All-solid-state secondary battery and charging method for all-solid-state secondary battery

Abstract

Provided is an all-solid-state secondary battery that can suppress deterioration of battery performance due to charging and discharging even without application of external pressure or under low confining pressure. An all-solid-state secondary battery including a positive electrode layer, a negative electrode layer, and a solid electrolyte layer provided between the positive electrode layer and the negative electrode layer, the negative electrode layer contains amorphous carbon and one or more materials selected from the group consisting of gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, and zinc, the solid electrolyte layer includes a first solid electrolyte, a second solid electrolyte, and a binder; the first solid electrolyte is a lithium-containing sulfide-containing solid electrolyte, the second solid electrolyte is a molecular crystal, The all-solid-state secondary battery comprises one or more Li salts selected from the group consisting of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and one or more ligands selected from the group consisting of tetramethylethylenediamine (TMEDA), tetraethylethylenediamine (TEEDA), and tetramethylpropylenediamine (TMPDA).

Description

[Technical Field]

[0001] The present invention relates to an all-solid-state secondary battery and a method for charging an all-solid-state secondary battery. [Background technology]

[0002] For example, as shown in Patent Document 1, when charging and discharging a precipitation-type all-solid-state secondary battery in which lithium metal is precipitated in the negative electrode layer, conventionally, the all-solid-state lithium-ion secondary battery is sandwiched between end plates or the like in the thickness direction and charged and discharged while a high external pressure is applied, so that the lithium metal in the negative electrode layer is uniformly precipitated along the shape of the negative electrode layer and the effect of volumetric changes in the active material during charging and discharging is suppressed.

[0003] The presence of a pressure jig for applying a high external pressure to an all-solid-state secondary battery is not only disadvantageous in terms of cost, but also causes a decrease in the energy density of the entire battery module including the all-solid-state secondary battery and the pressure jig.

[0004] Therefore, it is required to minimize the external pressure applied to the all-solid-state secondary battery. For example, Patent Document 1 discusses the use of a solid electrolyte containing a specific organic electrolyte in addition to a lithium salt and a lithium-containing sulfide solid electrolyte as an all-solid-state secondary battery. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-198270 Summary of the Invention [Problem to be solved by the invention]

[0006] However, a technology for sufficiently reducing the external pressure applied to all-solid-state secondary batteries has not yet been established, and further improvements are required.

[0007] The present invention has been made in view of the above-mentioned problems, and aims to provide an all-solid-state secondary battery that can suppress deterioration of battery performance even when charged and discharged without applying external pressure or under a low confining pressure that can be achieved with a simple external pressure application mechanism. The low confining pressure means, for example, a confining pressure of 1.0 MPa or less, more preferably 0.5 MPa or less. [Means for solving the problem]

[0008] That is, the all-solid-state secondary battery and the charging method thereof according to the present invention are as follows. [1] An all-solid-state secondary battery comprising a positive electrode layer, a negative electrode layer, and a solid electrolyte layer provided between the positive electrode layer and the negative electrode layer, the negative electrode layer contains amorphous carbon and one or more materials selected from the group consisting of gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, and zinc, the solid electrolyte layer includes a first solid electrolyte, a second solid electrolyte, and a binder; the first solid electrolyte is a lithium-containing sulfide-containing solid electrolyte, the second solid electrolyte is a molecular crystal, The all-solid-state secondary battery comprises one or more lithium salts selected from the group consisting of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and one or more ligands selected from the group consisting of tetramethylethylenediamine (TMEDA), tetraethylethylenediamine (TEEDA), and tetramethylpropylenediamine (TMPDA). [2] The all-solid-state secondary battery according to [1], wherein the mass ratio of the first solid electrolyte to the second solid electrolyte in the solid electrolyte layer (first solid electrolyte:second solid electrolyte) is within a range of 98:2 to 80:20, both ends of which are inclusive. [3] The all-solid-state secondary battery according to [1] or [2], wherein the negative electrode layer contains silver and amorphous carbon. [4] The all-solid-state secondary battery according to any one of [1] to [3], wherein the ratio of the initial charge capacity of the positive electrode layer to the initial charge capacity of the negative electrode layer satisfies the following formula (1): 0.01 a: Initial charge capacity of the positive electrode layer (mAh) b: Initial charge capacity of the negative electrode layer (mAh) [5] A method for charging an all-solid-state secondary battery, comprising charging the all-solid-state secondary battery according to any one of [1] to [4] above the charge capacity of the negative electrode layer. [6] The method for charging an all-solid-state secondary battery according to [5], wherein charging is performed within a range of 2 to 100 times the charge capacity of the negative electrode layer. [Effects of the Invention]

