrode tab portions <NUM> and negative-electrode tab portions <NUM> extend to the sealing plate <NUM> side. The positive-electrode tab portions <NUM> are disposed on one end side in the x-direction of the outer covering body <NUM>, are aligned with the positive electrode terminal <NUM> in the y-direction and are electrically connected to that terminal via a positive-electrode current collector <NUM>. The negative-electrode tab portions <NUM> are disposed on the other end side in the x-direction of the outer covering body <NUM>, are aligned with the negative electrode terminal <NUM> in the y-direction and are electrically connected to that terminal via a negative-electrode current collector <NUM>. A current blocking mechanism may be provided in a conducting pathway between the positive electrodes and the positive electrode terminal <NUM> or a conducting pathway between the negative electrodes and the negative electrode terminal <NUM>. The current blocking mechanism has a function that when the pressure inside the battery reaches a predetermined value or more, operates to shut off the conducting pathway.

<FIG> is an exploded perspective view of the electrode assembly <NUM>. As illustrated in <FIG>, the electrode assembly <NUM> has a stacked structure in which a plurality of positive electrodes <NUM> and a plurality of negative electrodes <NUM> are alternately stacked on a one-by-one basis via respective separators <NUM>. Unlike a wound-type electrode assembly formed by winding a positive electrode and a negative electrode, in the stack-type electrode assembly <NUM>, electrodes are not bent and dead space is small in comparison with the wound-type electrode assembly. Therefore, in the stack-type electrode assembly <NUM>, a packing density of active material layers can be increased and thus an energy density of the battery can easily be enhanced in comparison with the round-type electrode assembly.

Each positive electrode <NUM> comprises a positive-electrode electrode current collector <NUM> and a positive-electrode active material layer <NUM> provided on a surface of the positive-electrode electrode current collector <NUM>. The positive-electrode active material layer <NUM> is preferably provided on each of opposite surfaces of the positive-electrode electrode current collector <NUM>. The positive-electrode electrode current collector <NUM> has a positive-electrode base portion <NUM> in which the electrode current collector surface is covered by the positive-electrode active material layer <NUM>, and a positive-electrode tab portion <NUM> projecting from the positive-electrode base portion <NUM>. In the positive-electrode tab portion <NUM>, the positive-electrode active material layer <NUM> is not provided but there is an exposed part 24a in which the electrode current collector surface is exposed.

Each negative electrode <NUM> comprises a negative-electrode electrode current collector <NUM> and a negative-electrode active material layer <NUM> provided on a surface of the negative-electrode electrode current collector <NUM>. The negative-electrode active material layer <NUM> is preferably provided in each of opposite sides of the negative-electrode electrode current collector <NUM>. The negative-electrode electrode current collector <NUM> has a negative-electrode base portion <NUM> in which the electrode current collector surface is covered by the negative-electrode active material layer <NUM>, and a negative-electrode tab portion <NUM> projecting from the negative-electrode base portion <NUM>. In the negative-electrode tab portion <NUM>, the negative-electrode active material layer <NUM> is not provided but there is an exposed part 34a in which the electrode current collector surface is exposed.

In the present embodiment, the positive-electrode active material layer <NUM> is provided over an entire area of each of opposite surfaces of the positive-electrode base portion <NUM>. Generally, a positive electrode <NUM> is manufactured by providing a positive-electrode active material layer <NUM> on a surface of a metal foil or the like that is to be a positive-electrode electrode current collector <NUM> and then cutting the metal foil or the like into a shape and a size of the electrode, and thus, the positive-electrode active material layer <NUM> slightly remains also in a root of a positive-electrode tab portion <NUM>. Likewise, the negative-electrode active material layer <NUM> is provided over an entire area of each of opposite surfaces of the negative-electrode base portion <NUM> and slightly remains also in a root of the negative-electrode tab portion <NUM>.

Each of the positive-electrode base portions <NUM>, the positive-electrode tab portions <NUM>, the negative-electrode base portions <NUM> and the negative-electrode tab portions <NUM> is formed, for example, in a substantially quadrilateral shape. In the example illustrated in <FIG>, as each positive electrode <NUM> is viewed from the thickness direction (z-direction), a positive-electrode tab portion <NUM> projects from one end side of one edge (upper edge) of a positive-electrode base portion <NUM>. Also, a negative-electrode tab portion <NUM> projects from the other end side of one edge (upper edge) of a negative-electrode base portion <NUM>. In other words, the respective tab portions of the positive electrodes <NUM> and the negative electrodes <NUM> extend in a same direction (direction toward the sealing plate <NUM>) and the positive-electrode tab portions <NUM> and the negative-electrode tab portions <NUM> are disposed so as to be located on the respective sides opposite to each other in the x-direction. Note that in the case of a lithium ion battery, in order to prevent deposition of lithium ions, the negative-electrode base portions <NUM> are formed so as to have an area that is larger than that of the positive-electrode base portions <NUM>, and the positive electrodes <NUM> and the negative electrodes <NUM> are disposed in such a manner that the entire positive-electrode active material layers <NUM> face the respective negative-electrode active material layers <NUM>.

