Silicon-based negative electrode material and preparation method thereof, negative electrode plate and all-solid-state battery

Abstract

The invention relates to the technical field of solid-state batteries, and discloses a silicon-based negative electrode material and a preparation method thereof, a negative electrode plate and an all-solid-state battery. The silicon-based negative electrode material comprises a silicon-based substrate, an inner coating layer arranged on the silicon-based substrate, and an outer coating layer arranged on the inner coating layer, wherein the Young modulus of the silicon-based substrate is recorded as A, the Young modulus of the inner coating layer is recorded as B, and the Young modulus of the outer coating layer is recorded as C; wherein A, B and C meet a relational expression Bgt; agt; c; the Young modulus difference degree of the inner coating layer and the silicon-based substrate is defined as alpha, and alpha is equal to (B-A) / A; the Young modulus difference degree of the outer coating layer and the silicon-based substrate is defined as beta, and beta is equal to (C-A) / A; alpha and beta satisfy 0 < alpha < 4 and-1 < beta < 0. The silicon-based negative electrode material provided by the invention can stabilize a solid-solid interface, improve the interface compatibility, improve the cycling stability and rate capability of an all-solid-state battery while improving the lithium ion transmission rate, and is suitable for popularization.

Description

Technical Field

[0001] The present invention relates to the technical field of solid-state batteries, and in particular to a silicon-based negative electrode material and a preparation method thereof, a negative electrode pole piece and an all-solid-state battery. Background Art

[0002] With the rapid development of portable electronic devices, electric vehicles and other products, the market has put forward higher and higher requirements on the performance of batteries such as energy density, safety and cycle life. Traditional lithium-ion batteries have safety risks such as thermal runaway, fire and explosion due to the use of flammable liquid electrolytes, and their energy density is close to the theoretical limit. All-solid-state batteries use solid electrolytes to replace flammable liquid electrolytes, and are expected to become the key technology for the next generation of energy storage devices with higher safety and energy density. Among them, sulfide all-solid-state batteries have become an important development direction because their ionic conductivity is comparable to that of liquid electrolytes and they are easy to process.

[0003] Silicon-based negative electrode materials are widely used in liquid battery systems due to their high specific capacity. However, the performance of silicon-based negative electrode materials in sulfide all-solid-state battery systems is much lower than that of liquid systems. This is mainly because: 1. During the cycle of all-solid-state batteries, silicon-based negative electrode materials will undergo huge volume changes due to the insertion and extraction of lithium ions. The huge internal stress released by this will easily lead to pulverization and cracking of silicon-based negative electrode materials and sulfide solid electrolytes with low mechanical strength, thereby causing solid-solid interface contact failure, resulting in inactivation of negative electrode active materials and solid electrolytes, and degradation of electrical performance; 2. Rigid silicon-based negative electrode materials and flexible sulfide solid electrolytes have poor compatibility. The composite pole pieces of the two have the problems of high processing difficulty, low pole piece density, and small effective contact area; these problems will cause the internal resistance of all-solid-state batteries to increase sharply, and the cycle performance and rate performance will drop significantly; 3. There is also a problem of loose solid-solid contact between sulfide solid electrolytes and silicon-based negative electrode materials during static and dynamic evolution, which aggravates the battery performance degradation.

[0004] Surface modification of silicon-based negative electrode materials is an effective approach. A reasonable coating layer can improve the physical contact of the interface, the stability of the interface electrochemistry and ion transmission. CN118763202A discloses a silicon-based negative electrode and its preparation method, and an all-solid-state battery. By coating the surface of the silicon material with a lithium-conducting polymer layer, the lithium ion transmission rate between the sulfide electrolyte and the silicon-based material is accelerated, and the lithium ion transmission kinetics are significantly improved. However, this technical solution mainly focuses on improving the lithium ion transmission rate at the solid-solid interface between the silicon-based negative electrode material and the sulfide solid electrolyte, and does not solve the problem of stress distribution at the interface and the problem of instability of the mechanical structure of the interface. This may cause the interface to rupture under high stress conditions, affecting the cycle stability and safety of the battery.

[0005] Therefore, at this stage, there is an urgent need to develop a silicon-based negative electrode material, a negative electrode sheet and a preparation method thereof that can improve the lithium ion transmission rate while also improving the cycle stability and rate performance of all-solid-state batteries. Summary of the invention

[0006] The purpose of the present invention is to solve the problems of poor compatibility of silicon-based negative electrode materials with sulfide solid electrolytes, uneven interface stress distribution, poor stability of interface mechanical structure, easy rupture, poor tightness of solid-solid interface contact when prepared into pole pieces, and to provide a silicon-based negative electrode material, a negative electrode pole piece and a preparation method thereof, and an all-solid-state battery.

[0007] In order to achieve the above-mentioned object, a first aspect of the present invention provides a silicon-based negative electrode material, wherein the silicon-based negative electrode material comprises a silicon-based substrate, an inner coating layer arranged on the silicon-based substrate, and an outer coating layer arranged on the inner coating layer;

[0008] Among them, the Young's modulus of the silicon-based substrate is recorded as A, the Young's modulus of the inner coating layer is recorded as B, and the Young's modulus of the outer coating layer is recorded as C; wherein A, B, and C satisfy the relationship B>A>C; the difference in Young's modulus between the inner coating layer and the silicon-based substrate is defined as α, α=(BA) / A; the difference in Young's modulus between the outer coating layer and the silicon-based substrate is defined as β, β=(CA) / A; α, β satisfy, 0<α<4, -1<β<0.

[0009] A second aspect of the present invention provides a method for preparing a silicon-based negative electrode material, wherein the method comprises the following steps:

[0010] (1) mixing a silicon-based substrate, an inner-conducting electron medium, an inner-conducting ion medium or an inner-conducting ion medium precursor with a first solvent, and stirring to obtain a first dispersion;

[0011] (2) removing the first solvent in the first dispersion and performing a first heat treatment to obtain an intermediate I having an inner coating layer formed on a silicon-based substrate;

[0012] (3) mixing the intermediate I, the external electron-conducting medium, the external ion-conducting medium or the external ion-conducting medium precursor with a second solvent, and stirring to obtain a second dispersion;

[0013] (4) After removing the second solvent in the second dispersion, a second heat treatment is performed to obtain a silicon-based negative electrode material coated with an inner coating layer and an outer coating layer.

[0014] The third aspect of the present invention provides a negative electrode plate, wherein the negative electrode plate comprises the silicon-based negative electrode material described in the first aspect of the present invention or the silicon-based negative electrode material prepared by the preparation method described in the second aspect of the present invention.

