All-solid-state battery, method for manufacturing all-solid-state battery, and method for recovering all-solid-state battery

Abstract

The main object of the present disclosure is to provide an all-solid battery with a good capacity maintenance rate. In the present disclosure, the above problem is solved by providing an all-solid battery having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, the negative electrode layer containing granules, the granules having a Si-based active material and a molten salt in a solid state at 25°C.

Description

Technical Field

[0001] This disclosure relates to all-solid-state batteries. Background Technology

[0002] All-solid-state batteries are batteries with a solid electrolyte layer between the positive and negative electrode layers. Compared to liquid batteries with electrolytes containing flammable organic solvents, they offer the advantage of simplified safety devices. Furthermore, Si-based active materials are known as active materials used in all-solid-state batteries. For example, Patent Document 1 discloses an all-solid-state battery using a Si-containing active material as the negative electrode active material.

[0003] On the other hand, molten salts with good ionic and electronic conductivity are known. For example, Patent Document 2 discloses molten salts containing a specific first imidazole. Salt and a specific second salt of molten salt.

[0004] Prior art literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2020-004685

[0006] Patent Document 2: International Publication No. 2011 / 074325 Summary of the Invention

[0007] Si has a large theoretical capacity, which is effective for achieving high energy density in all-solid-state batteries. However, on the other hand, Si undergoes significant volume changes during charge and discharge, making it prone to cracking in the negative electrode layer if repeatedly charged and discharged. If cracks form in the negative electrode layer, the ion and electron conduction pathways are interrupted, and the capacity retention decreases over time.

[0008] This disclosure was made in view of the above-mentioned circumstances, and its main purpose is to provide an all-solid-state battery with good capacity retention.

[0009] In this disclosure, an all-solid-state battery is provided, having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer. The negative electrode layer contains a granulator having a Si-based active material and a molten salt that is solid at 25°C.

[0010] According to this disclosure, the negative electrode layer contains granules containing Si-based active materials and molten salt, thus becoming an all-solid-state battery with good capacity retention.

[0011] In the above disclosure, the melting point of the molten salt can be above 30°C and below 120°C.

[0012] In the above disclosure, the molten salt may contain anion having a sulfonamide structure.

[0013] In the above disclosure, the negative electrode layer may contain lithium bis(trifluoromethanesulfonyl)imide as the molten salt.

[0014] In the above disclosure, the negative electrode layer may contain a sulfide solid electrolyte.

[0015] In the above disclosure, the average particle size (D) of the Si-based active material is... 50 It can be below 2μm.

[0016] In addition, this disclosure provides a method for manufacturing an all-solid-state battery, the all-solid-state battery having a positive electrode layer, a negative electrode layer and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, the manufacturing method having a negative electrode layer forming step, the negative electrode layer forming step forming the negative electrode layer containing granules, the granules having a Si-based active material and a molten salt that is solid at 25°C.

[0017] According to this disclosure, an all-solid-state battery with good capacity retention can be obtained by forming a negative electrode layer comprising granules containing Si-based active materials and molten salt.

[0018] In the above disclosure, the negative electrode layer forming process may include a granulation body forming process, a negative electrode mixture preparation process, and a negative electrode layer forming process. In the granulation body forming process, the Si-based active material and the molten salt are kneaded to form the granulation body. In the negative electrode mixture preparation process, the negative electrode mixture is prepared by stirring a mixture obtained by adding at least one of a solid electrolyte and a conductive material to the granulation body. In the negative electrode layer forming process, the negative electrode layer is formed using the negative electrode mixture.

[0019] In addition, this disclosure provides a method for recovering an all-solid-state battery, the all-solid-state battery having a positive electrode layer, a negative electrode layer and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, the negative electrode layer containing a granulator, the granulator having a Si-based active material and a molten salt that is solid at 25°C, the recovery method having a high-temperature charge-discharge step, the high-temperature charge-discharge step being performed at a temperature above the melting point of the molten salt.

[0020] According to this disclosure, the capacity retention rate can be restored by charging and discharging an all-solid-state battery having a negative electrode layer containing granules at a temperature above the melting point of molten salt, wherein the granules contain a Si-based active material and molten salt.

[0021] This disclosure provides the effect of providing an all-solid-state battery with good capacity retention. Attached Figure Description

[0022] Figure 1This is a schematic cross-sectional view illustrating the all-solid-state battery of this disclosure.

[0023] Figure 2 This is a schematic cross-sectional view illustrating a method for manufacturing an all-solid-state battery according to the present disclosure.

[0024] Figure 3 This is a flowchart illustrating the recovery method of the all-solid-state battery in this disclosure.

[0025] Figure 4 The results are obtained by DSC analysis of the molten salt obtained in Example 1.

