JP2021089814A - All-solid battery - Google Patents

Abstract

To provide an all-solid battery with high charge/discharge efficiency.SOLUTION: An all-solid battery using precipitation-dissolution reaction of metallic lithium as reaction of a negative electrode includes a negative electrode current collector, a Li storage layer containing a spherical carbon material and a resin, a metal M layer containing a metal M capable of alloying with lithium, a solid electrolyte layer, and a positive electrode layer in this order. The thickness of the metal M layer is 30 nm or more and 5 μm or less.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to an all-solid-state battery.

With the rapid spread of information-related devices such as personal computers, video cameras and mobile phones, and communication devices in recent years, the development of batteries used as their power sources has been emphasized. In addition, the automobile industry and the like are also developing high-output and high-capacity batteries for electric vehicles or hybrid vehicles.
Among the batteries, the lithium metal secondary battery is attracting attention because it uses lithium, which has the highest ionization tendency among metals, as the negative electrode, so that the potential difference from the positive electrode is large and a high output voltage can be obtained.
Further, the all-solid-state battery is attracting attention in that a solid electrolyte is used instead of an electrolytic solution containing an organic solvent as an electrolyte interposed between the positive electrode and the negative electrode.

In the field of lithium metal secondary batteries, the occurrence of short circuits due to dendrites is known. The short circuit occurs when lithium deposited on the negative electrode layer during charging grows in the direction of the positive electrode layer and physically contacts the negative electrode layer and the positive electrode layer. Development is underway to prevent short circuits caused by the growth of dendrites.

Patent Document 1 discloses a lithium solid-state battery having a Li-precipitated negative electrode having a Li storage layer made of a carbon material and a resin between a negative electrode current collector and a solid electrolyte layer.

JP-A-2019-033053

The lithium solid-state battery described in Patent Document 1 is provided with a Li storage layer made of a carbon material and a resin between the negative electrode current collector and the solid electrolyte layer to suppress a short circuit and improve the reversible capacity of the lithium solid-state battery. There was room for further improvement in charge / discharge efficiency.
An object of the present disclosure is to provide an all-solid-state battery having high charge / discharge efficiency in view of the above circumstances.

The present disclosure is an all-solid-state battery that utilizes a precipitation-dissolution reaction of metallic lithium as a reaction of the negative electrode.
It has a negative electrode current collector, a Li storage layer containing a spherical carbon material and a resin, a metal M layer containing a metal M capable of alloying with lithium, a solid electrolyte layer, and a positive electrode layer in this order.
Provided is an all-solid-state battery characterized in that the thickness of the metal M layer is 30 nm or more and 5 μm or less.

The present disclosure can provide an all-solid-state battery having high charge / discharge efficiency.

It is sectional drawing which shows an example of the all-solid-state battery of this disclosure.

The present disclosure is an all-solid-state battery that utilizes a precipitation-dissolution reaction of metallic lithium as a reaction of the negative electrode.
It has a negative electrode current collector, a Li storage layer containing a spherical carbon material and a resin, a metal M layer containing a metal M capable of alloying with lithium, a solid electrolyte layer, and a positive electrode layer in this order.
Provided is an all-solid-state battery characterized in that the thickness of the metal M layer is 30 nm or more and 5 μm or less.

In the present disclosure, the lithium metal secondary battery means a battery in which at least one of metallic lithium and a lithium alloy is used as the negative electrode active material, and the precipitation-dissolution reaction of metallic lithium is used as the reaction of the negative electrode. Further, in the present disclosure, the negative electrode means one including a negative electrode layer.
In the present disclosure, the fully charged state of the all-solid-state battery means the time when the charge state value (SOC: State of Charge) of the all-solid-state battery is 100%. SOC indicates the ratio of the charge capacity to the full charge capacity of the battery, and the full charge capacity is 100% SOC.
The SOC may be estimated from, for example, the open circuit voltage (OCV: Open Circuit Voltage) of the all-solid-state battery.

