JP7024540B2 - Electrochemical element - Google Patents

Description

The present invention relates to an electrochemical device.

For the purpose of reducing the weight of the battery and increasing the degree of freedom in battery design, an electrochemical element using a laminated film obtained by laminating a metal foil and a resin as an exterior body has been put into practical use. Further, in recent years, there has been a demand for higher energy density of batteries, and the development of thinner and lighter laminated films is being promoted. The laminated film covers the power generation element of the electrochemical element and prevents the power generation element from coming into contact with water or air.

On the other hand, in response to the recent demand for higher capacity and higher energy density of batteries, for example, in lithium ion secondary batteries, it is considered to use a high capacity negative electrode material such as silicon instead of the conventional graphite negative electrode. The theoretical capacity of silicon and silicon oxide is much larger than the theoretical capacity of graphite, but the volume expansion during charging is also very large. Therefore, a large stress is applied to the exterior body due to charging and discharging.

In Patent Document 1, at least an exterior body for an electrochemical element in which a sheet-like laminate in which a base material layer, a metal layer, and a sealant layer are laminated in this order is formed, and corners of the formed metal layer are formed. For an electrochemical element in which the thickness of each curved portion a and c to be formed and the thickness of a portion b located in the middle of each curved portion satisfy a specific relationship (a ≧ b> c or a ≧ c> b). The exterior is disclosed.

International Publication No. 2016/0437389

The laminated film-like exterior body as described above is thinner than the metal exterior body, and pinholes and cracks are likely to occur due to the expansion / contraction stress of the electrochemical element during manufacturing and charging / discharging. In recent years, thinner and lighter laminated films have an even greater risk. If a sealing defect such as a pinhole or a crack occurs in the outer body of the electrochemical element, water may be mixed inside the battery, which may cause various problems such as gas generation in the non-aqueous electrochemical element. However, in the layer structure of the exterior body as disclosed in Patent Document 1, although a certain effect can be expected to prevent pinholes and cracks during manufacturing, the electrochemical element when the electrochemical element is charged and discharged is expected. Sufficient effect was not obtained on the expansion and contraction stress of.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an electrochemical element having an exterior body that can withstand the expansion / contraction stress of the electrochemical element due to charging / discharging and is less likely to cause pinholes or cracks.

As a result of diligent studies, the present inventors have made a predetermined portion of the exterior body in order to provide an electrochemical element having an exterior body that can withstand the expansion and contraction stress of the electrochemical element due to charging and discharging and is less likely to cause pinholes and cracks. It has been found that it is effective for the thickness to have a specific relationship. Specifically, in an electrochemical element including a laminate in which a positive electrode and a negative electrode face each other via a separator and an exterior body covering the laminate, an exterior body covering the upper surface and the lower surface of the laminate in the stacking direction. It is effective that the thickness A of the first portion of the above and the thickness B of the second portion of the exterior body covering the side surface of the laminated body have a relationship of 1.02 ≦ B / A ≦ 1.33. I found that. That is, the present invention provides the following means for solving the above problems.

(1) The electrochemical element according to the first aspect includes a laminated body in which a positive electrode and a negative electrode face each other via a separator, and an exterior body covering the laminated body, and has an upper surface surface in the stacking direction of the laminated body and an outer body covering the laminated body. The relationship between the thickness A of the first portion of the exterior body covering the lower surface and the thickness B of the second portion of the exterior body covering the side surface of the laminated body is 1.02 ≦ B / A ≦ 1.33. Meet.

(2) In the electrochemical device according to the above embodiment, the thickness A may be 45 to 110 μm, and the thickness B may be 50 to 120 μm.

(3) In the electrochemical device according to the above aspect, the exterior body has a metal layer, and the thickness a of the metal layer in the first portion and the thickness b of the metal layer in the second portion are 1.05. The relationship of ≦ b / a ≦ 1.5 may be satisfied.

(4) In the electrochemical device according to the above embodiment, the thickness a may be 10 to 40 μm, and the thickness b may be 15 to 45 μm.

(5) In the electrochemical element according to the above aspect, the negative electrode may contain any one of silicon, a silicon oxide, and a silicon alloy as an active material.

By using the electrochemical element according to the above aspect, it is possible to withstand the expansion / contraction stress of the electrochemical element due to charging / discharging, and it is possible to prevent pinholes and cracks from occurring in the exterior body. In addition, the energy density of the electrochemical element can be improved.