[0026] Figure 5 The results are obtained by XRD analysis of the molten salt and its raw materials obtained in Example 1.

[0027] Figure 6 These are the results of charge-discharge tests on the evaluation batteries prepared in Example 1 and Comparative Example 1.

[0028] Explanation of reference numerals in the attached figures

[0029] 1… Positive electrode layer

[0030] 2… Negative electrode layer

[0031] 3… Solid electrolyte layer

[0032] 4…Positive current collector

[0033] 5… Negative current collector

[0034] 10… All-solid-state batteries Detailed Implementation

[0035] The following describes in detail the manufacturing method of the all-solid-state battery, the method for manufacturing the all-solid-state battery, and the method for recovering the all-solid-state battery as disclosed in this disclosure.

[0036] A. All-solid-state battery

[0037] Figure 1 This is a schematic cross-sectional view illustrating the all-solid-state battery of this disclosure. Figure 1 The all-solid-state battery 10 shown includes: a positive electrode layer 1, a negative electrode layer 2, a solid electrolyte layer 3 disposed between the positive electrode layer 1 and the negative electrode layer 2, a positive current collector 4 for collecting current in the positive electrode layer 1, and a negative current collector 5 for collecting current in the negative electrode layer 2. The negative electrode layer 2 contains granules, which have a Si-based active material and a molten salt that is solid at 25°C.

[0038] According to this disclosure, the negative electrode layer contains granules, which contain Si-based active materials and molten salt, thus creating an all-solid-state battery with good capacity retention. As mentioned above, Si-based active materials, represented by Si, undergo large volume changes during charge and discharge, making them prone to cracking in the negative electrode layer during repeated charge and discharge cycles. If cracks form in the negative electrode layer, ion and electron conduction pathways are interrupted, and the capacity retention decreases over time. In contrast, this disclosure uses granules containing Si-based active materials and molten salt. For example, the solid-state molten salt can act as a moderating material for the expansion and contraction of the Si-based active materials in an environment below the melting point of the molten salt, thereby suppressing cracking in the negative electrode layer. Alternatively, the cracks in the negative electrode layer can be repaired by filling them with liquid molten salt in an environment above the melting point of the molten salt. Thus, an all-solid-state battery with good capacity retention can be obtained by using granules containing Si-based active materials and molten salt.

[0039] 1. Negative electrode layer

[0040] The negative electrode layer of this disclosure contains specific granules. These granules contain Si-based active materials and a molten salt that is solid at 25°C. The molten salt in this disclosure is equivalent to an ionic compound that is solid at 25°C (room temperature). This molten salt differs from ionic liquids (Room Temperature Ionic Liquid, RTIL) that are liquid at 25°C. The granules are formed by the aggregation of multiple Si-based active material particles via the molten salt. Whether the negative electrode layer contains these granules can be determined, for example, by observing the cross-section of the negative electrode layer using scanning electron microscopy-energy dispersive X-ray diffraction (SEM-EDX). Specifically, based on cross-sectional EDX analysis, if it is confirmed that the Si element contained in the Si-based active material and the constituent elements of the molten salt are concentrated in the same location, and further, based on image analysis of the cross-sectional SEM image, it is confirmed that the Si-based active material particles have aggregated together, then it can be determined that the negative electrode layer contains granules. Furthermore, the granules may or may not contain a binder. The granules may not contain a solid electrolyte. Similarly, granules may not contain conductive materials.

[0041] The melting point of molten salts is typically above 25°C, but can be above 30°C, 40°C, or even 50°C. If the melting point of the molten salt is too low, it is difficult to produce granules. On the other hand, the melting point of molten salts can be, for example, below 120°C, below 100°C, or even below 80°C. If the melting point of the molten salt is too high, it will be unable to fill cracks in the negative electrode layer, and the capacity retention rate may not be sufficiently suppressed over time.

[0042] Molten salts can have both cations and anions. Examples of cations include inorganic cations such as lithium ions, sodium ions, potassium ions, and cesium ions; ammonium cations, piperidine cations, etc. Cations, pyridine It is a cationic, imidazole Organic cations include pyridine cations, alicyclic amine cations, aliphatic amine cations, and aliphatic phosphorus cations. The molten salt may contain only one type of cation or two or more. Furthermore, the molten salt may simultaneously contain both inorganic and organic cations. Moreover, the molten salt preferably contains at least lithium ions as a cation, as this improves the lithium-ion conductivity of the granules.

[0043] Examples of anions with a sulfonamide structure include, for example, bis(trifluoromethanesulfonyl)imide, bis(fluorosulfonyl)amide, bis(pentafluoroethanesulfonyl)amide, and (fluorosulfonyl)(trifluoromethanesulfonyl)amide. Molten salts may have only one anion or more than two anions.