[0015] The fourth aspect of the present invention provides an all-solid-state battery, wherein the all-solid-state battery comprises the negative electrode plate described in the third aspect of the present invention.

[0016] Through the above technical solution, the beneficial technical effects achieved by the present invention are as follows:

[0017] 1) The silicon-based negative electrode material provided by the present invention can improve the lithium ion transmission rate between the interface of the silicon-based negative electrode material and the sulfide solid electrolyte by controlling the difference in Young's modulus between the inner coating layer and the silicon-based substrate and the difference in Young's modulus between the outer coating layer and the silicon-based substrate, and can also increase the contact area and affinity between the interface of the silicon-based negative electrode material and the sulfide solid electrolyte. While enhancing the solid-solid interface contact tightness, the stress is slowly released from the inside to the outside, ensuring that the stress is uniformly transferred between the silicon-based negative electrode material and the sulfide solid electrolyte, and reducing the risk of interface rupture under high stress conditions, thereby solving the problems of structural damage and cracks caused by uneven interface stress distribution between the two during the cycle process, which are ignored in the prior art when the problem of insufficient lithium ion transmission at the interface of the silicon negative electrode material is considered alone, and significantly improving the cycle performance and rate performance of the all-solid-state battery;

[0018] 2) The negative electrode plate provided by the present invention improves the processability and ductility of the plate by adding a flexible solid electrolyte additive with a lower Young's modulus than that of the sulfide solid electrolyte, so that the silicon-based negative electrode material and the sulfide solid electrolyte can be further closely contacted, and at the same time solves the problem of decreased ion conductivity of the plate caused by the use of excessive binder, which can reduce the internal resistance of the all-solid-state battery, help to further optimize the stress distribution at the interface, and reduce the risk of interface rupture under high stress conditions, thereby improving the rate performance and cycle life of the all-solid-state battery;

[0019] 3) The all-solid-state battery provided by the present invention has the advantages of good electrical performance, strong cycle stability and high safety, and is suitable for industrial promotion;

[0020] 4) The technical solution provided by the present invention, in the field of solid-state battery technology, by changing the Young's modulus and introducing a flexible electrolyte additive at the pole piece end, the closest contact of the solid-solid interface is achieved; this can not only increase the contact area of ​​the solid-solid interface, but also optimize the stress distribution at the interface, thereby improving the cycle stability and safety of the battery, and meeting the demand for high-performance batteries in the field of solid-state battery technology; in the field of interface engineering technology, the present invention provides a new interface modification method, that is, by adjusting the Young's modulus and introducing a flexible additive, the closest contact of the interface is achieved. This method can not only be applied to the interface modification between silicon-based negative electrode materials and sulfide solid electrolytes, but can also be extended to other solid-state battery systems, such as the interface modification between lithium-based negative electrode materials and oxide solid electrolytes, thereby promoting the development of interface engineering technology. In the field of materials science, the technical solution of adjusting the Young's modulus and introducing a flexible additive provided by the present invention provides a new idea for the design and synthesis of new materials. Through the technical solution provided by the present invention, the mechanical properties and electrochemical properties at the interface can be optimized, thereby developing new high-performance electrode materials and solid electrolyte materials, meeting the demand for new materials in the field of materials science. In general, the technical solution provided by the present invention has broad application prospects in application fields such as solid-state battery technology, interface engineering technology, and material science, and is expected to promote the development and progress of related technologies. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is the SEM image of silicon-based negative electrode material C1;

[0022] Figure 2 is a cross-sectional SEM image of the negative electrode piece PC1;

[0023] Figure 3 This is the first cycle charge and discharge curve of the all-solid-state battery made using the negative electrode PC1;

[0024] Figure 4 This is the rate and cycle performance diagram of the all-solid-state battery made using the negative electrode piece PC1. DETAILED DESCRIPTION

[0025] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0026] A first aspect of the present invention provides a silicon-based negative electrode material, wherein the material comprises a silicon-based substrate, an inner coating layer disposed on the silicon-based substrate, and an outer coating layer disposed on the inner coating layer;

[0027] Among them, the Young's modulus of the silicon-based substrate is recorded as A, the Young's modulus of the inner coating layer is recorded as B, and the Young's modulus of the outer coating layer is recorded as C; wherein A, B, and C satisfy the relationship B>A>C; the difference in Young's modulus between the inner coating layer and the silicon-based substrate is defined as α, α=(BA) / A; the difference in Young's modulus between the outer coating layer and the silicon-based substrate is defined as β, β=(CA) / A; α, β satisfy, 0<α<4, -1<β<0.

[0028] In a preferred embodiment of the present invention, the Young's modulus A of the silicon-based substrate is 2-80 GPa, preferably 5-50 GPa; the Young's modulus B of the inner coating layer is 20-160 GPa, preferably 50-135 GPa; and the Young's modulus C of the outer coating layer is 0.5-30 GPa, preferably 5-25 GPa.

[0029] Among them, in the present invention, the unit of Young's modulus is GPa, which is measured by AFM (atomic force microscope). The inventors of the present invention have found through research that when the Young's modulus of the silicon-based substrate, the inner coating layer and the outer coating layer satisfy B>A>C, 0<α<4, -1<β<0, on the one hand, it can inhibit the outward expansion of the silicon-based substrate, avoid surface cracks caused by outward expansion, and promote the formation of a stable interface layer; on the other hand, it can play a role in mechanical transition, so that the silicon-based negative electrode material transitions from a rigid interface to a flexible interface, which is conducive to the uniform release of stress and maintaining the stability of the interface.

[0030] In a preferred embodiment of the present invention, the α satisfies, 0.5≤α≤3.8; and the β satisfies, -0.8≤β≤-0.1.

[0031] In a preferred embodiment of the present invention, the silicon-based substrate is selected from one or more of silicon-oxygen materials, silicon-carbon, and pure silicon.

[0032] Among them, in the present invention, the silicon-oxygen material is a composite of silicon and silicon dioxide in any proportion, including a silicon-oxygen material that has not been pre-lithiated, and a pre-lithiated silicon-oxygen material that has been pre-lithiated. Silicon carbon can be silicon carbon that has not been pre-lithiated, or pre-lithiated silicon carbon that has been pre-lithiated. Pre-lithiation treatment is common knowledge in the art, and the present invention will not be repeated.

[0033] In a preferred embodiment of the present invention, both the inner coating layer and the outer coating layer have electron / ion dual particle transport channels, each comprising an ion-conducting medium and an electron-conducting medium.

