JP7263977B2 - All-solid battery - Google Patents

Description

The present disclosure relates to all-solid-state batteries.

2. Description of the Related Art In recent years, with the rapid spread of information-related equipment and communication equipment such as personal computers, video cameras, and mobile phones, the development of batteries used as power sources for these devices has been emphasized. In addition, in the automobile industry and the like, development of high-output and high-capacity batteries for electric vehicles or hybrid vehicles is underway.
Among batteries, lithium secondary batteries are attracting attention because they use lithium, which has the highest ionization tendency among metals, as the negative electrode, resulting in a large potential difference from the positive electrode and high output voltage.
In addition, all-solid-state batteries are attracting attention in that they use a solid electrolyte instead of an electrolyte solution containing an organic solvent as an electrolyte interposed between a positive electrode and a negative electrode.

Patent Document 1 discloses a negative electrode for an all-solid secondary battery, which is characterized by comprising a coating layer that covers a negative electrode current collector and allows metallic lithium to deposit through a lithium alloy layer during charging. and that the coating layer contains zinc.

JP 2018-129159 A

When metallic Li is deposited and dissolved on a Zn-coated collector foil, Zn diffuses into the deposited metallic Li, resulting in low cycle characteristics of the battery. The present disclosure has been made in view of the above circumstances, and a main object thereof is to provide an all-solid-state battery with good cycle characteristics.

In the present disclosure, an all-solid-state battery that utilizes a deposition-dissolution reaction of metallic lithium as a negative electrode reaction,
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—Zn—O composite oxide, a solid electrolyte layer, and a positive electrode layer in this order. to provide an all-solid-state battery.

The present disclosure can provide an all-solid-state battery with good cycle characteristics.

It is a cross-sectional schematic diagram showing an example of an all-solid-state battery of the present disclosure. 4 is a graph showing the rate of increase in resistance of each evaluation battery after a charge/discharge test. 4 is a graph showing the element ratio of Li in each protective layer.

In the present disclosure, an all-solid-state battery that utilizes a deposition-dissolution reaction of metallic lithium as a negative electrode reaction,
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—Zn—O composite oxide, a solid electrolyte layer, and a positive electrode layer in this order. to provide an all-solid-state battery.

In the present disclosure, a lithium secondary battery refers to a battery that uses at least one of metallic lithium and a lithium alloy as a negative electrode active material, and that utilizes deposition-dissolution reaction of metallic lithium as a negative electrode reaction. Further, in the present disclosure, a negative electrode means one including a negative electrode layer.
In the present disclosure, when the all-solid-state battery is fully charged means when the state-of-charge (SOC) value of the all-solid-state battery is 100%. The SOC indicates the ratio of the charge capacity to the full charge capacity of the battery, and the full charge capacity is SOC 100%.
The SOC may be estimated, for example, from the open circuit voltage (OCV) of the all-solid-state battery.

In all-solid-state batteries, when metallic Li is used for the negative electrode layer, since Li exhibits high reactivity (reducing power), it 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 formed 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 quickly exhausted.
When a protective layer containing Zn is formed on the negative electrode current collector in order to solve the above problem, an all-solid-state battery including the protective layer has a problem of low cycle characteristics.
The low cycle characteristics of all-solid-state batteries are considered to be due to the following reasons. First, since the Zn contained in the protective layer on the current collector such as Ni foil is electronically conductive but not ionic conductive, metal Li precipitates between the protective layer and the solid electrolyte layer during charging of the all-solid-state battery. do. Then, an alloying reaction proceeds at the interface between Zn contained in the protective layer and the deposited metal Li. Since the Zn—Li alloy forms a solid solution, Zn diffuses into the precipitated metal Li. However, since the Zn concentration in the Zn—Li alloy obtained by the alloying reaction is low, the Zn—Li alloy layer formed is due to the metal Li and sulfidation at the interface between the Zn—Li alloy layer and the solid electrolyte layer. The effect of suppressing the reaction with the solid electrolyte is low. As a result, the reductive decomposition of the sulfide-based solid electrolyte progresses during the deposition and dissolution of metal Li during charging and discharging of the all-solid-state battery, forming a high-resistance layer, reducing the reversible capacity of the all-solid-state battery, and reducing the cycle characteristics. descend.
The Zn concentration in the Zn--Li alloy at the interface between the Zn--Li alloy layer obtained by the alloying reaction and the solid electrolyte layer decreases as the amount of metal Li precipitated increases. Therefore, in order to increase the capacity of the battery for electric vehicle (EV) applications, etc., if the conventional technology is applied with a design that increases the amount of metal Li deposited in the all-solid-state battery, a sulfide-based solid electrolyte with a Zn-Li alloy layer Since the effect of suppressing the reductive decomposition of is further reduced, it is easily assumed that the deterioration of the all-solid-state battery is accelerated.

