JP6984463B2 - Exterior for secondary battery and secondary battery - Google Patents

Description

The present invention relates to an exterior body for a secondary battery and a secondary battery.

Regarding the negative electrode of a non-aqueous electrolytic solution secondary battery represented by a lithium ion secondary battery, an alloy-based negative electrode such as silicon and a lithium metal negative electrode have a larger weight energy density than graphite originally used as a negative electrode active material. It is known to show that, and it is attracting attention as one of the attractive material groups.

However, since these material groups have a large volume expansion coefficient with charge and discharge, their cycle characteristics are worse than those of graphite. Therefore, as a means for improving the cycle characteristics, a method of fixing the electrode, a method of pressurizing the cell, and the like are known.

For example, Patent Document 1 discloses that by adopting a structure in which the thickness in the direction in which the electrodes are laminated is kept constant in the laminated cell, the shape stability of the negative electrode is enhanced and the cycle characteristics are extended. However, it is difficult to increase the energy density of the battery of Patent Document 1 because the structure becomes complicated especially when the number of layers is increased.

Further, in Patent Document 2, when an active material containing silicon is used, the cycle characteristics are improved by sandwiching a cell between flat plates sandwiching a spacer set in consideration of the thickness of the battery. Is disclosed.

Japanese Unexamined Patent Publication No. 5-290886 Japanese Unexamined Patent Publication No. 2012-256542

However, although the methods described in Patent Document 1 and Patent Document 2 show improvement in cycle characteristics, it cannot be said that the improvement is sufficient. The causes include deterioration of charge / discharge characteristics due to bending of the electrode laminate (power generation element) due to electrode expansion, liquid leakage due to damage to the exterior body, and inflow of atmospheric components into the battery. Further, in order to prevent the power generation element from being damaged when the electrode expands and contracts, a component for pressurizing the power generation element in the stacking direction is required. Therefore, the above-mentioned conventional method is sufficient from the viewpoint of weight energy density. Was hard to say.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an exterior body for a secondary battery having excellent cycle characteristics and a secondary battery using the same.

As a result of diligent studies, the present inventors have found that in order to improve the cycle characteristics, it is effective to make the pressure applied in the plane of the power generation element uniform, and the pressure may be about atmospheric pressure. .. Then, they have found that by covering the power generation element with an exterior body having a predetermined outer peripheral portion, a pressurization of about atmospheric pressure can be uniformly applied to the power generation element, and the cycle characteristics of the secondary battery are improved. That is, the present invention provides the following means for solving the above problems.

(1) The exterior body for a secondary battery according to the first aspect has a pair of facing surfaces and an outer peripheral portion connecting the pair of facing surfaces, and the outer peripheral portion has a crease structure and the outer peripheral portion. The portions are variable in the direction of varying the distance between the pair of facing surfaces.

(2) In the exterior body for a secondary battery according to the above aspect, the fold structure may have a hexagonal shape connecting the mountain folds of the folds.

(3) The secondary battery of the second aspect includes a power generation element having a positive electrode, a negative electrode, a separator for separating the positive electrode and the negative electrode, an electrolytic solution impregnated in the power generation element, and the power generation. A secondary battery exterior body according to the above aspect for covering the element is provided.

(4) In the secondary battery according to the above aspect, when the width when the outer peripheral portion of the secondary battery outer body is most extended is W and the thickness when the power generation element is fully charged is T, W ≧ When T is satisfied and the width when the outer peripheral portion of the secondary battery outer body is most contracted is w, and the thickness of the power generation element at full discharge is t, w <t may be satisfied. ..

(5) In the secondary battery according to the above aspect, the negative electrode is composed of a negative electrode mixture layer and a negative electrode current collector foil, and the negative electrode mixture layer may contain at least one element of silicon, tin, germanium, and lithium. good.

The secondary battery exterior body according to the above aspect can improve the cycle characteristics of the secondary battery using the outer body.

It is a schematic diagram of the secondary battery which concerns on this embodiment. It is sectional drawing of the secondary battery which concerns on this embodiment. It is a schematic diagram of the exterior body which concerns on an example of this invention. It is a schematic diagram of the exterior body which concerns on other example of this invention. It is a schematic diagram of the exterior body which concerns on still another example of this invention.

