Secondary battery and method for manufacturing the same

Abstract

To provide a secondary battery with a deposition-type lithium anode capable of reducing resistance after charging and discharging.SOLUTION: A disclosed secondary battery 100 includes: a positive electrode 10; a solid electrolyte layer 20; a protective layer 30; a negative electrode current collector 41; and a metallic lithium 42 that precipitates between the solid electrolyte layer 20 and the negative electrode current collector 41 by charging. The solid electrolyte layer 20 contains a sulfide solid electrolyte. The protective layer 30 exists between the solid electrolyte layer 20 and the negative electrode current collector 41. The protective layer 30 contains Li, P, and O as constituent elements.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 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. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-184513 [Patent Document 2] International Publication No. 2013 / 141241 [Overview of the project] [Problems that the invention aims to solve]

[0004] Secondary batteries equipped with a deposited metallic lithium anode have room for improvement in terms of resistance after charging and discharging. [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, a solid electrolyte layer, a protective layer, a negative electrode current collector, and metallic lithium deposited between the solid electrolyte layer and the negative electrode current collector upon charging, The solid electrolyte layer comprises a sulfide solid electrolyte, The protective layer is located between the solid electrolyte layer and the negative electrode current collector. The protective layer contains Li, P, and O as constituent elements. Secondary battery. <Aspect 2> The secondary battery according to Aspect 1, where the protective layer contains Li, P, O, and N as constituent elements. Secondary battery. <Aspect 3> The secondary battery according to Aspect 1 or 2, where the protective layer has a lithium ion conductivity of more than 10 -7 S / cm. Secondary battery. <Aspect 4> The secondary battery according to any one of Aspects 1 to 3, where the negative electrode current collector has a metal foil and a Mg-containing layer provided on the surface of the metal foil, and the Mg-containing layer is present between the protective layer and the metal foil. Secondary battery. <Aspect 5> A method for manufacturing a secondary battery, including coating one or both surfaces of a negative electrode current collector and a solid electrolyte layer with a protective layer to obtain a coated product, using the coated product to obtain a laminate having a positive electrode, a solid electrolyte layer, a protective layer, and a negative electrode current collector in this order, and charging the laminate to deposit metallic lithium between the solid electrolyte layer and the negative electrode current collector. The solid electrolyte layer contains a sulfide solid electrolyte, and the protective layer contains Li, P, and O. Manufacturing method.

Advantages of the Invention

[0006] The secondary battery of the present disclosure includes a deposited-type metallic lithium negative electrode and has a low resistance.

Brief Description of the Drawings

[0007] [Figure 1] Schematically shows the configuration of the secondary battery 100 after charging or discharging. [Figure 2]An example of the process for manufacturing the secondary battery 100 is schematically shown. [Figure 3] SEM secondary electron image and EDX mapping of the LiPON film surface of the LiPON-coated Mg-deposited current collector are shown. [Figure 4] The charge-discharge curve of the evaluation cell is shown. [Figure 5] The evaluation results of the cell impedance after the first charge are shown. [Figure 6] The evaluation results of the cell impedance after the first charge and discharge are shown. [Figure 7] The change over time of the 1s resistance of the cell when a 60°C storage test is performed in an open circuit after charging up to the upper cut-off potential of 4.2V is shown. [Figure 8] Cross-sectional SEM secondary electron image and EDX mapping at the LiPON-coated Mg negative electrode-solid electrolyte layer interface after charging at 60°C are shown.

Mode for Carrying Out the Invention

[0008] 1. Secondary Battery Hereinafter, the secondary battery according to the embodiment will be described while referring to the drawings, but the technology of the present disclosure is not limited to the following embodiments. FIG. 1 shows the configuration of a secondary battery 100 according to an embodiment. As shown in FIG. 1, the secondary battery 100 includes a positive electrode 10, a solid electrolyte layer 20, a protective layer 30, a negative electrode current collector 41, and metallic lithium 42 that is deposited between the solid electrolyte layer 20 and the negative electrode current collector 41 by charging. The solid electrolyte layer 20 includes a sulfide solid electrolyte. The protective layer 30 exists between the solid electrolyte layer 20 and the negative electrode current collector 41. The protective layer 30 includes Li, P, and O as constituent elements.

