JP7657573B2 - Flat non-aqueous electrolyte battery - Google Patents

Description

The present invention relates to a flat nonaqueous electrolyte battery that can reduce internal resistance while suppressing cracking of a positive electrode having a molded body of a positive electrode mixture.

A laminated electrode body having a positive electrode and a negative electrode is housed in an exterior body having a positive electrode can and a negative electrode can, and a positive electrode having a molded body (pellet, positive electrode mixture layer, etc.) of a positive electrode mixture containing a positive electrode active material, etc., is used widely in flat nonaqueous electrolyte batteries today in the form of primary batteries and secondary batteries.

Generally, the positive and negative electrode cans that make up the exterior of a flat nonaqueous electrolyte battery function as current collectors by making their inner surfaces in contact with the positive and negative electrodes.

In the case of flat non-aqueous electrolyte batteries such as those described above, the negative electrode shrinks with discharge in the case of primary batteries, and expands and shrinks with charging and discharging in the case of secondary batteries. When the negative electrode shrinks as the battery is discharged, the electrical connection with the inner surface of the negative electrode can becomes insufficient, and the battery may not be able to fully utilize its inherent capacity.

Although not intended to solve the current collection problem caused by the shrinkage of the negative electrode accompanying the discharge of the battery as described above, Patent Document 1 proposes a technology in which a conductive carbon sheet or the like is placed between the negative electrode can and the negative electrode. Depending on the degree of shrinkage of the negative electrode accompanying discharge, the action of the carbon sheet may be able to maintain a certain degree of electrical connection between the negative electrode and the inner surface of the negative electrode can. However, in batteries in which the negative electrode shrinks significantly during discharge, the electrical connection between the negative electrode and the inner surface of the negative electrode can may be insufficient, leaving room for improvement.

On the other hand, as described in the above Patent Document 1, for example, a spring is placed in a compressed state between the positive electrode and the positive electrode can, and when the negative electrode shrinks, the restoring force of the spring is used to press the negative electrode against the inner surface of the negative electrode can from the positive electrode side, thereby ensuring good contact with the inner surface of the negative electrode can even if the negative electrode shrinks. However, when used in a battery in which the negative electrode shrinks significantly due to discharge, if a spring with a large restoring force is used to maintain sufficient contact between the negative electrode and the negative electrode can due to the shrinkage, there is a problem that cracks occur in the molded body of the positive electrode mixture, reducing the battery capacity.

JP 2010-212130 A (Claim 1, [0024], [0033], FIG. 1, etc.)

The present invention was made in consideration of the above circumstances, and its purpose is to provide a flat nonaqueous electrolyte battery that can reduce internal resistance while suppressing cracking of a positive electrode having a molded body of a positive electrode mixture.

The flat nonaqueous electrolyte battery of the present invention is characterized in that a laminated electrode body having a positive electrode and a negative electrode is housed in an exterior body having a positive electrode can and a negative electrode can, the positive electrode has a molded body of a positive electrode mixture containing a positive electrode active material, a conductive layer mainly composed of carbon is disposed on the positive electrode can side of the positive electrode, and a metal member having an elastic portion is disposed between the positive electrode can and the conductive layer mainly composed of carbon.

In the battery industry, flat batteries whose diameter is greater than their height are called coin batteries or button batteries, but there is no clear difference between coin batteries and button batteries, and the flat nonaqueous electrolyte battery of the present invention includes both coin batteries and button batteries.

The present invention provides a flat nonaqueous electrolyte battery that can reduce internal resistance while suppressing cracking of a positive electrode having a molded body of a positive electrode mixture.

1 is a cross-sectional view that illustrates a schematic diagram of an example of a flat nonaqueous electrolyte battery of the present invention.

Figure 1 shows a cross-sectional view of a flat nonaqueous electrolyte battery according to the present invention. The flat nonaqueous electrolyte battery 1 shown in Figure 1 has a laminated electrode body having a positive electrode 10 and a negative electrode 20 enclosed in an exterior body formed of a positive electrode can (exterior can) 40, a negative electrode can (sealing can) 50, and a gasket 60 interposed between them. A separator 30 is usually interposed between the positive electrode 10 and the negative electrode 20, but when the flat nonaqueous electrolyte battery 1 is a solid electrolyte battery, a solid electrolyte layer 30 is interposed between the positive electrode 10 and the negative electrode 20 instead of a separator.

The negative electrode can 50 is fitted into the opening of the positive electrode can 40 via a gasket 60, and the open end of the positive electrode can 40 is tightened inward, so that the gasket 60 abuts against the negative electrode can 50, sealing the opening of the positive electrode can 40 and sealing the inside of the battery. In the flat nonaqueous electrolyte battery 1, the positive electrode can 40 also serves as the positive electrode terminal, and the negative electrode can 50 also serves as the negative electrode terminal. In the flat nonaqueous electrolyte battery 1 shown in FIG. 1, the outer can is the positive electrode can 40 and the sealing can is the negative electrode can 50, but in the flat nonaqueous electrolyte battery of the present invention, the sealing can can be the positive electrode can and the outer can can be the negative electrode can.

In the flat nonaqueous electrolyte battery 1 shown in FIG. 1, the positive electrode 10 has a molded body of a positive electrode mixture containing a positive electrode active material and the like. A conductive layer 70 mainly composed of carbon is disposed on the positive electrode can 40 side of the positive electrode 10, and a metal member 80 having an elastic portion is disposed between the positive electrode can 40 and the conductive layer 70 mainly composed of carbon.

In this way, the flat nonaqueous electrolyte battery of the present invention has an exterior body having a positive electrode can and a negative electrode can, and a laminated electrode body including a positive electrode having a molded body of a positive electrode mixture containing a positive electrode active material, and a negative electrode. A conductive layer mainly composed of carbon is disposed on the positive electrode can side of the positive electrode, and a metal member having an elastic portion is disposed between the positive electrode can and the conductive layer mainly composed of carbon.

