JP2012156405A - Electricity storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electricity storage device which can efficiently manufacture an electrode group composed of positive electrodes and negative electrodes in a short time, and has a structure preferable for achieving high output.SOLUTION: An electrode group 11 of a lithium-ion capacitor is formed by using a band-shaped negative electrode 31, a band-shaped separator 41, and a plurality of positive electrodes 21 which are not bent and have a flat-plate shape. The electrode group 11 has a structure in which the band-shaped negative electrode 31 and the band-shaped separator 41 are superimposed and folded in a bellows-shape, and in which the flat-plate shaped positive electrodes 21 are put between flat portions of the folded negative electrode 31 through the separator 41. In the electrode group 11, an electrode area of the positive electrode 21 is smaller than an electrode area of the negative electrode 31, and the outer periphery of the positive electrode 21 is disposed on an inner side of the outer periphery of the negative electrode 31 in a plane view.

Description

  The present invention relates to an electricity storage device including an electrode group including a positive electrode, a negative electrode, and a separator.

  Energy storage systems such as load leveling devices such as photovoltaic power generation and wind power generation, instantaneous voltage drop countermeasure devices for electronic devices such as computers, and energy regeneration devices for electric vehicles and hybrid cars have a large energy capacity. There is a need for an electricity storage device that can be rapidly charged and discharged. Conventional lead-acid batteries and other secondary batteries are difficult to charge and discharge with a large current and have a short cycle life, so it is difficult to cope with the power storage system. Accordingly, in recent years, non-aqueous power storage devices have attracted attention as new power storage devices that can solve these problems.

  Currently, a lithium ion capacitor has been proposed as an electric storage device capable of rapid charging / discharging and extending the life (see Patent Document 1). As this lithium ion capacitor, there are known a wound type configured by winding electrodes in a roll shape and a stacked type configured by stacking plate-shaped electrodes. For this purpose, a multilayer type capacitor is used.

  In the laminated type lithium ion capacitor, as shown in FIGS. 14 and 15, a flat positive electrode 61, a negative electrode 62 and a separator 63 are used, and the positive electrode 61 and the negative electrode 62 are alternately stacked via the separator 63. Thus, the electrode group 65 is formed.

JP 2006-12702 A JP 2010-161249 A

  By the way, in the laminated type lithium ion capacitor, since it is necessary to form the electrode group 65 by stacking the electrodes 61 and 62 and the separator 63 one by one, the forming process becomes complicated and takes time. Specifically, when the stacked electrode group 65 is formed, it takes three times or more time as compared with the wound type.

  On the other hand, a wound-type lithium ion capacitor is highly productive, but has a structure in which an external terminal is connected to the end of a cylindrical electrode group for current collection, resulting in high electrical resistance and high output. It is unsuitable. Furthermore, when the electrode group has a cylindrical shape, there is a problem that it is difficult to connect an external terminal.

  In view of this, the present inventors have proposed a lithium ion capacitor in which an electrode group is configured using a strip-like positive electrode, a strip-like separator, and a plurality of flat plate-like negative electrodes (see Patent Document 2). In the lithium ion capacitor of Patent Document 2, a belt-like positive electrode and a belt-like separator are overlapped and wound into a flat roll shape or folded into a bellows shape, and the separator is interposed between the flat portions of the wound positive electrode or the folded positive electrode. An electrode group is fabricated by sandwiching a negative electrode. This simplifies the electrode group forming process.

  However, the capacity of the lithium ion capacitor depends on the capacity of the positive electrode. For this reason, when the electrode group is formed by winding the positive electrode into a flat roll shape or folding it into a bellows shape, the capacity of the positive electrode varies and it becomes difficult to form a capacitor having a capacity within the product specification. Further, since the electrode area of the negative electrode is smaller than the electrode area of the positive electrode, current concentration tends to occur at the end of the negative electrode, and lithium metal is likely to be deposited.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide an electricity storage device that can efficiently manufacture an electrode group including a positive electrode, a negative electrode, and a separator in a short time and that has a structure suitable for achieving high output. To provide a device.

  Means [1] to [4] for solving the above problems are listed below.