[0044] The molten salt preferably contains at least lithium bis(trifluoromethanesulfonyl)imide (Li-TFSA), and may also contain lithium bis(trifluoromethanesulfonyl)imide (Li-TFSA) and tetrabutylammonium bis(trifluoromethanesulfonyl)amide (TBA-TFSA). The molar ratio of TBA-TFSA to Li-TFSA is, for example, 0.5 or more, and may be 1 or more, or 2 or more. On the other hand, the above molar ratio is, for example, 100 or less, and may be 50 or less.

[0045] Furthermore, the molten salt preferably contains at least lithium bis(fluorosulfonyl)imide (Li-FSA), and may also contain lithium bis(fluorosulfonyl)imide (Li-FSA) and cesium bis(fluorosulfonyl)imide (Cs-FSA). The molar ratio of Cs-FSA to Li-FSA is, for example, 0.5 or more, and may be 1 or more, or 2 or more. On the other hand, the above molar ratio is, for example, 100 or less, and may be 50 or less.

[0046] In addition, the molten salt may contain a cation represented by general formula (1) and a first imidazole having an anion of MX4 (M is a transition metal and X is a halogen). Salts, and second salts containing monovalent cations and halogens.

[0047] First imidazole Salts have cations represented by general formula (1).

[0048]

[0049] In general formula (1), R1 and R2 are alkyl groups having 1 to 10 carbon atoms, or they may be alkyl groups having 1 to 4 carbon atoms. Examples of alkyl groups include ethyl, methyl, propyl, and butyl. R1 and R2 may be the same as or different from each other.

[0050] Additionally, bisimidazole The salt has an MX4 structure (where M is a transition metal and X is a halogen). Examples of M include Fe, Cr, V, Co, Mn, Ti, Ru, and Pb. Examples of X include F, Cl, Br, and I. Furthermore, the valence of M in the MX4 structure is preferably divalent or trivalent.

[0051] On the other hand, the second salt has a monovalent cation. As an example of a monovalent cation, a cation represented by general formula (2) can be cited.

[0052]

[0053] R3 and R4 in general formula (2) are the same as R1 and R2 mentioned above, so they are omitted here. In addition, R3 can be the same as R1, and R4 can be the same as R2.

[0054] Other examples of monovalent cations in the second salt include alkali metal ions such as lithium ions, sodium ions, and potassium ions.

[0055] In addition, the second salt contains a halogen. Examples of halogens in the second salt include F, Cl, Br, and I.

[0056] First imidazole The ratio of salt and second salt in the molten salt is not particularly limited, when the first imidazole is added... When the salt is set to 100 moles, the proportion of the second salt is, for example, 100 moles or less, which can be 80 moles or less, or 50 moles or less. On the other hand, the above-mentioned proportion of the second salt is, for example, 1 mole or more.

[0057] Molten salts with high Li ion conductivity are preferred. For example, the Li ion conductivity of molten salts at 25°C is 1 × 10⁻⁶. -6 S / cm or higher, or 1×10 -5 S / cm or higher. Additionally, molten salts with high electronic conductivity are preferred.

[0058] Si-based active materials are active materials containing the element Si. Examples of Si-based active materials include elemental Si, Si alloys, and Si oxides. Si alloys preferably contain Si as the main component.

[0059] Examples of the shapes of Si-based active materials include granular forms. The average particle size (D) of Si-based active materials... 50 There are no specific limitations; for example, it can be below 10 μm, below 5 μm, or below 2 μm. If the average particle size of the Si-based active material is too large, the size of the granules will also increase, making it easier for cracks caused by volume changes during charging and discharging to occur in the negative electrode layer. On the other hand, the average particle size (D) of the Si-based active material... 50 For example, the average particle size should be above 0.1 μm. If the average particle size of Si-based active materials is too small, it is difficult to manufacture Si-based active materials. Average particle size (D) 50 For example, it can be calculated using a laser diffraction particle size analyzer or a scanning electron microscope (SEM).

[0060] The ratio of Si-based active material to molten salt in the granules is not particularly limited. For example, the molten salt can be 1 part by weight or more, 5 parts by weight or more, or 10 parts by weight or more, relative to 100 parts by weight of Si-based active material. If the proportion of molten salt is too small, it may not be able to adequately suppress the decrease in capacity retention over time. On the other hand, the molten salt can be 30 parts by weight or less, 20 parts by weight or less, or 15 parts by weight or less, relative to 100 parts by weight of Si-based active material. If the proportion of molten salt is too large, the proportion of Si-based active material becomes relatively small, and the volumetric energy density may decrease.

[0061] The proportion of granules contained in the negative electrode layer is, for example, 40% by weight or more, 50% by weight or more, or 60% by weight or more. On the other hand, the proportion of granules contained in the negative electrode layer is, for example, 95% by weight or less.