Hereinafter, the present embodiment will be described in detail with reference to the drawings as appropriate. The drawings used in the following description may be enlarged for convenience in order to make the features of the present invention easy to understand, and the dimensional ratios of each component may differ from the actual ones. be. The materials, dimensions, and the like exemplified in the following description are examples, and the present invention is not limited thereto, and can be appropriately modified and carried out within the range in which the effect is exhibited.

[Secondary battery]
FIG. 1 is a schematic diagram of a non-aqueous electrolytic solution secondary battery according to the present embodiment. The secondary battery 100 shown in FIG. 1 includes a power generation element 10, two terminals 20 (positive electrode terminal 21 and negative electrode terminal 22), and an exterior body 30. The power generation element 10 is housed in a storage space K provided in the exterior body 30. FIG. 1 illustrates a state immediately before the power generation element 10 is housed in the exterior body 30 for easy understanding.

(Power generation element)
FIG. 2 is a schematic cross-sectional view of the secondary battery according to the present embodiment. The power generation element 10 shown in FIG. 2 has a positive electrode 1, a negative electrode 2, and a separator 3. The power generation element 10 shown in FIG. 2 is a laminated body in which a positive electrode 1 and a negative electrode 2 are arranged so as to face each other with the separator 3 interposed therebetween. The power generation element 10 may be a wound body in which a laminated body in which a positive electrode 1 and a negative electrode 2 are arranged so as to face each other with the separator 3 interposed therebetween is wound.

The positive electrode 1 has a plate-shaped (film-shaped) positive electrode current collector 1A and a positive electrode active material layer 1B. The positive electrode active material layer 1B is formed on at least one surface of the positive electrode current collector 1A. The negative electrode 2 has a plate-shaped (film-shaped) negative electrode current collector 2A and a negative electrode active material layer 2B. The negative electrode active material layer 2B is formed on at least one surface of the negative electrode current collector 2A. The positive electrode active material layer 1B and the negative electrode active material layer 2B are impregnated with an electrolytic solution. Ions are exchanged between the positive electrode 1 and the negative electrode 2 via this electrolytic solution.

The positive electrode current collector 1A may be a conductive plate material, and for example, a thin metal plate of aluminum, copper, or nickel foil can be used.

The positive electrode active material used for the positive electrode active material layer 1B can reversibly proceed with occlusion and release of ions, desorption and insertion (intercalation) of ions, or doping and dedoping of ions and counter anions. Electrode active material can be used. As the ion, for example, lithium ion, sodium ion, magnesium ion and the like can be used, and it is particularly preferable to use lithium ion.

For example, in the case of a lithium ion secondary battery, lithium cobalt oxide (LiCoO _2), lithium nickelate (LiNiO _2), lithium manganate (LiMnO _2), lithium manganese spinel (LiMn ₂ O _4), and the general formula: LiNi _{x Co y Mn z M a O 2} (x + y + z + a = 1,0 ≦ x <1,0 ≦ y <1,0 ≦ z <1,0 ≦ a <1, M is Al, Mg, Nb, Ti, Cu, Zn , One or more elements selected from Cr), lithium vanadium compound (LiV ₂ O ₅ ), olivine type LiMPO ₄ (where M is Co, Ni, Mn, Fe, Mg, nb, shows Ti, Al, one or more elements or VO selected from Zr), lithium titanate _{(Li 4 Ti 5 O 12)} , LiNi x Co y Al z O 2 (0.9 <x + y + z <1. Composite metal oxides such as 1), polyacetylene, polyaniline, polypyrrole, polythiophene, polyacene and the like can be used as the positive electrode active material.

Further, the positive electrode active material layer 1B may have a conductive material. Examples of the conductive material include carbon powder such as carbon black, carbon nanotube, carbon material, metal fine powder such as copper, nickel, stainless steel and iron, a mixture of carbon material and metal fine powder, and conductive oxide such as ITO. Be done. When sufficient conductivity can be ensured only by the positive electrode active material, the positive electrode active material layer 1B may not contain the conductive material.

Further, the positive electrode active material layer 1B contains a binder. As the binder, a known binder can be used. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoro Fluororesin such as ethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), polyvinyl fluoride (PVF) and the like can be mentioned.

