Secondary battery and method for manufacturing the same

Abstract

To improve coulomb efficiency of a secondary battery comprising a metal lithium anode.SOLUTION: A secondary battery comprises a cathode active material layer, a solid electrolyte layer and an anode active material layer. The anode active material layer contains a first material and a second material. The first material is at least one of an alloy of Li and an element X and a composition of Li and the element X. The second material is at least one of an elementary substance of a metal element M, an alloy of Li and the metal element M and a composition of Li and the metal element M. Generation energy ELiX of the first material is lower than generation energy EMX of a composition of the metal element M and the element X.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This application discloses a secondary battery and a method for manufacturing the same. [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 a Li-Mg alloy deposited between the solid electrolyte layer and the negative electrode current collector upon charging. Patent Document 2 discloses a negative electrode material used in a metal secondary battery, comprising MgH2 and a metal catalyst that contacts the MgH2 and improves the reversibility of the conversion reaction. Patent Document 3 discloses an all-solid-state lithium secondary battery comprising a positive electrode, a solid electrolyte layer, a negative electrode, and a predetermined metal layer formed between the solid electrolyte layer and the negative electrode. Patent Document 4 discloses a negative electrode for an all-solid-state secondary battery comprising a negative electrode current collector and a coating layer that covers the negative electrode current collector and allows metallic lithium to be deposited via the lithium alloy layer upon charging. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-184513 [Patent Document 2] Japanese Patent Publication No. 2012-038697 [Patent Document 3] International Publication No. 2013 / 131241 [Patent Document 4] Japanese Patent Publication No. 2018-129159 [Overview of the project] [Problems that the invention aims to solve]

[0004] Secondary batteries equipped with a metallic lithium anode have room for improvement in terms of Coulomb efficiency. [Means for solving the problem]

[0005] This application discloses several embodiments as means for solving the above-mentioned problems. <Aspect 1> A secondary battery comprising a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer, The negative electrode active material layer comprises a first substance and a second substance, The first substance is at least one of an alloy of Li and element X, and a compound of Li and element X. The second substance is at least one of the following: a pure element of metal element M, an alloy of Li and metal element M, and a compound of Li and metal element M. Energy of formation E of the first substance LiX However, the formation energy E of the compound between the metal element M and the element X MX Lower than Secondary battery. <Aspect 2> The negative electrode active material layer includes the first substance formed in a film, The thickness of the first substance formed in the form of a film is 10 nm or more and 50 μm or less. A secondary battery according to embodiment 1. <Aspect 3> A secondary battery comprising a positive electrode active material layer, a solid electrolyte layer, a negative electrode current collector, and metallic lithium deposited between the solid electrolyte layer and the negative electrode current collector upon charging, A compound of metal element M and element X exists between the solid electrolyte layer and the negative electrode current collector, Formation energy E of the compound of the aforementioned metal element M and element X MX However, the formation energy E of the compound of Li and the element X LiX Higher than, Secondary battery. <Aspect 4> The system is configured such that during charging, a compound of the metal element M and the element X decomposes, and a compound of the Li and the element X is formed on the surface of the negative electrode current collector. A secondary battery according to embodiment 3. <Aspect 5> The metal element M and the element X satisfy the following relationships (1) and (2): A secondary battery according to any one of Aspects 1 to 4: (1) The formation energy E of the compound of the metal element M and the element X MX is lower than the formation energy E of the compound of Li and the metal element M, and LiM (2) The formation energy E of the compound of Li and the element X is lower than the formation energy E of the compound of the metal element M and the element X. LiX MX <Aspect 6> The metal element M is Mg. A secondary battery according to any one of Aspects 1 to 5. <Aspect 7> The element X is at least one of Bi, Sb, In, Sn, H, I, Ga, Te, Hg, Cd, Si, B, As, Zn, Ge, Br, P, and Se. The secondary battery of Aspect 6. <Aspect 8> The element X is at least one of H, B, and P. A secondary battery according to any one of Aspects 1 to 7. <Aspect 9> The difference between the formation energy E MX and the formation energy E LiX is 0.027 eV / atom or more. A secondary battery according to any one of Aspects 1 to 8. <Aspect 10> A method for manufacturing a secondary battery, comprising: obtaining a laminate having a positive electrode active material layer, a solid electrolyte layer, a negative electrode current collector, and a compound of a metal element M and an element X disposed between the solid electrolyte layer and the negative electrode current collector; and charging the laminate to supply lithium ions between the solid electrolyte layer and the negative electrode current collector to cause a conversion reaction of the compound of the metal element M and the element X to generate a first substance and a second substance, where the first substance is at least one of an alloy of Li and the element X and a compound of Li and the element X. The second substance is at least one of the following: a pure element of metal element M, an alloy of Li and metal element M, and a compound of Li and metal element M. Manufacturing method. [Effects of the Invention]

[0006] The secondary battery of this disclosure comprises a metallic lithium anode and has excellent Coulomb efficiency. [Brief explanation of the drawing]

[0007] [Figure 1] The configuration of the secondary battery 101 is shown in general terms. [Figure 2] The configuration of the secondary battery 102 is shown in general terms. [Figure 3] This diagram schematically shows the changes in the configuration of secondary batteries 101 and 102 during charging and discharging. [Figure 4] This diagram outlines the manufacturing process for secondary batteries 101 and 102, from the stacking of each layer to charging. [Figure 5] The structure of the evaluation cells is shown in general terms. [Figure 6] This graph compares the Coulomb efficiency of the evaluation cells. [Figure 7] The cross-section of the evaluation cell in Comparative Example 3 shows the structure and Mg distribution before and after charging. [Figure 8] The cross-section of the evaluation cell in Example 3 shows the structure and Mg distribution before and after charging. [Figure 9] The cross-section of the evaluation cell in Example 3 shows the distribution of S, Mg, and Ni after charging. [Figure 10] The CV measurement results for the evaluation cell in Example 3 are shown. [Figure 11] This shows the XRD measurement results at a predetermined location in the evaluation cell of Example 3. [Figure 12] The cross-section of the evaluation cell in Example 4 shows the distribution of S, Mg, and Ni after charging. [Modes for carrying out the invention]

[0008] The secondary battery and its manufacturing method according to the embodiments will be described below with reference to the drawings, but the technology of this disclosure is not limited to the following embodiments.

[0009] 1. Secondary battery (first form) Figure 1 schematically shows the configuration of a secondary battery 101 according to the first embodiment. As shown in Figure 1, the secondary battery 101 comprises a positive electrode active material layer 10, a solid electrolyte layer 20, and a negative electrode active material layer 30. The negative electrode active material layer 30 contains a first substance 31 and a second substance 32. The first substance 31 is at least one of an alloy of Li and element X, and a compound of Li and element X. The second substance 32 is at least one of a pure metal element M, an alloy of Li and metal element M, and a compound of Li and metal element M. The formation energy E of the first substance 31 LiX The formation energy E of the compound between the metal element M and the element X is MX It is lower than that.

[0010] 1.1 Cathode active material layer The positive electrode active material layer 10 contains a positive electrode active material and may optionally contain an electrolyte, a conductive additive, a binder, etc. Furthermore, the positive electrode active material layer 10 may contain various additives. The respective content amounts of the positive electrode active material, electrolyte, conductive additive, binder, etc. in the positive electrode active material layer 10 can be appropriately determined according to the desired battery performance. For example, with the entire positive electrode active material layer 10 (total solid content) as 100% by mass, the content of the positive electrode active material may be 40% by mass or more, 50% by mass or more, or 60% by mass or more, or it may be 100% by mass or less, or 90% by mass or less. The shape of the positive electrode active material layer 10 is not particularly limited and may, for example, be a sheet with a substantially flat surface. The thickness of the positive electrode active material layer 10 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, or it may be 2 mm or less, 1 mm or less, 500 μm or less, or 100 μm or less.

[0011] 1.1.1 Cathode active material The positive electrode active material can be any known positive electrode active material for secondary batteries that can release Li ions during charging and absorb Li ions during discharging. For example, lithium cobalt oxide, lithium nickel oxide, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 Various lithium-containing oxides such as O2, lithium manganese oxide, and spinel-based lithium compounds can be used. Alternatively, elemental sulfur or sulfur with lithium adsorbed onto it can be used as the positive electrode active material. In particular, when the positive electrode active material layer 10 contains a lithium-containing oxide as the positive electrode active material, Li ions can be supplied more appropriately from the positive electrode active material to the negative electrode side during charging, and the expansion and contraction of the positive electrode active material during charging and discharging is reduced, making it easier 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 particulate, for example, and its size is not particularly limited. The particles of the positive electrode active material may be solid particles, hollow particles, or particles with voids. The particles of the positive electrode active material may be primary particles, or secondary particles formed by the aggregation of multiple primary particles. The average particle diameter (D50) of the positive electrode active material particles may be, for example, 1 nm or more, 5 nm or more, or 10 nm or more, or it may be 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less. In this application, the average particle diameter D50 refers to the particle diameter (median diameter) at 50% of the cumulative value in the volume-based particle size distribution determined by laser diffraction-scattering.

[0012] The surface of the positive electrode active material may be coated with an ion-conducting oxide. That is, the positive electrode active material layer 10 may contain a composite comprising the positive electrode active material and an ion-conducting oxide coating its surface. This makes it easier to suppress reactions between the positive electrode active material and sulfides (for example, sulfide solid electrolytes described later). Examples of ion-conducting oxides that coat and protect the surface of the positive electrode active material include Li3BO3, LiBO2, Li2CO3, LiAlO2, Li4SiO4, Li2SiO3, Li3PO4, Li2SO4, Li2TiO3, and Li4Ti5O 12 At least one selected from Li2Ti2O5, Li2ZrO3, LiNbO3, Li2MoO4, and Li2WO4 is an example. The coverage rate (area ratio) of the ion-conducting oxide on 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 ion-conducting oxide layer may be, for example, 0.1 nm or more, 1 nm or more, 100 nm or less, or 20 nm or less.