[0009] According to the present invention, the solid electrolyte layer includes a first solid electrolyte and a second solid electrolyte, and the second solid electrolyte contains a specific type of molecular crystal. Therefore, even when no external pressure or a low external pressure is applied, deterioration of battery performance can be sufficiently suppressed. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a graph comparing battery characteristics of an example according to the present invention and a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0011] Preferred embodiments of the present invention will be described in detail below.

[0012] <1. Basic configuration of the all-solid-state secondary battery according to this embodiment> The all-solid-state secondary battery according to this embodiment is an all-solid-state secondary battery including a positive electrode layer, a negative electrode layer, and a solid electrolyte layer.

[0013] (1-1. Positive electrode layer) ​The positive electrode layer includes a positive electrode current collector and a positive electrode composite layer. Examples of the positive electrode current collector include a plate or foil made of indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof. The positive electrode current collector may be omitted.

[0014] The positive electrode mixture layer includes a positive electrode active material and a solid electrolyte. The solid electrolyte included in the positive electrode is a sulfide solid electrolyte of the same type or a different type from that described in the section on the solid electrolyte layer.

[0015] The positive electrode active material may be any positive electrode active material that can reversibly store and release lithium ions.

[0016] For example, the positive electrode active material can be formed using lithium salts such as lithium cobalt oxide (hereinafter referred to as LCO), lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel aluminum oxide (hereinafter referred to as NCA), lithium nickel cobalt manganese oxide (hereinafter referred to as NCM), lithium manganate, lithium iron phosphate, nickel sulfide, copper sulfide, lithium sulfide, sulfur, iron oxide, vanadium oxide, etc. These positive electrode active materials may be used alone or in combination of two or more.

[0017] Further, the positive electrode active material is preferably formed by including a lithium salt of a transition metal oxide having a layered rock salt structure among the above-described lithium salts. Here, the "layered rock salt structure" is a structure in which oxygen atom layers and metal atom layers are alternately and regularly arranged in the <111> direction of the cubic rock salt structure, and as a result, each atom layer forms a two-dimensional plane. The "cubic rock salt structure" represents a sodium chloride type structure which is one type of crystal structure. Specifically, it represents a structure in which the face-centered cubic lattices formed by each of the cations and anions are arranged so as to be shifted from each other by 1 / 2 of the edge of the unit lattice.

[0018] Examples of the lithium salt of the transition metal oxide having such a layered rock salt structure include, for example, LiNi x Co y Al z O2 (NCA), or LiNi x Co y Mn z O2 (NCM) (however, 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1), and lithium salts of ternary transition metal oxides such as these can be mentioned.

[0019] When the positive electrode active material includes a lithium salt of the ternary transition metal oxide having the above-described layered rock salt structure, the energy density and thermal stability of the all-solid-state secondary battery can be improved.

[0020] The positive electrode active material may be covered with a coating layer. Here, the coating layer of the present embodiment may be any coating layer known as a coating layer for the positive electrode active material of the all-solid-state secondary battery. Examples of the coating layer include, for example, Li2O-ZrO2 and the like.