  [1] A container, a positive electrode having a structure in which a positive electrode is formed on a positive electrode current collector, a negative electrode having a structure in which a negative electrode is formed on a negative electrode current collector, and being interposed between the positive electrode and the negative electrode A positive electrode external terminal connected to the positive electrode current collector and the negative electrode current collector, wherein an electrode group including the positive electrode, the negative electrode, and the separator is accommodated in the container together with an electrolyte containing metal ions. In the electricity storage device in which the negative electrode external terminals connected to the electric body are both pulled out from the container, the electrode group uses a strip-shaped negative electrode, a strip-shaped separator, and a flat plate and a plurality of positive electrodes without bending. The belt-like negative electrode and the belt-like separator are overlapped and folded in a bellows shape, and the positive electrode is sandwiched between the flat portions of the folded negative electrode through the separator, and Energy storage device serial electrode area of the positive electrode is made smaller than the electrode area of the negative electrode, the outer periphery of the positive electrode in a plan view and having a structure inside the outer periphery of the negative electrode.

  According to the invention described in Means 1, since the electrode group is formed by stacking the strip-shaped negative electrode and the strip-shaped separator and folding them in a bellows shape, the electrode group is formed by stacking the negative electrode and the separator one by one. Compared with the case where it does, the formation process can be simplified. In the electrode group of the present invention, since a plurality of positive electrodes formed in a flat plate shape without bending are sandwiched, the capacity variation of the positive electrode is suppressed as compared with the case where the electrode group is formed by bending a belt-like positive electrode. Therefore, an electricity storage device having a capacity within the product specification can be reliably formed. In addition, since the electrode area of the negative electrode is larger than the electrode area of the positive electrode and the outer periphery of the negative electrode is outside the outer periphery of the positive electrode, current concentration at the negative electrode is less likely to occur, and lithium metal is one factor that hinders high output Precipitation can be avoided. Furthermore, an external terminal can be easily connected to the flat portion of the negative electrode and the flat positive electrode constituting the electrode group. In addition, since the electrode group has a structure in which positive electrodes and negative electrodes are alternately stacked via separators, an electricity storage device excellent in rapid charge / discharge can be realized. Furthermore, unlike the conventional cylindrical roll shape, the electrode group is formed in a bellows shape, so that the structure can be pressed in the thickness direction of the electrode group, which also contributes to high output.

  [2] A container, a positive electrode having a structure in which a positive electrode is formed on a positive electrode current collector, a negative electrode having a structure in which a negative electrode is formed on a negative electrode current collector, and the positive electrode and the negative electrode A positive electrode external terminal connected to the positive electrode current collector and the negative electrode current collector, wherein an electrode group including the positive electrode, the negative electrode, and the separator is accommodated in the container together with an electrolyte containing metal ions. In the electricity storage device in which the negative electrode external terminals connected to the electric body are both pulled out from the container, the electrode group uses a strip-shaped negative electrode, a strip-shaped separator, and a flat plate and a plurality of positive electrodes without bending. The belt-like negative electrode and the belt-like separator are overlapped and wound into a flat roll shape, and the positive electrode is sandwiched between the flat portions of the negative electrode in a wound state via the separator, One electric storage device the electrode area of the positive electrode was smaller than the electrode area of the negative electrode, the outer periphery of the positive electrode in a plan view and having a structure inside the outer periphery of the negative electrode.

  According to the invention described in Means 2, since the electrode group is formed by superimposing the strip-shaped negative electrode and the strip-shaped separator and winding them in a flat roll shape, the electrode group is formed by superimposing the negative electrode and the separator one by one. The formation process can be simplified compared with the case of forming. In the electrode group of the present invention, since a plurality of positive electrodes formed in a flat plate shape without bending are sandwiched, the variation in the capacity of the positive electrode is compared with the case where the electrode group is formed by bending a belt-like positive electrode. Therefore, an electricity storage device having a capacity within the product standard can be reliably formed. In addition, since the electrode area of the negative electrode is larger than the electrode area of the positive electrode and the outer periphery of the negative electrode is outside the outer periphery of the positive electrode, current concentration at the negative electrode is less likely to occur, and lithium metal is one factor that hinders high output Precipitation can be avoided. Furthermore, the external electrode can be easily connected to the flat portion of the negative electrode and the flat positive electrode constituting the electrode group. In addition, since the electrode group has a structure in which positive electrodes and negative electrodes are alternately stacked via separators, an electricity storage device excellent in rapid charge / discharge can be realized. Further, unlike the conventional cylindrical roll shape, the electrode group is formed into a flat roll shape, so that the electrode group can be pressurized in the thickness direction, which also contributes to higher output.