In the flat nonaqueous electrolyte battery of the present invention, even if the negative electrode shrinks due to discharge, the negative electrode is pressed against the inner surface of the negative electrode can from the positive electrode side by the action of the metal member having an elastic part arranged on the positive electrode side, so that the electrical connection between the negative electrode and the inner surface of the negative electrode can is maintained well, and the internal resistance can be kept low. In addition, a conductive layer mainly composed of carbon is arranged between the positive electrode and the metal member having an elastic part, so that even if stress is applied to the positive electrode by the restoring force of the metal member having an elastic part, the conductive layer mainly composed of elastically deformable carbon acts as a cushion, and the occurrence of cracks in the positive electrode (molded body of the positive electrode mixture) can be suppressed.

In addition, when the positive electrode and the metal member having the elastic portion are in direct contact with each other, the electrical connection between them tends to be insufficient. However, by interposing a conductive layer between them that is mainly composed of carbon and has a wide range of work functions, the electrical connection between the positive electrode and the metal member having the elastic portion can be improved.

In the flat nonaqueous electrolyte battery of the present invention, the above-mentioned actions make it possible to reduce the internal resistance while suppressing cracking of the positive electrode mixture compact.

The flat nonaqueous electrolyte battery of the present invention includes primary batteries and secondary batteries. The flat nonaqueous electrolyte battery of the present invention also includes batteries that use a nonaqueous electrolyte such as a nonaqueous electrolyte solution (nonaqueous electrolyte primary batteries, nonaqueous electrolyte secondary batteries) and solid electrolyte batteries that have a solid electrolyte layer between the positive and negative electrodes (solid electrolyte primary batteries, solid electrolyte secondary batteries).

(Carbon-based conductive layer)
In a flat nonaqueous electrolyte battery, the conductive layer mainly composed of carbon and arranged on the positive electrode can side of the positive electrode may be, for example, a conductive layer containing carbon as a main component and also containing a binder or the like.

In the case of a conductive layer containing carbon and a binder, the carbon is preferably fibrous carbon such as carbon fiber, carbon nanotube, or vapor-grown carbon fiber, and the binder is preferably styrene butadiene rubber, nitrile rubber, or the like.

In a conductive layer containing carbon and a binder, carbon is the main component, and the carbon content is preferably more than 50 mass% (more preferably 70 mass% or more) and 99 mass% or less. In addition, the binder content in a conductive layer containing carbon and a binder is preferably 1 mass% or more and less than 50 mass% (more preferably 30 mass% or less).

A conductive layer containing carbon and a binder can be formed, for example, by applying a conductive layer-forming composition prepared by dispersing carbon and a binder in water or an organic solvent (the binder may be dissolved) to the surface of the positive electrode and drying it.

For the conductive layer mainly composed of carbon, various carbon sheets, for example, porous carbon sheets composed of fibrous carbon such as carbon paper, carbon cloth, and carbon felt, can be preferably used, and these carbon sheets can be arranged on the positive electrode can side of the positive electrode to form the conductive layer (the carbon sheet and the positive electrode do not need to be bonded, but may be bonded).

These carbon sheets may have a single layer structure, a multi-layer structure in which carbon papers are laminated together, carbon cloths are laminated together, or carbon felts are laminated together, or a multi-layer structure in which two or more of carbon papers, carbon cloths, and carbon felts are laminated together.

The fiber diameter of the fibrous carbon that constitutes the porous carbon sheet is preferably 2 to 30 μm, taking into consideration electrical conductivity, etc.

The thickness of the conductive layer mainly composed of carbon is preferably 10 μm or more, and more preferably 50 μm or more, from the viewpoint of improving the effect of suppressing the occurrence of cracks in the molded body of the positive electrode mixture due to the action of the metal member having an elastic portion. In addition, from the viewpoint of reducing the occupancy rate of the battery internal volume by the conductive layer mainly composed of carbon and making it possible to increase the thickness of the electrode as much as possible, thereby making it possible to increase the battery capacity, the thickness of the conductive layer mainly composed of carbon is preferably 200 μm or less, and more preferably 100 μm or less.

(Metal member having elastic portion)
In a flat nonaqueous electrolyte battery, the metal member having an elastic part disposed between the positive electrode can and the conductive layer mainly composed of carbon is made of a conductive metal, preferably stainless steel. Note that the "metal member having an elastic part" according to the present invention is not required to be elastic in its entirety, but it is sufficient that it has a part having an elasticity (i.e., an elastic part) that can press the negative electrode of the laminated electrode body against the inner surface of the negative electrode can from the positive electrode side.

The characteristics of the metal member having an elastic portion used in a flat nonaqueous electrolyte battery are such that the restoring force is preferably at least half the thickness of the negative electrode, and more preferably equal to or greater than the thickness of the negative electrode.

Specific examples of metal components with elastic parts include springs such as leaf springs (thin leaf springs, disc springs, etc.), wave washers, and coil springs; retaining rings; etc.

(Positive electrode)
The positive electrode of the flat nonaqueous electrolyte battery is composed of a molded body of a positive electrode mixture, and examples of the positive electrode of the flat nonaqueous electrolyte battery include a positive electrode composed of only a molded body of a positive electrode mixture and a positive electrode mixture layer formed on a current collector.

