Secondary battery

Abstract

To reduce resistance of a secondary battery having a deposition type lithium anode to improve cycle characteristics.SOLUTION: A secondary battery of the present disclosure includes: a cathode; a solid electrolyte layer; an anode current collector; and metal lithium as an anode active material deposited between the solid electrolyte layer and the anode current collector by charging. An Mg mixture layer is present between the solid electrolyte layer and the anode current collector. The solid electrolyte layer contains a first solid electrolyte. The Mg mixture layer contains Mg and a second solid electrolyte. The Young's modulus of the second solid electrolyte is lower than the Young's modulus of the first solid electrolyte.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present application discloses a secondary battery. [Background technology]

[0002] Patent Document 1 discloses an all-solid-state battery comprising a positive electrode, a solid electrolyte layer, a negative electrode current collector, and metallic lithium as a negative electrode active material that is precipitated between the electrolyte layer and the negative electrode current collector upon charging. In Patent Document 1, a metallic Mg layer is disposed between the solid electrolyte layer and the negative electrode current collector, so that a Li-Mg alloy as the metallic lithium can be precipitated during charging. Patent Document 2 discloses a battery comprising a positive electrode, a solid electrolyte layer, a protective layer, and a negative electrode, in which the negative electrode contains metallic lithium and the protective layer contains a predetermined Li composite oxide. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-184513 A [Patent Document 2] JP 2020-184407 A Summary of the Invention [Problem to be solved by the invention]

[0004] Secondary batteries equipped with a precipitated metallic lithium negative electrode have room for improvement in terms of resistance and cycle characteristics. [Means for solving the problem]

[0005] The present application discloses the following aspects as means for solving the above problems. <Aspect 1> A secondary battery comprising: a positive electrode; a solid electrolyte layer; a negative electrode current collector; and metallic lithium as a negative electrode active material that is deposited between the solid electrolyte layer and the negative electrode current collector upon charging; a Mg mixture layer is present between the solid electrolyte layer and the negative electrode current collector, the solid electrolyte layer comprises a first solid electrolyte; the Mg mixture layer contains Mg and a second solid electrolyte, The Young's modulus of the second solid electrolyte is lower than the Young's modulus of the first solid electrolyte. Secondary battery. <Aspect 2> The Young's modulus of the second solid electrolyte is 1 GPa or more and 20 GPa or less. The secondary battery of embodiment 1. <Aspect 3> The first solid electrolyte is a sulfide solid electrolyte. 3. The secondary battery according to claim 1 or 2. <Aspect 4> The second solid electrolyte is a complex hydride containing Li. The secondary battery according to any one of aspects 1 to 3. <Aspect 5> a protective layer is present between the Mg mixture layer and the negative electrode current collector; The protective layer contains Mg and does not contain an electrolyte. The secondary battery according to any one of aspects 1 to 4. <Aspect 6> The positive electrode contains a lithium-containing oxide as a positive electrode active material. The secondary battery according to any one of aspects 1 to 5. <Aspect 7> The negative electrode current collector comprises stainless steel. The secondary battery according to any one of aspects 1 to 6. Effect of the Invention

[0006] The secondary battery of the present disclosure has low resistance and excellent cycle characteristics while being equipped with a deposition-type metallic lithium negative electrode. [Brief description of the drawings]

[0007] [Figure 1] 1A and 1B are schematic diagrams illustrating an example of the configuration of the secondary battery 100 after charging and after discharging. [Diagram 2]1A and 1B are schematic diagrams illustrating an example of the configuration of the secondary battery 100 after charging and after discharging. [Diagram 3] 1 shows an example of a flow of a manufacturing method for the secondary battery 100. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] 1. Secondary battery Hereinafter, a secondary battery according to an embodiment will be described with reference to the drawings, but the technology of the present disclosure is not limited to the following embodiment. FIG. 1 shows a configuration of a secondary battery 100 according to an embodiment. As shown in FIG. 1, the secondary battery 100 includes a positive electrode 10, a solid electrolyte layer 20, a negative electrode current collector 31, and metallic lithium 32 as a negative electrode active material that is deposited between the solid electrolyte layer 20 and the negative electrode current collector 31 by charging. Between the solid electrolyte layer 20 and the negative electrode current collector 31, an Mg mixture layer 33 is present. The solid electrolyte layer 20 includes a first solid electrolyte, and the Mg mixture layer 33 includes Mg and a second solid electrolyte. The Young's modulus of the second solid electrolyte is lower than that of the first solid electrolyte.

[0009] 1.1 Positive electrode The positive electrode 10 includes at least a positive electrode active material. When the secondary battery 100 is charged, lithium ions released from the positive electrode active material reach between the solid electrolyte layer 20 and the negative electrode current collector 31 through the solid electrolyte layer 20, receive electrons, and are precipitated as metallic lithium 32. When the battery is discharged, the metallic lithium 32 between the solid electrolyte layer 20 and the negative electrode current collector 31 is dissolved (ionized) and returned to the positive electrode 10. The form of the positive electrode 10 may be any form known as a positive electrode for a secondary battery. For example, as shown in FIG. 1, the positive electrode 10 may include a positive electrode current collector 11 and a positive electrode active material layer 12.

[0010] 1.1.1 Positive electrode current collector The positive electrode collector 11 may be any material capable of functioning as a positive electrode collector of a secondary battery. The positive electrode collector 11 may be a metal foil or a metal mesh. In particular, a metal foil is excellent in terms of ease of handling. The positive electrode collector 11 may be made of a plurality of metal foils. Examples of metals constituting the positive electrode collector 11 include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, and stainless steel. In particular, the positive electrode collector 11 may contain Al from the viewpoint of ensuring oxidation resistance. The positive electrode collector 11 may have some kind of coating layer on its surface for the purpose of adjusting resistance, etc. In addition, when the positive electrode collector 11 is made of a plurality of metal foils, some kind of layer may be present between the plurality of metal foils. The thickness of the positive electrode collector 11 is not particularly limited. For example, it may be 0.1 μm or more or 1 μm or more, and may be 1 mm or less or 100 μm or less.

[0011] 1.1.2 Cathode active material layer The positive electrode active material layer 12 includes a positive electrode active material, and may further include an electrolyte, a conductive assistant, a binder, and the like. Furthermore, the positive electrode active material layer 12 may include various additives. The content of each of the positive electrode active material, electrolyte, conductive assistant, binder, and the like in the positive electrode active material layer 12 may be appropriately determined according to the target battery performance. For example, the content of the positive electrode active material may be 40 mass% or more, 50 mass% or more, or 60 mass% or more, and may be 100 mass% or less, or 90 mass% or less, assuming that the entire positive electrode active material layer 12 (total solid content) is 100 mass%. The shape of the positive electrode active material layer 12 is not particularly limited, and may be, for example, a sheet shape having a substantially flat surface. The thickness of the positive electrode active material layer 12 is not particularly limited and may be, for example, 0.1 μm or more, 1 μm or more, 10 μm or more, or 30 μm or more, and may be 2 mm or less, 1 mm or less, 500 μm or less, or 100 μm or less.