In each positive-electrode electrode current collector <NUM>, a cutout <NUM> is formed from the root of the positive-electrode tab portion <NUM> to the positive-electrode base portion <NUM>. In each positive electrode <NUM>, cracking that easily occurs in the root of the positive-electrode tab portion <NUM> and a vicinity thereof is sufficiently curbed by the cutout <NUM>. Although in the present embodiment, a cutout <NUM> is formed in each of the positive-electrode electrode current collectors <NUM> only but a cutout <NUM> may be formed in each of the negative-electrode electrode current collectors <NUM>. The battery electrode comprising a cutout according to the present disclosure may be applied to positive electrodes only or may be applied to negative electrodes only, or may be applied to both of positive electrodes and negative electrodes.

The positive electrodes <NUM>, the negative electrodes <NUM> and the separators <NUM> forming the electrode assembly <NUM>, particularly, the positive electrodes <NUM> each including a cutout <NUM>, will be described in detail below.

As described above, each positive electrode <NUM> comprises a positive-electrode electrode current collector <NUM> and a positive-electrode active material layer <NUM> provided on each of opposite surfaces of the positive-electrode electrode current collector <NUM>. For the positive-electrode electrode current collector <NUM>, e.g., a foil of a metal that is stable within a potential range of the positive electrodes such as aluminum or an aluminum alloy or a film with the metal disposed on a surface layer thereof can be used. The positive-electrode active material layer <NUM> contains a positive-electrode active material, a binder, and a conductive agent. Each positive electrode <NUM> can be manufactured by, for example, applying a positive electrode mixture slurry containing, e.g., a positive-electrode active material, a binder, and a conductive agent to a positive-electrode electrode current collector <NUM>, drying the resulting coating films and compressing positive-electrode active material layers <NUM> that are the dried coating films via a roller.

The positive-electrode active material is formed using a lithium-containing metal composite oxide as a main component. Examples of a metal element contained in the lithium-containing metal composite oxide can include, e.g., Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, W, Ca, Sb, Pb, Bi and Ge. A preferable example of the lithium-containing metal composite oxide is a composite oxide containing at least one of Ni, Co, Mn, and Al.

Examples of the conductive agent contained in the positive-electrode active material layer <NUM> can include carbon materials such as carbon black, acetylene black, ketjen black, and graphite. Examples of the binder contained in the positive-electrode active material layer <NUM> can include fluorine resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide, acrylic resins, and polyolefin. Any of these resins and, e.g., carboxymethyl cellulose (CMC) or a salt thereof or polyethylene oxide (PEO) may be used together.

The packing density of each positive-electrode active material layer <NUM> can appropriately be changed according to, e.g., usage of the battery <NUM>, and in each positive electrode, the packing density can be enhanced by a function of the cutout <NUM>. The packing density of each positive-electrode active material layer <NUM> is, for example, no less than <NUM>/cm<NUM> and may be adjusted within a range of <NUM>/cm<NUM> to <NUM>/cm<NUM>. An effect of the cutout <NUM> is more significantly exerted when the packing density of the positive-electrode active material layer <NUM> is high. Also, although a thickness of each positive-electrode active material layer <NUM> is not specifically limited, as an example, the thickness is <NUM> to <NUM> or <NUM> to <NUM> on one side of the positive-electrode electrode current collector <NUM>.

In the present embodiment, a protection layer <NUM> is provided on the root of each positive-electrode tab portion <NUM>. The protection layer <NUM> is provided within a range in which the protection layer <NUM> faces the corresponding negative electrode <NUM> via the corresponding separator <NUM>, the range being a part, in which the positive-electrode active material layer <NUM> is not provided, of the root of each positive-electrode tab portion <NUM>. Also, the protection layer <NUM> is provided adjacent to the positive-electrode active material layer <NUM> with no gap between the protection layer <NUM> and the positive-electrode active material layer <NUM>. The provision of the protection layer <NUM> can curb, for example, low-resistant short-circuiting that can occur as a result of an entry of a conductive foreign object between the positive-electrode tab portion <NUM> and the negative electrode <NUM> and also reinforces the root of the positive-electrode tab portion <NUM> and thereby curbs breakage of the positive-electrode electrode current collector <NUM>. The protection layer <NUM> is provided on each of opposite surfaces of the positive-electrode tab portion <NUM> at the root of the positive-electrode tab portion <NUM>. A thickness of the protection layer <NUM> is smaller than the thickness of the positive-electrode active material layer <NUM>, and for example, is <NUM> to <NUM> on one side of the positive-electrode electrode current collector <NUM>.