In the case where the flat non-aqueous electrolyte battery is a primary battery, the same positive electrode active material as that used in the conventionally known non-aqueous electrolyte primary battery can be used.Specific examples of the positive electrode active material include manganese dioxide, lithium-containing manganese oxides (e.g., LiMn ₃ O ₆ , and composite oxides having the same crystal structure as manganese dioxide (β-type, γ-type, or a structure in which β-type and γ-type are mixed, etc.) and a Li content of 3.5 mass% or less, preferably 2 mass% or less, more preferably 1.5 mass% or less, and particularly preferably 1 mass% or less), lithium-containing composite oxides such as Li _a Ti _5/3 O ₄ (4/3≦a<7/3); vanadium oxide; niobium oxide; titanium oxide; sulfides such as iron disulfide; graphite fluoride; silver sulfides such as Ag ₂ S; nickel oxides such as NiO ₂ ; and the like.

In addition, when the flat nonaqueous electrolyte battery is a secondary battery, the same positive electrode active material as that used in conventionally known nonaqueous electrolyte secondary batteries, that is, the same active material capable of absorbing and releasing Li (lithium) ions, can be used. Specifically, a spinel-type lithium manganese composite oxide represented by Li _1-x M _r Mn _2-r O ₄ (wherein M is at least one element selected from the group consisting of Li, Na, K, B, Mg, Ca, Sr, Ba, Ti, V, Cr, Zr, Fe, Co, Ni, Cu, Zn, Al, Sn, Sb, In, Nb, Ta, Mo, W, Y, Ru, and Rh, and 0≦x≦1, 0≦r≦1), Li _r Mn _(1-s-t) Ni _s M _t O _(2-u) F _v a layered compound represented by Li 1-x Co 1-r M r O 2 (wherein M is at least one element selected from the group consisting of Co, Mg, Al, B, Ti, V, Cr, Fe, Cu, Zn, Zr, Mo, Sn, Ca, Sr, and W, and 0≦r≦1.2, 0<s<0.5, 0≦t≦0.5, u+v<1, -0.1≦u≦0.2, 0≦v≦0.1); a lithium cobalt composite oxide represented by Li _1-x Ni _1-r M _r O ₂ (wherein M is at least one element selected from the group consisting of Al, Mg, Ti, V, Cr, Zr, Fe, Ni, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb, and Ba, and 0≦ _x ≦1 _{, 0} ≦ _r ≦ _0.5); a lithium nickel composite oxide represented by Li 1+s-x M 1-r N r PO 4 F s (wherein M is at least one element selected from the group consisting of Al, Mg, Ti, Zr, Fe, Co, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb, and Ba, and 0≦x≦1, 0≦r≦0.5); an olivine type composite oxide represented by Li _2-x M _{1-r N r} P ₂ O ₇ (wherein M is at least one element selected from the group consisting of Fe, Mn, and Co, and N is at least one element selected from the group consisting of Al, Mg, Ti, Zr, Ni, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb, V, and Ba, and 0≦x≦ ₁ , 0≦r≦0.5, ₀ ≦ _s ≦1 _{) ;} (wherein M is at least one element selected from the group consisting of Fe, Mn, and Co, and N is at least one element selected from the group consisting of Al, Mg, Ti, Zr, Ni, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb, V, and Ba, and 0≦x≦2, 0≦r≦0.5), and the like can be exemplified. Among these, only one type may be used, or two or more types may be used in combination.

When the flat nonaqueous electrolyte battery is a solid electrolyte secondary battery, the average particle size of the positive electrode active material is preferably 1 μm or more, more preferably 2 μm or more, and preferably 10 μm or less, more preferably 8 μm or less. The positive electrode active material may be primary particles or secondary particles formed by agglomeration of primary particles. When a positive electrode active material with an average particle size in the above range is used, a large interface with the solid electrolyte contained in the positive electrode can be obtained, and the load characteristics of the battery are further improved.

The average particle diameter of various particles (such as positive electrode active material and solid electrolyte) referred to in this specification means the 50% diameter value ( _D50 ) in the volume-based integrated fraction when the integrated volume is calculated from particles with small particle sizes using a particle size distribution measurement device (such as the Microtrack particle size distribution measurement device "HRA9320" manufactured by Nikkiso Co., Ltd.).

When the flat nonaqueous electrolyte battery is a solid electrolyte secondary battery, it is preferable that the positive electrode active material has a reaction suppression layer on its surface to suppress reaction with the solid electrolyte contained in the positive electrode.

If the positive electrode active material and the solid electrolyte come into direct contact within the positive electrode mixture molded body, the solid electrolyte may oxidize to form a resistive layer, which may reduce the ionic conductivity within the molded body. By providing a reaction suppression layer on the surface of the positive electrode active material that suppresses reaction with the solid electrolyte and preventing direct contact between the positive electrode active material and the solid electrolyte, it is possible to suppress the reduction in ionic conductivity within the molded body due to oxidation of the solid electrolyte.

The reaction suppression layer may be made of a material that has ion conductivity and can suppress the reaction between the positive electrode active material and the solid electrolyte. Examples of materials that can form the reaction suppression layer include oxides containing Li and at least one element selected from the group consisting of Nb, P, B, Si, Ge, Ti and Zr, more specifically, Nb-containing oxides such as LiNbO ₃ , Li ₃ PO ₄ , Li ₃ BO ₃ , Li ₄ SiO ₄ , Li ₄ GeO ₄ , LiTiO ₃ , LiZrO ₃ , Li ₂ WO ₄ and the like. The reaction suppression layer may contain only one of these oxides, or may contain two or more of them, and further, a plurality of these oxides may form a composite compound. Among these oxides, it is preferable to use an Nb-containing oxide, and it is more preferable to use LiNbO ₃ .

It is preferable that the reaction suppression layer is present on the surface in an amount of 0.1 to 1.0 parts by mass per 100 parts by mass of the positive electrode active material. This range can effectively suppress the reaction between the positive electrode active material and the solid electrolyte.

Methods for forming a reaction suppression layer on the surface of a positive electrode active material include the sol-gel method, mechanofusion method, CVD method, PVD method, and ALD method.

