JP2006134697A - Lithium-ion rechargeable battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium-ion rechargeable battery capable of reducing its thickness without impairing an electric capacity. <P>SOLUTION: In a lithium-ion rechargeable battery 1, sheet-like negative electrodes 10, 10 and positive electrodes 7', 7 are laminated in order, and the first type positive electrode 7' is sandwitched by the a pair of the negative electrodes 10, 10 with a separator 3 in between respective adjoining electrodes, and a pair of the second type positive electrodes 7, 7 are disposed on the other side of the first type positive electrode 7' across the negative electrodes 10, 10 respectively. The battery 1 is provided with a cell 20 which is symmetric upward/downward in the thickness direction with a symmetry plane of an only-one current collector 5' the first type positive electrode 7', and comprises one or more repetition of the cell 20. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a lithium ion secondary battery. In particular, the present invention relates to a lithium ion secondary battery having, as a minimum unit structure, a cell in which sheet-like positive electrodes and negative electrodes are sequentially stacked.

  Today, lithium ion secondary batteries are widely used as power sources for various electronic devices such as mobile communication devices and portable computers. Lithium ion secondary batteries have advantages such as being able to obtain large electric energy while being small and light, having excellent charge / discharge cycle characteristics, and being capable of rapid charging.

  The simplest lithium ion secondary battery cell comprises, for example, a single positive electrode, a single negative electrode, and a separator that insulates them from each other as disclosed in Patent Document 1. If a metal mesh is used as a current collector for exchanging electrons, the cell 80 shown in FIG. 4A can be realized. The cell 80 includes a positive electrode 81, a negative electrode 83, and a separator 85. The positive electrode 81 (or the negative electrode 83) includes a positive electrode current collector 81c (negative electrode collector) that transfers electrons between the positive electrode active material layer 81a (negative electrode active material layer 83a) that causes an electrochemical reaction and the positive electrode active material layer 81a. Electric body 83c).

  By the way, when designing a lithium ion secondary battery, there is a technical problem of how to secure a required electric capacity. In order to increase the electric capacity, it is considered that the molar amount of the active material may be simply increased. However, an increase in the molar amount of the active material means an increase in the thickness of the active material layer containing the active material. When the thickness of the active material layer becomes too large, the apparent current density between the positive electrode and the negative electrode becomes large, which causes a problem that the charge / discharge efficiency is reduced at a large current. Therefore, it is difficult to secure a large electric capacity in the single cell shown in FIG.

  One solution for avoiding the above-described problems while increasing electric capacity is a spiral cell. While the spiral cell can easily increase the electrode area and is excellent in productivity, it has disadvantages such as a limitation in shape and difficulty in realizing a reduction in thickness.

  As another solution for increasing electric capacity, there is a structure in which a plurality of cells 80 shown in FIG. 4A are stacked as shown in FIG. 4B. However, if the cells 80 are simply stacked, the positive electrode 81 and the negative electrode 83 are short-circuited. Therefore, it is necessary to interpose an insulating layer 87 as shown in FIG. Since this insulating layer 87 does not contribute to the power generation itself, the energy density is reduced. Although there is an idea that the insulating layer 87 is made of the same material as that of the separator 85, there is a possibility that lithium ions are occluded / released between the central positive electrode 81 and the negative electrode 83. In that case, it is expected that the both-side electrodes will cause a problem such as a decrease in charge / discharge efficiency at a large current.

Therefore, a cell having a structure shown in FIG. 5, that is, a so-called bicell 90 is generally employed. As disclosed in Patent Document 2, the bicell 90 includes a central negative electrode 93 (including a negative electrode active material layer 93a and a negative electrode current collector 93c) as positive electrodes 91 and 91 (positive electrode active material layer 91a) on both sides. And a positive electrode current collector 91c). By stacking the bicells 90, an electric capacity corresponding to the number of layers can be obtained. Further, it is not necessary to insulate adjacent bicelles, and the capacity balance between the positive electrode and the negative electrode can be considered in units of bicelles.
JP 2002-260739 A JP 2000-311718 A

  By the way, recently, demands for thinning, high capacity, and low cost of lithium ion secondary batteries have become stronger. Accordingly, an object of the present invention is to provide a lithium ion secondary battery having a structure capable of reducing the thickness without sacrificing the electric capacity and reducing the cost. To do.