The protection layer <NUM> may be formed of a resin alone but preferably contains inorganic particles and a binder. The protection layer <NUM> containing inorganic particles as a main component does not easily break even an entered conductive foreign object strongly abuts against the protection layer <NUM>. Specific examples of the inorganic particles can include at least one selected from aluminum oxide (alumina), titanium oxide (titania), manganese oxide and silicon oxide (silica). Among these, alumina or titania is preferably used. For the binder contained in the protection layer <NUM>, a binder of a type that is the same as that used in the positive-electrode active material layers <NUM> can be used. Note that a conductive agent may be added in the protection layer <NUM>.

The cutout <NUM> formed in the root of each positive-electrode tab portion <NUM> and the vicinity thereof will be described in detail below with reference to <FIG> is an enlarged view of a positive-electrode tab portion <NUM> and a vicinity thereof in a positive electrode <NUM>.

As illustrated in <FIG>, a cutout <NUM> is formed from a root of a positive-electrode tab portion <NUM> to a positive-electrode base portion <NUM> in each positive-electrode electrode current collector <NUM>. Then, an edge of the cutout <NUM> is formed by a curve <NUM> (first curve) formed of an arc (first arc) and a straight line <NUM>. In other words, in the root of the positive-electrode tab portion <NUM> and the vicinity thereof, a cutout <NUM> defined by a curve <NUM> and a straight line <NUM> is formed as the positive electrode <NUM> is viewed from the thickness direction (z-direction). Note that instead of the straight line <NUM>, a second curve formed of a second arc that is smaller in curvature than the first arc may be used, which is an embodiment not according to the present invention. For example, the curvature of the second curve is less than <NUM>% of the curvature of the first curve and the second curve may be a slight curve that is close to the straight line <NUM>.

The cutout <NUM> curbs occurrence of cracking in the root of the positive-electrode tab portion <NUM> and the vicinity thereof when a positive-electrode active material layer <NUM> is compressed and at the time of charging/discharging. Where no cutout <NUM> is provided, if an active material layer is strongly compressed, a part, in which the active material layer is provided, of the electrode current collector stretches but a part, in which the active material layer is not provided, of the electrode current collector does not stretch, and thus, for example, large stress acts on a boundary part between the parts, which may cause developing a crack from a corner between the tab portion and the based portion to the electrode current collector. Formation of the cutout <NUM> in the positive-electrode electrode current collector <NUM> can reduce stress generated because of the difference in stretch of the positive-electrode electrode current collector <NUM> and thus can curb occurrence of cracking.

As a result of the present inventors' study, it has turned out that a probability of occurrence of cracking largely changes depending on the shape of the cutout <NUM>. A cutout <NUM> defined by a curve <NUM> and a straight line <NUM> largely reduces a probability of occurrence of cracking in comparison with, for example, a cutout defined by a curve <NUM> alone. An increase in packing density of the positive-electrode active material layer <NUM> causes cracking to be more likely to occur, and the effect of the cutout <NUM> is more significant when the packing density is high.

A cutout <NUM> is formed in the root of each positive-electrode tab portion <NUM> and the vicinity thereof. The cutout <NUM> is formed in a part adjacent to the positive-electrode tab portion <NUM> in an upper end portion of the positive-electrode base portion <NUM>, and extends to the transverse end portion side of the positive-electrode electrode current collector <NUM> across an imaginary line α that is an extension of a side edge of the positive-electrode tab portion <NUM>. Here, the side edge is an edge portion of the positive-electrode tab portion <NUM> along the up-down direction (y-direction) in which the positive-electrode tab portion <NUM> projects. The cutout <NUM>, an edge of which continues from the root of the positive-electrode tab portion <NUM> to the positive-electrode base portion <NUM> with no disconnection, is formed as a single cut portion. Therefore, in the positive-electrode electrode current collector <NUM>, there is no acute-angle corner in a boundary part between the positive-electrode tab portion <NUM> and the positive-electrode base portion <NUM>.

