Stacked battery and method of manufacturing same

A stacked battery including two kinds of electrodes 1, 2 and separators 3 through each of which one of the two kinds of electrodes 1 is stacked on another of the two kinds of electrodes 2, each of separators 3 including bonding portion 7 in which separator 3 stacked on the one of the two kinds of electrodes 1 and separator 3 stacked on the another of the two kinds of electrodes 2 are partly bonded to each other on a lateral side of the one of the two kinds of electrodes 1, and non-bonding portion 8 in a curve form which extends at least from a position in which separator 3 is contacted with an end surface of the another of the two kinds of electrodes 2 toward a lateral side of the another of the two kinds of electrodes 2.

TECHNICAL FIELD

The present invention relates to a stacked battery constructed such that one or two kinds of electrodes (positive electrodes and negative electrodes) is stacked on another of the two kinds of electrodes through each of separators, and a method of manufacturing the stacked battery.

BACKGROUND ART

A stacked battery constructed such that one of two kinds of electrodes (positive electrodes and negative electrodes) is stacked on another of the two kinds of electrodes through each of separators has a battery characteristic that is lowered when there occurs positional displacement of each of the electrodes. In order to prevent the battery characteristic from being lowered, each of the separators is prepared in the form of a one open ended bag, and one of the two kinds of electrodes (positive electrode) is inserted into the bag-shaped separator. As a result, positional displacement of the one of the two kinds of electrodes can be prevented. However, in this construction, another of the two kinds of electrodes (negative electrode) is disposed on an outside of the bag-shaped separator, whereby there is a possibility that positional displacement of the another of the two kinds of electrodes occurs.

In contrast, in an embodiment of a stacked battery recited in Patent Literature 1, a sheet of an elongated separator is folded in a zigzag form such that there are provided multiple open portions including open portions opened in one direction and open portions opened in the other direction. One of two kinds of electrodes is inserted into the open portions opened in one direction, and another of the two kinds of electrodes is inserted into the open portions opened in the other direction. In this construction, an end face of each of the two kinds of electrodes abuts on a fold of the zigzag-folded separator, so that each of the two kinds of electrodes can be held in place with respect to the direction in which each of the two kinds of electrodes is inserted into the separator.

Further, in another embodiment of the stacked battery recited in Patent Literature 1, a plurality of separators double folded over such that one of the two kinds of electrodes is interposed between opposing faces of each of the separators are prepared, and the plurality of separators are stacked on one another via another of the two kinds of electrodes. After that, the plurality of separators are fused to each other such that the another of the two kinds of electrodes is interposed between the separators to thereby be held in place.

CITATION LIST

Patent Literature

Patent Literature 1: Japanese Patent Application Unexamined Publication No. 2009-218105

SUMMARY OF INVENTION

Technical Problem

In the conventional method of restricting displacement of both of the two kinds of electrodes, a restricting section is provided on only one side of a plurality of sides of one of the two kinds of electrodes or both of the two kinds of electrodes, or the restricting step is complicated. For instance, in the method of restricting displacement of both of the two kinds of electrodes by utilizing a fold of each of the separators, there exists a problem that displacement of the two kinds of electrodes in a direction opposite to the fold, cannot be restricted by only the fold of each separator. Further, in a case where displacement of both of the two kinds of electrodes is restricted by the method of fusing an outer periphery of each of the separators on the sides of the two kinds of electrodes, even when using the fold of each of the separators, the manufacturing process will be considerably complicated as recited in Patent Literature 1, thereby causing a prolonged manufacturing time.

An object of the present invention is to provide a stacked battery in which displacement of an electrode, particularly, positional displacement of both of two kinds of electrodes can be readily prevented or suppressed, and a method of manufacturing the stacked battery.

Solution to Problem

In one aspect of the present invention, there is provided a stacked battery including:

two kinds of electrodes; and

separators through each of which one of the two kinds of electrodes is stacked on another of the two kinds of electrodes,

wherein each of the separators includes a bonding portion in which the separator stacked on the one of the two kinds of electrodes and the separator stacked on the another of the two kinds of electrodes are partly bonded to each other on a lateral side of the one of the two kinds of electrodes, and a non-bonding portion in a curved form which extends at least from a position in which the separator is contacted with an end surface of the another of the two kinds of electrodes toward a lateral side of the another of the two kinds of electrodes.