[0009] 1.1 Positive Electrode The positive electrode 10 includes at least a positive electrode active material. During charging of the secondary battery 100, lithium ions released from the positive electrode active material reach the space between the solid electrolyte layer 20 and the negative electrode current collector 41 via the solid electrolyte layer 20, receive electrons, and precipitate as metallic lithium 42. During discharge of the battery, the metallic lithium 42 between the solid electrolyte layer 20 and the negative electrode current collector 41 dissolves (ionizes) and is returned to the positive electrode 10. The form of the positive electrode 10 may be any form known as a positive electrode for a secondary battery. For example, as shown in Figure 1, the positive electrode 10 may comprise a positive electrode current collector 11 and a positive electrode active material layer 12.

[0010] The positive electrode current collector 11 can be any material capable of functioning as a positive electrode current collector for a secondary battery. The positive electrode current collector 11 may be a metal foil or a metal mesh. In particular, metal foil offers superior handling. The positive electrode current collector 11 may consist of multiple metal foils. Examples of metals that make up the positive electrode current collector 11 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 11 may contain Al. The positive electrode current collector 11 may have some kind of coating layer on its surface for the purpose of adjusting resistance, etc. Also, if the positive electrode current collector 11 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 11 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.

[0011] The positive electrode active material layer 12 contains a positive electrode active material and may optionally also contain an electrolyte, a conductive additive, a binder, etc. The respective amounts of the positive electrode active material, electrolyte, conductive additive, and binder, etc. in the positive electrode active material layer 12 can be appropriately determined according to the desired battery performance. The shape of the positive electrode active material layer 12 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 12 can be appropriately determined according to the desired battery performance.

[0012] The positive electrode active material can be any known positive electrode active material for secondary batteries, provided that it can supply lithium to the negative electrode side during charging. For example, various lithium-containing oxides such as lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, and spinel-based lithium compounds can be used as the positive electrode active material. Alternatively, a material in which lithium is adsorbed onto sulfur can be used as the positive electrode active material. In particular, when the positive electrode 10 contains a lithium-containing oxide as the positive electrode active material, lithium ions can be appropriately supplied from the positive electrode active material to the negative electrode side during charging, and the expansion and contraction of the positive electrode active material during charging and discharging is small, 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 in particulate form, for example, and its size is not particularly limited. The surface of the positive electrode active material may be coated with an ion-conducting oxide. This makes it easier to suppress reactions between the positive electrode active material and other battery materials (for example, sulfide solid electrolytes described later). Examples of ion-conducting oxides that coat the surface of the positive electrode active material include Li3BO3, LiBO2, Li2CO3, LiAlO2, Li4SiO4, Li2SiO3, Li3PO4, Li2SO4, Li2TiO3, and Li4Ti5O 12 It may be at least one selected from Li2Ti2O5, Li2ZrO3, LiNbO3, Li2MoO4, and Li2WO4. 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 or 1 nm or more, 100 nm or less, or 20 nm or less.

[0013] The electrolyte contained in the positive electrode active material layer 12 may be a solid electrolyte, a liquid electrolyte (electrolyte solution), or a combination thereof. In particular, when the positive electrode active material layer 12 contains a solid electrolyte, an even greater effect can be expected from the technology of this disclosure. The solid electrolyte may be one of those known as solid electrolytes for 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 them sulfide solid electrolytes containing at least Li, S, and P as constituent elements, have particularly high performance. Details of sulfide solid electrolytes will be described later. The solid electrolyte may be amorphous or crystalline. The solid electrolyte may be particulate. Only one type of solid electrolyte may be used alone, or two or more types may be used in combination.

[0014] Examples of conductive additives that may be included in the positive electrode active material layer 12 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.

[0015] Examples of binders that may be included in the positive electrode active material layer 12 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.

[0016] 1.2 Solid electrolyte layer The solid electrolyte layer 20 contains at least a sulfide solid electrolyte. The sulfide solid electrolyte contained in the solid electrolyte layer 20 may be the same type as or different from the sulfide solid electrolyte that may be contained in the positive electrode active material layer 12 described above. The solid electrolyte layer 20 may contain other electrolytes together with the sulfide solid electrolyte. The other electrolyte may be a solid electrolyte or an electrolyte solution. The solid electrolyte layer 20 may further optionally contain binders and various additives. The binder that may be contained in the solid electrolyte layer 20 may be the same type as or different from the binder that may be contained in the positive electrode active material layer 12 described above. In the solid electrolyte layer 20, only one type of 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 solid electrolyte and binder in the solid electrolyte layer 20 is not particularly limited. For example, with the entire solid electrolyte layer 20 (total solid content) being 100% by mass, the solid electrolyte content may be 50% by mass or more, 60% by mass or more, or 70% by mass or more, or 100% by mass or less, or 90% by mass or less. The thickness of the solid electrolyte layer 20 is not particularly limited and may be, for example, 0.1 μm or more, or 1 μm or more, or 2 mm or less, or 1 mm or less.