[0021] Further, when the positive electrode active material is formed of a lithium salt of a ternary transition metal oxide such as NCA or NCM and includes nickel (Ni) as the positive electrode active material, the capacity density of the all-solid-state secondary battery can be increased and the metal elution from the positive electrode active material in the charged state can be reduced. Thereby, the all-solid-state secondary battery according to the present embodiment can improve the long-term reliability and cycle characteristics in the charged state.

[0022] Here, examples of the shape of the positive electrode active material include particle shapes such as spherical and oval spheres. The particle size of the positive electrode active material is not particularly limited, and may be within a range applicable to positive electrode active materials in conventional all-solid-state secondary batteries. The content of the positive electrode active material in the positive electrode is also not particularly limited, and may be within a range applicable to positive electrodes in conventional all-solid-state secondary batteries.

[0023] In addition to the above-mentioned positive electrode active material and solid electrolyte, the positive electrode may contain additives such as a conductive aid, a binder, a filler, a dispersant, an ion conductive aid, etc., as appropriate.

[0024] Examples of conductive additives that can be incorporated into the positive electrode include graphite, carbon black, acetylene black, ketjen black, carbon fiber, and metal powder. Examples of binders that can be incorporated into the positive electrode include styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, and polyethylene. Furthermore, fillers, dispersants, ion conductive additives, and the like that can be incorporated into the positive electrode include known materials that are generally used in electrodes of all-solid-state secondary batteries.

[0025] (1-2. Negative electrode layer) The negative electrode layer includes a negative electrode current collector and a negative electrode composite layer laminated on the negative electrode current collector. The negative electrode current collector is preferably made of a material that does not react with lithium, i.e., does not form any alloy or compound with lithium. Examples of materials that can be used for the negative electrode current collector include copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), and nickel (Ni).

[0026] The negative electrode mixture layer contains a negative electrode active material, amorphous carbon, and a binder. Examples of the negative electrode active material include alloy-forming elements that form alloys or compounds with lithium through an electrochemical reaction during charging. The alloying element may be at least one selected from the group consisting of gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, and zinc.

[0027] When one or more of gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, and zinc are used as the alloying element, the negative electrode active material is, for example, granular, and the particle size is preferably 4 μm or less, more preferably 300 nm or less. In this case, the characteristics of the all-solid-state secondary battery are further improved. Here, the particle size of the negative electrode active material is measured, for example, using a laser particle size distribution system, as the median diameter (so-called D 50 ) can be used.

[0028] Examples of the amorphous carbon include carbon black, graphene, etc. Examples of carbon black include acetylene black, furnace black, ketjen black, etc.

[0029] In addition to the above, the negative electrode mixture layer may also contain additives used in conventional all-solid-state secondary batteries, such as fillers, dispersants, ion conductive agents, solid electrolytes, etc., as appropriate.

[0030] (1-3.Solid electrolyte layer) The solid electrolyte layer is a layer provided between the positive electrode layer and the negative electrode layer, and contains a solid electrolyte. The configuration of the solid electrolyte layer is a characteristic feature of the all-solid-state secondary battery according to this embodiment, and will be described in detail later.

[0031] (1-4. Relationship between charge capacity of positive electrode layer and negative electrode layer) The all-solid-state secondary battery according to this embodiment is preferably configured so that the ratio of the charge capacity of the positive electrode mixture layer to the charge capacity of the negative electrode mixture layer, i.e., the capacity ratio, satisfies the requirement of the following mathematical formula (1). 0.01 a: Charging capacity of the positive electrode composite layer (mAh) b: Charging capacity of the negative electrode composite layer (mAh)

