Nanofiber conductor material, all-solid-state negative plate, preparation method of all-solid-state negative plate and all-solid-state battery

Abstract

The invention provides a nanofiber conductor material, an all-solid-state negative plate, a preparation method of the all-solid-state negative plate and an all-solid-state battery, and relates to the technical field of batteries. According to the nanofiber conductor material, a fiber matrix is used as a supporting matrix, a first coating layer and a second coating layer are formed on the surface of the fiber matrix from inside to outside, and the nanofiber conductor material is not prone to agglomeration, deformation and distortion and has good ion and electron conductivity; the invention further provides an all-solid-state negative electrode plate, by introducing the nanofiber conductor material, the nanofiber conductor material and negative electrode active material particles can form richer contact sites, a smooth ion-electron network channel is provided when a negative electrode expands and contracts, the circulation and rate performance is improved, meanwhile, the use of a conventional conductive agent is omitted, and the cost is reduced. The side reaction between the sulfide electrolyte and a carbon conductive agent commonly used for a negative electrode is avoided, the stability of an interface and a sulfide electrolyte body is optimized, the cycle life is greatly prolonged, the volume expansion stress can be dispersed, and the problem of cycle cracking of a high-silicon pole piece is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and relates to a nanofiber conductor material, an all-solid-state negative electrode sheet and a preparation method thereof, and an all-solid-state battery. Background Art

[0002] In the application of all-solid-state batteries, high-silicon negative electrodes usually have two failure points: ① The large expansion and contraction of the silicon negative electrode causes the contact between the active particles and the solid electrolyte and the conductive agent to deteriorate, and the ion transport and electron conduction network are not smooth, resulting in an increase in the internal resistance of the battery, a decrease in capacity performance and rate performance; ② The redox side reaction of the sulfide electrolyte itself with the commonly used conductive agents (such as C, vapor-grown carbon fiber VGCF, carbon nanotube CNT) of the negative electrode at low potential causes the failure of the electrolyte body and the contact interface, a decrease in the ability to transport ions, an increase in the internal resistance of the battery, and cycle failure. The above failure points affect the application of high-silicon negative electrodes in all-solid-state batteries.

[0003] In view of this, the present invention is specifically proposed. Summary of the Invention

[0004] Aiming at the deficiencies and defects existing in the prior art, the present invention aims to provide a nanofiber conductor material, an all-solid-state negative electrode sheet and a preparation method thereof, and an all-solid-state battery.

[0005] In order to achieve the above object, the following technical solutions are adopted:

[0006] The first object of the present invention is to provide a nanofiber conductor material, which includes a fiber matrix, a first coating layer coated on the surface of the fiber matrix, and a second coating layer dot-coated on the surface of the first coating layer;

[0007] Wherein, the first coating layer includes a metal and / or a metal oxide electronic conductor; the second coating layer includes a sulfide solid electrolyte.

[0008] Further, on the basis of the above technical solution of the present invention, the length of the fiber matrix is 10-300 μm, and the diameter is 10-150 nm;

[0009] And / or, the surface of the fiber matrix has one or more functional groups such as carboxyl, hydroxyl or aldehyde groups;

[0010] And / or, the metal in the first coating layer includes at least one of silver, titanium, manganese or copper;

[0011] And / or, the metal oxide electronic conductor in the first coating layer includes at least one of manganese oxide or tin oxide;

[0012] And / or, the sulfide electrolyte in the second coating layer adheres to the surface of the first coating layer in a dot-like or island-like form, and the sulfide electrolyte includes at least one of LPSCl, LPSBr, or LPSI.

[0013] Furthermore, based on the above technical solution of the present invention, in the nanofiber conductor material, the mass ratio of the fiber matrix, the metal and / or metal oxide electronic conductor, and the sulfide solid electrolyte is (70-90):(5-30):(1-15).

[0014] The second object of the present invention is to provide a method for preparing the above nanofiber conductor material, including the following steps:

[0015] S1. Provide a dispersion containing a fiber matrix, a raw material for forming the first coating layer, and a raw material for forming the second coating layer;

[0016] S2. Mix and stir, and optionally grind, the dispersion containing the fiber matrix with the raw material for forming the first coating layer, and then dry to form the first coating layer on the surface of the fiber matrix to obtain a fiber-coated material A;

[0017] S3. Mix the fiber-coated material A with the raw material for forming the second coating layer, grind, and then dry to form the second coating layer on the surface of the first coating layer to obtain the nanofiber conductor material.

[0018] Furthermore, based on the above technical solution of the present invention, in step S1, the dispersion containing the fiber matrix is mainly made of the fiber matrix and water, and the solid content of the fiber matrix in the dispersion containing the fiber matrix is 1%-20%;

[0019] And / or, the raw material for forming the first coating layer includes at least one of a metal salt solution, a metal powder, and / or a metal oxide powder;

[0020] And / or, the raw material for forming the second coating layer is a sulfide electrolyte, or a slurry B made of a sulfide electrolyte and a solvent, and the solid content of the sulfide electrolyte in the slurry B is 60-90%;

[0021] And / or, in step S2, the mixing and stirring time is 2-3 h; and / or, the grinding is ball milling, the ball milling time is 1-5 h, and the ball milling speed is 500-1500 rmp; and / or, the drying temperature is 70-90 °C, and the drying time is 2-4 h;

[0022] And / or, in step S3, the grinding is ball milling, the ball milling time is 2-5 h, and the ball milling speed is 500-1500 rmp; and / or, the drying is vacuum drying, the drying temperature is 70-90 °C, the drying time is 2-4 h, and the vacuum degree is -85~-95 kPa.

[0023] The third object of the present invention is to provide an all-solid-state negative electrode sheet, comprising a current collector and a negative electrode material film arranged on the surface of the current collector, the raw materials used to form the negative electrode material film include: negative electrode active material, adhesive, sulfide solid electrolyte and the nanofiber conductor material provided by the first or second object of the present invention, and does not include a conductive agent.

[0024] Further, based on the above technical solution of the present invention, the negative electrode active material includes one or more of silicon oxygen, silicon carbon, graphite or pure silicon;

[0025] And / or, the adhesive comprises one or more of PTFE, PEO, PVD or SBR;

[0026] And / or, the sulfide solid electrolyte includes at least one of LPSCl, LPSBr or LPSI;

[0027] And / or, the mass ratio of the negative electrode active material, the binder, the sulfide solid electrolyte and the nanofiber conductor material is (10-95):(1-10):(1-50):(1-20), preferably (65-85):(1-5):(10-30):(5-20).

[0028] The fourth object of the present invention is to provide a method for preparing the above-mentioned all-solid-state negative electrode sheet, comprising the following steps:

[0029] (a) mixing and stirring a negative electrode active material, a sulfide solid electrolyte and a nanofiber conductor material to obtain a powder material I;

[0030] (b) mixing and stirring the powder material I and the binder to obtain the powder material II;

[0031] The powder material II is heated and kept warm to obtain a fluffy powder material III;

[0032] (c) air-jet-crushing the powder III to obtain a wire-drawing powder IV;

[0033] (d) rolling the powder IV to obtain a negative electrode material film;

[0034] (e) Laminating the current collector and the negative electrode material film and rolling them to obtain an all-solid-state negative electrode sheet.

