All-solid-state batteries

Abstract

To provide an all-solid battery capable of simplifying the battery structure while improving cycle characteristics.SOLUTION: The all-solid battery is an all-solid battery that uses the deposition and dissolution reaction of metallic lithium as the negative electrode reaction. The battery has a negative electrode current collector, solid electrolyte layers A and B, and a positive electrode active material layer in this order in the thickness direction. The solid electrolyte layer A contains first and second sulfide solid electrolytes. The solid electrolyte layer B contains a third sulfide solid electrolyte. The first sulfide solid electrolyte is sulfide solid electrolyte that has a reduction reaction peak between 0.3 V and 1.0 V in CV measurement, and contains an element M (M is at least one of Sn, Al, Zn, In, Ge, Si, Sb, Ga, and Bi). The second sulfide solid electrolyte is sulfide solid electrolyte that does not have a reduction reaction peak between 0.3 V and 1.0 V in CV measurement. In the solid electrolyte layer A, the ratio of the first sulfide solid electrolyte to the total of the first and second sulfide solid electrolytes is greater than 0 wt.% and less than or equal to 45 wt.%.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to all-solid-state batteries. [Background technology]

[0002] All-solid-state batteries are batteries that have a solid electrolyte layer between a positive electrode active material layer and a negative electrode active material layer, and have the advantage of being easier to simplify safety devices compared to liquid-based batteries that use electrolytes containing flammable organic solvents. In the field of all-solid-state batteries, batteries that utilize the deposition and dissolution reaction of metallic lithium as the negative electrode reaction are also known.

[0003] For example, Patent Document 1 discloses an all-solid-state battery that utilizes a deposition and dissolution reaction of metallic lithium as the anode reaction, and that has, in this order, a negative electrode current collector, a Li-sorption layer containing a spherical carbon material and a resin, a metal M layer containing metal M that can be alloyed with lithium, a solid electrolyte layer, and a positive electrode layer, and the thickness of the metal M layer is 30 nm or more and 5 μm or less. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-89814 Summary of the Invention [Problem to be solved by the invention]

[0005] In all-solid-state batteries that use the deposition and dissolution reaction of metallic lithium as the anode reaction, a typical anode active material layer (a layer containing anode active material particles that absorb and release Li) is not typically provided during the fabrication of the all-solid-state battery; instead, a Li-containing anode active material layer is formed during the initial charge, which has the advantage of making it easy to simplify the manufacturing process and improve energy density. On the other hand, from the perspective of improving energy density and battery performance, there is a demand for all-solid-state batteries that combine a simplified battery structure with improved cycle characteristics.

[0006] The present disclosure has been made in view of the above circumstances, and has as its main object to provide an all-solid-state battery that achieves both a simplified battery structure and improved cycle characteristics. [Means for solving the problem]

[0007] [1] An all-solid-state battery that utilizes a deposition and dissolution reaction of metallic lithium as a negative electrode reaction, a negative electrode current collector, a solid electrolyte layer A, a solid electrolyte layer B, and a positive electrode active material layer, in this order in the thickness direction; the solid electrolyte layer A contains a first sulfide solid electrolyte and a second sulfide solid electrolyte, the solid electrolyte layer B contains a third sulfide solid electrolyte, The first sulfide solid electrolyte exhibited a voltage drop of 0.3 V (vs Li / Li) in cyclic voltammetry measurements. + ) or more 1.0V (vs Li / Li + ) or less, and contains an M element (M is at least one of Sn, Al, Zn, In, Ge, Si, Sb, Ga, and Bi), The second sulfide solid electrolyte showed a voltage drop of 0.3 V (vs Li / Li) in cyclic voltammetry measurements. + ) or more 1.0V (vs Li / Li + ) The following is a sulfide solid electrolyte that does not have a reduction reaction peak, an all-solid-state battery, wherein in the solid electrolyte layer A, a proportion of the first sulfide solid electrolyte to the total of the first sulfide solid electrolyte and the second sulfide solid electrolyte is greater than 0 wt % and 45 wt % or less.

[0008] [2] [1] The all-solid-state battery according to [1], wherein in the solid electrolyte layer A, a proportion of the first sulfide solid electrolyte with respect to a total of the first sulfide solid electrolyte and the second sulfide solid electrolyte is 5 wt % or more and 40 wt % or less.

[0009] [3] The above third sulfide solid electrolyte exhibited a voltage drop of 0.3 V (vs Li / Li) in cyclic voltammetry measurements. + ) or more 1.0V (vs Li / Li + ) The all-solid-state battery according to [1] or [2], wherein the sulfide solid electrolyte does not have a reduction reaction peak.

[0010] [4] The first sulfide solid electrolyte contains Li, the M element, and S, The all-solid-state battery according to any one of [1] to [3], wherein the element M is at least one of Sn, Al, Zn, and In.

