WO2019151517A1 - Non-aqueous electrolyte secondary cell - Google Patents

Abstract

This non-aqueous electrolyte secondary cell is provided with: a power generation element in which a positive electrode and a negative electrode exchange ions through an electrolyte; two terminals respectively connected to the positive electrode and the negative electrode; and an exterior body covering the power generation element and the two terminals so that one end of the two terminals extend out to the exterior. The exterior body has a metal layer and resin layers covering both surfaces of the metal layer. The capacitance between the metal layer and the power generation element is 2.0 nF or above.

Description

Non-aqueous electrolyte secondary battery

The present invention relates to a non-aqueous electrolyte secondary battery.
The present invention claims priority based on Japanese Patent Application No. 2018-017617 filed on Feb. 2, 2018, the contents of which are incorporated herein by reference.

For the purpose of reducing the weight of the battery and increasing the degree of freedom in battery design, a laminated film obtained by laminating a metal layer and a resin layer as an exterior body is used to hermetically seal a battery element in which electrodes are laminated or wound. Laminated cells have been put into practical use.

The laminate film has a metal layer and a resin layer covering both sides thereof. If a crack or the like occurs in a part of the resin layer of the laminate film, the metal layer constituting the laminate film may react with the electrolyte. For example, a precipitation reaction in which conductive ions are precipitated as a metal, an alloying reaction in which conductive ions and a metal constituting the metal layer are alloyed, or the like occurs. When these reactions occur, the metal layer of the outer package is corroded and the gas barrier properties of the laminate film are lowered. The deterioration of the gas barrier property of the laminate film reduces the long-term reliability of the nonaqueous electrolyte secondary battery.

For example, Patent Document 1 describes that a metal layer of a laminate film and a positive electrode are electrically connected to prevent the potential of the metal layer from being lowered. By increasing the potential of the metal layer, the reduction reaction of the conductive ions that causes the above reaction can be suppressed.

For example, Patent Document 2 describes an inspection method in which a voltage is applied between a metal terminal and a metal layer of an exterior body. By measuring the change in the voltage waveform, it is possible to detect an insulation failure between the metal terminal and the metal layer of the exterior body.

JP 2000-353502 A International Publication No. 2011/040446

However, when the positive electrode and the metal layer are electrically connected as described in Patent Document 1, an overvoltage may be applied to the positive electrode due to a short circuit of the metal layer with an external power source or the like. Moreover, even if the insulation failure of the laminate film is inspected by the inspection method described in Patent Document 2, it is not possible to deal with the case where the laminate film cracks during use of the non-aqueous electrolyte secondary battery.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a non-aqueous electrolyte secondary battery capable of suppressing corrosion of a metal layer in the exterior body even when a crack occurs in the exterior body. And

Investigated the mechanism of corrosion when cracks occur in the resin layer of the exterior body. Part of the metal constituting the negative electrode may be ionized and eluted in the electrolyte before the first charge, and may re-deposit as dendrite on the negative electrode surface during the charge. In addition, when using lithium metal for the negative electrode or providing lithium ions released from the positive electrode as lithium on the negative electrode current collector without providing a negative electrode active material layer, lithium dendrite is deposited on the negative electrode surface. . Dendrites grow according to the electric field. The electric field acting between the positive electrode and the negative electrode greatly spreads outward at the edge portion of the electrode. Since the edge part of an electrode is located in the edge part of a battery element, the dendrite which grows in an edge part spreads outside the battery element, and grows. Further, reprecipitation tends to concentrate on the edge portion. Furthermore, cracks in the resin layer of the outer package are likely to occur near the end of the battery element where the refracting portion and the sealing portion are concentrated. Therefore, if there is a crack in the resin layer, there is a high possibility that the grown dendrite will reach the exposed metal layer. When the metal layer and the negative electrode are short-circuited by dendrite, the potential of the metal layer is lowered, and a reduction reaction (corrosion) of the metal layer occurs.

The inventors studied to suppress a short circuit between the metal layer and the negative electrode caused by this dendrite. As a result of intensive studies, it has been found that when the capacitance between the metal layer and the power generation element is set to a certain level or more, conduction due to dendrite can be removed when the metal layer and the negative electrode are short-circuited.
That is, in order to solve the above problems, the following means are provided.

(1) A non-aqueous electrolyte secondary battery according to a first aspect includes a power generation element in which a positive electrode and a negative electrode exchange ions via an electrolytic solution, and 2 connected to each of the positive electrode and the negative electrode. Two terminals, and an exterior body covering each of the power generation element and the two terminals by extending one end of each of the two terminals outward, and the exterior body includes a metal layer and both surfaces of the metal layer. And a capacitance between the metal layer and the power generation element is 2.0 nF or more.