It is sectional drawing of the cross section of the electrochemical element which concerns on this embodiment. It is an enlarged view of the X part of FIG. It is a figure which shows the method of manufacturing the exterior body used for the electrochemical element which concerns on 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, etc. exemplified in the following description are examples, and the present invention is not limited thereto, and the present invention can be appropriately modified without changing the gist thereof.

[Electrochemical element]
FIG. 1 is a schematic cross-sectional view of an electrochemical device according to the present embodiment. As shown in FIG. 1, the electrochemical element 1 has a power generation element 10 forming a laminated body and an exterior body 20. The power generation element 10 is impregnated with an electrolytic solution. The exterior body 20 prevents the electrolytic solution from leaking to the outside and prevents external air and moisture from reaching the power generation element 10.

(Power generation element)
The power generation element 10 has a positive electrode 101, a negative electrode 102, and a separator 103. In FIG. 1, the power generation element 10 refers to the entire laminated body in which a plurality of positive electrodes 101 and a plurality of negative electrodes 102 are arranged to face each other with a plurality of separators 103 interposed therebetween. The number of laminated positive electrodes 101 and 102 is not limited. Further, although the structure of the power generation element 10 is shown as a laminated type in FIG. 1, the structure is not particularly limited, and for example, the structure of the power generation element 10 may be a winding type.

<Positive electrode>
The positive electrode 101 has a positive electrode current collector 101A and a positive electrode active material layer 101B provided on at least one surface thereof. The positive electrode current collector 101A may be made of a conductive 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 101B includes storage and release of lithium ions, desorption and insertion (intercalation) of lithium ions, or counter anions of lithium ions and lithium ions (for example, PF _6- ⁾ . An electrode active material capable of reversibly advancing the doping and dedoping of the above can be used.

For example, lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganate (LiMnO ₂ ), lithium manganese spinel (LiMn ₂ O ₄ ), and general formula: LiNi _{x Coy} Mn _{z Ma} O. ₂ (x + y + z + a = 1, 0≤x <1, 0≤y <1, 0≤z <1, 0≤a <1, M is one type selected from Al, Mg, Nb, Ti, Cu, Zn, Cr. Composite metal oxide represented by the above elements), lithium vanadium compound (LiV ₂ O ₅ ), olivine type LiMPO ₄ (however, M is Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, Zr. (Representing one or more elements or VOs selected from the above), oxidation of composite metals such as lithium titanate (Li ₄ Ti ₅ O ₁₂ ), LiNi _x Coy Al _z O ₂ (0.9 <x + _y + z <1.1). Examples include compounds, polyacetylene, polyaniline, polypyrrole, polythiophene, polyacene and the like.

Further, the positive electrode active material layer 101B 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 101 may not contain the conductive material.

Further, the positive electrode active material layer 101B 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.

<Negative electrode>
The negative electrode 102 has a negative electrode current collector 102A and a negative electrode active material layer 102B provided on at least one surface thereof. As the negative electrode current collector 102A, the conductive material and the binder, the same ones as those of the positive electrode 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 negative electrode active material used for the negative electrode active material layer 102B may be any compound that can occlude / release (precipitate / dissolve, alloying / non-alloying) lithium ions, and a known negative electrode active material can be used. Examples of the negative electrode active material include lithium metal, carbon materials capable of storing and releasing lithium ions (natural graphite, artificial graphite), carbon nanotubes, carbon refractory carbon, easily graphitized carbon, and carbon materials such as low temperature fired carbon. Metals that can be combined with lithium such as aluminum, silicon, and tin, silicon oxide SiO _x (0 <x <2), amorphous compounds mainly composed of oxides such as tin dioxide, lithium titanate (Li) Examples thereof include particles containing ₄ Ti ₅ O ₁₂ ) and the like. The negative electrode active material used for the negative electrode active material layer 102B preferably contains any one of silicon, a silicon oxide, and a silicon alloy in order to realize high capacity and high energy density of the electrochemical element.

When lithium metal is used in the negative electrode 102, the lithium metal is deposited on the negative electrode current collector 102A, and the lithium metal is dissolved at the time of discharge. In this case, the negative electrode active material layer 102B may not be present in the initial state. On the other hand, since the precipitated lithium metal remains after charging once or more, the layer containing the lithium metal can be regarded as the negative electrode active material layer 102B. Further, in preparation for a shortage of the amount of lithium that contributes to charging / discharging, a lithium foil may be provided as the negative electrode active material layer 102B on one surface of the negative electrode current collector 102A from the initial state before charging / discharging.

