All-solid-state secondary battery and charging method therefor

Abstract

Disclosed is an all-solid-state secondary battery comprising a positive electrode layer, a negative electrode layer, and a solid electrolyte layer between the positive electrode layer and the negative electrode layer. The negative electrode layer comprises amorphous carbon and any one material selected from the group consisting of gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, and zinc. The solid electrolyte layer comprises a first solid electrolyte, a second solid electrolyte, and a binder. The first solid electrolyte is a lithium-containing sulfide solid electrolyte, the second solid electrolyte is a molecular crystal, and the molecular crystal comprises: a lithium salt including at least one selected from the group consisting of lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI); and a ligand including at least one selected from the group consisting of tetramethylethylenediamine (TMEDA), tetraethylethylenediamine (TEEDA), and tetramethylpropylenediamine (TMPDA).

Description

All-solid-state secondary battery and charging method thereof

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

[0002] When charging and discharging a precipitation-type all-solid-state secondary battery, it is necessary to ensure uniform deposition of lithium metal regardless of the shape of the negative electrode layer and to suppress volume changes in the active material. Conventionally, all-solid-state lithium-ion secondary batteries were charged and discharged using a pressurizing jig while applying high external pressure in the thickness direction.

[0003] The use of a pressurizing jig that applies high external pressure to an all-solid-state secondary battery is not only disadvantageous in terms of price, but also reduces the energy density of the secondary battery module.

[0004] Accordingly, the external pressure applied to all-solid-state secondary batteries needs to be as low as possible. For example, in addition to lithium salt and lithium-containing sulfide solid electrolytes, the use of solid electrolytes containing organic electrolytes is being considered. However, technology for sufficiently reducing the external pressure applied to all-solid-state secondary batteries has not yet been established, and further improvements are needed.

[0005] The present invention is intended to solve the aforementioned problems, and aims to provide an all-solid-state secondary battery capable of suppressing performance degradation even when charging and discharging under low confining pressure without applying external pressure or using a simple external pressure applying mechanism. The low confining pressure is, for example, 1.0 MPa or less, more preferably 0.5 MPa or less.

[0006] According to one embodiment of the present invention, an all-solid-state secondary battery is provided, including a cathode layer, a cathode layer, and a solid electrolyte layer between the cathode layer and the cathode layer. The cathode layer includes amorphous carbon and one selected from the group consisting of gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, and zinc, and the solid electrolyte layer includes a first solid electrolyte, a second solid electrolyte, and a binder, wherein the first solid electrolyte is a lithium-containing sulfide solid electrolyte, the second solid electrolyte is a molecular crystal, and the molecular crystal may include a lithium salt having at least one selected from the group consisting of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and a ligand having at least one selected from the group consisting of tetramethylethylenediamine (TMEDA), tetraethylethylenediamine (TEEDA), and tetramethylpropylenediamine (TMPDA).

[0007] The mass ratio of the first solid electrolyte and the second solid electrolyte (first solid electrolyte: second solid electrolyte) may be from 98:2 to 80:20 (including the values ​​at both ends).

[0008] The above cathode layer may contain silver and amorphous carbon.

[0009] The capacity ratio of the initial charge capacity of the positive electrode layer and the initial charge capacity of the negative electrode layer can satisfy the following mathematical expression 1.

[0010] [Mathematical Formula 1]

[0011] 0.01

[0012] a: Initial charge capacity of the positive electrode layer (mAh)

[0013] b: Initial charge capacity of the cathode layer (mAh)

[0014] ​According to one embodiment of the present invention, a charging method for an all-solid-state secondary battery is provided. The method can charge the aforementioned all-solid-state secondary battery beyond the charging capacity of the negative electrode layer.

[0015] It can be charged within a range of 2 to 100 times the charging capacity of the above cathode layer.

[0016] According to the present invention, the solid electrolyte layer comprises a first solid electrolyte and a second solid electrolyte, wherein the second solid electrolyte contains a specific type of molecular crystal. Accordingly, performance degradation can be sufficiently suppressed even when no external pressure is applied or when a low external pressure is applied.

[0017] Figure 1 is a graph comparing battery characteristics of examples and comparative examples according to the present invention.

[0018] Hereinafter, the optimal embodiments of the present invention will be described in detail.

[0019] <1. Basic configuration of the all-solid-state secondary battery according to this embodiment>

[0020] The all-solid-state secondary battery according to the present embodiment may include a positive electrode layer, a negative electrode layer, and a solid electrolyte layer.