[0034] In a preferred embodiment of the present invention, the inner coating layer comprises an inner ion conducting medium and an inner conducting electron medium, and the mass ratio of the inner ion conducting medium to the inner conducting electron medium is 0.5: 1-10: 1, preferably 2: 1-8: 1. In the present invention, ignoring errors, the mass ratio of the inner ion conducting medium to the inner conducting electron medium is equal to the theoretical feed amount.

[0035] In a preferred embodiment of the present invention, the Young's modulus of the inner ion conducting medium is 30-180 GPa, and the ionic conductivity is ≥10 -10 S / cm.

[0036] In a preferred embodiment of the present invention, the inner ion conducting medium is selected from lithium-containing oxides, and is further preferably selected from LiNbO3, Li2CO3, Li2SiO3, Li3PO4, LiAlO2, Li4Ti5O 12 , LiTaO3, Li2O, Li3VO4, LiNbO3, Li2ZrO3, one or more, preferably one or more of LiNbO3, Li2ZrO3, LiTaO3.

[0037] Among them, in the present invention, the lithium-containing oxide can react with the silicon in the silicon-based matrix, so that the interface between the inner coating layer and the inner core silicon-based matrix can be connected in the form of chemical bonds, thereby increasing the interface connection strength, being able to withstand greater stress release from the inner core, and stabilizing the particle structure.

[0038] In a preferred embodiment of the present invention, the electronic conductivity of the internal conducting electron medium is 10-5000 S / cm.

[0039] In a preferred embodiment of the present invention, the internal conductive electronic medium is selected from conductive carbon and / or nano-conductive metal; wherein the conductive carbon is selected from carbon nanotubes and / or conductive carbon black, preferably carbon nanotubes, and further preferably aqueous single-walled carbon nanotubes; the nano-conductive metal is selected from one or more of Ag, Sn, and Cu, preferably Ag.

[0040] In a preferred embodiment of the present invention, the outer coating layer comprises an outer ion-conducting medium and an outer electron-conducting medium; wherein the mass ratio of the outer ion-conducting medium to the outer electron-conducting medium is 0.5:1-4.5:1, preferably 1:1-2.5:1. In the present invention, ignoring errors, the mass ratio of the outer ion-conducting medium to the outer electron-conducting medium is equal to the theoretical feed amount.

[0041] In a preferred embodiment of the present invention, the Young's modulus of the external ion conducting medium is 0.5-30 GPa, and the ionic conductivity is ≥10 -8 S / cm.

[0042] In a preferred embodiment of the present invention, the external ion-conducting medium is selected from a sulfide electrolyte doped with a modifying element, and the chemical formula is LiXPSCl; wherein the doping modifying element X is selected from one or more of transition metals, Group IIIA, Group IVA, and Group VA elements, preferably selected from one or more of Si, Sn, Ge, Y, In, Al, As, and Zn; further preferably, the external ion-conducting medium is one or more of LiSiPSCl, LiSnPSCl, LiGePSCl, LiYPSCl, LiInPSCl, and LiAlPSCl, more preferably one or more of LiSiPSCl, LiSnPSCl, and LiGePSCl.

[0043] In a preferred embodiment of the present invention, the electronic conductivity of the external conductive electronic medium is 10-5000 S / cm.

[0044] In a preferred embodiment of the present invention, the external conductive electronic medium is selected from conductive carbon and / or nano conductive metal; wherein the conductive carbon is selected from carbon nanotubes and / or conductive carbon black, preferably carbon nanotubes, and further preferably oil-based single-walled carbon nanotubes; the nano conductive metal is selected from one or more of Sn, In, and Ga, preferably Sn and / or In.

[0045] Among them, in the present invention, the types of the inner conducting electronic medium and the outer conducting electronic medium can be the same or different. The inner conducting electronic medium and the outer conducting electronic medium both have high crystallinity, which can not only improve the conductivity, but also be relatively friendly to the sulfide solid electrolyte and will not catalyze excessive decomposition of the sulfide solid electrolyte.

[0046] In a preferred embodiment of the present invention, the mass ratio of the silicon-based substrate, the inner coating layer and the outer coating layer is 100:0.2:2-100:10:40, preferably 100:1:5-100:8:20.

[0047] In a preferred embodiment of the present invention, the thickness of the inner coating layer is 1-10 nm, preferably 2-5 nm; the thickness of the outer coating layer is 5-100 nm, preferably 10-50 nm. In the present invention, the electrical properties of the silicon-based negative electrode material can be further optimized by adjusting the coating thickness of the inner coating layer and the outer coating layer.

[0048] In a preferred embodiment of the present invention, the median particle size of the silicon-based negative electrode material is between 100 nm and 16 μm, preferably between 200 nm and 12 μm; the specific surface area is between 0.5 and 160 m 2 / g, preferably 1-50m 2 / g.

[0049] Among them, in the present invention, by controlling the median particle size and specific surface area of ​​the silicon-based negative electrode material, the compatibility between the sulfide solid electrolyte and the silicon-based negative electrode material can be further improved, which helps to increase the contact area between the two, reduce the porosity of the electrode sheet, increase the solid-solid transmission channel, and improve the lithium ion diffusion rate.

[0050] The second aspect of the present invention provides a method for preparing a silicon-based negative electrode material. In fact, the method comprises the following steps:

[0051] (1) mixing a silicon-based substrate, an inner-conducting electron medium, an inner-conducting ion medium or an inner-conducting ion medium precursor with a first solvent, and stirring to obtain a first dispersion;

[0052] (2) removing the first solvent in the first dispersion and performing a first heat treatment to obtain an intermediate I having an inner coating layer formed on a silicon-based substrate;

[0053] (3) mixing the intermediate I, the external electron-conducting medium, the external ion-conducting medium or the external ion-conducting medium precursor with a second solvent, and stirring to obtain a second dispersion;

[0054] (4) After removing the second solvent in the second dispersion, a second heat treatment is performed to obtain a silicon-based negative electrode material coated with an inner coating layer and an outer coating layer.

[0055] In step (1):

[0056] In a preferred embodiment of the present invention, the silicon-based matrix is ​​selected from one or more of silicon-oxygen materials, silicon carbon, and pure silicon. Among them, the silicon-oxygen materials include silicon-oxygen materials that have not been pre-lithiated, and pre-lithiated silicon-oxygen materials that have been pre-lithiated. The silicon carbon can be silicon-carbon that has not been pre-lithiated, or pre-lithiated silicon-carbon that has been pre-lithiated.