<Separator>
The separator 103 may be formed of an electrically insulating porous structure, for example, a monolayer of a film made of polyethylene, polypropylene or polyolefin, a laminated body or a stretched film of a mixture of the above resins, or cellulose, polyester and the like. Examples thereof include fibrous nonwoven fabrics made of at least one constituent material selected from the group consisting of polypropylene.

<Electrolytic solution>
The electrolytic solution is impregnated in the power generation element 10. As the electrolytic solution, an electrolyte solution containing a lithium salt or the like (an aqueous electrolyte solution, a non-aqueous electrolyte solution using an organic solvent) can be used. However, since the decomposition voltage of the aqueous electrolyte solution is electrochemically low, the withstand voltage during charging is low and limited. Therefore, it is preferable to use an electrolyte solution (non-aqueous electrolyte solution) that uses an organic solvent.

The non-aqueous electrolyte solution has an electrolyte dissolved in a non-aqueous solvent, and may contain a cyclic carbonate and a chain carbonate as the non-aqueous solvent. Further, a mixture of an ionic liquid and a lithium salt may be used as the non-aqueous electrolyte solution.

As the cyclic carbonate, one capable of solvating an electrolyte can be used. For example, ethylene carbonate, propylene carbonate, butylene carbonate and the like can be used.

The chain carbonate can reduce the viscosity of the cyclic carbonate. For example, diethyl carbonate, dimethyl carbonate and ethylmethyl carbonate can be mentioned. 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.

The ratio of cyclic carbonate to chain carbonate in the non-aqueous solvent is preferably 1: 9 to 1: 1 in volume.

Examples of the electrolyte include 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 , and 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 and other lithium salts 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 .

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, the increase in the viscosity of the non-aqueous electrolyte solution can be suppressed, the mobility of lithium ions can be sufficiently secured, and a sufficient capacity can be obtained 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.

(Exterior body)
The exterior body 20 seals the power generation element 10 and the electrolytic solution inside the exterior body 20. The exterior body 20 suppresses leakage of the electrolytic solution to the outside and invasion of moisture or the like into the inside of the electrochemical element 1 from the outside.

As shown in FIGS. 1 and 2, the exterior body 20 has a heat-sealed resin layer 201, a metal layer 202, and a heat-resistant resin layer 203 in this order from the power generation element 10. As the material of the heat-sealed resin layer 201, polyolefins such as polyethylene and polypropylene can be used. As the material of the metal layer 202, aluminum, stainless steel, or the like can be used. As the material of the heat-resistant resin layer 203, a polymer having a high melting point, for example, polyethylene terephthalate (PET), polyamide (PA) or the like can be used.

In the exterior body 20, the thickness A of the first portion of the exterior body 20 covering the upper surface and the lower surface in the stacking direction of the laminated body (power generation element 10) in which the positive electrode 101 and the negative electrode 102 face each other via the separator 103, and the above-mentioned stacking. The thickness B of the second portion of the exterior body 20 that covers the side surface of the body satisfies the relationship of 1.02 ≦ B / A ≦ 1.33. Here, when the power generation element 10 expands during charging and the exterior body 20 is greatly stretched, it is the second portion that the amount of displacement is the largest and stress is applied. On the other hand, the stress of the first portion is relatively small. Therefore, by setting B (thickness of the second portion) / A (thickness of the first portion) ≥ 1.02, it is possible to prevent the occurrence of pinholes, cracks, and the like in the exterior body 20. Further, since the thickness A of the first portion, which has a relatively small stress due to expansion during charging, can be kept thin, the volume and weight of the exterior body 20 can be suppressed, and therefore the energy density of the electrochemical element 1 as a whole can be reduced. Can be improved. When B / A> 1.33, it is difficult to manufacture the exterior body 20 because cracks and layer bonding defects occur at the thickness stepped portion. Further, it is more preferable that the thickness A and the thickness B satisfy the relationship of 1.04 ≦ B / A ≦ 1.20.

In the exterior body 20, the thickness A is preferably 45 to 110 μm, and the thickness B is preferably 50 to 120 μm. By setting the thickness A and the thickness B to the above range while satisfying the relationship of 1.02 ≦ B / A ≦ 1.33, even in a thin exterior body 20 of 120 μm or less, pinholes during charging and discharging can be achieved. It is possible to prevent the occurrence of cracks and the like. Further, since the thin exterior body 20 can be used, the volume and weight of the electrochemical element 1 can be suppressed and the energy density can be improved. Further, the thickness A is more preferably 45 to 100 μm, and the thickness B is more preferably 50 to 110 μm.