  [3] The electricity storage device according to means 1 or 2, wherein the thickness of the positive electrode is twice or more the thickness of the negative electrode.

  According to the invention described in Means 3, since the negative electrode formed thinner than the positive electrode is wound in a flat roll shape or folded in a bellows shape, an electrode group can be easily formed.

  [4] The electrolyte includes a lithium salt, the positive electrode is made of a carbon material, the negative electrode is made of a material capable of occluding and releasing lithium, and the negative electrode is doped with lithium ions in advance. An electricity storage device.

  According to the invention described in means 4, a lithium ion capacitor using a carbon material for the positive electrode and the negative electrode can be realized. In this lithium ion capacitor, lithium ions are supported on the negative electrode, but since the negative electrode is connected in a strip shape, the potential of the negative electrode is likely to be uniform, and doping of lithium ions can be performed in a short time. In particular, when the electrode group is formed in a bellows shape as in the means 1, the number of side electrodes is reduced, so that the doping amount of lithium ions can be reduced.

  As described in detail above, according to the inventions described in the means 1 to 4, an electricity storage device that can efficiently produce an electrode group composed of a positive electrode, a negative electrode, and a separator in a short time and has a structure suitable for achieving high output. Can be provided.

The side view which shows the lithium ion capacitor of 1st Embodiment. The top view which shows the lithium ion capacitor of 1st Embodiment. Sectional drawing which shows the electrode group of 1st Embodiment. Sectional drawing in the AA in the electrode group of FIG. The top view which shows a positive electrode, a negative electrode, and a separator. The perspective view which shows a positive electrode, a negative electrode, and a separator. (A)-(c) is explanatory drawing which shows the manufacturing method of the electrode group of 1st Embodiment. Sectional drawing which shows the electrode group of 2nd Embodiment. (A)-(c) is explanatory drawing which shows the manufacturing method of the electrode group of 2nd Embodiment. The top view which shows the lithium ion capacitor of another embodiment. The top view which shows the negative electrode of another embodiment. The top view which shows the electrode group of another embodiment. Sectional drawing which shows the electrode group of another embodiment. The top view which shows the conventional positive electrode, the negative electrode, and a separator. The top view which shows the conventional electrode group.

[First Embodiment]
Hereinafter, a first embodiment in which the present invention is embodied in a lithium pre-doped lithium ion capacitor as an electricity storage device will be described in detail with reference to the drawings. FIG. 1 is a side view showing a lithium ion capacitor 10 according to the present embodiment, and FIG. 2 is a plan view of the lithium ion capacitor 10. 3 is a sectional view showing the electrode group 11 constituting the lithium ion capacitor 10, and FIG. 4 is a sectional view taken along the line AA in the electrode group 11 of FIG. FIG. 5 is a plan view showing the positive electrode 21, the negative electrode 31, and the separator 41 that constitute the electrode group 11.

  As shown in FIGS. 1 to 5, the lithium ion capacitor 10 of the present embodiment includes an electrode group 11 including a positive electrode 21, a negative electrode 31, and a separator 41 interposed between the positive electrode 21 and the negative electrode 31. . In the electrode group 11 of the present embodiment, the strip-shaped negative electrode 31 and the strip-shaped separator 41 are overlapped and folded in a bellows shape, and the flat-plate-shaped positive electrode 21 is interposed between the flat portions of the folded negative electrode 31 via the separator 41. Has a structure sandwiched between. The electrode group 11 is hermetically housed in the container 51 (housing body) together with the electrolyte.

  The positive electrode 21 is about 80 μm thick and has a structure in which a positive electrode 22 made of a carbon material is formed on a positive electrode current collector 23 (see FIG. 5). In the present embodiment, the positive electrode current collector 23 is formed in a rectangular flat plate shape having a tab 24, and on the positive electrode current collector 23, the positive electrode 22 in a planar shape with the tab 24 part left. Is coated.