[0057] In a preferred embodiment of the present invention, the internal conductive electronic medium is selected from conductive carbon and / or nano-conductive metal; wherein the conductive carbon is selected from carbon nanotubes and / or conductive carbon black, preferably carbon nanotubes, and further preferably aqueous single-walled carbon nanotubes; the nano-conductive metal is selected from one or more of Ag, Sn, and Cu, preferably Ag.

[0058] In a preferred embodiment of the present invention, the inner ion conducting medium is selected from lithium-containing oxides; wherein the lithium-containing oxide is selected from LiNbO3, Li2ZrO3, LiTaO3, Li2CO3, Li2SiO3, Li3PO4, LiAlO2, Li4Ti5O 12 , Li2O, Li3VO4, preferably one or more of LiNbO3, Li2ZrO3, LiTaO3.

[0059] In a preferred embodiment of the present invention, the inner ion medium precursor is a raw material required for synthesizing the inner ion medium by a method known in the art. In the present invention, taking LiNbO3 as an example, the inner ion medium precursor is a soluble lithium-containing compound and a soluble niobium-containing compound, for example, niobium oxalate and lithium hydroxide.

[0060] In a preferred embodiment of the present invention, the first solvent is selected from water and / or ethanol.

[0061] In a preferred embodiment of the present invention, the mass ratio of the silicon-based substrate, the internal electron-conducting medium, and the internal ion-conducting medium is 100:0.5:0.5-100:4.5:4.5.

[0062] In a preferred embodiment of the present invention, the inner ion conducting medium precursor is a raw material required for synthesizing the inner ion conducting medium, and the amount of the inner ion conducting medium precursor is calculated based on the mass of the corresponding inner ion conducting medium.

[0063] In step (2):

[0064] In a preferred embodiment of the present invention, the present invention does not specifically limit the method for removing the first solvent in the first dispersion, for example, it may be evaporative drying.

[0065] In a preferred embodiment of the present invention, the first heat treatment conditions include: the heating rate of the first heat treatment is 1-10°C / min, preferably 4-6°C / min; the temperature of the first heat treatment is 400-1000°C, preferably 500-700°C; the time of the first heat treatment is 1-8h, preferably 3-5h.

[0066] Among them, in the present invention, the first heat treatment is carried out under the protection of an inert gas (such as nitrogen). By controlling the operating conditions of the first heat treatment, especially the operating temperature, the Young's modulus of the inner coating layer can be significantly changed, thereby changing the difference in Young's modulus between the inner coating layer and the silicon-based substrate, thereby improving the performance of the silicon-based negative electrode material.

[0067] In step (3):

[0068] In a preferred embodiment of the present invention, the external conductive electronic medium is selected from conductive carbon and / or nano conductive metal; wherein the conductive carbon is selected from carbon nanotubes and / or conductive carbon black, preferably carbon nanotubes, and further preferably oil-based single-walled carbon nanotubes; the nano conductive metal is selected from one or more of Sn, In, and Ga, preferably Sn and / or In.

[0069] In a preferred embodiment of the present invention, the external ion-conducting medium is selected from a sulfide electrolyte doped with a modifying element, and the chemical formula is LiXPSCl; wherein the doping modifying element X is selected from one or more of transition metals, group IIIA, group IVA, and group VA elements, preferably one or more of Si, Sn, Ge, Y, In, Al, As, and Zn. Further preferably, the external ion-conducting medium is one or more of LiSiPSCl, LiSnPSCl, LiGePSCl, LiYPSCl, LiInPSCl, and LiAlPSCl, and more preferably one or more of LiSiPSCl, LiSnPSCl, and LiGePSCl.

[0070] In a preferred embodiment of the present invention, the external ion conducting medium precursor is a raw material required to synthesize the external ion conducting medium by a method known in the art. In the present invention, taking LiSiPSCl as an example, the external ion conducting medium precursor is one or more of Li2S, SnS2, P2S5, and LiCl.

[0071] In a preferred embodiment of the present invention, the second solvent is selected from one or more of acetonitrile, tetrahydrofuran and ethanol.

[0072] In a preferred embodiment of the present invention, the mass ratio of the intermediate I, the external electron-conducting medium, and the external ion-conducting medium is 100:2:2-100:20:20.

[0073] In a preferred embodiment of the present invention, the external ion-conducting medium precursor is a raw material required for synthesizing the external ion-conducting medium, and the amount of the external ion-conducting medium precursor is calculated based on the mass of the corresponding external ion-conducting medium.

[0074] In step (4):

[0075] In a preferred embodiment of the present invention, the present invention does not specifically limit the method for removing the second solvent in the second dispersion, for example, it may be evaporative drying.

[0076] In a preferred embodiment of the present invention, the operating conditions of the second heat treatment include: the heating rate of the second heat treatment is 1-10°C / min, preferably 4-6°C / min; the temperature of the second heat treatment is 300-600°C, preferably 400-500°C; the time of the second heat treatment is 1-8h, preferably 3-5h.

[0077] Among them, in the present invention, the second heat treatment is carried out under the protection of an inert gas (such as nitrogen). By controlling the operating conditions of the second heat treatment, especially the operating temperature, the Young's modulus of the outer coating layer can be significantly changed, thereby changing the difference in Young's modulus between the outer coating layer and the silicon-based substrate, thereby improving the performance of the silicon-based negative electrode material.

[0078] The third aspect of the present invention provides a negative electrode plate, wherein the negative electrode plate comprises the silicon-based negative electrode material described in the first aspect of the present invention or the silicon-based negative electrode material prepared by the preparation method described in the second aspect of the present invention.

[0079] Among them, in the present invention, the silicon-based negative electrode material can reduce the risk of interface rupture under high stress conditions and accelerate the lithium ion transmission speed between the sulfide solid electrolyte and the silicon-based negative electrode material. In addition, the silicon-based negative electrode material has good compatibility with the sulfide solid electrolyte, low processing difficulty, and a large contact area, strong affinity, and good contact tightness at the interface between the silicon-based negative electrode material and the sulfide solid electrolyte, which can significantly increase the density of the negative electrode sheet, thereby improving the cycle performance and rate performance of the all-solid-state battery prepared using the negative electrode sheet.

[0080] In a preferred embodiment of the present invention, the negative electrode plate further comprises a flexible solid electrolyte additive; wherein the Young's modulus of the flexible solid electrolyte additive is lower than the Young's modulus of the sulfide solid electrolyte.