[0032] Here, the charge capacity of the positive electrode mixture layer is obtained by multiplying the charge capacity density (mAh / g) of the positive electrode active material by the mass of the positive electrode active material in the positive electrode mixture layer. When multiple types of positive electrode active materials are used, the value of charge capacity density x mass is calculated for each positive electrode active material, and the sum of these values ​​is the charge capacity of the positive electrode mixture layer. The charge capacity of the negative electrode mixture layer is calculated in a similar manner. That is, the charge capacity of the negative electrode mixture layer is obtained by multiplying the charge capacity density (mAh / g) of the negative electrode active material by the mass of the negative electrode active material in the negative electrode mixture layer. When multiple types of negative electrode active materials are used, the value of charge capacity density x mass is calculated for each negative electrode active material, and the sum of these values ​​is the capacity of the negative electrode mixture layer. Here, the charge capacity densities of the positive electrode active material layer and the negative electrode active material are capacities estimated using an all-solid-state half cell using lithium metal as the counter electrode. In practice, the charge capacities of the positive electrode mixture layer and the negative electrode mixture layer are directly measured by measurement using an all-solid-state half cell.

[0033] ​Specific methods for directly measuring the charge capacity include the following. First, the charge capacity of the positive electrode composite layer is measured by preparing a test cell using the positive electrode composite layer as the working electrode and Li as the counter electrode, and performing CC-CV charging from the open circuit voltage (OCV) to the upper charge voltage limit. The upper charge voltage limit is specified in JIS C 8712:2015, and refers to 4.25 V for lithium cobalt oxide-based positive electrode composite layers, and the voltage determined by applying the provisions of A.3.2.3 (Safety requirements when applying different upper charge voltages) of JIS C 8712:2015 for other positive electrode composite layers. The charge capacity of the negative electrode composite layer is measured by preparing a test cell using the negative electrode composite layer as the working electrode and Li as the counter electrode, and performing CC-CV charging from the open circuit voltage (OCV) to 0.01 V.

[0034] The test cell described above can be prepared, for example, as follows: The positive electrode composite layer or negative electrode composite layer for which the charge capacity is to be measured is punched into a disk shape with a diameter of 13 mm. 200 mg of the same solid electrolyte powder used in all-solid-state secondary batteries is compacted at 40 MPa to form a pellet with a diameter of 13 mm and a thickness of approximately 1 mm. This pellet is placed inside a cylinder with an inner diameter of 13 mm, and the punched disk-shaped positive electrode composite layer or negative electrode composite layer is placed on one side, and a lithium foil with a diameter of 13 mm and a thickness of 0.03 mm is placed on the other side. A stainless steel disk is then placed on each side, and the entire contents are compressed axially at 300 MPa for one minute to integrate the contents. The integrated contents are then removed from the cylinder and sealed in a case under a constant pressure of 22 MPa to form a test cell. The charge capacity of the positive electrode composite layer can be measured by, for example, CC charging the test cell prepared as described above at a current density of 0.1 mA, followed by CV charging to 0.02 mA.

[0035] The charge capacity density is calculated by dividing this charge capacity by the mass of each active material. The initial charge capacities of the positive electrode composite layer and the negative electrode composite layer may be the initial charge capacities measured during the first charge cycle. This value was used in the examples described below.

[0036] In this way, it is preferable to make the charge capacity of the positive electrode mixture layer excessively large relative to the charge capacity of the negative electrode mixture layer. As will be described later, in this embodiment, the all-solid-state secondary battery is charged beyond the charge capacity of the negative electrode mixture layer. That is, the negative electrode mixture layer is overcharged. At the beginning of charging, lithium is absorbed into the negative electrode mixture layer. That is, the negative electrode active material forms an alloy with lithium ions that have migrated from the positive electrode layer. When further charging is performed beyond the capacity of the negative electrode mixture layer, lithium is precipitated on the back side of the negative electrode mixture layer, i.e., between the negative electrode current collector and the negative electrode mixture layer, and a lithium precipitate layer is formed by this lithium. The lithium precipitate layer is mainly composed of lithium (mainly metallic lithium), although it also contains trace amounts of elements other than lithium. This phenomenon occurs when the negative electrode active material contains a specific substance, i.e., an alloying element that forms an alloy or compound with lithium. During discharge, lithium in the negative electrode mixture layer and the lithium deposit layer ionizes and migrates to the positive electrode layer. Therefore, in the all-solid-state secondary battery according to this embodiment, the precipitated lithium can be used as the negative electrode active material. Furthermore, since the negative electrode composite layer covers the lithium precipitate layer, it functions as a protective layer for the lithium precipitate layer and can suppress the precipitation and growth of dendrites. This suppresses short circuits and capacity reduction in the all-solid-state secondary battery, and ultimately improves the characteristics of the all-solid-state secondary battery.