(2) In the non-aqueous electrolyte secondary battery according to the above aspect, the product of the potential of the metal layer with respect to the negative electrode when the power generation element is fully charged and the capacitance is 5.0 nC or more. Good.

(3) In the non-aqueous electrolyte secondary battery according to the above aspect, even if the capacitance per unit area of the negative electrode obtained by dividing the capacitance by the area of the negative electrode is 2.9 pF / cm ² or more. Good.

(4) In the non-aqueous electrolyte secondary battery according to the above aspect, the electrolyte constituting the electrolyte may be impregnated on the surface of the resin layer on the power generation element side of the exterior body.

According to the nonaqueous electrolyte secondary battery according to the above aspect, it is possible to provide a nonaqueous electrolyte secondary battery that can suppress the corrosion of the metal layer in the exterior body even when the exterior body is cracked.

It is a schematic diagram which shows an example of the nonaqueous electrolyte secondary battery concerning this embodiment. It is a cross-sectional schematic diagram which shows an example of the nonaqueous electrolyte secondary battery concerning this embodiment. It is an image figure when a power generation element and the metal layer of an exterior body short-circuit. It is the figure which showed typically the equivalent circuit of a positive electrode, a negative electrode, and a metal layer. It is the figure which showed typically the equivalent circuit of a positive electrode, a negative electrode, and a metal layer.

Hereinafter, preferred examples of the present embodiment will be described in detail with reference to the drawings as appropriate. In the drawings used in the following description, in order to make the characteristics of the present invention easier to understand, there are cases where the characteristic parts are enlarged for the sake of convenience, and the dimensional ratios of the respective components are different from actual ones. is there. The materials, dimensions, and the like exemplified in the following description are examples, and the present invention is not limited to them, and can be appropriately modified and implemented without departing from the scope of the invention. In other words, the present invention is not limited to the embodiments described below, and can be implemented with appropriate modifications within the scope of the effects. For example, numbers, numerical values, quantities, ratios, shapes, positions, and characteristics can be omitted, added, or changed without departing from the gist of the present invention.

[Nonaqueous electrolyte secondary battery]
FIG. 1 is a schematic view schematically showing an example of a non-aqueous electrolyte secondary battery according to the present embodiment. A nonaqueous electrolyte secondary battery 100 shown in FIG. 1 includes a power generation element 10, two terminals 20 (a positive terminal 21 and a negative terminal 22), and an exterior body 30. The power generation element 10 is accommodated in an accommodation space K provided in the exterior body 30. In FIG. 1, a state immediately before the power generation element 10 is accommodated in the exterior body 30 is illustrated for easy understanding.

(Power generation element)
FIG. 2 is a schematic cross-sectional view schematically showing a cross section of an example of the nonaqueous electrolyte secondary battery according to the present embodiment. A power generating element 10 illustrated in FIG. 2 includes a positive electrode 1, a negative electrode 2, and a separator 3. A power generating element 10 shown in FIG. 2 is a laminate in which a positive electrode 1 and a negative electrode 2 are disposed to face each other with a separator 3 interposed therebetween. The number of stacked positive electrodes 1, negative electrodes 2, and separators 3 in the stacked body is not particularly limited. The power generating element 10 may be a wound body in which a laminated body in which the positive electrode 1 and the negative electrode 2 are disposed to face each other with the separator 3 interposed therebetween is wound. Since dendrites tend to concentrate on the edge portion of the negative electrode, a wound body with fewer edge portions is preferred.

The positive electrode 1 has a plate-like (film-like) 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-like (film-like) 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. Through this electrolytic solution, the positive electrode 1 and the negative electrode 2 exchange ions.

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

The positive electrode active material used for the positive electrode active material layer 1B can reversibly advance ion storage and release, ion desorption and insertion (intercalation), or ion and counteranion doping and dedoping. Any electrode active material can be used. As the ions, for example, lithium ions, sodium ions, magnesium ions and the like can be used, and it is particularly preferable to use lithium ions.

For example, in the case of a lithium ion secondary battery, but are not limited to these examples, lithium cobaltate (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 a composite metal oxide represented by Al, Mg, Nb, Ti, Cu, Zn, or Cr), a lithium vanadium compound (LiV ₂ O ₅ ), an olivine-type LiMPO ₄ (however, M is, Co, showing Ni, Mn, Fe, Mg, Nb, Ti, Al, one or more elements or VO selected from Zr), lithium titanate _(Li 4 Ti _{O 12), LiNi x Co y} Al z O 2 (0.9 <x + y + z <1.1) mixed metal oxide such as polyacetylene, polyaniline, polypyrrole, polythiophene, polyacene, etc., are preferably used as the positive electrode active material it can.