FIG. 1 is a schematic cross-sectional view showing an example of the all-solid-state battery of the present disclosure.
As shown in FIG. 1, the all-solid-state battery 100 includes a negative electrode current collector 11, a solid electrolyte layer 12, a positive electrode layer 13, and a positive electrode current collector 14 in this order, and the negative electrode current collector 11 and the solid electrolyte layer 12 are provided. In between, a Li storage layer 15 and a metal M layer 16 containing a metal M capable of alloying with Li are provided in this order from the negative electrode current collector 11 side. The metal M layer 16 may be a Li—M alloy layer containing an alloy of lithium and the metal M when fully charged after the initial charge. Although the negative electrode layer is not shown in FIG. 1, in the present disclosure, a negative electrode layer may be present between the negative electrode current collector 11 and the solid electrolyte layer 12. If the negative electrode layer is between the negative electrode current collector 11 and the solid electrolyte layer 12, it is between the negative electrode current collector 11 and the Li storage layer 15, between the Li storage layer 15 and the metal M layer 16, and between the negative electrode current collector 11 and the solid electrolyte layer 12. , May be present at at least one position between the metal M layer 16 and the solid electrolyte layer 12. Further, when the negative electrode layer is made of metallic lithium, the negative electrode layer may be present in the all-solid-state battery 100 when fully charged, and the negative electrode layer is melted in the all-solid-state battery 100 before the first charge or after the complete discharge. May have disappeared.

[Negative electrode current collector]
The material of the negative electrode current collector may be a material that does not alloy with Li, and examples thereof include SUS, copper, and nickel. Examples of the form of the negative electrode current collector include a foil shape and a plate shape. The plan view shape of the negative electrode current collector is not particularly limited, and examples thereof include a circular shape, an elliptical shape, a rectangular shape, and an arbitrary polygonal shape. The thickness of the negative electrode current collector varies depending on the shape, but may be, for example, in the range of 1 μm to 50 μm and may be in the range of 5 μm to 20 μm.

[Li occlusion layer]
The Li occlusion layer is a layer of a mixture containing a spherical carbon material and a resin, and is a layer arranged between a negative electrode current collector and a solid electrolyte layer.
Examples of the spherical carbon material include Ketjen Black (KB) and the like.
Examples of the resin include acrylonitrile-butadiene rubber (ABR), butadiene rubber (BR), polyvinylidene fluoride (PVdF), styrene-butadiene rubber (SBR), and the like.
The mass ratio of the spherical carbon material and the resin in the Li storage layer is not particularly limited, but the mass ratio when the total mass of these two types of materials is 100% by mass is the spherical carbon material: resin = 10: 90 to It may be 90:10, or may be spherical carbon material: resin = 25:75 to 75:25.
Examples of the method for producing a mixture composed of a spherical carbon material and a resin include manual mixing using a mortar and a pestle, a homogenizer, and mechanical milling. The mechanical milling may be a dry mechanical milling or a wet mechanical milling.
The mechanical milling is not particularly limited as long as it is a method of mixing the spherical carbon material and the resin while applying mechanical energy, and examples thereof include a ball mill, a vibration mill, a turbo mill, a mechanofusion, and a disc mill. It can be a ball mill, especially a planetary ball mill.
Examples of the liquid used when preparing the mixture using the homogenizer include aprotic liquids such as polar aprotic liquids and non-polar aprotic liquids.
The thickness of the Li storage layer is not particularly limited, but may be 3 to 20 μm.

[Metal M layer]
The metal M layer contains a metal M that can be alloyed with Li, and is a layer arranged between the Li storage layer and the solid electrolyte layer. Examples of the metal M that can be alloyed with Li include at least one metal selected from the group consisting of Mg, Au, Al, and Sn, and may be Mg (metal magnesium). Only one kind of metal M may be contained in the metal M layer, two or more kinds of metal M may be contained, or two or more kinds of metal M may be alloyed and contained. As long as the metal M layer contains the metal M as a main component, other metals may be contained. In the present disclosure, the principal component means a component contained in an amount of 50% by mass or more when the total mass of the layer is 100% by mass.
Since the thickness of the metal M layer is 30 nm to 5 μm, the charge / discharge efficiency of the all-solid-state battery can be increased and the energy density can be increased.