The researchers found that by placing a protective layer containing a Li—Zn—O composite oxide between the negative electrode current collector and the solid electrolyte layer, it is possible to provide an all-solid-state battery with good cycle characteristics. clarified.
Since the Li—Zn—O composite oxide contained in the protective layer has ionic conductivity, metal Li is deposited between the protective layer and the negative electrode current collector during charging of the all-solid-state battery. Then, when the all-solid-state battery is charged, the protective layer containing the Li—Zn—O composite oxide is present between the negative electrode layer made of the deposited metal lithium and the solid electrolyte layer, so that the metal Li and the sulfide-based solid Direct contact with the electrolyte can be prevented, and reductive decomposition of the sulfide-based solid electrolyte by metal Li can be suppressed, resulting in good cycle characteristics of the all-solid-state battery.

FIG. 1 is a cross-sectional schematic diagram showing an example of a fully charged 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. Between them, a negative electrode layer 15 and a protective layer 16 containing a Li—Zn—O composite oxide are provided in this 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 dissolve and disappear in the all-solid-state battery 100 before the initial 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, such as SUS, copper, and nickel. Examples of the shape of the negative electrode current collector include a foil shape and a plate shape. The shape of the negative electrode current collector in a plan view is not particularly limited, but 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 is, for example, within the range of 1 μm to 50 μm, and may be within 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. Examples of lithium alloys include Li—Au, Li—Mg, Li—Sn, Li—Si, Li—Al, Li—B, 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, 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 a negative electrode active material as a main component, it may also contain other conventionally known negative electrode active materials. In the present disclosure, the main component means a component that is 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 depositing 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—Zn—O composite oxide, is a layer arranged between the negative electrode current collector and the solid electrolyte layer, and is between the negative electrode layer and the solid electrolyte layer when the all-solid-state battery is fully charged. may be placed in
In the all-solid-state battery of the present disclosure, the protective layer is arranged between the negative electrode current collector and the solid electrolyte layer, so that the protective layer prevents direct contact between the solid electrolyte layer and the deposited metal Li, and the deposited metal Since the reductive decomposition of the solid electrolyte by Li is suppressed, the cycle characteristics of the all-solid-state battery are improved.
The Li--Zn--O composite oxide is not particularly limited as long as it contains lithium element, zinc element and oxygen element in a predetermined ratio.
The element ratio of the lithium element in the Li—Zn—O composite oxide is not particularly limited, but may be 1.3 atomic % or more and 12.2 atomic % or less. The element ratio of the lithium element in the Li—Zn—O composite oxide can be controlled, for example, by controlling the thickness of the ZnO layer, which is the material layer of the protective layer.
The element ratio in the Li—Zn—O composite oxide can be calculated by analyzing the Li—Zn—O composite oxide by inductively coupled plasma (ICP) analysis or X-ray photoelectron spectroscopy (XPS). . In addition, the element ratio in the Li—Zn—O composite oxide is calculated from the atomic weight of the element contained in the Li—Zn—O composite oxide and the amount of change in the mass of the Li—Zn—O composite oxide with respect to the raw material. You can also
The method for forming the protective layer is not particularly limited. A ZnO layer (raw material layer) containing good too.
The thickness of the ZnO layer is not particularly limited, but may be 30 nm or more and 300 nm or less.
Another example of the method for forming the protective layer is protection by depositing a Li—Zn—O composite oxide 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 layered.