[0017] 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. When 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. 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. The sulfide solid electrolyte may also contain S as the main component of the anionic element. 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. M may be at least one selected from P, Si, Ge, B, Al, Ga, or In.) 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 be of 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 from 0 or more to 2 or less). a may be 0, or may be greater than 0. In the latter case, a may be 0.1 or more, may be 0.5 or more, or may be 1 or more. Also, a may be 1.8 or less, may be 1.5 or less.

[0018] 1.3 Protective Layer As shown in FIG. 1, the protective layer 30 exists between the solid electrolyte layer 20 and the negative electrode current collector 41. According to the findings of the present inventor, in a conventional secondary battery, when the precipitation and dissolution of metallic lithium are repeated between the solid electrolyte layer and the negative electrode current collector, metallic lithium reacts with the sulfide solid electrolyte contained in the solid electrolyte layer, and the sulfide solid electrolyte is reductively decomposed, etc., and the resistance tends to increase. In contrast, in the secondary battery 100 of the present disclosure, due to the presence of the protective layer 30 between the solid electrolyte layer 20 and the negative electrode current collector 41, direct contact between the solid electrolyte layer 20 and the metallic lithium 42 is suppressed during the precipitation of the metallic lithium 42, and the reaction between the sulfide solid electrolyte contained in the solid electrolyte layer 20 and the metallic lithium 42 is likely to be suppressed. Further, by including the following constituent elements in the protective layer 30, lithium ion conductivity is ensured in the protective layer 30. As a result, according to the secondary battery 100, an increase in resistance after charge and discharge can be suppressed.

[0019] The protective layer 30 contains Li, P, and O as constituent elements. The protective layer 30 may also contain Li, P, O, and N as constituent elements. The protective layer 30 containing Li, P, and O as constituent elements has excellent lithium ion conductivity. The protective layer 30 is, for example, 10 -7 The protective layer may have a lithium ion conductivity greater than S / cm. The Li, P, and O contained in the protective layer 30 may be derived from a phosphate compound. In other words, the protective layer 30 may contain a phosphate compound containing Li, P, and O. The protective layer 30 does not need to contain S. The ratio of Li, P, O, and N in the protective layer 30 is not particularly limited. When the surface of the protective layer 30 is analyzed by XPS, the elemental ratio Li / P between Li and P may be, for example, greater than 0 and 5.0 or less, the elemental ratio O / P may be, for example, greater than 0 and 5.0 or less, and the elemental ratio N / P may be, for example, 0 or more and 2.0 or less.

[0020] The protective layer 30 may, for example, cover at least a portion of the surface of the solid electrolyte layer 20 on the negative electrode current collector 41 side (for example, 50% to 100% of the surface of the solid electrolyte layer 20, 75% to 100% of the surface, or 90% to 100% of the surface), or it may cover at least a portion of the surface of the negative electrode current collector 41 on the solid electrolyte layer 20 side (for example, 50% to 100% of the surface of the negative electrode current collector 41, 75% to 100% of the surface, or 90% to 100% of the surface). In either case, metallic lithium 42 may be deposited between the protective layer 30 and the negative electrode current collector 41 during charging. The thickness of the protective layer 30 is not particularly limited and may be, for example, 5 nm to 500 μm, 10 nm to 50 μm, or 50 nm to 1 μm. The secondary battery 100 may have only one protective layer 30, or it may have two or more layers.

[0021] 1.4 Negative electrode current collector The negative electrode current collector 41 can be any material capable of functioning as a negative electrode current collector for a secondary battery. The negative electrode current collector 41 may be a metal foil, a metal mesh, or a carbon sheet. Metal foil is particularly advantageous in terms of handling. The negative electrode current collector 41 may consist of multiple metal foils or sheets. Examples of metals that make up the negative electrode current collector 41 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 prone to alloying with lithium, the negative electrode current collector 41 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 41 may have some kind of coating layer on its surface. Also, if the negative electrode current collector 41 consists of multiple metal foils, there may be some kind of layer between the multiple metal foils. The thickness of the negative electrode current collector 41 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.