The method for forming the metal M layer is not particularly limited, but the metal M layer may be formed by vacuum-depositing the metal M on at least one surface of the solid electrolyte layer or the Li storage layer using an electron beam vapor deposition apparatus.

[Li-M alloy layer]
After the initial charge of the all-solid-state battery, the metal M layer may be a Li-M alloy layer containing a Li-M alloy in which the metal M reacts with lithium ions by the initial charge. Further, the Li-M alloy layer may be formed by vacuum-depositing the Li-M alloy on at least one surface of the solid electrolyte layer or the Li storage layer using an electron beam vapor deposition apparatus.
The element ratio of the lithium element in the Li—M alloy may be 30.0 atomic% or more and 99.8 atomic% or less when the all-solid-state battery is fully charged. The element ratio in the alloy can be calculated by analyzing the alloy by inductively coupled plasma (ICP) analysis or X-ray photoelectron spectroscopy (XPS). As a method for calculating the element ratio of the alloy, for example, in a fully charged all-solid-state battery, the Li-M alloy layer is taken out from the all-solid-state battery, the Li-M alloy layer is subjected to ICP analysis, and the Li-M alloy layer is calculated. Examples thereof include a method of calculating the element ratio of the alloy contained in.

[Negative electrode layer]
In the present disclosure, for example, an all-solid-state battery in which a negative electrode layer is provided between the Li storage layer and the negative electrode current collector at the time of assembly, or a negative electrode layer is not provided between the Li storage layer and the negative electrode current collector at the time of assembly, and then An all-solid-state battery may be provided with a negative electrode layer formed by precipitating metallic lithium as a negative electrode active material by charging the all-solid-state battery. Further, after the initial charging, the metallic lithium precipitated between the negative electrode current collector and the solid electrolyte layer is used as the negative electrode active material. Further, the Li-M alloy layer may function as a negative electrode layer.
The negative electrode layer contains a negative electrode active material.
Examples of the negative electrode active material include metallic lithium (Li) and lithium alloys, and examples of the lithium alloy include Li-Au, Li-Mg, Li-Sn, Li-Si, Li-Al, Li-B, and Li-. C, Li-Ca, Li-Ga, Li-Ge, Li-As, Li-Se, Li-Ru, Li-Rh, Li-Pd, Li-Ag, Li-Cd, Li-In, Li-Sb, Examples thereof include Li-Ir, Li-Pt, Li-Hg, Li-Pb, Li-Bi, Li-Zn, Li-Tl, Li-Te, and Li-At. As long as the negative electrode layer contains metallic lithium or a lithium alloy as the main component of the negative electrode active material, a conventionally known negative electrode active material may be contained.
The thickness of the negative electrode layer is not particularly limited, but may be 30 nm or more and 5000 nm or less.

[Solid electrolyte layer]
The solid electrolyte layer contains at least a solid electrolyte.
As the solid electrolyte contained in the solid electrolyte layer, a known solid electrolyte that can be used in an all-solid-state battery can be appropriately used, and examples thereof include an oxide-based solid electrolyte and a sulfide-based solid electrolyte.
The sulfide-based solid electrolyte, for _{example, Li 2 S-P 2 S} 5, Li 2 S-SiS 2, LiX-Li 2 S-SiS 2, LiX-Li 2 S-P 2 S 5, LiX-Li 2 Examples thereof include O-Li _{2 SP 2} S ₅ , LiX-Li ₂ S-P ₂ O ₅ , LiX-Li ₃ PO _4- P ₂ S ₅ , and Li ₃ PS _4. The above description of "Li ₂ SP ₂ S ₅ " means a material made of a raw material composition containing _{Li 2} S and P ₂ S _{5, and the same applies to other descriptions.} Further, "X" of the above LiX indicates a halogen element. The raw material composition containing LiX may contain one or more LiX. When two or more types of LiX are contained, the mixing ratio of the two or more types is not particularly limited.
The molar ratio of each element in the sulfide-based solid electrolyte can be controlled by adjusting the content of each element in the raw material. Further, the molar ratio and composition of each element in the sulfide-based solid electrolyte can be measured by, for example, ICP emission spectrometry.