[0035] Further, based on the above technical solution of the present invention, in step (a), the mixing and stirring speed is 300-500 rpm / min, and the stirring time is 30-50 min;

[0036] And / or, in step (b), the rotation speed of the mixing and stirring is 1000 - 1500 rpm / min, and the stirring time is 30 - 50 min; and / or, the temperature of the heating and heat preservation is 60 - 70 °C, and the heating and heat preservation time is 30 - 50 min; and / or, the density of powder III is 0.8 - 1.0 g / cm 3 ;

[0037] And / or, in step (c), the air pressure during air jet milling is 0.5 - 0.7 MPa; and / or, the density of powder IV is 0.7 - 0.8 g / cm 3 ;

[0038] And / or, in step (d), the roll pressing and forming includes vertical roll pressing and horizontal roll pressing, and the pressure of the roll pressing and forming is 3 - 7 T;

[0039] And / or, in step (e), the thickness of the all - solid - state negative electrode sheet is 60 - 100 μm, and the areal density is 84 - 120 g / m 2 。

[0040] The fifth object of the present invention is to provide an all - solid - state battery, including the above - mentioned all - solid - state negative electrode sheet or the all - solid - state negative electrode sheet prepared by the above - mentioned preparation method.

[0041] Compared with the prior art, the technical solution of the present invention has at least the following technical effects:

[0042] (1) The present invention provides a nanofiber conductor material, which uses a fiber matrix as a support matrix, and a double - layer coating layer of a first coating layer and a second coating layer is formed from the inside to the outside on the surface of the fiber matrix. Among them, the first coating layer is made of electrochemically stable nano - metals and / or metal oxide electron conductors, and its main function is to provide a continuous and stable electron - conducting network phase to enhance electron conductivity. The second coating layer shows local dot - like coating on the surface of the first coating layer and is mainly made of sulfide solid electrolyte. The main purpose of using sulfide solid electrolyte is to subsequently apply it in the negative electrode sheet to form more continuous phases with the sulfide electrolyte and active materials inside the negative electrode sheet, thereby facilitating the provision of a three - dimensional ion - conducting continuous phase and facilitating ion conduction between negative electrode particles. This nanofiber conductor material is rigid, not easy to agglomerate, deform or twist, and has good ion - electron conductivity, and can be applied to the preparation of negative electrode sheets.

[0043] (2) The present invention also provides a preparation method of the above - mentioned nanofiber conductor material, which has the characteristics of high uniformity and good ion - electron conductivity after processing the electrode sheet.

[0044] (3) The present invention provides an all-solid-state negative electrode sheet. A nanofiber conductor material with an aspect ratio is introduced into the all-solid-state negative electrode sheet. Since the nanofiber conductor material is rigid and not prone to agglomeration, deformation, or distortion, it is easy to form a three-dimensional network structure with a high specific surface area and a high interweaving dimension in the electrode sheet. There are more abundant contact sites with the negative electrode active material particles. Thus, a smooth ion and electron network channel can be provided during the expansion and contraction of the negative electrode, thereby reducing the internal resistance and improving the capacity utilization and rate performance. At the same time, the use of conventional conductive agents is eliminated, avoiding side reactions between the sulfide electrolyte and common conductive agents for the negative electrode (such as C, VGCF, CNT), optimizing the interface and the stability of the sulfide electrolyte bulk, and thus greatly improving the cycle life. In addition to the above effects, this network structure also has a slight effect of suppressing material expansion and absorbing and dispersing the stress inside the negative electrode sheet caused by high expansion and contraction during charge and discharge, avoiding stress concentration and improving the cracking situation of the negative electrode sheet during cycling, thereby indirectly optimizing the cycle performance. Description of the Drawings

[0045] Figure 1 SEM image of the fiber coating material A in Example 1 of the present invention;

[0046] Figure 2 SEM image of the nanofiber conductor material in Example 1 of the present invention;

[0047] Figure 3 Full charge disassembly interface diagram of the battery cell prepared in Example 6 of the present invention after 70 cycles;

[0048] Figure 4 Full charge disassembly interface diagram of the battery cell prepared in Comparative Example 6 of the present invention after 70 cycles. Detailed Embodiments

[0049] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Those skilled in the art should understand that the described embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention. The process parameters without specific conditions noted in the following embodiments are usually in accordance with conventional conditions.

[0050] In the ranges disclosed in the present invention, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values and individual point values of each range, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in the present invention.

[0051] According to a first aspect of the present invention, there is provided a nanofiber conductor material, comprising a fiber matrix, a first coating layer coated on the surface of the fiber matrix, and a second coating layer dot-coated on the surface of the first coating layer;

[0052] Wherein, the first coating layer comprises a metal and / or a metal oxide electronic conductor; the second coating layer comprises a sulfide solid electrolyte.

[0053] Specifically, the nanofiber conductor material uses the fiber matrix as a support matrix, and a double coating layer of a first coating layer and a second coating layer is formed from the inside to the outside on the surface of the fiber matrix. Among them, the first coating layer is made of electrochemically stable nano-metal and / or metal oxide electronic conductors, and its main function is to provide a continuous and stable electronic conductive network phase to improve electronic conductivity. The second coating layer is locally dot-coated on the surface of the first coating layer, that is, it does not completely cover the surface of the first coating layer. If the second coating layer completely covers the surface of the first coating layer, the nano-metal and / or metal oxide electronic conductors in the first coating layer will be covered, and the electronic conductivity between the negative electrode material particles will be lost during the subsequent processing of the electrode sheet.

[0054] The second coating layer is mainly made of a sulfide solid electrolyte. The main purpose of using the sulfide solid electrolyte is to subsequently apply it to the negative electrode sheet to form more continuous phases with the sulfide electrolyte and the active material inside the negative electrode sheet, thereby facilitating the provision of a three-dimensional ion conductive continuous phase and facilitating ion conduction between the negative electrode particles. The nanofiber conductor material is rigid, not easily agglomerated, deformed or twisted (such as Figure 1 )), and has good ion and electronic conductive properties, and can be applied to the preparation of negative electrode sheets.

[0055] There is no specific limitation on the source of the fiber matrix, which can be prepared by conventional preparation methods in the art or obtained by commercial purchase.

[0056] The size of the fiber matrix is further optimized. As an alternative implementation of the technical solution of the present invention, the length of the fiber matrix is 10-300 μm (such as 10 μm, 20 μm, 30 μm, 50 μm, 80 μm, 100 μm, 120 μm, 150 μm, 180 μm, 200 μm, 220 μm, 250 μm, 280 μm or 300 μm, etc.), and the diameter is 10-150 nm (such as 10 nm, 50 μm, 80 μm, 100 μm, 120 μm or 150 μm, etc.). By further limiting the length and diameter of the fiber matrix, the obtained nanofiber conductor material has a specific aspect ratio, which is beneficial to its good ion and electronic conduction ability.

[0057] As an alternative embodiment of the technical solution of the present invention, the surface of the fiber matrix has one or more functional groups such as carboxyl, hydroxyl or aldehyde groups. Preferably, it is a needle-shaped nanofiber with an aldehyde group on the surface, and the preferred length is 10-50 μm.

[0058] By further defining the type of functional groups on the surface of the fiber matrix and the size and shape of the fiber matrix, it is beneficial to obtain a vertically and horizontally intertwined structure with a larger specific surface area and match the thickness of the subsequent negative electrode sheet. The above-mentioned functional groups on the surface of the fiber matrix can be obtained in the following ways. For example, 2,2,6,6-tetramethylpiperidine oxide (abbreviated as TEMPO), which is a stable water-soluble nitro radical, can fully oxidize the fiber structure of the fiber matrix (lignocellulose) in the suspension reaction system, and oxidize the hydroxyl group at the C6 position on the fiber surface into carboxyl and / or aldehyde groups.

[0059] In addition to the above optimizations for the fiber matrix, there are further optimizations for the composition of the first coating layer and the second coating layer.

[0060] As an alternative embodiment of the technical solution of the present invention, the metal in the first coating layer includes at least one of silver, titanium, manganese or copper, preferably silver; and / or, the metal oxide electronic conductor in the first coating layer includes at least one of manganese oxide or tin oxide.