The cutout <NUM> is formed so as to have a size that prevents occurrence of a trouble such as a resistance increase while curbing cracking of the positive-electrode electrode current collector <NUM>. As described above, since the positive-electrode tab portion <NUM> is formed in a substantially quadrilateral shape, a width of the positive-electrode tab portion <NUM> is smaller in the root in which the cutout <NUM> is formed than in a distal end. A width W<NUM> (length in the x-direction/transverse direction) in a part, in which the cutout <NUM> is not formed, of the positive-electrode tab portion <NUM> is, for example, <NUM> to <NUM> or <NUM> to <NUM>. A width W<NUM> of a part, in which the cutout <NUM> is formed, of the positive-electrode tab portion <NUM>, that is, the smallest width of the positive-electrode tab portion <NUM> is, for example, <NUM> to <NUM> or <NUM> to <NUM>. Where the widths W<NUM>, W<NUM> fall within the respective ranges, generally, no trouble such as a resistance increase occurs and it is possible to, while curbing generation of heat at the time of high-rate charging/discharging, curb wrinkling and deflection of the positive-electrode tab portion <NUM> due to the charging/discharging.

The cutout <NUM> is preferably formed from each of opposite sides in the width direction of the positive-electrode tab portion <NUM> to the positive-electrode base portion <NUM>. The cutout <NUM> may be formed on one side in the width direction of the positive-electrode tab portion <NUM> alone, but preferably, one cutout <NUM> is formed on each of the opposite sides in the width direction of the positive-electrode tab portion <NUM>. The two cutouts <NUM> are formed so as to, for example, be symmetrical to each other with respect to an imaginary line (not illustrated) extending in a center in the width direction of the positive-electrode tab portion <NUM>. In other words, the two cutouts 25a are substantially the same in terms of a width W<NUM> (length in the x-direction/transverse direction) of the cutouts <NUM>, a width W<NUM> of a part cut inward from the side edge of the positive-electrode tab portion <NUM> and later-described lengths L<NUM>, L<NUM>.

The width W<NUM> of the cutouts <NUM> are, for example, <NUM>% to <NUM>% or <NUM>% to <NUM>% of the width W<NUM> of the positive-electrode tab portion <NUM>, and a specific example of the width W<NUM> is <NUM> to <NUM>. The width W<NUM> of the part cut inward is, for example, <NUM>% to <NUM>% or <NUM>% to <NUM>% of the width W<NUM> of the positive-electrode tab portion <NUM> and a specific example of the width W<NUM> is <NUM> to <NUM>. Where the widths W<NUM>, W<NUM> fall within the respective ranges, it is possible to sufficiently curb occurrence of cracking in the root of the positive-electrode tab portion <NUM> and the vicinity thereof while curbing a capacity decrease due to reduction of the positive-electrode active material layers <NUM>.

An edge of each cutout <NUM> includes a first end P<NUM> on the positive-electrode tab portion <NUM> side and a second end P<NUM> in the positive-electrode base portion <NUM>. The first end P<NUM> is located at a point of intersection between the side edge of the positive-electrode tab portion <NUM> and the edge of the cutout <NUM> and the second end P<NUM> is located at a point of intersection between an upper edge of the positive-electrode base portion <NUM> and the edge of the cutout <NUM>. A length L<NUM> in the up-down direction (y-direction) from the first end P<NUM> to a lower end of the cutout <NUM> is, for example, <NUM>% to <NUM>% of a length of the positive-electrode tab portion <NUM>, and a specific example of the length L<NUM> is <NUM> to <NUM>. A length L<NUM> in the up-down direction from the upper edge of the positive-electrode base portion <NUM> to the lower end of the cutout <NUM> is, for example, <NUM>% to <NUM>% of the length of the positive-electrode tab portion <NUM>, and a specific example of the length L<NUM> is <NUM> to <NUM>.

As the lengths L<NUM>, L<NUM>, particularly, the length L<NUM>, are made to be longer, occurrence of cracking in the root of the positive-electrode tab portion <NUM> and the vicinity can more easily be curbed. However, where the length L<NUM> is made to be longer, the area of a cut-off part of the positive-electrode active material layer <NUM> becomes large, which results in a decrease in battery capacity. Therefore, it is important to determine the size of the cutout <NUM> in consideration of crack curbing and the capacity. The straight line <NUM> forming a part of the edge of the cutout <NUM> largely contributes not only to curbing of cracking but also to curbing of a capacity decrease. Where the lengths L<NUM>, L<NUM> fall within the respective ranges, it is possible to sufficiently curb occurrence of cracking in the root of the positive-electrode tab portion <NUM> and the vicinity thereof while curbing a capacity decrease due to reduction of the cracking positive-electrode active material layers <NUM>.