[0012] The positive electrode active material is a known positive electrode active material for secondary batteries, and any material capable of supplying lithium to the negative electrode side during charging may be used. For example, lithium cobalt oxide, lithium nickel oxide, LiNi1 / 3 Co 1 / 3 Mn 1 / 3 Various lithium-containing oxides such as O2, lithium manganate, and spinel-based lithium compounds can be used. Alternatively, a material in which lithium is absorbed in sulfur can be used as the positive electrode active material. In particular, when the positive electrode 10 contains a lithium-containing oxide as the positive electrode active material, lithium ions can be appropriately supplied from the positive electrode active material to the negative electrode side during charging, and the positive electrode active material is less likely to expand and contract during charging and discharging, making it easy to obtain high performance. Only one type of positive electrode active material may be used alone, or two or more types may be used in combination. The positive electrode active material may be, for example, particulate, and the size is not particularly limited. The particles of the positive electrode active material may be solid particles, hollow particles, or particles having voids. The particles of the positive electrode active material may be primary particles, or secondary particles in which a plurality of primary particles are aggregated. The average particle diameter (D50) of the particles of the positive electrode active material may be, for example, 1 nm or more, 5 nm or more, or 10 nm or more, and may be 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less. Note that the average particle diameter D50 referred to in this application is the particle diameter (median diameter) at an integrated value of 50% in a volume-based particle size distribution obtained by a laser diffraction / scattering method.

[0013] The surface of the positive electrode active material may be covered with a protective layer containing an ion-conductive oxide. That is, the positive electrode active material layer 12 may contain a composite having the above-mentioned positive electrode active material and a protective layer provided on the surface thereof. This makes it easier to suppress the reaction between the positive electrode active material and a sulfide (for example, a sulfide solid electrolyte described later). Examples of the ion-conductive oxide that covers and protects the surface of the positive electrode active material include Li3BO3, LiBO2, Li2CO3, LiAlO2, Li4SiO4, Li2SiO3, Li3PO4, Li2SO4, Li2TiO3, Li4Ti5O 12, Li2Ti2O5, Li2ZrO3, LiNbO3, Li2MoO4, and Li2WO4. The coverage (area ratio) of the protective layer to the surface of the positive electrode active material may be, for example, 70% or more, 80% or more, or 90% or more. The thickness of the protective layer may be, for example, 0.1 nm or more or 1 nm or more, and may be 100 nm or less, or 20 nm or less.

[0014] The electrolyte that can be contained in the positive electrode active material layer 12 may be a solid electrolyte, a liquid electrolyte (electrolytic solution), or a combination thereof. In particular, when the positive electrode active material layer 12 contains a solid electrolyte (particularly, a sulfide solid electrolyte), the technology of the present disclosure can be expected to provide even greater effects.

[0015] The solid electrolyte may be any known solid electrolyte for secondary batteries. The solid electrolyte may be an inorganic solid electrolyte or an organic polymer electrolyte. In particular, inorganic solid electrolytes are excellent in ion conductivity and heat resistance. Examples of inorganic solid electrolytes include oxide solid electrolytes and sulfide solid electrolytes. Examples of oxide solid electrolytes include lithium lanthanum zirconate, LiPON, Li 1+X Al X Ge 2-X The sulfide solid electrolyte may be one or more selected from (PO4)3, Li-SiO-based glass, Li-Al-SO-based glass, etc. The sulfide solid electrolyte may be one or more of those exemplified as the first solid electrolyte described later. Among inorganic solid electrolytes, sulfide solid electrolytes, and among them, sulfide solid electrolytes containing at least Li, S, and P as constituent elements, have high performance. The solid electrolyte may be amorphous or crystalline. The solid electrolyte may be, for example, particulate. Only one type of solid electrolyte may be used alone, or two or more types may be used in combination.

[0016] The electrolyte may contain, for example, lithium ions as carrier ions. The electrolyte may be, for example, a non-aqueous electrolyte. For example, the electrolyte may be a carbonate-based solvent in which a lithium salt is dissolved at a predetermined concentration. Examples of the carbonate-based solvent include fluoroethylene carbonate (FEC), ethylene carbonate (EC), and dimethyl carbonate (DMC). Examples of the lithium salt include hexafluorophosphate.

[0017] Examples of the conductive assistant that may be included in the positive electrode active material layer 12 include carbon materials such as vapor grown carbon fiber (VGCF), acetylene black (AB), ketjen black (KB), carbon nanotubes (CNT), and carbon nanofibers (CNF); and metal materials such as nickel, aluminum, and stainless steel. The conductive assistant may be, for example, particulate or fibrous, and the size is not particularly limited. Only one type of conductive assistant may be used alone, or two or more types may be used in combination.

[0018] Examples of binders that can be included in the positive electrode active material layer 12 include butadiene rubber (BR)-based binders, butylene rubber (IIR)-based binders, acrylate butadiene rubber (ABR)-based binders, styrene butadiene rubber (SBR)-based binders, polyvinylidene fluoride (PVdF)-based binders, polytetrafluoroethylene (PTFE)-based binders, polyimide (PI)-based binders, polyacrylic acid-based binders, etc. Only one type of binder may be used alone, or two or more types may be used in combination.

[0019] 1.2 Solid electrolyte layer The solid electrolyte layer 20 includes at least a first solid electrolyte. The first solid electrolyte included in the solid electrolyte layer 20 may be the same type as or different from the solid electrolyte that may be included in the above-mentioned positive electrode active material layer 12. The solid electrolyte layer 20 may further include an arbitrary binder, various additives, and the like. The binder included in the solid electrolyte layer 20 may be the same type as or different from the binder that may be included in the above-mentioned positive electrode active material layer 12. In the solid electrolyte layer 20, the first solid electrolyte and the binder may each be used alone, or two or more types may be used in combination. The solid electrolyte layer 20 does not need to be formed entirely of a solid, and may include various liquids as long as it can function appropriately as a secondary battery. The contents of the first solid electrolyte and the binder, etc. in the solid electrolyte layer 20 are not particularly limited. For example, the content of the first solid electrolyte may be 50 mass% or more, 60 mass% or more, or 70 mass% or more, and 100 mass% or less, or 90 mass% or less, where the entire solid electrolyte layer 20 (total solid content) is taken as 100 mass%. The thickness of the solid electrolyte layer 20 is not particularly limited, and may be, for example, 0.1 μm or more, or 1 μm or more, and 2 mm or less, or 1 mm or less.

[0020] In the secondary battery 100, the Young's modulus of the first solid electrolyte contained in the solid electrolyte layer 20 is higher than the Young's modulus of the second solid electrolyte contained in the Mg mixture layer 33 described later. That is, the first solid electrolyte is harder than the second solid electrolyte described later. The Young's modulus of the first solid electrolyte may be, for example, more than 20 GPa. In the present application, the "Young's modulus" refers to the Young's modulus at 25°C. There are various types of hard first solid electrolytes. For example, when the first solid electrolyte is an inorganic solid electrolyte, particularly a sulfide solid electrolyte, higher performance is likely to be exhibited.