The positive electrode active material layer 1B may further include a conductive material. Examples of the conductive material include, but are not limited to, carbon powders such as carbon blacks, carbon nanotubes, carbon materials, fine metal powders such as copper, nickel, stainless steel, and iron, a mixture of carbon materials and fine metal powders, ITO, etc. These conductive oxides can be mentioned. In the case where sufficient conductivity can be ensured with only the positive electrode active material, the positive electrode active material layer 1B may not include a conductive material.

The positive electrode active material layer 1B contains a binder. A well-known thing can be used for a binder. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoro Fluorine resins such as ethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), and polyvinyl fluoride (PVF).

In addition to the above, as the binder, for example, vinylidene fluoride-hexafluoropropylene fluorine rubber (VDF-HFP fluorine rubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene fluorine rubber (VDF-HFP-) TFE fluorine rubber), vinylidene fluoride-pentafluoropropylene fluorine rubber (VDF-PFP fluorine rubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene fluorine rubber (VDF-PFP-TFE fluorine rubber), Vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene fluororubber (VDF-PFMVE-TFE fluororubber), vinylidene fluoride-chlorotrifluoroethylene Tsu and containing rubbers (VDF-CTFE-based fluorine rubber) vinylidene fluoride-based fluorine rubbers such as may be used.

The negative electrode active material used for the negative electrode active material layer 2B may be a compound that can occlude / release ions, and a negative electrode active material used for a known nonaqueous electrolyte secondary battery can be used. Examples of the negative electrode active material include alkali metals such as metallic lithium, alkaline earth metals, graphite capable of occluding and releasing ions (natural graphite, artificial graphite), carbon nanotubes, non-graphitizable carbon, and graphitizable carbon. Mainly composed of carbon materials such as low-temperature calcined carbon, metals that can be combined with metals such as lithium such as aluminum, silicon and tin, and oxides such as SiO _x (0 <x <2) and tin dioxide And particles containing an amorphous compound, lithium titanate (Li ₄ Ti ₅ O ₁₂ ), or the like. Further, the lithium ion released from the positive electrode 1 may be directly deposited on the negative electrode current collector 2A as lithium without providing the negative electrode active material layer 2B.

As the negative electrode current collector 2A, the conductive material, and the binder of the negative electrode 2, those similar to the positive electrode current collector 2A, the conductive material, and the binder of the positive electrode 1 can be used, respectively. The binder used for the negative electrode 2 may be, for example, cellulose, styrene / butadiene rubber, ethylene / propylene rubber, polyimide resin, polyamideimide resin, acrylic resin, or the like, in addition to those listed for the positive electrode.

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

The separator 3 may have a functional layer such as a heat-resistant layer containing inorganic particles or a heat-resistant resin or an adhesive layer containing an adhesive resin on one side or both sides.

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

The non-aqueous electrolyte 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 the cyclic carbonate and the chain carbonate in the non-aqueous solvent is preferably 1: 9 to 1: 1 by 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.

Chain carbonate reduces the viscosity of cyclic carbonate. For example, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate or the like is used as the chain carbonate. Other chain esters such as methyl acetate, ethyl acetate, methyl propionate and ethyl propionate, cyclic esters such as γ-butyrolactone, nitriles such as acetonitrile, propionitrile, glutaronitrile and adiponitrile, 1,2 A mixture of -dimethoxyethane, 1,2-diethoxyethane, etc. may be used.

An additive may be appropriately added to the electrolytic solution. Additives include vinylene carbonate, vinylethylene carbonate, fluoroethylene carbonate, propane sultone, butane sultone, adiponitrile, succinonitrile, glutaronitrile, diphenyl carbonate, cyclohexylbenzene, tert-butylbenzene, lithium bisoxalate borate, lithium bis (Trifluoromethanesulfonyl) imide and the like can be used. One additive may be used, or two or more additives may be mixed and used.

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 , lithium salts such as LiBOB can be used. In addition, these lithium salts may be used individually by 1 type, and may use 2 or more types together. In particular, from the viewpoint of the degree of ionization, it is preferable to include LiPF ₆ as the electrolyte.

When LiPF ₆ is dissolved in a non-aqueous solvent, the concentration of the electrolyte in the non-aqueous electrolyte is preferably adjusted 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 nonaqueous electrolytic solution can be sufficiently secured, and a sufficient capacity can be easily obtained during charging and discharging. Moreover, by suppressing the electrolyte concentration to within 2.0 mol / L, it is possible to suppress an increase in the viscosity of the non-aqueous electrolyte, to sufficiently secure the mobility of lithium ions, and to obtain a sufficient capacity during charging and discharging. It becomes easy.

Even when LiPF ₆ is mixed with other electrolytes, it is preferable to adjust the concentration of all lithium ions in the non-aqueous electrolyte to 0.5 to 2.0 mol / L, and the concentration of lithium ions from LiPF ₆ is More preferably, it is contained in an amount of 50 mol% or more.