The sulfide-based solid electrolyte may be sulfide glass, crystallized sulfide glass (glass ceramics), or a crystalline material obtained by solid-phase reaction treatment on the raw material composition. ..
The crystal state of the sulfide-based solid electrolyte can be confirmed, for example, by performing powder X-ray diffraction measurement of the sulfide-based solid electrolyte using CuKα rays.

Sulfide glass can be obtained by amorphizing a raw material composition (eg, _{a mixture of Li 2} S and P ₂ S _5). Examples of the amorphous treatment include mechanical milling.

Glass ceramics can be obtained, for example, by heat-treating sulfide glass.
The heat treatment temperature may be higher than the crystallization temperature (Tc) observed by the thermal analysis measurement of the sulfide glass, and is usually 195 ° C. or higher. On the other hand, the upper limit of the heat treatment temperature is not particularly limited.
The crystallization temperature (Tc) of sulfide glass can be measured by differential thermal analysis (DTA).
The heat treatment time is not particularly limited as long as the desired degree of crystallinity of the glass ceramic can be obtained, but is, for example, in the range of 1 minute to 24 hours, and in particular, in the range of 1 minute to 10 hours. Can be mentioned.
The method of heat treatment is not particularly limited, and examples thereof include a method using a firing furnace.

Examples of the oxide-based solid electrolyte include Li _6.25 La ₃ Zr ₂ Al _0.25 O ₁₂ , Li ₃ PO ₄ , and Li _{3 + x} PO _4-x N _x (1 ≦ x ≦ 3).

The shape of the solid electrolyte may be particulate from the viewpoint of good handleability.
The average particle size (D50) of the particles of the solid electrolyte is not particularly limited, but the lower limit may be 0.5 μm or more, and the upper limit may be 2 μm or less.

In the present disclosure, the average particle size of the particles is a volume-based median size (D50) value measured by laser diffraction / scattering type particle size distribution measurement, unless otherwise specified. Further, in the present disclosure, the median diameter (D50) is a diameter (volume average diameter) at which the cumulative volume of the particles is half (50%) of the total volume when the particles are arranged in ascending order of particle size.

As the solid electrolyte, one kind alone or two or more kinds can be used. When two or more kinds of solid electrolytes are used, two or more kinds of solid electrolytes may be mixed, or two or more layers of each solid electrolyte may be formed to form a multilayer structure.
The ratio of the solid electrolyte in the solid electrolyte layer is not particularly limited, but may be, for example, 50% by mass or more, 60% by mass or more and 100% by mass or less, and 70% by mass or more and 100% by mass. It may be in the range of mass% or less, or may be 100 mass%.

The solid electrolyte layer may contain a binder from the viewpoint of exhibiting plasticity and the like. As such a binder, a material or the like exemplified as a resin used for the Li storage layer can be exemplified. However, in order to facilitate high output, it is contained in the solid electrolyte layer from the viewpoint of preventing excessive aggregation of the solid electrolyte and enabling the formation of a solid electrolyte layer having a uniformly dispersed solid electrolyte. The binder may be 5% by mass or less.

The thickness of the solid electrolyte layer is not particularly limited, and is usually 0.1 μm or more and 1 mm or less.
Examples of the method for forming the solid electrolyte layer include a method of pressure molding a powder of a solid electrolyte material containing a solid electrolyte and, if necessary, other components. When the powder of the solid electrolyte material is pressure-molded, a press pressure of about 1 MPa or more and 600 MPa or less is usually applied.
The pressurizing method is not particularly limited, and examples thereof include the pressurizing method exemplified in the formation of the positive electrode layer described later.

[Positive layer]
The positive electrode layer contains a positive electrode active material, and may contain a solid electrolyte, a conductive material, a binder, and the like as optional components.