[0061] Conventional carbon materials (such as conductive carbon like SP and CNT) have an adverse effect on the sulfide electrolyte in the silicon negative electrode. However, compared with conventional carbon materials, the above-mentioned specific types of metals and / or metal oxides used in the first coating layer are more stable in terms of the electrochemical performance of the sulfide electrolyte.

[0062] As an alternative embodiment of the technical solution of the present invention, the sulfide electrolyte particles in the second coating layer are mainly attached to the surface of the first coating layer in a dot-like or island-like form, that is, they are not completely coated on the surface of the first coating layer. The sulfide electrolyte includes at least one of LPSCl, LPSBr or LPSI. The above-mentioned sulfide electrolyte has high ionic conductivity and soft texture, has better contact with the active material, and is more likely to achieve all-solid state.

[0063] As an alternative embodiment of the technical solution of the present invention, in the nanofiber conductor material, the mass ratio of the fiber matrix, the metal and / or metal oxide electronic conductor, and the sulfide solid electrolyte is (70-90):(5-30):(1-15). If the mass ratio of the fiber matrix in the nanofiber conductor material is too large and the mass ratio of the metal and / or metal oxide electronic conductor or the sulfide solid electrolyte is too small, it is likely to cause insufficient continuous phases for electronic conduction and ionic conduction in the nanofiber conductor material, resulting in a decrease in electronic conductance and ionic conductance when processed into a pole piece. If the mass ratio of the fiber matrix is too small and the mass ratio of the metal and / or metal oxide electronic conductor or the sulfide solid electrolyte is too large, it is likely to affect the energy density of the battery after the battery is subsequently fabricated, failing to achieve the effect of a three-dimensional framework. Therefore, typical but non-limiting mass ratios are 70:5:1, 70:5:10, 70:5:15, 70:10:1, 70:20:1, 70:30:1, 70:20:10, 70:15:15, 70:25:5, 70:30:15, 76:6:18, 76:12:12, 76:18:6, 80:5:1, 80:15:5, 80:10:10, 80:20:5, 80:20:10, 80:20:15, 80:30:5, 80:30:15, 90:5:1, 90:10:5, 90:20:10, 90:30:1, 90:30:5, 90:30:10 or 90:30:15, etc.

[0064] By further defining the mass ratio of the fiber matrix, the metal and / or metal oxide electronic conductor, and the sulfide solid electrolyte in the nanofiber conductor material, the ionic conduction and electronic conduction of the conductor material are balanced.

[0065] According to the second aspect of the present invention, there is provided a method for preparing the above-mentioned nanofiber conductor material of the present invention, comprising the following steps:

[0066] S1. Provide a dispersion containing a fiber matrix, a raw material for forming a first coating layer, and a raw material for forming a second coating layer;

[0067] S2. Mix and stir, and optionally grind, the dispersion containing the fiber matrix with the raw material for forming the first coating layer, and then dry to form a first coating layer on the surface of the fiber matrix, obtaining a fiber-coated material A;

[0068] S3. Mix the fiber-coated material A with the raw material for forming the second coating layer, grind, and then dry to form a second coating layer on the surface of the first coating layer, obtaining the nanofiber conductor material.

[0069] The method for preparing the nanofiber conductor material provided by the present invention has the characteristics of high uniformity and good ionic and electronic conductivity after processing the pole piece.

[0070] As an alternative embodiment of the technical solution of the present invention, in step S1, the dispersion liquid containing the fiber matrix is mainly made of the fiber matrix and water. The solid content (mass content) of the fiber matrix in the dispersion liquid containing the fiber matrix is 1%-20%, for example, 1%, 2%, 5%, 8%, 10%, 12%, 15%, 18% or 20%, etc.

[0071] As an alternative embodiment of the technical solution of the present invention, the raw materials for forming the first coating layer include at least one of a metal salt solution, a metal powder and / or a metal oxide powder. Among them, the type of metal ions in the metal salt solution mainly corresponds to the type of metal in the first coating layer. For example, when the metal is silver, copper, manganese or titanium, the metal salt solution for forming the first coating layer can be silver nitrate, copper sulfate, manganese nitrate or titanium chloride solution, etc. The metal powder and / or metal oxide powder mainly corresponds to the type of metal and / or metal oxide in the first coating layer. For example, when the metal is silver, titanium, manganese or copper, the metal powder for forming the first coating layer is correspondingly silver powder, titanium powder, manganese powder or copper powder. When the metal oxide is manganese oxide or tin oxide, the metal oxide for forming the first coating layer is correspondingly manganese oxide powder or tin oxide powder.

[0072] As a preferred embodiment of the technical solution of the present invention, the first coating layer contains silver, and the raw material for forming the first coating layer is a silver nitrate solution (for example, with a concentration of 1-5 mol / L) or nano silver powder, preferably a silver nitrate solution. The first coating layer can be obtained by the silver mirror reaction of the surface functional groups of the fiber matrix with the silver nitrate solution, or by liquid-phase dispersion ball milling with nano silver powder.

[0073] As an alternative embodiment of the technical solution of the present invention, the raw material for forming the second coating layer is a sulfide electrolyte, or a slurry B made of a sulfide electrolyte and a solvent. The solid content of the sulfide electrolyte in the slurry B is 60-90% (for example, 60%, 70%, 80% or 90%, etc.). That is, the second coating layer can be obtained by dry mixing and ball milling the sulfide electrolyte with the fiber matrix having the first coating layer formed on its surface, or by dispersion ball milling the slurry B with the fiber matrix having the first coating layer formed on its surface.

[0074] As an alternative embodiment of the technical solution of the present invention, in step S2, the mixing and stirring time is 2-3 h (for example, 2 h, 2.5 h or 3 h, etc.), and the mixing and stirring is carried out at room temperature (for example, 25±5 °C);

[0075] And / or, in step S2, the grinding is ball milling, the ball milling time is 1 - 5 h (such as 1 h, 2 h, 3 h, 4 h or 5 h, etc.), and the ball milling rotation speed is 500 - 1500 rmp (such as 500 rmp, 800 rmp, 1000 rmp, 1200 rmp or 1500 rmp, etc.);

[0076] And / or, in step S2, the drying temperature is 70 - 90 °C (such as 70 °C, 80 °C or 90 °C, etc.), and the drying time is 2 - 4 h (such as 2 h, 3 h or 4 h, etc.).

[0077] As an alternative embodiment of the technical solution of the present invention, in step S3, the grinding is ball milling, the ball milling time is 2 - 5 h (such as 2 h, 3 h, 4 h or 5 h, etc.), and the ball milling rotation speed is 500 - 1500 rmp (such as 500 rmp, 800 rmp, 1000 rmp, 1200 rmp or 1500 rmp, etc.).

[0078] As an alternative embodiment of the technical solution of the present invention, in step S3, the drying is vacuum drying, the drying temperature is 70 - 90 °C (such as 70 °C, 80 °C or 90 °C, etc.), the drying time is 2 - 4 h (such as 2 h, 3 h or 4 h, etc.), and the vacuum degree is -85 to -95 kPa (such as -85 kPa, -90 kPa or -95 kPa, etc.).

[0079] As an alternative embodiment of the technical solution of the present invention, step S3 is completed in a drying room with a dew point less than -40 °C or in a glove box.

[0080] According to the third aspect of the present invention, there is also provided an all-solid-state negative electrode sheet, including a current collector and a negative electrode material film disposed on the surface of the current collector. The raw materials for forming the negative electrode material film include: a negative electrode active material, a binder, a sulfide solid electrolyte, and the nanofiber conductor material provided in the first or second aspect of the present invention, and do not include a conductive agent.

