JP2021034200A - All-solid battery - Google Patents

Abstract

To provide an all-solid battery having a high charge/discharge efficiency.SOLUTION: An all-solid battery is arranged so as to utilize a precipitation-dissolution reaction of metallic lithium as a reaction of a negative electrode. When being full-charged, the all-solid battery has a negative electrode current collector, a negative electrode layer, a protection layer containing Li-Ba-TiO3 composite oxide, a solid electrolyte layer, and a positive electrode layer in this order. The element rate of a lithium element in the Li-Ba-TiO3 composite oxide is 0.2 atomic% or more and 3.6 atomic% or less.SELECTED DRAWING: Figure 2

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 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.

Patent Document 1 discloses a negative electrode for an all-solid-state secondary battery, which comprises a coating layer that covers a negative electrode current collector and allows metallic lithium to precipitate via a lithium alloy layer during charging. It is stated that the coating layer contains zinc.

Patent Document 2 discloses a current collector for a lithium secondary battery having a dielectric on the surface and exposing at least a part of the surface from between the dielectrics. It is described that the area of the exposed surface to be exposed is 30% or more of the area of the surface, the dielectric has BaTiO ₃ , and a non-aqueous electrolyte solution is used as the electrolytic solution.

JP-A-2018-129159 JP-A-2018-170128

When the technique described in Patent Document 2 is applied to an all-solid-state battery, the contact between the current collector and the solid electrolyte layer deteriorates due to the exposed surface of the current collector, and metallic lithium is seen from the exposed surface of the current collector. As a result, the current is concentrated on the portion of the dielectric in contact with the solid electrolyte layer to generate lithium, the irreversible capacity is increased, and the charge / discharge efficiency of the battery is lowered. The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide an all-solid-state battery having high charge / discharge efficiency.

In the present disclosure, the all-solid-state battery utilizes the precipitation-dissolution reaction of metallic lithium as the reaction of the negative electrode.
When the all-solid-state battery is fully charged, it has a negative electrode current collector, a negative electrode layer, _{a protective layer containing a Li-Ba-TiO 3} composite oxide, a solid electrolyte layer, and a positive electrode layer in this order.
Provided is an all-solid-state battery characterized in that the element ratio of the lithium element in the Li-Ba-TiO _{3 composite oxide is 0.2 atomic% or more and 3.6 atomic% 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. It is a graph which shows the average charge / discharge efficiency of each evaluation battery.

In the present disclosure, the all-solid-state battery utilizes the precipitation-dissolution reaction of metallic lithium as the reaction of the negative electrode.
When the all-solid-state battery is fully charged, it has a negative electrode current collector, a negative electrode layer, _{a protective layer containing a Li-Ba-TiO 3} composite oxide, a solid electrolyte layer, and a positive electrode layer in this order.
Provided is an all-solid-state battery characterized in that the element ratio of the lithium element in the Li-Ba-TiO _{3 composite oxide is 0.2 atomic% or more and 3.6 atomic% or less.}

In the present disclosure, the lithium secondary battery refers to 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.

When metal Li is used for the negative electrode layer in an all-solid-state battery, Li exhibits high reactivity (reducing power), and therefore reacts with a sulfide-based solid electrolyte (SE) to form a high resistance layer.
For example, there is a problem that a high resistance layer is generated between the solid electrolyte layer and the negative electrode layer during the cycle test of the all-solid-state battery, the charge / discharge efficiency of the all-solid-state battery is lowered, and the battery life is shortened.
When a ZnO layer containing ZnO is formed on the negative electrode current collector in order to solve the above problem, the all-solid-state battery provided with the ZnO layer as a protective layer is charged and discharged at a relatively early stage of about 1 to 3 cycles. There is a problem of low efficiency.
The low charge / discharge efficiency of the all-solid-state battery is considered to be due to the following reasons.
When the all-solid-state battery is charged for the first time, lithium ions pass through the ZnO layer and metallic Li is deposited on the negative electrode current collector. Then, the alloying reaction proceeds at the interface between ZnO contained in the protective layer and the precipitated metal Li to generate a Li—Zn—O composite oxide, which protects between the solid electrolyte layer and the precipitated metal Li. A Li—Zn—O composite oxide layer, which is a layer, is formed.
At this time, since a large amount of lithium elements are contained in the Li—Zn—O composite oxide layer, it is considered that the irreversible capacity of the all-solid-state battery increases, and as a result, the charge / discharge efficiency of the all-solid-state battery decreases.