[0021] (1-1. Bipolar layer)

[0022] The positive electrode layer may include a positive electrode current collector and a positive electrode composite material layer.

[0023] The positive electrode current collector may be composed of, for example, indium, copper, magnesium, stainless steel, titanium, iron, cobalt, nickel, zinc, aluminum, germanium, lithium, or an alloy thereof. The positive electrode current collector may have a plate shape or a foil shape. The positive electrode current collector may be omitted.

[0024] The positive electrode composite material layer may include a positive electrode active material and a solid electrolyte. Meanwhile, the solid electrolyte of the positive electrode composite material layer may be the same as or different from that described in the section on solid electrolyte layer below.

[0025] The cathode active material can reversibly absorb and desorb lithium ions.

[0026] The cathode active material may be formed of a lithium salt including, for example, lithium cobalt oxide (hereinafter referred to as LCO), lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel cobalt aluminum oxide (hereinafter referred to as NCA), lithium nickel cobalt manganese oxide (hereinafter referred to as NCM), lithium manganate, and lithium iron phosphate. Furthermore, the cathode active material may be formed of nickel sulfide, copper sulfide, lithium sulfide, sulfur, iron oxide, or vanadium oxide. These cathode active materials may each be used alone, or may be formed by combining two or more types.

[0027] It is preferable that the cathode active material contains a lithium salt of a transition metal oxide having a layered rock salt structure. Here, the 'layered rock salt structure' means a cubic rock salt structure. <111> It is a structure in which oxygen and metal atomic layers are arranged alternately and regularly in a direction, and as a result, each atomic layer forms a two-dimensional plane. The 'cubic rock salt structure' refers to the sodium chloride structure, which is one of the crystal structures, and specifically, it refers to a structure in which the face-centered cubic lattices formed by each of the cations and anions are arranged offset from each other by half of the ridge of the unit cell.

[0028] Lithium salts of transition metal oxides having this layered rock salt structure are, for example, LiNi x Co y Al z O2(NCA) or LiNi x Co y Mn z O2(NCM) (but, 0 <x <1, 0 <y <1, 0 <z <1, 그리고 x+y+z=1)과 같은 삼원계 전이 금속산화물의 리튬염을 포함할 수 있다.

[0029] When the positive electrode active material contains a lithium salt of a ternary transition metal oxide having the layered rock salt structure, the energy density and thermal stability of the all-solid-state secondary battery can be improved.

[0030] The positive electrode active material may be covered by a coating layer. The coating layer of the present embodiment may be any known coating layer for the positive electrode active material of an all-solid-state secondary battery. The coating layer may be, for example, Li2-ZrO2.

[0031] Furthermore, when the positive electrode active material is formed of a lithium salt of a ternary transition metal oxide such as NCA or NCM and contains nickel, the capacity density of the all-solid-state secondary battery increases, and metal dissolution into the positive electrode active material in a charged state can be reduced. Accordingly, the long-term reliability and cycle characteristics in a charged state of the solid-state secondary battery according to the present embodiment can be improved.

[0032] Here, the positive electrode active material may have a particle shape, such as a true spherical shape or an elliptical spherical shape. Furthermore, 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 of conventional all-solid-state secondary batteries. Meanwhile, the content of the positive electrode active material in the positive electrode layer is not particularly limited, and may be within a range applicable to positive electrode layers of conventional all-solid-state secondary batteries.

[0033] In addition, in addition to the above-described positive electrode active material and solid electrolyte, additives such as a conductive additive, a binder, a filler, a dispersant, or an ion conductive additive may be additionally and appropriately blended into the positive electrode composite material layer.

[0034] The conductive agent may be, for example, graphite, carbon black, acetylene black, ketjen black, carbon fiber, or metal powder. The binder may be, for example, styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, or polyethylene. The filler, dispersant, and ion conductive agent that can be mixed into the positive electrode composite material layer may be any known material that can be used in the electrode of an all-solid-state secondary battery.

[0035] (1-2. Cathode layer)

[0036] The negative electrode layer may include a negative electrode current collector and a negative electrode composite material layer laminated on the negative electrode current collector. The negative electrode current collector is preferably composed of a material that does not react with lithium, i.e., does not form both an alloy and a compound. The material constituting the negative electrode current collector may be, for example, copper, stainless steel, titanium, iron, cobalt, or nickel.