The type of positive electrode active material is not particularly limited, and any material that can be used as an active material for an all-solid-state battery can be used. When the all-solid-state battery is an all-solid-state lithium metal secondary battery, the positive electrode active material is, for example, metallic lithium (Li), lithium alloy, LiCoO ₂ , LiNi _x Co _1-x O ₂ (0 <x <1), LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiMnO ₂ , dissimilar element substituted Li-Mn spinel (eg LiMn _1.5 Ni _0.5 O ₄ , LiMn _1.5 Al _0.5 O ₄ , LiMn _1.5 Mg _0.5 O ₄ , LiMn _1.5 Co _0.5 O ₄ , Limn _1.5 Fe _0.5 O ₄ , Limn _1.5 Zn _0.5 O ₄ etc.), Lithium titanate (Limn 1.5 Zn 0.5 O 4 etc.), Lithium titanate ( For example, Li ₄ Ti ₅ O ₁₂ ), lithium metal phosphate (eg LiFePO ₄ , LiMnPO ₄ , LiCoPO ₄ , and _{LiNiPO 4,} etc.), _{lithium compounds such as LiCoN, Li 2} SiO ₃ , and Li ₄ SiO ₄ , transition metal oxidation. (Eg V ₂ O ₅ and MoO _3, etc.), TiS ₂ , Si, SiO ₂ , and lithium-storing metal-to-metal compounds (eg Mg ₂ Sn, Mg ₂ Ge, Mg ₂ Sb, Cu ₃ Sb, etc.) Can be mentioned. Examples of the lithium alloy include lithium alloys exemplified as lithium alloys used for the negative electrode active material.
The shape of the positive electrode active material is not particularly limited, but may be in the form of particles.
A coat layer containing a Li ion conductive oxide may be formed on the surface of the positive electrode active material. This is because the reaction between the positive electrode active material and the solid electrolyte can be suppressed.
Examples of the Li ion conductive oxide include LiNbO ₃ , Li ₄ Ti ₅ O ₁₂ , Li ₃ PO _{4, and the} like. The thickness of the coat layer is, for example, 0.1 nm or more, and may be 1 nm or more. On the other hand, the thickness of the coat layer is, for example, 100 nm or less, and may be 20 nm or less. The coverage of the coat layer on the surface of the positive electrode active material is, for example, 70% or more, and may be 90% or more.

As the solid electrolyte, a solid electrolyte that can be contained in the above-mentioned solid electrolyte layer can be exemplified.
The content of the solid electrolyte in the positive electrode layer is not particularly limited, but may be in the range of, for example, 1% by mass to 80% by mass when the total mass of the positive electrode layer is 100% by mass.

As the conductive material, a known material can be used, and examples thereof include a carbon material and metal particles. Examples of the carbon material include at least one selected from the group consisting of carbon black such as acetylene black and furnace black, VGCF, carbon nanotubes, and carbon nanofibers. Among them, from the viewpoint of electron conductivity, It may be at least one selected from the group consisting of VGCF, carbon nanotubes, and carbon nanofibers. Examples of the metal particles include particles such as Ni, Cu, Fe, and SUS.
The content of the conductive material in the positive electrode layer is not particularly limited.

As the binder, a material or the like exemplified as a resin used for the Li storage layer can be exemplified. The content of the binder in the positive electrode layer is not particularly limited.

The thickness of the positive electrode layer is not particularly limited.

The positive electrode layer can be formed by a conventionally known method.
For example, a positive electrode active material and, if necessary, other components are put into a solvent and stirred to prepare a slurry for the positive electrode layer, and the slurry for the positive electrode layer is used on one surface of a support such as a positive electrode current collector. A positive electrode layer is obtained by applying it on top and drying it.
Examples of the solvent include butyl acetate, butyl butyrate, heptane, N-methyl-2-pyrrolidone and the like.
The method of applying the positive electrode layer slurry on one surface of a support such as a positive electrode current collector is not particularly limited, and is a doctor blade method, a metal mask printing method, an electrostatic coating method, a dip coating method, a spray coating method, and a roll. Examples include a coating method, a gravure coating method, and a screen printing method.
As the support, one having self-supporting property can be appropriately selected and used, and is not particularly limited, and for example, metal foils such as Cu and Al can be used.

