JP7657576B2 - Positive electrode for all-solid-state battery and all-solid-state battery - Google Patents

Description

The present invention relates to an all-solid-state battery with excellent load characteristics and a positive electrode that can be used to configure the all-solid-state battery.

In recent years, with the development of portable electronic devices such as mobile phones and notebook personal computers, and the practical application of electric vehicles, there is a growing need for small, lightweight batteries with high capacity and high energy density.

Currently, lithium batteries that can meet this demand, particularly lithium ion batteries, use an organic electrolyte solution containing an organic solvent and a lithium salt as the non-aqueous electrolyte.

As devices that use lithium-ion batteries continue to develop, there is a demand for longer life, higher capacity, and higher energy density lithium-ion batteries, as well as a high demand for the reliability of these longer life, higher capacity, and higher energy density lithium-ion batteries.

However, the organic electrolyte used in lithium-ion batteries contains organic solvents, which are flammable substances, and so the organic electrolyte may generate abnormal heat if an abnormality such as a short circuit occurs in the battery. In addition, with the recent trend toward higher energy density in lithium-ion batteries and an increasing amount of organic solvent in the organic electrolyte, there is a demand for even greater reliability in lithium-ion batteries.

In light of the above, all-solid-state lithium batteries (all-solid-state batteries) that do not use organic solvents are attracting attention. All-solid-state batteries use a molded solid electrolyte that does not use organic solvents instead of the conventional organic solvent-based electrolyte, and are highly safe with no risk of abnormal heat generation from the solid electrolyte.

In addition to being highly safe, solid-state batteries are also highly reliable and environmentally resistant, and have a long lifespan, making them promising maintenance-free batteries that can contribute to social development while also continuing to contribute to safety and security. Providing solid-state batteries to society can contribute to the achievement of Goal 12 (Ensure sustainable consumption and production patterns), Goal 3 (Ensure healthy lives and promote well-being for all at all ages), Goal 7 (Ensure access to affordable, reliable, sustainable and modern energy for all), and Goal 11 (Make cities and human settlements inclusive, safe, resilient and sustainable) out of the 17 Sustainable Development Goals (SDGs) established by the United Nations.

In addition, various improvements have been attempted in all-solid-state batteries. For example, Patent Document 1 proposes a technology to increase the utilization rate of active materials in all-solid-state batteries by applying an electrode that uses a mixture of an active material having a specific particle size and a solid electrolyte having a specific particle size in a specific weight ratio.

Patent Document 2 also proposes a technology for reducing the interfacial resistance between the positive electrode active material layer or the negative electrode active material layer and the solid electrolyte layer by setting the ratio of the particle size of the positive electrode active material in the positive electrode active material layer of the positive electrode layer or the particle size of the negative electrode active material in the negative electrode active material layer of the negative electrode layer to the particle size of the solid electrolyte in the solid electrolyte layer adjacent to these layers within a specific range.

Japanese Patent Application Publication No. 8-195219 JP 2016-1596 A

Currently, the range of applications for all-solid-state batteries is expanding rapidly, and they may be used in applications that require discharging at a large current, for example. Therefore, there is a demand to improve the load characteristics to meet this demand.

The present invention was made in consideration of the above circumstances, and its purpose is to provide an all-solid-state battery with excellent load characteristics and a positive electrode capable of forming the all-solid-state battery.

The positive electrode for an all-solid-state battery of the present invention has a positive electrode active material consisting of primary particles, and a molded body of a positive electrode mixture containing a solid electrolyte, the positive electrode active material having a reaction suppression layer on the surface thereof for suppressing a reaction between the positive electrode active material and the solid electrolyte, and the ratio ra/rs of the average particle diameter ra of the positive electrode active material to the average particle diameter rs of the solid electrolyte is 2 or more and 20 or less.

The all-solid-state battery of the present invention has a positive electrode, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode, and is characterized in that the positive electrode is the positive electrode for the all-solid-state battery of the present invention.

The all-solid-state battery of the present invention includes primary batteries (all-solid-state primary batteries) and secondary batteries (all-solid-state secondary batteries).

The present invention provides an all-solid-state battery with excellent load characteristics and a positive electrode that can be used to configure the all-solid-state battery.

FIG. 1 is a cross-sectional view illustrating a schematic diagram of an example of an all-solid-state battery of the present invention. FIG. 2 is a plan view illustrating another example of the all-solid-state battery of the present invention. 3 is a cross-sectional view taken along line II in FIG. 2.