In the present embodiment, the protection layer <NUM> is provided on the root of each positive-electrode tab portion <NUM>, and a part of each cutout <NUM> is formed in a part, in which the protection layer <NUM> is provided, of the positive-electrode tab portion <NUM>. Formation of the cutout <NUM> in the part in which the protection layer <NUM> is provided enables curbing the positive-electrode electrode current collector <NUM> breaking from the edge of the cutout <NUM>. In the example illustrated in <FIG>, the first end P<NUM> of the cutout <NUM> is located in the part in which the protection layer <NUM> is provided. Also, in the positive-electrode tab portion <NUM>, an entirety of the cutout <NUM> is formed in the part in which the protection layer <NUM> is provided and a part in which the positive-electrode active material layer <NUM> is provided. In other words, the cutout <NUM> is not formed in the exposed part 24a.

The straight line <NUM> forming a part of the edge of the cutout <NUM> is formed from the second end P<NUM> on the positive-electrode base portion <NUM> side. Also, the curve <NUM> forming a part of the edge of the cutout <NUM> is formed from the first end P<NUM> on the positive-electrode tab portion <NUM> side. The curve <NUM> is formed so as to have a length enough to extend from the first end P<NUM> to the positive-electrode base portion <NUM> and is connected to the straight line <NUM>. A point of intersection between the curve <NUM> and the straight line <NUM> is located, for example, at the lower end of the cutout <NUM>. Here, the lower end of the cutout <NUM> is a position at which a length in the up-down direction from the first end P<NUM>, which is an upper end of the cutout <NUM>, is the largest.

The curve <NUM> is formed of a part of the first arc. The first arc may be an arc of a perfect circle or may be an arc of an ellipse; however, in order to efficiently prevent occurrence of cracking while curbing a capacity decrease, the first arc is preferably an arc of an ellipse. For example, a major axis of the elliptic extends in the transverse direction (x-direction) of the positive electrode <NUM> and a center of the elliptic is located on the second end P<NUM> side relative to an intersection point Q. Here, the intersection point Q is a point of intersection between the imaginary line α and an imaginary line β that is an extension of the upper edge of the positive-electrode base portion <NUM>, and is a position at which a corner is formed where no cutout <NUM> is provided. The perfect circle or the ellipse corresponding to the first arc may be a perfect circle or an ellipse centered at the intersection point Q.

The straight line <NUM> is formed so as to have a length from the second end P2 of the cutout <NUM>, the length preventing the straight line <NUM> from extending across the imaginary line α that is an extension of the side edge of the positive-electrode tab portion <NUM>. In other words, a part of the positive-electrode base portion <NUM>, the part overlapping the positive-electrode tab portion <NUM> in the up-down direction, the straight line <NUM> is not formed but only the curve <NUM> is formed. The curve <NUM> largely curves toward the center side in the width direction of the positive-electrode tab portion <NUM>. The straight line <NUM> intersects with the upper edge of the positive-electrode base portion <NUM> at an obtuse angle and is formed obliquely from the second end P<NUM> toward the lower end of the cutout <NUM>. The angle formed by the upper edge of the positive-electrode base portion <NUM> and the straight line <NUM> is, for example, <NUM>° to <NUM>° or <NUM>° to <NUM>°.

Note that in an embodiment, which is not part of the present invention, the edge of the cutout <NUM> may include another curve or straight line in addition to the curve <NUM> and the straight line <NUM> as long as such other curve or straight line does not hinder an objective of the present disclosure. For example, a second straight line may be formed from the first end P<NUM> of the cutout <NUM>.

<FIG> illustrate cutouts 25x, 25y, each of which is another example of the embodiment. The cutouts 25x illustrated in <FIG> are in common with the cutouts <NUM> in that a part of an edge of each cutout 25x is formed from a root of a positive-electrode tab portion <NUM> to a positive-electrode base portion <NUM>, by a curve <NUM> formed of a part of an arc of an ellipse. However, the cutouts 25x are different from the cutouts <NUM> in that a remaining part of the edge of each cutout 25x is formed by a straight line 27x that substantially perpendicularly intersects with an upper edge of the positive-electrode base portion <NUM>. The straight line 27x is formed from the upper edge of the positive-electrode base portion <NUM> to a lower end of the cutout 25x and an angle formed by the straight line 27x and the upper edge of the positive-electrode base portion <NUM> is approximately <NUM>°. In this case, the area of a part cut off from a positive-electrode active material layer <NUM> can be reduced in comparison with that of the form illustrated in <FIG>.