The non-aqueous electrolyte may be a gel electrolyte held in a polymer material. Examples of the polymer material include polyvinylidene fluoride and a copolymer of polyvinylidene fluoride. Examples of the copolymer monomer that may be used as the polymer material include hexafluoropropylene and tetrafluoroethylene. These polyvinylidene fluorides and copolymers thereof are preferable because high battery characteristics can be obtained.

In addition, for example, polyacrylonitrile and a copolymer of polyacrylonitrile can be used as the polymer material. The copolymer monomer that may be used as a polymer material includes, for example, vinyl acetate, vinyl acetate, methyl methacrylate, butyl methacrylate, methyl acrylate, butyl acrylate, itaconic acid, methyl hydride. Examples thereof include acrylate, hydrogenated ethyl acrylate, acrylamide, vinyl chloride, vinylidene fluoride, and vinylidene chloride. In addition, acrylonitrile butadiene rubber, acrylonitrile butadiene styrene resin, acrylonitrile chlorinated polyethylene propylene diene styrene resin, acrylonitrile chlorinated polyethylene propylene diene styrene resin, acrylonitrile vinyl chloride resin, acrylonitrile methacrylate resin or acrylonitrile acrylate resin may be used.

As the polymer material, for example, polyethylene oxide and a copolymer of polyethylene oxide may be used. Examples of the copolymerizable monomer that may be used as the polymer material include polypropylene oxide, methyl methacrylate, butyl methacrylate, methyl acrylate, and butyl acrylate. In addition, polyether-modified siloxane and copolymers thereof may be used.

(Terminal)
There are two terminals 20, one being a positive terminal 21 and the other being a negative 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 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.

A sealant made of resin may be installed in a seal portion between the positive electrode terminal 21 and the negative electrode terminal 22 with the exterior body 30. The sealant prevents the positive electrode terminal 21 and the negative electrode terminal 22 and the metal layer 31 of the exterior body 30 from being short-circuited during heat sealing. The resin preferably contains polyethylene (PE) or polypropylene (PP) in consideration of sealing properties with the exterior body.

(Exterior body)
The exterior body 30 seals the power generation element 10 and the electrolytic solution therein. The exterior body 30 includes a metal layer 31, a resin layer 32 that covers the inner surface of the metal layer 31 on the power generation element 10 side, and a resin layer 33 that covers the outer surface of the metal layer 31 opposite to the power generation element 10. . The exterior body 30 is a so-called metal laminate film.

Polymer layers such as polypropylene can be used for the resin layer 32 and the resin layer 33. The material constituting the resin layer 32 and the material constituting the resin layer 33 may be different. For example, a polymer having a high melting point such as polyethylene terephthalate (PET) or polyamide (PA) is used as the outer material, and polyethylene (PE) or polypropylene (PP) is used as the material of the inner polymer film. be able to.

1, the first surface 30A and the second surface 30B having concave portions are folded to form the accommodation space K. The first surface 30A and the second surface 30B are in close contact with each other by sealing the outer periphery. As shown in FIG. 1, the exterior body 30 is not limited to one in which the first surface 30 </ b> A and the second surface 30 </ b> B are folded to form the accommodation space K, and may be one in which two films are joined. A recessed part may be provided in each of two films, and may be provided only in one film.

"Relationship between exterior body and power generation element"
The electrostatic capacitance between the metal layer 31 of the outer package 30 and the power generation element 10 is 2.0 nF or more, more preferably 3.5 nF or more, and further preferably 6.0 nF or more. The electrostatic capacitance here is an electrostatic capacitance in a state where the metal layer 31 of the exterior body 30 and the power generation element 10 are not short-circuited. The capacitance between them can be measured using an oscilloscope or the like. Specifically, the potential difference between the positive electrode terminal 21 electrically connected to the power generation element 10 and the metal layer 31 of the exterior body 30 is measured. The potential observed between them decreases according to V (t) = V ₀ × exp (−t / τ). In the equation, V (t) is a potential change, V ₀ is an initial voltage, τ is a relaxation time, and t is an elapsed time. Then, the capacitance is calculated by dividing the relaxation time τ of the potential change V (t) by the input resistance of the oscilloscope.

A dendrite that connects the metal layer 31 and the negative electrode 2 when the metal layer 31 and the negative electrode 2 are short-circuited when the capacitance between the metal layer 31 of the outer package 30 and the power generation element 10 is 2.0 nF or more. Conduction due to can be removed. In addition, when the capacitance is 3.5 nF or more, this effect can be suitably obtained, and it is more preferably 6.0 nF or more.

FIG. 3 is an image diagram when the power generation element 10 and the metal layer 31 of the exterior body 30 are short-circuited. In FIG. 3, for the sake of simplicity, the positive electrode 1, the negative electrode 2, and the separator 3 included in the power generation element 10 are illustrated as only one layer, but the present invention is not limited thereto.