[0011] [5] The all-solid-state battery according to any one of [1] to [4], further comprising a protective layer containing Li and M between the negative electrode current collector and the solid electrolyte layer A. [Effects of the Invention]

[0012] The all-solid-state battery according to the present disclosure has the effect of achieving both a simplified battery structure and improved cycle characteristics. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic cross-sectional view illustrating an example of an all-solid-state battery according to the present disclosure. [Figure 2] FIG. 1 is a schematic cross-sectional view illustrating an example of an all-solid-state battery according to the present disclosure. [Figure 3] FIG. 1 is a schematic cross-sectional view illustrating an example of an all-solid-state battery according to the present disclosure. [Figure 4] 1 shows the results of the capacity retention rates of the cells produced in Examples 1 to 3, Comparative Examples 1 to 5, and Reference Examples 1 to 3. DETAILED DESCRIPTION OF THE INVENTION

[0014] The all-solid-state battery according to the present disclosure will be described in detail below with reference to the drawings. The drawings are schematic diagrams, and the size and shape of each part are appropriately exaggerated for ease of understanding.

[0015] 1 and 2 are schematic cross-sectional views illustrating an example of an all-solid-state battery according to the present disclosure. More specifically, FIG. 1 illustrates an example of an all-solid-state battery before the first charge, and FIG. 2 illustrates an example of an all-solid-state battery after the first charge. The all-solid-state battery 10 shown in FIG. 1 includes a negative electrode current collector 1, a solid electrolyte layer 2A (solid electrolyte layer A), a solid electrolyte layer 2B (solid electrolyte layer B), a positive electrode active material layer 3, and a positive electrode current collector 4 arranged in a thickness direction D T In this order, the solid electrolyte layer 2A contains a first sulfide solid electrolyte having a relatively low reduction resistance and a second sulfide solid electrolyte having a relatively high reduction resistance, in a predetermined ratio. The solid electrolyte layer 2B contains a third sulfide solid electrolyte. Meanwhile, as shown in FIG. 2, when the all-solid-state battery 10 shown in FIG. 1 is charged, a protective layer 5 containing Li and M (a specific metal element contained in the first sulfide solid electrolyte) is formed between the negative electrode current collector 1 and the solid electrolyte layer 2A.

[0016] According to the present disclosure, in a battery utilizing the deposition and dissolution reaction of metallic lithium as the anode reaction, two types of sulfide solid electrolytes are used for the solid electrolyte layer A: a first sulfide solid electrolyte with relatively low reduction resistance and a second sulfide solid electrolyte with relatively high reduction resistance, resulting in an all-solid-state battery that achieves both a simplified battery structure and improved cycle characteristics. Furthermore, since the solid electrolyte layer includes solid electrolyte layer A and solid electrolyte layer B, and solid electrolyte layer A significantly contributes to improving the cycle characteristics, the range of materials that can be selected for solid electrolyte layer B is broadened. For example, by selecting a third sulfide solid electrolyte with relatively high reduction resistance, the cycle characteristics can be further improved. Generally, when a sulfide solid electrolyte undergoes reductive decomposition, its ionic conductivity drops significantly, so a material with high reduction resistance is used for the sulfide solid electrolyte used in the solid electrolyte layer. In particular, in batteries that utilize a deposition and dissolution reaction of metallic lithium as the anode reaction, the reaction potential of the anode is lower than that of batteries that use, for example, a graphite-based active material as the anode active material. Therefore, sulfide solid electrolytes, which have excellent reduction resistance, have conventionally been used.

[0017] In contrast, in the present disclosure, a sulfide solid electrolyte (second sulfide solid electrolyte) with excellent reduction resistance is used in addition to a sulfide solid electrolyte (first sulfide solid electrolyte) with lower reduction resistance than the second sulfide solid electrolyte in a predetermined ratio. Surprisingly, the combined use of the first sulfide solid electrolyte and the second sulfide solid electrolyte provides an excellent effect of improving cycle characteristics compared to the use of the second sulfide solid electrolyte with excellent reduction resistance alone. The reason for the improved cycle characteristics is presumed to be that the first sulfide solid electrolyte contains a specific M element, which generates a LiM alloy as a decomposition product of the first sulfide solid electrolyte, and the generated LiM alloy functions as a protective layer that protects the decomposition of the sulfide solid electrolyte. Furthermore, the formation of a protective layer derived from the first sulfide solid electrolyte eliminates the need for another protective layer to protect the solid electrolyte layer, and allows the thickness of the other protective layer to be reduced. Therefore, it is possible to achieve both a simplified battery structure and improved cycle characteristics.

[0018] 1.Solid electrolyte layer The solid electrolyte layer has, in order from the negative electrode current collector side, a solid electrolyte layer A and a solid electrolyte layer B. The solid electrolyte layer A and the solid electrolyte layer B are usually layers with different compositions.

[0019] (1) Solid electrolyte layer A The solid electrolyte layer A contains a first sulfide solid electrolyte and a second sulfide solid electrolyte as sulfide solid electrolytes. The sulfide solid electrolyte is typically a solid electrolyte containing sulfur (S) as a main anion element.

[0020] (i) Primary sulfide solid electrolyte The first sulfide solid electrolyte is a sulfide solid electrolyte having lower reduction resistance than the second sulfide solid electrolyte described below. Specifically, the first sulfide solid electrolyte has a voltage drop of 0.3 V (vs Li / Li) in cyclic voltammetry measurement. + ) or more 1.0V (vs Li / Li + The reduction reaction peak occurs when the potential is 0.3 V (vs. Li / Li + ) or more 1.0V (vs Li / Li + ) or less, a reduction reaction caused by the metal element M, which will be described later, usually occurs. Note that, when the first sulfide solid electrolyte contains the non-metal element P, when the potential is 1.0 V (vs. Li / Li + ), a reduction reaction caused by the P element may occur. To eliminate the influence of the P element, the upper limit is set to 1.0 V (vs Li / Li + The details of the cyclic voltammetry measurement will be explained in the examples below.