[0022] As shown in Figure 1, the negative electrode current collector 41 may have a metal foil 41a and a Mg-containing layer 41b provided on the surface of the metal foil 41a, and the Mg-containing layer 41b may be located between the protective layer 30 and the metal foil 41a. It is believed that the presence of the Mg-containing layer 41b in the negative electrode current collector 41 promotes the diffusion of Li on the surface of the negative electrode current collector 41, increases the affinity of metallic lithium 42 to the negative electrode current collector 41, suppresses the void between the negative electrode current collector 41 and the metallic lithium 42, and allows for more uniform deposition of metallic lithium 42 on the surface of the negative electrode current collector 41. The Mg-containing layer 41b 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 Mg-containing layer 41b may be, for example, 50 mol% or more and 100 mol% or less, or 70 mol% or more, 80 mol% or more, or 90 mol% or more. The Mg-containing layer 41b may be, for example, a thin metal film containing Mg (e.g., a vapor-deposited film), or a layer containing Mg particles. The thin metal film containing Mg may be composed of Mg or an Mg alloy. 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 the total constituent elements are Mg). The Mg alloy particles may contain at least one of the metals other than Mg, such as Li, Au, Al, and Ni. The Mg alloy particles may or may not contain Li. The Mg alloy particles may contain a β single-phase alloy of Li and Mg. Alternatively, the Mg particles may be oxide particles containing Mg and O (Mg oxide particles). The 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, 10 nm or more and 100 μm or less.The thickness of the Mg-containing layer 41b may be, for example, 10 nm to 100 μm, 50 nm or more, 100 nm or more, 50 μm or less, 10 μm or less, or 5 μm or less. The Mg-containing layer 41b can be formed, for example, on the surface of the metal foil 41a that constitutes the negative electrode current collector 41. Alternatively, the Mg-containing layer 41b may be formed by pressing Mg particles on the surface of the negative electrode current collector 41. As a method for forming the Mg-containing layer 41b on the surface of the metal foil 41a, for example, PVD methods such as vapor deposition and sputtering; plating methods such as electrolytic plating and electroless plating; and coating methods using slurry can be employed.

[0023] 1.5 Lithium Metal as a Negative Electrode Active Material The secondary battery 100 is equipped with a lithium-deposited negative electrode. Specifically, as shown in Figure 1, during charging, metallic lithium 42 is deposited between the solid electrolyte layer 20 and the negative electrode current collector 41 (particularly between the protective layer 30 and the negative electrode current collector 41). The metallic lithium 42 deposited between the solid electrolyte layer 20 and the negative electrode current collector 41 dissolves (ionizes) during discharge and is returned to the positive electrode 10. In this application, "metallic lithium" is a concept that includes not only elemental lithium but also lithium alloys. The lithium alloy may be at least one selected from 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 amount of metallic lithium 42 deposited between the solid electrolyte layer 20 and the negative electrode current collector 41 is not particularly limited and can be adjusted as appropriate according to the desired battery performance.

[0024] 1.6 Other Configurations The secondary battery 100 may have other configurations in addition to the above configuration. For example, the secondary battery 100 may have tabs or terminals connected to each of the above configurations, an outer casing that houses each of the above configurations, each of the above configurations may be sealed with resin, and a restraining member for restraining each of the above configurations in the thickness direction.

[0025] 2. Manufacturing method of secondary batteries The secondary battery 100 of this disclosure can be manufactured, for example, as follows. That is, as shown in Figure 2, a method for manufacturing the secondary battery 100 according to one embodiment may include: obtaining a coated object 50 by covering one or both surfaces of the negative electrode current collector 41 and the solid electrolyte layer 20 with a protective layer 30; obtaining a laminate 60 having the positive electrode 10, the solid electrolyte layer 20, the protective layer 30 and the negative electrode current collector 41 in this order using the coated object 50; and charging the laminate 60 to deposit metallic lithium 42 between the solid electrolyte layer 20 and the negative electrode current collector 41. Here, the solid electrolyte layer 20 contains a sulfide solid electrolyte, and the protective layer 30 contains Li, P, and O.