[0081] Among them, in the present invention, the inventors have found through research that by introducing a flexible solid electrolyte additive with a lower Young's modulus than the sulfide solid electrolyte in the process of electrode manufacturing, the processability and ductility of the electrode can be further improved, the solid-solid interface contact area between the silicon-based negative electrode material and the sulfide solid electrolyte can be maximized, the tortuosity of lithium ion transmission between the silicon-based negative electrode material and the sulfide solid electrolyte can be reduced, a good lithium ion transmission channel can be constructed, and the electrochemical performance of the solid-state battery can be improved.

[0082] In a preferred embodiment of the present invention, the Young's modulus of the flexible solid electrolyte additive is ≤5.0 GPa.

[0083] In a preferred embodiment of the present invention, the flexible solid electrolyte additive is selected from halide electrolytes and / or polymer electrolytes.

[0084] In a preferred embodiment of the present invention, the chemical formula of the halide electrolyte is LiX, m Y, n, wherein X is a metal element selected from one or more of In, As, Ta, Y, Sr, Sn, Al, and Ti, Y is a halogen selected from one or more of F, Cl, Br, and I, 0<m<1, 0<n<1; further preferably, the flexible solid electrolyte additive is selected from one or more of LiYCl, LiInCl, LiTaCl, LiTiCl, LiAlCl, LiAsCl, LiYI, and LiInI, preferably one or more of amorphous LiInCl, LiTaCl, LiTiCl, and LiAlCl.

[0085] In a preferred embodiment of the present invention, the polymer electrolyte is selected from PEO-based polymer electrolytes, PAN-based polymer electrolytes, PDMA-based polymer electrolytes, and PDOL-based polymer electrolytes, preferably PEO-based polymer electrolytes.

[0086] In a preferred embodiment of the present invention, the negative electrode plate includes a current collector and 50-90 parts by weight of a silicon-based negative electrode material, 0-20 parts by weight of a flexible solid electrolyte additive, 10-40 parts by weight of a sulfide solid electrolyte, 1-10 parts by weight of a conductive agent and 0.1-2 parts by weight of a binder arranged on the current collector.

[0087] In a preferred embodiment of the present invention, the negative electrode plate includes a current collector and 60-80 parts by weight of a silicon-based negative electrode material, 5-10 parts by weight of a flexible solid electrolyte additive, 20-30 parts by weight of a sulfide solid electrolyte, 2-5 parts by weight of a conductive agent and 0.5-1 parts by weight of a binder arranged on the current collector.

[0088] Among them, in the present invention, when the usage of silicon-based negative electrode material, sulfide solid electrolyte, flexible solid electrolyte additive, conductive agent and binder is within the above preferred range, the comprehensive performance of the negative electrode plate is better.

[0089] In a preferred embodiment of the present invention, the current collector is selected from carbon-coated copper foil and / or copper foil, preferably copper foil, and more preferably porous copper foil.

[0090] In a preferred embodiment of the present invention, the sulfide solid electrolyte is selected from argyrodite-type electrolyte; preferably, the chemical formula of the argyrodite-type electrolyte is Li 7-c PS 6-c Cl c , wherein 0≤c≤1.5, further preferably selected from Li6PS5Cl, Li 6.5 PS 5.5 Cl 0.5 , Li 5.5 PS 4.5Cl 1.5 One or more of .

[0091] In a preferred embodiment of the present invention, the conductive agent is selected from one or more of Ketjen black, acetylene black, carbon nanotubes, carbon nanocages, carbon nanofibers, and graphene, preferably one or more of acetylene black, carbon nanofibers, and graphene.

[0092] In a preferred embodiment of the present invention, the binder is selected from one or more of polyacrylonitrile, polyurethane, polyacrylic acid, polyvinylidene fluoride, polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene copolymer, polypropylene, polyimide, preferably polytetrafluoroethylene.

[0093] The fourth aspect of the present invention provides an all-solid-state battery, wherein the all-solid-state battery comprises the negative electrode plate described in the third aspect of the present invention.

[0094] Among them, in the present invention, the all-solid-state battery including the negative electrode plate described in the third aspect of the present invention has the advantages of high cycle stability and safety, broad commercial prospects, and is suitable for industrial promotion.

[0095] The present invention will be described in detail below through examples.

[0096] Preparation Example 1 of Silicon-based Negative Electrode Material

[0097] (1) 10 g of pure silicon with a median particle size of 3 μm and 20 g of aqueous single-walled carbon nanotubes (SWCNTs) with a solid content of 0.5 wt% were dispersed in 100 mL of water, and a uniformly dispersed suspension a was obtained by stirring and ultrasonic treatment;

[0098] 0.73 g of niobium oxalate was added to 50 mL of water, and the mixture was stirred and ultrasonically treated to obtain a fully dissolved solution b; 0.0674 g of lithium hydroxide monohydrate was added to 50 mL of water, and the mixture was stirred and ultrasonically treated to obtain a fully dissolved solution c;

[0099] Solution b was added to suspension a, and stirred at 400 r / min for 15 min to obtain suspension d; solution c was added dropwise to suspension d at 500 r / min, and after the addition was complete, the solution was stirred at the same speed for 2 h to obtain a first dispersion;

[0100] (2) subjecting the first dispersion to rotary evaporation at 100° C. to remove water and obtain a dry black-gray powder; then transferring the obtained black-gray powder to a tube furnace, heating it to a first heat treatment temperature of 700° C. at a heating rate of 5° C. / min under an inert gas atmosphere, and keeping the temperature for 3 h. After cooling, an intermediate I having an inner coating layer formed on a silicon-based substrate is obtained;

[0101] (3) In an environment with a dew point below -60°C, 0.5 g of LiSiPSCl was weighed and dissolved in 40 mL of acetonitrile, and then 10 g of oil-based single-walled carbon nanotubes with a solid content of 2.5 wt% were added for dispersion to obtain a suspension e;

[0102] 10 g of the intermediate I was added to the suspension e, and stirred in a closed container at a speed of 500 r / min for 5 h to obtain a second dispersion;

[0103] (4) opening the sealed container, placing the second dispersion in a vacuum drying oven, evaporating and drying at 60° C. under a vacuum degree of 0.1 Pa to remove acetonitrile, and obtaining a mixed powder;

[0104] The mixed powder was placed in a quartz glass tube under an argon atmosphere, and the vacuum was 0.2 Pa. The tube was sealed with an oxyhydrogen flame gun. The quartz glass tube encapsulating the powder was placed in a muffle furnace and heated to a second heat treatment temperature of 500°C at a heating rate of 5°C / min. The tube was kept warm for 6 hours. After cooling, a silicon-based negative electrode material having an outer coating layer was formed on the inner coating layer of the intermediate I, which was denoted as C1, wherein the mass ratio of the silicon-based substrate, the inner coating layer and the outer coating layer was 100:5:7.5.