[0062] The negative electrode layer may also contain at least one of a solid electrolyte, a conductive material, and a binder. Examples of solid electrolytes include inorganic solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and halide solid electrolytes. In particular, a sulfide solid electrolyte is preferred in the negative electrode layer because it exhibits excellent ionic conductivity. Furthermore, the molten salt has high chemical stability and is unlikely to react with the sulfide solid electrolyte.

[0063] The sulfide solid electrolyte preferably contains, for example, Li, X (X is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, In), and S. Additionally, the sulfide solid electrolyte may contain at least one of Cl, Br, and I as a halogen element. Furthermore, the sulfide solid electrolyte may contain O.

[0064] Sulfide solid electrolytes can be glass-based, glass-ceramic-based, or crystalline. Furthermore, when the sulfide solid electrolyte has a crystalline phase, examples of crystalline phases include the Thio-LISICON type, the LGPS type, and the sterhenite type. Additionally, known solid electrolytes can be used as oxide, nitride, or halide solid electrolytes.

[0065] Solid electrolytes are preferably those with high Li-ion conductivity. For example, the Li-ion conductivity of a solid electrolyte at 25°C is 1 × 10⁻⁶. -4 S / cm or higher, preferably 1×10 -3 S / cm or higher. Furthermore, as for the shape of solid electrolytes, granular form is an example. The average particle size (D) of solid electrolytes... 50 For example, 0.1 μm or larger and 50 μm or smaller.

[0066] Examples of conductive materials include carbon materials, metal particles, and conductive polymers. Examples of carbon materials include granular carbon materials such as acetylene black (AB) and Ketjen black (KB), as well as fibrous carbon materials such as carbon fibers, carbon nanotubes (CNTs), and carbon nanofibers (CNFs). Examples of adhesives include fluorinated adhesives such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), rubber-based adhesives such as butadiene rubber, and acrylic adhesives. The thickness of the negative electrode layer is, for example, 0.1 μm or more and 1000 μm or less.

[0067] 2. Positive electrode layer

[0068] The positive electrode layer in this disclosure is a layer containing at least a positive electrode active material. Additionally, as needed, the positive electrode layer may also contain at least one of a solid electrolyte, a conductive material, and a binder.

[0069] Oxide active materials are typically used as positive electrode active materials. Examples of oxide active materials include LiCoO2, LiMnO2, LiNiO2, LiVO2, and LiNi. 1 / 3 Co 1 / 3 Mn 1 / 3 O2 and other layered active substances in rock salt, LiMn2O4, Li(Ni)0.5 Mn 1.5 Spinel-type active substances such as O4, and olivine-type active substances such as LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4.

[0070] Furthermore, the surface of the positive electrode active material can be covered with a coating layer. This coating layer can suppress the reaction between the positive electrode active material and the solid electrolyte (especially a sulfide solid electrolyte). Examples of coating layers include Li-containing oxides such as LiNbO3, Li3PO4, and LiPON. The average thickness of the coating layer is, for example, 1 nm or more. On the other hand, the average thickness of the coating layer is, for example, 20 nm or less, or even 10 nm or less.

[0071] The solid electrolyte, conductive materials, and binders used in the positive electrode layer are the same as those described in "1. Negative Electrode Layer" above, so they are omitted here. The thickness of the positive electrode layer is, for example, 0.1 μm or more and 1000 μm or less.

[0072] 3. Solid electrolyte layer

[0073] The solid electrolyte layer in this disclosure is a layer formed between the positive electrode layer and the negative electrode layer, and contains at least a solid electrolyte. Additionally, the solid electrolyte layer may also contain a binder, if necessary. The content regarding the solid electrolyte and binder is the same as described in "1. Negative Electrode Layer" above, so it is omitted here. Furthermore, the thickness of the solid electrolyte layer is, for example, 0.1 μm or more and 1000 μm or less.

[0074] 4. Other structures

[0075] The all-solid-state battery disclosed herein preferably comprises a positive current collector for collecting current in the positive electrode layer, a negative current collector for collecting current in the negative electrode layer, and a battery casing housing the aforementioned components. Examples of materials for the positive current collector include Al, SUS, and Ni. Examples of materials for the negative current collector include Cu, SUS, and Ni. Known casings can be used as the battery casing.

[0076] The all-solid-state battery of this disclosure may have a constraint clamp that applies constraint pressure to the positive electrode layer, the solid electrolyte layer, and the negative electrode layer along the thickness direction. By applying constraint pressure, good ion conduction paths and electron conduction paths are formed. The constraint pressure may be, for example, 0.1 MPa or more, 1 MPa or more, or 5 MPa or more. On the other hand, the constraint pressure may be, for example, 100 MPa or less, 50 MPa or less, or 20 MPa or less. The type of constraint clamp is not particularly limited; for example, a constraint clamp that applies constraint torque by means of bolts can be cited.