[0013] 1.1.2 Electrolytes The electrolyte contained in the positive electrode active material layer 10 may be a solid electrolyte, a liquid electrolyte (electrolyte solution), or a combination thereof. In particular, when the positive electrode active material layer 10 contains a solid electrolyte (especially a sulfide solid electrolyte), an even greater effect can be expected from the technology of this disclosure.

[0014] The solid electrolyte can be any known solid electrolyte used in secondary batteries. The solid electrolyte may be an inorganic solid electrolyte or an organic polymer electrolyte. In particular, inorganic solid electrolytes have excellent ionic conductivity and heat resistance. Examples of inorganic solid electrolytes include oxide solid electrolytes and sulfide solid electrolytes. Among inorganic solid electrolytes, sulfide solid electrolytes, and among those, sulfide solid electrolytes containing at least Li, S, and P as constituent elements, have particularly high performance. The solid electrolyte may be amorphous or crystalline. The solid electrolyte may be particulate. The average particle size (D50) of the solid electrolyte may be, for example, 10 nm to 10 μm. The ionic conductivity of the solid electrolyte at 25°C is, for example, 1 × 10⁻⁶. -4 S / cm or more, or 1 × 10 -3 The ratio may be S / cm or higher. The solid electrolyte may be used alone or in combination of two or more types.

[0015] Oxide solid electrolytes include lithium lanthanum zirconate, LiPON, and Li 1+X Al X Ge 2-X (PO4)3, Li-SiO glass, Li-Al-SO glass, and one or more other materials may be selected from these.

[0016] 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 may have a glass transition temperature (Tg). Furthermore, if the sulfide solid electrolyte has a crystalline phase, examples of the crystalline phase include a thio-LISICON type crystalline phase, an LGPS type crystalline phase, and an argyrodite type crystalline phase.

[0017] The sulfide solid electrolyte may contain, for example, Li, X (where 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 elements. Furthermore, the sulfide solid electrolyte may contain S as the main component of the anionic element.

[0018] Sulfide solid electrolytes include, for example, 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 one of 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 one of P, Si, Ge, B, Al, Ga, or In.) At least one of these may be selected.

[0019] The composition of the sulfide solid electrolyte is not particularly limited, but examples include xLi2S·(100-x)P2S5 (70≦x≦80), yLiI·zLiBr·(100-yz)(xLi2S·(1-x)P2S5) (0.7≦x≦0.8, 0≦y≦30, 0≦z≦30), etc. Alternatively, the sulfide solid electrolyte may have the general formula: Li 4-x Ge 1-x P xIt may have a composition represented by 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, or may be 1.5 or less.

[0020] The electrolytic solution may contain, for example, lithium ions as carrier ions. The electrolytic solution may be, for example, a non-aqueous electrolytic solution. For example, as the electrolytic solution, a solution in which a lithium salt is dissolved in a carbonate solvent at a predetermined concentration can be used. Examples of the carbonate solvent include fluoroethylene carbonate (FEC), ethylene carbonate (EC), dimethyl carbonate (DMC), and the like. Examples of the lithium salt include hexafluorophosphate and the like.

[0021] [[ID=1,4]]1.1.3 Conductive Aid Examples of conductive additives that may be included in the positive electrode active material layer 10 include carbon materials such as vapor-processed carbon fiber (VGCF), acetylene black (AB), Ketjenblack (KB), carbon nanotubes (CNT), and carbon nanofibers (CNF); and metallic materials such as nickel, aluminum, and stainless steel. The conductive additive may be in the form of parts or fibers, and its size is not particularly limited. One type of conductive additive may be used alone, or two or more types may be used in combination.

[0022] 1.1.4 Binder Examples of binders that may be included in the positive electrode active material layer 10 include butadiene rubber (BR) binders, butylene rubber (IIR) binders, acrylate butadiene rubber (ABR) binders, styrene butadiene rubber (SBR) binders, polyvinylidene fluoride (PVdF) binders, polytetrafluoroethylene (PTFE) binders, polyimide (PI) binders, and polyacrylic acid binders. A single binder may be used alone, or two or more binders may be used in combination.

[0023] 1.2 Solid electrolyte layer The solid electrolyte layer 20 contains at least a solid electrolyte. The solid electrolyte contained in the solid electrolyte layer 20 may be of the same type as the solid electrolyte contained in the positive electrode active material layer 10 described above, or a different type. In particular, when the solid electrolyte layer 20 contains an inorganic solid electrolyte, an even higher effect can be expected from the technology of this disclosure. Examples of inorganic solid electrolytes include the oxide solid electrolyte and sulfide solid electrolyte described above. Among inorganic solid electrolytes, sulfide solid electrolytes, and among them sulfide solid electrolytes containing at least Li, S, and P as constituent elements, have particularly high performance. Specific examples of oxide solid electrolytes and sulfide solid electrolytes are as described above. The solid electrolyte layer 20 may further optionally contain binders and various additives. The binder contained in the solid electrolyte layer 20 may be of the same type as the binder contained in the positive electrode active material layer 10 described above, or a different type. In the solid electrolyte layer 20, only one type of solid electrolyte and binder may be used individually, or two or more types may be used in combination. The solid electrolyte layer 20 may be entirely made of solid material, or it may contain both a solid electrolyte and a liquid. The content of the solid electrolyte and binder in the solid electrolyte layer 20 is not particularly limited. For example, if the entire solid electrolyte layer 20 (total solid content) is 100% by mass, the solid electrolyte content may be 50% by mass or more, 60% by mass or more, 70% by mass or more, 100% by mass or less, or 90% by mass or less. The thickness of the solid electrolyte layer 20 is not particularly limited; for example, it may be 0.1 μm or more, 1 μm or more, 2 mm or less, or 1 mm or less.

[0024] 1.3 Negative electrode active material layer As shown in Figure 1, the negative electrode active material layer 30 includes a first substance 31 and a second substance 32. The first substance 31 is at least one of an alloy of Li and element X, and a compound of Li and element X. The second substance 32 is at least one of a pure metal element M, an alloy of Li and the metal element M, and a compound of Li and the metal element M. Here, the formation energy E of the first substance 31 LiX The formation energy E of a compound between a metal element M and element X isMX It is lower than that.

[0025] As shown in Figure 3, during discharge of the secondary battery 101, Li ions are released from the first substance 31 (alloy or compound of Li and metal element M) and the second substance 32 (alloy or compound of Li and element X) contained in the negative electrode active material layer 30 toward the positive electrode, and the volume of the negative electrode active material layer 30 may change. The Li ions released from the negative electrode active material layer 30 reach the positive electrode active material layer 10 via the solid electrolyte layer 20 and can be absorbed into the positive electrode active material contained in the positive electrode active material layer 10. As shown in Figure 3, after its discharge, the secondary battery 101 may have the same configuration as the secondary battery 102 of the second form described later. Alternatively, the discharge of the secondary battery 101 may be controlled to stop before it reaches the same configuration as the secondary battery 102 of the second form described later. In other words, after discharge, the secondary battery 101 may have a compound of metal element M and element X between the solid electrolyte layer 20 and the negative electrode current collector 50, or it may have a negative electrode active material layer 30.

[0026] During charging of the secondary battery 101, Li ions are released from the positive electrode active material layer 10. Specifically, the Li ions released from the positive electrode active material layer 10 reach the space between the solid electrolyte layer 20 and the negative electrode current collector 50 via the solid electrolyte layer 20, and may be deposited as the second material 32 or metallic lithium. As shown in Figures 1 and 3, in the secondary battery 101 after charging, a negative electrode active material layer 30 may be formed between the solid electrolyte layer 20 and the negative electrode current collector 50. This negative electrode active material layer 30 includes the first material 31 and the second material 32 described above. The thickness of the negative electrode active material layer 30 after charging is not particularly limited and may be, for example, 0.1 μm or more or 1 μm or more, or 2 mm or less or 1 mm or less. The amount of metallic lithium deposited between the solid electrolyte layer 20 and the negative electrode current collector 50 is not particularly limited and may be adjusted as appropriate according to the desired battery performance. However, if too much metallic lithium is deposited, there are concerns about pressure concentration and other issues. In this regard, as a guideline for the amount of metallic lithium deposited, the charging capacity of the secondary battery 101 should be, for example, 1 mAh / cm². 2 More than 5mAh / cm 2The following quantities are also acceptable.

[0027] 1.3.1 First substance The first substance 31 is at least one of an alloy of Li and element X, and a compound of Li and element X. That is, in the first substance 31, element X may be in solid solution with metallic Li, or it may be compounded with metallic Li. In one embodiment, the negative electrode active material layer 30 contains a compound of Li and element X as the first substance 31. In one embodiment, the negative electrode active material layer 30 contains an alloy of Li and element X as the first substance 31. The molar ratio of Li to element X is not particularly limited and depends on the type of element X and the first substance 31.

[0028] Energy of formation E of substance 31 LiX The formation energy E of a compound between a metal element M and element X is MX It is lower than that. In other words, element X is relatively highly reactive with Li and relatively low reactive with metallic element M. As long as these conditions are met, there are no particular restrictions on the type of element X that constitutes the first substance 31. Element X may be a metallic element or a nonmetallic element. For example, if element X is at least one of H, B, and P, the first substance 31 will have excellent lithium-ion conductivity, and the performance of the secondary battery 101 will be more easily improved. For example, the first substance 31 may be at least one selected from compounds of Li and B, compounds of Li and P, compounds of Li and H, composite compounds thereof, and mixtures thereof. Alternatively, if the metallic element M described later is Mg, and element X is at least one of Bi, Sb, In, Sn, H, I, Ga, Te, Hg, Cd, Si, B, As, Zn, Ge, Br, P, and Se, the performance of the secondary battery 101 will also be more easily improved.