[0105] Preparation Example 2 of Silicon-based Negative Electrode Material

[0106] The same as Example 1, except that in step (1),

[0107] The aqueous single-walled carbon nanotubes (SWCNTs) were replaced with 0.1 g of Ag powder to obtain suspension a;

[0108] 0.56 g of zirconium nitrate pentahydrate (Zr(NO3)4·5H2O) was added to 50 mL of water, and a fully dissolved solution b was obtained by stirring and ultrasonic treatment;

[0109] 0.11 g of lithium hydroxide monohydrate (LiOH·5H2O) was added to 50 mL of water, and a fully dissolved solution c was obtained by stirring and ultrasonic treatment;

[0110] The other steps are the same, and the obtained silicon-based negative electrode material is denoted as C2.

[0111] Preparation Example 3 of Silicon-based Negative Electrode Material

[0112] Same as Example 1, except that

[0113] In step (1), solution c is omitted, 0.56 g of tantalum hydroxide (Ta(OH)5) and 0.56 g of lithium hydroxide monohydrate (LiOH·5H2O) are added to 50 mL of an aqueous solution containing 0.1 mol of citric acid, and a fully dissolved solution b is obtained by stirring and ultrasonic treatment; solution b is added to suspension a, and stirred at 400 r / min for 1 h to obtain a first dispersion;

[0114] In step (3), the oil-based single-walled carbon nanotubes (SWCNTs) were replaced with 0.25 g Sn powder;

[0115] The other steps are the same, and the obtained silicon-based negative electrode material is recorded as C3.

[0116] Preparation Example 4 of Silicon-based Negative Electrode Material

[0117] The same as Example 1, except that the mass of the external ion conducting medium (LiSiPSCl) is replaced by LiSnPSCl, and the obtained silicon-based negative electrode material is recorded as C4.

[0118] Preparation Example 5 of Silicon-based Negative Electrode Material

[0119] The same as Example 1, except that the mass of the external ion conducting medium (LiSiPSCl) is replaced by LiGePSCl, and the obtained silicon-based negative electrode material is recorded as C5.

[0120] Preparation Example 6 of Silicon-based Negative Electrode Material

[0121] The same as Example 1, except that the mass ratio of the silicon-based substrate, the inner coating layer and the outer coating layer is 100:8:5, and the obtained silicon-based negative electrode material is recorded as C6.

[0122] Preparation Example 7 of Silicon-based Negative Electrode Material

[0123] The same as Example 1, except that the mass ratio of the silicon-based substrate, the inner coating layer and the outer coating layer is 100:1:20, and the obtained silicon-based negative electrode material is recorded as C7.

[0124] Preparation Example 8 of Silicon-based Negative Electrode Material

[0125] The same as Example 1, except that the first heat treatment temperature is adjusted to 500° C., and the obtained silicon-based negative electrode material is recorded as C8.

[0126] Preparation Example 9 of Silicon-based Negative Electrode Material

[0127] The same as Example 1, except that the first heat treatment temperature is adjusted to 900° C., and the obtained silicon-based negative electrode material is recorded as C9.

[0128] Preparation Example 10 of Silicon-based Negative Electrode Material

[0129] The same as Example 1, except that the second heat treatment temperature is adjusted to 300° C., and the obtained silicon-based negative electrode material is recorded as C10.

[0130] Preparation Example 11 of Silicon-Based Anode Material

[0131] The same as Example 1, except that the second heat treatment temperature is adjusted to 600° C., and the obtained silicon-based negative electrode material is recorded as C11.

[0132] Preparation of silicon-based negative electrode material Comparative Example 1

[0133] The same as Example 1, except that the preparation of the outer coating layer is omitted, and the obtained silicon-based negative electrode material is recorded as D1.

[0134] Preparation of silicon-based negative electrode material Comparative Example 2

[0135] The same as Example 1, except that the preparation of the inner coating layer is omitted, and the obtained silicon-based negative electrode material is recorded as D2.

[0136] Preparation of silicon-based negative electrode material Comparative Example 3

[0137] The same as Example 1, the difference is that the order of the inner and outer coating layers is exchanged, the outer coating layer of Example 1 is prepared first, and then the inner coating layer of Example 1 is prepared. The obtained silicon-based negative electrode material is recorded as D3.

[0138] Preparation of silicon-based negative electrode material Comparative Example 4

[0139] The same as Example 1, the difference is that there is no inner coating layer or outer coating layer, and pure silicon is directly used as the silicon-based negative electrode material, which is recorded as D4.

[0140] Preparation of silicon-based negative electrode material Comparative Example 5

[0141] The same as Example 1, except that the first heat treatment temperature is adjusted to 1200° C., the second heat treatment temperature is adjusted to 800° C., and the obtained silicon-based negative electrode material is recorded as D5.

[0142] Test Example 1

[0143] The Young's modulus of the silicon-based substrate, the Young's modulus of the inner coating layer, the Young's modulus of the outer coating layer, the difference α of the Young's modulus between the inner coating layer and the silicon-based substrate, the difference β of the Young's modulus between the outer coating layer and the silicon-based substrate in the silicon-based negative electrode materials prepared in Examples 1-11 and Comparative Examples 1-5, and the mass ratios of the silicon-based substrate, the inner coating layer and the outer coating layer are shown in Table 1.

[0144] Among them, Young's modulus is measured by AFM. AFM force curve is a more mature method for detecting Young's modulus of samples. Its basic principle is that the AFM probe penetrates a certain depth into the sample surface under a certain force. According to the Sneddon model, the relationship between force and penetration depth is:

[0145]

[0146] In the formula, F is the interaction force between the probe and the material; δ is the depth of the probe penetrating into the material; E is the Young's modulus of the material; θ is the half angle of the needle tip; ν is the Poisson's ratio of the material. By fitting a quadratic function to F and δ, the Young's modulus can be obtained based on the quadratic term coefficient.

[0147] The specific test steps are:

[0148] Material preparation: in diameter A stainless steel gasket with the same diameter is placed at the bottom of the stainless steel grinding tool, 100 mg of the sample to be tested is placed on the gasket, and it is pressed into shape under a pressure of 5 kN. The sample disc to be tested is obtained by demolding.

[0149] AFM test: Place the sample to be tested in the instrument sample chamber, use the AFM tapping mode to obtain the topography of the sample to be tested, then switch to the contact mode, make a force curve in the contact mode, and the needle tip penetrates deeper than 20nm to facilitate the subsequent fitting of the force curve. Perform a force curve scanning analysis in the 500×500nm area, fit the obtained force curve with the Sneddon model, obtain the Young's modulus distribution diagram of the sample, and take the average of the Young's modulus to obtain the Young's modulus value of the final material.