[0021] The sulfide solid electrolyte may be a glass-based sulfide solid electrolyte (sulfide glass), a glass ceramic-based sulfide solid electrolyte, or a crystalline sulfide solid electrolyte. The sulfide glass is amorphous. The sulfide glass preferably has a glass transition temperature (Tg). In addition, when the sulfide solid electrolyte has a crystalline phase, examples of the crystalline phase include a Thio-LISICON type crystalline phase, a LGPS type crystalline phase, and an Argyrodite type crystalline phase.

[0022] The sulfide solid electrolyte preferably contains, for example, Li, X (X is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In), and S. The sulfide solid electrolyte may further contain at least one of O and halogen. The sulfide solid electrolyte preferably contains S as a main component of anion elements.

[0023] Examples of sulfide solid electrolytes include Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-GeS2, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-P2S5-LiI-LiBr, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-ZmSn (where m and n are positive numbers, and Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, and Li2S-SiS2-Li x MO y (wherein x and y are positive numbers, and M is any one of P, Si, Ge, B, Al, Ga, and In).

[0024] The composition of the sulfide solid electrolyte is not particularly limited. For example, xLi2S·(100 - x)P2S5 (70 ≤ x ≤ 80), yLiI·zLiBr·(100 - y - z)(xLi2S·(1 - x)P2S5) (0.7 ≤ x ≤ 0.8, 0 ≤ y ≤ 30, 0 ≤ z ≤ 30), etc. may be mentioned. Alternatively, the sulfide solid electrolyte has a general formula: Li 4-x Ge 1-x P x S4 (0 < x < 1). In the above general formula, at least a part of Ge may be substituted with at least one of Sb, Si, Sn, B, Al, Ga, In, Ti, Zr, V, and Nb. In the above general formula, at least a part of P may be substituted with at least one of Sb, Si, Sn, B, Al, Ga, In, Ti, Zr, V, and Nb. In the above general formula, a part of Li may be substituted with at least one of Na, K, Mg, Ca, and Zn. In the above general formula, a part of S may be substituted with a halogen (at least one of F, Cl, Br, and I). Alternatively, the sulfide solid electrolyte is Li 7-a PS 6-a X a (X is at least one of Cl, Br, and I, and a is a number of 0 or more and 2 or less). a may be 0, or may be greater than 0. In the latter case, a may be 0.1 or more, may be 0.5 or more, or may be 1 or more. Also, a may be 1.8 or less, may be 1.5 or less.

[0025] The shape of the sulfide solid electrolyte may be, for example, particulate. The average particle diameter (D50) of the sulfide solid electrolyte may be, for example, 10 nm or more and 10 μm or less. The ionic conductivity of the sulfide solid electrolyte at 25°C may be, for example, 1×10 -4 S / cm or more, or 1×10 -3 S / cm or more.

[0026] 1.3 Negative electrode current collector The negative electrode current collector 31 may be any material capable of functioning as a negative electrode current collector for a secondary battery. The negative electrode current collector 31 may be a metal foil or a metal mesh, or may be a carbon sheet. In particular, a metal foil is excellent in terms of ease of handling. The negative electrode current collector 31 may be made of a plurality of metal foils or sheets. Examples of metals constituting the negative electrode current collector 31 include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, stainless steel, and the like. In particular, from the viewpoint of ensuring reduction resistance and being difficult to alloy with lithium, the negative electrode current collector 31 may be at least one metal selected from Cu, Ni, and stainless steel, and may include stainless steel in particular. The negative electrode current collector 31 may have some kind of coating layer on its surface. For example, the surface of the negative electrode current collector 31 may be covered with a protective layer 34 described later. Alternatively, the negative electrode current collector 31 may have a coating layer other than the protective layer 34 on its surface. In addition, when the negative electrode current collector 31 is made of a plurality of metal foils, some layer may be present between the plurality of metal foils. The thickness of the negative electrode current collector 31 is not particularly limited. For example, it may be 0.1 μm or more or 1 μm or more, and may be 1 mm or less or 100 μm or less.

[0027] 1.4 Metallic lithium as a negative electrode active material The secondary battery 100 includes a lithium precipitation type negative electrode. Specifically, as shown in FIG. 1, metallic lithium 32 is precipitated as a negative electrode active material between the solid electrolyte layer 20 and the negative electrode current collector 31 by charging. In the secondary battery 100, as shown in FIG. 1, metallic lithium 32 is considered to be precipitated at least between the Mg mixture layer 33 and the negative electrode current collector 31. However, as shown in FIG. 1, metallic lithium 32 may be precipitated between the Mg mixture layer 33 and the negative electrode current collector 31, may be precipitated inside the Mg mixture layer 33, or may be precipitated between the solid electrolyte layer 20 and the Mg mixture layer 33. The metallic lithium 32 precipitated between the electrolyte layer 20 and the negative electrode current collector 31 is dissolved (ionized) during discharge and returned to the positive electrode 10.

[0028] In the present application, the term "metallic lithium" is a concept including lithium alloys as well as simple lithium. That is, in the secondary battery 100, the metallic lithium 32 may be precipitated as simple lithium or may be precipitated as an alloy with other metals. Examples of the lithium alloy include Li-Au, Li-Mg, Li-Sn, 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. The lithium alloy may be one type or two or more types. As described later, in the secondary battery 100, a Mg mixture layer 33 is disposed between the solid electrolyte layer 20 and the negative electrode current collector 31. Therefore, when the secondary battery 100 is charged, the metallic lithium 32 can be alloyed with the Mg contained in the Mg mixture layer 33 and precipitated as a Li-Mg alloy.

[0029] The amount of metallic lithium 32 precipitated between the solid electrolyte layer 20 and the negative electrode current collector 31 is not particularly limited. It may be adjusted appropriately depending on the intended battery performance. However, if the amount of precipitated metallic lithium 32 is too large, there is a concern that pressure may be concentrated. In this regard, as a guideline for the amount of precipitated metallic lithium 32, it is recommended that the charge capacity of the secondary battery 100 is, for example, 1 mAh / cm 2 More than 5mAh / cm 2 The amount may be such that:

[0030] According to the findings of the present inventor, in a conventional secondary battery having a lithium precipitation type negative electrode, when the deposition and dissolution of metallic lithium is repeated between the electrolyte layer and the negative electrode current collector, the metallic lithium is likely to be deposited and dissolved unevenly. This problem is particularly likely to occur when the current load is high. In some cases, the metallic lithium grows locally and excessively. In addition, when the metallic lithium is deposited and dissolved unevenly, the resistance of the secondary battery increases and the cycle characteristics are likely to decrease. That is, the secondary battery having a lithium precipitation type negative electrode has room for improvement in terms of resistance and cycle characteristics. In the secondary battery 100 of the present disclosure, the Mg mixture layer 33 is disposed between the solid electrolyte layer 20 and the negative electrode current collector 31, so that the deposition and dissolution of metallic lithium 32 is likely to occur uniformly, and the resistance and cycle characteristics can be improved.