In addition to the above, as binders, for example, vinylidene fluoride-hexafluoropropylene fluororubber (VDF-HFP fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene fluororubber (VDF-HFP-). TFE-based fluororubber), vinylidene fluoride-pentafluoropropylene-based fluororubber (VDF-PFP-based fluororubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-PFP-TFE-based fluororubber), Vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene fluororubber (VDF-PFMVE-TFE fluororubber), vinylidene fluoride-chlorotrifluoroethylene fluororubber (VDF-CTFE fluororubber), etc. A fluororubber may be used.

The negative electrode active material used in the negative electrode active material layer 2B may be any compound that can occlude and release ions, and a known negative electrode active material used in a non-aqueous electrolytic solution secondary battery can be used. Examples of the negative electrode active material include alkali or alkaline earth metals such as metallic lithium, graphite capable of storing and releasing ions (natural graphite, artificial graphite), carbon nanotubes, carbon refractory carbon, carbon easily graphitized, and low temperature. Mainly composed of carbon materials such as calcined carbon, metals that can be combined with metals such as lithium such as silicon, tin, germanium, and aluminum, and oxides such as silicon oxide SiO _x (0 <x <2) and tin dioxide. Examples thereof include particles containing an amorphous compound, lithium titanate (Li ₄ Ti ₅ O ₁₂ ), and the like.

Of the above substances, particularly preferably in the present embodiment, the negative electrode active material layer 2B has a large volume expansion rate during charging and discharging of a metal or alloy containing elements such as silicon, tin, and germanium, and a weight of metallic lithium. A substance with a high energy density is used.

As the negative electrode current collector 2A, the conductive material, and the binder, the same ones as those of the positive electrode 1 can be used. As the binder used for the negative electrode, for example, cellulose, styrene / butadiene rubber, ethylene / propylene rubber, polyimide resin, polyamide-imide resin, acrylic resin and the like may be used in addition to those listed for the positive electrode.

The separator 3 may be formed of an electrically insulating porous structure, for example, a monolayer of a film made of a polyolefin such as polyethylene or polypropylene, a laminate, a stretched film of a mixture of the above resins, or cellulose or polyester. , Polyacrylonitrile, polyamide, polyethylene and a fiber non-woven fabric made of at least one constituent material selected from the group consisting of polypropylene.

As the electrolytic solution, an electrolytic solution (electrolyte aqueous solution, non-aqueous electrolytic solution) containing a salt or the like can be used. The electrolyte aqueous solution has a low electrochemical decomposition voltage and a low withstand voltage during charging. Therefore, it is preferable to use a non-aqueous electrolytic solution. As the non-aqueous electrolytic solution, a non-aqueous solvent such as an organic solvent is used as the solvent.

The non-aqueous electrolyte solution contains a salt (electrolyte) and a non-aqueous solvent. The non-aqueous solvent may contain a cyclic carbonate and a chain carbonate. The ratio of cyclic carbonate to chain carbonate in the non-aqueous solvent is preferably 1: 9 to 1: 1 in volume.

As the cyclic carbonate, one that can solvate the electrolyte is used. For example, ethylene carbonate, propylene carbonate, butylene carbonate and the like are used as the cyclic carbonate.

The chain carbonate reduces the viscosity of the cyclic carbonate. For example, diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate and the like are used as the chain carbonate. In addition, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane and the like may be mixed and used.

An ionic liquid may be used as the non-aqueous solvent. P13-FSA (N-methyl Npropylpyrrolidinium bis (fluorosulfonyl) imide), PP13-TFSA (N-methyl N-propylpiperidinium bis (trifluoromethanesulfonyl) imide), EMI-BF4 (1 ethyl 3 methylimidazolium tetra) Fluoroboronate) and the like.

As the electrolyte, a metal salt can be used. For example, LiPF ₆ , LiClO ₄ , LiBF ₄ , LiCF ₃ SO ₃ , LiCF ₃ CF ₂ SO ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (CF ₃ CF ₂ SO ₂ ). ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiN (CF ₃ CF ₂ CO) ₂ , LiBOB, LiFSA (lithium bis (fluorosulfonyl) imide) and LiTFSA (lithium (trifluoromethanesulfonyl) imide) ) Etc. can be used. It should be noted that one of these lithium salts may be used alone, or two or more thereof may be used in combination. In particular, from the viewpoint of the degree of ionization, it is preferable to contain _{LiPF 6 as the electrolyte.}