The content of the positive electrode active material in the positive electrode mixture is preferably 60 to 98 mass%.

The positive electrode mixture can contain a conductive assistant. Specific examples include carbon materials such as graphite (natural graphite, artificial graphite), graphene, carbon black, carbon nanofibers, and carbon nanotubes. For example, when Ag ₂ S is used as the active material, conductive Ag is generated during the discharge reaction, so the conductive assistant does not need to be contained. When the conductive assistant is contained in the positive electrode mixture, the content is preferably 1 to 10 mass%.

The positive electrode mixture may contain a binder. A specific example of such a binder is a fluororesin such as polyvinylidene fluoride (PVDF). Note that the positive electrode mixture does not need to contain a binder if good moldability can be ensured in forming a positive electrode mixture compact without using a binder, such as when a sulfide-based solid electrolyte is contained in the positive electrode mixture (described in detail later).

When a binder is required in the positive electrode mixture, the content is preferably 15 mass% or less, and preferably 0.5 mass% or more. On the other hand, when the positive electrode mixture contains a sulfide-based solid electrolyte and thus can be molded without the need for a binder, the content is preferably 0.5 mass% or less, more preferably 0.3 mass% or less, and even more preferably 0 mass% (i.e., no binder is contained).

When the flat nonaqueous electrolyte battery is a solid electrolyte battery, the positive electrode mixture contains a solid electrolyte. The solid electrolyte is not particularly limited as long as it has lithium ion conductivity, and examples of the solid electrolyte that can be used include sulfide-based solid electrolytes, hydride-based solid electrolytes, halide-based solid electrolytes, and oxide-based solid electrolytes.

Examples of sulfide-based solid electrolytes include particles of Li ₂ S-P ₂ S ₅ , Li ₂ S-SiS ₂ , Li ₂ S-P ₂ S ₅ -GeS ₂ , and Li ₂ S- _{B 2 S 3 based} glass. In addition, thio-LISICON type electrolytes, which have been attracting attention in recent years for their high Li _ion conductivity, are Li _{12-12a-b+c+6d-e M 1 3 + a-b-c-d} M ² _b M ³ _c M ⁴ _d M ^{5 12} _{-e X e} (wherein M ¹ is Si, Ge, or Sn, and M ^M2 is P or V, ^M3 is Al, Ga, Y or Sb, ^M4 is Zn, Ca or Ba, ^M5 is S or either S and O, and X is F, Cl, Br or I, 0≦a<3, 0≦b+c+d≦3, 0≦e≦3] or argyrodite type compounds (such as _Li6PS5Cl , which are represented by Li7 _{-f+gPS6 - xClx +y} (where 0.05≦f≦0.9, -3.0f+1.8≦g≦-3.0f+5.7 ₎ , or Li7 _{-hPS6 - hCliBrj} (where h=i+j, 0<h≦1.8, 0.1≦i/j≦10.0)) can also be used.

Examples of hydride-based solid electrolytes include LiBH ₄ , solid solutions of LiBH ₄ and the following alkali metal compounds (for example, those in which the molar ratio of LiBH ₄ to the alkali metal compound is 1:1 to 20:1), etc. Examples of the alkali metal compounds in the solid solutions include at least one selected from the group consisting of lithium halides (LiI, LiBr, LiF, LiCl, etc.), rubidium halides (RbI, RbBr, RbF, RbCl, etc.), cesium halides (CsI, CsBr, CsF, CsCl, etc.), lithium amide, rubidium amide, and cesium amide.

Examples of halide-based solid electrolytes include monoclinic LiAlCl ₄ , defective spinel or layered structure LiInBr ₄ , and monoclinic Li _6-3m Y _m X ₆ (wherein 0<m<2 and X=Cl or Br). Other known solid electrolytes that can be used include those described in, for example, WO 2020/070958 and WO 2020/070955.

Examples of oxide-based solid electrolytes include garnet-type Li ₇ La ₃ Zr ₂ O ₁₂ , NASICON-type Li _1+O Al _1+O Ti _2-O (PO ₄ ) ₃ and Li _1+p Al _1+p Ge _2-p (PO ₄ ) ₃ , and perovskite-type Li _3q La _2/3-q TiO ₃ .

Among these solid electrolytes, sulfide-based solid electrolytes are preferred due to their high lithium ion conductivity, sulfide-based solid electrolytes containing Li and P are more preferred, and argyrodite-type sulfide-based solid electrolytes, which have particularly high lithium ion conductivity and high chemical stability, are even more preferred.

The average particle size of the solid electrolyte is preferably 0.1 μm or more, more preferably 0.2 μm or more, from the viewpoint of reducing grain boundary resistance, while it is preferably 10 μm or less, more preferably 5 μm or less, from the viewpoint of forming a sufficient contact interface between the active material and the solid electrolyte.

The solid electrolyte content in the positive electrode mixture is preferably 4 to 40 mass %.

When a current collector is used for the positive electrode, the current collector can be made of metal foil such as aluminum or stainless steel, punched metal, mesh, expanded metal, foamed metal; carbon sheet; etc.

The positive electrode mixture compact can be formed, for example, by compressing the positive electrode mixture prepared by mixing the positive electrode active material with conductive additives, binders, solid electrolytes, etc., which are added as necessary, by pressure molding or the like.

In the case of a positive electrode having a current collector, it can be manufactured by bonding the molded body of the positive electrode mixture formed by the method described above to the current collector by pressing, etc.

Alternatively, the positive electrode mixture may be mixed with a solvent to prepare a positive electrode mixture-containing composition, which may then be applied to a substrate such as a current collector or a solid electrolyte layer (when forming a solid electrolyte battery) that faces the positive electrode, dried, and then pressed to form a molded body of the positive electrode mixture.