The cutouts 25y illustrated in <FIG> are in common with the cutouts <NUM>, 25x in that each cutout 25y is defined by a curve 26y and a straight line 27y. However, the cutouts 25y are different from the cutouts <NUM>, 25y in that each cutout 25y is formed only in a part of a positive-electrode base portion <NUM>, the part adjacent to a positive-electrode tab portion <NUM>, and is not formed in a root of the positive-electrode tab portion <NUM>. Each curve 26y is formed so as to be continuous with a side edge of the positive-electrode tab portion <NUM>. In this case, a width of the positive-electrode tab portion <NUM> is constant from a distal end to the root.

Here, an example of a method for manufacturing a positive electrode <NUM> comprising the above configuration will be described in detail.

A positive electrode <NUM> is manufactured through a process of providing a positive-electrode active material layer <NUM> on at least a surface of a positive-electrode base portion <NUM> of a positive-electrode electrode current collector <NUM> or a part that is to be the positive-electrode base portion <NUM>, forming a cutout <NUM> from a root of a positive-electrode tab portion <NUM> or a part that is to be the positive-electrode tab portion <NUM> to the positive-electrode base portion <NUM> or the part that is to be the positive-electrode base portion <NUM>, and compressing the positive-electrode active material layer <NUM> after the formation of the cutout <NUM>. In forming the cutout <NUM>, an edge of the cutout <NUM> is formed by a first curve formed of a first arc and a straight line. The cutout <NUM> may be formed after compression of the positive-electrode active material layer <NUM>; however, in order to curb cracking of the positive-electrode electrode current collector <NUM>, which can occur during compression of the active material layer, preferably, the cutout <NUM> is formed before compression of the active material layer. Also, from the perspective of, e.g., productivity, the cutout <NUM> is preferably formed after provision of the positive-electrode active material layer <NUM>.

The positive electrode <NUM> is manufactured by cutting an elongated body with the positive-electrode active material layer <NUM> provided on each of opposite surfaces of an elongated electrode current collector that is to be the positive-electrode electrode current collector <NUM> (hereinafter referred to as "elongated body Z") into a predetermined shape and size in a subsequent process. An example of the process of manufacturing a positive electrode <NUM> includes: a first step of providing a positive-electrode active material layer <NUM> by applying a positive electrode mixture slurry to each of opposite surfaces of an elongated electrode current collector and drying the resulting coating films; a second step of forming a positive-electrode tab portion <NUM> and a cutout <NUM> by cutting an elongated body Z with the positive-electrode active material layer <NUM> provided on each of the opposite surfaces of the elongated electrode current collector; a third step of compressing the positive-electrode active material layer <NUM> (elongated body Z); and a fourth step of obtaining a positive electrode <NUM> by cutting the elongated body Z into a predetermined size.

In the first step, a positive-electrode active material layer <NUM> is provided by applying a positive electrode mixture slurry except a band-like electrode current collector exposed part extending along a longitudinal direction of an elongated electrode current collector. The exposed part is formed from an end in a width direction of the elongated electrode current collector so as to have a substantially constant width and becomes an exposed part 24a provided in a positive-electrode tab portion <NUM> in a subsequent process. Where a protection layer <NUM> is provided, simultaneously with the application of the positive electrode mixture slurry or in another step, a slurry for the protection layer <NUM> is applied to each of opposite surfaces of the elongated electrode current collector.

In the second step, the positive-electrode tab portion <NUM> is formed by cutting a part, in which the positive-electrode active material layer <NUM> is provided, of the elongated body Z along the exposed part and cutting the exposed part at a substantially constant cycle. A cutout <NUM> may be formed simultaneously with the formation of the positive-electrode tab portion <NUM> or may be formed after the formation of the positive-electrode tab portion <NUM>. The elongated body Z can be cut via a conventionally known method, for example, mold pressing, a cutter or laser irradiation. Note that the elongated body Z can be cut along a position of a boundary between the part in which the positive-electrode active material layer <NUM> is provided and the exposed part; however, in this case, slight deviation of the cutting position unfavorably causes formation of an exposed part of the electrode current collector surface in a part other than the positive-electrode tab portion <NUM>.

Also, the positive-electrode tab portion <NUM> and the cutout <NUM> may be formed via different methods. For example, the cutout <NUM> may be formed by forming the positive-electrode tab portion <NUM> via press punching and then performing irradiation with an energy ray such as laser. Where the cutout <NUM> is formed by means of laser irradiation, an edge portion of the cutout <NUM> is smoothed, which is advantageous for curbing cracking.