[0077] 5. All-solid-state batteries

[0078] The type of all-solid-state battery disclosed herein is not particularly limited, but typically an all-solid-state lithium-ion secondary battery is used. Applications of all-solid-state batteries include, for example, power sources for vehicles such as hybrid electric vehicles, electric vehicles, gasoline vehicles, and diesel vehicles. They are particularly preferred for use as power sources for driving hybrid electric vehicles or electric vehicles. Furthermore, the all-solid-state batteries disclosed herein can be used as power sources for mobile bodies other than vehicles (e.g., railways, ships, and aircraft), and also as power sources for electrical appliances such as information processing devices.

[0079] B. Manufacturing method of all-solid-state batteries

[0080] Figure 2 This is a flowchart illustrating a method for manufacturing an all-solid-state battery according to the present disclosure. Figure 2 The method for manufacturing the all-solid-state battery shown includes a negative electrode layer formation step. In the negative electrode layer formation step, firstly, a Si-based active material and a molten salt are kneaded to form a granule (granule formation process). Next, a negative electrode binder is prepared by stirring a mixture obtained by adding a solid electrolyte, a conductive material, and a binder to the obtained granule (negative electrode binder preparation process). Then, a negative electrode layer is formed using the obtained negative electrode binder (negative electrode layer formation process). Thus, a negative electrode layer is obtained. Additionally, a positive electrode layer is formed through a positive electrode layer formation step, and a solid electrolyte layer is formed through a solid electrolyte layer formation step. Finally, by sequentially stacking the positive electrode layer, the solid electrolyte layer, and the negative electrode layer in the thickness direction, an all-solid-state battery is obtained.

[0081] According to this disclosure, an all-solid-state battery with good capacity retention can be obtained by forming a negative electrode layer comprising granules containing Si-based active materials and molten salt.

[0082] 1. Negative electrode layer formation process

[0083] The negative electrode layer forming process in this disclosure is a process of forming a negative electrode layer containing granules, wherein the granules have a Si-based active material and a molten salt. The method for forming the negative electrode layer is not particularly limited; for example, it is preferable to perform a granule forming process, a negative electrode mixture preparation process, and a negative electrode layer forming process.

[0084] (1) Granulation process

[0085] The granulation process is a process of kneading a Si-based active material and a molten salt to form granules. Specifically, the kneading process is performed on a mixture (a first mixture) containing at least a Si-based active material and a molten salt. The first mixture may have a dispersion medium. By using a dispersion medium, the dispersibility of the Si-based active material and the molten salt is improved. When the first mixture has a dispersion medium, the concentration of the solids component of the first mixture is, for example, 50% by weight or more and 90% by weight or less, and may be 60% by weight or more and 80% by weight or less.

[0086] The first mixture may or may not contain a binder. Additionally, the first mixture may not contain a solid electrolyte. Similarly, the first mixture may not contain a conductive material.

[0087] There are no particular limitations on the type of kneading process; for example, a self-rotating mixer can be used. When kneading with a self-rotating mixer, crushing balls may or may not be used. The rotational speed of the self-rotating mixer is, for example, 300 rpm or more and 600 rpm or less. The processing time of the self-rotating mixer is, for example, 1 hour or more and 100 hours or less.

[0088] (2) Negative electrode preparation and processing

[0089] The negative electrode mixture is prepared by stirring a mixture (second mixture) obtained by adding at least one of a solid electrolyte and a conductive material to the granulated body described above. The second mixture may further contain a binder. Additionally, the second mixture may contain a dispersion medium. By using the dispersion medium, a negative electrode slurry can be obtained.

[0090] (3) Negative electrode layer formation process

[0091] The negative electrode layer formation process is a process of forming a negative electrode layer using the aforementioned negative electrode mixture. In the negative electrode layer formation process, for example, a negative electrode layer is obtained by coating a negative electrode mixture (negative electrode slurry) containing a dispersion medium and then drying it. Alternatively, the negative electrode slurry can be coated onto a negative electrode current collector. For example, a doctor blade coating method can be used as a coating method for the negative electrode mixture.

[0092] 2. Other processes

[0093] The method for manufacturing the all-solid-state battery disclosed herein may also include a positive electrode layer formation step. The method for forming the positive electrode layer is not particularly limited; for example, a method of coating and drying a positive electrode slurry containing a positive electrode active material and a dispersion medium may be cited. The positive electrode slurry may further contain at least one of a conductive material, a solid electrolyte, and a binder. Additionally, the positive electrode slurry may be coated onto a positive electrode current collector.