[0029] The shape of the first substance 31 and its location in the negative electrode active material layer 30 are not particularly limited. The first substance 31 may be particulate, layered (including aggregates of multiple particles), or film-like (multiple particles in a two-dimensional wayThe first substance 31 may be aggregated or amorphous. The first substance 31 may be dispersed or unevenly distributed in the negative electrode active material layer 30. In particular, high performance is easily ensured when the negative electrode active material layer 30 includes the first substance 31 formed in a film, and the thickness of the first substance 31 formed in a film is 10 nm or more and 50 μm or less. The thickness may be 30 nm or more and 40 μm or less, 50 nm or more and 30 μm or less, 70 nm or more and 20 μm or less, or 100 nm or more and 10 μm or less. The thickness may also be 0.05% or more and 100% or 1% or more and less than 100% of the total thickness of the negative electrode active material layer 30. When the negative electrode active material layer 30 includes the first substance 31 formed in a film, the first substance 31 formed in a film may or may not be in contact with the negative electrode current collector 50. Furthermore, the first substance 31 formed in a film may or may not be in contact with the solid electrolyte layer 20. In particular, when the first substance 31 formed in a film is in contact with the negative electrode current collector 50, in other words, when the first substance 31 formed in a film covers the surface of the negative electrode current collector 50, the first substance 31 functions as a protective film, making it easier to ensure high performance. The area of ​​the first substance 31 formed in a film may be 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, 95% or more, or 99% or more of the area of ​​the negative electrode active material layer 30 (the area of ​​the surface of the negative electrode active material layer 30 that faces the negative electrode current collector 50).

[0030] The amount of the first substance 31 in the negative electrode active material layer 30 is not particularly limited. For example, the negative electrode active material layer 30 may contain more than 0% by mass and up to 80% by mass of the first substance 31. The amount of the first substance 31 may be 0.01% by mass or more and 70% by mass or less, 0.1% by mass or more and 60% by mass or less, 1% by mass or more and 50% by mass or less, or 10% by mass or more and 40% by mass or less.

[0031] 1.3.2 Second substance The second substance 32 is at least one of the following: a pure element of metal element M, an alloy of Li and the metal element M, and a compound of Li and the metal element M. That is, in the second substance 32, metal element M may exist as a pure element without being combined with other elements, may be in solid solution with metal Li, or may be compounded with metal Li. In one embodiment, the negative electrode active material layer 30 contains a compound of Li and the metal element M as the second substance 32. In one embodiment, the negative electrode active material layer 30 contains an alloy of Li and the metal element M as the first substance 31. The molar ratio of Li to metal element M is not particularly limited and depends on the type of metal element M and the second substance 32.

[0032] As mentioned above, the formation energy E of the first substance 31 LiX The formation energy E of a compound between a metal element M and element X is MX It is lower than that. In other words, in the negative electrode active material layer 30, the first material 31 and the second material 32 tend to exist stably. That is, the reaction between element X constituting the first material 31 and metal element M constituting the second material 32 is easily suppressed by Li. As long as these conditions are met, there are no particular restrictions on the type of metal element M constituting the second material 32. It is preferable that metal element M is an element that can be alloyed with Li. In particular, when metal element M is at least one of Mg, Sn, Zn, In, Al, Fe, Ni, Mn, Cr, Ag, Ga, Si, Sb, Pb, Bi, Cd, Sr, Ge, and As, and especially when metal element M is Mg, the above relationship of formation energy is satisfied, and the deposition and dissolution reactions of Li during charging and discharging tend to be homogenized, making it easier to ensure high performance. For example, the second material 32 may be pure Mg, an alloy of Li and Mg, or a compound of Li and Mg.

[0033] The shape of the second substance 32 and its location within the negative electrode active material layer 30 are not particularly limited. The second substance 32 may be particulate or layered (multiple particles) gatherThe second substance 32 may be in the form of a composite (including a combination of particles), a film (including a planar aggregation of multiple particles), or an amorphous form. The second substance 32 may be dispersed or unevenly distributed in the negative electrode active material layer 30. In particular, high performance is easily ensured when the negative electrode active material layer 30 includes the second substance 32 formed in layers, and the thickness of the layers of the second substance 32 is 100 nm or more and 500 μm or less. When the negative electrode active material layer 30 includes the second substance 32 formed in layers, the layers of the second substance 32 may or may not be in contact with the solid electrolyte layer 20. Also, the layers of the second substance 32 may or may not be in contact with the negative electrode current collector 50. In particular, when the layers of the second substance 32 are in contact with the solid electrolyte layer 20, the deposition and dissolution reactions of Li during charging and discharging are easily homogenized, and high performance is easily ensured. The area of ​​the second substance 32 layer may be 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, 95% or more, or 99% or more of the area of ​​the negative electrode active material layer 30 (the area of ​​the surface of the negative electrode active material layer 30 that faces the solid electrolyte layer 20).

[0034] The amount of the second substance 32 in the negative electrode active material layer 30 is not particularly limited. For example, the negative electrode active material layer 30 may contain 1% by mass or more and less than 100% by mass of the second substance 32.

[0035] 1.3.3 Supplementary Information on Metallic Element M and Element X In the secondary battery 101, higher performance is more easily ensured when the metal element M and the element X satisfy the following relationships (1) and (2). That is, when the following relationships (1) and (2) are satisfied, during charging of the secondary battery 101, the compound of metal element M and element X decomposes in the conversion reaction described below, and during discharge of the secondary battery 101, the reverse reaction of the conversion reaction occurs, making it easy to return to a compound of metal element M and element X. (1) Formation energy E of the compound of the metal element M and the element X MX However, the formation energy E of the compound of Li and the aforementioned metal element M LiM It is lower than that. (2) Formation energy E of the compound of Li and the element X LiX However, the formation energy E of the compound between the metal element M and the element X MX It is lower than that.

[0036] In the secondary battery 101, the above-mentioned generation energy E MX and the energy of creation E LiX A larger difference is considered to make it easier to secure a better effect. In this regard, in secondary battery 101, the generated energy E MX and the energy of creation E LiX The difference E MX -E LiX However, it may also be 0.027 eV / atom or higher, 0.032 eV / atom or higher, 0.050 eV / atom or higher, 0.075 eV / atom or higher, 0.100 eV / atom or higher, 0.150 eV / atom or higher, or 0.200 eV / atom or higher. Note that the energy of formation E MX , Energy of formation E LiM , and the energy of formation E LiX This can be confirmed in various databases.

[0037] 1.3.4 Other Ingredients The negative electrode active material layer 30 may contain other components in addition to the first substance 31 and the second substance 32 described above. For example, the negative electrode active material layer 30 may contain a compound of metal element M and element X as unreacted material from the conversion reaction described later. The negative electrode active material layer 30 may also contain metallic lithium deposited during charging. Here, "metallic lithium" is a concept that includes not only elemental lithium but also lithium alloys. That is, the negative electrode active material layer 30 may contain elemental lithium or a lithium alloy. The second substance 32 described above is an example of a lithium alloy. Alternatively, the negative electrode active material layer 30 may contain, in addition to the second material 32 described above, at least one lithium alloy selected from, for example, 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 consist of only one type or two or more types.

[0038] 1.4 Other Configurations The secondary battery 101 only needs to have at least the above-described configurations, and may have other configurations as well. The configurations described below are examples of other configurations that the secondary battery 101 may have.

[0039] 1.4.1 Positive electrode current collector As shown in Figure 1, the secondary battery 101 may include a positive electrode current collector 40 that contacts the positive electrode active material layer 10. Any material capable of functioning as a positive electrode current collector for a secondary battery can be used for the positive electrode current collector 40. The positive electrode current collector 40 may be a metal foil or a metal mesh. In particular, metal foil offers superior handling. The positive electrode current collector 40 may consist of multiple metal foils. Examples of metals that make up the positive electrode current collector 40 include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, stainless steel, etc. In particular, from the viewpoint of ensuring oxidation resistance, the positive electrode current collector 40 may contain Al. The positive electrode current collector 40 may have some kind of coating layer on its surface for the purpose of adjusting resistance, etc. Also, if the positive electrode current collector 40 consists of multiple metal foils, there may be some kind of layer between the multiple metal foils. The thickness of the positive electrode current collector 40 is not particularly limited. For example, the thickness may be 0.1 μm or more, or 1 μm or more, or 1 mm or less, or 100 μm or less.

[0040] 1.4.2 Negative electrode current collector As shown in Figure 1, the secondary battery 101 may include a negative electrode current collector 50 that is in contact with the negative electrode active material layer 30. Any material capable of functioning as a negative electrode current collector for a secondary battery can be used for the negative electrode current collector 50. The negative electrode current collector 50 may be a metal foil or a metal mesh, or it may be a carbon sheet. Metal foil is particularly advantageous in terms of handling, etc. The negative electrode current collector 50 may consist of multiple metal foils or sheets. Examples of metals that make up the negative electrode current collector 50 include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, stainless steel, etc. In particular, from the viewpoint of ensuring reduction resistance and being less likely to alloy with lithium, the negative electrode current collector 50 may contain at least one metal selected from Cu, Ni, and stainless steel, and more specifically, at least one of Ni and stainless steel. The negative electrode current collector 50 may have some kind of coating layer on its surface. Furthermore, if the negative electrode current collector 50 consists of multiple metal foils, there may be some layer between the multiple metal foils. The thickness of the negative electrode current collector 50 is not particularly limited. For example, it may be 0.1 μm or more or 1 μm or more, or 1 mm or less or 100 μm or less.

[0041] In the secondary battery 101, the negative electrode current collector 50 may have some kind of protective layer on its surface. For example, the negative electrode current collector 50 may have a conductive substrate selected from the above-mentioned metal foil, metal mesh, or carbon sheet, and a protective layer formed on the surface of the conductive substrate, and the protective layer may be disposed between the conductive substrate and the negative electrode active material layer 30. The protective layer may, for example, contain Mg and not contain a compound of Mg and element X. It is believed that by having a protective layer containing Mg on the negative electrode current collector 50, the diffusion of Li on the surface of the negative electrode current collector 50 is promoted, the affinity of metallic lithium to the negative electrode current collector 50 is increased, the void between the negative electrode current collector 50 and the metallic lithium is suppressed, and metallic lithium is deposited more uniformly on the surface of the negative electrode current collector 50.