<Cathode for all-solid-state batteries>
The positive electrode for an all-solid-state battery of the present invention has a molded body of a positive electrode mixture containing a positive electrode active material composed of primary particles and a solid electrolyte, the positive electrode active material has a reaction suppression layer on a surface thereof for suppressing a reaction between the positive electrode active material and the solid electrolyte, and a ratio ra/rs of an average particle diameter ra of the positive electrode active material to an average particle diameter rs of the solid electrolyte is 2 or more and 20 or less.

To improve the load characteristics of all-solid-state batteries, it is desirable to enable lithium ions to move more smoothly between the positive electrode active material and the solid electrolyte in the positive electrode.

In the present invention, the positive electrode active material having a reaction suppression layer on its surface for suppressing reaction with the solid electrolyte is contained in the form of primary particles in the positive electrode mixture compact that constitutes the positive electrode, and the ratio of the average particle size of the positive electrode active material to the average particle size of the solid electrolyte is set within a specific range, thereby improving the contact between the positive electrode active material and the solid electrolyte and allowing the smooth movement of lithium ions between the two, thereby improving the load characteristics of the all-solid-state battery.

The positive electrode for the all-solid-state battery of the present invention has a molded body of a positive electrode mixture, and examples thereof include one consisting of only a molded body of a positive electrode mixture, and one having a structure in which a layer (positive electrode mixture layer) consisting of a molded body of a positive electrode mixture is formed on a current collector.

In the case of an all-solid-state battery positive electrode used in an all-solid-state primary battery, the base material of the positive electrode active material (positive electrode active material having a reaction suppression layer on the surface) to be contained in the positive electrode mixture can be the same as the positive electrode active material used in conventionally known non-aqueous electrolyte primary batteries.Specific examples 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.

Furthermore, in the case of an all-solid-state battery positive electrode used in an all-solid-state secondary battery, the base material of the positive electrode active material (positive electrode active material having a reaction suppression layer on its surface) contained in the positive electrode mixture can be the same as the positive electrode active material used in conventionally known non-aqueous electrolyte secondary batteries, that is, the same active material capable of absorbing and releasing Li (lithium) ions. Specifically, there is 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 (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 layered compound represented by Li _1-x Co _1-r M _r O ₂ 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, Ba, Mn, Bi, Ca, F, P, Sr, W, Si, Ta, K, S, Er, and Na, and 0≦x≦1, 0≦r≦0.5); lithium nickel composite oxide represented by Li ₁₊ s-x M _1-r N _r PO ₄ (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) _{; Fs} (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) _, and Li2 _{-xM1 - rNrP2O7} (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.

For the positive electrode of an all-solid-state secondary battery, among the positive electrode active materials exemplified above, the lithium cobalt composite oxide (A) represented by the following general formula (1) is preferably used.

LiCo _1-a-b-c Al _a M ¹ _b M ² _c O ₂ (1)

In the general formula (1), ^M1 is at least one element selected from the group consisting of Mg, Ni, and Na, ^M2 is at least one element selected from the group consisting of Mn, Fe, Cu, Zr, Ti, Bi, Ca, F, P, Sr, W, Ba, Nb, Si, Zn, Mo, V, Sn, Sb, Ta, Ge, Cr, K, S, and Er, and 0<a<0.1, 0<b<0.1, a+b<0.1, and 0≦c.

When the lithium cobalt composite oxide (A) is used as a positive electrode active material for a non-aqueous electrolyte secondary battery using an organic electrolyte, the lithium cobalt composite oxide (A) is a material that increases the internal resistance of the battery due to the action of the additive elements such as Al and ^M1 element contained therein. However, in the case of a non-aqueous electrolyte secondary battery having an organic electrolyte, since the electrolyte that transfers ions between the positive electrode and the negative electrode is liquid (electrolytic solution), the original internal resistance is small, and therefore the increase in internal resistance due to the lithium cobalt composite oxide (A) hardly affects the battery characteristics. On the other hand, in an all-solid-state secondary battery in which the transfer of ions between the positive electrode and the negative electrode is performed by a solid electrolyte, it is expected that the increase in internal resistance due to the action of the positive electrode active material will cause a decrease in battery characteristics such as load characteristics.

However, contrary to such expectations, when the lithium-cobalt composite oxide (A) is used as the positive electrode active material of an all-solid-state secondary battery, it is possible to reduce the internal resistance compared to when, for example, LiCoO ₂ is used as the positive electrode active material, and the load characteristics of the all-solid-state secondary battery can be further improved.