Means for Solving the Problems and Effects of the Invention

  In order to solve the above-mentioned problems, the present invention can charge and discharge by inserting and extracting lithium ions between a first electrode and a second electrode having different polarities. A lithium ion secondary battery having a form in which two electrodes are stacked in order, wherein the second electrode is a first type second electrode disposed between a pair of first electrodes via a separator, It consists of a pair of second-type second electrodes arranged on the opposite side of the first-type second electrode across the electrode, and has a thickness with the only current collector of the first-type second electrode as the symmetry plane The main feature is that it has a unit structure that is symmetrical in the vertical direction and is constituted by one or a repetition of the unit structure.

  In another aspect, the present invention is capable of charging / discharging by inserting and extracting lithium ions between a first electrode and a second electrode having different polarities from each other. A lithium ion secondary battery having a configuration in which two electrodes are stacked in order, wherein the second electrode is composed of a first type second electrode and a second type second electrode having different electric capacities, A first type second electrode including a first type second electrode current collector and a first type second electrode active material layer disposed on both surfaces of the first type second electrode current collector is a set of first A second type second electrode second electrode current collector disposed between the electrodes and including a second type second electrode current collector and a second type second electrode active material layer disposed on both surfaces of the second type second electrode current collector The electrode is disposed on the opposite side of the first type second electrode across the first electrode, the first type second electrode and the first electrode, and the second type second electrode. And the first electrode are separated by a separator, and the current collector constituting the first and second electrodes is used as a symmetry plane, and has a unit structure that is symmetrical vertically in the thickness direction. The main feature is that it is configured by repetition.

  Specifically, the first electrode can be a negative electrode and the second electrode can be a positive electrode.

  Improvement of energy density is indispensable for achieving both thinning and high capacity of the battery. The unit structure (see FIG. 1) of the lithium ion secondary battery according to the present invention corresponds to a structure in which two conventional bicells shown in FIG. 5 are stacked. As can be seen from FIG. 5, when the two bicells 90 and 90 are stacked, the central portion of the stacked body is constituted by the positive electrodes 91 and 91. The positive electrodes 91 and 91 each independently include a positive electrode current collector 91c. On the other hand, in the unit structure of the lithium ion secondary battery according to the present invention, the central part of the unit structure is constituted by the positive electrode (second electrode), but the central positive electrode current collector has a vertically symmetrical surface. The unit structure can be configured to include. That is, the current collector can be reduced by one sheet as compared with the stacked body of the pair of bicells 90 and 90. By reducing the current collector that does not directly contribute to power generation, the energy density is increased. Further, since the number of parts is reduced, the parts cost can be reduced. In addition, when assembling a lithium ion secondary battery, it is necessary to perform a process of bundling the current collector tabs (power extraction parts) of the same polarity together by welding or the like, but if the number of current collectors used decreases There is also an advantage that the process is facilitated. Moreover, the process of stacking cells is halved compared to the case of manufacturing a lithium ion secondary battery using the bicell 90.

  There is also a concern that the battery characteristics may be affected by reducing the number of positive electrode current collectors used. However, as is clear from the experimental results described later, it is a melancholy. For example, charge / discharge of a lithium ion secondary battery is limited by diffusion of lithium ions between the positive electrode and the negative electrode. That is, when a large current discharge is simply considered, it is desirable that the electrodes (positive electrode and negative electrode) are thin, specifically, the movement distance of lithium ions is short. If this point is applied to the present invention, the number of current collectors used is certainly reduced, but the active material layer itself is not thickened. Therefore, when the lithium ion secondary battery of the present invention is compared with the conventional product, it is considered that there is no difference in battery characteristics. This obstructs the current collector and increases the diffusion area of lithium ions, which is rather advantageous for large current discharge.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1A is a schematic cross-sectional view of a cell 20 (unit structure) that forms a main part of a lithium ion secondary battery 1 (hereinafter also simply referred to as a battery 1) of the present invention. 2 is a schematic sectional view of the battery 1. FIG. As shown in FIG. 1 (b), the battery 1 has a structure in which a cell stack 2 formed by stacking a plurality of cells 20 is sealed in a battery container 4. Since the cell 20 is actually designed in a thin flat plate shape, the cell stack 2 and the battery 1 have a plate shape. Moreover, although the shape of the cell 20 is assumed to be a square shape, various shapes such as a polygonal shape other than the rectangular shape, a circular shape, and an elliptical shape can be employed. Such a high degree of freedom in shape is one of the advantageous features of the stacked lithium ion secondary battery 1. Further, in FIG. 1, the battery 1 is configured using a plurality of cells 20, but a lithium ion secondary battery including only one cell 20 can also be manufactured.