In the second step, the cutout <NUM> is formed by forming a curve <NUM> formed of a first arc and a straight line <NUM> in a root of the positive-electrode tab portion <NUM> (or a part that is to be the root of the positive-electrode tab portion <NUM>) and the positive-electrode base portion <NUM> (or a part that is to be the positive-electrode base portion <NUM>) and thereby cutting off a part of the elongated body Z. In the present embodiment, the curve <NUM> is formed from a part, in which the protection layer <NUM> is provided, of the root of the positive-electrode tab portion <NUM> to the positive-electrode base portion <NUM> and the straight line <NUM> is formed from an upper edge of the positive-electrode base portion <NUM> so as to be continuous with the curve <NUM>. The curve <NUM> is formed as a part of the first arc of an elliptic and largely curves to the center side in the width direction of the positive-electrode tab portion <NUM>. The straight line <NUM> intersects with the upper edge of the positive-electrode base portion <NUM> at an obtuse angle and is formed obliquely from the upper edge of the positive-electrode base portion <NUM> toward a lower end of the curve <NUM> (cutout <NUM>).

In the third step, the positive-electrode active material layers <NUM> provided on the opposite surfaces of the elongated electrode current collector are compressed using a roller. The positive-electrode active material layers <NUM> can be compressed via a conventionally known method, and for example, is compressed by letting the elongated body Z through between a pair of rollers. A packing density of the positive-electrode active material layer <NUM> can be adjusted by, e.g., a composition and an amount of application of the positive electrode mixture slurry and/or pressure for compressing the positive-electrode active material layers <NUM>. The packing density of the positive-electrode active material layer <NUM> is adjusted to, for example, no less than <NUM>/cm<NUM>; however, if the packing density is high, cracking is likely to occur in the root of the positive-electrode tab portion <NUM> and a vicinity thereof.

In the present manufacturing process, a probability of occurrence of cracking in the third step can substantially be reduced by compressing the positive-electrode active material layers <NUM> after formation of the cutout <NUM>. As described above, the cutout <NUM> defined by a curve <NUM> and a straight line <NUM> reduces stress acting on the positive-electrode tab portion <NUM> and the vicinity thereof in the third step and thereby curbs occurrence of cracking.

As described above, each negative electrode <NUM> has a negative-electrode electrode current collector <NUM> and a negative-electrode active material layer <NUM> provided each of opposite surfaces of the negative-electrode electrode current collector <NUM>. For the negative-electrode electrode current collector <NUM>, e.g., a foil of a metal that is stable within a potential range of the negative electrode <NUM> such as copper or a copper alloy or a film with the metal disposed on a surface layer thereof can be used. The negative-electrode active material layer <NUM> contains a negative-electrode active material and a binder. Each negative electrode <NUM> can be manufactured by, for example, applying a negative electrode mixture slurry containing, e.g., a negative-electrode active material and a binder to a negative-electrode electrode current collector <NUM>, drying the resulting coating films and compressing negative-electrode active material layers <NUM> that are the dried coating films via a roller.

For the negative-electrode active material, generally, a carbon material that reversibly occludes and releases lithium ions. A preferable example of the carbon material is graphite that is natural graphite such as scaly graphite, bulk graphite or earthy graphite or artificial graphite such as bulk artificial graphite or graphitized mesophase carbon microbeads. Each negative-electrode active material layer <NUM> may contain an Si-containing compound as the negative-electrode active material. Also, for the negative-electrode active material, e.g., a metal to be alloyed with lithium other than Si, an alloy containing the metal or a compound containing the metal may be used.

For the binder contained in each negative-electrode active material layer <NUM>, as in the case of the positive electrodes <NUM>, e.g., a fluorine resin, PAN, a polyimide resin, an acrylic resin or a polyolefin resin may be used, but preferably, styrene-butadiene rubber (SBR) or a modified product thereof is used. Each negative-electrode active material layer may contain, for example, CMC or a salt thereof, a polyacrylic acid (PAA) or a salt thereof, or polyvinyl alcohol in addition to, e.g., SBR.

For the separator <NUM>, a porous sheet having ion permeability and an insulation property is used. Specific examples of the porous sheet include, e.g., a microporous thin film, a woven fabric, and a non-woven fabric. For a material of the separator <NUM>, e.g., an olefin-based resin such as polyethylene, polypropylene or a copolymer containing at least one of ethylene and propylene, or cellulose is favorable. The separator <NUM> may have a single-layer structure or a layer stack structure. On a surface of the separator <NUM>, e.g., a heat-resistant layer may be formed.

The present disclosure will further be described below based on an example; however, the present disclosure is not limited to these examples.