[0026] 2.1 Covering In the manufacturing method according to this embodiment, a coated object 50 is obtained by coating one or both surfaces of the negative electrode current collector 41 and the solid electrolyte layer 20 with a protective layer 30. The method for coating the surfaces of the negative electrode current collector 41 and the solid electrolyte layer 20 with the protective layer 30 is not particularly limited. For example, the surfaces of the negative electrode current collector 41 and the solid electrolyte layer 20 can be coated with the protective layer 30 by a coating method using a solution or slurry. Alternatively, a transfer material having a layer consisting of the protective layer 30 formed on a substrate can be obtained, and the protective layer 30 can be transferred from the transfer material to the surfaces of the negative electrode current collector 41 and the solid electrolyte layer 20. Alternatively, the protective layer 30 can be formed on the surfaces of the negative electrode current collector 41 and the solid electrolyte layer 20 by sputtering or the like.

[0027] 2.2 Fabrication of Laminates In the manufacturing method according to this embodiment, a laminate 60 having a positive electrode 10, a solid electrolyte layer 20, a protective layer 30, and a negative electrode current collector 41 in that order is obtained using the above-described coating 50. The laminate 60 can be easily obtained by molding and laminating each of the above-described materials, for example, by coating, transferring, bonding, or pressing the materials. The laminate 60 comprises at least one laminated unit of the above-described positive electrode current collector 11, positive electrode active material layer 12, solid electrolyte layer 20, protective layer 30, and negative electrode current collector 41. In the laminate 60, multiple laminated units may be electrically connected in series, in parallel, or not electrically connected to each other. Before or after obtaining the laminate 60, pressure may be applied to each of the above-described layers or the laminate 60 in the thickness direction (lamination direction). Each layer or the laminate 60 can be pressurized by known means. The magnitude of the pressure applied to each layer or the laminate 60 in the stacking direction can be appropriately determined according to the performance of the intended battery. This 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. The pressurization time and pressurization temperature of each layer or the laminate 60 are not particularly limited.

[0028] 2.3 Charging In the manufacturing method according to this embodiment, the laminate 60 described above is charged to deposit metallic lithium 42 between the solid electrolyte layer 20 and the negative electrode current collector 41. By charging the laminate 60, lithium ions are conducted from the positive electrode active material contained in the positive electrode active material layer 12 to the negative electrode current collector 41 side via the solid electrolyte layer 20, and these lithium ions receive electrons between the solid electrolyte layer 20 and the negative electrode current collector 41, depositing as metallic lithium 42. The laminate 60 can be charged in the same way as a general battery charging method. For example, charging can be performed by connecting an external power supply to the positive electrode current collector 11 and the negative electrode current collector 41.

[0029] 2.4 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 60 inside the outer casing, or connecting tabs to the laminate 60. [Examples]

[0030] 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.

[0031] 1. Fabrication of the negative electrode current collector A magnesium-deposited current collector was obtained by depositing magnesium (Mg) onto the surface of a stainless steel foil. The thickness of the Mg-deposited film was 1.0 μm.

[0032] 2. Covering with a protective layer A LiPON-coated Mg current collector was obtained by sputtering a LiPON protective layer onto the Mg of an Mg-deposited current collector. The thickness of the LiPON film was 100 nm.

[0033] 3. Fabrication of the positive electrode A positive electrode slurry was obtained by adding the components to butyl butyrate as a solvent in a mass ratio of positive electrode active material (NCA): sulfide solid electrolyte (Li2S-P2S5-LiI-LiBr): binder (PVdF): conductive additive (AB) = 84.7:13.4:0.6:1.27. The positive electrode slurry was coated onto an Al foil with a coating gap of 225 μm, pre-dried at 60°C, and fully dried at 165°C for 1 hour to obtain the positive electrode. The basis weight of the composite material in the positive electrode was 18.7 mg / cm². 2 The design capacity is 3.0mAh / cm². 2 That is the case.

[0034] 4. Fabrication of the solid electrolyte layer A solid electrolyte slurry was obtained by adding each component to butyl butyrate as a solvent in a mass ratio of sulfide solid electrolyte (same as above):binder (same as above) = 92.6:7.4. The solid electrolyte slurry was coated onto a release film with a coating gap of 325 μm, pre-dried at room temperature for 3 hours, and then fully dried at 165°C for 1 hour. Two φ14.5 mm coated films were punched out after drying, and the coated surfaces were overlapped and pressed with 7t. After pressing, the release film was peeled off to obtain the solid electrolyte layer.