[0081] The all-solid-state negative electrode sheet provided by the present invention introduces a nanofiber conductor material (ionic and electronic mixed conductor) with an aspect ratio. This nanofiber conductor material is rigid, not easily agglomerated, deformed or twisted, and is easy to form a three-dimensional network structure with a high specific surface area and a high interweaving dimension in the electrode sheet ( Figure 2After silver plating, the morphology is such that there are more abundant contact sites with the negative electrode active material particles, thus providing a smooth ion-electron network channel during the expansion and contraction of the negative electrode, thereby reducing the internal resistance, improving the capacity utilization and rate performance; at the same time, the use of conventional conductive agents is eliminated, avoiding side reactions between the sulfide electrolyte and common conductive agents for the negative electrode (such as C, VGCF, CNT), optimizing the interface and the stability of the sulfide electrolyte bulk, and thus significantly improving the cycle life. In addition to the above effects, this network structure also has a slight effect of suppressing material expansion, and absorbing and dispersing the stress inside the negative electrode plate caused by high expansion and contraction during charge and discharge, avoiding stress concentration, and improving the cracking situation of the negative electrode plate during cycling, thereby indirectly optimizing the cycle performance.

[0082] As an alternative embodiment of the technical solution of the present invention, the negative electrode active material includes one or more of silicon oxide, silicon carbide, graphite (VH), or pure silicon, preferably including silicon oxide blended with graphite, and in the silicon oxide blended with graphite, SiO:VH=(30-80):(20-70), and the further selected ratio is SiO:VH=80:20.

[0083] As an alternative embodiment of the technical solution of the present invention, the binder includes one or more of polytetrafluoroethylene (PTFE), polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), or styrene-butadiene rubber (SBR), preferably including polytetrafluoroethylene (PTFE).

[0084] As an alternative embodiment of the technical solution of the present invention, the sulfide solid electrolyte in the negative electrode material film includes at least one of LPSCl, LPSBr, or LPSI, preferably LPSCl, with a particle size of 300-700 nm, such as 300 nm, 400 nm, 500 nm, 600 nm, or 700 nm, etc.

[0085] As an alternative embodiment of the technical solution of the present invention, the mass ratio of the negative electrode active material, binder, sulfide solid electrolyte, and nanofiber conductor material is (10-95):(1-10):(1-50):(1-20), such as 50:10:20:20, 60:2:19:19, 64:2:17:17, 74:2:12:12, 74:2:18:6, 74:2:6:18, 84:2:7:7, 90:2:4:4, etc., and preferably (65-85):(1-5):(10-30):(5-20).

[0086] By further limiting the mass ratio of the negative electrode active material, binder, sulfide solid electrolyte, and nanofiber conductor material, the negative electrode sheet prepared therefrom has both high rate and low expansion performance.

[0087] According to a fourth aspect of the present invention, there is provided a method for preparing the above-mentioned all-solid-state negative electrode sheet, comprising the following steps:

[0088] (a) mixing and stirring a negative electrode active material, a sulfide solid electrolyte and a nanofiber conductor material to obtain a powder material I;

[0089] (b) mixing and stirring the powder material I and the binder to obtain the powder material II;

[0090] The powder material II is heated and kept warm to obtain a fluffy powder material III;

[0091] (c) air-jet-crushing the powder III to obtain a wire-drawing powder IV;

[0092] (d) rolling the powder IV to obtain a negative electrode material film;

[0093] (e) Laminating the current collector and the negative electrode material film and rolling them to obtain an all-solid-state negative electrode sheet.

[0094] The present invention adopts a dry method to prepare an all-solid-state negative electrode sheet, forming more abundant contact sites between the nanofiber conductor material with a high specific surface area and high interwoven dimension three-dimensional network structure and the negative electrode active material particles, providing a smooth ion electron network channel when the negative electrode expands and contracts, improving the cycle and rate performance, and dispersing the volume expansion stress to improve the problem of high silicon electrode sheet cycle cracking. At the same time, the raw materials are easy to obtain, the entire preparation method is simple and easy, and has the feasibility of industrial continuous production.

[0095] As an optional implementation of the technical solution of the present invention, in step (a), the mixing and stirring rotation speed is 300-500 rpm (for example, 300 rpm, 400 rpm or 500 rpm, etc.), and the stirring time is 30-50 min (for example, 30 min, 40 min or 50 min, etc.).

[0096] As an optional implementation of the technical solution of the present invention, in step (b), the mixing and stirring speed is 1000-1500rpm / min (for example, 1000rpm, 1200rpm, 1400rpm or 1500rpm, etc.), and the stirring time is 30-50min (for example, 30min, 40min or 50min, etc.); and / or, the heating and insulation temperature is 60-70℃ (for example, 60℃, 65℃ or 70℃, etc.), and the heating and insulation time is 30-50min (for example, 30min, 40min or 50min, etc.); and / or, the density of powder III is 0.8-1.0g / cm 3 (For example, 0.8 g / cm 3 , 0.9g / cm 3 or 1.0g / cm 3 wait).

[0097] As an alternative embodiment of the technical solution of the present invention, in step (c), during air pulverization, the air pressure is 0.5 - 0.7 MPa (such as 0.5 MPa, 0.6 MPa, or 0.7 MPa, etc.); and / or, the density of powder IV is 0.7 - 0.8 g / cm 3 (such as 0.7 g / cm 3 , 0.72 g / cm 3 , 0.76 g / cm 3 or 0.8 g / cm 3 etc.).

[0098] As an alternative embodiment of the technical solution of the present invention, in step (d), roll pressing and forming includes vertical roll pressing and horizontal roll pressing, and the pressure of roll pressing and forming is 5T.

[0099] For example, for vertical roll pressing of powder IV, powder IV passes through the gap between two hot pressing rolls from top to bottom and is formed under the extrusion of the two hot pressing rolls. The pressure of vertical roll pressing is 3 - 7T (such as 3T, 5T, 6T, or 7T, etc.), the temperature of vertical roll pressing is 90 - 120 °C (such as 90 °C, 100 °C, 110 °C, or 120 °C, etc.), and the gap width between the two hot pressing rolls is 1 - 10 μm (such as 1 μm, 3 μm, 5 μm, 8 μm, or 10 μm, etc.);

[0100] After vertical roll pressing, the powder IV is subjected to horizontal roll pressing. The powder IV passes through the gap between two horizontal rolls in the horizontal direction and is formed under the extrusion of the two horizontal rolls to obtain a negative electrode material film. The pressure of horizontal roll pressing is 3 - 7T (such as 3T, 5T, 6T, or 7T, etc.), and the gap width between the two horizontal rolls is 1 - 10 μm (such as 1 μm, 3 μm, 5 μm, 8 μm, or 10 μm, etc.); the thickness of the negative electrode material film is 60 - 100 μm (such as 60 μm, 70 μm, 80 μm, 90 μm, or 100 μm, etc.).

[0101] As an alternative embodiment of the technical solution of the present invention, in step (e), the negative electrode material film and the current collector (such as copper foil) enter the laminating roll together. Under the extrusion of the laminating roll, the negative electrode material film adheres to the surface of the current collector to obtain a negative electrode plate, whose surface is flat and has no wrinkles, and the thickness can reach 60 - 100 μm (such as 60 μm, 70 μm, 80 μm, 90 μm, or 100 μm, etc.), and the areal density is 84 - 120 g / m 2 (such as 84 g / m 2 , 90 g / m 2 , 100 g / m 2 , 110 g / m 2 or 120 g / m 2 etc.).