[0031] 1.5 Mg mixture layer The Mg mixture layer 33 contains Mg and a second solid electrolyte. According to the inventor's new findings, by disposing such an Mg mixture layer 33 between the solid electrolyte layer 20 and the negative electrode current collector 31, during charging of the secondary battery 100, lithium ions are conducted from the positive electrode 10 to the negative electrode current collector 31 side through the solid electrolyte layer 20, and Mg in the Mg mixture layer 33 and lithium undergo an alloying reaction. Here, it is considered that the Mg mixture layer 33 forms an interface three-dimensionally, and the frequency factor of the interface reaction is improved. In addition, it is considered that the metallic lithium 32 is precipitated while being alloyed with Mg in the Mg mixture layer 33, so that the metallic lithium 32 and the Mg mixture layer 33 are adhered to each other by an anchor effect, and the interface between the metallic lithium 32 and the Mg mixture layer 33 is well maintained. It is believed that maintaining a good interface between the metallic lithium 32 and the Mg mixture layer 33 suppresses interruption of the conductive path and concentration of power due to peeling of the metallic lithium 32, and also makes it easier for the metallic lithium 32 to redissolve uniformly during discharge. In this way, in the secondary battery 100, by disposing the Mg mixture layer 33 between the solid electrolyte layer 20 and the negative electrode current collector 31, the input / output characteristics of lithium between the solid electrolyte layer 20 and the negative electrode current collector 31 are improved, and local growth during precipitation of the metallic lithium 32 can be suppressed, which is believed to improve the cycle characteristics of the secondary battery 100 and reduce the resistance of the secondary battery 100.

[0032] In addition, according to the inventor's new findings, the second solid electrolyte contained in the Mg mixture layer 33 is softer than the first solid electrolyte contained in the solid electrolyte layer 20, so that the resistance of the secondary battery 100 is more likely to be reduced and the cycle characteristics are more likely to be improved. Specifically, the second solid electrolyte contained in the Mg mixture layer 33 is softer than the first solid electrolyte contained in the solid electrolyte layer 20, so that the second solid electrolyte is easily deformed and the gap between the solid electrolyte layer 20 and the negative electrode current collector 31 is easily eliminated by the second solid electrolyte. In addition, the deformation of the second solid electrolyte makes it easier to increase the filling rate of the Mg mixture layer 33 itself. Furthermore, the presence of the soft second solid electrolyte makes it easier to suppress interfacial peeling. As a result, it is believed that the conductive path and the ion conductive path are better maintained between the solid electrolyte layer 20 and the negative electrode current collector 31, so that the resistance of the secondary battery 100 is more likely to be reduced and the cycle characteristics are more likely to be improved.

[0033] 1, the Mg mix layer 33 may or may not be in contact with the solid electrolyte layer 20. Even if some intermediate layer exists between the Mg mix layer 33 and the solid electrolyte layer 20, the effect of the Mg mix layer 33 can be exhibited. However, when the Mg mix layer 33 is in contact with the solid electrolyte layer 20, a higher effect is likely to be ensured.

[0034] 1.5.1 Mg In the Mg mixture layer 33, Mg may be present as Mg particles. Nuclei of metallic lithium 32 are likely to be formed stably on the Mg particles. Therefore, by including Mg particles in the Mg mixture layer 33, metallic lithium 32 is more likely to precipitate stably. In addition, Mg has a wide composition range in which it can form a single phase with Li, which allows for more efficient dissolution and precipitation of lithium.

[0035] The Mg particles may be particles of simple Mg, or may be particles containing Mg and an element other than Mg. Examples of elements other than Mg include various metal elements, semimetal elements, and nonmetal elements. For example, the Mg particles may be alloy particles (Mg alloy particles) containing Mg and a metal other than Mg. The Mg alloy particles are preferably alloys containing Mg as a main component (alloys in which 50 mol % or more of all constituent elements is Mg). The Mg alloy particles may contain at least one of Li, Au, Al, and Ni as the metal M other than Mg. The Mg alloy particles may or may not contain Li. The Mg alloy particles may contain a β single-phase alloy of Li and Mg. Alternatively, the Mg particles may be oxide particles (Mg oxide particles) containing Mg and O. The Mg oxide particles may be, for example, particles of an oxide consisting only of Mg and O, or particles of a composite oxide represented by Mg-M'-O (M' is at least one of Li, Au, Al, and Ni). When the Mg oxide particles contain M', it is preferable that M' contains at least Li. M' may or may not contain a metal other than Li. In the former case, M' may be one metal other than Li, or two or more metals.

[0036] The Mg particles may be primary particles or secondary particles formed by agglomeration of primary particles. The average particle diameter (D50) of the Mg particles is preferably small. It is considered that when the average particle diameter of the Mg particles is small, the dispersibility of the Mg particles in the Mg mixture layer 33 is improved, the precipitation starting points of Li are increased, and the metallic lithium 32 can be more uniformly precipitated. The average particle diameter (D50) of the Mg particles may be, for example, 100 nm or more and 100 μm or less, 200 nm or more, 300 nm or more, 400 nm or more, 500 nm or more, 600 nm or more, 700 nm or more, or 800 nm or more, or 50 μm or less, 40 μm or less, 30 μm or less, 20 μm or less, 10 μm or less, 5 μm or less, or 3 μm or less. The average particle diameter (D50) of the Mg particles may be the same as the average particle diameter (D50) of the second solid electrolyte described later, or may be larger or smaller than it.

[0037] The amount of Mg contained in the Mg mixture layer 33 is not particularly limited. From the viewpoint of increasing the starting points of precipitation of Li described above, the amount of Mg may be large, and from the viewpoint of increasing the ion conductivity in the Mg mixture layer 33, the amount of Mg may be small. For example, the Mg mixture layer 33 may contain 10 mass % or more and 90 mass % or less of Mg. The Mg content in the Mg mixture layer 33 may be 20 mass % or more, 30 mass % or more, or 40 mass % or more, and may be 80 mass % or less, 70 mass % or less, or 60 mass % or less.

[0038] 1.5.2 Second solid electrolyte The Young's modulus of the second solid electrolyte contained in the Mg mixture layer 33 is lower than that of the first solid electrolyte contained in the solid electrolyte layer 20. That is, the second solid electrolyte is softer than the first solid electrolyte. The Young's modulus of the second solid electrolyte may be, for example, 1 GPa or more and 20 GPa or less. It is considered that the lower the Young's modulus of the second solid electrolyte, the more the deformation performance of the second solid electrolyte is improved, and the effect of eliminating the above-mentioned gap is easily exhibited. In this regard, the Young's modulus of the second solid electrolyte may be 18 GPa or less, 16 GPa or less, 14 GPa or less, 12 GPa or less, 10 GPa or less, 8 GPa or less, 6 GPa or less, 4 GPa or less, or 2 GPa or less. In the Mg mixture layer 33, various soft second solid electrolytes can be adopted.