[0037] Here, the capacity ratio is preferably greater than 0.01. By setting the capacity ratio to 0.01 or greater, it is possible to suppress deterioration in the characteristics of the all-solid-state secondary battery. The reason for this is that the anode composite layer sufficiently functions as a protective layer that suppresses collapse of the anode composite layer due to repeated charge and discharge and suppresses the precipitation and growth of dendrites. Furthermore, the capacity ratio is preferably less than 0.5. By setting the capacity ratio to less than 0.5, it is possible to ensure the amount of lithium precipitation in the anode layer and suppress a decrease in battery capacity. For the same reason, it is considered more preferable that the capacity ratio be less than 0.25. Furthermore, by setting the capacity ratio to less than 0.25, it is possible to further improve the output characteristics of the battery.

[0038] The thickness of the negative electrode composite layer is preferably 1 μm or more and 20 μm or less, which is a range that satisfies the requirement of the above mathematical formula (1), and more preferably 1 μm or more and 10 μm or less. By making the thickness of the negative electrode composite layer 1 μm or more, the characteristics of the all-solid-state secondary battery can be sufficiently improved. By making the thickness of the negative electrode composite layer 20 μm or less, the resistance value of the negative electrode composite layer can be kept as low as possible, and as a result, the characteristics of the all-solid-state secondary battery can be further improved. The thickness of the negative electrode mixture layer can be estimated, for example, by assembling an all-solid-state secondary battery, pressure-molding the battery, and then observing the average thickness of the cross section with a scanning electron microscope (SEM).

[0039] 2. Characteristic Configuration of the All-Solid-State Secondary Battery According to the Present Embodiment The solid electrolyte layer in this embodiment contains, for example, a first solid electrolyte, a second solid electrolyte, and a binder (a binder for the solid electrolyte layer).

[0040] The first solid electrolyte is a lithium-containing sulfide solid electrolyte that contains lithium. Examples of lithium-containing sulfide solid electrolytes include Li2S-P2S5, Li2S-P2S5-LiX (X is a halogen element, for example, I, Br, or Cl), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, and Li2S-Si These solid electrolytes contain one or more solid electrolyte materials selected from the group consisting of S2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-ZmSn (m and n are positive numbers, Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, and Li2S-SiS2-LipMOq (p and q are positive numbers, M is P, Si, Ge, B, Al, Ga, or In). Such solid electrolytes are prepared by processing starting materials (e.g., Li2S, P2S5, etc.) using methods such as melt quenching and mechanical milling. These processes may be followed by further heat treatment. The solid electrolyte may be amorphous, crystalline, or a mixture of both.

[0041] The second solid electrolyte is a molecular crystal containing a lithium salt and a ligand. The lithium salt is at least one selected from the group consisting of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The ligand is at least one selected from the group consisting of tetramethylethylenediamine (TMEDA), tetraethylethylenediamine (TEEDA), and tetramethylpropylenediamine (TMPDA).

[0042] The content of the first solid electrolyte relative to the entire solid electrolyte layer (i.e., when the mass of the entire solid electrolyte layer is 100% by mass) is preferably more than 80% by mass and not more than 98% by mass, more preferably 85% by mass or more and 98% by mass or less, and even more preferably 90% by mass or more and 98% by mass or less.