[0021] The first sulfide solid electrolyte may be a glass-based (amorphous) sulfide solid electrolyte, a glass-ceramic sulfide solid electrolyte, or a crystalline sulfide solid electrolyte.

[0022] The first sulfide solid electrolyte usually contains Li element, M element (M is at least one of Sn, Al, Zn, In, Ge, Si, Sb, Ga and Bi), and S element. All of the M elements are elements that can be alloyed with Li. The first sulfide solid electrolyte preferably further contains P element. Also, the first sulfide solid electrolyte may contain halogen elements such as F, Cl, Br, I. Further, in the first sulfide solid electrolyte, a part of the S element may be replaced by an O element.

[0023] The first sulfide solid electrolyte may have a crystalline phase. Examples of the crystalline phase include, for example, LGPS-type crystalline phase, Thio-LISICON-type crystalline phase, and argyrodite-type crystalline phase.

[0024] The composition of the first sulfide solid electrolyte is not particularly limited. For example, Li 4-x Sn 1-x P x S4(0 < x < 1) can be mentioned. At least a part of Sn may be replaced by at least one of Al, Zn, In, Ge, Si, Sb, Ga and Bi. Similarly, at least a part of P may be replaced by at least one of Al, Zn, In, Ge, Si, Sb, Ga and Bi. Also, a part of Li may be replaced by at least one of Na, K, Mg, Ca and Zn. Further, a part of S may be replaced by halogen (F, Cl, Br, I) or may be replaced by oxygen (O).

[0025] Another example of the composition of the first sulfide solid electrolyte is xLi2S-(1-x)SnS2-yLiX(0 < x < 1, 0 ≦ y < 1, X is one or more halogens). At least a part of Sn may be replaced by at least one of Al, Zn, In, Ge, Si, Sb, Ga and Bi. Also, a part of Li may be replaced by at least one of Na, K, Mg, Ca and Zn. Further, a part of S may be replaced by oxygen (O).

[0026] The first sulfide solid electrolyte may be, for example, particulate. The first sulfide solid electrolyte may have an average particle size of, for example, 0.5 μm or more and 30 μm or less. In the present disclosure, the average particle size is defined as the volume cumulative particle size D measured by a laser diffraction / scattering particle size distribution analyzer. 50 This refers to...

[0027] (ii) Secondary sulfide solid electrolyte The second sulfide solid electrolyte is a sulfide solid electrolyte having higher reduction resistance than the first sulfide solid electrolyte. Specifically, the first sulfide solid electrolyte has a voltage drop of 0.3 V (vs Li / Li) in cyclic voltammetry measurement. + ) or more 1.0V (vs Li / Li + ) or less, there is no reduction reaction peak.

[0028] The second sulfide solid electrolyte may be a glass-based (amorphous) sulfide solid electrolyte, a glass-ceramic sulfide solid electrolyte, or a crystalline sulfide solid electrolyte.

[0029] The second sulfide solid electrolyte usually contains at least Li and S. Preferably, the second sulfide solid electrolyte further contains P. The second sulfide solid electrolyte may contain a halogen element such as F, Cl, Br, or I. The second sulfide solid electrolyte may also contain O. Preferably, the second sulfide solid electrolyte does not contain any metal element other than Li, but may contain metal elements other than Li as long as the metal elements do not affect the reduction resistance.

[0030] The second sulfide solid electrolyte may have a crystalline phase, such as a Thio-LISICON-type crystalline phase, an Argyrodite-type crystalline phase, or an LGPS-type crystalline phase.

[0031] The composition of the second sulfide solid electrolyte is not particularly limited, but examples include xLiS·(1-x)P2S5 (0.5≦x<1), yLiI·zLiBr·(100-yz)(xLiS·(1-x)P2S5) (0.5≦x<1, 0≦y≦30, 0≦z≦30). In these compositions, x preferably satisfies 0.7≦x≦0.8. In these compositions, a portion of Li may be substituted with at least one of Na, K, Mg, Ca, and Zn. Furthermore, a portion of S may be substituted with oxygen (O).

[0032] Other examples of the composition of the second sulfide solid electrolyte include Li 7-x-2y PS 6-x-y X y X is at least one of F, Cl, Br, and I, and x and y satisfy the relationship 0≦x, 0≦y. A portion of Li may be substituted with at least one of Na, K, Mg, Ca, and Zn. Furthermore, a portion of S may be substituted with oxygen (O).

[0033] The second sulfide solid electrolyte may be in the form of particles, for example, and may have an average particle size of, for example, 0.5 μm or more and 30 μm or less.

[0034] (iii) Solid electrolyte layer A The solid electrolyte layer A contains a first sulfide solid electrolyte and a second sulfide solid electrolyte. In the solid electrolyte layer A, the first sulfide solid electrolyte and the second sulfide solid electrolyte are preferably uniformly dispersed. In the solid electrolyte layer A, the proportion of the first sulfide solid electrolyte relative to the total of the first sulfide solid electrolyte and the second sulfide solid electrolyte is greater than 0% by weight and less than 45% by weight. The proportion of the first sulfide solid electrolyte may be 1% by weight or more, 3% by weight or more, or even 5% by weight or more. The proportion of the first sulfide solid electrolyte may be 40% by weight or less, or 30% by weight or less. The proportion of the first sulfide solid electrolyte may be around 10% by weight (5% by weight or more and 15% by weight or less). In the solid electrolyte layer A, the total proportion of the first sulfide solid electrolyte and the second sulfide solid electrolyte is, for example, 80% by weight or more, 90% by weight or more, or 95% by weight or more.