For a positive-electrode active material, a lithium nickel cobalt manganese composite oxide was used. A positive electrode mixture slurry was prepared by mixing the positive-electrode active material, PVdF and acetylene black at a mass ratio of <NUM>:<NUM>:<NUM> and adding a proper amount of N-methyl-<NUM>-pyrrolidone (NMP). The positive electrode mixture slurry was applied to each of opposite surfaces of an elongated electrode current collector formed of an aluminum foil having a thickness of <NUM> except a predetermined electrode current collector exposed part and the resulting coating films were dried to obtain an elongated body Z with a positive-electrode active material layer provided on each of the opposite surfaces of the elongated electrode current collector. Also, a protection layer containing alumina and PVdF was formed on a part of the electrode current collector exposed part, the part being adjacent to the positive-electrode active material layer.

Next, a part, in which the positive-electrode active material layer is provided, of the elongated body Z was cut along the electrode current collector exposed part and the electrode current collector exposed part was cut at a substantially constant cycle to form a tab portion having a width of <NUM> and a length of <NUM>. Subsequently, a cutout having the shape illustrated in <FIG>, the cutout being defined by a curve and a straight line, was formed from each of opposite end portions in a width direction of a root of the tab portion to a based portion of the electrode current collector. The curve forming a part of an edge of the cutout was formed of a part of an arc of an ellipse having a major axis of <NUM> and a minor axis of <NUM>. The straight line forming a part of the edge of the cutout was formed so as to have a length of <NUM> from an upper edge of the based portion. An angle formed by the straight line and the upper edge of the based portion was <NUM>°. Also, a width W<NUM> of the root of the tab portion in which the cutouts were formed was <NUM>, a width W<NUM> of the cutouts was <NUM>, a width W<NUM> was <NUM>, a length L<NUM> was <NUM> and a length L<NUM> was <NUM>.

Next, the positive-electrode active material layers were compressed by letting the elongated body Z with the cutouts formed therein through between a pair of rollers. Note that positive electrode (<NUM>) including positive-electrode active material layers having a packing density of <NUM>/cm<NUM> and positive electrode (<NUM>) including positive-electrode active material layers having a packing density of <NUM>/cm<NUM> were fabricated by adjusting an amount of application of the positive electrode mixture slurry and a force of compression of the elongated body Z. For each of the positive electrodes, whether or not a crack was developed in the tab portion and a vicinity thereof was confirmed and a result of evaluation was indicated in Table <NUM>.

Two types of positive electrodes including respective positive-electrode active material layers having different packing densities were manufactured in a manner that is similar to example <NUM> except that instead of the cutouts illustrated in <FIG>, the cutouts illustrated in <FIG> (cutouts each defined by a curve formed of a part of an arc of an elliptic alone), and the above evaluation was performed. Note that a width W<NUM> of a root of a tab portion with the cutouts formed therein was <NUM>, a width W<NUM> of the cutouts was <NUM>, a width W<NUM> was <NUM>, a length L<NUM> was <NUM> and a length L<NUM> was <NUM>.

Two types of positive electrodes including respective positive-electrode active material layers having different packing densities were manufactured in a manner that is similar to example <NUM> except that instead of the cutouts illustrated in <FIG>, the cutouts illustrated in <FIG> (cutouts each defined by a curve formed of a part of an arc of a perfect circle alone), and the above evaluation was performed. Note that a width W<NUM> of a root of a tab portion with the cutouts formed therein was <NUM>, a width W<NUM> of the cutouts was <NUM>, a width W<NUM> was <NUM>, a length L<NUM> was <NUM> and a length L<NUM> was <NUM>.

Claim 1:
A battery electrode (<NUM>, <NUM>) comprising an electrode current collector (<NUM>, <NUM>), and an active material layer (<NUM>, <NUM>) provided on a surface of the electrode current collector (<NUM>, <NUM>), wherein:
the electrode current collector (<NUM>, <NUM>) has a based portion (<NUM>, <NUM>) in which the electrode current collector (<NUM>, <NUM>) surface is covered by the active material layer (<NUM>, <NUM>) and a tab portion (<NUM>, <NUM>) projecting from the based portion (<NUM>, <NUM>);
in the electrode current collector (<NUM>, <NUM>), a cutout (<NUM>) is formed from a root of the tab (<NUM>, <NUM>) portion to the based portion (<NUM>, <NUM>) or in a part of the based portion (<NUM>, <NUM>), the part being adjacent to the tab portion (<NUM>, <NUM>); and characterized in that
an edge of the cutout (<NUM>) consists of a curve (<NUM>) formed of an arc and a straight line (<NUM>).