[0043] The content of the second solid electrolyte relative to the entire solid electrolyte layer (i.e., when the mass of the entire solid electrolyte layer is 100% by mass) is preferably more than 1% by mass and not more than 19% by mass, more preferably 1% by mass or more and 10% by mass or less, and even more preferably 2% by mass or more and 5% by mass or less.

[0044] The mass ratio of the first solid electrolyte to the second solid electrolyte contained in the solid electrolyte layer is preferably first solid electrolyte:second solid electrolyte=98:2 to 80:20 (inclusive of both end values).

[0045] The binder for the solid electrolyte layer is, for example, one or more selected from the group consisting of styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, etc. The binder in the solid electrolyte layer may be the same as or different from the binder contained in the positive electrode mixture layer and the negative electrode mixture layer.

[0046] The content of the binder for the solid electrolyte relative to the entire solid electrolyte layer (i.e., when the mass of the entire solid electrolyte layer is 100% by mass) is preferably 0.1% by mass or more and 5% by mass or less, and more preferably 0.5% by mass or more and 3% by mass or less.

[0047] 3. Method for manufacturing the all-solid-state secondary battery according to this embodiment Next, a method for manufacturing the all-solid-state secondary battery according to this embodiment will be described. The all-solid-state secondary battery according to this embodiment can be manufactured by first manufacturing a positive electrode, a negative electrode, and a solid electrolyte layer, and then laminating the above-mentioned layers.

[0048] (3-1. Positive electrode layer manufacturing process) First, a mixture of materials (positive electrode active material, solid electrolyte, binder, etc.) that constitute the positive electrode composite layer is processed into a sheet. The positive electrode composite sheet thus obtained is cut into an appropriate shape and stacked on a positive electrode current collector as a positive electrode composite layer material, and the resulting stack is pressurized (for example, pressurized using hydrostatic pressure) to produce a positive electrode layer comprising a positive electrode current collector and a positive electrode composite layer.

[0049] (3-2. Negative electrode layer manufacturing process) First, a slurry is prepared by adding materials for the negative electrode composite layer (negative electrode active material, non-alloying element, binder, etc.) to a polar or non-polar solvent. The obtained slurry is then applied to a negative electrode current collector and dried. The obtained laminate is then pressed (for example, by applying hydrostatic pressure) to prepare the negative electrode layer. The pressing step may be omitted. Alternatively, the negative electrode layer may be prepared by separately forming a negative electrode composite layer, then stacking it on the negative electrode current collector and applying pressure.

[0050] (3-3. Solid electrolyte sheet manufacturing process) The solid electrolyte layer can be produced, for example, by mixing the first solid electrolyte, the second solid electrolyte, and a binder, adding a solvent and a binder if necessary, mixing the mixture, and then coating, drying, and pressing to form a solid electrolyte sheet.

[0051] (3-4. Assembly process of all-solid-state secondary batteries) The positive electrode layer and the negative electrode layer prepared by the above method are stacked so as to sandwich the solid electrolyte sheet, and then pressurized (for example, by applying pressure using hydrostatic pressure), thereby making it possible to prepare an all-solid-state secondary battery in which the solid electrolyte layer is disposed between the positive electrode layer and the negative electrode layer.

[0052] 4. Charging Method of the All-Solid-State Secondary Battery According to the Present Embodiment Next, a method for charging an all-solid-state secondary battery will be described. In this embodiment, as described above, the all-solid-state secondary battery is charged beyond the charge capacity of the negative electrode mixture layer. That is, the negative electrode mixture layer is overcharged. At the beginning of charging, lithium is absorbed in the negative electrode mixture layer. When charging is performed beyond the charge capacity of the negative electrode mixture layer, lithium is precipitated on the back side of the negative electrode mixture layer, i.e., between the negative electrode current collector and the negative electrode mixture layer, and this lithium forms a lithium precipitate layer that was not present at the time of manufacturing. During discharge, the lithium in the negative electrode mixture layer and the lithium precipitate layer is ionized and moves to the positive electrode layer side. The charge amount is preferably set to a value between 2 and 100 times the charge capacity of the negative electrode mixture layer, and more preferably in the range of 4 to 100 times. The thickness of the lithium deposition layer deposited in the negative electrode during charging is preferably 10 μm or more, more preferably 30 μm or more, and is preferably in the range of 60 μm or less, which is the upper limit value achievable for an all-solid-state secondary battery. The thickness of this lithium deposition layer can be estimated by observing the average thickness of a cross section of the all-solid-state secondary battery after charging with a scanning electron microscope (SEM).