The solvent for the positive electrode mixture-containing composition can be water or an organic solvent such as N-methyl-2-pyrrolidone (NMP). When the positive electrode mixture-containing composition also contains a solid electrolyte, it is preferable to select a solvent that does not easily deteriorate the solid electrolyte. In particular, since sulfide-based solid electrolytes and hydride-based solid electrolytes undergo chemical reactions due to a small amount of water, it is preferable to use a non-polar aprotic solvent represented by a hydrocarbon solvent such as hexane, heptane, octane, nonane, decane, decalin, toluene, or xylene. In particular, it is more preferable to use an ultra-dehydrated solvent with a water content of 0.001 mass% (10 ppm) or less. In addition, fluorine-based solvents such as "Vertrel (registered trademark)" manufactured by Mitsui DuPont Fluorochemicals, "Zeorolla (registered trademark)" manufactured by Nippon Zeon Co., Ltd., and "Novec (registered trademark)" manufactured by Sumitomo 3M Co., Ltd., as well as non-aqueous organic solvents such as dichloromethane and diethyl ether can also be used.

The thickness of the positive electrode mixture compact (in the case of an electrode having a current collector, the thickness of the positive electrode mixture compact per one side of the current collector; the same applies below) is usually 50 μm or more, but from the viewpoint of increasing the capacity of the battery, it is preferably 200 μm or more. In addition, the thickness of the positive electrode mixture compact is usually 3000 μm or less.

In addition, in the case of a positive electrode manufactured by forming a positive electrode mixture layer consisting of a molded positive electrode mixture on a current collector using a positive electrode mixture-containing composition containing a solvent, the thickness of the positive electrode mixture layer is preferably 50 to 1000 μm.

(Negative electrode)
The negative electrode of the flat nonaqueous electrolyte battery has a negative electrode mixture compact containing a negative electrode active material, a lithium sheet, or a lithium alloy sheet.

When the negative electrode is a compact of a negative electrode mixture containing a negative electrode active material, examples of the structure include a compact (such as a pellet) made by molding the negative electrode mixture, and a structure in which a layer (negative electrode mixture layer) made of a compact of the negative electrode mixture is formed on a current collector.

When the negative electrode has a molded body of a negative electrode mixture, examples of the negative electrode active material include carbon materials such as graphite, simple substances containing elements such as Si and Sn, compounds (oxides, etc.) and alloys thereof. Lithium metal and lithium alloys (lithium-aluminum alloy, lithium-indium alloy, etc.) can also be used as the negative electrode active material.

The content of the negative electrode active material in the negative electrode mixture is preferably 10 to 99 mass %.

The negative electrode mixture may contain a conductive additive. Specific examples include the same conductive additives as those exemplified above as those that may be contained in the positive electrode mixture. The content of the conductive additive in the negative electrode mixture is preferably 1 to 10 mass %.

The negative electrode mixture may contain a binder. Specific examples include the same binders as those exemplified above as those that may be contained in the positive electrode mixture. Note that, for example, in the case where the negative electrode mixture contains a sulfide-based solid electrolyte (described in detail below), if good moldability can be ensured in forming a compact of the negative electrode mixture without using a binder, the negative electrode mixture does not need to contain a binder.

When a binder is required in the negative electrode mixture, the content is preferably 15% by mass or less, and more preferably 0.5% by mass or more. On the other hand, when the negative electrode mixture contains a sulfide-based solid electrolyte and thus can be molded without the need for a binder, the content is preferably 0.5% by mass or less, more preferably 0.3% by mass or less, and even more preferably 0% by mass (i.e., no binder is contained).

When the flat nonaqueous electrolyte battery is a solid electrolyte battery, the negative electrode mixture contains a solid electrolyte. Specific examples include the same solid electrolytes as those exemplified above as those that can be contained in the positive electrode mixture. Among the solid electrolytes exemplified above, it is more preferable to use a sulfide-based solid electrolyte, since it has high lithium ion conductivity and also has the function of increasing the moldability of the negative electrode mixture.

The solid electrolyte content in the negative electrode mixture is preferably 4 to 49 mass %.

When a current collector is used for a negative electrode having a molded negative electrode mixture, the current collector can be made of copper or nickel foil, punched metal, mesh, expanded metal, foamed metal; carbon sheet; etc.

The negative electrode mixture compact can be formed, for example, by compressing the negative electrode mixture prepared by mixing the negative electrode active material, and optionally the conductive additive, solid electrolyte, and binder, by pressure molding or the like. In the case of a negative electrode consisting only of a negative electrode mixture compact, it can be manufactured by the above-mentioned method.

In the case of a negative electrode having a current collector, it can be manufactured by bonding the negative electrode mixture formed by the method described above to the current collector by pressing it.

In addition, in the case of a negative electrode having a current collector, a negative electrode mixture-containing composition (paste, slurry, etc.) in which the negative electrode active material, and optionally added conductive additives, solid electrolyte, binder, etc. are dispersed in a solvent can be applied to the current collector, dried, and then pressure-molded, such as by calendaring, as necessary, to form a molded body of the negative electrode mixture (negative electrode mixture layer) on the surface of the current collector.

As the solvent for the negative electrode mixture-containing composition, an organic solvent such as water or NMP can be used. However, when the negative electrode mixture-containing composition also contains a solid electrolyte, it is preferable to select a solvent that is unlikely to deteriorate the solid electrolyte, and it is preferable to use the same solvents as those exemplified above for the positive electrode mixture-containing composition that contains a solid electrolyte.

The thickness of the negative electrode mixture compact (in the case of an electrode having a current collector, the thickness of the negative electrode mixture compact per one side of the current collector; the same applies below) is usually 50 μm or more, but from the viewpoint of increasing the capacity of the battery, it is preferably 200 μm or more. In addition, the thickness of the negative electrode mixture compact is usually 3000 μm or less.