[0102] According to the fifth aspect of the present invention, a all-solid-state battery is provided, which includes the all-solid-state negative electrode sheet provided by the third aspect of the present invention or the all-solid-state negative electrode sheet prepared by the preparation method provided by the fourth aspect of the present invention.

[0103] It should be noted that the process of assembling the all-solid-state negative electrode sheet into a solid-state battery needs to be completed in a drying room with a dew point less than -40°C or in a glove box.

[0104] The present invention will be further described in detail below with specific examples and comparative examples.

[0105] Example 1

[0106] This example provides a nanofiber conductor material, which includes a fiber matrix, a first coating layer coated on the surface of the fiber matrix, and a second coating layer dot-coated on the surface of the first coating layer;

[0107] Among them, the fiber matrix is a nanofiber with aldehyde groups on its surface, with an average length of 30 μm and a diameter of 10 - 150 nm; the first coating layer contains conductive metal silver, and the second coating layer contains sulfide solid electrolyte LPSCl. The second coating layer presents local dot coating on the surface of the first coating layer, that is, it does not completely cover the surface of the first coating layer.

[0108] In the nanofiber conductor material, the mass ratio of the fiber matrix, the conductive metal silver in the first coating layer, and the sulfide solid electrolyte LPSCl = 76:12:12.

[0109] The preparation method of the nanofiber conductor material in this example includes the following steps:

[0110] S1. Provide a dispersion liquid containing the fiber matrix: Disperse 76 g of nanofibers into water to obtain a dispersion liquid containing the fiber matrix with a solid content of 10%;

[0111] Provide the raw material for forming the first coating layer: a silver nitrate solution with a concentration of 1 mol / L;

[0112] Provide the raw material for forming the second coating layer: Disperse 12 g of LPSCl in xylene solution to obtain slurry I with a solid content of 80%;

[0113] S2. While stirring, add the dispersion liquid containing the fiber matrix to 111 ml of a silver nitrate solution with a concentration of 1 mol / L. After complete addition, stir at room temperature for 2 h, and then dry in a forced-air drying oven at 80°C for 2 h to form the first coating layer on the surface of the fiber matrix, obtaining fiber-coated material A;

[0114] S3. Mix the fiber coating material A with Slurry I and stir evenly, then ball mill for 3 h at a rotation speed of 1000 rmp. Subsequently, dry it in a vacuum oven with a vacuum degree of -90 Kpa for 2 h at a temperature of 80 °C to obtain the nanofiber conductor material.

[0115] Example 2

[0116] This example provides a nanofiber conductor material and its preparation method. Except that the fiber matrix is a nanofiber with an average length of 10 μm and an aldehyde group on the surface, the structures, preparation methods, and process parameters of the remaining nanofiber conductor materials are the same as those in Example 1.

[0117] Example 3

[0118] This example provides a nanofiber conductor material and its preparation method. Except that in step S1 of the preparation method, the raw material for forming the first coating layer is replaced from silver nitrate solution with 12 g of silver nanoflakes. In step S1 when preparing the dispersion liquid containing the fiber matrix, 76 g of nanofibers are dispersed in water, and the solid content of the fiber matrix is 75% (the main reason for increasing the solid content here is to better achieve the ball milling effect for the dispersion liquid containing the fiber matrix and silver nanoflakes in the subsequent process); and,

[0119] In step S2, add 12 g of silver nanoflakes to the dispersion liquid containing the fiber matrix while stirring, then ball mill for 3 h at a rotation speed of 1000 rmp, and then dry it in a forced-air oven at 80 °C for 2 h to form the first coating layer on the surface of the fiber matrix to obtain the fiber coating material A;

[0120] The remaining preparation methods and process parameters are the same as those in Example 1.

[0121] Example 4

[0122] This example provides a nanofiber conductor material and its preparation method. Except that in the nanofiber conductor material of Example 1, the mass ratio of the fiber matrix, the conductive metal silver in the first coating layer, and the sulfide solid electrolyte LPSCl is adjusted from 76:12:12 to 76:18:6. At the same time, in the preparation method, the dosage of silver nitrate in step S2 is adjusted from 111 ml to 166 ml, the mass of LPSCl in the formation of Slurry I in step S1 is adjusted from 12 g to 6 g, and the solid content of Slurry I remains unchanged at 80%. The structures, preparation methods, and process parameters of the remaining nanofiber conductor materials are the same as those in Example 1.

[0123] Example 5

[0124] This embodiment provides a nanofiber conductor material and a preparation method thereof. Except that in the nanofiber conductor material of Embodiment 1, the mass ratio of the fiber matrix, the conductive metal silver and the sulfide solid electrolyte LPSCl in the first coating layer is adjusted from 76:12:12 to 76:6:18. At the same time, in the preparation method, the dosage of silver nitrate in step S2 is adjusted from 111 ml to 55 ml, and the mass of LPSCl in the slurry Ⅰ formed in step S1 is adjusted from 12 g to 18 g. The structures, preparation methods and process parameters of the remaining nanofiber conductor materials are the same as those in Embodiment 1.

[0125] Comparative Example 1

[0126] This comparative example provides a nanofiber conductor material, comprising a fiber matrix and a first coating layer coated on the surface of the fiber matrix;

[0127] Among them, the fiber matrix is a nanofiber with aldehyde groups on the surface, its average length is 30 μm, and its diameter is 10 - 150 nm; the first coating layer contains conductive metal silver;

[0128] In the nanofiber conductor material, the mass ratio of the fiber matrix to the conductive metal silver in the first coating layer = 76:24.

[0129] The preparation method of the nanofiber conductor material in this comparative example includes the following steps:

[0130] S1. Provide a dispersion liquid containing the fiber matrix: Disperse 76 g of nanofibers into water to obtain a dispersion liquid containing the fiber matrix with a solid content of 10%;

[0131] Provide raw materials for forming the first coating layer: a silver nitrate solution with a concentration of 1 mol / L;

[0132] S2. Add the dispersion liquid containing the fiber matrix to 222 ml of a silver nitrate solution with a concentration of 1 mol / L while stirring. After complete addition, stir at room temperature for 2 h, and then dry at 80 °C in a forced-air drying oven for 2 h to form the first coating layer on the surface of the fiber matrix, obtaining the nanofiber conductor material.

[0133] Comparative Example 2

[0134] This comparative example provides a nanofiber conductor material and a preparation method thereof. Except that in step S1 of the preparation method of Embodiment 3, the raw material for forming the first coating layer is replaced from 12 g of nano silver powder with 12 g of conductive carbon (SP), the remaining preparation methods and process parameters are the same as those in Embodiment 3.

[0135] Example 6

[0136] This embodiment provides an all-solid-state negative electrode sheet, which includes a current collector and a negative electrode material film disposed on the surface of the current collector. The raw materials used to form the negative electrode material film include: a negative electrode active material, a binder, a sulfide solid electrolyte, and the nanofiber conductor material provided in Embodiment 1, and do not include other conductive agents.

[0137] Among them, the current collector is a copper foil, the negative electrode active material is silicon oxide and graphite (mass ratio 8:2), the binder is PTFE, the sulfide solid electrolyte is LPSCl, and the mass ratio of the negative electrode active material, binder, sulfide solid electrolyte, and nanofiber conductor material is 74:2:12:12.