Further, as another method of forming the positive electrode layer, the positive electrode layer may be formed by pressure molding a powder of the positive electrode mixture containing the positive electrode active material and, if necessary, other components. When the powder of the positive electrode mixture is pressure-molded, a press pressure of about 1 MPa or more and 600 MPa or less is usually applied.
The pressurizing method is not particularly limited, and examples thereof include a method of applying pressure using a flat plate press, a roll press, or the like.

[Positive current collector]
An all-solid-state battery usually has a positive electrode current collector that collects electricity from the positive electrode layer.
As the positive electrode current collector, known metals, carbon, and the like that can be used as current collectors for all-solid-state batteries can be used. Such metals include one or more elements selected from the group consisting of Cu, Ni, Al, V, Au, Pt, Mg, Fe, Ti, Co, Cr, Zn, Ge, and In. Metallic materials can be exemplified.
The form of the positive electrode current collector is not particularly limited, and various forms such as a foil shape and a mesh shape can be used.

The all-solid-state battery includes, if necessary, an exterior body that houses a positive electrode layer, a negative electrode layer, a solid electrolyte layer, and the like.
The material of the exterior body is not particularly limited as long as it is stable to the electrolyte, and examples thereof include resins such as polypropylene, polyethylene, and acrylic resin.

The all-solid-state battery may be a primary battery or a secondary battery, and may be a secondary battery. This is because it can be charged and discharged repeatedly and is useful as an in-vehicle battery, for example. Further, the all-solid-state battery may be an all-solid-state lithium metal secondary battery.
Examples of the shape of the all-solid-state battery include a coin type, a laminated type, a cylindrical type, and a square type.

In the method for manufacturing an all-solid-state battery of the present disclosure, for example, first, a solid electrolyte layer is formed by pressure molding a powder of a solid electrolyte material. Then, the positive electrode layer is obtained by pressure molding the powder of the positive electrode mixture containing the positive electrode active material containing the lithium element on one surface of the solid electrolyte layer. After that, a slurry containing the Li storage layer material is applied on one surface of the negative electrode current collector and dried to form a Li storage layer, and further, metal M is vacuum-deposited on one surface of the Li storage layer to form the metal M layer. Negative electrode formed to obtain a negative electrode current collector-Li storage layer-metal M layer laminate, and the negative electrode so that the metal M layer is in contact with the solid electrolyte layer on the surface opposite to the surface on which the positive electrode layer of the solid electrolyte layer is formed. A collector-Li storage layer-metal M layer laminate is attached. Then, if necessary, the positive electrode current collector may be mounted on the surface of the positive electrode layer opposite to the solid electrolyte layer to form the all-solid-state battery of the present disclosure.
In this case, the press pressure for pressure molding the powder of the solid electrolyte material and the powder of the positive electrode mixture is usually about 1 MPa or more and 600 MPa or less.
The pressurizing method is not particularly limited, and examples thereof include the pressurizing method exemplified in the formation of the positive electrode layer.

(Example 1)
[Preparation of Li storage layer]
Weigh KB as a spherical carbon material and PVDF as a resin so that the mass ratio is 75:25, mix by hand, add heptane, and mix for 3 minutes using a homogenizer (manufactured by SMT Co., Ltd., UH-50). A Li storage layer material, which is a material for the Li storage layer, was obtained.
A Cu foil was prepared as a negative electrode current collector, and a Li storage layer material was applied onto one surface of the Cu foil and dried to form a Li storage layer on one surface of the Cu foil. The thickness of the Li occlusion layer was 20 μm.

[Preparation of metal M layer]
Metal Mg is formed as metal M on one surface of the Li storage layer using a vacuum vapor deposition apparatus, a metal Mg layer is formed on one surface of the Li storage layer, and a negative electrode current collector-Li storage layer-metal Mg layer. A laminate was obtained. The thickness of the metal Mg layer was 30 nm.