In addition, in the case of a negative electrode manufactured by forming a negative electrode mixture layer consisting of a molded negative electrode mixture on a current collector using a negative electrode mixture-containing composition containing a solvent, the thickness of the negative electrode mixture layer is preferably 50 to 1000 μm.

In the case of a negative electrode having a lithium sheet or a lithium alloy sheet, one consisting of only these sheets or one consisting of these sheets bonded to a current collector is used.

The alloying elements in the lithium alloy include aluminum, lead, bismuth, indium, and gallium, with aluminum and indium being preferred. The proportion of the alloying elements in the lithium alloy (the total proportion when multiple alloying elements are included) is preferably 50 atomic % or less (in this case, the remainder is lithium and inevitable impurities).

In addition, in the case of a negative electrode having a lithium alloy sheet, a laminate is used in which a layer containing an alloying element for forming a lithium alloy is laminated on the surface of a lithium layer (a layer containing lithium) composed of a metallic lithium foil or the like, for example, by pressing the layer, and the laminate is brought into contact with a non-aqueous electrolyte (such as a non-aqueous electrolyte solution) or a solid electrolyte in a battery to form a lithium alloy on the surface of the lithium layer to form a negative electrode. In the case of such a negative electrode, a laminate having a layer containing an alloying element on only one side of the lithium layer may be used, or a laminate having layers containing an alloying element on both sides of the lithium layer may be used. The laminate can be formed, for example, by pressing a metallic lithium foil and a foil composed of an alloying element.

The current collector can also be used when forming a lithium alloy in a battery to form a negative electrode. For example, a laminate having a lithium layer on one side of the negative electrode current collector and a layer containing an alloying element on the side of the lithium layer opposite the negative electrode current collector may be used, or a laminate having lithium layers on both sides of the negative electrode current collector and each lithium layer having a layer containing an alloying element on the side opposite the negative electrode current collector may be used. The negative electrode current collector and the lithium layer (metallic lithium foil) may be laminated by crimping or the like.

The layer containing the alloying elements in the laminate to be used as the negative electrode can be, for example, a foil composed of these alloying elements. The thickness of the layer containing the alloying elements is preferably 1 μm or more, more preferably 3 μm or more, and is preferably 20 μm or less, and more preferably 12 μm or less.

For the lithium layer of the laminate to be used as the negative electrode, for example, metallic lithium foil can be used. The thickness of the lithium layer is preferably 0.1 to 1.5 mm. In addition, the thickness of the sheet for the negative electrode having a lithium or lithium alloy sheet is also preferably 0.1 to 1.5 mm.

In addition, when a negative electrode having a lithium sheet or a lithium alloy sheet has a current collector, the current collector can be the same as the current collectors exemplified above as those usable for a negative electrode having a molded body of a negative electrode mixture.

(Solid electrolyte layer)
When the flat nonaqueous electrolyte battery is a solid electrolyte battery (a solid electrolyte primary battery or a solid electrolyte secondary battery), a solid electrolyte layer is interposed between the positive electrode and the negative electrode.

The solid electrolyte constituting the solid electrolyte layer can be one or more of the various sulfide-based solid electrolytes, hydride-based solid electrolytes, halide-based solid electrolytes, and oxide-based solid electrolytes exemplified above as those usable for the positive electrode. However, in order to improve the battery characteristics, it is preferable to contain a sulfide-based solid electrolyte, and it is more preferable to contain an Argyrodite-type sulfide-based solid electrolyte. It is even more preferable to contain a sulfide-based solid electrolyte in both the positive electrode and the solid electrolyte layer, and in the negative electrode, if the negative electrode is a molded body of a negative electrode mixture containing a solid electrolyte, and it is particularly preferable to contain an Argyrodite-type sulfide-based solid electrolyte.

The solid electrolyte layer may have a porous body such as a resin nonwoven fabric as a support.

The solid electrolyte layer can be formed by compressing the solid electrolyte by pressure molding or the like; or by applying a composition for forming the solid electrolyte layer, which is prepared by dispersing the solid electrolyte in a solvent, onto the substrate, positive electrode, or negative electrode, drying the composition, and, if necessary, performing pressure molding such as pressing.

It is desirable to select a solvent that is unlikely to deteriorate the solid electrolyte for use in the composition for forming the solid electrolyte layer, and it is preferable to use the same solvents as those exemplified above for the positive electrode mixture-containing composition that contains the solid electrolyte.

The thickness of the solid electrolyte layer is preferably 100 to 400 μm.

(Separator)
When the flat nonaqueous electrolyte battery is a battery other than a solid electrolyte battery, the separator interposed between the positive electrode and the negative electrode is preferably one that has sufficient strength and can hold a large amount of nonaqueous electrolyte. From this viewpoint, a microporous film or nonwoven fabric containing polyethylene, polypropylene, or an ethylene-propylene copolymer and having a thickness of 10 to 50 μm and an opening ratio of 30 to 70% is preferred.

(Non-aqueous electrolyte)
In the case where the flat nonaqueous electrolyte battery is a battery other than a solid electrolyte battery, a nonaqueous liquid electrolyte (hereinafter, referred to as a "nonaqueous electrolyte") is usually used as the nonaqueous electrolyte. The nonaqueous electrolyte is obtained by dissolving an electrolyte salt such as a lithium salt in an organic solvent. The organic solvent is not particularly limited, but examples thereof include chain esters such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and methyl propyl carbonate; cyclic esters with high dielectric constants such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate; mixed solvents of chain esters and cyclic esters; and the like. In particular, a mixed solvent of a chain ester and a cyclic ester as the main solvent is suitable.