[0039] For example, the second solid electrolyte may be a complex hydride containing Li. The complex hydride satisfies the above Young's modulus and has low reactivity with the sulfide solid electrolyte. That is, when a sulfide solid electrolyte is adopted as the first solid electrolyte, the reaction between the first solid electrolyte and the second solid electrolyte can be suppressed, and the durability of the battery is likely to be improved. The complex hydride may be composed of Li ions and complex ions containing H. The complex ion containing H may have, for example, an element M containing at least one of a nonmetallic element, a semimetallic element, and a metallic element, and H bonded to the element M. In addition, the complex ion containing H may be a complex ion in which the element M as a central element and H surrounding the element M are bonded to each other via a covalent bond. In addition, the complex ion containing H may be a complex ion containing (M m H n ) α- In this case, m is any positive number, and n and α can be any positive number depending on m and the valence of element M. Element M may be a nonmetallic element or a metallic element capable of forming a complex ion. For example, element M may contain at least one of B, C, and N as a nonmetallic element, or may contain B. Also, for example, element M may contain at least one of Al, Ni, and Fe as a metallic element. In particular, when the complex ion contains B, or contains C and B, softness and higher ionic conductivity are likely to be ensured. Specific examples of complex ions containing H include (CB9H 10 ) - , (C.B. 11 H 12 ) - , (B 10 H 10 ) 2- , (B 12 H 12 ) 2- , (BH4) - , (NH2) - , (AlH4) - , and combinations thereof. In particular, (CB9H 10 ) - , (C.B. 11 H 12 ) -In other words, the Li-containing complex hydride may contain Li, C, B, and H.

[0040] The second solid electrolyte may be a salt having multiple types of cations and / or multiple types of anions, or may be a molten salt obtained by melting multiple types of salts. In this case, the second solid electrolyte may contain an organic cation or an organic anion. Some of these salts satisfy the above Young's modulus.

[0041] When the second solid electrolyte is a salt, the second solid electrolyte may have, for example, a first cation and a second cation, the first cation may be at least one selected from an ammonium ion, a phosphonium ion, a pyridinium ion, and a pyrrolidinium ion, and the second cation may be a lithium ion. The first cation may be a tetraalkylammonium ion, and the second cation may be a lithium ion. When the second solid electrolyte has an organic cation as the first cation, the Young's modulus is likely to be lower than when the second solid electrolyte does not have the first cation. The molar ratio of the first cation and the second cation constituting the second solid electrolyte is not particularly limited. From the viewpoint of further increasing the ion conductivity, the molar ratio of the second cation to the first cation (second cation / first cation) may be 0.05 or more and 19.0 or less. The molar ratio may be 0.1 or more, 0.2 or more, 0.3 or more, 0.4 or more, 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more, 0.9 or more, or 1.0 or more, and may be 10.0 or less, 9.5 or less, 9.0 or less, 8.5 or less, 8.0 or less, 7.5 or less, 7.0 or less, 6.5 or less, 6.0 or less, 5.5 or less, or 5.0 or less. The cations constituting the second solid electrolyte may be composed of only the first cation and the second cation, or may contain other cations different from the first cation. Examples of the other cations include ions containing poor metal elements. Examples of poor metals include Al and Ga. The total proportion of the first cation and the second cation in all the cations constituting the second solid electrolyte may be 50 mol% or more and 100 mol% or less, or may be 60 mol% or more, 70 mol% or more, 80 mol% or more, 90 mol% or more, 95 mol% or more, 99 mol% or more, or 100 mol%.

[0042] When the second solid electrolyte is a salt, the second solid electrolyte may have, for example, various anions. For example, the second solid electrolyte may have at least one anion selected from a halogen ion, a halide ion, a hydrogen sulfate ion, a sulfonyl amide ion, and a complex ion containing H. Alternatively, the second solid electrolyte may have one or both of a first anion and a second anion, the first anion may be one or both of a halogen ion and a hydrogen sulfate ion, and the second anion may be a sulfonyl amide anion. Alternatively, the second solid electrolyte may have a sulfonyl amide ion. The halogen ion may be, for example, one or both of a bromide ion and a chloride ion. Examples of the sulfonyl amide anion include a trifluoromethanesulfonyl amide anion (TFSA anion, (CF3SO2)2N - ), Fluorosulfonylamide anion (FSA anion, (FSO2)2N - ), Fluorosulfonyl(trifluoromethanesulfonyl)amide anion (FTA anion, FSO2(CF3SO2)N - ) and the like. The sulfonylamide anion may be one type only, or two or more types may be combined. Among the above sulfonylamide anions, the TFSA anion has low polarity and is particularly low in reactivity with other materials. In this respect, when the second solid electrolyte has a TFSA anion, for example, the reaction with the sulfide solid electrolyte is easily suppressed. The complex ion containing H is as described above.

[0043] The amount of the second solid electrolyte contained in the Mg mixture layer 33 is not particularly limited. From the viewpoint of more easily eliminating the gap generated between the solid electrolyte layer 20 and the negative electrode current collector 31 and from the viewpoint of increasing ion conductivity, the amount of the second solid electrolyte may be large, and from the viewpoint of increasing Mg and increasing the starting points of Li precipitation, the amount of the second solid electrolyte may be small. For example, the Mg mixture layer 33 may contain 10% by mass or more and 90% by mass or less of the second solid electrolyte. The content of the second solid electrolyte in the Mg mixture layer 33 may be 20% by mass or more, 30% by mass or more, or 40% by mass or more, and may be 80% by mass or less, 70% by mass or less, or 60% by mass or less.

[0044] 1.5.3 Other ingredients The Mg mixture layer 33 may contain a binder as necessary. This can suppress cracking and the like in the Mg mixture layer 33. The binder may be appropriately selected from, for example, those exemplified as binders that can be contained in the above-mentioned positive electrode active material layer. The binder that can be contained in the Mg mixture layer 33 may be the same type as or different from the binder that can be contained in the above-mentioned positive electrode active material layer. Only one type of binder may be used alone, or two or more types may be used in combination.

[0045] 1.5.4 Filling rate The filling rate of the Mg mixture layer 33 is not particularly limited. When the filling rate of the Mg mixture layer 33 is high, the cycle characteristics of the secondary battery tend to be better. The filling rate of the Mg mixture layer 33 may be, for example, 70% or more and 100% or less. The filling rate may be 80% or more, 90% or more, 95% or more, or 98% or more. The filling rate of the Mg mixture layer 33 can be calculated by the following method. That is, the weight of each material (Mg particles, second solid electrolyte, etc.) contained in the Mg mixture layer 33 is divided by the true density of each material to obtain a total volume, which is defined as the "volume of the Mg mixture layer calculated from the true density," and the volume calculated from the actual dimensions of the Mg mixture layer is defined as the "actual volume of the Mg mixture layer," and the filling rate (%) can be calculated from the following formula. Filling rate (%) = (volume of Mg mixture layer calculated from true density) / (actual volume of Mg mixture layer) × 100

[0046] 1.5.5 Thickness etc. The secondary battery 100 may include only one Mg mixture layer 33, or may include two or more layers. The total thickness of the Mg mixture layer 33 may be, for example, 0.1 μm or more and 1000 μm or less. The Mg mixture layer 33 may be formed, for example, by applying a slurry containing at least Mg particles and a second solid electrolyte onto a substrate. Alternatively, a method may be used in which a particle layer containing Mg particles is formed, and then the particle layer is impregnated with an electrolyte solution in which the second solid electrolyte is dissolved, and then the layer is dried.