In a further aspect of the present invention, there is provided a method of manufacturing a stacked battery including two kinds of electrodes and separators through each of which one of the two kinds of electrodes is stacked on another of the two kinds of electrodes, the method including steps of:

preparing the separators each having a multilayer construction in which a heat-shrinkable layer and a low heat-shrinkable layer are laminated on each other;

stacking the one of the two kinds of electrodes on the another of the two kinds of electrodes through each of the separators each that the one of the two kinds of electrodes is interposed between the low heat-shrinkable layers of the separators which are opposed to each other, and the another of the two kinds of electrodes is interposed between the heat-shrinkable layers of the separators which are opposed to each other;

partly bonding the opposed low heat-shrinkable layers of the separators to each other on a lateral side of the one of the two kinds of electrodes; and

heating the heat-shrinkable layer of a non-bonding portion of each of the separators to undergo heat shrinkage to form the separator into a curved shape extending at least from a position in which the separator is contacted with an end surface of the another of the two kinds of electrodes toward a lateral side of the another of the two kinds of electrodes.

Effect of Invention

According to the present invention, it is possible to readily prevent or suppress positional displacement of electrodes of a stacked battery. Further, when preventing or suppressing positional displacement of both of two kinds of electrodes, opposing separators are bonded to each other only on lateral sides of one of the two kinds of electrodes, and are not bonded to each other on lateral sides of another of the two kinds of electrodes. Therefore, the number of a bonding operation for bonding the opposing separators is relatively small, so that the bonding step can be readily carried out and the manufacturing cost can be reduced.

DESCRIPTION OF EMBODIMENTS

In the following, embodiments of the present invention are explained by referring to accompanying drawings.

FIG. 1shows a stacked battery according to a first embodiment of the present invention.FIG. 2is a sectional view taken alone line A-A as shown inFIG. 1, which shows a central part of the stacked battery.FIG. 3is a sectional view taken along line B-B as shown inFIG. 1, which shows connection portions and non-connection portions disposed in an essential part of the stacked battery.FIG. 4is a sectional view taken along line C-C as shown inFIG. 1, which shows the connection portions disposed in as essential part of the stacked battery.FIG. 5is a sectional view taken along line D-D as shown inFIG. 1, which shows the non-connection portions disposed in an essential part of the stacked battery. In the stacked battery, a stacked body is formed of two kinds of electrodes, i.e., positive electrodes (one of the two kinds of electrodes)1and negative electrodes (another of the two kinds of electrodes)2and separators3, each positive electrode1and each negative electrode2being alternately stacked on one another through each separator3. The stacked body is covered with laminate films4on both one surface (upper surface) thereof and an opposite surface (lower surface) thereof (laminate films4are not shown inFIGS. 2-5 and 8-10). After injecting an electrolyte solution between laminate films4, laminate films4are sealed to complete a stacked battery. Connection electrode5connected to positive electrodes1and connection electrode6connected to negative electrodes2extend through a bonding portion of laminate films4, and are exposed to an outside. Separator3is a multi-layer structure constituted of, for instance, heat-shrinkable layer3aformed of a stretched film made of a polyolefin-based resin (such as polypropylene, polyethylene, etc.) as a generally used material for a separator and low heat-shrinkable layer3bformed of a porous layer made of an inorganic material such as ceramics, which layers are laminated on each other. The plurality of separators3are stacked while alternately turning upside down such that positive electrode1is interposed between low heat-shrinkable layers3bof opposing separators3and negative electrode2is interposed between heat-shrinkable layers3aof opposing separators3.

In this embodiment, separator3disposed between positive electrode1and negative electrode2includes bonding portion7and non-bonding portions8which are located on lateral sides of each of positive electrode1and negative electrode2. In the construction shown inFIG. 1, separator3includes one bonding portion7and non-bonding portions8disposed on both sides of the one bonding portion7, along each of left and right side surfaces of electrodes1,2. As shown inFIGS. 3 and 4, in bonding portion7, low heat-shrinkable layer3bof one separator3is bonded to low heat-shrinkable layer3bof another separator3which is opposed to the one separator3such that positive electrode1is interposed therebetween. On the other hand, as shown inFIGS. 3 and 5, in each of non-bonding portions8, heat-shrinkable layer3aof separator3is formed into a curved shape which extends at least from a position in which heat-shrinkable layer3ais contacted with an end surface (a lateral side surface) of negative electrode2toward the lateral side of the negative electrode2due to heat shrinkage. In this construction, negative electrode2is disposed to be interposed between heat-shrinkable layers3aof separators3which are opposed to each other, so that both separator3located on a lower layer side of the negative electrode2and separator3located on an upper layer side of the negative electrode2are curved toward the lateral side of negative electrode2. Therefore, there occurs such an effect that the end surface of negative electrode2is hooked on the upper layer side separator3and the lower layer side separator3. Accordingly, positive electrode1is restrained from moving by bonding portion7of separator3which is located on each of the lateral sides of positive electrode1, so that positional displacement of positive electrode1can be prevented. Negative electrode2also can be prevented from positional displacement by being hooked on non-bonding portions8(curved portions) of separator3which are located on each of the lateral sides of negative electrode2. More specifically, relative displacement of positive electrode1and separator3can be prevented, and relative displacement of negative electrode2and separator3can be suppressed. Consequently, relative displacement of positive electrode1and negative electrode2can be suppressed. Thus, one sheet of separator3can perform an effect of simultaneously suppressing positional displacement of positive electrode1disposed adjacent to one surface of separator3and positional displacement of negative electrode2disposed adjacent to an opposite surface of separator3.