When a battery using LiCoO ₂ as a positive electrode active material is charged, Co expands due to a change in valence. In a battery using an organic electrolyte, even if the volume of the positive electrode active material changes due to this, the electrolyte that transfers ions is liquid, so the contact with the positive electrode active material is not impaired. On the other hand, in an all-solid-state secondary battery, the electrolyte that transfers ions in the positive electrode is solid (solid electrolyte), so that the volume of the positive electrode active material changes due to charging and discharging the battery, resulting in a gap between the solid electrolyte, and the internal resistance of the positive electrode and, ultimately, the internal resistance of the battery increases.

However, in the case of the lithium cobalt composite oxide (A) represented by the general formula (1), even in a charged state, the expansion of Co is suppressed by the action of Al and element M ¹ , so that the expansion amount (volume change amount) of the entire positive electrode active material is small. Therefore, by using a positive electrode for an all-solid-state battery containing the lithium cobalt composite oxide (A) as the positive electrode active material, the contact between the lithium cobalt composite oxide (A) and the solid electrolyte in the positive electrode can be maintained well even during charging and discharging, and the internal resistance can be kept low, so that an all-solid-state secondary battery with better load characteristics can be obtained.

In the lithium cobalt composite oxide (A), Al is an element substituted at the Co site, and ^M1 is an element substituted at the Li site. Both have the effect of reducing the amount of expansion of Co (the amount of expansion of the lithium cobalt composite oxide (A)) during charging.

The lithium cobalt composite oxide (A) may contain at least one element selected from Mg, Ni, and Na as the element ^M1 . Mg is preferred because it has an equivalent ionic radius to the Li that it substitutes and does not cause a change in valence during charging and discharging.

In the lithium cobalt composite oxide (A), from the viewpoint of suppressing the amount of expansion during charging, the amount a of Al is greater than 0 and less than 0.1, the amount b of element ^M1 is greater than 0 and less than 0.1, and a + b is less than 0.1. The amount a of Al is preferably 0.005 or more, and the amount b of element ^M1 is preferably 0.005 or more. Furthermore, the amount a of Al is preferably 0.08 or less, and the amount b of element ^M1 is preferably 0.08 or less.

The lithium cobalt composite oxide (A) may or may not contain the element ^M2 (the amount c may be 0), but if the amount of the element ^M2 is too large, for example, the amount of Co may be reduced, and the capacity of the lithium cobalt composite oxide (A) may be reduced. Therefore, the amount c of the element ^M2 is preferably 0.05 or less.

The positive electrode mixture compact contains the positive electrode active material in the form of primary particles. This improves the contact between the positive electrode active material in the positive electrode mixture compact and the solid electrolyte, improving the load characteristics of the all-solid-state battery.

The positive electrode mixture compact may contain a positive electrode active material existing as a secondary particle together with a positive electrode active material consisting of primary particles. Examples of the positive electrode active material existing as a secondary particle include secondary particles of the various positive electrode active materials exemplified above as materials that can be contained in the positive electrode mixture. However, the proportion of the positive electrode active material existing as a secondary particle in the positive electrode mixture in the total amount of the positive electrode active material is preferably as low as possible, and is preferably 20 mass% or less, and more preferably 10 mass% or less. In addition, the positive electrode active material in the positive electrode mixture may be a positive electrode active material consisting entirely of primary particles. Therefore, the lower limit of the proportion of the positive electrode active material existing as a secondary particle in the total amount of the positive electrode active material is 0 mass%.

As the positive electrode active material made of primary particles, commercially available positive electrode active materials can be used. It is also possible to use positive electrode active materials that contain some secondary particles but are mostly made of primary particles.

The positive electrode active material (positive electrode active material consisting of primary particles) contained in the positive electrode mixture compact 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.

When the positive electrode mixture compact also contains a positive electrode active material that exists as a secondary particle, it is preferable that the positive electrode active material that exists as a secondary particle (the primary particle of the positive electrode active material that constitutes the secondary particle) also has the reaction suppression layer.

The content of the positive electrode active material in the positive electrode mixture is preferably 60 to 95 mass%.

The solid electrolyte to be contained in the positive electrode mixture compact is not particularly limited as long as it has lithium ion conductivity, and examples 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 solid electrolyte content in the positive electrode mixture is preferably 4 to 40 mass %.