[0042] The protective layer may be the layer in which the molar ratio of Mg is the highest among all its constituent elements. The molar ratio of Mg in the entire protective layer may be, for example, 50 mol% to 100 mol%, 70 mol% or more, 80 mol% or more, or 90 mol% or more. The protective layer may be, for example, a metal thin film containing Mg (e.g., a vapor-deposited film), or a layer containing Mg particles. Alternatively, the protective layer may be a layer containing only Mg particles. A metal thin film containing Mg may be composed of Mg or an Mg alloy. Furthermore, the Mg particles may be particles of pure Mg, or particles containing Mg and elements other than Mg. Examples of elements other than Mg include various metallic elements, metalloid elements, and nonmetallic elements. For example, the Mg particles may be alloy particles (Mg alloy particles) containing Mg and metals other than Mg. The Mg alloy particles may be an alloy containing Mg as the main component (an alloy in which 50 mol% or more of all constituent elements are Mg). Mg alloy particles may contain at least one of the following metals as Mg: Li, Au, Al, and Ni. Mg alloy particles may or may not contain Li. Mg alloy particles may contain a β single-phase alloy of Li and Mg. Alternatively, Mg particles may be oxide particles containing Mg and O (Mg oxide particles). Mg oxide particles may be oxide particles consisting only of Mg and O, or composite oxide particles represented as Mg-M'-O (where M' is at least one of Li, Au, Al, and Ni). When 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 of the metals other than Li, or two or more. Mg particles may be primary particles, or secondary particles formed by the aggregation of primary particles. 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.

[0043] The thickness of the protective layer may be, for example, 10 nm or more and 10 μm or less. The thickness of the protective layer 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. In the secondary battery 101, the negative electrode current collector 50 may not have a protective layer, may have only one protective layer, or may have two or more layers. Methods for forming the protective layer include forming a protective layer on the surface of the conductive substrate constituting the negative electrode current collector 50, or pressing Mg particles. As methods for forming a protective layer on the surface of the conductive substrate, for example, PVD methods such as vapor deposition and sputtering, or plating methods such as electroplating and electroless plating, or coating methods using a slurry can be employed.

[0044] 1.4.3 Exterior The secondary battery 101 may have all of the above components housed inside an outer casing. More specifically, the parts of the secondary battery 101 excluding tabs or terminals for drawing power to the outside may be housed inside the outer casing. Any known type of battery casing can be used. For example, laminate film may be used as the casing. Alternatively, multiple secondary batteries 101 may be electrically connected and stacked as desired to form a battery pack. In this case, the battery pack may be housed inside a known battery case.

[0045] 1.4.4 Sealing resin In the secondary battery 101, each of the above components may be sealed with a resin. For example, at least the sides (surfaces along the stacking direction) of each layer shown in Figure 1 may be sealed with a resin. This makes it easier to suppress the ingress of moisture into the interior of each layer. Known curable resins and thermoplastic resins can be used as the sealing resin.

[0046] 1.4.5 Restraining Members The secondary battery 101 may have a restraining member to constrain each of the above components in the thickness direction. The internal resistance of the battery is easily reduced by applying restraining pressure with the restraining member. There are no particular restrictions on the restraining pressure applied by the restraining member. The restraining pressure applied by the restraining member may be 5 MPa or less, 3 MPa or less, or 1 MPa or less.

[0047] 2. Secondary battery (second form) Figure 2 shows the configuration of a secondary battery 102 according to the second embodiment. As shown in Figure 2, the secondary battery 102 comprises a positive electrode active material layer 10, a solid electrolyte layer 20, a negative electrode current collector 50, and metallic lithium deposited between the solid electrolyte layer 20 and the negative electrode current collector 50 upon charging. A compound 33 of metal element M and element X exists between the solid electrolyte layer 20 and the negative electrode current collector 50. Here, the formation energy E of the compound 33 of metal element M and element X is MX This is the formation energy E of a compound of Li and the element X (corresponding to the first substance 31 in the first embodiment described above). LiX It's higher than that.

[0048] 2.1 Positive electrode active material layer, solid electrolyte layer, and negative electrode current collector The positive electrode active material layer 10, the solid electrolyte layer 20, and the negative electrode current collector 50 may be the same as those in the first embodiment. As shown in Figure 3, during charging of the secondary battery 102, Li ions released from the positive electrode active material layer 10 reach the space between the solid electrolyte layer 20 and the negative electrode current collector 50 via the solid electrolyte layer 20, receive electrons, and are deposited as metallic lithium. During discharge of the battery, the metallic lithium between the solid electrolyte layer 20 and the negative electrode current collector 50 dissolves (ionizes) and is returned to the positive electrode active material layer 10.

[0049] 2.2 Lithium Metal as a Negative Electrode Active Material The secondary battery 102 is equipped with a lithium-deposited negative electrode. Specifically, as shown in Figures 2 and 3, metallic lithium is deposited between the solid electrolyte layer 20 and the negative electrode current collector 50 during charging. The metallic lithium deposited between the solid electrolyte layer 20 and the negative electrode current collector 50 dissolves (ionizes) during discharge and is returned to the positive electrode active material layer 10. Here, "metallic lithium" is a concept that includes not only elemental lithium but also lithium alloys. That is, in the secondary battery 102, metallic lithium may be deposited as elemental lithium or as an alloy with other metals. Specific examples of lithium alloys are as described above. In the secondary battery 102, a predetermined compound 33 exists between the solid electrolyte layer 20 and the negative electrode current collector 50. In this case, during charging, the lithium supplied from the positive electrode active material layer 10 to the solid electrolyte layer 20 and the negative electrode current collector 50 causes a conversion reaction of the compound 33, resulting in the formation of a compound or alloy of lithium and element X (corresponding to the first substance 31), as well as fresh metal M (corresponding to the second substance 32). Furthermore, the fresh metal M and lithium alloy together, potentially precipitating a lithium alloy as metallic lithium (corresponding to the second substance 32), or a compound of metallic element M and Li (corresponding to the second substance 32).

[0050] 2.3 Compounds of a metallic element M and element X The compound 33 of metal element M and element X exists between the solid electrolyte layer 20 and the negative electrode current collector 50. Here, the formation energy E of the compound 33 of metal element M and element X is MX This is the formation energy E of a compound of Li and element X (corresponding to the first substance 31). LiXThe concentration is higher than that of the other element. In other words, a compound of Li and element X is more easily formed than a compound 33 of metal element M and element X. Therefore, when Li ions are supplied between the solid electrolyte layer 20 and the negative electrode current collector 50 during charging of the secondary battery 102, the compound 33 present between the solid electrolyte layer 20 and the negative electrode current collector 50 is decomposed by a conversion reaction as shown in the following reaction equation (1), and a compound of Li and element X (corresponding to the first substance 31) is produced along with fresh metal M (corresponding to the second substance 32). As charging continues, this fresh metal element M and Li undergo an alloying reaction as shown in the following reaction equation (2), and a lithium alloy as metallic lithium (corresponding to the first substance 31) and a compound of metal element M and Li (corresponding to the second substance 32) are deposited. MX+Li⇒LiX+M ···(1) Li+M⇒LiM ···(2)

[0051] The metal element M only needs to satisfy the above relationship of formation energy and be able to carry out the above conversion reaction. Preferably, the metal element M is an element that can alloy with Li. In particular, when the metal element M is at least one of Mg, Sn, Zn, In, Al, Fe, Ni, Mn, Cr, Ag, Ga, Si, Sb, Pb, Bi, Cd, Sr, Ge, and As, and especially when the metal element M is Mg, the deposition and dissolution reactions of Li during charging and discharging tend to be more uniform, and high performance is more easily ensured.

[0052] Element X only needs to satisfy the above relationship of formation energy and be able to carry out the above conversion reaction. Element X may be a metallic element or a nonmetallic element. In particular, if the product after the conversion reaction (first substance 31) has excellent lithium-ion conductivity, the performance of the secondary battery is likely to be higher. When considering how to make the conversion reaction more efficient and how to produce a product with excellent lithium-ion conductivity, element X may be at least one of H, B, and P. Alternatively, if the metallic element M is Mg, higher performance is likely to be ensured if element X is at least one of Bi, Sb, In, Sn, H, I, Ga, Te, Hg, Cd, Si, B, As, Zn, Ge, Br, P, and Se.

[0053] The compound 33 of metal element M and element X may be at least one selected from compounds of Mg and B (e.g., magnesium diboride: MgB2), compounds of Mg and P (e.g., magnesium phosphide: Mg3P2), compounds of Mg and H (e.g., magnesium hydride: MgH2), composite compounds thereof, and mixtures thereof.

[0054] In the secondary battery 102, as with the secondary battery 101, higher performance is more easily ensured when the metal element M and the element X satisfy the following relationships (1) and (2). That is, when the following relationships (1) and (2) are satisfied, during charging of the secondary battery 102, the compound of metal element M and element X decomposes in the above-mentioned conversion reaction, and during discharging of the secondary battery 102, the reverse reaction of the conversion reaction occurs, making it easy to return to a compound of metal element M and element X. (1) Formation energy E of the compound of the metal element M and the element X MX However, the formation energy E of the compound of Li and the aforementioned metal element M LiM It is lower than that. (2) Formation energy E of the compound of Li and the element X LiX However, the formation energy E of the compound between the metal element M and the element X MX It is lower than that.