[0037] The negative electrode composite layer may include a negative electrode active material, amorphous carbon, and a binder.

[0038] The negative active material may be, for example, an element that forms an alloy or compound with lithium through an electrochemical reaction during charging (i.e., an alloy-forming element). The alloy-forming element may include one or more elements selected from the group consisting of gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, and zinc.

[0039] When one or more of gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, and zinc are used as alloying elements, the negative active material is preferably in the form of particles, for example, 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 can be further improved. Here, the particle size of the negative active material can be, for example, a median diameter (i.e., D50) measured using a laser particle size distribution meter.

[0040] The amorphous carbon may be, for example, carbon black or graphene. The carbon black may be acetylene black, furnace black, or ketjen black.

[0041] In addition to the above, the negative electrode composite material layer may appropriately contain additives used in conventional all-solid-state secondary batteries (e.g., fillers, dispersants, ion conductors, or solid electrolytes).

[0042] (1-3. Solid electrolyte layer)

[0043] A solid electrolyte layer may be laminated between the positive electrode layer and the negative electrode layer and may include a solid electrolyte. The composition of the solid electrolyte layer is a characteristic feature of the all-solid-state secondary battery related to the present embodiment, and will be described in detail later.

[0044] (1-4. Relationship between the charging capacity of the positive and negative layers)

[0045] It is preferable that the all-solid-state secondary battery according to the present embodiment be configured so that a comparison (i.e., capacity ratio) between the charging capacity of the positive electrode composite material layer and the charging capacity of the negative electrode composite material layer satisfies the following mathematical expression 1.

[0046] [Mathematical Formula 1]

[0047] 0.01

[0048] a: Charging capacity (mAh) of the positive electrode composite layer

[0049] b: Charge capacity (mAh) of the negative composite layer

[0050] Here, the charge capacity of the positive electrode composite material layer can be obtained by multiplying the charge capacity density (mAh / g) of the positive electrode active material by the mass of the positive electrode active material. When multiple types of positive electrode active materials are used, the value of charge capacity density × mass is calculated for each positive electrode active material, and the sum of these can be referred to as the charge capacity of the positive electrode composite material layer. The charge capacity of the negative electrode composite material layer is also calculated in the same way. In other words, the charge capacity of the negative electrode composite material layer can be obtained by multiplying the charge capacity density (mAh / g) of the negative electrode active material by the mass of the negative electrode active material. When multiple types of negative electrode active materials are used, the value of charge capacity density × mass is calculated for each negative electrode active material, and the sum of these can be referred to as the capacity of the negative electrode composite material layer. Here, the charge capacity densities of the positive electrode active material layer and the negative electrode active material can be calculated using an all-solid-state half cell using lithium metal as the counter electrode. In practice, the charge capacities of the positive electrode composite material layer and the negative electrode composite material layer are directly measured using an all-solid-state half cell.

[0051] ​A specific method for directly measuring the charge capacity may be as follows. A test cell is manufactured using a positive electrode composite material layer as the working electrode and Li as the counter electrode, and CC-CV charging is performed from the OCV (open circuit voltage) to the upper limit charge voltage, and the charge capacity of the positive electrode composite material layer is measured. The upper limit charge voltage can be determined by the standard of JIS C 8712:2015. The upper limit charge voltage for a positive electrode composite material layer of lithium cobalt acid type is 4.25 V, and the upper limit charge voltage for other positive electrode composite material layers can be obtained by applying the provisions of A.3.2.3 (Safety requirements when applying a different upper limit charge voltage) of JIS C 8712:2015. A test cell is manufactured using a negative electrode composite material layer as the working electrode and Li as the counter electrode, and CC-CV charging is performed from the OCV (open circuit voltage) to 0.01 V, and the charge capacity of the negative electrode composite material layer is measured.

[0052] The above-described test cell can be manufactured, for example, by the following method. The positive electrode composite layer or negative electrode composite layer, the charge capacity of which is to be measured, is formed into a 13 mm diameter disc shape. 200 mg of solid electrolyte powder, similar to that 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. A disc-shaped positive electrode composite layer or negative electrode composite layer is placed on one side of the cylinder, and a lithium foil with a diameter of 13 mm and a thickness of 0.03 mm is placed on the opposite side. One stainless steel disc is placed on each side of the cylinder, and the entire body is pressurized at 300 MPa for 1 minute in the axial direction of the cylinder to integrate the contents. The integrated contents are removed from the cylinder and sealed in a case so that a constant pressure of 22 MPa is applied, thereby creating a test cell. The test cell manufactured in the above manner can be CC-charged at a current density of, for example, 0.1 mA and then CV-charged to 0.02 mA, so that the charge capacity of the positive electrode composite material layer can be measured.