The present researchers can provide an all-solid-state battery with high charge / discharge efficiency by arranging a protective layer containing a _{Li-Ba-TiO 3} composite oxide between the negative electrode current collector and the solid electrolyte layer. Clarified.
The Li-Ba-TiO ₃ composite oxide is a Li conductor, and the Li-Ba-TiO ₃ composite oxide layer is arranged so as to prevent direct contact between the solid electrolyte layer and the precipitated metal Li. Lithium that acts as a protective layer that suppresses the reductive decomposition of the solid electrolyte by the metal Li at the interface between the solid electrolyte layer and the precipitated metal Li, and is contained in the protective layer containing the _{Li-Ba-TiO 3 composite oxide.} Since the element ratio of the elements is smaller than that of the protective layer containing the Li—Zn—O composite oxide having the same thickness, the irreversible capacity of the all-solid-state battery is small, and the charge / discharge efficiency of the all-solid-state battery is high.

FIG. 1 is a schematic cross-sectional view showing an example of an all-solid-state battery when fully charged according to 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. A protective layer 16 containing a _{negative electrode layer 15 and a Li-Ba-TiO 3} composite oxide is provided between them in order from the negative electrode current collector 11 side. When the negative electrode layer 15 is made of metallic lithium, the negative electrode layer 15 may be dissolved and disappear in the all-solid-state battery 100 before the first charge or after the complete discharge.

[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.

[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. 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 negative electrode layer when the all-solid-state battery is fully charged is 100% by mass.
The thickness of the negative electrode layer is not particularly limited, but may be 30 nm or more and 5000 nm or less when the all-solid-state battery is fully charged.
In the present disclosure, for example, a negative electrode layer formed by precipitating metallic lithium as a negative electrode active material may be provided by initial charging of an all-solid-state battery.

[Protective layer]
The protective layer contains a Li-Ba-TiO ₃ composite oxide and is arranged between the negative electrode current collector and the solid electrolyte layer. When the all-solid-state battery is fully charged, the protective layer is formed between the negative electrode layer and the solid electrolyte layer. It may be arranged between them.
By arranging the protective layer between the negative electrode current collector and the solid electrolyte layer, the protective layer prevents direct contact between the solid electrolyte layer and the precipitated metal Li, and the precipitated metal Li reduces and decomposes the solid electrolyte. Because it is suppressed and _{the element ratio of lithium element contained in the protective layer containing the Li-Ba-TiO 3} composite oxide is smaller than that of the protective layer containing the Li-Zn-O composite oxide having the same thickness. The irreversible capacity of the all-solid-state battery is small, and the charge / discharge efficiency of the all-solid-state battery is high.
The Li-Ba-TiO ₃ composite oxide is not particularly limited as long as it contains a lithium element, a barium element, a titanium element, and an oxygen element in a predetermined ratio.
The element ratio of the lithium element in the Li-Ba-TiO ₃ composite oxide may be 0.2 atomic% or more and 3.6 atomic% or less. The element ratio of the lithium element in the Li-Ba-TiO ₃ composite oxide can be controlled, for example, by controlling the thickness of the _{BaTiO 3} layer, which is the raw material layer of the protective layer.
Li-Ba-TiO ₃ element ratio in the composite oxide, it is calculated by analyzing the Li-Ba-TiO ₃ composite oxide by inductively coupled plasma (ICP) analysis or X-ray photoelectron spectroscopy (XPS) Can be done. Further, Li-Ba-TiO ₃ element ratio in the composite oxide, the atomic weight of elements in Li-Ba-TiO ₃ composite oxide, the change in mass of Li-Ba-TiO ₃ composite oxide to the raw material It can also be calculated from the quantity.
_{The method for forming the protective layer is not particularly limited, and for example, BaTIO 3} is vapor-deposited as a raw material of the protective layer on at least one surface of the negative electrode current collector or at least one surface of the solid electrolyte layer using an electron beam vapor deposition apparatus. ₃ to form a BaTiO ₃ layer (material layer) containing, followed by the charging of the precursor cells, by reacting lithium ions and BaTiO _3, which has been moved from the positive electrode layer, a BaTiO ₃ Li-BaTiO ₃ composite oxide It may be used as a protective layer.
The thickness of the BaTIO ₃ layer is not particularly limited, but may be 30 nm or more and 100 nm or less.
_{As another example of the method of forming the protective layer, a Li-Ba-TiO 3} composite oxide is vapor-deposited on at least one surface of the negative electrode current collector or on at least one surface of the solid electrolyte layer using an electron beam vapor deposition apparatus. It may be used as a protective layer.