When the average particle diameter of the solid electrolyte contained in the compact of the positive electrode mixture is rs (μm) and the average particle diameter of the positive electrode active material consisting of primary particles contained in the compact of the positive electrode mixture is ra (μm), the ratio of ra to rs, ra/rs, is 2 or more and 20 or less. When the value of ra/rs is within the above range, the contact between the positive electrode active material and the solid electrolyte in the compact of the positive electrode mixture is good, and ions can move smoothly between them, so that the resistance value of the positive electrode for the all-solid-state battery can be reduced and the load characteristics of the all-solid-state battery (the all-solid-state battery of the present invention) in which this positive electrode is used can be improved. The value of ra/rs is more preferably 5 or more and more preferably 15 or less.

The average particle size of the solid electrolyte is preferably 0.4 μm or more and 2.5 μm or less.

Furthermore, the average particle diameter of the positive electrode active material consisting of primary particles is preferably 2 μm or more, more preferably 5 μm or more, and is preferably 30 μm or less, more preferably 10 μm or less.

In addition, when the positive electrode mixture compact contains a positive electrode active material that exists in the form of secondary particles, it is preferable that the average particle size of the secondary particles is approximately the same as the average particle size of the positive electrode active material that is made up of primary particles.

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.).

The average particle diameter of the positive electrode active material and the solid electrolyte can also be determined by observing the surface of the positive electrode mixture compact with a scanning electron microscope (SEM) and calculating the average (number average) of all the particle diameter values measured using the SEM scale for a specific number (e.g., 30) of positive electrode active materials and solid electrolytes. The inventors have confirmed that the average particle diameter of the positive electrode active material and the average particle diameter of the solid electrolyte determined by this method are approximately equal to the average particle diameter of the positive electrode active material and the average particle diameter of the solid electrolyte determined using the particle size distribution measuring device.

The molded body of 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 positive electrode active material, conductive Ag is generated during the discharge reaction, so the conductive assistant does not need to be contained. When the molded body of the positive electrode mixture contains a conductive assistant, the content in the positive electrode mixture is preferably 1 to 10 mass%.

The molded body of the positive electrode mixture may or may not contain a resin binder. Examples of the resin binder include fluororesins such as polyvinylidene fluoride (PVDF). However, since the resin binder acts as a resistance component in the molded body of the positive electrode mixture, it is desirable that the amount of the resin binder is as small as possible. Therefore, in the molded body of the positive electrode mixture, it is preferable that the resin binder is not contained, or if it is contained, the content in the positive electrode mixture is 0.5 mass% or less. It is more preferable that the content of the resin binder in the positive electrode mixture is 0.3 mass% or less, and even more preferable that it is 0 mass% (i.e., no resin binder is contained).

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 it together.

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 made 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.

<All-solid-state battery>
The all-solid-state battery of the present invention has a positive electrode, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode, and the positive electrode is the positive electrode for the all-solid-state battery of the present invention.

(Negative electrode)
The negative electrode of the all-solid-state battery can have, for example, a molded body of a negative electrode mixture containing a negative electrode active material and a solid electrolyte, and can be made of only a molded body of a negative electrode mixture, or a structure in which a layer (negative electrode mixture layer) made of a molded body of a negative electrode mixture is formed on a current collector.

When the all-solid-state battery is a primary battery, examples of the negative electrode active material include metallic lithium and lithium alloys (lithium-aluminum alloys).

When the all-solid-state battery is a secondary battery, examples of the negative electrode active material include metallic lithium, lithium alloys (lithium-aluminum alloys), carbon materials such as graphite, pyrolytic carbon, cokes, glassy carbon, fired organic polymer compounds, mesocarbon microbeads, carbon fibers, and activated carbon; alloys containing elements that can be alloyed with lithium, such as Si and Sn; and oxides of Si and Sn.

The content of the negative electrode active material in the negative electrode mixture is preferably 40 to 95 mass %.

A solid electrolyte is contained in the negative electrode mixture compact. Specific examples include the same solid electrolytes as those exemplified above as those that can be contained in the positive electrode mixture compact. 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 %.

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

The negative electrode mixture compact may or may not contain a resin binder. Examples of resin binders include fluororesins such as polyvinylidene fluoride (PVDF). However, since the resin binder acts as a resistance component even in the negative electrode mixture compact, it is desirable that the amount of the resin binder is as small as possible. Therefore, it is preferable that the negative electrode mixture compact does not contain a resin binder, or if it does contain one, the content in the negative electrode mixture is 0.5 mass% or less. It is more preferable that the content of the resin binder in the negative electrode mixture is 0.3 mass% or less, and even more preferable that it is 0 mass% (i.e., no resin binder is contained).