[0055] The shape of the compound 33 of metal element M and element X is not particularly limited and may be a thin film, a layer, particulate, or a layer containing particulate compound 33. As detailed in the manufacturing methods of secondary batteries 101 and 102, the compound 33 may coat the surface of the negative electrode current collector 50. Also, as shown in Figure 2, the compound 33 may be in contact with the solid electrolyte layer 20 before the conversion reaction. If the compound 33 is particulate, its average particle size (D50) may be, for example, 100 nm or more and 100 μm or less, 200 nm or more, 400 nm or more, 600 nm or more, 800 nm or more, 1 μm or more, 5 μm or more, or 10 μm or more, or 90 μm or less, 80 μm or less, 70 μm or less, 60 μm or less, or 50 μm or less. The amount of compound 33 between the solid electrolyte layer 20 and the negative electrode current collector 50 is not particularly limited and can be appropriately determined considering the battery performance. For example, when compound 33 exists as a thin film or layer between the solid electrolyte layer 20 and the negative electrode current collector 50, its thickness may be 10 nm or more and 100 μm or less, 20 nm or more, 30 nm or more, 40 nm or more, 100 nm or more, 200 nm or more, 400 nm or more, 600 nm or more, 800 nm or more, 1 μm or more, 5 μm or more, or 10 μm or more, or 90 μm or less, 80 μm or less, 70 μm or less, 60 μm or less, 50 μm or less, 40 μm or less, 30 μm or less, 20 μm or less, 10 μm or less, 1 μm or less, or 800 nm or less. Furthermore, if a layer consisting of particles of compound 33 is formed between the solid electrolyte layer 20 and the negative electrode current collector 50, the number of particles in the thickness direction of the layer may be one or more.

[0056] In the secondary battery 102, as with the secondary battery 101, the above-mentioned generation energy E MX and the energy of creation E LiX A larger difference between these two factors makes it easier to promote the conversion reaction described above and to ensure the effects described above. In this regard, in secondary battery 102, the generated energy E MX and the energy of creation E LiX The difference E MX-E LiX However, it may also be 0.027 eV / atom or higher, 0.032 eV / atom or higher, 0.050 eV / atom or higher, 0.075 eV / atom or higher, 0.100 eV / atom or higher, 0.150 eV / atom or higher, or 0.200 eV / atom or higher.

[0057] 2.4 Compounds of Li and Element X As described above, in the secondary battery 102, a compound of Li and element X can be produced by a conversion reaction of compound 33 of metal element M and element X. The type of Li and element X compound depends on the type of compound 33. As described above, when element X is at least one of H, B, and P, the conversion reaction of compound 33 can be made more efficient, and a product with excellent lithium ion conductivity can be produced. That is, the Li and element X compound may be at least one selected from a Li and B compound, a Li and P compound, a Li and H compound, a composite compound thereof, and a mixture thereof. The shape of the Li and element X compound also depends on the shape of compound 33. That is, as described above, the shape of the Li and element X compound may be a thin film, a layer, a particulate, or a layer containing a particulate compound. The amount of the Li and element X compound between the solid electrolyte layer 20 and the negative electrode current collector 50 after the conversion reaction also depends on the amount of compound 33. A compound of Li and element X may, for example, coat the surface of the negative electrode current collector 50 to protect it.

[0058] 2.5 Other Configurations The secondary battery 102 only needs to have at least the above-described components, and may have other components as well. The other components are the same as those described in the first embodiment. For example, the secondary battery 102 may include a positive electrode current collector 40. The secondary battery 102 may also include a predetermined outer casing. The secondary battery 102 may also include a predetermined sealing resin. The secondary battery 102 may also include a predetermined restraining member.

[0059] 3. Functions and Effects of Secondary Batteries (First and Second Forms) According to the inventors' findings, in conventional secondary batteries equipped with a metallic lithium anode, when metallic lithium is deposited and dissolved repeatedly between the solid electrolyte layer and the negative electrode current collector, the metallic lithium is deposited and dissolved unevenly, and voids are created between the solid electrolyte layer and the metallic lithium, resulting in a decrease in Coulomb efficiency. Furthermore, when metallic lithium is deposited and dissolved unevenly, the resistance of the secondary battery increases, and the cycle characteristics tend to deteriorate. In contrast, the secondary batteries 101 and 102 of this disclosure are thought to be able to suppress voids during the deposition of metallic lithium, for example, and thus improve Coulomb efficiency and other properties. Specifically, these are as follows.

[0060] 3.1 Function and Effects of Secondary Batteries (First Form) As shown in Figure 3, during the discharge of the secondary battery 101, the second substance 32 releases Li ions, and fresh metal M is generated as a result. This fresh metal M functions as a deposition site for metallic lithium (second substance 32) during the charging of the secondary battery 101, making it easier for metallic lithium to precipitate uniformly, slowly, and efficiently. By suppressing uneven deposition of metallic lithium, the secondary battery 101 has excellent Coulomb efficiency. Also, as shown in Figure 3, during the discharge of the secondary battery 101, the first substance 31 may release Li ions, or it may remain as the first substance 31. If the first substance 31 releases Li ions, the remaining element X can react with the fresh metal M mentioned above. This can generate a compound 33 (MX) of metallic element M and element X. During charging of the secondary battery 101, compound 33 reacts with Li ions to undergo the conversion reaction described above, potentially producing the first substance 31 (LiX) and fresh metal M. As described above, this fresh metal M functions as a deposition site for metallic lithium, and metallic lithium (second substance 32) is uniformly and slowly deposited during charging of the secondary battery 101.

[0061] As described above, during charging and discharging of the secondary battery 101, the negative electrode active material layer 30 contains fresh metal M, which serves as a deposition site for metallic lithium during charging. That is, during charging of the secondary battery 101, metallic lithium (Li-M alloy) can be deposited uniformly, slowly, and efficiently, starting from this fresh metal M. In addition, the affinity of deposited Li to the solid electrolyte layer 20 is increased, making it easier to suppress voids that occur at the interface between the solid electrolyte layer 20 and the deposited Li. Furthermore, voids in the negative electrode active material layer 30 are also easier to suppress. In this way, by suppressing uneven deposition of metallic lithium, the secondary battery 101 has excellent Coulomb efficiency. Moreover, if the first substance 31 (LiX) and the second substance (fresh metal M) are generated in the negative electrode active material layer 30 by the above conversion reaction, the layer consisting of LiX and fresh metal M will have a storage structure, and it can be expected that the volume change of the secondary battery during charging and discharging will be reduced.

[0062] 3.2 Function and Effects of Secondary Batteries (Second Form) As described above, during charging of the secondary battery 102, the compound 33 of metal element M and element X reacts with Li ions, and through the above conversion reaction, fresh metal M can be generated between the solid electrolyte layer 20 and the negative electrode current collector 50 (for example, at the interface between the solid electrolyte layer 20 and compound 33, or at the interface between the solid electrolyte layer 20 and the compound of Li and element X (first substance 31)). This fresh metal M between the solid electrolyte layer 20 and the negative electrode current collector 50 allows for uniform, gradual, and efficient deposition of metallic lithium. Therefore, it is thought that the void between the solid electrolyte layer 20 and the negative electrode current collector 50 can be suppressed during the deposition of metallic lithium. Furthermore, the affinity of metallic lithium to the solid electrolyte layer 20 is likely to increase, and the void at the interface between the solid electrolyte layer 20 and metallic lithium can also be suppressed. In this way, by suppressing the void between the solid electrolyte layer 20 and the negative electrode current collector 50, reaction unevenness during charging and discharging is eliminated, and the Coulomb efficiency of the secondary battery is easily improved. Furthermore, if the above conversion reaction generates LiX and fresh metal M between the solid electrolyte layer 20 and the negative electrode current collector 50, the layer consisting of LiX and fresh metal M will have a storage structure, and it can be expected that the volume change of the secondary battery during charging and discharging will be reduced.

[0063] 3.3 Supplement In addition, while the above description has focused on the structural features of the secondary batteries 101 and 102 of this disclosure, the secondary batteries 101 and 102 can also be specified as follows from the viewpoint of their function.

[0064] The secondary battery 101 according to the first embodiment may be configured such that, during discharge, element X of the first substance 31 and the metal element M of the second substance 32 react to form a compound 33 of the metal element M and element X. More specifically, the secondary battery 101 may be configured such that, during discharge, element X of the first substance 31 and the metal element M of the second substance 32 react to form a compound 33 of the metal element M and element X on one or both of the surface of the solid electrolyte layer 20 and the surface of the negative electrode current collector 50. In one embodiment, the secondary battery 101 may be configured such that, during discharge, element X of the first substance 31 and the metal element M of the second substance 32 react to form a compound 33 of the metal element M and element X on the surface of the negative electrode current collector 50.

[0065] The secondary battery 102 according to the second embodiment may be configured such that, for example, during charging, the compound 33 of the metal element M and the element X decomposes to produce a compound of Li and the element X. More specifically, the secondary battery 102 may be configured such that during charging, the compound 33 of the metal element M and the element X decomposes to produce a compound of Li and the element X on one or both of the surface of the solid electrolyte layer 20 and the surface of the negative electrode current collector 50. In one embodiment, the secondary battery 102 may be configured such that during charging, the compound 33 of the metal element M and the element X decomposes to produce a compound of Li and the element X (first substance 31) on the surface of the negative electrode current collector 50.

[0066] As shown in Figures 1-3, the secondary battery of this disclosure has different structures before and after the conversion reaction. That is, before the conversion reaction (for example, before charging), a compound 33 of metal element M and element X may be present between the solid electrolyte layer 20 and the negative electrode current collector 50, while after the conversion reaction (for example, after charging), an alloy or compound (first substance 31) of Li and element X may be present between the solid electrolyte layer 20 and the negative electrode current collector 50. In other words, the secondary battery after the conversion reaction has the same configuration as the secondary battery 101 according to the first embodiment, and the secondary battery before the conversion reaction has the same configuration as the secondary battery 102 according to the second embodiment.