  Examples of the carbon material that forms the positive electrode 22 include activated carbon that has been subjected to an appropriate pulverization treatment. Such a carbon material is kneaded and molded with a conductive agent and a binder as necessary.

  Examples of the conductive agent include various graphite materials and carbon black. Among them, it is preferable to use conductive carbon blacks. Specific examples include channel black, oil furnace black, lamp black, thermal black, acetylene black, ketjen black, etc., but it is possible to select acetylene black in terms of excellent liquid retention and low electrical resistance. Particularly preferred.

  The binder is not particularly limited as long as it is insoluble in the organic electrolyte. For example, a fluorine-based resin such as polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyvinyl fluoride (PVF), or carboxymethylcellulose. Organic polymer compounds such as alkali metal salts or ammonium salts, polyimide resins, polyamide resins, polyacrylic acid and sodium polyacrylate are suitable.

  The positive electrode current collector 23 is a member for collecting current while supporting the positive electrode 22. For example, a conductive metal foil such as aluminum or stainless steel or a conductive metal plate is preferably used. Stainless steel is a suitable material in that it is not alloyed with lithium and is less susceptible to electrochemical oxidation.

  In the electrode group 11 folded in a bellows shape, the tab 24 portion (the end portion where the positive electrode 22 is not coated) of the positive electrode current collector 23 protrudes from the folded portion of the separator 41. A positive electrode external terminal 25 made of a conductive metal material is joined to the tab 24 of the positive electrode current collector 23 by welding.

  The negative electrode 31 has a thickness of about 30 μm and has a structure in which a negative electrode 32 made of a material capable of inserting and extracting lithium ions is formed on a negative electrode current collector 33. In the present embodiment, on the strip-shaped negative electrode current collector 33, the negative electrode 32 is coated in a planar shape with one end portion left in a line along the longitudinal direction. In addition, as a metal which supplies lithium ion, not only a lithium metal single-piece | unit is pointed out, but the substance which contains lithium at least and can supply lithium ion like a lithium-aluminum alloy is widely pointed out. .

Specific examples of the material for forming the negative electrode 32 include lithium metal, lithium-aluminum alloy, graphite material, graphitizable carbon material, non-graphitizable carbon material, niobium pentoxide (Nb ₂ O ₅ ), lithium titanate. (Li ₄ Ti ₅ O ₁₂ ), silicon monoxide (SiO), tin monoxide (SnO), composite oxide of tin and lithium (Li ₂ SnO ₃ ), composite oxide of lithium, phosphorus and boron (for example, LiP _0.4 B _0.6 O _2.9 ), etc. Among these, carbon materials such as graphite materials, graphitizable carbon materials, and non-graphitizable carbon materials are suitable as negative electrode materials because they have properties such as high reversibility.

  Examples of the carbon material that forms the negative electrode 32 include various natural graphites that have been appropriately pulverized, graphite materials such as synthetic graphite, expanded graphite, mesocarbon microbeads that have been carbonized, and mesophase pitch-based carbon. Examples thereof include carbon materials such as fibers, vapor-grown carbon fibers, pyrolytic carbon, petroleum coke, pitch coke, and needle coke, or a mixture thereof. The carbon materials for the negative electrode 32 listed here are kneaded and molded together with a conductive agent and a binder as necessary. As the conductive agent and the binder, the materials exemplified in the description of the positive electrode 22 can be used as they are.

  The negative electrode current collector 33 is a member for collecting current while supporting the negative electrode 32. For example, a conductive metal foil such as copper, nickel, stainless steel, or a conductive metal plate is preferably used. In addition, when a porous body is used as the negative electrode current collector 33, it is possible to increase the efficiency of lithium ion pre-doping.

  In this electrode group 11, one end portion 34 (an end portion where the negative electrode 32 is not coated) of the negative electrode current collector 33 protrudes from the folded portion of the separator 41. A negative electrode external terminal 35 made of a conductive metal material is joined to one end 34 of the negative electrode current collector 33 by welding.