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 solid electrolyte, and further, if necessary, conductive additives and binders, 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, solid electrolyte, and optionally added conductive additives and binders 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 a negative 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.

The negative electrode can be made of a metal foil that acts as the negative electrode active material, or it can be made of a laminate of a metal foil that acts as the negative electrode active material and a current collector.

In the case of a negative electrode having a structure in which a negative electrode active material and a current collector are laminated, the negative electrode can be obtained, for example, by bonding the metal foil and the current collector together by pressure bonding. In this case, the current collector can be the same as the one exemplified above as a current collector that can be used for a negative electrode having a molded body of a negative electrode mixture.

In the case of a negative electrode having a metal foil as the negative electrode active material, examples of the negative electrode active material include metallic lithium and lithium alloys. Examples of alloying elements in lithium alloys include aluminum, lead, bismuth, indium, and gallium, with aluminum and indium being preferred. The proportion of alloying elements in the lithium alloy (the total proportion of alloying elements when multiple types of alloying elements are included) is preferably 50 atomic % or less (in this case, the remainder is lithium and unavoidable impurities).

In the case of a negative electrode having a lithium alloy foil, 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 solid electrolyte in a battery to form a lithium alloy on the surface of the lithium layer, thereby forming 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 may 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 example, metallic lithium foil can be used for the lithium layer of the laminate to be used as the negative electrode. The thickness of the lithium layer is preferably 0.1 to 1.5 mm. In addition, the thickness of the foil for the negative electrode having metallic lithium foil or lithium alloy foil is also preferably 0.1 to 1.5 mm.

(Solid electrolyte layer)
The solid electrolyte constituting the solid electrolyte layer of the all-solid-state battery 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. And, it is even more preferable to contain a sulfide-based solid electrolyte in both the positive electrode and the solid electrolyte layer, and also in the negative electrode when 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.

(Electrode body)
The positive electrode and the negative electrode can be used in a battery in the form of a laminated electrode body in which the positive electrode and the negative electrode are laminated with a solid electrolyte layer interposed therebetween, or in the form of a wound electrode body in which this laminated electrode body is wound.

In addition, when forming the electrode body, it is preferable to pressure mold the positive electrode, negative electrode, and solid electrolyte layer in a stacked state in order to increase the mechanical strength of the electrode body.

(Battery type)
A cross-sectional view showing a schematic example of an all-solid-state battery of the present invention is shown in Fig. 1. In the all-solid-state battery 1 shown in Fig. 1, a positive electrode 10 for the all-solid-state battery of the present invention, a negative electrode 20, and a solid electrolyte layer 30 interposed between the positive electrode 10 and the negative electrode 20 are enclosed in an exterior body formed of an exterior can 40, a sealing can 50, and a resin gasket 60 interposed between them.

The sealing can 50 is fitted into the opening of the outer can 40 via a gasket 60, and the open end of the outer can 40 is tightened inward, so that the gasket 60 comes into contact with the sealing can 50, sealing the opening of the outer can 40 and creating an airtight structure inside the element.

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. Furthermore, if the battery is used in an application requiring heat resistance, a glass hermetic seal can be used for the sealing.

Figures 2 and 3 are diagrams showing schematic diagrams of other examples of the all-solid-state battery of the present invention. Figure 2 is a plan view of the all-solid-state battery, and Figure 3 is a cross-sectional view taken along line I-I in Figure 2.

The all-solid-state battery 100 shown in Figures 2 and 3 contains an electrode body 200 consisting of a positive electrode for the all-solid-state battery of the present invention, a solid electrolyte layer, and a negative electrode in a laminate film exterior body 500 composed of two metal laminate films, and the laminate film exterior body 500 is sealed at its outer periphery by heat-sealing the upper and lower metal laminate films. In Figure 3, in order to avoid cluttering the drawing, the layers constituting the laminate film exterior body 500 and the positive electrode, negative electrode, and separator constituting the electrode body are not shown separately.

The positive electrode of the electrode body 200 is connected to the positive electrode external terminal 300 within the battery 100, and although not shown, the negative electrode of the electrode body 200 is also connected to the negative electrode external terminal 400 within the battery 100. One end of the positive electrode external terminal 300 and the negative electrode external terminal 400 is extended to the outside of the laminate film exterior body 500 so that they can be connected to external devices, etc.