[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 SP 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 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 order from the smallest 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 binder used for the positive electrode layer described later 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 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 (eg Limn 1.5 Zn 0.5 O 4 etc.) Li ₄ Ti ₅ O ₁₂ ), lithium metal phosphates (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 oxides. (For example, V ₂ O ₅ and MoO _3, etc.), TiS ₂ , Si, SiO ₂ , and lithium-storable metal-to-metal compounds (for example, Mg ₂ Sn, Mg ₂ Ge, Mg ₂ Sb, Cu ₃ Sb, etc.), 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 such a solid electrolyte, the solid electrolyte can be exemplified as a solid electrolyte that can be contained in the above-mentioned solid electrolyte layer.
The content of the solid electrolyte in the positive electrode layer is not particularly limited, but is, for example, in the range of 1% by mass to 80% by mass when the total mass of the positive electrode layer before the initial charging of the all-solid-state battery is 100% by mass. May be good.

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.

Examples of the binder include acrylonitrile-butadiene rubber (ABR), butadiene rubber (BR), polyvinylidene fluoride (PVdF), styrene-butadiene rubber (SBR), and the like. 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 the 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, a known metal that can be used as a current collector for an all-solid-state battery 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. Examples of the positive electrode current collector include SUS, aluminum, nickel, iron, titanium and carbon.
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 shape of the exterior body is not particularly limited, and examples thereof include a laminated type.
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 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. Then, the BaTiO ₃ on one surface of the negative electrode current collector, to obtain an electron beam evaporator was deposited using to form a BaTiO ₃ layer negative electrode current collector -BaTiO ₃ layer laminate of a solid electrolyte layer positive electrode layer _{The negative electrode current collector-BaTIO 3-} layer laminate is attached _{so that the BaTiO 3} layer is in contact with the solid electrolyte layer on the surface opposite to the surface on which the above is formed. Then, if necessary, a positive electrode current collector is mounted on the surface of the positive electrode layer opposite to the solid electrolyte layer to form a precursor battery, and by charging the precursor battery, the BaTiO ₃ layer is transformed into a Li-Ba-TiO _{3 layer.} The all-solid-state battery of the present disclosure may be used as a protective layer containing a composite oxide.
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)
_{BaTiO 3} is prepared as a raw material for the protective layer, _{and a 30 nm-thick BaTiO 3} is formed on one surface of the Cu foil as the negative electrode current collector using an electron beam vapor deposition apparatus to protect the Cu foil on one surface. _Three BaTIO layers were formed as the raw material layer of the layer.
_{Then, 101.7 mg of a Li 2 SP 2} S ₅ system material containing LiBr and LiI was prepared as the sulfide-based solid electrolyte, and the sulfide-based solid electrolyte ^{was pressed at a pressure of 6 ton / cm 2} , and the solid electrolyte was pressed. A layer (thickness 500 μm) was obtained.
Next, the metal Li foil (thickness 150 μm) is arranged on one surface of the solid electrolyte layer, and the solid electrolyte layer and the BaTIO ₃ layer are formed on the surface of the solid electrolyte layer opposite to the surface on which the metal Li foil is arranged. _{Cu foils having 3} layers of BaTIO on one surface are placed so as to be in contact with each other, ^{and these are press-molded at a pressure of 1 ton / cm 2} , and then the molded body is restrained at 2 Nm, and Li metal foil and solid electrolyte are used. An evaluation battery 1 having a layer, a BaTiO ₃ layer, and a Cu foil in this order was obtained.

(Example 2)
An evaluation battery 2 was obtained in the same manner as in Example 1 except that a _{BaTIO 3} layer was formed on one surface of a Cu foil by 100 nm using an electron beam vapor deposition apparatus.