According to this embodiment, relative displacement of positive electrode1and negative electrode2can be prevented or suppressed in which direction thereof. In addition, bonding of separators3opposed to each other by heat fusion or ultrasonic fusion is carried out only on the lateral sides of positive electrode1, but is not carried out on the lateral sides of negative electrode2. Therefore, the number of the bonding portions is reduced, thereby facilitating the manufacturing process and reducing the manufacturing cost.

Examples of materials usable for heat-shrinkable layer3aand less heat-shrinkable layer3bof separator3are as follows.

Examples of the material for heat-shrinkable layer3amay include polyolefins such as polyethylene (PE) and polypropylene (PP). These materials may be used solely, and also may be used in combination of any two or more thereof by blending or polymerizing them with each other or further laminating them on each other. The materials are preferably monoaxially or biaxially stretched in order to impart heat shrinkage properties thereto. Further, it is preferred that heat-shrinkable layer3ahas a thickness of 5-30 μm and a void ratio of 30-70% in consideration of influence on battery characteristics.

Low heat-shrinkable layer3bis formed and laminated on heat-shrinkable layer3a. Low heat-shrinkable layer3bis not particularly limited to a specific one as long as the layer has heat shrinkage properties lower than a fine porous resin film that constitutes the above-described heat-shrinkable layer3a. Further, it is preferred that low heat-shrinkable layer3bhas a thickness of 1-20 μm and a void ratio of 30-70% in consideration of influence on battery characteristics and heat resistance.

Preferably, examples of the material for low heat-shrinkable layer3binclude a porous layer containing ceramics, a porous layer made of a heat-resistant resin, and a heat-resistant porous layer formed of a composite material of ceramics and a heat-resistant resin.

Examples of the ceramics may include alumina (Al2O3), silica (SiO2), magnesia (MgO), titania (TiO2), zirconia (ZrO2), etc. These ceramics may be used solely, and also may be used in combination of any two or more thereof by blending or sintering them with each other. The particle size of the ceramics is preferably 0.1-10 μm. In addition, upon forming a heat-resistant porous layer that contains these ceramics, a binder may be used as long as heat resistance and porous properties can be ensured. Examples of such a binder may include polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), etc. These binders may be used solely, and also may be used in combination of any two or more thereof by blending or polymerizing them with each other. In addition, the binder preferably is used in the substantially same amount as an amount of generally used binder. Specifically, the amount of the binder contained in the heat-resistant porous layer is 0.5-1.5% by mass, and more preferably, 1-10% by mass. For instance, the heat-resistant porous layer can be obtained by coating the fine porous resin film with a slurry (a heat-resistant porous layer forming material) prepared by dispersing the above-described ceramics and the above-described binder in a solvent such as N-methyl-2-pyrrolidone (NMP) and then drying the fine porous resin film thus coated.

Examples of the heat-resistant resin may include polyimides, aramids, polyamideimides, polyethyl sulfones, polyetherimides, polyphenylene ethers, etc. A porous layer of the heat-resistant resin can be obtained by coating a fine porous resin film with a solution prepared by dissolving these heat-resistant resins in a good solvent, and after that, contacting the coated fine porous resin film with a poor solvent to thereby deposit a heat-resistant resin on the fine porous resin film, and subjecting the thus treated fine porous resin film to desolventizing treatment. Examples of the good solvent may include N-methyl-2-pyrolidone (NMP), N,N-dimethylacetamide (DMA), dimethyl sulfoxide (DMSO), toluene, xylene, etc. Examples of the poor solvent may include water, ethanol, methanol, etc.