[0067] 4. Manufacturing method of secondary batteries The secondary batteries 101 and 102 described above can be manufactured, for example, as follows. That is, as shown in Figure 4, a method for manufacturing secondary batteries 101 and 102 according to one embodiment may include obtaining a laminate 70 having a positive electrode active material layer 10, a solid electrolyte layer 20, a negative electrode current collector 50, and a compound 33 of a metal element M and element X disposed between the solid electrolyte layer 20 and the negative electrode current collector 50, and charging the laminate 70 to supply lithium ions between the solid electrolyte layer 20 and the negative electrode current collector 50 to cause a conversion reaction of the compound 33 of the metal element M and element X to produce a first substance 31 and a second substance 32. Here, the first substance 31 is at least one of an alloy of Li and element X, and a compound of Li and element X, and the second substance 32 is at least one of a single metal element M, an alloy of Li and the metal element M, and a compound of Li and the metal element M. Furthermore, as shown in Figure 4, the laminate 70 may be obtained in the following manner. That is, the manufacturing method of the present disclosure may include coating the surface of the negative electrode current collector 50 with a compound 33 of the metal element M and the element X to obtain a coating 60, and laminating the positive electrode current collector 40, the positive electrode active material layer 10, the solid electrolyte layer 20, and the coating 60 to obtain the laminate 70.

[0068] 4.1 Covering As shown in Figure 4, in the manufacturing method according to this embodiment, the surface of the negative electrode current collector 50 may be coated with a compound 33 of metal element M and element X to obtain a coated object 60. As described above, the negative electrode current collector 50 may optionally have a protective layer or the like. The method for coating the surface of the negative electrode current collector 50 with compound 33 is not particularly limited. For example, the surface of the negative electrode current collector 50 may be coated with compound 33 by a coating method using a solution or slurry. Alternatively, a transfer material in which a layer of compound 33 is formed on a substrate may be obtained, and then the compound 33 may be transferred from the transfer material to the surface of the negative electrode current collector 50. Alternatively, the surface of the negative electrode current collector 50 may be coated with compound 33 by sputtering or the like. The metal elements M and X are as described above. That is, the metal element M may be Mg. Furthermore, element X may be at least one of Bi, Sb, In, Sn, H, I, Ga, Te, Hg, Cd, Si, B, As, Zn, Ge, Br, P, and Se, or at least one of H, B, and P.

[0069] 4.2 Fabrication of Laminates As shown in Figure 4, in the manufacturing method according to this embodiment, a laminate 70 having a positive electrode active material layer 10, a solid electrolyte layer 20, a compound 33, and a negative electrode current collector 50 in that order may be obtained using the above-described coating 60. As shown in Figure 4, the laminate 70 may also include a positive electrode current collector 40 that is in contact with the positive electrode active material layer 10. The laminate 70 can be easily obtained, for example, by molding and laminating each of the above-described materials by coating, transferring, bonding, or pressing them so that the positive electrode current collector 40, positive electrode active material layer 10, solid electrolyte layer 20, compound 33, and negative electrode current collector 50 are laminated in that order. The laminate 70 may contain at least one layer each of the positive electrode current collector 40, positive electrode active material layer 10, solid electrolyte layer 20, compound 33, and negative electrode current collector 50. The laminate 70 may comprise at least one stacking unit consisting of the positive electrode current collector 40, the positive electrode active material layer 10, the solid electrolyte layer 20, the compound 33, and the negative electrode current collector 50, and may comprise multiple such stacking units. Furthermore, in the laminate 70, multiple stacking units may be electrically connected in series, in parallel, or not electrically connected to each other. As is clear from Figures 2 and 4, the laminate 70 before charging, as described later, can have the same configuration as the secondary battery 102 according to the second embodiment.

[0070] Before or after obtaining the above-described laminate 70, pressure may be applied to each layer or the laminate 70 in the thickness direction (lamination direction). For example, each layer constituting the laminate 70 may be pressed together, or the gaps between each layer constituting the laminate 70 may be eliminated to reduce the interfacial resistance. Each layer or the laminate 70 can be pressurized by known means. For example, each layer or the laminate 70 can be pressurized in the lamination direction by various pressurizing methods such as CIP, HIP, roll press, uniaxial press, and die press. The magnitude of the pressure applied to each layer or the laminate 70 in the lamination direction can be appropriately determined according to the performance of the target battery. For example, if each layer or the laminate 70 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 integrating or eliminating gaps by plastically deforming the sulfide solid electrolyte. The pressurization time and pressurization temperature for each layer or laminate 70 are not particularly limited.

[0071] 4.3 Charging As shown in Figure 4, in the manufacturing method according to this embodiment, the laminate 70 obtained as described above is charged to deposit metallic lithium between the solid electrolyte layer 20 and the negative electrode current collector 50. Specifically, by charging the laminate 70, lithium ions are conducted from the positive electrode active material contained in the positive electrode active material layer 10 to the negative electrode current collector 50 side via the solid electrolyte layer 20, and between the solid electrolyte layer 20 and the negative electrode current collector 50, these lithium ions receive electrons and are deposited as metallic lithium. At this time, a conversion reaction of compound 33 occurs, producing fresh metal M (second substance 32) along with an alloy or compound of Li and element X (first substance 31), and alloy or compound of Li and metallic element M (second substance 32) may be deposited starting from this metal M. The charging may be, for example, the first charge after the laminate 70 has been prepared. The laminate 70 can be charged by the same method as a general battery charger. In other words, the positive electrode current collector 40 and the negative electrode current collector 50 of the laminated body 70 can be charged by connecting an external power supply. As is clear from Figures 1 and 4, the laminated body 70 after charging can have the same configuration as the secondary battery 101 according to the first embodiment.

[0072] 4.4 Other processes The manufacturing method according to this embodiment may include, in addition to the steps described above, general steps for manufacturing a secondary battery. For example, steps such as housing the laminate 70 inside an outer casing such as a laminate film, or connecting current-collecting tabs to the laminate 70. Specifically, for example, current-collecting tabs may be connected to the current-collecting elements 40 and 50 of the laminate 70 (parts of the current-collecting elements 40 and 50 may be made to protrude and used as tabs), and the laminate 70 may be housed inside a laminate film as an outer casing while the tabs are pulled out to the outside of the laminate film, the laminate film may be sealed, and then the laminate 70 may be charged via the tabs outside the laminate film.

[0073] Furthermore, the manufacturing method according to this embodiment may include selecting a type of compound 33 of metal element M and element X, and when selecting a type of compound 33 of metal element M and element X, it may also include confirming that the metal element M and element X satisfy the following relationships (1) and (2). This allows for the efficient selection of a more appropriate compound 33. The energy of formation for each can be confirmed, for example, in various databases. (1) Formation energy E of a compound between a metal element M and element X MX However, the formation energy E of the compound of Li and the aforementioned metal element M LiM It is lower than that. (2) Formation energy E of Li and element X LiX However, the formation energy E of the compound between the metal element M and the element X MX It is lower than that.

[0074] 5. Vehicles equipped with secondary batteries As described above, the secondary battery of this disclosure can suppress voids in the negative electrode active material layer and exhibits excellent Coulomb efficiency. Such a secondary battery can be suitably used in, for example, at least one type of vehicle selected from hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and battery electric vehicles (BEVs). That is, the technology of this disclosure relates to a vehicle having a secondary battery, wherein the secondary battery comprises the following configuration (A) or (B): (A) The secondary battery comprises a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer, The negative electrode active material layer comprises a first substance and a second substance, The first substance is at least one of an alloy of Li and element X, and a compound of Li and element X. The second substance is at least one of the following: a pure element of metal element M, an alloy of Li and metal element M, and a compound of Li and metal element M. Energy of formation E of the first substance LiX However, the formation energy E of the compound between the metal element M and the element X MX Lower than; (B) The secondary battery comprises a positive electrode active material layer, a solid electrolyte layer, a negative electrode current collector, and metallic lithium deposited between the solid electrolyte layer and the negative electrode current collector upon charging, A compound of metal element M and element X exists between the solid electrolyte layer and the negative electrode current collector, Formation energy E of the compound of the aforementioned metal element M and element X MX However, the formation energy E of the compound of Li and the element X LiX Higher than; It also has aspects of that. The details of the secondary battery's configuration are as described above.

[0075] 6. Conditioning methods for secondary batteries The technology of this disclosure also has an aspect as a method for conditioning secondary batteries. Specifically, the conditioning method of this disclosure includes preparing a secondary battery having a positive electrode active material layer, a solid electrolyte layer, a negative electrode current collector, and a compound of metal element M and element X disposed between the solid electrolyte layer and the negative electrode current collector, and charging the secondary battery to supply lithium ions between the solid electrolyte layer and the negative electrode current collector, thereby causing a conversion reaction of the compound of metal element M and element X to produce a compound of Li and element X. As described above, this makes it possible to increase the Coulomb efficiency of the secondary battery. [Examples]

[0076] As described above, one embodiment of the technology of this disclosure has been explained, but the technology of this disclosure can be modified in various ways other than the above embodiment without departing from its gist. The technology of this disclosure will be described in more detail below with reference to examples, but the technology of this disclosure is not limited to the following examples.

[0077] 1. Fabrication of MgX-coated current collectors A powder consisting of MgX was ground in a mortar for 10 minutes and classified using a 40 μm classifier. Then, 350 mg of mesitylene, 22 mg of a 5 wt% mesitylene solution of styrene-butadiene rubber (SBR), and 200 mg of MgX powder were placed in a container and dispersed for 30 seconds using an ultrasonic disperser. Subsequently, the mixture was mixed for 3 minutes using a shaker and dispersed again for 30 seconds using the ultrasonic disperser to obtain an MgX slurry. A Ni foil, to be used as the negative electrode current collector, was attached to a glass substrate, and the above MgX slurry was uniformly coated onto the surface of the Ni foil using an applicator to obtain an MgX-coated current collector. The thickness of the MgX layer was 10 μm, and the basis weight was 0.2 mg / cm². 2 In this example, one of MgF2, MgB2, Mg3P2, and MgH2 was used as MgX.