A part of the negative electrode current collector 2 </ b> A of the negative electrode 2 is eluted into the electrolytic solution when the non-aqueous electrolyte secondary battery 100 is manufactured. Some of the eluted metal ions may be deposited as dendrites 5 on the negative electrode current collector 2A when the non-aqueous electrolyte secondary battery 100 is charged. Precipitation tends to concentrate on the edge portion of the current collector 2A, and the electric field acting between the positive electrode 1 and the negative electrode 2 greatly spreads outward at the edge portion. The dendrite deposited on the edge portion also grows outside and easily reaches the inside of the exterior body 30.

As shown in FIG. 3, when a crack 31 a is generated in the resin layer 32 inside the outer package 30, when the dendrite 5 grown from the negative electrode 2 reaches the metal layer 31, the negative electrode 2 and the metal layer 31 are short-circuited. To do.

For example, when the metal layer 31 is aluminum and the conductive ions are lithium ions, when the negative electrode 2 and the metal layer 31 are short-circuited and the potential of the metal layer 31 is lowered, the following alloying reaction occurs.
_{^{Al + Li + x + xe -}} → Li x Al
When the metal layer 31 is alloyed, the gas barrier property of the outer package 30 is lowered, and the long-term reliability of the non-aqueous electrolyte secondary battery 100 is lowered.

On the other hand, when the electrostatic capacitance between the metal layer 31 of the outer package 30 and the power generation element 10 is 2.0 nF or more, a sufficient amount of electric charge is accumulated in the metal layer 31 of the outer package 30 from Coulomb's law. Or is ready to accumulate. The capacitance is more preferably 3.5 nF or more, and further preferably 6.0 nF or more.

4A and 4B are diagrams schematically showing an equivalent circuit of the positive electrode 1, the negative electrode 2, and the metal layer 31. 4A and 4B, V _cell is a potential difference between the positive electrode 1 and the negative electrode 2 (that is, a cell voltage of the nonaqueous electrolyte secondary battery 100), and Cx is an electrostatic potential between the positive electrode 1 and the metal layer 31. Rx is a resistance between the positive electrode 1 and the metal layer 31, Cy is a capacitance between the negative electrode 2 and the metal layer 31, and Ry is between the negative electrode 2 and the metal layer 31. It is a resistance, and V ₃₁ is the potential of the metal layer 31. The combined capacitance obtained by combining Cx and Cy corresponds to the capacitance between the metal layer 31 of the exterior body 30 and the power generation element 10. Cx and Cy cannot be distinguished in reality.
The potential V ₃₁ of the metal layer 31 with respect to the negative electrode 2 when the power generation element 10 is fully charged is calculated by subtracting V ₀ from the cell voltage. That is, the potential V ₃₁ of the metal layer 31 with respect to the negative electrode 2 when the power generation element 10 is fully charged is the difference between the cell voltage and V ₀ .

FIG. 4A is an equivalent circuit before a short circuit occurs. As shown in FIG. 3, an insulating resin layer 32 exists between the positive electrode 1 and the metal layer 31 and between the negative electrode 2 and the metal layer 31. Therefore, resistances Rx and Ry and capacitances Cx and Cy are generated between the potential V ₃₁ of the metal layer 31 as shown in FIG. 4A. The resistors Rx and Ry are high resistance because the resin layer 32 is insulative. Therefore, charges q _x and q _y are accumulated between the positive electrode 1 and the metal layer 31 and between the negative electrode 2 and the metal layer 31.

On the other hand, FIG. 4B is an equivalent circuit after a short circuit occurs. When the negative electrode 2 and the metal layer 31 are short-circuited by the dendrite 5, the resistance Ry between the negative electrode 2 and the metal layer 31 approaches zero. Therefore, the electrostatic capacity Cy between the negative electrode 2 and the metal layer 31 is discharged, and the accumulated charge q _y flows toward the negative electrode 2 (arrow F1 in FIG. 4B), and the electrostatic capacity of the positive electrode 1 and the metal layer 31. Cx is charged and more charge is accumulated (arrow F2 in FIG. 4B).

When the electrostatic capacitance between the metal layer 31 and the power generation element 10 is large, the conduction by the dendrite 5 disappears (inactivates). Although the process of removing conduction by the dendrite 5 is not clear, it is considered that the conduction by the dendrite 5 disappears (inactivates) for the following reason.

As a first reason, an effect due to Joule heat when current flows from the metal layer 31 toward the negative electrode 2 in association with the change of the charge can be considered. When a sufficient amount of current flows from the metal layer 31 toward the negative electrode 2, a part of the dendrite 5 reacts with the electrolytic solution to become non-conductive, and the conduction is broken. That is, even if the negative electrode 2 and the metal layer 31 are short-circuited, the short-circuit portion is immediately inactivated spontaneously, and the short-circuit portion is self-repaired.