[0047] 1.6 Protective layer As shown in FIG. 2, in the secondary battery 100, a protective layer 34 may be present between the Mg mixture layer 33 and the negative electrode current collector 31. The protective layer 34 may contain Mg and may not contain an electrolyte. By disposing the protective layer 34 between the Mg mixture layer 33 and the negative electrode current collector 31, the diffusion of Li can be further promoted. In addition, when the protective layer 34 is present, the second solid electrolyte contained in the Mg mixture layer 33 does not directly contact the negative electrode current collector 31, so that the precipitation starting point of the metallic lithium 32 can be substantially only on the Mg of the Mg mixture layer 33 and the protective layer 34. This allows the metallic lithium 32 to be precipitated more uniformly. Note that FIG. 2 shows a form in which an interface between the metallic lithium 32 and the protective layer 34 exists after charging the secondary battery 100, but the entire protective layer 34 may be alloyed with the metallic lithium 32.

[0048] The protective layer 34 is preferably a layer in which the molar ratio of Mg is the highest among all the constituent elements. The molar ratio of Mg in the entire protective layer 34 may be, for example, 50 mol% or more and 100 mol% or less, or 70 mol% or more, 80 mol% or more, or 90 mol% or more. The protective layer 34 may be, for example, either a metal thin film containing Mg (e.g., a vapor deposition film) or a layer containing Mg particles. The metal thin film containing Mg may be made of Mg or an Mg alloy. The Mg particles are as described above. The protective layer 34 may be a layer containing only Mg particles.

[0049] The thickness of the protective layer 34 may be, for example, 10 nm or more and 10 μm or less. The thickness of the protective layer 34 may be 50 nm or more or 100 nm or more, or 5 μm or less, 3 μm or less, 1 μm or less, or 700 nm or less. The secondary battery 100 may have only one protective layer 34, or may have two or more protective layers. Examples of a method for forming the protective layer 34 include a method of forming a film on the negative electrode current collector and a method of pressing Mg particles. Examples of a method for forming a film on the negative electrode current collector include PVD methods such as vapor deposition and sputtering, and plating methods such as electrolytic plating and electroless plating.

[0050] As shown in Fig. 2, the Mg mixture layer 33 and the protective layer 34 may be in contact with each other. Also, the Mg mixture layer 33 and the solid electrolyte layer 20 may be in contact with each other. Also, the protective layer 34 and the negative electrode current collector 31 may be in contact with each other. Alternatively, as shown in Fig. 1, the Mg mixture layer 33 and the negative electrode current collector 31 may be in contact with each other.

[0051] 1.7 Other materials The secondary battery 100 may have at least the above-mentioned components, and may further include other components. The components described below are examples of other components that the secondary battery 100 may have.

[0052] 1.7.1 Enclosure The secondary battery 100 may have each of the above-mentioned components housed inside an exterior body. More specifically, the portion excluding the tab or terminal for extracting power from the secondary battery 100 to the outside may be housed inside the exterior body. Any known exterior body for a battery may be adopted as the exterior body. For example, a laminate film may be used as the exterior body. Furthermore, a plurality of secondary batteries 100 may be electrically connected and arbitrarily stacked to form an assembled battery. In this case, the assembled battery may be housed inside a known battery case.

[0053] 1.7.2 Sealing resin In the secondary battery 100, each of the above components may be sealed with resin. For example, at least the side surfaces (surfaces along the stacking direction) of each layer shown in Fig. 1 may be sealed with resin. This makes it easier to prevent moisture from entering the inside of each layer. As the sealing resin, a known curable resin or thermoplastic resin may be used.

[0054] 1.7.3 Restraining members The secondary battery 100 may or may not have a restraining member for restraining each of the above components in the thickness direction. The restraining pressure applied by the restraining member tends to reduce the internal resistance of the battery. There is no particular limit to the restraining pressure applied by the restraining member. Even if the restraining pressure applied by the restraining member is small, the secondary battery 100 has low resistance and excellent cycle characteristics. In this regard, the restraining pressure applied by the restraining member may be 5 MPa or less, 3 MPa or less, or 1 MPa or less.

[0055] 2. Manufacturing method of secondary batteries The secondary battery 100 can be manufactured, for example, as follows. That is, as shown in FIG. 3, the method for manufacturing the secondary battery 100 according to the embodiment includes the following steps: A surface of the solid electrolyte layer 20 containing a first solid electrolyte is covered with an Mg mixture layer 33 containing Mg and a second solid electrolyte (FIG. 3(A)). The solid electrolyte layer 20 covered with the Mg mixture layer 33 is used to obtain a laminate 50 having a positive electrode 10, the solid electrolyte layer 20, the Mg mixture layer 33, and the negative electrode current collector 31 in this order ( FIG. 3(B) ); and The method includes charging the laminate 50 to deposit metallic lithium 32 between the solid electrolyte layer 20 and the negative electrode current collector 31 (FIG. 3(C)).

[0056] 2.1 Covering As shown in FIG. 3(A), in the manufacturing method according to the present embodiment, the surface of the solid electrolyte layer 20 containing the first solid electrolyte is covered with the Mg mixture layer 33 containing Mg and the second solid electrolyte. The solid electrolyte layer 20 is obtained, for example, by molding an electrolyte mixture containing the first solid electrolyte. The method of covering the surface of the solid electrolyte layer 20 with the Mg mixture layer 33 is not particularly limited. For example, the Mg mixture layer 33 can be formed on the surface of the solid electrolyte layer 20 by a coating method using a solution or a slurry. Alternatively, a transfer material having the Mg mixture layer 33 formed on a base material may be obtained, and then the Mg mixture layer 33 may be transferred from the transfer material to the surface of the solid electrolyte layer 20. The solid electrolyte layer 20 may be integrated in advance with the positive electrode active material layer 12 or the like.

[0057] 2.2 Preparation of the laminate As shown in FIG. 3(B), in the manufacturing method according to the present embodiment, a laminate 50 having a positive electrode 10, an electrolyte layer 20, an Mg mixture layer 33, and an anode current collector 31 in this order is obtained using the solid electrolyte layer 20 coated with the Mg mixture layer 33 as described above. The laminate 50 can be easily obtained by forming and laminating each of the above-mentioned materials by coating, transferring, adhering, or pressing the above-mentioned materials so that the above-mentioned positive electrode current collector 11, the positive electrode active material layer 12, the solid electrolyte layer 20, the Mg mixture layer 33, and the anode current collector 31 are laminated in this order. The above-mentioned protective layer 34 may be provided in advance on the surface of the anode current collector 31. The laminate 50 may include at least one each of the positive electrode current collector 11, the positive electrode active material layer 12, the solid electrolyte layer 20, the Mg mixture layer 33, and the anode current collector 31. That is, the laminate 50 may have at least one laminate unit of the above-mentioned positive electrode current collector 11, positive electrode active material layer 12, solid electrolyte layer 20, Mg mixture layer 33, and negative electrode current collector 31, and may have a plurality of such laminate units. In this case, the plurality of laminate units may be electrically connected to each other in series, in parallel, or not electrically connected.