When dissolving LiPF ₆ in a non-aqueous solvent, it is preferable to adjust the concentration of the electrolyte in the non-aqueous electrolyte solution to 0.5 to 2.0 mol / L. When the concentration of the electrolyte is 0.5 mol / L or more, the lithium ion concentration of the non-aqueous electrolyte solution can be sufficiently secured, and a sufficient capacity can be easily obtained at the time of charging / discharging. Further, by suppressing the concentration of the electrolyte to 2.0 mol / L or less, it is possible to suppress the increase in the viscosity of the non-aqueous electrolyte solution, sufficiently secure the mobility of lithium ions, and obtain a sufficient capacity during charging and discharging. It will be easier.

Even when LiPF ₆ is mixed with other electrolytes, it is preferable to adjust the lithium ion concentration in the non-aqueous electrolyte solution to 0.5 to 2.0 mol / L, and the lithium ion concentration from _{LiPF 6 is 50 mol% thereof.} It is more preferable that the above is contained.

(Terminal)
There are two terminals 20, one is a positive electrode terminal 21 and the other is a negative electrode terminal 22. One end (inner end) of the terminal 20 is connected to the power generation element 10, and the other end (outer end) extends to the outside of the exterior body 30. The two terminals 20 may extend in the same direction or may extend in different directions. The positive electrode terminal 21 is connected to the positive electrode current collector 1A, and the negative electrode terminal 22 is connected to the negative electrode current collector 2A. The connection method is not particularly limited, and welding, screwing, or the like can be used. A conductive material such as aluminum or nickel can be used for the terminal 20.

(Exterior body)
The exterior body 30 seals the power generation element 10 and the electrolytic solution inside. There are various structures of the secondary battery, but in the present embodiment, a film is used for forming the exterior body 30. The film for forming the exterior body 30 is a metal film (aluminum, stainless steel, nickel steel, etc.), a plastic film made of an organic material (thermoplastic film), an organic material (organic resin, fiber, etc.) and an inorganic material (ceramic). A single-layer film selected from a hybrid material film containing (etc.), a carbon-containing film (carbon film, graphite film, etc.) or a laminated film composed of a plurality of these is used. For example, a metal laminated film in which both sides of the metal film are coated with a polymer film can be used. As the metal film, for example, an aluminum foil can be used, and as the polymer film, a film such as polypropylene can be used. Further, the polymer films on both sides may be different. For example, as the material of the outer polymer film, a polymer having a high melting point, for example, polyethylene terephthalate (PET), polyamide (particularly nylon) or the like is preferable, and the inner polymer film is preferable. As the material of the polymer film, polyethylene (PE), polypropylene (PP) and the like are preferable. Above all, from the viewpoint of durability, heat dissipation, gas permeability and the like, it is preferable to use an aluminum laminated film in which layers made of nylon and polypropylene are added to each surface of the aluminum metal.

In the exterior body 30 shown in FIG. 1, the first surface 30A and the second surface 30B are folded to form an accommodation space K. The peripheral portions of the first surface 30A and the second surface 30B are sealed and sealed under reduced pressure (for example, under vacuum). As shown in FIG. 1, the exterior body 30 is not limited to the one in which the first surface 30A and the second surface 30B are folded to form the accommodation space K, and may be a bonded body of two films. The recess forming the accommodating space K may be provided in each of the two films, or may be provided in only one of the films.

As shown in FIG. 2, the exterior body 30 corresponds to a side wall connecting the first surface 30A (bottom surface in FIG. 2), the second surface 30B (upper surface in FIG. 2), and the first surface 30A and the second surface 30B. It has an outer peripheral portion 32 to form a storage space K. The accommodation space K has, for example, a polygonal tubular shape such as a quadrangle or a cylindrical shape.

The outer peripheral portion 32 has a crease structure. The outer peripheral portion 32 can be expanded and contracted by the crease structure, and the outer peripheral portion 32 changes the distance between the facing first surface 30A and the second surface 30B of the exterior body 30 (that is, the height of the accommodation space K). It is variable in the direction of making it. In the present application, the dimension of the outer peripheral portion 32 corresponding to the height of the accommodation space K is referred to as the "width" of the outer peripheral portion 32. Since the distance between the pair of facing surfaces is variable due to the crease structure, the pressure of about atmospheric pressure is uniformly applied to the surface of the power generation element 10, while the exterior body 30 and the power generation element contained therein are uniformly applied. It is possible to prevent an excessive load from being applied to 10.