The exterior body 20 has a metal layer, and the thickness a of the metal layer in the first portion and the thickness b of the metal layer in the second portion satisfy the relationship of 1.05 ≦ b / a ≦ 1.5. preferable. Here, when the power generation element 10 expands during charging and the exterior body 20 is greatly stretched, it is the metal layer portion of the second portion that has the largest displacement and is stressed. On the other hand, the stress of the metal layer portion of the first portion is relatively small. Therefore, by setting b (thickness of the metal layer portion of the second portion) / a (thickness of the metal layer portion of the first portion) ≥ 1.05, the occurrence of pinholes, cracks, etc. in the exterior body 20 is prevented. can do. Further, since the thickness a of the metal layer portion of the first portion, which has a relatively low stress due to expansion during charging, can be kept thin, the volume and weight of the exterior body 20 can be suppressed, and therefore the electrochemical element 1 as a whole can be suppressed. Energy density can be improved. When b / a> 1.5, it is difficult to manufacture the exterior body 20 because cracks and layer bonding defects occur at the thickness stepped portion. Further, it is more preferable that the thickness a and the thickness b satisfy the relationship of 1.07 ≦ b / a ≦ 1.33.

In the exterior body 20, the thickness a is preferably 10 to 40 μm, and the thickness b is preferably 15 to 45 μm. By setting the thickness a and the thickness b to the above range while satisfying the relationship of 1.05 ≦ B / A ≦ 1.5, even in the thin exterior body 20 having an internal metal layer of 45 μm or less, when charging / discharging It is possible to prevent the occurrence of pinholes and cracks. Further, since the thin exterior body 20 can be used, the volume and weight of the electrochemical element 1 can be suppressed and the energy density can be improved. Further, it is more preferable that the thickness a is 10 to 35 μm and the thickness b is 15 to 40 μm.

In the exterior body 20, it is preferable that the thickness C and the thickness B of the fused portion of the exterior body 20 satisfy the relationship of 1.01 ≦ B / C ≦ 1.5. Here, when the power generation element 10 expands during charging and the exterior body 20 is greatly stretched, it is the second portion that the amount of displacement is the largest and stress is applied. On the other hand, the stress of the fused portion is relatively small. Therefore, by setting B (thickness of the second portion) / C (thickness of the fused portion) ≥ 1.01, it is possible to prevent the occurrence of pinholes, cracks, and the like in the exterior body 20. Further, since the thickness C of the fused portion having a relatively low stress due to expansion during charging can be kept thin, the volume and weight of the exterior body 20 can be suppressed, and therefore the energy density of the entire electrochemical element 1 can be reduced. Can be improved. Further, it is more preferable that the thickness C and the thickness B satisfy the relationship of 1.02 ≦ B / C ≦ 1.33. Further, the thickness C is preferably 45 to 119 μm. As a result, even in the thin exterior body 20, the volume and weight of the electrochemical element 1 can be suppressed and the energy density can be improved while preventing the generation of pinholes and cracks during charging and discharging. Further, the thickness C is more preferably 45 to 110 μm.

In the exterior body 20, it is preferable that the thickness c of the metal layer in the fused portion and the thickness b of the metal layer in the second portion satisfy the relationship of 1.0 <b / c ≦ 1.5. Here, when the power generation element 10 expands during charging and the exterior body 20 is greatly stretched, it is the metal layer portion of the second portion that has the largest displacement and is stressed. On the other hand, the stress of the metal layer portion of the fused portion is relatively small. Therefore, by setting b (thickness of the metal layer portion of the second portion) / c (thickness of the metal layer portion of the fused portion) to> 1.0, pinholes, cracks, and the like are generated in the exterior body 20. Can be prevented. Further, since the thickness c of the metal layer portion of the fused portion where the stress due to expansion during charging is relatively low can be kept thin, the weight of the exterior body can be suppressed, and therefore the energy density of the entire electrochemical element can be reduced. Can be improved. When b / c> 1.5, it is difficult to manufacture the exterior body 20 because cracks and layer bonding defects occur at the thickness stepped portion. Further, it is more preferable that the thickness c and the thickness b satisfy the relationship of 1.01 ≦ b / c ≦ 1.33. Further, the thickness c is preferably 10 to 44 μm. As a result, even in the thin exterior body 20, the volume and weight of the electrochemical element 1 can be suppressed and the energy density can be improved while preventing the generation of pinholes and cracks during charging and discharging. Further, the thickness c is more preferably 10 to 40 μm.