[0053] <5. Effects of this embodiment> According to the solid electrolyte layer and solid secondary battery of this embodiment, even if the volume change of the battery is large, such as when the battery is overcharged beyond the negative electrode capacity and lithium is precipitated, as described above, it is possible to sufficiently suppress the deterioration of battery performance, and therefore the battery can be charged and discharged without any problem by applying no external pressure or by applying a sufficiently low external pressure.

[0054] <6. Other embodiments of the present invention> Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to these examples, and various modifications and combinations are possible within the scope of the technical idea of ​​the present invention. [Example]

[0055] The all-solid-state secondary battery according to the present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0056] Example 1 (Preparation of solid electrolyte layer) A mixture containing 97.5 parts by mass of Li6PS5Cl (first solid electrolyte), 1 part by mass of binder, and 2.5 parts by mass of Li(TFSA)(TMEDA) (second solid electrolyte) was stirred with xylene and isobutyl isobutyrate to produce a slurry. This slurry was applied to a PET film support using a blade coater, dried in air at 40°C, and then vacuum dried at 40°C for 12 hours. The sheet was then isostatically pressed at 490 MPa to obtain a solid electrolyte sheet with a solid electrolyte layer formed on the PET film.

[0057] (Fabrication of all-solid-state secondary batteries) 12 g of porous carbon black (amorphous carbon) and 4 g of silver particles (negative electrode active material) were placed in a container. An NMP solution containing 8% by mass of binder was added so that the binder mass was 7% of the total mass of the carbon black, silver particles, and binder. NMP was gradually added and stirred. The negative electrode composite layer slurry thus prepared was applied to a 10-micron-thick stainless steel foil using a blade coater and dried in air at 80°C for approximately 20 minutes. The resulting material was then vacuum-dried at 100°C for approximately 12 hours to form the negative electrode layer. Next, LiNi 0.8 Co 0.15 Mn 0.05 Using O2 (NCM), Li6PS5Cl (first solid electrolyte), conductive carbon nanotubes (CNT), and PTFE as a binder were mixed in a ratio of 85:14.45:0.25:0.3 (by mass) of positive electrode active material: first solid electrolyte: CNT: PTFE. The mixture was stretched into a sheet and formed into an approximately 2 cm square to form the positive electrode composite layer. This positive electrode composite layer was then layered on aluminum foil as a positive electrode current collector and subjected to isostatic pressure to form the positive electrode layer. The surface of the NCM was coated with Li2-ZrO2.

[0058] The resulting anode layer and solid electrolyte sheet are then stacked so that the solid electrolyte layer and anode composite layer are in contact, and the solid electrolyte layer is transferred onto the anode layer by isostatically pressing at 50 MPa and peeling off the PET film. The cathode is then placed on top of the integrated sheet of anode and solid electrolyte layer, and sealed in a laminate film in a vacuum to produce an all-solid-state secondary battery. Portions of the cathode current collector and anode current collector are exposed to the laminate film to avoid breaking the vacuum in the battery, and these exposed portions serve as the terminals for the cathode and anode layers, respectively. This all-solid-state secondary battery is subjected to isostatic pressure treatment at 490 MPa, which significantly improves the battery's properties. The charge-discharge characteristics of the all-solid-state lithium battery fabricated in this way at a confining pressure of 0.3 MPa were evaluated under the following conditions. The all-solid-state secondary battery was placed in a thermostatic chamber at 25°C and the charge-discharge current was 1.5 mA / cm until the battery voltage reached 4.25 V. 2 The battery was charged at a constant current of 0.5mA / cm 2 The battery was charged at a constant voltage of 4.25 V until the discharge rate reached 1.5 mA / cm. 2 The battery was discharged at a constant current of 100 V until the battery voltage reached 2.5 V. After repeating this charge and discharge cycle 100 times, the capacity retention rate was 94.4% and the average coulomb efficiency was 99.9%. The results are shown in Figure 1.