In the present embodiment, it is preferable that the elasticity of the outer peripheral portion 32 is designed as follows so that it can appropriately follow the expansion / contraction of the power generation element 10 due to charging / discharging. For example, in order to prevent an excessive load from being applied to the exterior body 30 and the power generation element 10 even when the power generation element 10 is fully charged and is most expanded, the width of the outer peripheral portion 32 when the outer peripheral portion 32 is most extended is set. When W and the thickness of the power generation element 10 when fully charged are T, it is preferable to satisfy the condition of W ≧ T. On the other hand, the outer peripheral portion is contracted most so that a uniform pressure can be applied to the plane of the power generation element at atmospheric pressure even in the initial stage of charging from the state where the power generation element 10 is fully discharged and most contracted. When the width of the time is w and the thickness of the power generation element 10 at full discharge is t, it is preferable to satisfy the condition of w <t. Here, "the width of the outer peripheral portion when it is most stretched" and "the width when the outer peripheral portion is most contracted" are defined as "stretching and contracting when the power generation element 10 is not provided inside". It means the maximum width that can be generated and the minimum width that can be contracted.

As the crease structure of the outer peripheral portion 32, any structure that enables expansion and contraction of the outer peripheral portion can be used, and examples thereof include a so-called bellows structure (also referred to as a bellows structure) and a twist fold. Some specific examples will be described below.

3A and 3B are schematic views of an exterior body 30 having an example of a typical bellows structure, FIG. 3A shows a perspective view of the exterior body 30, and FIG. 3B is an outer peripheral portion 32 of the exterior body 30. The development schematic diagram of is shown. As shown in the developed view of FIG. 3B, in such a bellows structure, the shape connecting the mountain folds of the folds is a shape in which hexagons are spread. Seen on the paper of FIG. 3 (b), each hexagon has three sets of opposite sides parallel to each other and equal in length to each other. Of these sides, the opposite sides of the lower and upper sides are long, and the other four sides are short. The short sides have the same length. The line of the valley fold is parallel to the lower and upper sides of each hexagon of the mountain fold on the paper surface of FIG. 3 (b), and the leftmost vertex (two sides on the left side) so as to divide the hexagon into two equal parts. (Intersection of diagonal lines) and the rightmost vertex (intersection of diagonal lines on the right side). In such a bellows structure, when fully extended, the creases are extended and the outer peripheral surface becomes flat. In such a bellows structure, the peripheral length of the exterior body 30 does not vary greatly depending on the position, and the yield can be increased at the time of manufacturing the exterior body. Further, since the bellows structure has less extra space, it is possible to avoid the battery from becoming large in size, and the electrolytic solution can be efficiently distributed to the power generation element 10.

FIG. 4 shows a schematic view of the exterior body 40 having another bellows structure. The exterior body 40 shown in FIG. 4 has an outer peripheral portion corresponding to a side wall connecting the first surface 40A (bottom surface in FIG. 4), the second surface 40B (upper surface in FIG. 4), and the first surface 40A and the second surface 40B. 42 and. The bellows structure of the exterior body 40 of FIG. 4 is different from the bellows structure of the exterior body 30 shown in FIG. There is.

FIG. 5 shows a schematic view of an exterior body 50 having an example of a twisted structure. FIG. 5A shows a perspective view of the exterior body 50, and FIG. 5B shows a development schematic view of the outer peripheral portion 52 of the exterior body 50. The exterior body 50 shown in FIG. 5 has an outer peripheral portion corresponding to a side wall connecting the first surface 50A (bottom surface in FIG. 5), the second surface 50B (upper surface in FIG. 5), and the first surface 50A and the second surface 50B. It has 52 and. The torsional structure, along with the bellows structure, is known as a foldable tubular structure. As shown in the developed schematic diagram of FIG. 5 (b), the torsional structure of this example has a shape in which pieces of triangles are combined, and at each node, four mountain fold lines and two mountain fold lines. The valley fold lines meet. The shape of connecting the lines of the mountain fold is a shape in which parallelograms are laid out.

[Manufacturing method of lithium ion secondary battery]
The method for manufacturing the lithium ion secondary battery according to the present embodiment can be manufactured by, for example, the following known method except for the molding step of the exterior body.