[0035] 5. Creation of evaluation cells 5.1 Examples The positive electrode described above was punched out to a diameter of φ11.28 mm, and the LiPON-coated Mg vapor-deposited current collector described above was punched out to a diameter of φ14.5 mm. The φ14.5 mm solid electrolyte layer described above was placed between the positive electrode and the LiPON-coated Mg vapor-deposited current collector (negative electrode), and Al was used for the positive electrode tab and Ni for the negative electrode tab, and the cells were vacuum-sealed within a laminate film. The sealed cells were isotropically pressed at 392 MPa using CIP (cold isotropic pressing) to produce laminate cells. To ensure that the confinement pressure remained constant regardless of the volume change of the cell, the fabricated cells were confined at 1 MPa using a constant-pressure jig with a spring inserted, and an evaluation cell with the configuration of Al foil / NCA positive electrode composite layer / solid electrolyte layer / LiPON protective layer / Mg layer / SUS foil was obtained.

[0036] In addition to the evaluation cell described above, a cell for evaluating the reactivity between the negative electrode and the solid electrolyte layer was prepared as follows: 100 mg of sulfide solid electrolyte was placed in a standard-sized cell, pressed at 1 ton, and then a LiPON-coated Mg vapor-deposited current collector punched out to a diameter of φ11.28 mm was attached to the sulfide solid electrolyte layer. The cell was then pressed at 6 ton to obtain a laminate, which was then restrained at 2 N·m.

[0037] 5.2 Comparative Examples The method is the same as in the example, except that a magnesium vapor-deposited current collector (without LiPON) was used instead of a LiPON-coated magnesium vapor-deposited current collector.

[0038] 6. Electrochemical Measurement With a cutoff voltage in the range of 4.2V-3.0V, it provides a constant current (current density: 0.15mA / cm²).2 (equivalent to 0.05C) - Constant voltage (cutoff current density: 0.03mA / cm²) 2 The initial charge and discharge of the constrained cells were performed at 60°C (equivalent to 0.01C). After standing in an open circuit for 1 hour at the upper and lower cutoff voltages, the cell impedance after the initial charge and after the charge and discharge at 60°C was measured using the AC impedance method, with an amplitude of 10mV and a frequency range of 1MHz-10mHz.

[0039] To evaluate the reactivity between the negative electrode and the solid electrolyte layer, and to evaluate aging in the charged state, the above cell fabrication and constant current (current density: 0.15 mA / cm²) were performed. 2 (equivalent to 0.05C) - Constant voltage (cutoff current density: 0.03mA / cm²) 2 After charging up to an upper cutoff voltage of 4.2V (equivalent to 0.01C), the cells were held in an open circuit at 60°C, and the cell impedance at 60°C was measured using the AC impedance method with an amplitude of 10mV and a frequency range of 1MHz-10mHz.

[0040] 7. Evaluation using SEM-EDX The surface of the LiPON film on a LiPON-coated Mg vapor-deposited current collector, as well as the cross-section after the initial charge, were observed using secondary electron imaging via SEM and EDX mapping at an applied voltage of 5kV.

[0041] 8. Evaluation Results 8.1 SEM observation and EDX mapping Figure 3 shows the SEM secondary electron image and EDX mapping of the LiPON film surface of the LiPON-coated Mg vapor-deposited current collector. As is clear from the EDX mapping, a uniform distribution of P, O, and N was observed on the surface. This suggests that the LiPON film is uniformly coated on the surface of the Mg vapor-deposited film.

[0042] 7.2 Charge-discharge curve Figure 4 shows the current density at 60°C and 0.15 mA / cm². 2The initial charge-discharge curves of the evaluation cell at (~C / 20) are shown. The charge capacity and discharge capacity, based on the positive electrode active material, were 214 mAh / g and 201 mAh / g for the example, and 205 mAh / g and 188 mAh / g for the comparative example. While there were no specific differences in the behavior of the charge-discharge curves with or without the LiPON coating, an increase in discharge capacity was observed, particularly in the example with the LiPON coating. This indicates that the LiPON coating improves the reversibility of the charge-discharge cycle.