Further, a porous layer made of a composite of ceramics and a heat-resistant resin can be obtained by coating a fine porous rosin film with a slurry (a heat-resistant porous layer forming material) prepared by blending and dispersing a ceramic powder in the above-described coating solution of the heat-resistant resin, and after that, conducting the same procedures as described above. The slurry may be applied to a whole surface of the fine porous resin film, or may be applied to a part of the surface of the fine porous resin film except for a portion to be used as bonding portion7as explained later and the vicinity thereof.

Next, a method of manufacturing the stacked battery according to the present invention is explained. Firstly, positive electrodes1, negative electrodes2and separators3are stacked on one another in the following order: negative electrode2, separator3, positive electrode1, negative electrode2, . . . . At this time, a plurality of separators3are stacked while turning upside down such that positive electrode1is interposed between low heat-shrinkable layers3bof separators3which are opposed to each other and negative electrode2is interposed between heat-shrinkable layers3aof separators3which are opposed to each other.

During the stacking step, on each of the lateral sides of each of positive electrodes1, separator3located on a lower layer side of the positive electrode1and separator3located on an upper layer side of the positive electrode1are partly overlapped with each other and bonded to each other to form bonding portion7. Examples of a method of forming bonding portion7may include a method of bonding low heat-shrinkable layers3bto each other with an adhesive such as a hot pressing adhesive, a solution coating adhesive, a thermosetting adhesive, an ultraviolet curable adhesive, etc., a method of bonding upper and lower heat-shrinkable layers3ato each other in which resins in the respective layers are melted and integrated while removing low heat-shrinkable layers3bby applying an ultrasonic wave during pressing with a mold, or a method of bonding upper and lower heat-shrinkable layers3ato each other by ultrasonic wave application or heat pressing after previously removing a part of each of low heat-shrinkable layers3b.

After that, a stacked body formed by stacking all of positive electrodes1, negative electrodes2and separators3is subjected to heating as a whole. By the heating, the stacked body is dried as a whole, and heat-shrinkable layer3aof non-bonding portions8located in outer periphery of each of separators3is heat-shrunk. Since separator3has a construction in which heat-shrinkable layer3aand low heat-shrinkable layer3bare laminated on each other, when heated, only heat-shrinkable layer3aas shrunk but low heat-shrinkable layer3bis not largely shrunk, so that there is generated a curved portion concave toward the side of heat-shrinkable layer3a. Each of negative electrodes2is interposed between heat-shrinkable layers3aof separators3which are opposed to each other, and therefore, both separator3located on a lower layer side of the negative electrode2and separator3located on an upper layer side of the negative electrode2are curved toward the lateral sides of the negative electrode2interposed therebetween. As a result, there occurs such a function that end surfaces of the negative electrode2are hooked on the separator3located on the lower layer side of the negative electrode2and the separator3located on the upper layer side of the negative electrode2.

The time at which bonding portion7is formed by overlapping and fusing separator3located on the lower layer side of positive electrode1and separator3located on the upper layer side of positive electrode1to each other by heat or ultrasonic waves is not particularly limited. Bonding portion7may be formed after stacking separator3on positive electrode1. Bonding portion7also may be formed by previously partially fusing a pair of separators3, and after that, inserting positive electrode1between the pair of separators3. Further, in end portions of the stacked battery in a longitudinal direction thereof (an upper end portion and a lower end portion as shown inFIG. 1), opposing separators3may be bonded to each other, or may be free from being bonded to each other. In a case where opposing separators3are bonded to each other in the longitudinal end portion of the stacked battery, the bonding operation may be carried out in a step separate from the above-described step of forming bonding portion7on each of the lateral sides of positive electrode1, and also may be simultaneously carried out to form the opposing separators3into a bag shape. In addition, the stacked body may be formed by folding an elongated multilayer film, placing the folds of the multilayer film in planes perpendicular to the lateral side surfaces of electrodes1,2, and inserting electrodes1,2between opposing faces of the folded multilayer film toward the corresponding folds.