The form of the all-solid-state battery may be one having an exterior body composed of an exterior can, a sealing can, and a gasket as shown in Figure 1, i.e., one generally known as a coin-type battery or button-type battery, or one having an exterior body composed of a resin film or a metal-resin laminate film as shown in Figures 2 and 3, or one having an exterior body made of a metal, bottomed, tubular (cylindrical or rectangular) exterior can and a sealing structure that seals the opening.

The all-solid-state battery of the present invention can be used in the same applications as conventionally known primary and secondary batteries, but since it has a solid electrolyte instead of an organic electrolyte, it has excellent heat resistance and can be preferably used in applications where it is exposed to high temperatures. In addition, the positive electrode for the all-solid-state battery of the present invention can constitute the all-solid-state battery of the present invention.

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 primary particle (positive electrode active material) _{of LiCo0.98Al0.01Mg0.01O2} having an average particle diameter _ra of 5 μm and a layer made _of LiNbO3 on the surface, _a sulfide-based solid electrolyte ( _Li6PS5Cl ) having an argyrodite structure with an average particle diameter rs of _0.6 μm, and acetylene black (conductive assistant) were mixed in a mass ratio of 65:32:3 and thoroughly kneaded to prepare a positive electrode mixture. Next, 75 mg of the positive electrode mixture was placed in a powder molding die with a diameter of 7.5 mm, and pressure molding was performed using a press machine to produce a positive electrode consisting of a cylindrical positive electrode mixture compact. The amount of the layer made of LiNbO ₃ on the surface of LiCo _0.98 Al _0.01 Mg _0.01 O ₂ was 1 part by mass with respect to 100 parts by mass of LiCo _0.98 Al _0.01 Mg _0.01 O ₂ .

<Formation of solid electrolyte layer>
Next, 9.6 mg of the same sulfide-based solid electrolyte as that used in producing the positive electrode was placed on the positive electrode mixture compact in the powder molding die, and pressure molding was performed using a press to form a solid electrolyte layer on the positive electrode mixture compact, thereby obtaining a laminate of the positive electrode and the solid electrolyte layer.

<Preparation of negative electrode>
The negative electrode was prepared by laminating a metallic Li foil and a metallic In foil formed into a cylindrical shape.

<Battery assembly>
The negative electrode was placed on the inner bottom surface of a stainless steel sealed can with a polypropylene ring gasket fitted in, with the metal In foil side facing the inner surface of the sealed can. Next, the laminate of the positive electrode and the solid electrolyte layer was stacked so that the solid electrolyte layer was on the negative electrode side, and then a stainless steel outer can was placed over it. The open end of the outer can was then crimped inward to seal, thereby forming a laminated electrode body consisting of the positive electrode, the solid electrolyte layer, and the negative electrode, and producing an all-solid-state battery with a diameter of approximately 9 mm.

Example 2
A positive electrode made of a positive electrode mixture _compact was produced in the same manner as _in Example _{1 ,} except that the positive electrode active material was changed to primary particles of _{LiCo0.98Al0.01Mg0.01O2} having an average particle diameter ra of _{2 μm} and a layer made of _LiNbO3 on the surface (the amount of the layer made _of LiNbO3 _on the surface was 1 part by mass per ₁₀₀ parts by mass of LiCo0.98Al0.01Mg0.01O2), and the solid electrolyte was changed to _Li6PS5Cl having an average particle diameter rs of 0.9 μm. A solid-state battery was produced in the same manner as in Example 1, except that this positive electrode was used.

Example 3
A positive electrode made of a positive electrode mixture compact was prepared in the same manner as in Example 2, except that the solid electrolyte was changed to Li ₆ PS ₅ Cl having an average particle size rs of 0.4 μm. A solid-state battery was prepared in the same manner as in Example 1, except that this positive electrode was used.

Example 4
A positive electrode made of a positive electrode _{mixture compact} was produced in the same manner as in _{Example 1 ,} except that the positive electrode active material was changed to primary particles of _{LiCo0.98Al0.01Mg0.01O2} having an average particle diameter ra of _{27 μm} and a layer made of LiNbO3 on the surface (the amount of the layer made _of LiNbO3 _on the surface was 1 part by mass per 100 parts by mass of _{LiCo0.98Al0.01Mg0.01O2} ), and the solid electrolyte was changed to _Li6PS5Cl having an average particle diameter rs of 2 μm. A solid-state battery was produced in the same manner as in Example 1, except that this positive electrode was used.