[0053] The charge capacity density is calculated by dividing this charge capacity by the mass of each active material. The initial charge capacity of the positive electrode composite material layer and the negative electrode composite material layer may be the initial charge capacity measured during the first charge cycle. The examples described below use this value.

[0054] As described below, in this embodiment, the all-solid-state secondary battery is charged beyond the charging capacity of the negative electrode composite layer. In other words, the negative electrode composite layer is overcharged. At the initial stage of charging, lithium is absorbed into the negative electrode composite layer. In other words, the negative electrode active material forms an alloy with lithium ions that have migrated from the positive electrode layer. When the charging is further performed beyond the capacity of the negative electrode composite layer, lithium is deposited on the back side of the negative electrode composite layer, that is, between the negative electrode current collector and the negative electrode composite layer, and a lithium deposition layer is formed by this lithium. The lithium deposition layer contains trace amounts of elements other than lithium, but is mainly composed of lithium (mainly metallic lithium).

[0055] This phenomenon occurs because the negative active material contains a specific substance (i.e., an alloy-forming element that forms an alloy or compound with lithium). During discharge, lithium within the negative electrode composite layer and lithium precipitation layer ionizes and migrates toward the positive electrode layer.

[0056] Therefore, the all-solid-state secondary battery according to the present embodiment can use precipitated lithium as an anode active material. Furthermore, since the anode composite material layer covers the lithium precipitate layer, it functions as a protective layer for the lithium precipitate layer while simultaneously suppressing the precipitation and growth of dendrites. As a result, short-circuiting and capacity reduction of the all-solid-state secondary battery can be suppressed, and furthermore, the characteristics of the all-solid-state secondary battery can be improved.

[0057] Here, it is preferable that the capacity ratio is 0.01 or more. When the capacity ratio is 0.01 or more, the collapse of the negative electrode composite material layer due to repeated charge and discharge can be suppressed, and the negative electrode composite material layer can sufficiently function as a protective layer that suppresses the precipitation and growth of dendrites. Therefore, when the capacity ratio is 0.01 or more, the deterioration of the characteristics of the all-solid-state secondary battery can be suppressed. In addition, it is preferable that the capacity ratio is 0.5 or less. When the capacity ratio is 0.5 or less, the amount of lithium precipitation in the negative electrode layer can be secured, and the decrease in battery capacity can be suppressed. For the same reason, it is considered more preferable that the capacity ratio is less than 0.25. In addition, when the capacity ratio is less than 0.25, the output characteristics of the secondary battery can be further improved.

[0058] The thickness of the negative electrode composite material layer is preferably 1 ㎛ to 20 ㎛, which is a range satisfying mathematical expression 1, and more preferably 1 ㎛ to 10 ㎛. When the thickness of the negative electrode composite material layer is 1 ㎛ or more, the characteristics of the all-solid-state secondary battery can be sufficiently improved. When the thickness of the negative electrode composite material layer is 20 ㎛ or less, the resistance value of the negative electrode composite material layer is small, so the characteristics of the all-solid-state secondary battery can be further improved.

[0059] The thickness of the aforementioned negative composite material layer can be estimated, for example, by observing the average thickness of a cross-section after assembling and pressurizing an all-solid-state secondary battery using a scanning electron microscope (SEM).

[0060] <2. Characteristic configuration of an all-solid-state secondary battery according to an embodiment of the present invention>

[0061] The solid electrolyte layer in this embodiment may include, for example, a first solid electrolyte, a second solid electrolyte, and a binder (binder for the solid electrolyte layer).

[0062] The first solid electrolyte may be a lithium-containing sulfide solid electrolyte containing lithium. The lithium-containing sulfide solid electrolyte may be, for example, Li2S-P2S5, Li2S-P2S5-LiX (X is a halogen element, for example, I, Br, Cl), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (m, n are defined numbers, Z is any one of Ge, Zn or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, and Li2S-SiS2-Li p MO q (p, q are integers, M is any one of P, Si, Ge, B, Al, Ga or In) may be at least one selected from the group consisting of. This first solid electrolyte may be formed by treating a starting material (e.g., Li2S, P2S5, etc.) by a melt-quenching method or mechanical milling. In addition, an additional heat treatment may be provided after this treatment. The first solid electrolyte may be amorphous, crystalline, or a mixed state thereof.