  As shown in FIG. 1A, the cell 20 includes a plurality of positive electrodes 7 ′ and 7 formed into a sheet shape, a plurality of negative electrodes 10 and 10 that are also in the form of a sheet, and the positive electrodes 7 ′ and 7 and the negative electrode 10. , 10 and a plurality of separators 3 that are separated from each other. The battery 1 is charged / discharged by occlusion / release of lithium ions in the positive electrodes 7 ′ and 7 and the negative electrodes 10 and 10. For each cell 20, three layers of positive electrodes 7 ', 7, two layers of negative electrodes 10, 10, and four separators 3 are provided.

  The positive electrodes 7 ′ and 7 are composed of a first type positive electrode 7 ′ and a pair of second type positive electrodes 7 and 7 having different electric capacities. The difference in electric capacity means a difference in the molar amount of the active material. The first type positive electrode 7 ′ is disposed between the pair of negative electrodes 10, 10, that is, located in the center of the cell 20, and is adjusted to be thicker than the second type positive electrode 7, 7. The second type positive electrodes 7, 7 are arranged on the opposite side of the negative electrodes 10, 10 from the side where the first type positive electrode 7 ′ is located, that is, are located at both ends of the cell 20. By adjusting the thickness of the positive electrodes 7, 7 ′ and 7, a balance with the negative electrodes 10, 10 is achieved so that no surplus of active material is generated.

  The first type positive electrode 7 ′ includes a first type positive electrode current collector 5 ′ and first type positive electrode active material layers 6 ′ and 6 ′ disposed on both surfaces of the first type positive electrode current collector 5 ′. . Similarly, the second type positive electrode 7 includes a second type positive electrode current collector 5 and second type positive electrode active material layers 6 and 6 disposed on both surfaces of the second type positive electrode current collector 5. The electric capacity of the first type positive electrode active material layer 6 ′ is adjusted to approximately twice the electric capacity of the second type positive electrode active material layer 6. Since the area in the in-plane direction of the battery 1 is the same for the first type positive electrode active material layer 6 ′ and the second type positive electrode active material layer 6, the layer thickness may be considered to be about twice. The first type positive electrode current collector 5 ′ and the second type positive electrode current collector 5 are actually the same parts. The negative electrode 10 includes a negative electrode current collector 8 and negative electrode active material layers 9 and 9 disposed on both surfaces of the negative electrode current collector 8. As can be seen from FIG. 1A, the cell 20 is symmetrical in the vertical direction in the thickness direction with the first-type second positive-electrode current collector 5 'as a symmetry plane.

  The cell 20 can have an electric capacity corresponding to two of the bicell 90 of FIG. On the other hand, the first-type second positive electrode 7 'has a structure different from that obtained by superimposing two bicells 90 in that it includes only one first-type second positive-electrode current collector 5'. That is, it is possible to reduce the number of current collectors used while ensuring the same capacity. The fact that the number of the first-type second positive electrode current collector 5 ′ is only one means a substantial number in the thickness direction of the battery 1. For example, even if two sheets are arranged in the same plane, it is regarded as substantially one sheet.

  The arrangement of the positive electrodes 7 ′ and 7 and the negative electrode 10 may be interchanged. That is, a cell having a structure similar to that shown in FIG. 1A can be realized with a three-layer negative electrode and a two-layer positive electrode. However, it is preferable to arrange the positive electrode and the negative electrode as in the present embodiment (FIG. 1A) for the following reason. In general, the electronic conductivity of a positive electrode current collector made of aluminum is lower than the electronic conductivity of a negative electrode current collector made of Cu. Therefore, the structure of the three-layer positive electrode and the two-layer negative electrode as shown in FIG. 1A has a good balance of the electronic conductivity of the entire battery. Further, since the thickness of the normal positive electrode is thicker than that of the negative electrode having the same capacity, the battery having the structure as shown in FIG. 1 (a) has an advantage that the manufacturing process of the film to be the active material layer is easy. There is.

  Another reason is that in a lithium ion secondary battery, the expansion and contraction of the electrode volume accompanying charge / discharge is larger in the negative electrode than in the positive electrode. 1A has a structure in which the negative electrodes 10 and 10 are held by the positive electrodes 7 ′ and 7 from both ends. Therefore, when the expansion and contraction are repeated, the negative electrode active material layers 9 and 9 and the negative electrode collection are arranged. It is easy to maintain adhesion with the electric body 8. This is important for obtaining excellent charge / discharge cycle characteristics.