[0138] The preparation method of the all-solid-state negative electrode sheet in this embodiment includes the following steps:

[0139] (a) Put 74 g of negative electrode active material, 12 g of sulfide solid electrolyte, and 12 g of nanofiber conductor material into a dry-mixing blender and mix and stir at a rotation speed of 300 - 500 rpm / min for 30 min to obtain powder I;

[0140] (b) Add 2 g of binder PTFE to powder I and mix and stir at a rotation speed of 1000 - 1500 rpm / min for 30 min to obtain powder II;

[0141] Put powder II into an oven at 60 °C for heating and keep it warm for 30 min to make the whole powder fluffy, and obtain powder III with a fluffy density of 0.9 g / cm 3 ;

[0142] (c) Put powder III into a jet mill, with an air flow pressure of 0.5 MPa. Under the impact of the air flow, powder III changes from a fluffy state to a wire-drawing state, and obtain powder IV with a wire-drawing density of 0.76 g / cm 3 ;

[0143] (d) Perform vertical roll pressing on powder IV. Powder IV passes through the gap between two hot pressing rollers from top to bottom and forms under the extrusion of the two hot pressing rollers. The pressure of vertical roll pressing is 5 T, the temperature of vertical roll pressing is 110 °C, and the gap width between the two hot pressing rollers is 1 μm;

[0144] Perform horizontal roll pressing on the vertically roll-pressed powder IV. Powder IV passes through the gap between two horizontal rollers in the horizontal direction and forms under the extrusion of the two horizontal rollers. The pressure of horizontal roll pressing is 5 T, the gap width between the two horizontal rollers is 1 μm, and obtain a negative electrode material film with a film thickness of 70 μm;

[0145] (e) Feed the negative electrode material diaphragm and copper foil (with a thickness of 6 μm) into the laminating roller together. Under the extrusion of the laminating roller, the negative electrode material diaphragm adheres to the surface of the copper foil, obtaining a fully solid negative electrode sheet with a flat surface and no wrinkles. The thickness can reach 60 μm, and the areal density is 84 g / cm 2 .

[0146] Example 7

[0147] This example provides a fully solid negative electrode sheet and its preparation method. In the negative electrode material diaphragm, except for using the nanofiber conductor material provided in Example 2, the other electrode structures, compositions, and preparation methods are the same as those in Example 6.

[0148] Example 8

[0149] This example provides a fully solid negative electrode sheet and its preparation method. In the negative electrode material diaphragm, except for using the nanofiber conductor material provided in Example 3, the other electrode structures, compositions, and preparation methods are the same as those in Example 6.

[0150] Example 9

[0151] This example provides a fully solid negative electrode sheet and its preparation method. In the negative electrode material diaphragm, except for using the nanofiber conductor material provided in Example 4, the other electrode structures, compositions, and preparation methods are the same as those in Example 6.

[0152] Example 10

[0153] This example provides a fully solid negative electrode sheet and its preparation method. In the negative electrode material diaphragm, except for using the nanofiber conductor material provided in Example 5, the other electrode structures, compositions, and preparation methods are the same as those in Example 6.

[0154] Example 11

[0155] This example provides a fully solid negative electrode sheet. Except for adjusting the mass ratio of the negative electrode active material, binder, sulfide solid electrolyte, and nanofiber conductor material in Example 6 from 74:2:12:12 to 84:2:7:7, the other electrode structures and compositions are the same as those in Example 6.

[0156] The preparation method of the fully solid negative electrode sheet in this example, except for correspondingly adjusting the masses of the negative electrode active material, binder, sulfide solid electrolyte, and nanofiber conductor material in steps (a) and (b), that is, 84 g of the negative electrode active material, 7 g of the sulfide solid electrolyte, 7 g of the nanofiber conductor material, and 2 g of the binder, while keeping the areal capacity unchanged, the other steps and process parameters are the same as those in Example 6.

[0157] Example 12

[0158] This embodiment provides a all-solid-state negative electrode sheet. Except that the mass ratio of the negative electrode active material, binder, sulfide solid electrolyte and nanofiber conductor material in Example 6 is adjusted from 74:2:12:12 to 64:2:17:17, the rest of the electrode sheet structure and composition are the same as those in Example 6.

[0159] The preparation method of the all-solid-state negative electrode sheet in this embodiment. Except that the masses of the negative electrode active material, binder, sulfide solid electrolyte and nanofiber conductor material are adjusted correspondingly in steps (a) and (b), that is, 64 g of negative electrode active material, 17 g of sulfide solid electrolyte, 17 g of nanofiber conductor material and 2 g of binder, the rest of the steps and process parameters are the same as those in Example 6.

[0160] Example 13

[0161] This embodiment provides a all-solid-state negative electrode sheet. Except that the mass ratio of the negative electrode active material, binder, sulfide solid electrolyte and nanofiber conductor material in Example 6 is adjusted from 74:2:12:12 to 74:2:18:6, the rest of the electrode sheet structure and composition are the same as those in Example 6.

[0162] The preparation method of the all-solid-state negative electrode sheet in this embodiment. Except that the masses of the negative electrode active material, binder, sulfide solid electrolyte and nanofiber conductor material are adjusted correspondingly in steps (a) and (b), that is, 74 g of negative electrode active material, 18 g of sulfide solid electrolyte, 6 g of nanofiber conductor material and 2 g of binder, the rest of the steps and process parameters are the same as those in Example 6.

[0163] Example 14

[0164] This embodiment provides a all-solid-state negative electrode sheet. Except that the mass ratio of the negative electrode active material, binder, sulfide solid electrolyte and nanofiber conductor material in Example 6 is adjusted from 74:2:12:12 to 74:2:6:18, the rest of the electrode sheet structure and composition are the same as those in Example 6.

[0165] The preparation method of the all-solid-state negative electrode sheet in this embodiment. Except that the masses of the negative electrode active material, binder, sulfide solid electrolyte and nanofiber conductor material are adjusted correspondingly in steps (a) and (b), that is, 74 g of negative electrode active material, 6 g of sulfide solid electrolyte, 18 g of nanofiber conductor material and 2 g of binder, the rest of the steps and process parameters are the same as those in Example 6.

[0166] Comparative Example 3

[0167] This comparative example provides a all-solid-state negative electrode sheet and its preparation method. Except that the nanofiber conductor material provided in Comparative Example 1 is used in the negative electrode material film, the rest of the electrode sheet structure, composition and preparation method are the same as those in Example 6.

[0168] Comparative Example 4

[0169] This comparative example provides an all-solid-state negative electrode sheet and a preparation method thereof. Except for using the nanofiber conductor material provided in Comparative Example 2 in the negative electrode material film, the rest of the electrode sheet structure, composition, and preparation method are the same as those in Example 6.

[0170] Comparative Example 5

[0171] This comparative example provides an all-solid-state negative electrode sheet and a preparation method thereof. Except for replacing the nanofiber conductor material provided in Example 1 of Example 6 with an equal amount of the uncoated fiber matrix in Example 1 (i.e., nanofibers with aldehyde groups on the surface), and at the same time adjusting step (a) of Example 6 to: putting 74 g of negative electrode active material, 12 g of sulfide solid electrolyte, 2 g of conductive agent (VGCF), and 10 g of uncoated fiber matrix into a dry mixing blender and mixing and stirring at a rotation speed of 300 - 500 rpm / min for 30 min to obtain powder I, the rest of the electrode sheet structure, composition, and preparation method are the same as those in Example 6.

[0172] Comparative Example 6

[0173] This comparative example provides an all-solid-state negative electrode sheet and a preparation method thereof. Except for replacing the nanofiber conductor material provided in Example 1 of Example 6 with an equal amount of vapor-grown carbon fiber (VGCF) with an average length of 10 μm and an average diameter of 300 nm, the rest of the electrode sheet structure, composition, and preparation method are the same as those in Example 6.