As described above, in the electrochemical element 1 of the present invention, in order to realize high capacity and high energy density, it is preferable to use a high capacity negative electrode material such as silicon instead of the conventional graphite negative electrode. The capacity of the electrochemical element mainly depends on the active material of the electrode. The theoretical capacity of silicon and silicon oxide is much larger than the theoretical capacity of graphite. However, since the silicon-based material has a much larger volume expansion during charging than the conventional graphite, the entire electrochemical element 1 expands and contracts significantly with charging and discharging. Specifically, the volume expansion when lithium ions are occluded is about 1.2 times that of the graphite material, whereas the volume expansion of the silicon material is up to 4 times when silicon and lithium are alloyed. As a result, a large amount of stress is applied to the exterior body 20, and problems such as pinholes, cracks, and peeling of the adhesive portion are likely to occur. In the present invention, by using the exterior body 20 having the above configuration, it is possible to solve the above-mentioned problems and provide the electrochemical element 1 having an improved energy density.

[Method for manufacturing electrochemical device 1]
The power generation element of the electrochemical element 1 can be manufactured by, for example, the following known method except for the molding step of the exterior body 20.

First, the positive electrode 101 and the negative electrode 102 are manufactured. The positive electrode 101 and the negative electrode 102 differ only in the material used as the active material, and can be produced by the same 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% by mass to 98% by mass: 0.1% by mass to 10% by mass: 0.1% by mass to 10% by mass in terms of mass ratio. These mass ratios are adjusted to be 100% by mass 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 101A. The coating method is not particularly limited, and a method usually adopted when manufacturing an electrode can be used. For example, a slit die coat method and a doctor blade method can be mentioned. Similarly, for the negative electrode, the paint is applied on the negative electrode current collector 102A.

Subsequently, the solvent in the paint applied on the positive electrode current collector 101A and the negative electrode current collector 102A is removed. The removal method is not particularly limited. For example, the positive electrode current collector 101A and the negative electrode current collector 102A coated with the paint may be dried in an atmosphere of 80 ° C. to 150 ° C. Then, the positive electrode 101 and the negative electrode 102 are completed.

Finally, the power generation element 10 is manufactured by sandwiching the positive electrode 101 and the negative electrode 102 with the separator 103.

Next, as shown in FIG. 3, the exterior body 20 is manufactured. As a method for producing the exterior body 20, first, each film to be a heat-sealed resin layer 201, a metal layer 202, and a heat-resistant resin layer 203 is prepared. A film having a specific thickness structure is produced as follows.

First, as shown in FIG. 3A, the portion (first portion) of the metal layer film 202 corresponding to the upper surface and the lower surface in the stacking direction of the power generation element 10 is preliminarily thinned by pressing using the mold 30. .. Here, since the film is likely to be damaged at the edge portion of the mold 30, the corners are rounded (R) as shown in FIG. 3 (B) which is a cross-sectional view taken along the line YY'in FIG. 3 (A). It is preferable to use the mold 30.

Next, the metal layer film 202 and the heat-sealed resin layer film 201 are bonded to each other via the adhesive layer 204. This may be performed by sequentially laminating the adhesive layer 204 and the heat-sealing resin layer film 201 that have been formed in advance to the metal layer film 202. After that, the metal layer film 202 and the heat-resistant resin layer film 203 are bonded to each other via the adhesive layer 205. Similarly, the adhesive layer 205 and the heat-resistant resin layer film 203, which have been formed in advance, may be bonded to the metal layer film 202 in sequence. Here, an electrolyte-resistant adhesive (urethane-based adhesive or the like) can be used for the adhesive layers 204 and 205. When reliability is particularly required, an acid (maleic anhydride) modification having adhesiveness to the heat-sealed resin layer 201 itself is performed without using an adhesive between the heat-sealed resin layer 201 and the metal layer 202. It is preferable to use a heat-sealed resin made of polyolefin.

Here, when the heat-sealed resin layer 201, the metal layer 202, and the heat-resistant resin layer 203 are bonded together, is it possible to use the mold 30 having rounded corners (R) as shown in FIG. 3C? , Or, as shown in FIG. 3D, it is preferable to use a mold in which the cushioning material 32 is bonded around the metal roll 31. As a result, damage to the heat-sealed resin layer 201 that comes into contact with the molds 30 and 32 can be reduced, and the plastic can be bonded without any trouble such as holding air in the stepped portion.

Then, the exterior body 20 is manufactured by combining two laminated films for an exterior body obtained by laminating each layer so that the heat-sealing resin layer 201 is on the inside and heat-sealing the three sides.

Finally, the produced power generation element 10 is enclosed in the exterior body 20, and the electrolytic solution is injected into the exterior body 20. Then, the remaining one side of the exterior body is sealed by heat fusion to complete the electrochemical element 1.