  In addition, a lithium application part (not shown) is provided in a predetermined part (for example, upper and lower parts on the external terminal side) of the electrode group 11, and a lithium metal foil (not shown) for pre-doping is provided on the lithium application part. (Omitted) is affixed. The lithium metal foil dissolves and disappears when the pre-doping is completed.

  In the electrode group 11 of the present embodiment, the electrode area of the positive electrode 21 is made smaller than the electrode area of the flat portion of the negative electrode 31, and the outer periphery of the positive electrode 21 is arranged inside the outer periphery of the negative electrode 31 in plan view. In the electrode group 11 of the present embodiment, the strip-shaped separator 41 and the negative electrode 31 are folded at a position spaced from the end of the positive electrode 21. Further, in the negative electrode 31 folded in a bellows shape, the bent portion located at the end of the flat portion has a shape bent in a curved shape without a fold.

  The separator 41 interposed between the negative electrode 31 and the positive electrode 21 is durable to an organic electrolyte, an electrode active material, and the like, and is made of a non-conductive porous body having continuous air holes. Usually, a cloth, a nonwoven fabric or a porous body made of glass fiber, polyethylene, polypropylene or the like is used. The thickness of the separator 41 is preferably thin in order to reduce the internal resistance of the capacitor, but can be appropriately set in consideration of the amount of organic electrolyte retained, flowability, strength, and the like.

The separator 41 is usually impregnated with a liquid organic electrolyte, but a gel or solid organic electrolyte may be used to prevent leakage. Here, the organic electrolyte is obtained by dissolving a compound capable of generating a doped lithium ion in an aprotic organic solvent. Examples of the compound include organic lithium salts. Preferred examples thereof include lithium hexafluorophosphate represented as LiPF ₆ and lithium bis (trifluoromethanesulfone) represented as LiN (CF ₃ SO ₂ ) _2. Examples include imide and lithium bis (pentafluoroethanesulfone) imide represented by LiN (C ₂ F ₅ SO ₂ ) ₂ . Moreover, as a suitable example of the said aprotic organic solvent, propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), (gamma) -butyrolactone (GBL), vinylene carbonate (VC), acetonitrile (AN), for example ), Dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC) and derivatives thereof, or a mixed solvent thereof.

  The container 51 of the lithium ion capacitor 10 is a soft container processed into a rectangular bag shape using an aluminum laminate film obtained by laminating an aluminum foil on a resin film. The opening is sealed by heat sealing. Sealing by thermal fusion is performed in a state where the positive electrode external terminal 25 and the negative electrode external terminal 35 are sandwiched between the fusion portions.

  When the electrode group 11 is housed in the container 51 in this way, the positive electrode external terminal 25 is drawn out from one end (the left end in FIG. 1) of the container 51 and the other end (in FIG. 1). The negative external terminal 35 is pulled out from the right end). The container 51 may be formed using a metal laminate film made of a metal foil other than the aluminum foil.

  Next, a method for manufacturing the above-described lithium ion capacitor 10 will be described.

  First, a strip-like negative electrode 31, a strip-like separator 41, and a flat plate-like and plural positive electrodes 21 without bending are prepared (see FIG. 5).

  The positive electrode 21 is produced by the following procedure. First, a mixed slurry containing a carbon material, a conductive agent and a binder is prepared, and this is applied to an aluminum foil having a thickness of 20 μm which is the positive electrode current collector 23 to form the positive electrode 22. After the positive electrode 22 is dried and pressed, it is cut into a predetermined size with a mold to obtain a flat positive electrode 21. The negative electrode 31 is produced by the following procedure. First, a mixed slurry containing a carbon material and a binder is prepared, and this is applied to a copper foil having a thickness of 12 μm, which is the negative electrode current collector 33, thereby forming the negative electrode 32. After the negative electrode 32 is dried and pressed, it is cut into a predetermined size with a mold to form a strip-shaped negative electrode 31. Further, the separator base paper is cut to obtain a strip-shaped separator 41.