[0035] The solid electrolyte layer A may contain a binder. Examples of binders include rubber-based binders such as butylene rubber (BR) and styrene butadiene rubber (SBR), and fluoride-based binders such as polyvinylidene fluoride (PVDF). The thickness of the solid electrolyte layer A is, for example, 0.5 μm or more and 250 μm or less.

[0036] (2) Solid electrolyte layer B The solid electrolyte layer B contains a third sulfide solid electrolyte as the sulfide solid electrolyte. The solid electrolyte layer B may contain one type of third sulfide solid electrolyte, or may contain two or more types of third sulfide solid electrolytes.

[0037] The third sulfide solid electrolyte, like the first sulfide solid electrolyte described above, exhibited a voltage drop of 0.3 V (vs Li / Li) in cyclic voltammetry measurements. + ) or more 1.0V (vs Li / Li + ) or less. Conversely, solid electrolyte layer B does not have to contain sulfide solid electrolyte α.

[0038] The third sulfide solid electrolyte, like the second sulfide solid electrolyte described above, exhibited a voltage drop of 0.3 V (vs Li / Li) in cyclic voltammetry measurements. + ) or more 1.0V (vs Li / Li + ) or less, the sulfide solid electrolyte β may be one that does not have a reduction reaction peak. Conversely, the solid electrolyte layer B does not need to contain the sulfide solid electrolyte β.

[0039] The solid electrolyte layer B may contain both the sulfide solid electrolyte α and the sulfide solid electrolyte β as the third sulfide solid electrolyte. In this case, the ratio of the sulfide solid electrolyte α to the total of the sulfide solid electrolyte α and the sulfide solid electrolyte β is defined as R B In addition, in the solid electrolyte layer A, the ratio of the first sulfide solid electrolyte to the total of the first sulfide solid electrolyte and the second sulfide solid electrolyte is R A (% by weight) R A is R B Larger is preferable. R A and R B The difference is preferably, for example, 3% by weight or more.

[0040] The third sulfide solid electrolyte may be a glass-based (amorphous) sulfide solid electrolyte, a glass-ceramic sulfide solid electrolyte, or a crystalline sulfide solid electrolyte. Details of the third sulfide solid electrolyte are the same as those described for the first sulfide solid electrolyte and the second sulfide solid electrolyte.

[0041] The solid electrolyte layer B may be composed of a single layer or multiple layers. In the entire solid electrolyte layer, one or more solid electrolyte layers located closer to the positive electrode than the solid electrolyte layer A correspond to the solid electrolyte layer B.

[0042] In the solid electrolyte layer B, the proportion of the third sulfide solid electrolyte is, for example, 80% by weight or more, or may be 90% by weight or more, or may be 95% by weight or more. The solid electrolyte layer B may contain a binder. Examples of binders include rubber-based binders such as butylene rubber (BR) and styrene butadiene rubber (SBR), and fluoride-based binders such as polyvinylidene fluoride (PVDF). The thickness of the solid electrolyte layer B is, for example, 0.5 μm or more and 250 μm or less. The thickness of the solid electrolyte layer B is, for example, 1.0 times or more, or may be 1.5 times or more, or may be 2.0 times or more, the thickness of the solid electrolyte layer A.

[0043] 2. Positive electrode The positive electrode in the present disclosure includes a positive electrode current collector and a positive electrode active material layer. The positive electrode active material layer contains at least a positive electrode active material. The positive electrode active material layer may also contain at least one of a solid electrolyte, a conductive material, and a binder.

[0044] The positive electrode active material may be, for example, an oxide active material, such as LiCoO2 or LiNi. 1 / 3 Co 1 / 3 Mn 1 / 3 O2, etc., rock salt layered active materials, LiMn2O4, Li4Ti5O 12 and olivine type active materials such as LiFePO4.

[0045] Examples of conductive materials include carbon materials. Examples of carbon materials include particulate carbon materials such as acetylene black (AB) and ketjen black (KB); and fibrous carbon materials such as carbon fiber, carbon nanotubes (CNT), and carbon nanofibers (CNF). The solid electrolyte and binder are the same as those described above in "1. Solid Electrolyte Layer."

[0046] Examples of materials for the positive electrode current collector include SUS, aluminum, nickel, and carbon. Examples of the shape of the positive electrode current collector include foil. The thickness of the positive electrode current collector is, for example, 1 μm or more and 500 μm or less.

[0047] 3.Negative electrode The negative electrode in the present disclosure has at least a negative electrode current collector. Furthermore, as shown in Fig. 3, the negative electrode 1 may have, for example, an Mg layer 6, which will be described later. On the other hand, it is preferable that the negative electrode does not have a negative electrode active material layer containing negative electrode active material particles.

[0048] Examples of materials for the negative electrode current collector include SUS, copper, nickel, and carbon. Examples of the shape of the negative electrode current collector include foil. The thickness of the negative electrode current collector is, for example, 1 μm or more and 500 μm or less.