[0058] Before or after obtaining the laminate 50, pressure may be applied to each layer or laminate 50 in the thickness direction (stacking direction). For example, each layer constituting the laminate 50 may be pressed to be integrated, or gaps between each layer constituting the laminate 50 may be eliminated to reduce the interface resistance. Each layer or laminate 50 may be pressurized by a known means. For example, each layer or laminate 50 may be pressurized in the stacking direction by various pressing methods such as CIP, HIP, roll press, uniaxial press, and mold press. The magnitude of pressure in the stacking direction applied to each layer or laminate 50 may be appropriately determined according to the performance of the target battery. For example, when each layer or laminate 50 contains a sulfide solid electrolyte, the pressure may be 100 MPa or more, 150 MPa or more, 200 MPa or more, 250 MPa or more, 300 MPa or more, or 350 MPa or more from the viewpoint of easily performing the integration or elimination of the gaps by plastically deforming the sulfide solid electrolyte. The pressing time and pressing temperature of each layer or laminate 50 are not particularly limited.

[0059] 2.3 Charging As shown in FIG. 3(C), in the manufacturing method according to the present embodiment, the laminate 50 obtained as described above is charged, and metallic lithium 32 is precipitated between the solid electrolyte layer 20 and the negative electrode current collector 31. Specifically, by charging the laminate 50, lithium ions are conducted from the positive electrode active material contained in the positive electrode active material layer 12 to the negative electrode current collector 31 side through the solid electrolyte layer 20, and the lithium ions receive electrons between the solid electrolyte layer 20 and the negative electrode current collector 31, and are precipitated as metallic lithium 32. The charging may be the first charging after the preparation of the laminate 50, or may be the second or subsequent charging. The laminate 50 may be charged by a method similar to the charging method of a general battery. That is, charging may be performed by connecting an external power source to the positive electrode current collector 11 and the negative electrode current collector 31 of the laminate 50.

[0060] 2.4 Other processes The manufacturing method according to the present embodiment may include general steps for manufacturing a secondary battery in addition to the above-mentioned steps. For example, the steps include a step of housing the laminate 50 inside an exterior body such as a laminate film, a step of connecting a current collecting tab to the laminate 50, and the like. Specifically, for example, after connecting a current collecting tab to the current collectors 11 and 31 of the laminate 50 (parts of the current collectors 11 and 31 may be protruded and used as tabs), the laminate 50 may be housed in a laminate film as an exterior body, while the laminate film may be sealed with the tab pulled out to the outside of the laminate film, and then the laminate 50 may be charged via the tab outside the laminate film.

[0061] 3. Vehicles equipped with secondary batteries As described above, the secondary battery of the present disclosure can deposit metallic lithium uniformly between the solid electrolyte layer and the negative electrode current collector, and has low resistance and excellent cycle characteristics. Such a secondary battery can be suitably used in at least one vehicle selected from, for example, a hybrid vehicle (HEV), a plug-in hybrid vehicle (PHEV), and an electric vehicle (BEV). That is, the technology of the present disclosure is a vehicle having a secondary battery, the secondary battery comprising a positive electrode, an electrolyte layer, a negative electrode current collector, and metallic lithium as a negative electrode active material deposited between the electrolyte layer and the negative electrode current collector by charging, and a Mg mixture layer is present between the solid electrolyte layer and the negative electrode current collector, the solid electrolyte layer includes a first solid electrolyte, the Mg mixture layer includes Mg and a second solid electrolyte, and the Young's modulus of the second solid electrolyte is lower than that of the first solid electrolyte. Details of the configuration of the secondary battery are as described above. EXAMPLES

[0062] As described above, one embodiment of the technology of the present disclosure has been described, but the technology of the present disclosure can be modified in various ways other than the above embodiment without departing from the gist of the technology. The technology of the present disclosure will be described in more detail below while showing examples, but the technology of the present disclosure is not limited to the following examples.

[0063] 1. Preparation of Positive Electrode Mixture Ternary cathode active material (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 800 mg of O2, 127 mg of sulfide solid electrolyte (LiBr-LiI-Li2S-P2S5), and 12 mg of VGCF as a conductive additive were dispersed in dehydrated heptane using an ultrasonic homogenizer. The mixture was then dried at 100°C for 1 hour to obtain a positive electrode mixture.

[0064] 2. Preparation of Mg-coated SUS current collector foil (Mg-SUS foil) Mg was evaporated onto the surface of the SUS foil, and a Mg layer was formed as a protective layer on the surface of the SUS foil to obtain a Mg-coated SUS current collector foil (Mg-SUS foil). The thickness of the Mg layer was 700 nm.

[0065] 3. Preparation of Mg mixture layer 3.1 Comparative Example 1 A solution containing SBR as a binder and a solvent (mesitylene, dibutyl ether) were put into a PP container and mixed for 3 minutes with a shaker. Then, sulfide solid electrolyte particles (average particle diameter D50: 800 nm, Young's modulus: 23.2 GPa) and Mg particles (average particle diameter D50: 800 nm) were weighed to a mass ratio of 50:50 and put into a PP container. After mixing for 3 minutes with a shaker, the mixture was mixed for 30 seconds with an ultrasonic dispersion device, and this was repeated twice to obtain a Mg mixture slurry. Next, the Mg mixture slurry was applied onto an Al foil using an applicator with a coating gap of 25 μm. After visually confirming that the surface after coating was dry, the mixture was dried on a hot plate at 100 ° C. for 30 minutes to form a Mg mixture layer according to Comparative Example 1 on the Al foil.

[0066] 3.2 Example 1 Instead of sulfide solid electrolyte particles, complex hydride particles ([LiCB9H 10 ] 0.7 [LiCB 11 H 12 ] 0.3A Mg mixture layer was formed on an Al foil in the same manner as in the comparative example, except that a magnesium alloy powder (Mg alloy powder, average particle size D50: 2 μm, Young's modulus: 1.5 GPa) was used.