  Moreover, the positive electrode located on the outer side may have different thicknesses, that is, electric capacities, of the second type positive electrode active material layers disposed on both surfaces of the positive electrode current collector. Specifically, the cell 20K shown in FIG. The cell 20K has an electric capacity of the second type positive electrode active material layer 6L on the side adjacent to the separator 3 out of the second type positive electrode active material layers 6S and 6L arranged on both surfaces of the second type positive electrode current collector 5. The electric capacity of the other second type positive electrode active material layer 6S is adjusted to be larger. This cell 20K can be used in place of the cell 20 in FIG. In that case, the battery 1 has improved large-current discharge characteristics. The cell 20 and the cell 20K are common in that the electric capacity of the central first-type positive electrode 7 'is equal to the total capacity of the second-type positive electrodes 7, 7 on both sides or the second-type positive electrodes 7K, 7K.

Next, specific materials for each component will be described. The positive electrode active material layers 6 and 6 ′ are configured to include a positive electrode active material, a conductive additive, and a polymer substrate. The negative electrode active material layer 9 includes a negative electrode active material, a conductive additive, and a polymer substrate. The separator 3, the positive electrode active material layers 6, 6 ′ and the negative electrode active material layer 9 have a porous form, and nonaqueous electrolysis in which a lithium salt such as LiPF ₆ is dissolved in an organic solvent such as ethylene carbonate or propylene carbonate. The liquid is impregnated. That is, the battery 1 is configured as a lithium ion polymer secondary battery.

  Examples of the polymer substrate of the positive electrode active material layers 6 and 6 ′ and the negative electrode active material layer 9 include fluorine resins such as polyvinylidene fluoride (PVDF), hexafluoropropylene (HFP), and polytetrafluoroethylene (PTEF), or these A copolymer of fluororesin can be used.

As the positive electrode active material constituting the positive electrode active material layers 6 and 6 ′, a lithium composite oxide containing a transition metal or a typical metal such as LiMnO ₂ , LiCoO ₂ , or LiNiO ₂ can be used. As the negative electrode active material constituting the negative electrode active material layer 9, a graphite-based carbon material such as a mesofuse carbon material is suitable. In addition, conductive carbon such as acetylene black can be used as the conductive auxiliary agent (conductive substance).

  The positive electrode current collectors 5 'and 5 can be made of a foil made of Al or an Al alloy, or a metal mesh. The second type positive electrode current collector 5 is important to be a metal mesh so that the outermost positive electrode active material layers 6 and 6 can store and release lithium ions. The negative electrode current collector 8 can be composed of a foil made of Cu or a Cu alloy, or a metal mesh. Among these, it is preferable to use a metal mesh from the viewpoints of maintaining adhesion with the active material layer, securing the volume of the active material layer, diffusibility of lithium ions, and the like. As the metal mesh, any of expanded metal, etching metal and punching metal can be used.

The separator 3 can be composed of a microporous film of an insulating resin such as polyethylene or polypropylene. It is also possible to use a material similar to the polymer substrate contained in the positive electrode active material layers 6 'and 6 and the negative electrode active material layer 9, such as PVDF, HFP, or a copolymer thereof (SiO ₂ or the like). May be mixed). Furthermore, a microporous membrane having a multi-layer structure in which polyethylene is sandwiched between polypropylene, a microporous membrane having a resin layer such as polyethylene or polypropylene, and a resin layer made of PVDF, HFP, or a copolymer thereof, etc. It can also be used as a material for the separator 3.

  As shown in FIG. 1B, one end of strip-like lead terminals 12 and 13 is connected to the cell stack 2. The other ends of the lead terminals 12 and 13 extend outward through the fusion allowance 11 (sealing portion) of the battery container 4. Specifically, the power extraction portions 50 of the positive electrode current collectors 5 ′ and 5 are bundled together and one end of the positive lead terminal 12 is connected. The power extraction portion 80 of the negative electrode current collector 8 is bundled together, and one end of the negative electrode lead terminal 13 is connected. In this way, the cells 20 are connected in parallel. The positive lead terminal 12 may be made of, for example, aluminum or an aluminum alloy. The lead terminal 13 for the negative electrode is preferably composed of copper, copper alloy, nickel, nickel alloy, nickel-plated copper, or nickel-plated copper alloy.