[Preparation of positive electrode mixture]
_{Particles of LiNi 1/3} Co _1/3 Mn _1/3 O ₂ (manufactured by Nichia Corporation) were used as the positive electrode active material. The particles of the positive electrode active material are subjected to surface treatment of _{LiNbO 3 in advance.} This positive electrode active material, VGCF (manufactured by Showa Denko Co., Ltd.) and sulfide-based solid electrolyte (Li _{2 SP 2} S _5- based material containing LiBr and LiI) as a conductive material are used in a mass ratio of 85.3: 1.3: Weighed to 13.4, and the mixture was used as a positive electrode mixture.

[Making all-solid-state batteries]
Prepare 101.7 mg of powder of sulfide-based solid electrolyte (Li _{2 SP 2} S _5- based material containing LiBr and LiI) in a ceramic mold (cross-sectional area: 1 cm ^{2, using a cylindrical container).} Press molding was performed at a pressure of 1 ton / cm ^{2 to obtain a solid electrolyte layer.}
To one side of the solid electrolyte layer, 31.3 mg of the above positive electrode mixture was added and pressed at 6 ton / cm ² to form a positive electrode layer.
A negative electrode current collector-Li storage layer-metal Mg layer laminate is placed on the surface of the solid electrolyte layer opposite to the positive electrode layer so that the metal Mg layer is in contact with the solid electrolyte layer, and pressed ^{at 1 ton / cm 2.} This made it a dust cell.
By arranging the positive electrode current collector (aluminum foil) on the positive electrode layer side of the dust cell and restraining it, the all-solid-state lithium metal secondary battery of Example 1 was obtained. All the operations using the sulfide-based solid electrolyte were performed in a glove box in a dry Ar atmosphere.

(Example 2)
An all-solid-state lithium metal secondary battery was obtained in the same manner as in Example 1 except that the thickness of the metal Mg layer was 5 μm.

(Example 3)
An all-solid-state lithium metal secondary battery was obtained in the same manner as in Example 1 except that the thickness of the Li storage layer was 3 μm and the thickness of the metal Mg layer was 5 μm.

(Comparative Example 1)
An all-solid-state lithium metal secondary battery was obtained in the same manner as in Example 1 except that the Li storage layer and the metal Mg layer were not formed.

(Comparative Example 2)
An all-solid-state lithium metal secondary battery was obtained in the same manner as in Example 1 except that the metal Mg layer was not formed on one surface of the Li storage layer.

(Comparative Example 3)
An all-solid-state lithium metal secondary battery was obtained in the same manner as in Example 1 except that a metal Mg layer having a thickness of 100 nm was formed on one surface of a Cu foil without forming a Li storage layer.

[Evaluation]
(Charge / discharge measurement)
Using the all-solid-state lithium metal secondary battery obtained in Example 1, charge / discharge measurement was performed after leaving the battery in a constant temperature bath at 60 ° C. for 3 hours in advance. As measurement conditions, the battery is charged at a constant current (CC) at 60 ° C. and a current density of 8.7 mA / cm ² (rate: 2C), and when the charging capacity reaches 4.35 mAh / cm ² , charging is completed and the battery is used for 10 minutes. I paused. Then, CC discharge was performed at 60 ° C. and a current density of 0.435 mA / cm ² (rate: 0.1 C), and when the lower limit voltage reached 3.0 V, the discharge was terminated.
From the discharge capacity and charge capacity of the all-solid-state lithium metal secondary battery obtained in Example 1, the charge / discharge efficiency was calculated from the following formula.
Charge / discharge efficiency (%) = (discharge capacity / charge capacity) x 100
The charge / discharge tests were also performed on the all-solid-state lithium metal secondary batteries obtained in Examples 2 to 3 and Comparative Examples 1 to 3 in the same manner as in the all-solid-state lithium metal secondary battery of Example 1, and the charge / discharge efficiencies were obtained. Asked.
The results are shown in Table 1.