Examples of electrolyte salts to be dissolved in an organic solvent in preparing a nonaqueous electrolyte include _LiPF6 , LiBF4, _LiAsF6 , LiSbF6, _LiCF3SO3 , _LiC4F9SO3 , _LiCF3CO2 , _{Li2C2F4 (} SO3 _{) 2 , LiCnF2n +} 1SO3 (n≧ ₂ ), LiN _{( RfSO2 )} ( _Rf'SO2 ), LiC( _{RfSO2 ) 3} , _and LiN( _RfOSO2 ) ₂ (wherein Rf and _{Rf '} are fluoroalkyl groups) may be used alone or in combination of two or more. The concentration of the electrolyte salt in the nonaqueous electrolyte is not particularly limited, but is preferably 0.3 mol/L or more, more preferably 0.4 mol/L or more, and is preferably 1.7 mol/L or less, more preferably 1.5 mol/L or less.

In addition to the nonaqueous electrolyte solution, the nonaqueous electrolyte of a flat nonaqueous electrolyte battery can also be a gel electrolyte obtained by gelling the nonaqueous electrolyte solution with a gelling agent such as a polymer.

(Laminated electrode body)
The positive electrode and the negative electrode are stacked with a solid electrolyte layer or a separator interposed therebetween to form a stacked electrode assembly, which is used in the battery.

When forming a laminated electrode body having a solid electrolyte layer, it is preferable to pressure mold the positive electrode, negative electrode, and solid electrolyte layer in a laminated state in order to increase the mechanical strength of the laminated electrode body.

(Exterior body)
The exterior body of the flat nonaqueous electrolyte battery has an exterior can and a sealed can. As described above, in the flat nonaqueous electrolyte battery 1 shown in Fig. 1, the positive electrode can is the exterior can and the negative electrode can is the sealed can, but the negative electrode can may be the exterior can and the positive electrode can may be the sealed can.

As shown in FIG. 1, examples of the exterior body include an exterior can and a sealing can that are crimped together via a gasket, and an exterior can and a sealing can that are bonded together with resin.

The outer can and the sealing can can be made of stainless steel or the like. The gasket can be made of polypropylene, nylon, or the like. If heat resistance is required for the battery's intended use, fluororesins such as tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA), or heat-resistant resins with melting points exceeding 240°C, such as polyphenylene ether (PEE), polysulfone (PSF), polyarylate (PAR), polyethersulfone (PES), polyphenylene sulfide (PPS), and polyetheretherketone (PEEK), can also be used. If the battery is used in an application requiring heat resistance, a glass hermetic seal can be used for the sealing.

The shape of the exterior body of a flat nonaqueous electrolyte battery in a plan view may be circular or polygonal, such as a quadrilateral (square or rectangle). If the exterior body is polygonal, the corners may be curved.

The flat nonaqueous electrolyte battery of the present invention can be used in the same applications as conventionally known flat nonaqueous electrolyte batteries (primary batteries or secondary batteries).

The present invention will be described in detail below based on examples. However, the following examples do not limit the present invention.

Example 1
<Preparation of Positive Electrode>
A positive electrode mixture was prepared by mixing Ag ₂ S (positive electrode active material) and a sulfide-based solid electrolyte (Li ₆ PS ₅ Cl) in a volume ratio of 1: 1. 152 mg of this positive electrode mixture was placed in a powder molding die having a diameter of 7.4 mm and molded at a pressure of 4 tonf/cm ² using a press machine to produce a positive electrode made of a cylindrical positive electrode mixture compact.

<Formation of solid electrolyte layer>
On top of the positive electrode in the powder molding die, 30 mg of the same sulfide-based solid electrolyte as that used for the positive electrode was placed, and molding was performed using a press at a pressure of 1 tonf/ ^cm2 to form a solid electrolyte layer on the positive electrode mixture compact, thereby producing a laminate of the positive electrode and the solid electrolyte.

<Preparation of negative electrode>
A metallic lithium foil having a thickness of 450 μm was cut into a circle to prepare a negative electrode.

<Battery assembly>
The negative electrode was placed on the inner bottom surface of a stainless steel sealed can (negative electrode can) fitted with a polypropylene ring gasket. Next, a laminate of a positive electrode and a solid electrolyte was stacked so that the solid electrolyte layer was on the negative electrode side, and carbon paper (carbon sheet, Toyo Tanso Co., Ltd. "PF-10HP", thickness 100 μm) punched to the same size as the positive electrode was placed on top of it as a conductive layer mainly composed of carbon, and a wave washer (metal member having an elastic part, Misumi Corporation "PACK-WVWS-V5-D7") was placed on top of it, and then a stainless steel exterior can (cathode can) was placed on top of it, and the open end of the exterior can was crimped inward to seal it, forming a laminated electrode body consisting of a positive electrode, a solid electrolyte layer, and a negative electrode, and a flat nonaqueous electrolyte battery (solid electrolyte primary battery) with a diameter of about 9 mm was produced in which a wave washer (metal member having an elastic part) and carbon paper (conductive layer mainly composed of carbon) were placed between the inner surface of the exterior can and the laminated electrode body.

Example 2
A flat nonaqueous electrolyte battery was fabricated in the same manner as in Example 1, except that the metal member having the elastic portion was changed to a leaf spring ("SSRBN8-B" manufactured by Misumi Corporation).

Example 3
A flat nonaqueous electrolyte battery was fabricated in the same manner as in Example 1, except that the metal member having the elastic portion was changed to a wheel stopper (manufactured by Ochiai Corporation, "CSTW-3-SUS").

Comparative Example 1
A flat nonaqueous electrolyte battery was fabricated in the same manner as in Example 1, except that the wave washer was not used.

Comparative Example 2
A flat nonaqueous electrolyte battery was fabricated in the same manner as in Example 1, except that no wave washer was used and stainless steel (SUS) foil (thickness: 10 μm) was used instead of carbon paper.