[Solid electrolyte layer]
The solid electrolyte layer contains at least a solid electrolyte.
As the solid electrolyte to be contained in the solid electrolyte layer, known solid electrolytes that can be used in all-solid-state batteries can be appropriately used, and examples thereof include oxide-based solid electrolytes and sulfide-based solid electrolytes.
Examples of sulfide solid electrolytes include Li ₂ SP ₂ S ₅ , Li ₂ S—SiS ₂ , LiX—Li ₂ S—SiS ₂ , LiX—Li ₂ SP ₂ S ₅ , LiX—Li ₂ O—Li ₂ SP ₂ S ₅ , LiX—Li ₂ SP ₂ O ₅ , LiX—Li ₃ PO ₄ —P ₂ S ₅ , Li ₃ PS ₄ and the like. The above description of "Li ₂ SP ₂ S ₅ " means a material obtained by using a raw material composition containing Li ₂ S and P ₂ S ₅ , and the same applies to other descriptions. "X" in LiX above represents a halogen element. One or more kinds of LiX may be contained in the raw material composition containing LiX. When two or more types of LiX are included, 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. Also, the molar ratio and composition of each element in the sulfide-based solid electrolyte can be measured, for example, by 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 of a raw material composition. .
The crystalline state of the sulfide-based solid electrolyte can be confirmed, for example, by subjecting the sulfide-based solid electrolyte to powder X-ray diffraction measurement using CuKα rays.

Sulfide glass can be obtained by subjecting a raw material composition (for example, a mixture of Li ₂ S and P ₂ S ₅ ) to amorphous processing. Examples of amorphous processing include mechanical milling.

Glass-ceramics can be obtained, for example, by heat-treating sulfide glass.
The heat treatment temperature may be any temperature higher than the crystallization temperature (Tc) observed by thermal analysis measurement of 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-ceramics is obtained. is mentioned.
The method of heat treatment is not particularly limited, but for example, a method using a kiln can be mentioned.

Examples of oxide-based solid electrolytes 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 ease of handling.
Moreover, the average particle diameter (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, unless otherwise specified, the average particle diameter of particles is the volume-based median diameter (D50) measured by laser diffraction/scattering particle size distribution measurement. In the present disclosure, the median diameter (D50) is the diameter (volume average diameter) at which the cumulative volume of particles is half (50%) of the total volume when the particles are arranged in order from the smallest particle size.

Solid electrolytes can be used singly or in combination of two or more. Moreover, when using two or more kinds of solid electrolytes, 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 proportion of the solid electrolyte in the solid electrolyte layer is not particularly limited. It may be within the range of mass % or less, and may be 100 mass %.

The solid electrolyte layer may contain a binder from the viewpoint of exhibiting plasticity. Examples of such a binder include the materials exemplified as binders used in the positive electrode layer to be described later. 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 making it possible to form 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 powder of a solid electrolyte material containing a solid electrolyte and, if necessary, other components. When the solid electrolyte material powder is pressure-molded, a press pressure of about 1 MPa to 600 MPa is normally applied.
The pressurization method is not particularly limited, but includes the pressurization method exemplified in the later-described formation of the positive electrode layer.

[Positive electrode 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.

There are no particular restrictions on the type of positive electrode active material, and any material that can be used as an active material for an all-solid-state battery can be used. When the all-solid battery is an all-solid 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 , heteroelement-substituted Li—Mn spinels (e.g., LiMn _1.5 Ni _0.5 O ₄ , LiMn _1.5 Al _0.5 O ₄ , LiMn _{1 .5Mg0.5O4 , LiMn1.5Co0.5O4 , LiMn1.5Fe0.5O4} , and _{LiMn1.5Zn0.5O4 , etc. )} , _lithium titanate _{( e.g.} Li ₄ Ti ₅ O ₁₂ ), lithium metal phosphates (e.g. LiFePO ₄ , LiMnPO ₄ , LiCoPO ₄ and LiNiPO ₄ ), lithium compounds such as LiCoN, Li ₂ SiO ₃ and Li ₄ SiO ₄ , transition metal oxides (e.g. V ₂ O ₅ and MoO ₃ etc.), TiS ₂ , Si, SiO ₂ and lithium storage intermetallic compounds (e.g. Mg ₂ Sn, Mg ₂ Ge, Mg ₂ Sb and Cu ₃ Sb etc.) etc. can be mentioned. Examples of lithium alloys include the lithium alloys exemplified as the lithium alloys used for the negative electrode active material.
Although the shape of the positive electrode active material is not particularly limited, it may be particulate.
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.
Li ion conductive oxides include, for example, 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.

The solid electrolyte can be exemplified by solid electrolytes that can be contained in the solid electrolyte layer described above.
The content of the solid electrolyte in the positive electrode layer is not particularly limited, but when the total mass of the positive electrode layer before the first charge of the all-solid-state battery is 100% by mass, for example, it is in the range of 1% by mass to 80% by mass. good too.