[Evaluation results]
The charge / discharge efficiency is the ratio of the discharge capacity to the charge capacity, and if a short circuit occurs or the movement of Li ions is hindered, the charge / discharge efficiency becomes low.
The all-solid lithium metal secondary batteries of Examples 1 to 3 having both a Li storage layer containing KB and a metal Mg layer are more than the all-solid lithium metal secondary batteries of Comparative Examples 1 and 3 having no Li storage layer. The charge / discharge efficiency was high. It is considered that this is because the occurrence of the short circuit due to the lithium dendrite could be suppressed by having the Li storage layer.
Further, the all-solid-state lithium metal secondary batteries of Examples 1 to 3 have a Li storage layer containing KB, but have a charge / discharge efficiency higher than that of the all-solid-state lithium metal secondary battery of Comparative Example 2 which does not have a metal Mg layer. Was expensive. The reason for this result is presumed to be as follows. If only the Li storage layer containing KB is provided as in the all-solid-state lithium metal secondary battery of Comparative Example 2, when a crack occurs in the Li storage layer, a part of metallic lithium is deposited on the crack and the crack is formed. It is considered that the deposited metallic lithium cannot come into contact with the solid electrolyte, and the metallic lithium cannot be dissolved when the all-solid-state battery is discharged. On the other hand, in the all-solid-state lithium metal secondary batteries of Examples 1 to 3, even if a crack occurs in the Li storage layer due to the presence of the metal Mg layer, at least a part of the surface of the crack occurs. Is covered with the metal Mg layer, and even if metallic lithium is deposited in the crack, the metal lithium deposited in the crack is ensured to be in contact with the metal Mg layer, and the metal deposited in the crack when the all-solid-state battery is discharged. Since lithium is dissolved and becomes Li ions and can be diffused to the metal Mg layer, and Li ions are easily transferred to the positive electrode layer, the all-solid-state battery is more than the case of the all-solid-state battery provided only with the Li storage layer. It is considered that the charge / discharge efficiency of the battery can be improved.
Comparing the all-solid-state lithium metal secondary batteries of Examples 1 and 2 in which the thickness of the Li storage layer is constant and only the thickness of the metal Mg layer is different, the thicker the metal Mg layer, the higher the charge / discharge efficiency. This is because the thicker the metal Mg layer, the larger the ratio of the metal Mg layer covering the surface of the crack when the Li storage layer is cracked, and the smaller the size of the crack. It is difficult for metallic lithium to be deposited on the surface, and even if metallic lithium is deposited on the crack, the contact area between the metallic lithium deposited on the crack and the metallic Mg layer becomes large, so that when the all-solid-state battery is discharged. It is considered that this is because the dissolution of metallic lithium deposited in the crack is promoted and Li ions are more easily transferred to the positive electrode layer. Therefore, the thickness of the metal Mg layer may be at least 30 nm or more, and it is considered that the thickness is preferably thicker as long as the energy density is not affected.
Comparing the all-solid-state lithium metal secondary batteries of Examples 2 to 3 in which the thickness of the metal Mg layer is constant and only the thickness of the Li storage layer is different, the charge / discharge efficiency is high regardless of the thickness of the Li storage layer. Therefore, it is considered that the charge / discharge efficiency can be improved regardless of the thickness of the Li storage layer if the Li storage layer and the metal Mg layer having a thickness of 30 nm or more are provided.
Therefore, according to the present disclosure, it has been demonstrated that an all-solid-state battery having high charge / discharge efficiency can be provided.

11 Negative electrode current collector 12 Solid electrolyte layer 13 Positive electrode layer 14 Positive electrode current collector 15 Li occlusion layer 16 Metal M layer 100 All-solid-state battery

Claims (1)

An all-solid-state battery that utilizes the precipitation-dissolution reaction of metallic lithium as the reaction of the negative electrode.
It has a negative electrode current collector, a Li storage layer containing a spherical carbon material and a resin, a metal M layer containing a metal M capable of alloying with lithium, a solid electrolyte layer, and a positive electrode layer in this order.
An all-solid-state battery characterized in that the thickness of the metal M layer is 30 nm or more and 5 μm or less.

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