[0094] The method for manufacturing the all-solid-state battery disclosed herein may also include a solid electrolyte layer forming step. The method for forming the solid electrolyte layer is not particularly limited; for example, a method of coating and drying a solid electrolyte slurry containing a solid electrolyte and a dispersion medium may be cited. The solid electrolyte slurry may further contain a binder. Alternatively, the solid electrolyte slurry may be coated onto a peelable metal foil.

[0095] The method for manufacturing an all-solid-state battery disclosed herein may also include a lamination process in which a positive electrode layer, a solid electrolyte layer, and a negative electrode layer are sequentially stacked in the thickness direction. In the lamination process, a pressing process is preferably performed to press the positive electrode layer, the solid electrolyte layer, and the negative electrode layer in the thickness direction.

[0096] Furthermore, this disclosure also provides a method for recovering an all-solid-state battery. The all-solid-state battery has a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer. The negative electrode layer contains a granulator, which has a Si-based active material and a molten salt that is solid at 25°C. The recovery method includes a high-temperature charge-discharge step of charging and discharging at a temperature above the melting point of the molten salt. According to this disclosure, by charging and discharging an all-solid-state battery having a negative electrode layer containing a granulator having a Si-based active material and a molten salt at a temperature above the melting point of the molten salt, capacity retention can be recovered. Figure 3 This is a flowchart illustrating the recovery method for an all-solid-state battery according to this disclosure. For example... Figure 3 As shown in this disclosure, an all-solid-state battery having a negative electrode layer comprising a granulated body containing Si-based active material and molten salt is charged and discharged at a temperature above the melting point of the molten salt (high-temperature charge-discharge process). This allows for the recovery of capacity retention. The timing of the high-temperature charge-discharge process is not particularly limited, but it is preferably performed after the initial charge-discharge of the all-solid-state battery. Furthermore, when the melting point of the molten salt is set to T... M In the case of high-temperature charging and discharging processes, the temperature is, for example, (T). M Above +5)℃, it can be (T) M +10)℃ or above, can also be (T) M +20)℃ or higher. On the other hand, the temperature in the high-temperature charge and discharge process is, for example, (T) M Below +50℃, it can also be (T) M +40)℃ or below.

[0097] Furthermore, this disclosure is not limited to the embodiments described above. The embodiments described above are illustrative, and all solutions that have substantially the same technical concept as those described in the scope of the patent claims of this disclosure and that achieve the same effect are included within the technical scope of this disclosure.

[0098] [Example]

[0099] [Example 1]

[0100] (Fabrication of the positive electrode layer)

[0101] A positive electrode slurry was prepared by stirring a mixture of positive electrode active material (NCA-based positive electrode active material), sulfide solid electrolyte (Li2S-P2S5-based sulfide solid electrolyte), conductive material (vapor-grown carbon fiber), binder (PVdF-based binder), and dispersion medium (butyl butyrate) using an ultrasonic dispersion device. The weight ratio of positive electrode active material: sulfide solid electrolyte: conductive material: binder was 100:16:2:0.75. The positive electrode slurry was then coated onto the positive electrode current collector (Al foil) using a doctor blade method and dried on a hot plate at 100°C for 30 minutes to obtain the positive electrode layer.

[0102] (Synthesis of molten salt)

[0103] Tetrabutylammonium bis(trifluoromethanesulfonyl)imide (TBA-TFSA) and lithium bis(trifluoromethanesulfonyl)imide (Li-TFSA) were prepared as raw materials. Then, TBA-TFSA and Li-TFSA were heated and mixed to achieve a molar ratio of 1:1 to obtain a molten salt. The obtained molten salt was analyzed by differential scanning calorimetry (DSC) at a rate of 1 °C / min. The results are shown below. Figure 4 .like Figure 4 As shown, the molten salt obtained has a melting point of 56℃ and is solid at room temperature (25℃). Furthermore, the melting points of TBA-TFSA and Li-TFSA are 90℃ and 235℃, respectively. Additionally, X-ray diffraction (XRD) measurements were performed on the obtained molten salt and each raw material at 25℃. The results are shown below. Figure 5 .like Figure 5 As shown, the obtained molten salt is confirmed to be a crystalline material.

[0104] (Fabrication of the negative electrode layer)

[0105] As raw materials, anode active material (Si particles), synthesized molten salt, and dispersion medium (diisobutyl ketone) were prepared. These mixtures (75% by weight solids) were kneaded using a rotary mixer to obtain granules. The kneading conditions of the rotary mixer were 2000 rpm, intermittent operation, for a total of 1 hour. Next, a sulfide solid electrolyte (Li2S-P2S5-based sulfide solid electrolyte), conductive material (vapor-grown carbon fiber), binder (BR-based binder), and dispersion medium (diisobutyl ketone) were further added to the obtained granules. The mixture was stirred using a thin-film cyclotron high-speed mixer (FILMIX) to prepare the anode slurry. The weight ratio of Si particles:molten salt:sulfide solid electrolyte:conductive material:binder was 100:11.5:76:15:4. The anode slurry was coated onto the anode current collector (Ni foil) using a doctor blade method and dried on a hot plate at 100°C for 30 minutes to obtain the anode layer.