(Comparative Example 1)
An evaluation battery C1 was obtained in the same manner as in Example 1 except that a ZnO layer was formed on one surface of the Cu foil by an electron beam vapor deposition apparatus in _{place of the BaTiO 3 layer at 30 nm.}

(Comparative Example 2)
An evaluation battery C2 was obtained in the same manner as in Example 1 except that a ZnO layer was formed on one surface of the Cu foil by an electron beam vapor deposition apparatus in _{place of the BaTiO 3 layer at 100 nm.}

[Charge / discharge test]
The evaluation battery 1 was allowed to stand in a constant temperature bath at 25 ° C. for 1 hour to make the temperature inside the evaluation battery 1 uniform.
Next, the evaluation battery 1 is charged with a constant current having a current density of 435 μA / cm ² to form a protective layer and a negative electrode layer containing a Li-Ba-TiO ₃ composite oxide, and the charging capacity of the evaluation battery 1 is 4. Charging was stopped when it reached .35 mAh / cm ^2. As a result, the evaluation battery 1 became an all-solid-state lithium secondary battery having a protective layer containing _{a Li-Ba-TiO 3 composite oxide and a negative electrode layer.}
Then, 10 minutes later, the evaluation battery 1 was ^{discharged with a constant current having a current density of 435 μA / cm 2} to dissolve the metallic Li, and the discharge was terminated when the voltage of the evaluation battery 1 reached 1.0 V.
The charge / discharge efficiency of the evaluation battery 1 was calculated from the following formula.
Charge / discharge efficiency (%) = (discharge capacity; capacity at the time of reaching 1.0 V [mAh / cm ² ] ÷ charge capacity; 4.35 [mAh / cm ² ]) × 100
Then, charging / discharging was repeated for a total of 3 cycles, with the period from the start of charging to the end of discharging as one cycle. The average charge / discharge efficiency was calculated from the charge / discharge efficiency of each cycle from 1 to 3 cycles of the evaluation battery 1. The results are shown in Table 1 and FIG.
The element ratio of Li element in the composite oxide of the protective layer formed at the time of initial charging is from the charge capacity from the open circuit potential of the negative electrode at the start of charging at the start of charging at the first cycle to the negative electrode potential of 0 V (Li reference). Calculated. The results are shown in Table 1.
For the evaluation batteries 2, C1 to C2, the average charge / discharge efficiency of each evaluation battery and the Li-Ba-TIO ₃ composite oxide or Li-Zn-O of each protective layer are used in the same manner as in the evaluation battery 1. The element ratio of the Li element in the composite oxide was calculated. The results are shown in Table 1.

[Evaluation results]
The average charge / discharge efficiency of the evaluation battery C1 of Comparative Example 1 having a protective layer containing a Li—Zn—O composite oxide is 98.1%.
On the other hand, the average charge / discharge efficiency of the evaluation battery 1 of Example 1 having the protective layer containing _{the Li-Ba-TiO 3} composite oxide formed so that the thickness of the raw material layer was 30 nm, which is the same as that of Comparative Example 1, was 98.7%. Yes, it is higher than the average charge / discharge efficiency of the evaluation battery C1 of Comparative Example 1.
Further, the average charge / discharge efficiency of the evaluation battery C2 of Comparative Example 2 having a protective layer containing a Li—Zn—O composite oxide is 97.9%.
On the other hand, the average charge / discharge efficiency of the evaluation battery 2 of Example 2 having the protective layer containing _{the Li-Ba-TiO 3} composite oxide formed so that the thickness of the raw material layer was 100 nm, which is the same as that of Comparative Example 2, was 100.0%. Yes, it is higher than the average charge / discharge efficiency of the evaluation battery C2 of Comparative Example 2, and is improved by about 2.1%.
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 Negative electrode layer 16 Protective 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.
When the all-solid-state battery is fully charged, it has a negative electrode current collector, a negative electrode layer, _{a protective layer containing a Li-Ba-TiO 3} composite oxide, a solid electrolyte layer, and a positive electrode layer in this order.
An all-solid-state battery characterized in that the element ratio of the lithium element in the Li-Ba-TiO _{3 composite oxide is 0.2 atomic% or more and 3.6 atomic% or less.}

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