[0049] As shown in FIG. 1, the negative electrode current collector 1 may be in direct contact with the solid electrolyte layer 2A. Alternatively, as shown in FIG. 3, an Mg layer containing Mg may be disposed between the negative electrode current collector 1 and the solid electrolyte layer 2A. The provision of the Mg layer further improves the cycle characteristics. The Mg layer may contain Mg metal (simple Mg) or an Mg alloy (an alloy containing Mg as the main component).

[0050] The Mg layer is preferably in close contact with the negative electrode current collector. That is, the Mg layer is preferably disposed so as to cover the surface of the negative electrode current collector. In the present disclosure, a member having a negative electrode current collector and an Mg layer disposed on the negative electrode current collector may be referred to as a coated current collector. In the coated current collector, the Mg layer and the negative electrode current collector may be in direct contact with each other, or may be disposed via another layer. On the other hand, the Mg layer and solid electrolyte layer A may be in direct contact with each other, or may be disposed via another layer.

[0051] The Mg layer is, for example, a thin film, preferably a vapor-deposited film. The thickness of the Mg layer is not particularly limited, but is, for example, 30 nm or more. On the other hand, the thickness of the Mg layer may be, for example, 2000 nm or less, or 1500 nm or less. The Mg layer can be formed by a vapor deposition method such as vacuum deposition.

[0052] The Mg layer may or may not contain Li. The former corresponds to, for example, the state of the Mg layer in an all-solid-state battery before the first charge, and the latter corresponds to, for example, the state of the Mg layer in an all-solid-state battery after the first charge. When Li is introduced into the Mg layer during the first charge, the Mg contained in the Mg layer is alloyed with Li. As a result, an alloy phase, such as an Mg-Li alloy phase, is formed in the Mg layer. Meanwhile, during discharge, Li migrates from the Mg layer alloyed with Li to the positive electrode side. Although not shown, the above-mentioned protective layer may be disposed between the Mg layer and the solid electrolyte layer A. A Li phase may be formed inside the Mg layer. A precipitated Li layer may be formed between the Mg layer and the solid electrolyte layer A. A precipitated Li layer may be formed between the Mg layer and the negative electrode current collector.

[0053] 4.All-solid-state battery As shown in FIG. 2, the all-solid-state battery 10 may have a protective layer 5 containing Li and the above-mentioned M (M is at least one of Sn, Al, Zn, In, Ge, Si, Sb, Ga, and Bi) between the negative electrode current collector 1 and the solid electrolyte layer 2A. The protective layer 5 typically contains an alloy phase such as a LiM alloy phase. The protective layer 5 may also contain a residual component of the sulfide solid electrolyte. Examples of the residual component of the sulfide solid electrolyte include a compound containing P and Li, and a compound containing S and Li (e.g., LiS). The thickness of the protective layer is not particularly limited, but is, for example, 5 nm to 100 nm. A Li phase may also be formed inside the protective layer. A precipitated Li layer may also be formed between the protective layer and the solid electrolyte layer A. A precipitated Li layer may also be formed between the protective layer and the negative electrode current collector.

[0054] The use of the all-solid-state battery in the present disclosure is not particularly limited, and examples thereof include power sources for vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), electric vehicles (BEVs), gasoline-powered vehicles, and diesel-powered vehicles. In particular, it is preferable that the all-solid-state battery be used as a driving power source for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or electric vehicles (BEVs). The all-solid-state battery may also be used as a power source for mobile objects other than vehicles (e.g., railways, ships, and aircraft), and may also be used as a power source for electrical appliances such as information processing devices.

[0055] The present disclosure can also provide a method for manufacturing the above-mentioned all-solid-state battery. Specifically, the method includes a preparation step of preparing an all-solid-state battery before initial charging, the all-solid-state battery having, in this order in the thickness direction, a negative electrode current collector, a solid electrolyte layer A, a solid electrolyte layer B, and a positive electrode active material layer, and a charging step of charging the all-solid-state battery before initial charging, wherein the solid electrolyte layer A contains a first sulfide solid electrolyte and a second sulfide solid electrolyte, the solid electrolyte layer B contains a third sulfide solid electrolyte, and the first sulfide solid electrolyte has a voltage of 0.3 V (vs Li / Li) in cyclic voltammetry measurement. + ) or more 1.0V (vs Li / Li + ) or less, and contains an element M (M is at least one of Sn, Al, Zn, In, Ge, Si, Sb, Ga, and Bi), and the second sulfide solid electrolyte has a reduction reaction peak of 0.3V (vs Li / Li) in cyclic voltammetry measurement. + ) or more 1.0V (vs Li / Li + ) or less, the sulfide solid electrolyte does not have a reduction reaction peak, in the solid electrolyte layer A, a ratio of the first sulfide solid electrolyte to a total of the first sulfide solid electrolyte and the second sulfide solid electrolyte is more than 0 wt % and 45 wt % or less, and a protective layer containing Li and M is formed between the negative electrode current collector and the solid electrolyte layer A by the charging step.

[0056] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any configuration that is substantially identical to the technical idea described in the claims of the present disclosure and that provides similar effects is included within the technical scope of the present disclosure. [Example]

[0057] [Example 1] (Preparation of sulfide solid electrolyte) Li2S, P2S5, and SnS2 were prepared as starting materials for the first sulfide solid electrolyte. These starting materials were mixed in a ball mill (mechanical milling) and sintered to obtain Li2S with an LGPS-type crystal phase. 10 SnP2S 12 Next, Li2S, P2S5, and LiI were prepared as starting materials for the second sulfide solid electrolyte. These starting materials were mixed in a ball mill (mechanical milling) and sintered to obtain Li3PS4 (second sulfide solid electrolyte) containing LiI.