  Then, as shown in FIG. 6, separators 41 are arranged on the front and back sides of the negative electrode 31, the negative electrodes 31 and the separators 41 are overlapped, and then a predetermined area is flattened and folded into a bellows shape. At this time, as shown in FIG. 7, the negative electrode 31 and the separator 41 are folded while the positive electrode 21 is sandwiched between the flat portions of the negative electrode 31 via the separator 41. Here, the separator 41 and the negative electrode 31 are bent at a position away from the end of the positive electrode 21. At this time, the separator 41 and the negative electrode 31 are bent in a curved shape so that the end of the flat portion is not creased. By repeating this, the electrode group 11 folded in a bellows shape (in other words, the zigzag electrode group 11) as shown in FIGS. 3 and 4 is produced. The bellows-like electrode group 11 as in the present embodiment can apply a pressing force in a direction perpendicular to the flat surfaces of the positive electrode 21 and the negative electrode 31 (that is, the electrode group thickness direction). Therefore, unlike the conventional cylindrical roll electrode group, it is easy to achieve high output.

  Thereafter, the positive electrode external terminal 25 is ultrasonically welded to the tab 24 of the positive electrode current collector 23, and the negative electrode external terminal 35 is ultrasonically welded to the end portion 34 of the negative electrode current collector 33. Next, the electrode group 11 with a terminal is accommodated in the container 51, and an opening part is closed. At this time, lithium metal is disposed above and below the electrode group 11 and stored in the container 51. Thereafter, the organic electrolyte is injected while evacuating, so that the accommodating space in the container 51 is surely filled with the organic electrolyte. Further, the container 51 is sealed and held for a predetermined time to advance lithium ion pre-doping. As a result, the lithium ion capacitor 10 shown in FIG. 1 is completed.

  Therefore, according to the present embodiment, the following effects can be obtained.

  (1) In the lithium ion capacitor 10 of the present embodiment, the electrode group 11 is formed by overlapping the belt-like negative electrode 31 and the belt-like separator 41 and folding them in a bellows shape. In this way, the formation process can be simplified as compared with a conventional capacitor in which the negative electrode 62 and the separator 63 are overlapped one by one to form the electrode group 65 (see FIG. 15). Specifically, when the electrode group 65 of FIG. 15 is manufactured, two loading robots for loading the poles 61 and 62 are required. In contrast, in the present embodiment, since only the positive electrodes 21 need to be loaded one by one, only one loading robot is required, and the configuration of the manufacturing apparatus can be simplified. In addition, in the electrode group 11, a plurality of positive electrodes 21 formed in a flat plate shape are sandwiched, so that variation in capacity of the positive electrode 21 is suppressed as compared with the case where the electrode group is formed by bending a belt-shaped positive electrode. Therefore, a capacitor having a capacity within the product standard can be reliably formed. Furthermore, since the electrode area of the negative electrode 31 is larger than the electrode area of the positive electrode 21 and the outer periphery of the negative electrode 31 is outside the outer periphery of the positive electrode 21, current concentration in the negative electrode 31 is less likely to occur, which hinders high output. It is possible to avoid the deposition of lithium metal which is the cause.

  (2) In the lithium ion capacitor 10 of the present embodiment, the external terminals 35 and 25 can be easily connected to the flat portion of the negative electrode 31 and the flat positive electrode 21 constituting the electrode group 11. Further, since the electrode group 11 has a structure in which the positive electrodes 21 and the negative electrodes 31 are alternately stacked via the separators 41, a capacitor excellent in rapid charge / discharge can be realized. Furthermore, unlike the conventional cylindrical roll shape, the electrode group 11 has a bellows shape, so that the electrode group 11 can be pressurized in the thickness direction, which also contributes to higher output.

  (3) In the lithium ion capacitor 10 of the present embodiment, the thickness of the positive electrode 21 constituting the electrode group 11 is at least twice the thickness of the negative electrode 31. In this lithium ion capacitor 10, the negative electrode 31 formed thinner than the positive electrode 21 is folded in a bellows shape, so that the electrode group 11 can be easily formed. Moreover, in the lithium ion capacitor 10, since the negative electrode 31 is connected in a strip shape, the potential of the negative electrode 31 is likely to be uniform, and lithium ions can be doped in a short time.

  (4) In the lithium ion capacitor 10 of the present embodiment, the negative electrode 31 is folded by bending the side surface of the electrode group 11 in a curved shape so that there is no crease. Is suppressed and current concentration is less likely to occur. Moreover, in the process of folding the negative electrode 31, it is not necessary to make a crease at an accurate position, so that the working efficiency can be improved.