[0174] Comparative Example 7

[0175] This comparative example provides an all-solid-state negative electrode sheet and a preparation method thereof. Except for changing the method of preparing the negative electrode sheet in Example 6 from a dry method to a conventional liquid-phase dispersion method, changing the binder PTFE to PVDF, and using toluene as the solvent, with the proportions of each part remaining unchanged, it specifically includes the following steps:

[0176] Disperse 74 g of negative electrode active material, 2 g of binder (PVDF), 12 g of sulfide solid electrolyte, and 12 g of nanofiber conductor material in toluene according to a mass ratio of 74:2:12:12, with a mechanical dispersion rotation speed of 2000 rpm, a vacuum degree of -90 kPa, and a time of 2 h, controlling the solid content to be 50%, and then scrape and coat it on a copper foil with a thickness of 6 μm, controlling the areal density after drying to be 84 g / cm 2 , and the drying conditions are a vacuum of -90 kPa, a temperature of 80 °C, and a time of 4 h. Finally, roll the electrode sheet to 60 μm to obtain an all-solid-state negative electrode sheet.

[0177] Comparative Example 8

[0178] This comparative example provides an all-solid-state negative electrode sheet. Except that the mass ratio of the negative active material, binder, sulfide solid electrolyte, and nanofiber conductor material in Example 10 is adjusted from 74:2:12:12 to 74:2:0:24, the rest of the electrode sheet structure and composition are the same as those in Example 10.

[0179] The preparation method of the all-solid-state negative electrode sheet in this comparative example, except that the masses of the negative active material, binder, sulfide solid electrolyte, and nanofiber conductor material are correspondingly adjusted in steps (a) and (b), that is, 74 g of negative active material, 0 g of sulfide solid electrolyte, 24 g of nanofiber conductor material, and 2 g of binder, the rest of the steps and process parameters are the same as those in Example 10.

[0180] In order to compare the technical effects of the above examples and comparative examples, the following experimental examples are specially set up.

[0181] Experimental Example 1

[0182] Taking Example 1 as an example, the specific morphologies of the fiber coating material A (silver-coated on the fiber matrix surface) and the nanofiber conductor material are detected, as shown in Figure 1 and Figure 2 respectively. It can be seen from Figure 2 that the prepared nanofiber conductor material presents a three-dimensional network structure with a high interweaving dimension.

[0183] Experimental Example 2

[0184] The all-solid-state negative electrode sheets prepared in each example and comparative example are made into all-solid-state (laminated) batteries. The specific steps are as follows:

[0185] (a) Preparation of the positive electrode sheet: NCM811, conductive agents (SP and VGCF, mass ratio 4:1), sulfide electrolyte (LPSCl), and binder (PVDF) are dispersed in NMP according to the ratio of 70:3:25:2, and then coated on an aluminum foil and dried to obtain a positive electrode sheet with a surface density of 520 g / m 2 , and a compaction density of 3.4 g / cm 3 ;

[0186] (b) Preparation of the negative electrode sheet: The all-solid-state negative electrode sheets prepared in each example and comparative example;

[0187] (c) Preparation of the solid electrolyte membrane: The sulfide electrolyte and the binder are dispersed in a toluene solution according to the ratio of 90:10, with a solid content of 30%. Then it is coated on a PET film, and after vacuum drying, the PET layer is peeled off to obtain a solid electrolyte membrane with a thickness of 20 μm;

[0188] (d) Battery assembly: The positive electrode sheet, solid electrolyte membrane, and negative electrode sheet are cut into electrode sheets with dimensions of 50 mm × 50 mm, 54 mm × 54 mm, and 52 mm × 52 mm respectively. Subsequently, they are stacked into a laminated sheet with a capacity of 3 AH (12 layers of positive electrodes). The obtained bare battery cell is hot-pressed. The hot-pressing process parameters are: temperature of 80 °C, pressure of 1000 KG, and holding pressure time of 60 s. Finally, the hot-pressed battery cell is assembled and encapsulated with an aluminum-plastic film to obtain a all-solid-state battery.

[0189] The electrochemical performance of the all-solid-state batteries prepared in the examples and comparative examples (3 parallel battery samples are set for each group of examples and comparative examples) was tested as follows:

[0190] (1) Cycling test: Charge and discharge rate of 0.5C, voltage of 2.5V - 4.3V, charging method is constant current and constant voltage, cut-off current of 0.05C, cycle until the capacity decays to 80% of the initial capacity, and the cycle life is denoted as D (unit: cycle);

[0191] (2) Rate discharge test after 50 cycles: After the battery is cycled 50 times, it is charged to full with constant current and constant voltage at 0.5C, cut-off current of 0.05C, cut-off voltage of 4.3V, and then discharged uniformly at 4C. The discharge capacity is denoted as K (unit: AH), the discharge capacity of the first cycle at 0.5C is denoted as C0 (unit: AH), and the 4C discharge retention rate is denoted as F, F = K / C0 × 100%;

[0192] (3) Charge and discharge test after 60 cycles: After the battery is cycled 60 times, it is charged to full with constant current and constant voltage at 4C, cut-off current of 0.05C, cut-off voltage of 4.3V. The charging constant current ratio is denoted as Q, and then discharged to 2.5V at 0.5C. The discharge capacity is denoted as C60, and the discharge retention rate is denoted as F2, F2 = C60 / C0 × 100%;

[0193] (4) Battery cell thickness change test: The thickness of the battery cell under a pressure of 200 kg in the dilatometer is denoted as E, the thickness after full charge in the second cycle is denoted as E1, the thickness after full charge in the 51st cycle is denoted as E2, and the thickness after full charge when the capacity decays to 80% of the initial capacity is denoted as E3. The initial expansion change rate H1 = (E1 - E) / E, the expansion change rate in the 51st cycle H2 = (E2 - E) / E, and the change rate when reduced to 80% of the initial capacity is denoted as H3, H3 = (E3 - E) / E;

[0194] (5) Battery cell internal resistance (DCR) test: After the battery cell is cycled 52 times, it is first charged to 0.5C0 at a rate of 0.1C, and the voltage V1 at this moment is recorded after leaving it for 30 min. Then it is charged at a rate of 2C for 10 s to obtain the voltage V2 at the 10th s. The internal resistance is denoted as R, R = (V2 - V1) / 2C;

[0195] (6) After individual battery cells are cycled 70 times and fully charged, they are disassembled to observe the appearance of the negative electrode surface.

[0196] The test results are shown in Tables 1 and 2.

[0197] Table 1

[0198]

[0199]

[0200] Table 2

[0201]

[0202]

[0203] For each item of Examples 6 - 14, the data is better than that of Comparative Example 6, indicating that the stability and rate performance of the nanofiber conductor material (nanofiber hybrid conductor) are stronger than those of conductive carbon.

[0204] Comparing Example 6 and Example 7, the former has higher F, D, and Q, and lower H2, H3, and R, indicating that the high aspect ratio of the nanofiber conductor material is beneficial for better ion - electron conduction of the negative electrode during volume change, improving swelling, thereby reducing impedance and enhancing rate performance and cycle life.

[0205] Comparing Example 6 and Example 8, the latter has significantly lower Q and D, indicating that the method of ball - milling and coating silver is less stable than the method of in - situ replacement silver plating, probably because silver falls off the nanofibers during subsequent cycles.

[0206] Comparing Example 6 with Examples 11 and 12 shows that the proportion of the nanofiber conductor material in the negative electrode should not be too much. Too much may damage the toughness of the negative electrode sheet, and too little may not achieve the three - dimensional effect.

[0207] Comparing Example 6 with Examples 13 and 14 shows that the ratio of the amount of the nanofiber conductor material to the amount of the sulfide solid electrolyte is preferably balanced. If there is too much nanofiber conductor material, the electronic conductivity is good and the rate performance is good, but with the progress of cycling, the ionic conductance transmission gradually deteriorates; if there is too much sulfide solid electrolyte, it may shield part of the electronic path, and with the volume expansion and contraction, the contact sites between the negative electrode active material particles and silver gradually decrease, affecting the cycle performance.