As a second reason, reionization due to the dendrite 5 becoming a high potential can be considered. The metal layer 31 has a high potential due to the balance between the resistance Rx between the positive electrode 1 and the metal layer 31 and the resistance Ry between the negative electrode 2 and the metal layer 31. When the high potential metal layer 31 and the dendrite 5 come into contact with each other, the reionization reaction of the dendrite 5 is promoted. As a result, a part of the dendrite 5 that connects the negative electrode 2 and the metal layer 31 disappears, and conduction is broken.

When the electrostatic capacitance between the metal layer 31 of the outer package 30 and the power generation element 10 is 2.0 nF or more, a sufficient amount of charge can be accumulated in the metal layer 31, and when the capacitance is 3.5 nF or more. When it exists, it is more preferable, and it is still more preferable that it is 6.0 nF or more.
The Therefore, even when the metal layer 31 and the negative electrode 2 are short-circuited, conduction due to the dendrite that connects the metal layer 31 and the negative electrode 2 in a self-repairing manner is removed.

In order to increase the electrostatic capacity between the metal layer 31 of the exterior body 30 and the power generation element 10, it is preferable that the surface of the resin layer 32 of the exterior body 30 is impregnated with an electrolyte constituting the electrolytic solution. When the resin layer 32 is impregnated with an electrolyte, the capacitance of the resin layer 32 increases. The capacitance of the resin layer 32 is mainly responsible for the capacitance between the metal layer 31 of the exterior body 30 and the power generation element 10. Therefore, when the resin layer 32 is impregnated with an electrolyte, the capacitance between the metal layer 31 of the outer package 30 and the power generation element 10 is increased. Moreover, the electrostatic capacitance between the metal layer 31 of the exterior body 30 and the power generation element 10 can be increased by increasing the electrolyte concentration in the electrolytic solution or by using an ionic liquid for part or all of the electrolytic solution. Can be raised. In addition, the electrostatic capacity can be increased by arranging a separator in which a functional layer containing inorganic particles such as alumina or a resin such as PVdF is laminated on one or both surfaces on the outermost periphery of the power generation element 10.

In addition, when the resin layer 32 is impregnated with an electrolyte, variation in capacitance is reduced. Here, the variation in capacitance is the variation in capacitance when a plurality of non-aqueous electrolyte secondary batteries are manufactured under the same conditions. If the variation in capacitance is small, the capacitance is predetermined. The proportion of non-aqueous electrolyte secondary batteries that are greater than or equal to the value increases.

6. The product of the potential V ₃₁ of the metal layer 31 with respect to the negative electrode 2 when the power generation element 10 is fully charged and the capacitance C between the power generation element 1 layer 31 is preferably 5.0 nC or more. It is more preferably 0 nC or more, further preferably 7.4 or more, and further preferably 10.0 nC or more. These products are the total amount of charges accumulated between the power generation element 10 and the metal layer 31. By increasing the amount of charge accumulated between them, the amount of electricity flowing at the time of a short circuit can be increased, and the removal of conduction by the dendrite 5 due to Joule heat or ionization is further promoted.

The total charge amount has been discussed so far, but there may be a case where a short circuit occurs due to the dendrite 5 at a plurality of locations. In order to remove conduction due to the plurality of dendrites 5, it is preferable that sufficient charges are accumulated in the metal layer 31 with respect to the area of the negative electrode. In order to accumulate sufficient charge in the metal layer 31 with respect to the area of the negative electrode, the electrostatic capacity per unit area of the negative electrode obtained by dividing the electrostatic capacity between the power generation element 10 and the metal layer 31 by the area of the negative electrode 2 There is preferably 2.9 pF / cm ² or more, more preferably 4.2 pF / cm ² or more, further preferably 6.0 pF / cm ² or more.

If the electrostatic capacity per unit area of the negative electrode is 2.9 pF / cm ² or more, the ability to remove conduction by the dendrite 5 exceeds the growth ability of the dendrite 5 growing on the negative electrode 2, and the negative electrode 2 and the metal layer 31. The insulation between the two can be maintained over a long period of time.

In addition, the area of the negative electrode means the total area of the stacked negative electrodes when the power generation element 10 is a laminate, and the total area of the wound negative electrode when the power generation element 10 is a wound body.

As described above, according to the nonaqueous electrolyte secondary battery according to the present embodiment, even when the metal layer 31 and the negative electrode 2 are short-circuited by the dendrite 5, conduction due to the dendrite can be removed. That is, even when the resin layer 32 on the inner surface of the exterior body 30 is damaged, the cycle characteristics of the nonaqueous electrolyte secondary battery can be maintained.