(5) In the lithium ion capacitor 10 of the present embodiment, since the negative electrode 31 is bent at the side surface portion of the electrode group 11, the thickness of the negative electrode 31 may be uneven. The side surface portion of the electrode group 11 is a portion where the positive electrode 21 and the negative electrode 31 do not face each other, and is an unnecessary portion that does not contribute to capacity. In particular, in the present embodiment, the negative electrode 31 is bent at a position away from the end of the positive electrode 21. In this case, even if current concentration occurs in the bent portion of the negative electrode 31 and lithium metal is deposited, the problem that the capacitor performance deteriorates is avoided because the positive electrode 21 does not face the deposited portion.
[Second Embodiment]

  Next, a second embodiment of the present invention will be described with reference to FIGS. In the present embodiment, the method of forming the electrode group 11A is different from that of the first embodiment, and other than that is the same as the lithium ion capacitor 10 of the first embodiment.

  Specifically, as shown in FIG. 8, the electrode group 11A of the present embodiment has a belt-like negative electrode 31 and a belt-like separator 41 overlapped and wound into a flat roll shape, and in a wound state. The flat cathode 21 is sandwiched between the flat portions of the anode 31 via the separator 41.

  Also in the case of forming the electrode group 11A of the present embodiment, as in the first embodiment, the strip-shaped negative electrode 31, the strip-shaped separator 41, and the flat and plural positive electrodes 21 without bending are used ( (See FIG. 5). Then, as shown in FIG. 9, separators 41 are arranged on the front and back sides of the negative electrode 31, and the negative electrode 31 and the separator 41 are overlapped, and then a predetermined area is flattened and wound into a flat roll shape. At this time, the negative electrode 31 and the separator 41 are sequentially wound while the positive electrode 21 is sandwiched between the flat portions of the negative electrode 31 via the separator 41. By repeating this, a flat roll electrode group 11A as shown in FIG. 8 is produced.

  Even when the electrode group 11A is formed as in the present embodiment, it is not necessary to superimpose the positive electrodes 61 and the separators 63 one by one as in the prior art, so that the formation process can be simplified. In the electrode group 11 </ b> A, the electrode area of the positive electrode 21 is made smaller than the electrode area of the flat part of the negative electrode 31, and the outer periphery of the positive electrode 21 is disposed inside the outer periphery of the negative electrode 31 in plan view. In this way, current concentration that is one cause of hindering high output is unlikely to occur, and precipitation of lithium metal can be avoided.

  In addition, you may change each embodiment of this invention as follows.

  In the lithium ion capacitor 10 of each of the above embodiments, the positive electrode external terminal 25 and the negative electrode external terminal 35 are drawn out in opposite directions, but the present invention is not limited to this. Specifically, for example, a positive electrode external terminal 25 and a negative electrode external terminal 35 may be drawn from the same direction of the container 51 as in the lithium ion capacitor 10A shown in FIG. In the lithium ion capacitor 10A of FIG. 10, the configuration of the electrode group 11 is the same as that of the first embodiment, and the direction in which the external terminals 25 and 35 are pulled out is not the left-right direction of the container 51, but above the container 51. Has been changed.

  Further, as shown in FIG. 11, on the strip-shaped negative electrode current collector 33, a line-shaped end portion where the negative electrode 32 is not coated is cut to have a tab-shaped electrode uncoated portion 34. The negative electrode 31A may be used. Specifically, the negative electrode 31A of FIG. 11 and the separator 41 are overlapped and folded in a bellows shape, and the positive electrode 21 is sandwiched between the flat portions of the negative electrode 31A via the separator 41, and the electrode group 11B as shown in FIG. Form. When a lithium ion capacitor is configured using this electrode group 11 </ b> B, the positive electrode external terminal 25 and the negative electrode external terminal 35 can be drawn out from the same direction of the container 51.