[0067] 4. Preparation of Evaluation Cell 4.1 Comparative Example 1 and Example 1 In a compaction type press cell (φ11.28 mm), 101.7 mg of sulfide solid electrolyte particles (Young's modulus: 23.2 GPa) were put in, and a press pressure of 1 ton was applied while standing for 1 minute to obtain a first pellet made of a solid electrolyte. Then, 31.3 mg of the above-mentioned positive electrode mixture was put in one side of the first pellet, and the mixture was left standing for 1 minute at a press pressure of 6 tons to obtain a second pellet made of a solid electrolyte layer-positive electrode mixture layer. Next, an Al foil with an Mg mixture layer formed thereon was put in the other side of the second pellet, and pressed at 1 ton to transfer the Mg mixture layer to the surface of the solid electrolyte layer, and the Al foil was peeled off to obtain a third pellet made of an Mg mixture layer-solid electrolyte layer-positive electrode mixture layer. Finally, a Mg-SUS foil (φ11.28 mm) was placed on the Mg mixture layer side of the third pellet and left to stand for 1 minute under a press pressure of 1 ton to obtain a fourth pellet consisting of SUS foil (negative electrode current collector), Mg layer (protective layer), Mg mixture layer, solid electrolyte layer, and positive electrode mixture layer. The fourth pellet was restrained with a torque of 1 MPa to obtain an evaluation cell.

[0068] 4.2 Comparative Example 2 An evaluation cell was obtained in the same manner as above, except that the Mg mixture layer was not transferred to the second pellet. That is, an Mg-SUS foil (φ11.28 mm) was placed on the other side of the second pellet and left to stand for 1 minute under a press pressure of 1 ton to obtain a pellet consisting of the SUS foil-Mg layer-solid electrolyte layer-positive electrode mixture layer, which was then restrained with a torque of 1 MPa to obtain an evaluation cell.

[0069] 5.Charge / Discharge Evaluation Each evaluation cell was soaked in a thermostatic chamber at 25°C or 60°C for 3 hours, and then charged and discharged for 3 cycles at 0.2 C, followed by a cycle test at 0.5 C. The resistance and capacity retention rate of each evaluation cell are shown in Table 1 below. The resistance shown in Table 1 is the resistance when discharged to SOC 60% in the 3rd cycle, and the capacity retention rate is the ratio of the capacity at the 10th cycle to the capacity at the 1st cycle.

[0070] [Table 1]

[0071] The results shown in Table 1 reveal the following: (1) When the Mg mixture layer was not disposed between the solid electrolyte layer and the SUS foil as in Comparative Example 2, neither the battery resistance nor the cycle characteristics were sufficient. (2) As in Comparative Example 1, when the Mg mixture layer is disposed between the solid electrolyte layer and the SUS foil and a hard sulfide solid electrolyte is used in the Mg mixture layer, the cycle characteristics are improved compared to Comparative Example 2, but the improvement effect is not sufficient. In addition, the battery resistance in Comparative Example 1 is slightly higher than that in Comparative Example 2. This is considered to be due to the DC resistance of the Mg mixture layer. In Comparative Example 1, the solid electrolyte contained in the solid electrolyte layer and the solid electrolyte contained in the Mg mixture layer are the same type and both are hard, so gaps are generated in the Mg mixture layer and the gaps cannot be eliminated by the solid electrolyte, and as a result, the improvement effect on the resistance and cycle characteristics is considered to be small. (3) As in Example 1, when an Mg mixture layer is disposed between the solid electrolyte layer and the SUS foil, and a soft complex hydride solid electrolyte is used in the Mg mixture layer, the resistance and cycle characteristics are significantly improved compared to Comparative Examples 1 and 2. In Example 1, the solid electrolyte contained in the solid electrolyte layer and the solid electrolyte contained in the Mg mixture layer are different types, and the solid electrolyte contained in the Mg mixture layer is soft, so that the soft solid electrolyte is deformed, etc., and the gaps in the Mg mixture layer and the like are eliminated, and as a result, it is considered that the effect of improving the resistance and cycle characteristics is large.

[0072] In the above embodiment, the surface of the SUS foil (negative electrode current collector) is protected by a Mg layer (protective layer), but the technology of the present disclosure is not limited to this. Even when the protective layer is omitted, the effect of improving the resistance and cycle characteristics is greater in Example 1 than in Comparative Examples 1 and 2. However, it is considered that the resistance and cycle characteristics are more easily improved when the protective layer is present.

[0073] In addition, in the above examples, a combination of a sulfide solid electrolyte and a complex hydride solid electrolyte is exemplified as a solid electrolyte, but the technology of the present disclosure is not limited thereto. It is considered that the desired effect is exhibited when the solid electrolyte (second solid electrolyte) contained in the Mg mixture layer is softer than the solid electrolyte (first solid electrolyte) contained in the solid electrolyte layer, that is, when it has a low Young's modulus. However, from the viewpoints of (1) that excellent ion conductivity is easily ensured by the sulfide solid electrolyte, (2) that the flexibility of the complex hydride solid electrolyte is easily able to improve resistance and cycle characteristics, and (3) that the reactivity of the complex hydride with respect to the sulfide solid electrolyte is small and deterioration of the electrolyte can be suppressed, it is considered that a higher effect is easily obtained when the sulfide solid electrolyte and the complex hydride solid electrolyte are combined in the secondary battery.

[0074] As described above, a secondary battery having the following configuration has low resistance and excellent cycle characteristics while having a deposition-type metallic lithium negative electrode. That is, the secondary battery of the present disclosure (I) has a positive electrode, a solid electrolyte layer, a negative electrode current collector, and metallic lithium as a negative electrode active material that is deposited between the solid electrolyte layer and the negative electrode current collector upon charging, (II) a Mg mixture layer is present between the solid electrolyte layer and the negative electrode current collector, (III) the solid electrolyte layer contains a first solid electrolyte, (IV) the Mg mixture layer contains Mg and a second solid electrolyte, and (V) the Young's modulus of the second solid electrolyte is lower than that of the first solid electrolyte. [Explanation of symbols]

[0075] 10 positive electrode 11 Positive electrode current collector 12 Cathode active material layer 20 Electrolyte layer 31 Negative electrode current collector 32 Metallic lithium 33 Mg mixture layer 34 Protective layer 50 Laminate 100 Secondary battery

Claims

1. A secondary battery comprising: a positive electrode; a solid electrolyte layer; a negative electrode current collector; and metallic lithium as a negative electrode active material that is deposited between the solid electrolyte layer and the negative electrode current collector upon charging; an Mg mixture layer is present between the solid electrolyte layer and the negative electrode current collector; the solid electrolyte layer includes a first solid electrolyte; the Mg mixture layer contains at least one of Mg particles and Mg alloy particles, and a second solid electrolyte; the Young's modulus of the second solid electrolyte is lower than the Young's modulus of the first solid electrolyte; The Young's modulus of the second solid electrolyte is 1 GPa or more and 20 GPa or less. Secondary battery.

2. The first solid electrolyte is a sulfide solid electrolyte. The secondary battery according to claim 1 .

3. the second solid electrolyte is a complex hydride containing Li; The secondary battery according to claim 1 or 2.

4. a protective layer is present between the Mg mixture layer and the negative electrode current collector, the protective layer contains Mg and does not contain an electrolyte; The secondary battery according to claim 1 or 2.

5. The positive electrode contains a lithium-containing oxide as a positive electrode active material. The secondary battery according to claim 1 or 2.

6. the negative electrode current collector comprises stainless steel; The secondary battery according to claim 1 or 2.

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