[Method for producing non-aqueous electrolyte secondary battery]
The manufacturing method of the non-aqueous electrolyte secondary battery 100 can be manufactured by a known method except that the capacitance between the metal layer 31 and the power generation element 10 is set. The capacitance between the metal layer 31 and the power generation element 10 can be freely designed depending on the thickness, area, material type, presence / absence of electrolyte impregnation, etc. of the resin layer 32 on the inner surface of the exterior body 30. Hereinafter, an example of a method for manufacturing the non-aqueous electrolyte secondary battery 100 will be specifically described.

First, the positive electrode 1 and the negative electrode 2 are produced. The positive electrode 1 and the negative electrode 2 are different only in a material that becomes an active material, and both can be manufactured by the same manufacturing method.

塗料 Prepare paint by mixing positive electrode active material, binder and solvent. A conductive material may be further added as necessary. As the solvent, for example, water, N-methyl-2-pyrrolidone, N, N-dimethylformamide or the like can be used. The constituent 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 mass ratio. These mass ratios are adjusted so as to be 100 wt% as a whole.

The mixing method of these components constituting the paint is not particularly limited, and the mixing order is not particularly limited. The paint is applied to the positive electrode current collector 1A. There is no restriction | limiting in particular as an application | coating method, The method employ | adopted when producing an electrode normally can be used. Examples thereof include a slit die coating method and a doctor blade method. Similarly, for the negative electrode, a paint is applied on the negative electrode current collector 2A. The paint applied to the negative electrode current collector 2A can be the same as the paint applied to the positive electrode current collector 1A.

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 to which the paint is applied may be 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 laminate, 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 any case, the separator 3 is disposed between the positive electrode 1 and the negative electrode 2.

The power generation element 10 is enclosed in the exterior body 30. The resin layer 32 on the inner surface of the outer package 30 is adjusted so that the electrostatic capacitance becomes a certain level or more. The resin layer 32 of the outer package 30 mainly serves as a capacitance between the power generation element 10 and the metal layer 31. By setting the capacitance of the resin layer 32 to a certain value or more, the capacitance between the power generation element 10 and the metal layer 31 is 2.0 nF or more, 3.5 nF or more, or 6.0 nF or more.
It becomes.

The nonaqueous electrolytic solution may be injected into the outer package 30 or the power generation element 10 may be impregnated with the nonaqueous electrolytic solution. And heat etc. are added and sealed to the exterior body 30, and a nonaqueous electrolyte secondary battery is produced.

When the battery size is large, there is a process demerit that the time required for the impregnation with the electrolytic solution becomes long. If the time required for the impregnation is long, it is necessary to take a long time from the injection of the electrolytic solution to the first charge, and the amount of the metal constituting the negative electrode increases, so that dendrites are likely to grow. Therefore, the footprint area of the cell is preferably 20000 mm ² or less, more preferably 15000 ² or less, more preferably 10000 mm ² or less. The electrode size is preferably 150 mm or less, more preferably 120 mm or less in the short direction.

Further, when the resin layer 32 of the outer package 30 is impregnated with the electrolyte in the electrolytic solution, it is preferable to subject the non-aqueous electrolyte secondary battery to a hot pressure treatment. The hot pressure treatment is a treatment for heating and pressurizing the non-aqueous electrolyte secondary battery.

As mentioned above, although this embodiment was explained in full detail with reference to drawings, each composition in each embodiment, those combinations, etc. are examples, and addition, abbreviation, and substitution of composition are within the range which does not deviate from the meaning of the present invention. , And other changes are possible.

"Example 1"
First, a positive electrode active material layer was applied to both surfaces of a positive electrode current collector made of aluminum foil to produce 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 (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 produce a positive electrode. The negative electrode active material layer is composed of 95 parts by mass of graphite (active material), 1 part by mass of carbon (conductive material), 1.5 parts by mass of styrene butadiene rubber (SBR, binder), and 2.5 parts by mass of graphite. Carboxymethylcellulose (CMC, binder).

Also, a heat resistant layer was applied to one side of the polyethylene microporous membrane to produce a separator. The heat-resistant layer has 97 parts by mass of alumina (heat-resistant filler) and 3 parts by mass of polyvinylidene fluoride (PVDF, binder). And the positive electrode, the negative electrode, and the separator were laminated | stacked, and the laminated body was produced. The number of negative electrodes in the laminate was 13, and the number of positive electrodes was 14. The amount of protrusion of the negative electrode with respect to the positive electrode when viewed from the stacking direction was 1 mm.

On the other hand, an aluminum laminate film was prepared as an exterior body. The resin layer inside the outer package was made of polypropylene (PP) having a thickness of 45 μm. A cutter with a blade thickness of 0.38 mm was used at the corner of the inner resin layer on the bottom side with respect to the power generation element of the outer package, and a 15 mm long scratch was made. It was confirmed with a microscope that the depth of the wound reached the metal layer. And a laminated body was accommodated in the exterior body, the nonaqueous electrolyte solution was inject | poured, and the nonaqueous electrolyte secondary battery was produced. The non-aqueous electrolyte 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 in a volume ratio of 35:35:30. The one to which LiPF ₆ was added was used.