When the power generation element 10 is enclosed, a stress stretched in the thickness direction of the power generation element 10 acts on the exterior body 20. Further, particularly when the thickness of the power generation element 10 is large, the exterior body 20 may be partially stretched in advance to adjust the shape in order to create a space for the power generation element 10. Further, in general, the power generation element 10 gradually deteriorates and irreversibly expands while repeating expansion and contraction due to charging and discharging, so that the exterior body 20 is stretched in the thickness direction of the power generation element 10. Therefore, when the exterior body 20 is manufactured by a normal method that does not create a thickness difference in the exterior body 20, the thickness A ≧ thickness B is generally obtained by the above steps and phenomena. In contrast, in the present invention, by adopting the above steps so that the thickness A <thickness B, the problem that defects such as pinholes and cracks are likely to occur is solved, and the energy density is improved. Electrochemical devices can be provided.

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.

[Examples 1 to 5: Preparation of an exterior body satisfying the relationship of 1.02 ≦ B (thickness of the second part) / A (thickness of the first part) ≦ 1.33]
"Example 1"
In the metal layer film 202 having a thickness of 16 μm, the portion (first portion) of the metal layer film 202 corresponding to the upper surface and the lower surface in the stacking direction of the power generation element 10 was made to have a thickness of 15 μm by pressing with a mold 30. After that, the heat-fused resin layer film 201 having a thickness of 20 μm and the heat-resistant resin layer film 203 having a thickness of 12 μm are bonded to each other via the adhesive layer 205 having a thickness of 2 μm with the metal layer film 202 interposed therebetween, and the thickness A is 49 μm. An exterior body 20 having a thickness B of 50 μm was produced.

"Example 2"
In the metal layer film 202 having a thickness of 15 μm, the portion (first portion) of the metal layer film 202 corresponding to the upper surface and the lower surface in the stacking direction of the power generation element 10 was made to have a thickness of 10 μm by pressing with a mold 30. After that, the heat-sealed resin layer film 201 having a thickness of 20 μm and the heat-resistant resin layer film 203 having a thickness of 13 μm are bonded to each other via the adhesive layer 205 having a thickness of 2 μm with the metal layer film 202 sandwiched therein, and the thickness A is 45 μm. The exterior body 20 having a thickness B of 50 μm was produced.

"Example 3"
In the metal layer film 202 having a thickness of 30 μm, the portion (first portion) of the metal layer film 202 corresponding to the upper surface and the lower surface in the stacking direction of the power generation element 10 was made to have a thickness of 20 μm by pressing with a mold 30. After that, the heat-fused resin layer film 201 having a thickness of 15 μm and the heat-resistant resin layer film 203 having a thickness of 13 μm are bonded to each other via the adhesive layer 205 having a thickness of 2 μm with the metal layer film 202 sandwiched therein, and the thickness A is 50 μm. The exterior body 20 having a thickness B of 60 μm was produced.

"Example 4"
In the metal layer film 202 having a thickness of 45 μm, the portion (first portion) of the metal layer film 202 corresponding to the upper surface and the lower surface in the stacking direction of the power generation element 10 was made 30 μm thick by pressing with a mold 30. After that, the heat-sealed resin layer film 201 having a thickness of 10 μm and the heat-resistant resin layer film 203 having a thickness of 4 μm are bonded to each other via the adhesive layer 205 having a thickness of 1 μm with the metal layer film 202 sandwiched therein, and the thickness A is 45 μm. The exterior body 20 having a thickness B of 60 μm was produced.

"Example 5"
In the metal layer film 202 having a thickness of 40 μm, the portion (first portion) of the metal layer film 202 corresponding to the upper surface and the lower surface in the stacking direction of the power generation element 10 was made 30 μm thick by pressing with a mold 30. After that, the heat-sealed resin layer film 201 having a thickness of 40 μm and the heat-resistant resin layer film 203 having a thickness of 38 μm are bonded to each other via the adhesive layer 205 having a thickness of 2 μm with the metal layer film 202 sandwiched therein, and the thickness A is 110 μm. The exterior body 20 having a thickness B of 120 μm was produced.

[Comparative Examples 1 and 2: Fabrication of an exterior body that does not satisfy the relationship of 1.02 ≦ B (thickness of the second part) / A (thickness of the first part) ≦ 1.33]
"Comparative Example 1"
A heat-fused resin layer film 201 having a thickness of 20 μm and a heat-resistant resin layer film 203 having a thickness of 13 μm are bonded to each other via an adhesive layer 205 having a thickness of 2 μm with a metal layer film 202 having a thickness of 15 μm interposed therebetween. An exterior body 20 having both B of 50 μm was produced.