First, the positive electrode 1 and the negative electrode 2 are manufactured. The positive electrode 1 and the negative electrode 2 differ only in the material used as the active material, and can be manufactured by the same manufacturing method.

A paint is prepared by mixing a positive electrode active material, a binder and a solvent. If necessary, a conductive material may be further added. As the solvent, for example, water, N-methyl-2-pyrrolidone, N, N-dimethylformamide and the like can be used. The composition ratio of the positive electrode active material, the conductive material, and the binder is preferably 80 wt% to 90 wt%: 0.1 wt% to 10 wt%: 0.1 wt% to 10 wt% in terms of mass ratio. These mass ratios are adjusted to be 100 wt% as a whole.

The method of mixing these components constituting the paint is not particularly limited, and the mixing order is also not particularly limited. The above paint is applied to the positive electrode current collector 1A. The coating method is not particularly limited, and a method usually adopted when manufacturing an electrode can be used. For example, the slit die coat method and the doctor blade method can be mentioned. Similarly, for the negative electrode, the paint is applied on the negative electrode current collector 2A.

Subsequently, the solvent in the paint applied on the positive electrode current collector 1A and the negative electrode current collector 2A is removed. The removal method is not particularly limited. For example, the positive electrode current collector 1A and the negative electrode current collector 2A coated with the paint are dried in an atmosphere of 80 ° C. to 150 ° C. Then, the positive electrode 1 and the negative electrode 2 are completed.

When the power generation element 10 is a laminated body, the positive electrode 1, the negative electrode 2 and the separator 3 are laminated. When the power generation element 10 is a wound body, the positive electrode 1, the negative electrode 2, and the separator 3 are wound around one end side as an axis. In either case, the separator 3 is arranged between the positive electrode 1 and the negative electrode 2.

The exterior body 30 is formed. As described above, there are various structures of the secondary battery, but in the present embodiment, a film is used for forming the exterior body 30. For example, an aluminum laminated film in which layers made of nylon and polypropylene are added to each surface of an aluminum metal film is used. A recess is formed in the film for the exterior body by processing, and a crease structure is provided by further pressing the recess to form a portion to be an outer peripheral portion of the exterior body.

The power generation element 10 is enclosed in the exterior body 30. The non-aqueous electrolytic solution may be injected into the exterior body 30, or the power generation element 10 may be impregnated into the non-aqueous electrolytic solution.

Finally, the peripheral portion of the exterior body 30 is sealed under reduced pressure (for example, under vacuum).

As described above, according to the lithium ion secondary battery according to the present embodiment, the accommodation space K of the exterior body is in a depressurized state, and the exterior body 30 expands and contracts according to the volume change of the power generation element 10 due to charging and discharging. By doing so, a uniform pressure can be applied in the plane of the power generation element 10, and the cycle characteristics are improved. It should be noted that the same can be made when using the exterior bodies 40 and 50 shown in FIG. 4 or 5 instead of the exterior body 30 shown in FIG.

Although the present embodiment has been described in detail with reference to the drawings, the configurations and combinations thereof in each embodiment are examples, and the configurations are added, omitted, or replaced within the range not deviating from the gist of the present invention. , And other changes are possible.

"Example 1"
First, a positive electrode active material layer was applied to both sides of a positive electrode current collector made of aluminum foil to prepare a positive electrode. The positive electrode active material layer has 94 parts by mass of LiCoO ₂ (active material), 2 parts by mass of carbon black (conductive material), and 4 parts by mass of polyvinylidene fluoride (PVDF, binder).

Similarly, a negative electrode active material layer was applied to both sides of a negative electrode current collector made of copper foil to prepare a positive electrode. The negative electrode active material layer consists of 95 parts by mass of silicon (active material), 1 part by mass of carbon black (conductive material), 1.5 parts by mass of styrene butadiene rubber (SBR, binder), and 2.5 parts by mass. Carboxymethyl cellulose sodium (CMC, binder) and.

In addition, polyethylene was prepared as a separator. Then, a positive electrode, a negative electrode, and a separator were laminated to prepare a power generation element (a laminated body of five layers).