  When the electrode group 11A is configured by winding the strip-shaped negative electrode 31 and the strip-shaped separator 41 into a flat roll shape as in the second embodiment, the number of wound electrodes of the negative electrode 31 increases. As the thickness increases, the area of the side surface that does not contribute to the capacitor capacity increases. In this way, when the electrode group 11A is thick, as shown in FIG. 13, the electrode group 11D may be configured by forming a plurality of electrode groups 11C with a small number of wrinkles and stacking them. When the electrode group 11D is configured in this manner, the area of the side surface that does not contribute to the capacitor capacity can be minimized.

  In the lithium ion capacitors 10 and 10A of the above embodiments, a soft container made of an aluminum laminate film is used as the container 51 for storing the electrode groups 11 and 11A. However, the present invention is not limited to this. You may use the hard container which consists of metal materials, such as.

  In the above embodiment, the present invention is embodied in the lithium ion capacitor 10, but the present invention is applied to other power storage devices (for example, a lithium ion secondary battery) as long as the power storage device uses an electrolytic solution containing metal ions. The invention can be embodied.

  Next, in addition to the technical ideas described in the claims, the technical ideas grasped by the respective embodiments described above are listed below.

  (1) In the means 1, in the negative electrode folded in the shape of a bellows in the electrode group, the bent portion located at the end has a shape bent in a curved shape without a fold. .

  (2) The electric storage device according to (1), wherein, in the negative electrode folded in a bellows shape in the electrode group, the negative electrode is folded at a position separated from an end of the positive electrode.

DESCRIPTION OF SYMBOLS 10,10A ... Lithium ion capacitor 11, 11A, 11B, 11D ... Electrode group 21 ... Positive electrode 22 ... Positive electrode 23 ... Positive electrode collector 25 ... External terminal for positive electrodes 31, 31A ... Negative electrode 32 ... Negative electrode 33 ... Negative electrode current collector Body 35 ... Negative electrode external terminal 41 ... Separator 51 ... Container as container

Claims (4)

A container, a positive electrode having a structure in which a positive electrode is formed on the positive electrode current collector, a negative electrode having a structure in which a negative electrode is formed on the negative electrode current collector, and a separator interposed between the positive electrode and the negative electrode. A positive electrode external terminal connected to the positive electrode current collector and the negative electrode current collector, the electrode group comprising the positive electrode, the negative electrode and the separator being housed in the container together with an electrolyte containing metal ions In the electricity storage device in which the connected negative electrode external terminals are both pulled out from the container,
The electrode group uses a strip-shaped negative electrode, a strip-shaped separator and an unbent flat plate and a plurality of positive electrodes, and the belt-shaped negative electrode and the strip-shaped separator are overlapped and folded in a bellows shape, and in a folded state A structure in which the positive electrode is sandwiched between the flat portions of the negative electrode via the separator, the electrode area of the positive electrode is smaller than the electrode area of the negative electrode, and the outer periphery of the positive electrode is inside the outer periphery of the negative electrode in plan view An electricity storage device comprising: A container, a positive electrode having a structure in which a positive electrode is formed on the positive electrode current collector, a negative electrode having a structure in which a negative electrode is formed on the negative electrode current collector, and a separator interposed between the positive electrode and the negative electrode. A positive electrode external terminal connected to the positive electrode current collector and the negative electrode current collector, the electrode group comprising the positive electrode, the negative electrode and the separator being housed in the container together with an electrolyte containing metal ions In the electricity storage device in which the connected negative electrode external terminals are both pulled out from the container,
The electrode group uses a strip-shaped negative electrode, a strip-shaped separator, and a flat plate and a plurality of positive electrodes without bending, and the strip-shaped negative electrode and the strip-shaped separator are overlapped and wound into a flat roll shape. The positive electrode is sandwiched between the flat portions of the negative electrode in a rotated state and the electrode area of the positive electrode is smaller than the electrode area of the negative electrode, and the outer periphery of the positive electrode is the outer periphery of the negative electrode in plan view. An electricity storage device having an internal structure.   The electrical storage device according to claim 1 or 2, wherein the thickness of the positive electrode is twice or more the thickness of the negative electrode.   The electrolyte solution includes a lithium salt, the positive electrode is made of a carbon material, the negative electrode is made of a material capable of inserting and extracting lithium, and the negative electrode is doped with lithium ions in advance. Item 4. The electricity storage device according to any one of Items 1 to 3.

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