[0063] The second solid electrolyte is a molecular crystal containing a lithium salt and a ligand. The lithium salt may include at least one selected from the group consisting of lithium bis(fluorosulfonyl) imide (LiFSI) and lithium bis(trifluoromethanesulfonyl) imide (LiTFSI). The ligand may include at least one selected from the group consisting of tetramethylethylene diamine (TMEDA), tetraethylethylene diamine (TEEDA), and tetramethylpropylene diamine (TMPDA).

[0064] The content of the first solid electrolyte in the entire solid electrolyte layer (i.e., when the mass of the entire solid electrolyte layer is 100 mass%) is preferably 80 mass% or more and 98 mass% or less, more preferably 85 mass% or more and 98 mass% or less, and still more preferably 90 mass% or more and 98 mass% or less.

[0065] The content of the second solid electrolyte in the entire solid electrolyte layer (i.e., when the mass of the entire solid electrolyte layer is 100 mass%) is preferably 1 mass% or more and 19 mass% or less, more preferably 1 mass% or more and 10 mass% or less, and still more preferably 2 mass% or more and 5 mass% or less.

[0066] It is preferable that the mass ratio of the first solid electrolyte and the second solid electrolyte is 98:2 to 80:20 (a range including the values ​​at both ends).

[0067] The binder for the solid electrolyte layer may include, for example, at least one selected from the group consisting of styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, and polyethylenep. The binder for the solid electrolyte layer may be the same as the binder contained in the positive electrode composite material layer and the negative electrode composite material layer, but is not limited thereto.

[0068] The content of the binder for the solid electrolyte in the entire solid electrolyte layer (i.e., when the mass of the entire solid electrolyte layer is 100 mass%) is preferably 0.1 mass% or more and 5 mass% or less, and more preferably 0.5 mass% or more and 3 mass% or less.

[0069] <3. Method for manufacturing an all-solid-state secondary battery according to an embodiment of the present invention>

[0070] A method for manufacturing an all-solid-state secondary battery according to the present embodiment is described. The all-solid-state secondary battery according to the present embodiment can be manufactured by manufacturing a positive electrode, a negative electrode, and a solid electrolyte layer, respectively, and then laminating the respective layers.

[0071] (3-1. Bipolar layer manufacturing process)

[0072] First, the cathode composite material (e.g., cathode active material, solid electrolyte, and binder) that constitutes the cathode composite material layer is mixed and processed into a sheet shape. The cathode composite material sheet thus obtained is cut into an appropriate shape and laminated on a cathode current collector to form a cathode laminate. The cathode laminate is pressed (e.g., using hydrostatic pressure) to manufacture a cathode layer comprising a cathode current collector and a cathode composite material layer.

[0073] (3-2. Cathode layer manufacturing process)

[0074] First, the negative electrode composite material (negative electrode active material, non-alloying element, binder, etc.) that constitutes the negative electrode composite layer is added to a polar or non-polar solvent to prepare a slurry. Next, the slurry is applied onto a negative electrode current collector and dried to form a negative electrode laminate. The negative electrode laminate is pressed (e.g., using hydrostatic pressure) to produce the negative electrode layer. The pressing process may be omitted.

[0075] Meanwhile, the negative electrode layer can also be manufactured by forming a separate negative electrode composite material layer, then laminating and pressing it on the negative electrode current collector.

[0076] (3-3. Solid electrolyte layer manufacturing process)

[0077] The solid electrolyte layer can be manufactured, for example, by mixing a first solid electrolyte, a second solid electrolyte, and a binder (a solvent is added if necessary), applying and drying the mixture, and then applying pressure.

[0078] (3-4. Assembly process of all-solid-state secondary batteries)

[0079] An all-solid-state secondary battery can be manufactured by laminating and pressurizing (for example, pressurizing using hydrostatic pressure) a solid electrolyte layer so that it is provided between the positive electrode layer and the negative electrode layer.