[0150] The mass ratios of the silicon-based substrate, the inner cladding layer, and the outer cladding layer were measured using the ICP method for measuring specific elements.

[0151] Table 1

[0152]

[0153] Test Example 2

[0154] The median particle size, thickness of the inner coating layer and the outer coating layer, and specific surface area of ​​the silicon-based negative electrode materials prepared in Examples 1-11 and Comparative Examples 1-5 were tested, and the results are shown in Table 2.

[0155] Among them, the median particle size of the silicon-based negative electrode material is measured using a scanning electron microscope (SEM). The sample to be tested is spread on a conductive tape and observed at a voltage of 15kV. At a magnification of 1000 times, the particle distribution and size are analyzed by particle size statistics software to obtain the median particle size information of the sample to be tested. The thickness of the inner and outer coating layers of the silicon-based negative electrode material is measured by high-resolution transmission electron microscopy (HRTEM) combined with electron energy loss spectroscopy (EELS). The specific surface area of ​​the silicon-based negative electrode material is measured in accordance with the national standard GB / T 19587-2017 "Determination of the specific surface area of ​​solid substances by gas adsorption BET method".

[0156] Table 2

[0157]

[0158]

[0159] The SEM characterization results of silicon-based negative electrode materials C1-C11 are similar to those of C1. Figure 1 shown.

[0160] Depend on Figure 1 It can be seen that the electronic signal on the surface of the silicon-based negative electrode material C1 is weak and the contrast is low, indicating that its outer coating layer contains a sulfide electrolyte with weaker conductivity, and the overall contrast of the particle surface is uniform, indicating that the coating layer is relatively complete and there is no uneven coating phenomenon.

[0161] Preparation Example 1 of Negative Electrode Plate

[0162] 67 mg of the silicon-based negative electrode material C1 prepared in Example 1, 25 mg of the sulfide solid electrolyte (Li6PS5Cl) and 5 mg of the flexible electrolyte additive (amorphous LiInCl, Young's modulus of 2.5 GPa) were placed in a grinding tube (2 mL) of a 2 mL micro vibration ball mill, and 10 1 mm ball milling beads were added for mixing. The working speed was 3000 rpm, the working frequency was 40 Hz, and the working time was 40 s to obtain a mixed powder A;

[0163] Add 1 mg of polytetrafluoroethylene (PTFE) and 2 mg of carbon nanofiber (VGCF) to the mixed powder A, continue mixing, the speed is 3500 rpm, the working frequency is 40 Hz, and the working time is 40 s to obtain a negative electrode powder;

[0164] In a glove box filled with argon, the button battery mold was placed in the center, and a copper foil with a diameter of 10 mm was placed at the bottom of the cylindrical tableting mold. Then 2 mg of the above negative electrode powder was weighed and evenly spread on the surface of the copper foil. A pressure of 350 MPa was applied at 30°C, and the two were pressed into sheets. The sheets were demolded to obtain the negative electrode sheet, which was recorded as PC1.

[0165] Preparation Examples 2-15 of Negative Electrode Sheets and Comparative Examples 1-6 of Negative Electrode Sheets

[0166] The preparation method is the same as Example 1 for preparing the negative electrode plate, except that the components and / or amounts are different, as shown in Table 3.

[0167] Among them, the flexible solid electrolyte additive added in the preparation example 12 of the negative electrode plate is amorphous LiTaCl, and the Young's modulus is 3 GPa; the non-flexible solid electrolyte additive, crystalline LATP, and the Young's modulus is 110 GPa added in the preparation example 14 of the negative electrode plate.

[0168] Table 3

[0169]

[0170] Note: The additives in Table 3 are none, flexible solid electrolyte additives or non-flexible solid electrolyte additives.

[0171] Negative electrode test example 1

[0172] The cross-sections of the negative electrode sheets PC1-PC15 were characterized by SEM. The SEM characterization results of PC2-PC15 were similar to those of PC1. Figure 2 shown.

[0173] Depend on Figure 2 It can be seen that the silicon-based negative electrode material and the sulfide solid electrolyte are in close contact, the electrode density is high, and no obvious pores are seen. This proves that the Young's modulus gradient design of the coating layer based on the silicon-based negative electrode material, combined with the use of flexible solid electrolyte additives at the electrode end, can improve the interface compatibility between the silicon-based negative electrode material and the sulfide solid electrolyte, increase the solid-solid contact area between the silicon-based negative electrode material and the sulfide solid electrolyte, and help improve the diffusion efficiency of lithium ions at the solid-solid interface and improve the overall lithium ion diffusion kinetics of the electrode.

[0174] Negative electrode test example 2

[0175] The Young's modulus and ionic conductivity of the negative electrode sheets prepared in Examples 1-15 for preparing the negative electrode sheets and the negative electrode sheets prepared in Comparative Examples 1-6 for preparing the negative electrode sheets were tested, and the test results are shown in Table 4.

[0176] Among them, the ionic conductivity parameters are measured by AC impedance method. The specific test includes: clamping the sample to be tested between two stainless steel disc electrodes, measuring the ionic conductivity (σ) by electrochemical impedance spectroscopy (EIS) in the frequency range of 1Hz-7MHz, with an AC amplitude of 10mV, and calculating according to the formula σ=L / (Rb×S); wherein Rb is the volume resistance of the sample to be tested (Rb is determined by impedance spectrum, unit: Ω), L (unit: cm) and S (unit: cm 2 ) are the thickness and area of ​​the sample to be tested.

[0177] Table 4

[0178]

[0179]

[0180] As can be seen from Table 4, compared with the comparative example, the Young's modulus of the negative electrode sheets PC1-PC15 provided in the present invention is smaller than that of PD1-PD6, and is between 15.3-20.4 GPa, which is comparable to the Young's modulus (16 GPa) of the sulfide solid electrolyte Li6PS5Cl. This not only shows that the compound use of silicon-based negative electrode materials and flexible solid electrolyte additives makes the negative electrode sheet show excellent compatibility, but also is more conducive to the stability of the electrode structure of the electrode sheet and the performance of the battery. In addition, the lower Young's modulus also reduces the risk of cracking of the electrode sheet under high stress conditions. Therefore, the silicon-based negative electrode sheet prepared by the present invention can withstand structural changes during cycling without cracks.