As the conductive material, a known material can be used, and examples thereof include carbon materials, metal particles, and the like. 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. At least one selected from the group consisting of VGCF, carbon nanotubes, and carbon nanofibers may be used. Metal particles include particles of Ni, Cu, Fe, SUS, and the like.
The content of the conductive material in the positive electrode layer is not particularly limited.

Examples of binders 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, the positive electrode active material and, if necessary, other components are put into a solvent and stirred to prepare a positive electrode layer slurry. The positive electrode layer is obtained by coating on top and drying.
Solvents include, for example, butyl acetate, butyl butyrate, heptane, N-methyl-2-pyrrolidone, and the like.
The method for applying the positive electrode layer slurry onto one surface of a support such as a positive electrode current collector is not particularly limited, and may be a doctor blade method, a metal mask printing method, an electrostatic coating method, a dip coating method, a spray coating method, a roll coating method, or the like. Examples include a coating method, a gravure coating method, and a screen printing method.
As the support, one having self-supporting properties can be appropriately selected and used, and there is no particular limitation. For example, metal foils such as Cu and Al can be used.

As another method of forming the positive electrode layer, the positive electrode layer may be formed by pressure-molding a powder of a 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 to 600 MPa is normally applied.
The pressurizing method is not particularly limited, but examples thereof include a method of applying pressure using a flat plate press, a roll press, and the like.

[Positive collector]
An all-solid-state battery usually has a positive electrode current collector that collects the current of the positive electrode layer.
A known metal that can be used as a current collector for an all-solid battery can be used as the positive electrode current collector. 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. A metal material can be exemplified. Examples of positive electrode current collectors include SUS, aluminum, nickel, iron, titanium and carbon.
The shape of the positive electrode current collector is not particularly limited, and various shapes such as a foil shape and a mesh shape can be used.

An all-solid-state battery is provided with an exterior body that accommodates a positive electrode layer, a negative electrode layer, a solid electrolyte layer, and the like, if necessary.
The shape of the exterior body is not particularly limited, but a laminate type or the like can be mentioned.
The material of the exterior body is not particularly limited as long as it is stable in the electrolyte, and examples thereof include polypropylene, polyethylene, and resins such as acrylic resins.

The all-solid-state battery may be a primary battery, a secondary battery, or a secondary battery. This is because they can be repeatedly charged and discharged, and are useful, for example, as batteries for vehicles. Also, the all-solid battery may be an all-solid lithium secondary battery.
Examples of the shape of the all-solid-state battery include coin type, laminate type, cylindrical type, rectangular type, and the like.

In the manufacturing method of the all-solid-state battery of the present disclosure, for example, first, the solid electrolyte layer is formed by pressure-molding the powder of the solid electrolyte material. Then, a positive electrode layer is obtained by pressure-molding a positive electrode mixture powder containing a positive electrode active material containing a lithium element on one surface of the solid electrolyte layer. After that, ZnO was vapor-deposited on one surface of the negative electrode current collector using an electron beam vapor deposition apparatus to form a ZnO layer, thereby obtaining a negative electrode current collector-ZnO layer laminate and forming a positive electrode layer of the solid electrolyte layer. A negative electrode current collector-ZnO layer laminate is mounted on the surface opposite to the surface so that the ZnO layer is in contact with the solid electrolyte layer. Then, if necessary, a positive electrode current collector is attached to the surface of the positive electrode layer opposite to the solid electrolyte layer to form a precursor battery, and the ZnO layer is subjected to Li—Zn—O composite oxidation by charging the precursor battery. The all-solid-state battery of the present disclosure may be a protective layer containing a substance.
In this case, the press pressure when the powder of the solid electrolyte material and the powder of the positive electrode material mixture is pressure-molded is usually about 1 MPa or more and 600 MPa or less.
The pressurization method is not particularly limited, but includes the pressurization method exemplified in the formation of the positive electrode layer.