[0078] 2. Fabrication of Mg-coated current collectors Mg was deposited onto the surface of a Ni foil to obtain an Mg-coated current collector (Mg-Ni foil). The thickness of the Mg layer was 700 nm.

[0079] 3. Preparation of uncoated current collectors I prepared Ni foil that was not coated with MgX or Mg.

[0080] 4. Creation of evaluation cells As shown in Figure 5, an evaluation cell was obtained by stacking a Li metal layer, a solid electrolyte layer, and the current collector described above. Specifically, 101.7 mg of sulfide-based solid electrolyte (Li2S-P2S5 material containing LiBr and LiI) was prepared, and a flow rate of 1 ton / cm³ was used. 2 A solid electrolyte layer was obtained by press molding with a pressure of 1 ton / cm². Next, the negative electrode current collector was placed at the bottom of the solid electrolyte layer, and the pressure was 1 ton / cm². 2 A laminate of a solid electrolyte layer and a negative electrode current collector was obtained by press molding under pressure. Furthermore, a Li foil was placed on top of the solid electrolyte layer of the laminate and press molded, and then restrained at 2 N·m to obtain an evaluation cell.

[0081] 4.1 Comparative Example 1 An evaluation cell was fabricated using an uncoated current collector (Ni foil) as described above.

[0082] 4.2 Comparative Example 2 An evaluation cell was fabricated using a magnesium-coated current collector (magnesium-coated nickel foil) as described above.

[0083] 4.3 Comparative Example 3 An evaluation cell was fabricated as described above, using an MgF2-coated current collector (MgF2-coated Ni foil) as the MgX-coated current collector.

[0084] 4.4 Example 1 An evaluation cell was fabricated as described above, using an MgB2-coated current collector (MgB2-coated Ni foil) as the MgX-coated current collector.

[0085] 4.5 Example 2 An evaluation cell was fabricated as described above, using an Mg3P2 coated current collector (Mg3P2 coated Ni foil) as the MgX coated current collector.

[0086] 4.6 Example 3 An evaluation cell was fabricated as described above, using an MgH2-coated current collector (MgH2-coated Ni foil) as the MgX-coated current collector.

[0087] 5. Evaluation of Coulomb Efficiency The evaluation cell was placed in a 60°C constant temperature bath for 3 hours to equalize the cell temperature. Next, the evaluation cell was subjected to a current density of 435 μA / cm². 2 It is charged with a constant current to deposit Li, resulting in a charging capacity of 4.35 mAh / cm². 2 Charging stopped upon reaching the target. After 10 minutes, the current density was 435 μA / cm². 2 The lithium was dissolved by discharging at a constant current, and the discharge was terminated when the voltage reached 1.0V. The Coulomb efficiency of each evaluation cell was calculated using the following formula. (Coulomb efficiency [%]) = [(discharge capacity) / (charge capacity)] × 100 =[(Capacity at 1.0V [mAh / cm²] 2 ]) / 4.35[mAh / cm 2 ]]×100

[0088] 6. Calculation of the energy produced Referencing the energy generation of the Material Project database, the energy generation of MgX (E MX [eV / atom]) and the energy of formation of LiX (E LiX [eV / atom]) and the difference (ΔE=E MX -E LiX ) was sought.

[0089] 7. Measurement of deposition overpotential (nucleation overpotential) For each evaluation cell, the nucleation overpotential was measured by reading the maximum voltage when Li was deposited up to a capacity of 1 mAh. The nucleation overpotential for the first charge-discharge cycle and the nucleation overpotential for the second charge-discharge cycle were determined separately.

[0090] 8. Observation of cell cross-sections before and after charging and discharging. (1) The fracture surface of the evaluation cell before charging was obtained. (2) 490 μA / cm 2 The fracture surface was obtained after charging with a constant current for 5 hours to deposit Li. (3) Cross-sectional observation of each fracture surface described in (1) and (2) above was performed using SEM-EDX.

[0091] 9. Evaluation Results 9.1 Coulomb Efficiency and Energy Generated Table 1 and Figure 6 below show the Coulomb efficiency [%] for each evaluation cell. Also, Table 1 below shows the energy of formation of MgX (E MX [eV / atom]) and the energy of formation of LiX (E LiX [eV / atom]) and its difference (ΔE=E MX -E LiX ) indicates.

[0092] [Table 1]

[0093] As shown in Table 1 and Figure 6, Examples 1-3, where ΔE was a positive value, showed improved Coulomb efficiency compared to Comparative Examples 1 and 2, which did not contain MgX, and Comparative Example 3, where ΔE was a negative value. When ΔE is a positive value, it is thought that a conversion reaction of MgX occurs during the charging of the evaluation cell, generating LiX and fresh Mg. In Examples 1-3, it is thought that this fresh Mg uniformly deposited metallic lithium (Li-Mg alloy) between the solid electrolyte layer and the negative electrode current collector, suppressing the generation of voids. Furthermore, the uniform deposition of metallic lithium near the surface of the solid electrolyte layer resulted in a good interface between the solid electrolyte layer and metallic lithium. In addition, the LiX generated by the conversion reaction ensured lithium ion conductivity, thus improving Coulomb efficiency.

[0094] Furthermore, in Comparative Example 1, which lacks Mg and MgX, the Coulomb efficiency is thought to have decreased significantly because metallic lithium was unevenly deposited between the solid electrolyte layer and the negative electrode current collector. In contrast, in Comparative Example 2, which contains Mg, the presence of Mg between the solid electrolyte layer and the negative electrode current collector allowed for the uniform deposition of Li-Mg alloy as metallic lithium between the solid electrolyte layer and the negative electrode current collector during charging, which is thought to have improved the Coulomb efficiency. Moreover, in Comparative Example 3, where ΔE is a negative value, the Coulomb efficiency was higher than in Comparative Example 1, which lacks Mg and MgX, but lower than in Comparative Example 2, which contains Mg. In Comparative Example 3, the conversion reaction of MgX did not proceed, and it is thought that MgX, which is unfavorable for the battery reaction, remains present even after charging.

[0095] 9.2 Nucleation overpotential (deposition overpotential) Table 2 below shows the nucleation overpotential (deposition overpotential) results for each evaluation cell.

[0096] [Table 2]

[0097] As shown in Table 2, Comparative Example 2 has a lower deposition overpotential than Comparative Example 1. Here, a lower deposition overpotential means that the energy barrier for depositing metallic lithium is smaller, and a lower deposition overpotential makes it easier for metallic lithium to deposit uniformly, thus increasing Coulomb efficiency. Comparative Example 2 shows that the deposition overpotential can be kept low by the alloying reaction between Mg and Li. In particular, the deposition overpotential tends to become even smaller from the second cycle onward, when the battery reaction stabilizes. On the other hand, in Examples 1 to 3, similar to Comparative Example 2, the deposition overpotential also decreased significantly from the second cycle onward. In Examples 1 to 3, it is thought that the conversion of MgX proceeded in the first cycle, producing fresh elemental Mg, and from the second cycle onward, metallic lithium was uniformly deposited starting from this elemental Mg. In other words, similar to the results of the generation energy difference ΔE shown in Table 1, the results in Table 2 also indicate that the conversion reaction proceeded in Examples 1 to 3. As shown in Table 2, the deposition overpotential in Comparative Example 3 decreased slightly from the second cycle onward, but it remained high. Furthermore, as shown in Table 1, the formation energy difference ΔE was also small. Therefore, it is considered that the conversion reaction did not proceed in Comparative Example 3.

[0098] 9.3 SEM / EDX before and after Li precipitation The cross-sections of the evaluation cells for Comparative Example 3 and Example 3 were observed and evaluated using SEM / EDX before and after Li precipitation. Figure 5 shows the results for Comparative Example 3, and Figures 6 and 7 show the results for Example 3.

[0099] As shown in Figure 7, in Comparative Example 3, there is no substantial change in the distribution of Mg in the cell cross-section before and after charging. Furthermore, no diffusion of Mg is observed in the precipitated metallic lithium after charging. In other words, in Comparative Example 3, it can be seen that the MgF2 conversion reaction does not proceed during charging.

[0100] As shown in Fig. 8, in Example 3, the distribution of Mg in the cell cross-section changes significantly before and after charging. Specifically, it can be seen that Mg diffuses into the deposited metallic lithium after charging. That is, in Example 3, the conversion reaction of MgH2 proceeds during charging, generating fresh Mg, which serves as the precipitation starting point of metallic lithium, and it can be seen that a Li-Mg alloy is precipitated.

[0101] As shown in Fig. 9, in Example 3, there is a region where neither Ni, Mg, nor S exists between the S existence region (corresponding to the solid electrolyte layer) and the Ni existence region (corresponding to the negative electrode current collector). It is considered that LiH generated by the conversion reaction exists here. Also in Examples 1 and 2, similar to Example 3, it is considered that the conversion reaction occurs during charging, and a Li-Mg alloy is precipitated starting from fresh Mg. From Fig. 9, it can be said that LiH exists in a film form, and its thickness is 10 nm or more and 50 μm or less.

[0102] 10. Further Consideration 10.1 Generation Energy Difference between LiX and MX and Generation Energy Difference between LiM and MX The generation energy (E LiM ) of the alloy (Li-Mg) of Li and Mg is -0.061 [eV / atom]. Comparing this E LiM with the E shown in Table 1 above LiX and the E shown in Table 1 above MX , it can be seen that the metal element M (Mg) and the element X adopted in Examples 1 to 3 satisfy the following relationships (1) and (2). (1) The generation energy E MX of the compound of the metal element M and the element X is lower than the generation energy E LiM of the compound of Li and the metal element M. (2) The generation energy E LiX of the compound of Li and the element X is lower than the generation energy E MX of the compound of the metal element M and the element X.