Example 5
A positive electrode made of a positive _{electrode mixture} molded body was prepared in the same manner as in Example ₃ , except that the positive electrode active material was changed to primary particles of _{LiCo0.98Al0.01Mg0.01O2} having an average particle diameter ra of _{8 μm and} a layer made of _LiNbO3 on the _surface (the amount of the layer made of LiNbO3 on the surface was 1 part by mass per 100 parts by mass of _{LiCo0.98Al0.01Mg0.01O2} ). A solid-state battery was prepared in the same manner as in Example 1, except that this positive electrode was used.

Comparative Example 1
A positive electrode made of a positive electrode _mixture molded body was prepared in the same _manner as in _{Example 1 ,} except that the positive electrode active material was changed to primary particles of _{LiCo0.98Al0.01Mg0.01O2} having an average particle diameter ra of _{1 μm and} a layer made of LiNbO3 on the _surface (the amount of the layer made of LiNbO3 on the surface was 1 part by mass per 100 parts by mass of _{LiCo0.98Al0.01Mg0.01O2} ). A solid-state battery was prepared in the same manner as in Example 1, except that this positive electrode was used.

Comparative Example 2
A positive electrode made of a positive electrode _mixture molded body was prepared in the same manner as in Example _{1 ,} except that the positive electrode active material was changed to primary particles of _{LiCo0.98Al0.01Mg0.01O2} having an average particle diameter ra of _{50 μm and} a layer made of _LiNbO3 on the _surface (the amount of the layer made of LiNbO3 on the surface was 1 part by mass per 100 parts by mass of _{LiCo0.98Al0.01Mg0.01O2} ). A solid-state battery was prepared in the same manner as in Example 1, except that this positive electrode was used.

Comparative Example 3
A positive electrode made of a positive electrode mixture compact was prepared in the same manner as in Example 1, except that the solid electrolyte was changed to Li ₆ PS ₅ Cl having an average particle size rs of 0.2 μm. A solid-state battery was prepared in the same manner as in Example 1, except that this positive electrode was used.

Comparative Example 4
A positive electrode made of a positive electrode mixture compact was prepared in the same manner as in Example 1, except that the solid electrolyte was changed to Li ₆ PS ₅ Cl having an average particle size rs of 3 μm. A solid-state battery was prepared in the same manner as in Example 1, except that this positive electrode was used.

Comparative Example 5
A positive electrode made of a positive electrode _{mixture compact was} produced in the same manner as in _{Example 1 ,} except that the positive electrode active material was changed to primary particles of _{LiCo0.98Al0.01Mg0.01O2} having an average particle diameter ra of _{0.3 μm} and a layer made of LiNbO3 on the _surface (the amount of the layer made of LiNbO3 _on the surface was 1 part by mass per ₁₀₀ parts by mass of LiCo0.98Al0.01Mg0.01O2), and the solid electrolyte was changed to _Li6PS5Cl having an average particle diameter rs of 0.3 μm. A solid-state battery was produced in the same manner as in Example 1, except that this positive electrode was used.

Comparative Example 6
A positive electrode made of a positive electrode _{mixture compact} was produced in the same manner as in _{Example 1 ,} except that the positive electrode active material was changed to primary particles of _{LiCo0.98Al0.01Mg0.01O2} having an average particle diameter ra of _{30 μm} and a layer made of LiNbO3 on the _surface (the amount of the layer made of LiNbO3 _on the surface was 1 part by mass per ₁₀₀ parts by mass of LiCo0.98Al0.01Mg0.01O2), and the solid electrolyte was changed to _Li6PS5Cl having an average particle diameter rs of 20 μm. A solid-state battery was produced in the same manner as in Example 1, except that this positive electrode was used.

Comparative Example 7
_A positive electrode made of a positive _electrode mixture compact was prepared in the same manner as in Example 1, except that the positive electrode active material was changed to primary particles of _{LiCo0.98Al0.01Mg0.01O2} having an average particle diameter _ra of ₅ μm (having no layer made of LiNbO3 on the surface). A solid-state battery was prepared in the same manner as in Example 1, except that this positive electrode was used.

Comparative Example 8
A positive electrode made of a positive electrode mixture molded body was _prepared in the _same manner as in _{Example 1 ,} except that the positive electrode active material was changed to secondary particles of _{LiCo0.98Al0.01Mg0.01O2} having an average particle diameter of ₅ μm _and a layer made of LiNbO3 on the _surface (the amount of the layer made of LiNbO3 on the surface was 1 part by mass per ₁₀₀ parts by mass of LiCo0.98Al0.01Mg0.01O2). A solid-state battery was prepared in the same manner as in Example 1, except that this positive electrode was used.