[0043] 7.3 Resistor Table 1, Figure 5, and Figure 6 below show the cell impedance and cell 1s resistance after the initial charge and after the initial charge-discharge. As shown in Table 1 and Figure 5, the cell impedance after the initial charge showed almost the same behavior regardless of the presence or absence of the LiPON coating, and there was almost no change in the cell 1s resistance. From this, it was found that the presence of the LiPON coating does not adversely affect Li deposition during charging. On the other hand, as shown in Table 1 and Figure 6, the semicircle due to interfacial resistance was significantly reduced in the example compared to the comparative example, and the cell 1s resistance decreased by 34%.

[0044] [Table 1]

[0045] As described above, coating the negative electrode current collector with LiPON simultaneously increased the reversible capacity during the initial discharge and decreased the cell resistance. It is presumed that the LiPON coating suppressed the reductive decomposition of the sulfide solid electrolyte by deposited Li during charging and discharging, and maintained the interface between the solid electrolyte layer and the deposited Li or negative electrode current collector. Furthermore, it is thought that the LiPON and the products at the LiPON / deposited Li interface possess lithium conductivity, thereby maintaining the lithium conduction path even after charging and discharging.

[0046] The stability of the LiPON coating at 60°C was confirmed. As shown in Table 2 below, in cells composed only of a solid electrolyte layer and a negative electrode, the cell 1s resistance was measured after a 5-day storage test at 60°C. No significant difference was observed between the comparative example and the example. This indicates that the LiPON coating does not cause an increase in resistance through spontaneous chemical reactions with either Mg or the sulfide solid electrolyte. Figure 7 shows the change in cell 1s resistance over time when a storage test was performed at 60°C in an open circuit after charging to an upper cutoff potential of 4.2V. As shown in Table 2 and Figure 7, the cell 1s resistance of the example in the 60°C charged state was approximately 53% of that of the comparative example. Furthermore, when comparing the increase in cell 1s resistance over time after the start of the storage test, both were proportional to the square root of time, and the slope was smaller for the example than for the comparative example. In other words, it can be seen that the LiPON coating suppresses both the absolute value and the rate of increase of the cell 1s resistance. Furthermore, Figure 8 shows a cross-sectional SEM secondary electron image and EDX mapping of the interface between the LiPON-coated Mg vapor-deposited current collector and the solid electrolyte layer after charging at 60°C. As shown in Figure 8, a layer of a different morphology exists between the current collector and the solid electrolyte layer, and P, O, and N are observed to be concentrated in this layer. In other words, it is inferred that LiPON is present at the interface between the current collector and the solid electrolyte layer even in the charged state. As described above, considering that the presence of the LiPON coating in the charged state does not contribute to the increase in resistance due to spontaneous chemical reactions, it is thought that the increase in interfacial resistance and cell resistance caused by the reductive decomposition of the sulfide solid electrolyte by deposited Li at the current collector-solid electrolyte layer interface during charging is suppressed by the LiPON coating, which functions as a protective layer.

[0047] [Table 2] [Explanation of symbols]

[0048] 10: Positive electrode 11: Positive electrode current collector 12: Positive electrode active material layer 20: Solid electrolyte layer 30: Protective layer 41: Negative electrode current collector 42: Lithium metal 50: Covering 60: Laminate 100: Secondary battery

Claims

1. A secondary battery comprising a positive electrode, a solid electrolyte layer, a protective layer, a negative electrode current collector, and metallic lithium deposited between the solid electrolyte layer and the negative electrode current collector upon charging, The solid electrolyte layer comprises a sulfide solid electrolyte, The protective layer is located between the solid electrolyte layer and the negative electrode current collector. The protective layer comprises Li, P, O, and N as constituent elements. The negative electrode current collector comprises a metal foil and an Mg-containing layer provided on the surface of the metal foil. The Mg-containing layer is located between the protective layer and the metal foil. Secondary battery.

2. A method for manufacturing a secondary battery, To obtain a coated object, one or both surfaces of the negative electrode current collector and the solid electrolyte layer are covered with a protective layer. Using the aforementioned coating, obtain a laminate having a positive electrode, a solid electrolyte layer, a protective layer, and a negative electrode current collector in that order, and This includes charging the laminate to deposit metallic lithium between the solid electrolyte layer and the negative electrode current collector, The solid electrolyte layer comprises a sulfide solid electrolyte, The protective layer comprises Li, P, O, and N. The negative electrode current collector comprises a metal foil and an Mg-containing layer provided on the surface of the metal foil. The Mg-containing layer is located between the protective layer and the metal foil. Manufacturing method.

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