[0103] 10.2 CV Measurement CV measurements were performed on the evaluation cell according to Example 3 described above under the following conditions. The results are shown in Figure 10. Measurement conditions: 1mV / s, -0.04V~3V, 60℃

[0104] As shown in Figure 10, a redox peak originating from the MgH2 conversion reaction was observed around 0.5V. Furthermore, it was confirmed that the evaluation cell continued to operate reversibly even after 80 cycles.

[0105] 10.3 XRD measurement For the evaluation cell in Example 3 described above, the current is 490 μA / cm². 2 After charging with a constant current for 6 hours (Li deposition), the cell was disassembled, and XRD measurements were performed targeting the interface between the solid electrolyte layer and the deposited Li. The XRD measurement conditions are as follows. The results are shown in Figure 11. Scan speed: 5° / min Scan range: 5-90° Step width: 0.02°

[0106] As shown in Figure 11, in the evaluation cell after charging, it was found that MgH2 was virtually absent at the interface between the solid electrolyte layer and deposited Li, while the solid electrolyte, Li-Mg, and LiH coexisted.

[0107] 10.4 When the position of MgX is changed (Example 4) An evaluation cell having the configuration shown in Figure 5 was obtained by laminating a Li metal layer, a solid electrolyte layer onto which MgH2 was transferred, and an uncoated current collector. Specifically, 101.7 mg of sulfide-based solid electrolyte (Li2S-P2S5 system material containing LiBr and LiI) was prepared, and 1 ton / cm³ was used. 2 A solid electrolyte layer was obtained by press molding with a pressure of 2 tons / cm². Next, a layer made of MgH2 was laminated onto the surface of the solid electrolyte layer, and then a layer was applied. 2 The solid electrolyte layer was press-molded at a pressure of 6 ton / cm² to transfer a layer of MgH2 to the surface. Next, the negative electrode current collector was placed below the MgH2 layer, and the pressure was 6 ton / cm². 2A laminate consisting of a solid electrolyte layer, an MgH2 layer, and a negative electrode current collector was obtained by press molding under pressure. Furthermore, a Li foil was placed on top of the solid electrolyte layer of the laminate and press molded, and then restrained at 2 N·m to obtain the evaluation cell according to Example 4.

[0108] For the obtained evaluation cells, 490 μA / cm² 2 After charging with a constant current for 5 hours to precipitate Li, a fracture surface was obtained, and the cross-section was observed using SEM-EDX. The results are shown in Figure 12. As shown in Figure 12, it was confirmed that LiH was present at the interface between the solid electrolyte layer and the Li-Mg layer. Furthermore, when the Coulomb efficiency was measured for this evaluation cell in the same manner as above, a Coulomb efficiency similar to that of Example 3 was obtained. From these results, it is considered that there are no particular restrictions on the position of LiX(LiH) in the negative electrode active material layer.

[0109] 10.5 Types of MgX In the above examples, H, B, and P were used as examples of element X, but element X is not limited to these. Referring to the generation energy of the Material Project database, elements other than H, B, and P that can be used as element X were extracted. Table 3 below shows examples of elements for which the above ΔE is a positive value. For reference, the ΔE when element X is H, B, and P is also shown. It is believed that if the elements exemplified below are used as element X above, the same effects as in Examples 1-3 will be achieved.

[0110] [Table 3]

[0111] 11. Supplementary Information and Summary In the above examples, specific compounds of metal element M and element X were given as examples, but it is thought that similar effects can be achieved with any MX that can undergo the above conversion reaction. In other words, metal element M is not limited to Mg. However, when metal element M is Mg, it is thought that the deposition of metallic lithium during charging will be more uniform. Also, element X is not limited to those exemplified above. However, when element X is at least one of H, B, and P, it is thought that the LiX after the conversion reaction will have high lithium ion conductivity, etc. Furthermore, as mentioned above, when the metal element is Mg, it is thought that excellent effects will be achieved when element X is at least one of Bi, Sb, In, Sn, H, I, Ga, Te, Hg, Cd, Si, B, As, Zn, Ge, Br, P, and Se.

[0112] In the above embodiment, an evaluation cell as shown in Figure 5 was prepared to simply evaluate the deposition behavior and Coulomb efficiency of metallic lithium. However, when constructing an actual secondary battery, a suitable configuration can be adopted as the positive electrode instead of Li foil.

[0113] In the above embodiment, a specific sulfide solid electrolyte was used in the solid electrolyte layer as an example, but the type of solid electrolyte included in the solid electrolyte layer is not limited to this. However, when a sulfide solid electrolyte is included in the solid electrolyte layer, higher performance as a secondary battery is more likely to be obtained.

[0114] In the above embodiment, a case in which Ni foil is used as the negative electrode current collector was illustrated, but the configuration of the negative electrode current collector is not limited to this. However, it is thought that if a negative electrode current collector containing at least one of Ni and stainless steel is used, alloying reactions between the negative electrode current collector and lithium can be suppressed.

[0115] As described above, a secondary battery having the following configuration can be said to have excellent Coulomb efficiency while having a deposited type metallic lithium anode. That is, the secondary battery of this disclosure has the following configuration (A) or (B).

[0116] (A) The secondary battery comprises a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer, The negative electrode active material layer comprises a first substance and a second substance, The first substance is at least one of an alloy of Li and element X, and a compound of Li and element X. The second substance is at least one of the following: a pure element of metal element M, an alloy of Li and metal element M, and a compound of Li and metal element M. Energy of formation E of the first substance LiX However, the formation energy E of the compound between the metal element M and the element X MX It is lower than that.

[0117] (B) The secondary battery comprises a positive electrode active material layer, a solid electrolyte layer, a negative electrode current collector, and metallic lithium deposited between the solid electrolyte layer and the negative electrode current collector upon charging, A compound of metal element M and element X exists between the solid electrolyte layer and the negative electrode current collector, Formation energy E of the compound of the aforementioned metal element M and element X MX However, the formation energy E of the compound of Li and the element X LiX It's higher than that. [Explanation of symbols]

[0118] 10 Cathode active material layer 20 Solid electrolyte layer 30 Negative electrode active material layer 31 First substance 32 Second substance 33 Compounds of metallic element M and element X 40 Positive electrode current collector 50 Negative electrode current collector 60 Covering 70-layer structure 101, 102 Secondary battery

Claims

1. A secondary battery comprising a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer, The negative electrode active material layer comprises a first substance and a second substance formed in a film-like manner. The first substance is a compound of Li and element X, The element X is at least one of B and P, The second substance is at least one of an alloy of Li and a metal element M, and a compound of Li and the metal element M. The aforementioned metal element M is Mg, Energy of formation E of the first substance ＬｉＸ However, the formation energy E of the compound between the metal element M and the element X ＭＸ Lower than, and The thickness of the first substance formed in the form of a film is 10 nm or more and 50 μm or less. Secondary battery.

2. A secondary battery comprising a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer, The solid electrolyte layer comprises a sulfide solid electrolyte, The negative electrode active material layer comprises a first substance and a second substance formed in a film-like manner. The first substance is a compound of Li and element X, The element X is at least one of H, B, and P. The second substance is at least one of an alloy of Li and a metal element M, and a compound of Li and the metal element M. The aforementioned metal element M is Mg, Energy of formation E of the first substance ＬｉＸ However, the formation energy E of the compound between the metal element M and the element X ＭＸ Lower than, and The thickness of the first substance formed in the form of a film is 10 nm or more and 50 μm or less. Secondary battery.

3. A secondary battery according to Claim 1, The solid electrolyte layer contains a sulfide solid electrolyte. Secondary battery.

4. The aforementioned generation energy E ＭＸ and the aforementioned generation energy E ＬｉＸ The difference is 0.027 eV / atom or greater. A secondary battery according to any one of claims 1 to 3.

5. A method for manufacturing a secondary battery, To obtain a laminate having a positive electrode active material layer, a solid electrolyte layer, a negative electrode current collector, and a compound of metal element M and element X disposed between the solid electrolyte layer and the negative electrode current collector, The process includes charging the laminate to supply lithium ions between the solid electrolyte layer and the negative electrode current collector, thereby causing a conversion reaction between the metal element M and the element X to produce a first substance and a second substance formed in a film, The first substance is a compound of Li and the element X, The element X is at least one of B and P, The second substance is at least one of an alloy of Li and the metal element M, and a compound of Li and the metal element M. The aforementioned metal element M is Mg, The thickness of the first substance formed in the form of a film is 10 nm or more and 50 μm or less. Manufacturing method.

6. A method for manufacturing a secondary battery, To obtain a laminate having a positive electrode active material layer, a solid electrolyte layer containing a sulfide solid electrolyte, a negative electrode current collector, and a compound of metal element M and element X disposed between the solid electrolyte layer and the negative electrode current collector, and The process includes charging the laminate to supply lithium ions between the solid electrolyte layer and the negative electrode current collector, thereby causing a conversion reaction between the metal element M and the element X to produce a first substance and a second substance formed in a film, The first substance is a compound of Li and the element X, The element X is at least one of H, B, and P. The second substance is at least one of an alloy of Li and the metal element M, and a compound of Li and the metal element M. The aforementioned metal element M is Mg, The thickness of the first substance formed in the form of a film is 10 nm or more and 50 μm or less. Manufacturing method.

7. A method for manufacturing a secondary battery according to Claim 5, The solid electrolyte layer contains a sulfide solid electrolyte. Manufacturing method.

8. A secondary battery comprising a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer, The solid electrolyte layer comprises a sulfide solid electrolyte, The negative electrode active material layer comprises a first substance and a second substance, The first substance is a compound of Li and element X, The element X is at least one of B and P, The second substance is at least one of the following: a pure element of metal element M, an alloy of Li and metal element M, and a compound of Li and metal element M. The aforementioned metal element M is Mg, and Energy of formation E of the first substance ＬｉＸ However, the formation energy E of the compound between the metal element M and the element X ＭＸ Lower than Secondary battery.

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