(Example 1)
ZnO is prepared as a raw material for the protective layer, and an electron beam vapor deposition apparatus is used to form a ZnO film having a thickness of 30 nm on one side of a Cu foil as a negative electrode current collector, and a protective layer is formed on one side of the Cu foil. A ZnO layer was formed as a raw material layer.
Then, as a sulfide-based solid electrolyte, 101.7 mg of Li ₂ SP ₂ S _5- based material containing LiBr and LiI was prepared, and the sulfide-based solid electrolyte was pressed at a pressure of 6 tons/cm ² to form a solid electrolyte. A layer (500 μm thick) was obtained.
Next, a metal Li foil (thickness of 150 μm) was placed on one side of the solid electrolyte layer, and the solid electrolyte layer and the ZnO layer were brought into contact with each other on the side opposite to the side of the solid electrolyte layer on which the metal Li foil was placed. A Cu foil having ^a ZnO layer on one side is arranged so as to be so that the Li metal foil, the solid electrolyte layer, An evaluation battery 1 having a ZnO layer and a Cu foil in this order was obtained.

(Example 2)
Evaluation battery 2 was obtained in the same manner as in Example 1, except that a ZnO layer of 100 nm was formed on one surface of the Cu foil using an electron beam vapor deposition apparatus.

(Example 3)
Evaluation battery 3 was obtained in the same manner as in Example 1, except that a ZnO layer of 300 nm was formed on one surface of the Cu foil 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 Zn layer of 100 nm was formed on one surface of the Cu foil instead of the ZnO layer using an electron beam vapor deposition apparatus.

[Charging and discharging test]
The evaluation battery 1 was placed in a constant temperature bath at 25° C. for 1 hour to equalize the temperature inside the evaluation battery 1 .
Next, evaluation battery 1 was charged at a constant current density of 435 μA/cm ² to form a protective layer containing a Li—Zn—O composite oxide and a negative electrode layer. Charging was stopped when 35 mAh/cm ² was reached. As a result, the evaluation battery 1 was an all-solid lithium secondary battery having a protective layer containing a Li--Zn--O composite oxide and a negative electrode layer.
After 10 minutes, evaluation battery 1 was discharged at a constant current density of 435 μA/cm ² to dissolve metal Li, and discharge was terminated when the voltage of evaluation battery 1 reached 1.0V.
The charge/discharge efficiency of Evaluation Battery 1 was obtained 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
A total of 7 cycles of charge/discharge were repeated, with one cycle from the start of charge to the end of discharge. The resistance value after one cycle is calculated from the dissolution overvoltage and current value of metallic lithium corresponding to the capacity of 1 mAh after one cycle of the evaluation battery 1, and the dissolution overvoltage and current value of metallic lithium corresponding to the capacity of 1 mAh after 7 cycles. From the resistance value after 1 cycle and the resistance value after 7 cycles, the resistance increase rate after 7 cycles was calculated. The results are shown in Table 1 and FIG.
In addition, the element ratio of the Li element in the composite oxide of the protective layer formed during the first charge is calculated from the charge capacity from the open circuit potential of the negative electrode at the start of charging during the first cycle charge to the negative electrode potential of 0 V (based on Li). Calculated. The results are shown in Table 1 and FIG.
For evaluation batteries 2 to 3 and C1, the same method as for evaluation battery 1 was used to determine the resistance increase rate of each evaluation battery and the Li—Zn—O composite oxide or Li—Zn alloy of each protective layer. Element ratios of the elements were calculated. The results are shown in Table 1 and FIG.

[Evaluation results]
The resistance increase rate of the evaluation battery C1 of Comparative Example 1, which has a protective layer containing a Li—Zn alloy, is 108%.
On the other hand, the resistance increase rate of the evaluation batteries 1 to 3 of Examples 1 to 3 having a protective layer containing a Li—Zn—O composite oxide is lower than the resistance increase rate of the evaluation battery C1 of Comparative Example 1. In particular, in the evaluation battery 1 of Example 1 in which the Li element ratio in the protective layer at full charge is 12.2 atomic %, the resistance increase rate is as low as 14%, and the battery characteristics are excellent.
Therefore, according to the present disclosure, it was demonstrated that an all-solid-state battery with good cycle characteristics 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 battery

Claims (1)

An all-solid-state battery that utilizes a deposition-dissolution reaction of metallic lithium as a negative electrode reaction,
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—Zn—O composite oxide, a solid electrolyte layer, and a positive electrode layer in this order,
An all-solid battery , wherein the element ratio of the Li element in the Li—Zn—O composite oxide is 1.3 atomic % or more and 12.2 atomic % or less .

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