[0058] (Preparation of composite material for solid electrolyte layer) The first sulfide solid electrolyte and the second sulfide solid electrolyte were weighed so that the ratio of the first sulfide solid electrolyte to the total of the first sulfide solid electrolyte and the second sulfide solid electrolyte was 10 wt %, and then mixed in a mortar. This produced a composite for solid electrolyte layer A. The second sulfide solid electrolyte was also prepared as a sulfide solid electrolyte for solid electrolyte layer B.

[0059] (Preparation of positive electrode) Butyl butyrate, a 5 wt% butyl butyrate solution of a polyvinylidene fluoride binder, nickel-cobalt-lithium aluminum oxide (positive electrode active material), the second sulfide solid electrolyte, and vapor-grown carbon fiber (VGCF) (conductive material) were added to a polypropylene container (PP container). The volume ratio of the positive electrode active material to the second sulfide solid electrolyte was 75:25. The PP container was then agitated for 30 seconds using an ultrasonic disperser (UH-50, manufactured by SMT). The PP container was then shaken for 30 minutes using a shaker (TTM-1, manufactured by Shibata Scientific Co., Ltd.) to obtain a slurry for the positive electrode active material layer. The slurry was then applied to an Al foil (positive electrode current collector) using an applicator by the blade method. The mixture was then air-dried and then dried on a hot plate at 100°C for 30 minutes. As a result, a positive electrode having a positive electrode current collector and a positive electrode active material layer was obtained.

[0060] (Preparation of negative electrode current collector) Ni foil was prepared as a negative electrode current collector. Mg was vapor-deposited on the surface of the Ni foil to form an Mg layer (thickness: 1000 nm). This resulted in a negative electrode current collector with an Mg layer.

[0061] (Cell preparation) Area 1cm 2 50 mg of the second sulfide solid electrolyte for solid electrolyte layer B was placed in a McCorm cylinder, and 1 ton / cm 2 The solid electrolyte layer B was formed by pressing the solid electrolyte layer B with a pressure of 1 ton / cm. 2 The solid electrolyte layer A was formed by pressing the cathode active material layer against the solid electrolyte layer B at a pressure of 1 ton / cm. 2 Next, a negative electrode current collector was placed on the surface of the solid electrolyte layer A so that the Mg layer faced the solid electrolyte layer A, and the negative electrode current collector was pressed at a pressure of 6 ton / cm. 2 The laminate obtained by pressing was connected to a positive and negative terminals and restrained with a pressure of 2 N m to obtain a cell. The resulting cell had two solid electrolyte layers.

[0062] [Example 2] A cell was obtained in the same manner as in Example 1, except that a composite material in which the ratio of the first sulfide solid electrolyte to the total of the first sulfide solid electrolyte and the second sulfide solid electrolyte was 30 wt % was used as the composite material for the solid electrolyte layer A. The cell was obtained. The number of solid electrolyte layers in the obtained cell was two.

[0063] [Example 3] A cell was obtained in the same manner as in Example 1, except that a composite material in which the ratio of the first sulfide solid electrolyte to the total of the first sulfide solid electrolyte and the second sulfide solid electrolyte was 40 wt % was used as the composite material for solid electrolyte layer A. The cell was obtained. The number of solid electrolyte layers in the obtained cell was two.

[0064] [Comparative Example 1] A cell was obtained in the same manner as in Example 1, except that the amount of the composite for solid electrolyte layer A was changed from 50 mg to 100 mg, solid electrolyte layer B was not formed, and a composite for solid electrolyte layer A in which the ratio of the first sulfide solid electrolyte to the total of the first sulfide solid electrolyte and the second sulfide solid electrolyte was 0 wt % was used. The number of solid electrolyte layers in the obtained cell was 1.

[0065] Comparative Example 2 A cell was obtained in the same manner as in Comparative Example 1, except that a composite in which the ratio of the first sulfide solid electrolyte to the total of the first sulfide solid electrolyte and the second sulfide solid electrolyte was 40 wt % was used as the composite for solid electrolyte layer A. The number of solid electrolyte layers in the obtained cell was 1.

[0066] Comparative Example 3 A cell was obtained in the same manner as in Comparative Example 1, except that a composite in which the ratio of the first sulfide solid electrolyte to the total of the first sulfide solid electrolyte and the second sulfide solid electrolyte was 50 wt % was used as the composite for solid electrolyte layer A. The number of solid electrolyte layers in the obtained cell was 1.

[0067] Comparative Example 4 A cell was obtained in the same manner as in Comparative Example 1, except that a composite in which the proportion of the first sulfide solid electrolyte to the total of the first sulfide solid electrolyte and the second sulfide solid electrolyte was 100 wt % was used as the composite for solid electrolyte layer A. The number of solid electrolyte layers in the obtained cell was 1.

[0068] Comparative Example 5 A cell was obtained in the same manner as in Example 1, except that a composite in which the ratio of the first sulfide solid electrolyte to the total of the first sulfide solid electrolyte and the second sulfide solid electrolyte was 50 wt % was used as the composite for solid electrolyte layer A. The number of solid electrolyte layers in the obtained cell was two.