[0059] <Comparative Example 1> An all-solid-state secondary battery was fabricated using a solid electrolyte sheet containing 99 parts by mass of Li6PS5Cl as the first solid electrolyte and 1 part by mass of binder, but not containing the second solid electrolyte (molecular crystal), and a charge-discharge test was carried out in the same manner as in Example 1. After 100 charge-discharge cycles, the capacity retention rate was 9.5% and the average coulombic efficiency was 96.8%. The results are shown in Figure 1.

[0060] From the above experimental results, it was found that in a precipitation-type all-solid-state secondary battery in which metallic lithium is precipitated on the negative electrode layer during charging, Example 1, in which the solid electrolyte layer contains the above-mentioned first solid electrolyte and second solid electrolyte, exhibits improved cycle characteristics and average coulombic efficiency under a sufficiently low confining pressure of 0.3 MPa compared to the conventional example (Comparative Example 1), in which the solid electrolyte layer does not contain the second solid electrolyte. In particular, a significant improvement was observed in the cycle characteristics. The reason for the significant improvement in battery performance under low confining pressure in Example 1 is that the molecular crystals, which have better formability than sulfide solid electrolytes, are crushed by isostatic pressing, filling the voids in the solid electrolyte sheet, allowing lithium metal to deposit uniformly in the anode layer along the shape of the anode layer. Another possible reason is the elimination of reaction distribution due to improved adhesion at the interface between the solid electrolyte layer and the cathode composite layer or the interface between the solid electrolyte layer and the anode composite layer.

Claims

1. An all-solid-state secondary battery including a positive electrode layer, a negative electrode layer, and a solid electrolyte layer provided between the positive electrode layer and the negative electrode layer, the negative electrode layer contains amorphous carbon and one or more materials selected from the group consisting of gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, and zinc, the solid electrolyte layer includes a first solid electrolyte, a second solid electrolyte, and a binder; the first solid electrolyte is a lithium-containing sulfide-containing solid electrolyte, the second solid electrolyte is a molecular crystal; The molecular crystal is one or more lithium salts selected from the group consisting of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI); An all-solid-state secondary battery comprising one or more ligands selected from the group consisting of tetramethylethylenediamine (TMEDA), tetraethylethylenediamine (TEEDA), and tetramethylpropylenediamine (TMPDA).

2. 2. The all-solid-state secondary battery according to claim 1, wherein a mass ratio of the first solid electrolyte to the second solid electrolyte in the solid electrolyte layer (first solid electrolyte:second solid electrolyte) is within a range of 98:2 to 80:20, both inclusive.

3. 2. The all-solid-state secondary battery according to claim 1, wherein the negative electrode layer contains silver and amorphous carbon.

4. 2. The all-solid-state secondary battery according to claim 1, wherein a ratio of an initial charge capacity of the positive electrode layer to an initial charge capacity of the negative electrode layer satisfies the following formula (1): 0.01<b / a<0.5 (1) a: initial charge capacity of the positive electrode layer (mAh) b: Initial charge capacity of the negative electrode layer (mAh)

5. A method for charging an all-solid-state secondary battery according to claim 1 , comprising charging the all-solid-state secondary battery beyond the charge capacity of the negative electrode layer.

6. The all-solid-state secondary battery charging method according to claim 5 , wherein charging is performed within a range of 2 to 100 times the charge capacity of the negative electrode layer.

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