Further, another example of the method of manufacturing the stacked battery according to the present invention is explained. When positive electrodes1, negative electrodes2and separators3are in turn stacked on one another, bonding portions7may be formed every time at which separator3is stacked on positive electrode1. Also, when stacking positive electrodes1, negative electrodes2and separators3in turn, separators3may be heated to shrink heat-shrinkable layers3athereof to form carved portions extending toward the lateral sides of negative electrode2interposed between the separators3every time at which negative electrode2is stacked on separator3, and every time at which another separator3is stacked on the negative electrode2. According to this method, the treatment of non-bonding portions8is conducted as follows. That is, firstly, separator3is heated at a time at which negative electrode2is stacked on the separator3, thereby curving non-bonding portions8of the separator3toward the lateral sides of the negative electrode2. Subsequently, at a time at which another separator3is stacked on the negative electrode2, the another separator3is heated to thereby curve non-bonding portions8thereof toward the lateral sides of the negative electrode2. At this time, each of the end surfaces of the negative electrode2is already covered with the non-bonding portions8(curved portions) of the separator3located on the lower layer side of the negative electrode2. Accordingly, as shown inFIG. 6, the end surface of the negative electrode2is brought into such a state that the end surface is further covered with the non-bonding portions8(curved portions) of the separator3located on the upper layer side of the negative electrode2from an outside of the non-bonding portions8(curved portions) of the separator3located on the lower layer side of the negative electrode2. According to this method, positional displacement of negative electrodes2can be prevented with higher reliability.

FIG. 7shows a stacked battery according to a second embodiment of the present invention. The stacked battery according to the second embodiment has same basic structure as that of the stacked battery according to the first embodiment, but differs from the first embodiment in arrangement of bonding portion7and non-bonding portion8.

In this embodiment, as shown inFIG. 7, bonding portion7is disposed in a position close to positive electrode1along each of lateral side surfaces of positive electrode1over a whole length of positive electrode1, and non-bonding portion8is disposed on an outer peripheral side of bonding portion7. Non-bonding portion8is a curved portion extending toward each of the lateral sides of negative electrode2. That is, in the first embodiment, bonding portion7and non-bonding portions8(curved portions) coexist along a direction parallel to the lateral side surface of positive electrode1. In contrast, in the second embodiment, bending portion7shown inFIG. 8and non-bonding portion8(curved portion) shown inFIG. 9coexist along a width direction of positive electrode1(a direction perpendicular to the lateral side surface thereof). According to the second embodiment, bonding portion7that serves to prevent positional displacement of positive electrode1and non-bonding portion8that serves to prevent positional displacement of negative electrode2are present over a whole length of the lateral side surface of each of positive electrode1and negative electrode2. With this arrangement, positional displacement of electrodes1,2can be prevented with high reliability.

Low heat-shrinkable layer3bof separator3may be formed over a whole area of one surface (upper or lower surface) of separator3with a uniform thickness, or may be formed in a part of the area of the one surface of separator3. For instance, low heat-shrinkable layer3bhas an end edge located in a region extending between the end of positive electrode1and bonding portion7, so that low heat-shrinkable layer3bis not formed in an outside of the region. The end edge of low heat-shrinkable layer3bmay be located to be retreated inwardly from the end of negative electrode2as long as separator3is curved toward the lateral side of negative electrode2. However, in such a case, a distance from the end of negative electrode2to the end edge of heat-shrinkable layer3ais preferably 1 mm or less, and more preferably, 0.5 mm or less.

In addition, a central portion of separator3may be a region (a double-face region) in which low heat-shrinkable layer3bis formed on both surfaces of heat-shrinkable layer3a, and an outer peripheral portion of separator3which is located on an outside of the central portion may be a region (a single-face region) in which low heat-shrinkable layer3bis formed on only one surface of heat-shrinkable layer3a. In such a case, the double-face region is not deformable, and the single-face region is deformable. Accordingly, a region of separator3in which positive electrode1and negative electrode2are overlapped with each other is not deformable, and an outside region thereof located on an outside of the central region is deformable. As a result, a curved portion of separator3can be generated only in the outside region in order to attain the object of the present invention (suppression of positional displacement of positive electrode1and negative electrode2), while maintaining adhesion in the region in which positive electrode1and negative electrode2are overlapped with each other.

In the above-described embodiment, all separators3in the stacked body have a construction (construction of a curving separator) in which low heat-shrinkable layer3bis formed on only one surface of heat-shrinkable layer3a. However, separators3may include non-deformable separator3such as separator3constituted of only low-heat-shrinkable layer3bor only heat-shrinkable layer3a, and separator3having low heat-shrinkable layer3bformed on both surfaces of heat-shrinkable layer3a, in addition to the curving separators3. In such a case, separators3that are curved toward the lateral sides of negative electrode2are not always located on both surfaces of the negative electrode2, but only one sheet of separator3that is curved toward the lateral sides of negative electrode2may be located on one surface of the negative electrode2. Even in this case, the function that the end surface of negative electrode2are hooked on separator3can be performed by the one sheet of separator3. Therefore, it is possible to suppress displacement of negative electrode2.