The produced non-aqueous electrolyte secondary battery was aged at 45 ° C. for 7 days and charged for the first time. And the non-aqueous-electrolyte secondary battery was heat-pressure-treated at 60 degreeC 4 atmospheres at the time of the first charge. The resin layer on the inner surface of the outer package was impregnated with an electrolyte (LiPF ₆ ) by hot pressing. For the impregnation of the electrolyte, the outer body of the non-aqueous electrolyte secondary battery manufactured under the same conditions was cut out, the inner side was thoroughly rinsed with dimethyl carbonate (DMC) and dried, and the inner surface was observed with ATR-IR. Judgment was made by the presence or absence of a peak derived from the origin.

Then the potential V ₃₁ of the electrostatic capacitance and the metal layer between the metal layer of the power generating element and the outer body, were measured using an oscilloscope. The measured results are summarized in Table 1. The cycle characteristics of the produced nonaqueous electrolyte secondary battery were also specified. The cycle characteristics were 800 cycles under the conditions of 45 ° C., charge 0.7 C / discharge 1.5 C. Here, C represents the C rate, and the amount of current that discharges the entire capacity of the battery in one hour is referred to as the 1C rate.

In the cycle test, the presence or absence of corrosion of the exterior body was confirmed by an appearance check every 20 cycles up to the 100th cycle and every 100 cycles after the 100th cycle. The cycle test was performed on ten samples prepared under the same conditions. In the cycle test, the rate of occurrence of corrosion (the number of samples in which 10 samples have been corroded) and the number of cycles in which corrosion has occurred (the number of cycles in which 10 samples have been corroded first are corroded). ) The results are shown in Table 1.

“Examples 2 to 12 and Comparative Examples 1 and 2”
In Examples 2 to 12, the amount of protrusion of the negative electrode with respect to the positive electrode when viewed from the stacking direction, the thickness of the resin layer, the cell size, and the like were changed, and the capacitance between the power generation element and the metal layer of the outer package was changed. changed. In each of Examples 2 to 9, the capacitance between the power generation element and the metal layer of the exterior body is 2.0 nF or more, and Comparative Examples 1 and 2 are between the power generation element and the metal layer of the exterior body. The capacitance was 1.0 nF. Also in Examples 2 to 12 and Comparative Examples 1 and 2, a cycle test was performed to confirm the presence or absence of corrosion of the exterior body. The results are shown in Table 1. The variation value in Table 1 means the variation in capacitance when a plurality of nonaqueous electrolyte secondary batteries are produced under the same conditions.

As shown in Table 1, the non-aqueous electrolyte secondary batteries shown in Comparative Examples 1 and 2 corrode the first sample exterior body in 100 cycles or less, and all the sample exterior bodies corroded at the time of 800 cycles. Was. In contrast, the non-aqueous electrolyte secondary batteries shown in Examples 1 to 12 were superior in cycle characteristics to Comparative Examples 1 and 2. In the non-aqueous electrolyte secondary batteries shown in Examples 1 to 12, even if dendrite is deposited between the negative electrode and the metal layer, the short circuit by the dendrite is not maintained, and the metal layer of the outer package is not corroded. It is thought.

DESCRIPTION OF SYMBOLS 1 Positive electrode 1A Positive electrode collector 1B Positive electrode active material layer 2 Negative electrode 2A Negative electrode collector 2B Negative electrode active material layer 3 Separator 5 Dendrite 10 Power generation element 20 Terminal 21 Positive electrode terminal 22 Negative electrode terminal 30 Exterior body 30A First surface 30B Second surface 31 Metal layer 31a Crack 32 Resin layer 33 Resin layer 100 Nonaqueous electrolyte secondary battery K accommodation space

Claims (4)

A power generation element in which a positive electrode and a negative electrode exchange ions via an electrolyte;
Two terminals connected to each of the positive electrode and the negative electrode;
An exterior body that extends one end of each of the two terminals outward to cover the power generation element and the two terminals;
The exterior body has a metal layer and a resin layer covering both surfaces of the metal layer,
A non-aqueous electrolyte secondary battery, wherein a capacitance between the metal layer and the power generation element is 2.0 nF or more. The non-aqueous electrolyte secondary battery according to claim 1, wherein a product of the potential of the metal layer with respect to the negative electrode when the power generating element is fully charged and the capacitance is 5.0 nC or more. The nonaqueous electrolyte secondary battery according to claim 1, wherein a capacitance per unit area obtained by dividing the capacitance by the area of the negative electrode is 2.9 pF / cm ² or more. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein a surface of the resin layer on the power generation element side of the outer package is impregnated with an electrolyte constituting the electrolyte.

Images