The produced power generation element was housed in the exterior, and 6 g of a non-aqueous electrolyte solution was injected to prepare a lithium ion secondary battery (non-aqueous electrolyte secondary battery). The design charge capacity of the lithium-ion secondary battery was 4.22 mAh. The non-aqueous electrolyte solution is 1.0 M (mol / L) as a lithium salt in a solvent in which ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) are mixed in a volume ratio of 35:35:30. The _{one to which LiPF 6} was added was used.

An aluminum laminated film was used as the exterior body. A recess was formed in the aluminum laminated film by processing, and the recess was further pressed to provide a crease structure. As the crease structure, a bellows structure (see FIG. 3) in which the shape connecting the lines of the mountain folds of the folds is hexagonal is adopted. Regarding the width of the outer peripheral portion and the thickness of the power generation element, the width when the outer peripheral portion is most extended is W, the width when the outer peripheral portion is most contracted is w, the thickness when the power generation element is fully charged is T, and power generation is performed. The crease structure is provided so as to satisfy the condition of W> T> t> w, where t is the thickness of the element when it is fully discharged. The creases are 5 steps.

The obtained lithium ion secondary battery was operated at a charge voltage of 4.3 V and a discharge voltage of 3 V at a charge / discharge rate of 0.1 C, and a charge / discharge test of 50 cycles was performed. The initial charge capacity was as designed. In addition, after 50 cycles, the battery was inspected and no deformation or damage was observed.

"Example 2"
In Example 2, as the crease structure of the outer peripheral portion, a bellows structure (see FIG. 4) in which mountain folds and valley folds that go around are alternately provided in parallel was used. As for other conditions, a battery was prepared in the same manner as in Example 1 and a charge / discharge test of 50 cycles was performed. The initial charge capacity was as designed, and no deformation or damage was observed in the battery even after 50 cycles.

"Example 3"
In Example 3, a twist-folded structure (see FIG. 5A) was used as the crease structure of the outer peripheral portion. As for other conditions, a battery was prepared in the same manner as in Example 1 and a charge / discharge test of 50 cycles was performed. The initial charge capacity was as designed, and no deformation or damage was observed in the battery even after 50 cycles.

"Example 4"
In Example 4, the conditions of the width of the outer peripheral portion and the thickness of the power generation element were T>W>t> w. As for other conditions, a battery was prepared in the same manner as in Example 1 and a charge / discharge test of 50 cycles was performed. Since T> W, the initial charge capacity was smaller than the design capacity. Further, although no damage was found in the exterior body, when the power generation element was taken out from the exterior body and examined, it was found that the thickness of the power generation element was uneven. It is considered that this is because a large load is applied to the edge portion of the electrode when the power generation element is expanded.

"Example 5"
In Example 5, the conditions of the width of the outer peripheral portion and the thickness of the power generation element were set to W>T>w> t. As for other conditions, a battery was prepared in the same manner as in Example 1 and a charge / discharge test of 50 cycles was performed. Since w> t, the initial charge capacity was smaller than the design capacity, but no deformation or damage was observed in the battery even after 50 cycles.

"Example 6"
In Example 6, tin was used as the negative electrode active material instead of silicon. As for other conditions, a battery was prepared in the same manner as in Example 1 and a charge / discharge test of 50 cycles was performed. The initial charge capacity was as designed, and no deformation or damage was observed in the battery even after 50 cycles.

"Example 7"
In Example 7, germanium was used as the negative electrode active material instead of silicon. Other conditions were the same as in Example 1, and a 50-cycle charge / discharge test was performed. The initial charge capacity was as designed, and no deformation or damage was observed in the battery even after 50 cycles.

"Example 8"
In Example 8, silicon oxide was used as the negative electrode active material. Other conditions were the same as in Example 1, and a 50-cycle charge / discharge test was performed. The initial charge capacity was as designed, and no deformation or damage was observed in the battery even after 50 cycles.

"Example 9"
In Example 8, metallic lithium was used instead of silicon as the negative electrode active material. Other conditions were the same as in Example 1, and a 50-cycle charge / discharge test was performed. The initial charge capacity was as designed, and no deformation or damage was observed in the battery even after 50 cycles.