  The battery container 4 is composed of a flexible sheet-like exterior material in which resin layers are provided on both surfaces of a metal foil such as aluminum. As the resin layer exposed to the outside of the battery container 4, for example, polyethylene terephthalate or biaxially stretched nylon is used, and for the inner resin layer, polyethylene, polypropylene, or the like is heat-fusible, resistant to electrolytes, and low in resistance. Materials with water vapor permeability are used. By sealing the inner resin layer and allowing the molten resin to function as an adhesive, the sealing portion 11 (fusing allowance) is formed.

Experimental example

  First, a lithium ion secondary battery (conventional product) in which the lithium ion secondary battery of the present invention (product of the present invention) and two bicells 90 shown in FIG.

(Preparation of positive electrode active material film)
Each material was weighed at the following mass ratio so that the total mass was 100 g, to prepare a positive electrode mixed powder. To this mixed powder for positive electrode, 100 g of acetone was added and kneaded for 30 minutes to obtain a slurry for positive electrode. This positive electrode slurry was applied onto a PET film and dried to obtain a positive electrode active material film. The thickness of the positive electrode active material film was 120 μm and 60 μm for the present product, and 60 μm for the conventional product.
LiCoO ₂ / acetylene black / binder (PVDF + HFP) / plasticizer (dibutyl phthalate) = 70/5/8/17

(Preparation of negative electrode active material film)
Each material was weighed at the following mass ratio so that the total mass was 100 g to prepare a negative electrode mixed powder. To this mixed powder for negative electrode, 100 g of acetone was added and kneaded for 30 minutes to obtain a slurry for negative electrode. This negative electrode slurry was applied onto a PET film and dried to obtain a negative electrode active material film having a thickness of 70 μm, which is common to the product of the present invention and the conventional product.
Mesocarbon microbead / acetylene black / binder (PVDF + HFP) / plasticizer (dibutyl phthalate) = 70/2/9/19

(Production of electrodes)
An aluminum punching metal having a thickness of 30 μm and an aperture ratio of 50% was prepared as the positive electrode current collectors 5 ′ and 5. A copper punching metal having a thickness of 30 μm and an aperture ratio of 50% was prepared as the negative electrode current collector 8. An active material film prepared in advance was placed on these current collectors, and thermal lamination was performed with a calender roll device, so that an electrode in the previous stage to be impregnated with the electrolyte was produced. Electrodes were produced for the products of the present invention and the conventional products.

(Battery assembly)
Next, a polyethylene microporous membrane was prepared as a separator, and a positive electrode, a negative electrode, and a separator were heat-laminated to obtain a cell having a structure shown in FIG. This cell is immersed in the reagent primary methyl alcohol for 1 hour to extract the plasticizer, and then placed in a container made of aluminum laminate packaging material (thickness 110 μm). The liquid was impregnated in a dry box with a dew point of −55 ° C. As the electrolytic solution, a solution obtained by adding LiPF ₆ at a concentration of 1 mol / liter to a solvent in which ethyl carbonate and ethyl methyl carbonate were mixed at a volume ratio of 1: 1 was used. And the container was temporarily sealed in the dry box, and the lithium ion secondary battery of this invention with a nominal capacity of 38 mAh was obtained. In addition, the lithium ion secondary battery is subjected to chemical conversion treatment in the atmosphere and then subjected to aging for another week, and the gas generated in the container is vented with a vacuum pump, and the inside of the container is decompressed, and then the final sealing To make a finished product. A battery in which two bicells 90 of FIG. Table 1 compares the dimensions and energy density of the battery according to the present invention (the product of the present invention) and the conventional battery (the conventional product).

  As shown in Table 1, when the lithium ion secondary battery having the same nominal capacity is manufactured using a conventional bicelle and when the structure of the present invention is adopted, the product of the present invention has a smaller thickness. Become. Of course, the product of the present invention also has a higher energy density.

(Load characteristic test)
The discharge load characteristics of the product of the present invention and the conventional product shown in Table 1 were examined. Specifically, after charging at a constant current and a constant voltage of 4.2 V and 1 CmA, and discharging 1 C and 2 C at a constant voltage of 3 V, the discharge load characteristics at the time of 0.2 C discharge Was taken as 100%. The test was performed at a constant temperature of 25 ° C. The test results are shown in FIG. FIG. 2A is a graph showing the result of the product of the present invention, and FIG. 2B is a graph showing the result of the conventional product. The discharge efficiency at the 3V cutoff is collectively shown in FIG. As can be seen from the results shown in FIG. 2, there was no difference in discharge load characteristics between the product of the present invention and the conventional product.