[0080] <4. Charging method of all-solid-state secondary battery according to an embodiment of the present invention>

[0081] Next, a charging method of an all-solid-state secondary battery is described. According to the present embodiment, the all-solid-state secondary battery is charged beyond the charging capacity of the negative electrode composite material layer. In other words, the negative electrode composite material layer is overcharged. At the initial stage of charging, lithium is absorbed into the negative electrode composite material layer. When the charging exceeds the charging capacity of the negative electrode composite material layer, lithium is deposited on the back side of the negative electrode composite material layer (i.e., between the negative electrode current collector and the negative electrode composite material layer). Accordingly, a lithium deposition layer that did not exist during manufacturing is formed. During discharge, lithium in the negative electrode composite material layer and the lithium deposition layer is ionized and moves toward the positive electrode layer.

[0082] Meanwhile, the charging amount is preferably 2 to 100 times the charging capacity of the negative composite material layer, more preferably 4 to 100 times the charging capacity of the negative composite material layer.

[0083] The thickness of the lithium precipitation layer is preferably 10 ㎛ or more, more preferably 30 ㎛ or more, and preferably 60 ㎛ or less, which is the upper limit feasible for an all-solid-state secondary battery. Meanwhile, the thickness of the lithium precipitation layer can be obtained by observing the average thickness of a cross-section after charging the all-solid-state secondary battery using a scanning electron microscope (SEM).

[0084] <5. Effects of the embodiment of the present invention>

[0085] According to this embodiment, even when the volume change of the secondary battery is large due to overcharging exceeding the charge capacity of the negative composite material layer and precipitating lithium, the deterioration of the secondary battery performance can be sufficiently suppressed, so that the secondary battery can be charged and discharged without problems by applying external pressure or by applying sufficiently low external pressure.

[0086] <6. About other embodiments of the present invention>

[0087] Above, the best embodiment of the present invention has been described in detail, but the present invention is not limited thereto, and various changes or combinations are possible within the scope of the technical idea of ​​the present invention.

[0088] Hereinafter, the all-solid-state secondary battery according to the present invention will be described in more detail, but the present invention is not limited to the embodiments described below.

[0089] <Example 1>

[0090] (Manufacture of solid electrolyte layer)

[0091] A slurry was prepared by adding xylene and isobutyl to a mixture containing 97.5 parts by mass of Li6PS5Cl as a first solid electrolyte, 1 part by mass of a binder, and 2.5 parts by mass of Li(TFSI)(TMEDA) as a second solid electrolyte, and stirring the mixture. The slurry was applied onto a PET film using a blade coater, dried in air at 40°C, and vacuum-dried at 40°C for 12 hours to form a pre-sheet. Thereafter, the pre-sheet was isostatically pressed at 490 MPa to obtain a solid electrolyte sheet having a solid electrolyte layer formed on the PET film.

[0092] (Manufacturing of all-solid-state secondary batteries)

[0093] 12 g of porous carbon black, which is an amorphous carbon, and 4 g of silver particles, which is an anode active material, were placed in a container. An NMP solution containing 8 mass% of binder was added thereto so that the mass of the binder was 7% of the total mass of the carbon black, silver particles, and binder. The NMP solution was added little by little while stirring to form a slurry for a cathode composite material layer. The slurry for a cathode composite material layer was applied onto a 10-micron-thick stainless steel foil using a blade coater and dried in the air at 80°C for about 20 minutes. Thereafter, the cathode layer was formed by vacuum drying at 100°C for about 12 hours.

[0094] Next, LiNi, the positive electrode active material 0.8 Co 0.1 Mn 0.05 O2(NCM), Li6PS5Cl as the first solid electrolyte, carbon nanotubes (CNT) as a conductor, and PTFE as a binder were mixed (their mixing ratio was 85: 14.45: 0.25: 0.3 (by mass)), stretched into a sheet shape, and a cathode composite layer was formed in a square shape of about 2 cm. The cathode composite layer was laminated on an aluminum foil as a cathode current collector and isotropically pressed to manufacture the cathode layer. Meanwhile, the surface of the aforementioned NCM was coated with Li2-ZrO2.

[0095] The solid electrolyte sheet and the negative electrode layer were overlapped so that the solid electrolyte layer and the negative electrode composite layer were in contact, and then isotropically pressurized at 50 MPa. After peeling off the PET film, the solid electrolyte layer was transferred onto the negative electrode layer. The positive electrode layer was provided on the negative electrode layer and the solid electrolyte layer, and sealed with a laminate film in a vacuum to manufacture an all-solid-state secondary battery. To prevent the vacuum of the secondary battery from being broken, a portion of each of the positive electrode current collector and the negative electrode current collector protruding from the laminate film became the terminals of the positive electrode layer and the negative electrode layer.