"Comparative Example 1"
In Comparative Example 1, as the shape of the exterior body, a conventional structure having no crease structure on the outer peripheral portion of the exterior body was adopted. Specifically, an aluminum laminated film was used as the exterior body. The aluminum laminated film was processed to form only recesses. The depth of the recess was set to the thickness when the power generation element was fully charged, that is, when it was most expanded. Other conditions were the same as in Example 1, and a 50-cycle charge / discharge test was attempted. However, a short circuit occurred during the test, and the charge / discharge test could not be continued. When the power generation element was taken out from the exterior body, the stacking of the exterior body was misaligned, which is considered to have caused a short circuit. It is considered that the cause is that the exterior body cannot continue to apply pressure in the plane of the power generation element due to the shrinkage of the negative electrode during discharge.

"Comparative Example 2"
In Comparative Example 2, the depth of the concave portion of the exterior body was set to the thickness when the power generation element was fully discharged, that is, when it was most contracted. Other conditions were the same as in Comparative Example 1, and a 50-cycle charge / discharge test was performed. Since the depth of the recess of the exterior body was set to the thickness of the power generation element at the time of contraction, the initial charge capacity was smaller than the design capacity as in the fourth embodiment. In addition, no damage was observed on the exterior body after the 50-cycle charge / discharge test. However, when the power generation element was taken out from the exterior body, the power generation element was found to be curved.

"Comparative Example 3"
In Comparative Example 3, tin was used as the negative electrode active material instead of silicon. As for other conditions, a battery was prepared in the same manner as in Comparative Example 2, and a 50-cycle charge / discharge test was performed. The initial charge capacity is smaller than the design capacity. In addition, damage was observed in the exterior body after 50 cycles of charge / discharge test.

"Comparative Example 4"
In Comparative Example 4, germanium was used instead of silicon as the negative electrode active material. As for other conditions, a battery was prepared in the same manner as in Comparative Example 2, and a 50-cycle charge / discharge test was performed. The initial charge capacity is smaller than the design capacity. In addition, damage was observed in the exterior body after 50 cycles of charge / discharge test.

"Comparative Example 5"
In Comparative Example 5, a silicon oxide was used as the negative electrode active material. As for other conditions, a battery was prepared in the same manner as in Comparative Example 2, and a 50-cycle charge / discharge test was performed. The initial charge capacity is smaller than the design capacity. In addition, damage was observed in the exterior body after 50 cycles of charge / discharge test.

"Comparative Example 6"
In Comparative Example 6, metallic lithium was used as the negative electrode active material. As for other conditions, a battery was prepared in the same manner as in Comparative Example 2, and a 50-cycle charge / discharge test was performed. The initial charge capacity is smaller than the design capacity. In addition, no damage was observed in the exterior body after the 50-cycle charge / discharge test, but bending was observed in the power generation element.

1 Positive electrode 1A Positive electrode current collector 1B Positive electrode active material layer 2 Negative electrode 2A Negative electrode current collector 2B Negative electrode active material layer 3 Separator 10 Power generation element (electrode laminate)
20 terminals 21 Positive terminal 22 Negative terminal 30, 40, 50 Exterior 30A, 40A, 50A First side 30B, 40B, 50B Second side 32 Outer circumference 100 Secondary battery K Storage space

Claims (3)

A power generation element having a positive electrode, a negative electrode, and a separator for separating the positive electrode and the negative electrode, and an electrolytic solution impregnated in the power generation element.
A secondary battery exterior body that covers the power generation element is provided.
The exterior body for a secondary battery has a pair of surfaces that sandwich the power generation element in the stacking direction of the power generation element and face each other, and an outer peripheral portion that connects the pair of facing surfaces.
The outer peripheral portion has a crease structure over the entire circumference of the outer peripheral portion.
The peripheral portion Ri variable der in the direction of changing the distance between the pair of opposed faces,
When the width when the outer peripheral portion of the secondary battery exterior is most extended is W and the thickness of the power generation element when fully charged is T, W ≧ T is satisfied and the secondary battery exterior is satisfied. when the width when the body was most contracted peripheral portion of w, the thickness at full discharging of the power generating element and t, a w <t, the secondary batteries. The folds structure was connected to the mountain-folded portion of the fold shape is bellows structure is hexagonal, secondary batteries according to claim 1. The secondary battery according to claim 1 or 2 , wherein the negative electrode comprises a negative electrode mixture layer and a negative electrode current collector foil, and the negative electrode mixture layer contains at least one element of silicon, tin, germanium, and lithium.

Images