  Next, the charge / discharge cycle characteristics of the product of the present invention and the conventional product were examined. Specifically, after charging with a constant current and a constant voltage of 4.2 V and 1 CmA, a discharge rate when a 1 C discharge (3 V cut-off) is repeated with a constant voltage of 3 V is set to 100 for the first discharge capacity. Investigated as%. The test was performed at a constant temperature of 25 ° C. The test results are shown in FIG. As can be seen from the results shown in FIG. 3, there was no difference in charge / discharge cycle characteristics between the product of the present invention and the conventional product.

  In the experimental examples, small-capacity products for small electronic devices such as mobile devices, computers, IC cards, etc. have been exemplified. Of course, this structure can be suitably employed.

  As described above, according to the present invention, it is possible to reduce the number of current collectors used without sacrificing electric capacity, thereby reducing the thickness of the battery. Further, as shown in FIG. 1B, when the battery 1 is assembled, the process of bundling the power extraction portions 50 of the positive electrode current collectors 5 ′ and 5 is facilitated. By reducing the number of current collectors used, parts costs can be reduced.

The cross-sectional schematic diagram of the cell structure of the lithium ion secondary battery concerning this invention. The graph of the load characteristic of this invention product and a conventional product. The graph of the charge / discharge cycle characteristics of the present product and the conventional product. The figure explaining the reason why a cell structure cannot be simply stacked. The cross-sectional schematic diagram of the cell structure of the conventional lithium ion secondary battery.

Claims (6)

  The sheet-like first electrode (10) can be charged and discharged by inserting and extracting lithium ions between the first electrode (10) and the second electrode (7 ', 7) having different polarities. And a lithium ion secondary battery (1) having a form in which the second electrodes (7 ', 7) are sequentially stacked, wherein the second electrodes (7', 7) are interposed via a separator (3). A first-type second electrode (7 ′) disposed between a pair of the first electrodes (10, 10) and the first-type second electrode (7 ′) with the first electrode (10) interposed therebetween ) And a pair of second-type second electrodes (7, 7) arranged on the opposite side, and the only current collector (5 ') of the first-type second electrode (7') is provided. A unit structure (20) that is symmetrical in the vertical direction in the thickness direction is provided as a symmetry plane, and the unit structure (20) is constituted by one or a repetition Lithium ion secondary battery, characterized by being (1). The sheet-like first electrode (10) can be charged and discharged by inserting and extracting lithium ions between the first electrode (10) and the second electrode (7 ', 7) having different polarities. And a lithium ion secondary battery (1) having a form in which the second electrodes (7 ', 7) are sequentially stacked,
The second electrode (7 ', 7) is composed of a first type second electrode (7') and a second type second electrode (7) having different electric capacities,
First type second electrode current collector (5 ′) and first type second electrode active material layer (6 ′, 6 ′) disposed on both sides of first type second electrode current collector (5 ′) And the first type second electrode (7 ′) including a pair of first electrodes (10, 10),
Second type second electrode current collector (5) and second type second electrode active material layer (6, 6) (6S, 6) disposed on both sides of said second type second electrode current collector (5) 6L) is disposed on the opposite side of the first second electrode (7 ′) across the first electrode (10), the second second electrode (7) (7K) including
The first second electrode (7 ') and the first electrode (10), and the second second electrode (7) and the first electrode (10) are separated by a separator (3). ,
The current collector (5 ′) constituting the first-type second electrode (7 ′) has a symmetrical structure and a unit structure (20) (20K) that is symmetrical vertically in the thickness direction,
A lithium ion secondary battery (1) comprising one or a repetition of the unit structure (20) (20K).   The capacitance of the first-type second electrode active material layer (6 ′, 6 ′) is substantially equal to the capacitance of the second-type second electrode active material layer (6, 6) (6S, 6L). The lithium ion secondary battery (1) according to claim 2, wherein the lithium ion secondary battery is adjusted to be doubled.   The lithium ion secondary battery (1) according to any one of claims 1 to 3, wherein the first electrode (10) is a negative electrode and the second electrode (7 ', 7) is a positive electrode.   The lithium ion secondary battery (1) according to any one of claims 2 to 4, wherein the second type second electrode current collector (5) is formed of a metal mesh.   Of the second type second electrode active material layers (6S, 6L) disposed on both surfaces of the second type second electrode current collector (5), the second side on the side adjacent to the separator (3). The lithium ion secondary according to claim 5, wherein the electric capacity of the second electrode active material layer (6L) is adjusted to be larger than the electric capacity of the other second type second electrode active material layer (6S). Battery (1).

Images