[0096] An all-solid-state secondary battery was isotropically pressurized at 490 MPa. This significantly improved the battery's characteristics.

[0097] The charge-discharge characteristics of the all-solid-state lithium secondary battery manufactured in this way were evaluated under the following conditions at a confining pressure of 0.3 MPa. These charge-discharge characteristics were measured in a constant-temperature chamber at 25°C. The current was 1.5 mA / cm until the voltage reached 4.25 V. 2 Charge with a constant current of 0.5 mA / cm 2 It was charged at a constant voltage of 4.25 V until it reached 1.5 mA / cm 2 The battery was discharged with a constant current until the voltage reached 2.5 V. After repeating this charging and discharging cycle 100 times, the capacity retention rate was 94.4%, and the average Coulombic efficiency was 99.9%. The results are shown in Figure 1.

[0098] <Comparative Example 1>

[0099] An all-solid-state secondary battery was manufactured using a solid electrolyte sheet containing 99 parts by mass of Li6PS5Cl as a first solid electrolyte and 1 part by mass of a binder, and no second solid electrolyte (molecular crystal), and was charged and discharged in the same manner as in Example 1. After repeating this charging and discharging 100 times, the capacity retention rate was 9.5%, and the average Coulombic efficiency was 96.8%. The results are shown in Fig. 1.

[0100] In a precipitation-type all-solid-state secondary battery in which lithium is precipitated on the negative electrode layer during charging, Example 1 (the solid electrolyte layer contains a first solid electrolyte and a second solid electrolyte) showed improved cycle characteristics and average coulombic efficiency at a sufficiently low confining pressure of 0.3 MPa compared to Comparative Example 1 (the solid electrolyte layer does not contain a second solid electrolyte). In particular, the cycle characteristics were significantly improved.

[0101] The reason why the secondary battery characteristics of Example 1 were significantly improved at low confining pressure is as follows. This is because the molecular crystals, which have superior formability compared to the sulfide solid electrolyte, are crushed by isotropic pressing, filling the gaps in the solid electrolyte layer and allowing lithium to be uniformly precipitated along the shape of the negative electrode layer. In addition, it appears that one reason is that the reaction distribution was improved due to improved adhesion at the interface between the solid electrolyte layer and the positive electrode composite material layer or between the solid electrolyte layer and the negative electrode composite material layer.

Claims

1. Including an anode layer, a cathode layer, and a solid electrolyte layer between the anode layer and the cathode layer, The cathode layer comprises one selected from the group consisting of gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, and zinc and amorphous carbon, The solid electrolyte layer includes a first solid electrolyte, a second solid electrolyte, and a binder, The above first solid electrolyte is a lithium-containing sulfide solid electrolyte, The above second solid electrolyte is a molecular crystal, The above molecular determination is: A lithium salt having at least one selected from the group consisting of lithium bis(fluorosulfonyl) imide (LiFSI), and lithium bis(trifluoromethanesulfonyl) imide (LiTFSI), and A ligand comprising at least one selected from the group consisting of tetramethylethylenediamine (TMEDA), tetraethylethylenediamine (TEEDA), and tetramethylpropylenediamine (TMPDA). All-solid-state secondary battery.

2. In claim 1, An all-solid-state secondary battery in which the mass ratio of the first solid electrolyte and the second solid electrolyte (first solid electrolyte: second solid electrolyte) is 98:2 to 80:

20.

3. In claim 1, The above cathode layer is an all-solid-state secondary battery containing silver and amorphous carbon.

4. In claim 1, An all-solid-state secondary battery in which the capacity ratio of the initial charge capacity of the positive electrode layer and the initial charge capacity of the negative electrode layer satisfies the following mathematical expression 1: [Mathematical Formula 1] 0.01 a: Initial charge capacity of the positive electrode layer (mAh) b: Initial charge capacity of the cathode layer (mAh).

5. Including charging the all-solid-state secondary battery described in claim 1 beyond the charging capacity of the negative electrode layer. Charging method of an all-solid-state secondary battery.

6. In claim 5, A charging method for an all-solid-state secondary battery, wherein charging is performed within a range of 2 to 100 times the charging capacity of the above-mentioned cathode layer. ​

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