[0069] [Reference example 1] A cell was obtained in the same manner as in Comparative Example 1, except that a composite in which the proportion of the first sulfide solid electrolyte relative to the total of the first sulfide solid electrolyte and the second sulfide solid electrolyte was 5 wt % was used as the composite for solid electrolyte layer A. The number of solid electrolyte layers in the obtained cell was 1.

[0070] [Reference example 2] A cell was obtained in the same manner as in Comparative Example 1, except that a composite in which the ratio of the first sulfide solid electrolyte to the total of the first sulfide solid electrolyte and the second sulfide solid electrolyte was 10 wt % was used as the composite for solid electrolyte layer A. The number of solid electrolyte layers in the obtained cell was 1.

[0071] [Reference example 3] A cell was obtained in the same manner as in Comparative Example 1, except that a composite in which the proportion of the first sulfide solid electrolyte relative to the total of the first sulfide solid electrolyte and the second sulfide solid electrolyte was 30 wt % was used as the composite for solid electrolyte layer A. The number of solid electrolyte layers in the obtained cell was 1.

[0072] [evaluation] (cyclic voltammetry measurement) The first sulfide solid electrolyte (Li 10 SnP2S 12Cyclic voltammetry (CV) measurements were carried out using the first sulfide solid electrolyte (Li3PS4 containing LiI). As a measurement sample, a mixture of the sulfide solid electrolyte and conductive material (VGCF) was placed on stainless steel (SUS), and a Li foil was laminated on the mixture to prepare a sample (thickness 1 mm). CV measurements were carried out at a sweep rate of 1 mV / sec. As a result, it was found that the first sulfide solid electrolyte (Li 10 SnP2S 12 ) is 0.3V (vs Li / Li + ) or more 1.0V (vs Li / Li + ) or less, and the second sulfide solid electrolyte (Li3PS4 containing LiI) has a reduction reaction peak at 0.3 V (vs Li / Li + ) or more 1.0V (vs Li / Li + ) below which it was confirmed that there was no reduction reaction peak.

[0073] (Evaluation of cycle characteristics) For each example, each comparative example, and the cells obtained in each comparative example, the temperature was 25°C, the voltage range was 3.0V to 4.2V, the CCCV mode was used, and the current value was 0.6mA / cm 2 (0.03mA / cm 2 Charge-discharge measurements were carried out under the conditions of (1) and (2). The capacity retention rate (%) was calculated from the discharge capacity at the 1st cycle and the discharge capacity at the 20th cycle. The results are shown in Table 1 and Figure 4.

[0074] [Table 1]

[0075] As shown in Table 1 and FIG. 4, it was confirmed that Examples 1 to 3 had higher capacity retention rates and better cycle characteristics than Comparative Examples 1 to 4. Furthermore, when Comparative Example 1 and Comparative Example 4 were compared, the capacity retention rate of Comparative Example 4 was significantly lower than that of Comparative Example 1. This is because the first sulfide solid electrolyte (Li 10 SnP2S 12This is presumably because the reduction resistance of the first sulfide solid electrolyte (Li3PS4 containing LiI) was lower than that of the second sulfide solid electrolyte (LiI-containing Li3PS4). On the other hand, when comparing Comparative Example 1 with Reference Examples 1 to 3, Reference Examples 1 to 3 had higher capacity retention rates than Comparative Example 1, despite including the first sulfide solid electrolyte with a relatively low reduction resistance. This is presumably because the reaction product between the first sulfide solid electrolyte and Li (particularly, the LiM alloy) functioned as a protective layer. Furthermore, when comparing Comparative Example 1 with Comparative Examples 2 and 3, Comparative Examples 2 and 3 had lower capacity retention rates than Comparative Example 1. This is presumably because the reaction product between the first sulfide solid electrolyte and Li functioned, conversely, as a resistive layer.

[0076] Comparing Example 1 and Reference Example 2, Example 1 had a higher capacity retention rate than Reference Example 2. Similarly, comparing Example 2 and Reference Example 3, Example 2 had a slightly higher capacity retention rate than Reference Example 3. As described above, it was confirmed that a good capacity retention rate can be obtained even when the solid electrolyte layer is composed of multiple layers and the first sulfide solid electrolyte, which has relatively low reduction resistance, is unevenly distributed in the layer on the negative electrode current collector side.

[0077] Comparing Reference Example 1 and Comparative Example 1, Reference Example 1 had a higher capacity retention rate than Comparative Example 1. This result, and the trends of Examples 1 and 2 and Reference Examples 2 and 3 described above, suggest that a good capacity retention rate can be obtained even when the solid electrolyte layer has solid electrolyte layer A and solid electrolyte layer B, and in solid electrolyte layer A, the proportion of the first sulfide solid electrolyte relative to the total of the first sulfide solid electrolyte and the second sulfide solid electrolyte is 5 wt %. Furthermore, comparing Comparative Example 3 and Comparative Example 5, Comparative Example 5 had a higher capacity retention rate than Comparative Example 3, but also a higher capacity retention rate than Comparative Example 1. This is presumably because, as described above, the reaction product of the first sulfide solid electrolyte and Li conversely functioned as a resistance layer.

[0078] [Reference example 4] (Preparation of sulfide solid electrolyte) In the same manner as in Example 1, Li3PS4 (second sulfide solid electrolyte) containing LiI was obtained.