"Comparative Example 2"
In the metal layer film 202 having a thickness of 40 μm, the portion (first portion) of the metal layer film 202 corresponding to the upper surface and the lower surface in the stacking direction of the power generation element 10 is formed to a thickness of 20 μm by pressing with a mold 30. , There was already a crack.

[Examples 6 to 10: Fabrication of electrochemical element and evaluation of cracks in exterior body]
"Example 6"
Ten electrochemical elements were produced using the exterior body of Example 1 (n = 10), charging and discharging were performed for 100 cycles, and the number of cracks and the like in the exterior body after 100 cycles was evaluated. The detailed production method is shown below.

First, a positive electrode active material layer was applied onto a positive electrode current collector made of aluminum foil to prepare a positive electrode. LiCoO ₂ was used as the positive electrode active material, carbon black was used as the conductive material, PVDF was used as the binder, and the mass ratio of the positive electrode active material, the conductive material and the binder was 95: 2: 3. After coating, the solvent was dried and removed, and then the positive electrode was roll-pressed.

Similarly, a negative electrode active material layer was applied to one surface of a negative electrode current collector made of copper foil to prepare a negative electrode. The negative electrode active material layer has 85 parts by mass of metallic silicon (active material), 5 parts by mass of carbon (conductive material), and 10 parts by mass of polyamide-imide resin (PAI).

A polyethylene film having a thickness of 12 μm was used as the separator. Then, a positive electrode, a negative electrode, and a separator were laminated to produce a power generation element. The number of layers of the positive electrode and the negative electrode was 30 layers.

Next, the two exterior films of Example 1 were combined so that the heat-sealing resin layer was on the inside, and the three sides were heat-sealed. Then, a power generation element manufactured from the opening on the remaining one side was inserted.

Arranged so that the opening of the exterior body faces upward, using a presser jig that sandwiches the electrochemical element at the position corresponding to both main surfaces of the electrochemical element, injects the electrolytic solution through the opening, and vacuum sealer. The opening was thermally fused while reducing the pressure. As the electrolytic solution, in a solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) in a volume ratio of 3: 4: 3, the lithium salt was 1.0 M (mol / L). The one to which LiPF ₆ was added was used. Then, the obtained electrochemical element is operated at a charge voltage of 4.3 V and a discharge voltage of 3 V at a charge / discharge rate of 0.2 C, charged / discharged for 100 cycles, and the number of cracks in the exterior body after 100 cycles is evaluated. did. The above evaluation experiment was performed with 10 pieces (n = 10). As a result, none of the exterior bodies had cracks or the like (0/10).

"Examples 7 to 10"
Using the exterior bodies of Examples 2 to 5, 10 electrochemical elements were produced in the same manner as in Example 6 (n = 10), and the number of cracks and the like in the exterior body after 100 cycles of charging and discharging was evaluated. .. The results are shown in Table 1 below.

[Comparative Examples 3 and 4: Fabrication of Electrochemical Element and Evaluation of Cracks in Exterior Body]
"Comparative Examples 3 and 4"
Using the exterior body of Comparative Example 1, 10 electrochemical elements were produced in the same manner as in Example 6 (n = 10), and the number of cracks and the like in the exterior body after 100 cycles of charging and discharging was evaluated (comparison). Example 3). In Comparative Example 2, the metal layer film had already cracked and it was difficult to fabricate the exterior body, so that it was evaluated as “difficult to fabricate” (Comparative Example 4). The results are shown in Table 1 below.

From Table 1, it was found that cracks and the like did not occur at all in the exterior body of the electrochemical device according to this embodiment. On the other hand, in the outer body of the electrochemical element according to the comparative example, cracks or the like occurred or it was difficult to manufacture.

[Examples 11 to 17: Preparation of an exterior body satisfying the relationship of 1.05 ≦ b (thickness of the metal layer of the second part) / a (thickness of the metal layer of the first part) ≦ 1.5]
"Example 11"
In the metal layer film 202 having a thickness of 15 μm, the portion (first portion) of the metal layer film 202 corresponding to the upper surface and the lower surface in the stacking direction of the power generation element 10 was made to have a thickness of 10 μm by pressing with a mold 30. After that, the heat-sealed resin layer film 201 having a thickness of 20 μm and the heat-resistant resin layer film 203 having a thickness of 18 μm are bonded to each other via the adhesive layer 205 having a thickness of 2 μm with the metal layer film 202 sandwiched therein, and the thickness A is 50 μm. The exterior body 20 having a thickness B of 55 μm was produced.