[0106] (Fabrication of the solid electrolyte layer)

[0107] A solid electrolyte slurry was prepared by stirring a solid electrolyte mixture containing a sulfide solid electrolyte (Li2S-P2S5-based sulfide solid electrolyzer), a binder (PVdF-based binder), and a dispersion medium (butyl butyrate) using an ultrasonic dispersion device. The weight ratio of the sulfide solid electrolyte to the binder was 99.6:0.4. The solid electrolyte slurry was then coated onto an Al foil using a doctor blade method and dried on a hot plate at 100°C for 30 minutes to obtain a peelable solid electrolyte layer.

[0108] (Fabrication of the positive electrode stack)

[0109] The positive electrode layer and the peelable solid electrolyte layer are laminated using an overlapping method. A roller press is used to press the layers at a pressure of 50 kN / cm and a temperature of 160°C. Then, the Al foil of the solid electrolyte layer is peeled off and punched into 1 cm pieces. 2 The size of the positive electrode stack is thus obtained.

[0110] (Fabrication of the negative electrode stack)

[0111] The negative electrode layer and the peelable solid electrolyte layer are laminated using an overlapping method. A roller press is used to press the layers at a pressure of 50 kN / cm and a temperature of 25°C. Then, the Al foil of the solid electrolyte layer is peeled off and punched into 1.08 cm pieces. 2 The size of the negative electrode laminate was determined, thus obtaining the negative electrode laminate. Then, the solid electrolyte layer and the peelable solid electrolyte layer of the negative electrode laminate were stacked in an overlapping manner. The laminate was temporarily pressed using a planar uniaxial press at a pressing pressure of 100 MPa and a temperature of 25°C. Then, the Al foil of the solid electrolyte layer was peeled off and punched into 1.08 cm pieces. 2 The size is determined to obtain a negative electrode stack with an additional solid electrolyte layer.

[0112] (Evaluation of battery manufacturing)

[0113] A positive electrode stack and a negative electrode stack with an additional solid electrolyte layer were overlapped using an additive surface overlap method. The stack was then pressed using a planar uniaxial press at a pressing pressure of 200 MPa and a temperature of 120°C to obtain a battery stack. The obtained battery stack was then clamped between two constraint plates, and the two constraint plates were clamped together with fasteners at a constraint pressure of 10 MPa to produce an evaluation battery.

[0114] [Comparative Example 1]

[0115] A negative electrode layer was fabricated without granulation, and an evaluation battery was fabricated in the same manner as in Example 1. Specifically, a negative electrode slurry was prepared by stirring a negative electrode mixture containing negative electrode active material (Si particles), synthesized molten salt, sulfide solid electrolyte (Li2S-P2S5-based sulfide solid electrolyte), conductive material (vapor-grown carbon fiber), binder (BR-based binder), and dispersion medium (diisobutyl ketone) using a thin-film cyclohexane mixer (FILMIX). The weight ratio of Si particles:molten salt:sulfide solid electrolyte:conductive material:binder was 100:11.5:76:15:4. An evaluation battery was fabricated using the obtained negative electrode slurry, except as in Example 1.

[0116] [Example 2]

[0117] The constraint pressure on the battery stack was changed to 5 MPa, and the evaluation battery was manufactured in the same manner as in Example 1.

[0118] [Comparative Example 2]

[0119] The constraint pressure on the battery stack was changed to 5 MPa, and the evaluation battery was manufactured in the same manner as in Comparative Example 1.

[0120] [evaluate]

[0121] The evaluation batteries obtained in Examples 1 and 2 and Comparative Examples 1 and 2 were subjected to charge-discharge tests. First, the initial charge-discharge was performed under the following conditions: constant current charging at 1 / 20C up to 4.05V, followed by constant voltage charging at 4.05V up to 1 / 100C of the termination current. Next, constant current discharging at 1 / 20C up to 2.5V, followed by constant voltage discharging at 2.5V up to 1 / 100C of the termination current.

[0122] Next, as a durability charge-discharge process, charge-discharge is performed under the following conditions.

[0123] Durable charging: 1 / 3C constant current charging up to 4.05V.

[0124] Durability discharge: Constant current discharge from 1 / 3C up to 2.5V.

[0125] In addition, the durability charge and discharge tests were performed at 25°C until the 105th cycle, and at 60°C thereafter.