[0079] (Fabrication of solid electrolyte layer) Heptane, a 5 wt% heptane solution of a polyvinylidene fluoride binder, and the second sulfide solid electrolyte were added to a polypropylene container (PP container). The PP container was then stirred for 30 seconds using an ultrasonic disperser (UH-50, manufactured by SMT). The PP container was then shaken for 30 minutes using a shaker (TTM-1, manufactured by Shibata Scientific Co., Ltd.) to obtain a slurry for the solid electrolyte layer. The slurry was then applied to a PET film by a blade method using an applicator. The film was then air-dried and then dried on a hot plate at 100°C for 30 minutes. After drying, two coated solid electrolyte layers were prepared, bonded together, and coated at a pressure of 7 ton / cm. 2 After pressing, the PET film was peeled off to obtain a free-standing solid electrolyte layer. Furthermore, a Sn layer (100 nm thick) was formed on one side of the solid electrolyte layer by sputtering.

[0080] (Preparation of positive electrode) A positive electrode was obtained in the same manner as in Example 1.

[0081] (Preparation of negative electrode current collector) In the same manner as in Example 1, a negative electrode current collector having an Mg layer was obtained.

[0082] (Cell preparation) A negative electrode current collector having an Mg layer and a solid electrolyte layer having an Sn layer were each punched out to a diameter of 14.5 mm. Next, the negative electrode current collector and the solid electrolyte layer were stacked so that the Mg layer and the Sn layer faced each other. Next, a positive electrode punched out to a diameter of 11.28 mm was placed on the solid electrolyte layer. A positive electrode terminal and a negative electrode terminal were connected to the resulting stack, and the stack was sealed with a laminate film. The sealed stack was subjected to cold isostatic pressing (CIP) at a pressure of 392 MPa. The CIP-treated stack was then restrained using a metal plate at a pressure of 1 MPa to obtain a cell.

[0083] [Reference examples 5~7] Cells were obtained in the same manner as in Reference Example 4, except that in the preparation of the solid electrolyte layer, sputtering of Al, Zn or In was carried out instead of sputtering of Sn.

[0084] [Reference example 8] A cell was obtained in the same manner as in Reference Example 4, except that no sputtering was performed when the solid electrolyte layer was produced.

[0085] [evaluation] The cells obtained in each of the reference examples were subjected to charge / discharge measurements in the same manner as above, and the capacity retention rate (%) was calculated. The results are shown in Table 2.

[0086] [Table 2]

[0087] As shown in Table 2, Reference Examples 4 to 7 were confirmed to have higher capacity retention rates and better cycle characteristics than Reference Example 8. All of the metals used in Reference Examples 4 to 7 are metals that can be alloyed with Li, and it is presumed that the higher capacity retention rates were achieved by alloying with Li during charging and functioning as a protective layer. This suggests that similarly good cycle characteristics can be obtained even when the first sulfide solid electrolyte contains the above metals. [Explanation of symbols]

[0088] 1...Negative electrode current collector 2...Solid electrolyte layer 3...Cathode active material layer 4...Positive electrode current collector 5...Mg layer 6...protective layer 10...All-solid-state battery

Claims

1. An all-solid-state battery that utilizes a deposition and dissolution reaction of metallic lithium as a negative electrode reaction, a negative electrode current collector, a solid electrolyte layer A, a solid electrolyte layer B, and a positive electrode active material layer, in this order in the thickness direction; the solid electrolyte layer A contains a first sulfide solid electrolyte and a second sulfide solid electrolyte, the solid electrolyte layer B contains a third sulfide solid electrolyte, The first sulfide solid electrolyte has a voltage of 0.3 V (vs Li / Li) in cyclic voltammetry measurement. ＋ ) or more 1.0V (vs Li / Li ＋ ) or less, and contains an M element (M is at least one of Sn, Al, Zn, In, Ge, Si, Sb, Ga, and Bi), The second sulfide solid electrolyte has a voltage of 0.3 V (vs Li / Li) in cyclic voltammetry measurement. ＋ ) or more 1.0V (vs Li / Li ＋ ) The following is a sulfide solid electrolyte that does not have a reduction reaction peak, an all-solid-state battery, wherein in the solid electrolyte layer A, a proportion of the first sulfide solid electrolyte with respect to a total of the first sulfide solid electrolyte and the second sulfide solid electrolyte is greater than 0 wt % and 45 wt % or less.

2. 2. The all-solid-state battery according to claim 1, wherein in the solid electrolyte layer A, a ratio of the first sulfide solid electrolyte to a total of the first sulfide solid electrolyte and the second sulfide solid electrolyte is 5 wt % or more and 40 wt % or less.

3. The third sulfide solid electrolyte has a voltage of 0.3 V (vs Li / Li) in cyclic voltammetry measurement. ＋ ) or more 1.0V (vs Li / Li ＋ 2. The all-solid-state battery according to claim 1, wherein the sulfide solid electrolyte does not have a reduction reaction peak at or below 0.1 V.

4. The first sulfide solid electrolyte contains a Li element, the M element, and an S element, 2. The all-solid-state battery according to claim 1, wherein the M element is at least one of Sn, Al, Zn, and In.

5. 2. The all-solid-state battery according to claim 1, further comprising a protective layer containing Li and M between the negative electrode current collector and the solid electrolyte layer A.

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