Comparative Example 3
A flat nonaqueous electrolyte battery was fabricated in the same manner as in Example 1, except that SUS foil (thickness: 10 μm) was used instead of the carbon paper.

The flat nonaqueous electrolyte batteries of Examples 1 to 3 and Comparative Examples 1 to 3 were evaluated as follows:

[Internal resistance measurement]
Five batteries each of Examples 1 to 3 and Comparative Examples 1 to 3 were prepared, and the internal resistance at 20° C. was measured at a frequency of 1 kHz by an AC impedance method, and the average value was calculated as the internal resistance of each battery.

[Discharge capacity measurement]
The batteries of Examples 1 to 3 and Comparative Examples 1 to 3 were discharged at a constant current of 0.1 mA, and the discharge capacity until the battery voltage dropped to 0 V was measured.

The above evaluation results are shown in Table 1 together with the configuration between the positive electrode can and the laminated electrode body. In Table 1, the measurement results of internal resistance and discharge capacity are all shown as relative values with the result of Comparative Example 1 set at 100.

As shown in Table 1, the flat nonaqueous electrolyte batteries of Examples 1 to 3, in which a metal member having an elastic portion and a conductive layer mainly made of carbon were arranged between the positive electrode can and the laminated electrode body in this order from the positive electrode can side, had lower internal resistance and greater discharge capacity than the battery of Comparative Example 1, in which only a conductive layer mainly made of carbon was arranged without using a metal member having an elastic portion.

The battery of Comparative Example 2, which did not use a metal member having an elastic portion and used SUS foil instead of a conductive layer mainly composed of carbon, and the battery of Comparative Example 3, which used SUS foil instead of a conductive layer mainly composed of carbon, had high internal resistance and very small discharge capacity. When these batteries were disassembled after discharge, cracks were found in the positive electrode.

Example 4
A flat nonaqueous electrolyte battery (solid electrolyte primary battery) was produced in the same manner as in Example 1, except that the positive electrode active material was changed to _NiO2 and the amount of the positive electrode mixture used was changed to 141 mg.

Comparative Example 4
A flat nonaqueous electrolyte battery was fabricated in the same manner as in Example 4, except that the wave washer was not used.

The flat nonaqueous electrolyte batteries of Example 4 and Comparative Example 4 were subjected to internal resistance and discharge capacity measurements in the same manner as the battery of Example 1. These results are shown in Table 2 together with the configuration between the positive electrode can and the laminated electrode body. In Table 2, the measurement results of internal resistance and discharge capacity are all shown as relative values with the result of Comparative Example 4 taken as 100.

As shown in Table 2, the flat nonaqueous electrolyte battery of Example 4, in which a metal member having an elastic portion and a conductive layer mainly made of carbon are sequentially arranged from the positive electrode can side between the positive electrode can and the laminated electrode body, had a lower internal resistance and a larger discharge capacity than the battery of Comparative Example 4, in which only a conductive layer mainly made of carbon is arranged without using a metal member having an elastic portion.

REFERENCE SIGNS LIST 1 Flat nonaqueous electrolyte battery 10 Positive electrode 20 Negative electrode 30 Separator or solid electrolyte layer 40 Positive electrode can 50 Negative electrode can 60 Gasket 70 Conductive layer mainly composed of carbon 80 Metal member having elastic portion

Claims (8)

A flat nonaqueous electrolyte battery including a laminated electrode assembly having a positive electrode and a negative electrode housed in an exterior body having a positive electrode can and a negative electrode can,
The positive electrode has a molded body of a positive electrode mixture containing a positive electrode active material,
a conductive layer that is elastically deformable and contains carbon as a main component is disposed on the positive electrode can side of the positive electrode;
the conductive layer containing carbon as a main component is made of a carbon sheet,
a metal member having an elastic portion disposed between the positive electrode can and the conductive layer containing carbon as a main component; A flat nonaqueous electrolyte battery including a laminated electrode assembly having a positive electrode and a negative electrode housed in an exterior body having a positive electrode can and a negative electrode can,
The positive electrode has a molded body of a positive electrode mixture containing a positive electrode active material,
a conductive layer mainly composed of carbon is disposed on the positive electrode can side of the positive electrode;
the conductive layer containing carbon as a main component is formed of a porous carbon sheet made of fibrous carbon,
a metal member having an elastic portion disposed between the positive electrode can and the conductive layer mainly composed of carbon; The flat nonaqueous electrolyte battery according to claim 1 or 2, wherein the exterior body is formed by crimping the positive electrode can and the negative electrode can via a gasket. The flat nonaqueous electrolyte battery according to any one of claims 1 to 3, wherein the negative electrode has a molded body of a negative electrode mixture containing a negative electrode active material, a lithium sheet, or a lithium alloy sheet. The flat nonaqueous electrolyte battery according to claim 4, wherein the positive electrode mixture compact contains a solid electrolyte, the negative electrode is a lithium sheet or a lithium alloy sheet, and a solid electrolyte layer containing a solid electrolyte is disposed between the positive electrode and the negative electrode. The flat nonaqueous electrolyte battery according to claim 5, wherein the solid electrolyte contained in the positive electrode mixture compact and the solid electrolyte contained in the solid electrolyte layer are sulfide-based solid electrolytes. The flat nonaqueous electrolyte battery according to claim 4, wherein the positive electrode mixture compact contains a solid electrolyte, the negative electrode is a negative electrode mixture compact containing a negative electrode active material and a solid electrolyte, and a solid electrolyte layer containing a solid electrolyte is disposed between the positive electrode and the negative electrode. The flat nonaqueous electrolyte battery according to claim 7, wherein the solid electrolyte contained in the positive electrode mixture compact, the solid electrolyte contained in the negative electrode mixture compact, and the solid electrolyte contained in the solid electrolyte layer are sulfide-based solid electrolytes.

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