[0126] During the 54th, 105th, and 156th cycles, instead of endurance charge-discharge, capacity verification charge-discharge was performed under the following conditions.

[0127] Capacity verification charging: constant current charging at 1 / 10C up to 4.05V, then constant voltage charging at 4.05V up to 1 / 100C of the termination current.

[0128] Capacity confirmation discharge: discharge at a constant current of 1 / 10C up to 2.5V, then discharge at a constant voltage of 2.5V up to 1 / 100C of the termination current.

[0129] In addition, capacity verification was performed by charging and discharging at 25°C.

[0130] Let the initial discharge capacity be C1, the discharge capacity of the 105th cycle be C2, and the discharge capacity of the 156th cycle be C3. Calculate the capacity retention ratios (C2 / C1, C3 / C1). The results are shown in Table 1. Additionally, Figure 6 This shows the relationship between the number of cycles and the capacity retention rate in Example 1 and Comparative Example 1.

[0131] Table 1

[0132]

[0133] like Figure 6 As shown, in Example 1 and Comparative Example 1, although the relationship between cycle number and capacity retention is similar, both C2 / C1 and C3 / C1 are larger in Example 1 compared to Comparative Example 1. In Example 1, granules of Si particles and molten salt were formed, but in Comparative Example 1, such granules were not formed, thus presumably resulting in a difference in capacity retention. In particular, if the discharge temperature is changed from 25°C to 60°C, the difference in capacity retention increases. This is presumably because the molten salt in a liquid state fills and repairs the cracks in the negative electrode layer caused by the expansion and contraction of Si particles. Furthermore, the same relationship as in Example 1 and Comparative Example 1 was also confirmed in Example 2 and Comparative Example 2, where the confinement pressure was changed to 5. Thus, by placing molten salts that can be melted and solidified according to temperature near the Si-based active material that expands and contracts with charging and discharging, and forming them into granules, a wider and longer Li ion conduction path can be formed within the negative electrode layer, resulting in a good all-solid-state battery with excellent capacity retention.

Claims

1. An all-solid-state battery, comprising a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer. The negative electrode layer contains a granulator, which has a Si-based active material and a molten salt that is solid at 25°C. The molten salt has a melting point above 30°C and below 120°C, and the molten salt contains anion with a sulfonamide structure. The negative electrode layer contains tetrabutylammonium bis(trifluoromethanesulfonyl)imide, i.e., TBA-TFSA, and lithium bis(trifluoromethanesulfonyl)imide, i.e., Li-TFSA, as the molten salt, and the molar ratio of TBA-TFSA to Li-TFSA is 0.5 or more and 50 or less.

2. The all-solid-state battery according to claim 1, wherein the negative electrode layer contains a sulfide solid electrolyte.

3. In the all-solid-state battery according to claim 1, the average particle size D of the Si-based active material is... 50 It is below 2μm.

4. A method for manufacturing an all-solid-state battery, the all-solid-state battery having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer. The manufacturing method includes a negative electrode layer formation step, which forms a negative electrode layer containing granules. The granules contain a Si-based active material and a molten salt that is solid at 25°C. The molten salt has a melting point above 30°C and below 120°C, and the molten salt contains anion with a sulfonamide structure. The negative electrode layer contains tetrabutylammonium bis(trifluoromethanesulfonyl)imide, i.e., TBA-TFSA, and lithium bis(trifluoromethanesulfonyl)imide, i.e., Li-TFSA, as the molten salt, and the molar ratio of TBA-TFSA to Li-TFSA is 0.5 or more and 50 or less.

5. The method for manufacturing an all-solid-state battery according to claim 4, wherein the negative electrode layer forming process includes granulation formation treatment, negative electrode agent preparation treatment, and negative electrode layer forming treatment. In the granulation process, the Si-based active material and the molten salt are kneaded together to form the granules. In the preparation process of the negative electrode mixture, the negative electrode mixture is prepared by stirring a mixture obtained by adding at least one of a solid electrolyte and a conductive material to the granulated body. In the negative electrode layer formation process, the negative electrode mixture is used to form the negative electrode layer.

6. A method for recovering an all-solid-state battery, the all-solid-state battery having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer. The negative electrode layer contains a granulator, which has a Si-based active material and a molten salt that is solid at 25°C. The molten salt has a melting point above 30°C and below 120°C, and contains anions with a sulfonamide structure. The negative electrode layer contains tetrabutylammonium bis(trifluoromethanesulfonyl)imide (TBA-TFSA) and lithium bis(trifluoromethanesulfonyl)imide (Li-TFSA) as the molten salt, and the molar ratio of TBA-TFSA to Li-TFSA is 0.5 or more and 50 or less. The recovery method includes a high-temperature charge-discharge step, wherein the high-temperature charge-discharge step is performed at a temperature above the melting point of the molten salt.

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