[0208] Comparing Example 6 with Comparative Examples 4 and 5, since nanofibers are used in both, the swelling rate has been correspondingly improved. From the perspective of capacity performance, rate performance, and cycle life, it shows that the silver in the first coating layer on the negative electrode side has higher stability for the sulfide solid electrolyte than carbon - based conductive agents.

[0209] Comparing Example 6 with Comparative Example 7, all parameters of Comparative Example 7 are poor, indicating that PVDF may be unstable at the negative electrode. At the same time, high-speed liquid-phase dispersion may lead to uneven dispersion of the nanofiber mixed conductor or damage the structure, failing to achieve a three-dimensional network of high-latitude interweaving.

[0210] Comparing Example 10 with the comparative example shows that the second coating layer of nanofibers can firmly form a continuous phase for conducting ions with three-dimensional interweaving, so as to better form better contact sites with the active material in subsequent cycles, which is beneficial to the improvement of cycle life.

[0211] In addition, after the full charge and disassembly of the battery cells prepared in Example 6 and Comparative Example 6 after 70 cycles, they are respectively as Figure 3 and Figure 4 shown. It can be seen that there is lithium deposition around the negative electrode sheet of Comparative Example 6, and the large area is prone to cracking, which may be caused by uneven internal stress due to volume change. There is no such situation in Example 6, indicating that the nanofiber conductor material has the effect of suppressing expansion and improving the cracking of the negative electrode sheet with a high silicon content.

[0212] The above data also prove that the high-latitude and high-interweaving network structure formed in the negative electrode sheet has the advantages of electrochemical stability, suppressing expansion, improving rate performance, and dispersing the stress of volume expansion and contraction to improve the cracking of the negative electrode sheet.

[0213] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention are within the scope of the claims of the present invention awaiting approval.

Claims

1. A nanofiber conductor material, characterized in that: It comprises a fiber matrix, a first coating layer coated on the surface of the fiber matrix, and a second coating layer coated on the surface of the first coating layer in a dotted manner; Wherein, the first coating layer comprises a metal and / or metal oxide electronic conductor; and the second coating layer comprises a sulfide solid electrolyte.

2. The nanofiber conductor material according to claim 1, characterized in that: The fiber matrix has a length of 10-300 μm and a diameter of 10-150 nm; And / or, the fiber matrix surface carries one or more functional groups of carboxyl, hydroxyl or aldehyde; and / or, the metal in the first coating layer includes at least one of silver, titanium, manganese or copper; and / or, the metal oxide electronic conductor in the first coating layer comprises at least one of manganese oxide or tin oxide; And / or, the sulfide electrolyte in the second coating layer is attached to the surface of the first coating layer in a dot-like or island-like form, and the sulfide electrolyte includes at least one of LPSCl, LPSBr or LPSI.

3. The nanofiber conductor material according to claim 1 or 2, characterized in that: In the nanofiber conductor material, the mass ratio of the fiber matrix, the metal and / or metal oxide electronic conductor, and the sulfide solid electrolyte is (70-90): (5-30): (1-15).

4. The method for preparing the nanofiber conductor material according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1 provides a dispersion containing a fiber matrix, a raw material for forming a first coating layer and a raw material for forming a second coating layer; S2. The dispersion containing the fiber matrix and the raw material for forming the first coating layer are mixed and stirred and optionally ground, and then dried to form a first coating layer on the surface of the fiber matrix to obtain a fiber coating material A; S3. The fiber coating material A is mixed with a raw material for forming a second coating layer, ground, and then dried to form a second coating layer on the surface of the first coating layer to obtain a nanofiber conductor material.

5. The method for preparing the nanofiber conductor material according to claim 4, characterized in that: In step S1, the dispersion liquid containing the fiber matrix is ​​mainly made of the fiber matrix and water, and the solid content of the fiber matrix in the dispersion liquid containing the fiber matrix is ​​1%-20%; and / or, the raw material for forming the first coating layer includes at least one of a metal salt solution, a metal powder and / or a metal oxide powder; And / or, the raw material for forming the second coating layer is a sulfide electrolyte, or a slurry B made of a sulfide electrolyte and a solvent, and the solid content of the sulfide electrolyte in the slurry B is 60-90%; and / or, in step S2, the mixing and stirring time is 2-3 hours; and / or, the grinding is ball milling, the ball milling time is 1-5 hours, and the ball milling speed is 500-1500 rpm; and / or, the drying temperature is 70-90° C., and the drying time is 2-4 hours; And / or, in step S3, grinding is ball milling, the ball milling time is 2-5h, and the ball milling speed is 500-1500rmp; and / or, the drying is vacuum drying, the drying temperature is 70-90°C, the drying time is 2-4h, and the vacuum degree is -85 to -95kPa.

6. An all-solid-state negative electrode sheet, characterized in that: It includes a current collector and a negative electrode material film arranged on the surface of the current collector, and the raw materials used to form the negative electrode material film include: negative electrode active material, adhesive, sulfide solid electrolyte and nanofiber conductor material, and do not include conductive agent; Wherein, the nanofiber conductor material is the nanofiber conductor material described in any one of claims 1-3 or the nanofiber conductor material prepared by the preparation method described in claim 4 or 5.

7. The all-solid-state negative electrode sheet according to claim 6, characterized in that: The negative electrode active material includes one or more of silicon oxygen, silicon carbon, graphite or pure silicon; And / or, the adhesive comprises one or more of PTFE, PEO, PVD or SBR; And / or, the sulfide solid electrolyte includes at least one of LPSCl, LPSBr or LPSI; And / or, the mass ratio of the negative electrode active material, the binder, the sulfide solid electrolyte and the nanofiber conductor material is (10-95):(1-10):(1-50):(1-20), preferably (65-85):(1-5):(10-30):(5-20).

8. The method for preparing the all-solid-state negative electrode sheet according to claim 6 or 7, characterized in that: The following steps are involved: (a) mixing and stirring a negative electrode active material, a sulfide solid electrolyte and a nanofiber conductor material to obtain a powder material I; (b) mixing and stirring the powder material I and the binder to obtain the powder material II; The powder material II is heated and kept warm to obtain a fluffy powder material III; (c) air-jet-crushing the powder III to obtain a wire-drawing powder IV; (d) rolling the powder IV to obtain a negative electrode material film; (e) Laminating the current collector and the negative electrode material film and rolling them to obtain an all-solid-state negative electrode sheet.

9. The method for preparing an all-solid-state negative electrode sheet according to claim 8, characterized in that: In step (a), the mixing speed is 300-500 rpm / min, and the mixing time is 30-50 min; and / or, in step (b), the mixing speed is 1000-1500 rpm / min, and the mixing time is 30-50 min; and / or, the heating and insulation temperature is 60-70°C, and the heating and insulation time is 30-50 min; and / or, the density of powder III is 0.8-1.0 g / cm 3 ; and / or, in step (c), the air flow pressure during air flow pulverization is 0.5-0.7 MPa; and / or, the density of powder IV is 0.7-0.8 g / cm 3 ; And / or, in step (d), the roll forming includes vertical roll forming and horizontal roll forming, and the pressure of the roll forming is 3-7T; And / or, in step (e), the thickness of the all-solid-state negative electrode sheet is 60-100 μm, and the surface density is 84-120 g / m 2 .

10. An all-solid-state battery, characterized in that: It includes the all-solid-state negative electrode sheet as described in claim 6 or 7 or the all-solid-state negative electrode sheet prepared by the preparation method as described in claim 8 or 9.

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