The load characteristics of the solid-state batteries of the examples and comparative examples were evaluated using the following method.

For each of the all-solid-state batteries in the examples and comparative examples, the batteries were charged at a constant current of 0.5 C until the voltage reached 4.0 V, then charged at a constant voltage of 0.02 C until the current reached 0.05 C until the voltage reached 2.6 V, and the initial capacity was measured.

After the initial characteristic evaluation, each battery was charged and discharged under the same conditions as when the initial capacity was measured, except that the current value during discharge was changed to 0.5 C, and the 0.5 C discharge capacity was measured. The 0.5 C discharge capacity of each battery was then divided by the initial capacity to obtain a capacity retention rate, expressed as a percentage, and the load characteristics of each battery were evaluated.

These results are shown in Table 1 together with the composition of the positive electrode active material and solid electrolyte in the positive electrode. Note that the average particle size of the positive electrode active material in Comparative Example 8 is the value of the secondary particles, and in Table 1, this value is listed in the "ra" column, and the ratio of the average particle size of this secondary particle to the average particle size of the solid electrolyte is listed in the "ra/rs" column.

As shown in Table 1, the all-solid-state batteries of Examples 1 to 5, which use a positive electrode active material made of primary particles having a reaction suppression layer on the surface and have a positive electrode made of a positive electrode mixture molded body with an appropriate ratio ra/rs of the average particle diameter ra of the positive electrode active material to the average particle diameter rs of the solid electrolyte, had a high capacity retention rate during the load characteristic evaluation and excellent load characteristics.

In contrast, the batteries of Comparative Examples 1 to 6, which have a positive electrode made of a positive electrode mixture molded body in which the positive electrode active material and solid electrolyte are combined so that the ra/rs value is inappropriate, the battery of Comparative Example 7, which has a positive electrode made of a positive electrode mixture molded body using a positive electrode active material that does not have a reaction suppression layer on its surface, and the battery of Comparative Example 8, which has a positive electrode made of a positive electrode mixture molded body using a positive electrode active material that exists as secondary particles, had lower capacity retention rates during the load characteristic evaluation and inferior load characteristics compared to the batteries of the Examples.

Reference Signs List 1, 100 All-solid-state secondary battery 10 Positive electrode 20 Negative electrode 30 Solid electrolyte layer 40 Outer can 50 Sealing can 60 Gasket 200 Electrode body 300 Positive electrode external terminal 400 Negative electrode external terminal 500 Laminate film outer case

Claims (5)

The battery has a positive electrode active material made of primary particles and a positive electrode mixture molded body containing a solid electrolyte,
the positive electrode active material has a reaction suppression layer on a surface thereof for suppressing a reaction between the positive electrode active material and the solid electrolyte;
a ratio ra/rs of an average particle diameter ra of the positive electrode active material to an average particle diameter rs of the solid electrolyte is 2 or more and 20 or less (excluding the case where it is 4.25);
The positive electrode for an all-solid-state battery, wherein the ra is 2 to 30 μm . The positive electrode for an all-solid-state battery according to claim 1, wherein the solid electrolyte has an average particle size rs of 0.4 to 2.5 μm. 3. The positive electrode for an all-solid-state battery according to claim 1 , wherein the reaction suppression layer contains Nb oxide. The positive electrode active material is represented by the following general formula (1):
LiCo _1-a-b-c Al _a M ¹ _b M ² _c O ₂ (1)
The positive electrode ^for an all-solid-state battery according to any one of claims 1 to 3, containing a lithium-cobalt composite oxide (A) represented by the following general formula (1): (in the general formula (1), M ¹ is at least one element selected from the group consisting of Mg, Ni, and Na, M 2 is at least one element selected from the group consisting of Mn, Fe, Cu, Zr, Ti, Bi, Ca, F, P, Sr, W, Ba, Nb, Si, Zn, Mo, V, Sn, Sb, Ta, Ge, Cr, K, S, and Er, and 0<a<0.1, 0<b<0.1, a+b< 0.1 , and 0≦c). An all-solid-state battery having a positive electrode, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode,
An all-solid-state battery comprising the positive electrode for an all-solid-state battery according to any one of claims 1 to 4 as the positive electrode.

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