"Examples 12 to 17"
Except for the fact that the metal layer films 202 having thicknesses of 15, 18, 21, 21, 30 and 45 μm, respectively, were pressed with a die 30 to have thicknesses of 14, 14, 14, 20, 20 and 40 μm, respectively. The exterior body 20 was produced in the same manner as in Example 11.

[Comparative Examples 5 and 6: Preparation of an exterior body that does not satisfy the relationship of 1.05 ≦ b (thickness of the metal layer of the second part) / a (thickness of the metal layer of the first part) ≦ 1.5]
"Comparative Example 5"
A heat-fused resin layer film 201 having a thickness of 20 μm and a heat-resistant resin layer film 203 having a thickness of 18 μm are bonded to each other via an adhesive layer 205 having a thickness of 2 μm with a metal layer film 202 having a thickness of 15 μm interposed therebetween. An exterior body 20 having both B of 55 μm was produced.

"Comparative Example 6"
In the metal layer film 202 having a thickness of 35 μm, the portion (first portion) of the metal layer film 202 corresponding to the upper surface and the lower surface in the stacking direction of the power generation element 10 is formed to a thickness of 15 μm by pressing with a mold 30. , There was already a crack.

[Examples 18 to 24: Fabrication of electrochemical element and evaluation of cracks in exterior body]
"Examples 18 to 24"
Using the exterior bodies of Examples 11 to 17, 10 electrochemical elements were produced in the same manner as in Example 6 (n = 10), and the number of cracks and the like in the exterior body after 100 cycles of charging and discharging was evaluated. .. The results are shown in Table 2 below.

[Comparative Examples 7 and 8: Fabrication of Electrochemical Element and Evaluation of Cracks in Exterior Body]
"Comparative Examples 7 and 8"
Using the exterior body of Comparative Example 5, 10 electrochemical elements were produced in the same manner as in Example 6 (n = 10), and the number of cracks and the like in the exterior body after 100 cycles of charging and discharging was evaluated (comparison). Example 7). In Comparative Example 6, the metal layer film had already cracked and it was difficult to fabricate the exterior body, so that it was evaluated as “difficult to fabricate” (Comparative Example 8). The results are shown in Table 2 below.

From Table 2, it was found that cracks and the like did not occur at all in the exterior body of the electrochemical element according to this embodiment. On the other hand, in the outer body of the electrochemical element according to the comparative example, cracks or the like occurred or it was difficult to manufacture.

1 Electrochemical element 10 Power generation element 101 Positive electrode 101A Positive electrode current collector 101B Positive electrode active material layer 102 Negative electrode 102A Negative electrode current collector 102B Negative electrode active material layer 103 Separator 20 Exterior body 201 Heat fusion resin layer 202 Metal layer 203 Heat resistant resin layer 204 Adhesive layer 205 Adhesive layer 30 Mold 31 Metal roll 32 Cushioning material

Claims (4)

A laminated body in which a positive electrode and a negative electrode face each other via a separator, and an exterior body covering the laminated body are provided.
The thickness A of the first portion of the exterior body covering the upper surface and the lower surface of the laminated body in the stacking direction and the thickness B of the second portion of the exterior body covering the side surface of the laminated body are 1.02 ≦. Satisfy the relationship of B / A ≤ 1.33 ,
An electrochemical device having a thickness A of 45 to 110 μm and a thickness B of 50 to 120 μm . The exterior body has a metal layer, and the thickness a of the metal layer in the first portion and the thickness b of the metal layer in the second portion satisfy the relationship of 1.05 ≦ b / a ≦ 1.5. , The electrochemical element according to claim 1 . A laminated body in which a positive electrode and a negative electrode face each other via a separator, and an exterior body covering the laminated body are provided.
The thickness A of the first portion of the exterior body covering the upper surface and the lower surface of the laminated body in the stacking direction and the thickness B of the second portion of the exterior body covering the side surface of the laminated body are 1.02 ≦. Satisfy the relationship of B / A ≤ 1.33 ,
The exterior body has a metal layer, and the thickness a of the metal layer in the first portion and the thickness b of the metal layer in the second portion satisfy the relationship of 1.05 ≦ b / a ≦ 1.5. ,
An electrochemical device having a thickness a of 10 to 40 μm and a thickness b of 15 to 45 μm . The electrochemical element according to any one of claims 1 to 3 , wherein the negative electrode contains any one of silicon, a silicon oxide, and a silicon alloy as an active material.

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