[0181] The ionic conductivity of the negative electrode sheets PC1-PC15 provided in the present invention is in the range of 2.5-5.1×10 -6 S / cm, indicating that the all-solid-state battery prepared using the negative electrode sheet provided in the present invention has a fast lithium ion migration speed, a small stress during the charge and discharge process, and can withstand more charge and discharge cycles, thereby improving the cycle stability of the battery.

[0182] Negative electrode test example 3

[0183] The negative electrode sheets PC1-PC15 and the negative electrode sheets PD1-PD6 were prepared into all-solid-state batteries, and then the 0.1C reversible capacity, first coulomb efficiency, 0.33C capacity retention rate and 1C capacity retention rate of the all-solid-state batteries were tested. The test cutoff voltage was 0.005-0.8V, and constant current charge and discharge were used for measurement. The test results are shown in Table 5.

[0184] Among them, the preparation method of all-solid-state battery:

[0185] First, 20 mg of Li6PS5Cl electrolyte powder is evenly spread on the surface of the negative electrode plate, and a pressure of 150 MPa is applied to pre-press the electrolyte to obtain the electrolyte plate; then, the Li-In alloy plate is placed on the electrolyte plate, and the pressure battery mold is assembled. After the assembly is completed, a pressure of 50 MPa is applied to obtain an all-solid-state lithium-ion battery.

[0186] The reversible capacity is the charge capacity at different rates.

[0187] First efficiency = first charge capacity / first discharge capacity × 100%.

[0188] Capacity retention rate = charging capacity at different rates / charging capacity at 0.1C rate × 100%.

[0189] Table 5

[0190]

[0191]

[0192] It can be seen from Tables 1 to 5 that the all-solid-state battery containing the silicon-based negative electrode material provided by the present invention has excellent electrochemical performance, that is, high initial efficiency, high rate performance and high cycle performance.

[0193] Figure 3 The first cycle charge and discharge curve of the all-solid-state battery made of the negative electrode PC1 is shown in Figure 2. Figure 3 It can be seen that the reversible capacity of PC1 at 0.1C is 3.85 mAh and the first efficiency is 89.25%. Figure 4 The rate and cycle performance diagram of the all-solid-state battery made of the negative electrode PC1 is shown in Figure 1. Figure 4 It can be seen that the capacity retention rate at 0.33C can reach 77.33%, and the capacity retention rate at 1C can reach 41.98%. Figure 3 and Figure 4 It can be seen that the all-solid-state battery made using the negative electrode piece PC1 not only has good electrical performance, but also has excellent cycle stability and rate performance.

[0194] (1) The synergistic effect of the inner and outer coating layers in silicon-based anode materials on battery performance

[0195] By comparing the example PC15 and the comparative examples PD1-PD5, it can be seen that the surface of the silicon-based substrate of PD1 only contains an inner coating layer, the surface of the silicon-based substrate of PD2 only contains an outer coating layer, the coating order of the inner and outer coating layers of PD3 is opposite to that of PC15, the surface of the silicon-based substrate of PD4 has neither an inner coating layer nor an outer coating layer, and the difference α and β of the coating layers on the surface of the silicon-based substrate of PD5 do not satisfy 0<α<4, -1<β<0. It can be seen from the results of Tables 4 and 5 that the coating order of the inner coating layer, the outer coating layer, the inner and outer coating layers, and the α and β ranges of the inner and outer coating layers have a significant effect on the performance of the all-solid-state battery. By comparing PC15 and comparative example PD5, it can be seen that in the present invention, by controlling the difference α between the Young's modulus of the inner coating layer and the silicon-based substrate and the difference β between the Young's modulus of the outer coating layer and the silicon-based substrate, it is not only helpful to improve the 0.1C reversible capacity and first effect of the all-solid-state battery, but also the 0.33C capacity retention rate of the all-solid-state battery can be increased from 24.32% to 62.47%, and the 1C capacity retention rate can be increased from 6.43% to 27.93%, thereby significantly improving the cycle performance of the all-solid-state battery. It can be seen that only by constructing the inner coating layer and the outer coating layer on the surface of the silicon substrate in sequence according to the present invention, and controlling the difference α, β of the coating layer on the surface of the silicon-based substrate to meet 0<α<4, -1<β<0, can the synergistic effect between the inner and outer coating layers be brought into play, which is conducive to reducing the lithium ion transmission barrier, significantly improving the lithium ion transmission kinetics, giving full play to the electrochemical properties of the material, and improving the first effect, rate performance and cycle performance of the battery.

[0196] (2) The impact of the synergistic effect of silicon-based anode materials and flexible solid electrolytes on battery performance

[0197] By comparing PC1, PC12, PC15 and comparative examples PD4 and PD6, it can be seen that a flexible solid electrolyte additive with a Young's modulus lower than that of a sulfide solid electrolyte is introduced in the manufacturing process of the negative electrode plate. The silicon-based negative electrode material and the flexible solid electrolyte additive work synergistically, so that the silicon-based negative electrode material and the sulfide solid electrolyte can be further in close contact. At the same time, it also solves the problem of decreased ion conductivity of the plate caused by the use of excessive binder, which can reduce the internal resistance of the all-solid-state battery, build a good lithium ion transmission channel, and help to further optimize the stress distribution at the interface, reduce the risk of interface rupture under high stress conditions, and thus improve the electrochemical performance of the solid-state battery. By comparing PC14 and PC15, it can be seen that compared with the non-flexible solid electrolyte additive LATP, the addition of the flexible solid electrolyte additive LiInCl is more conducive to improving the electrochemical performance of the solid-state battery.

[0198] (3) Effect of silicon-based negative electrode material preparation methods on battery performance

[0199] By comparing Example 1, Example 8 and Example 9, it can be seen that within the scope defined by the present invention, increasing the temperature of the first heat treatment can increase the Young's modulus of the inner coating layer. By comparing Example 1, Example 10 and Example 11, it can be seen that within the scope defined by the present invention, increasing the temperature of the second heat treatment can increase the Young's modulus of the outer coating layer. By comparing Example 1 and Comparative Example 5, it can be seen that when the first and second heat treatment temperatures are not within the defined conditions, in the prepared silicon-based negative electrode material, although the Young's modulus B of the inner coating layer and the Young's modulus C of the outer coating layer are within the scope defined by the present invention, the Young's modulus difference α between the inner coating layer and the silicon-based matrix and the Young's modulus difference β between the outer coating layer and the silicon-based matrix are not within the scope defined by the present invention. The present invention adjusts the difference α and β between the Young's modulus of the inner coating layer, the outer coating layer and the silicon-based matrix by controlling the preparation method of the silicon-based negative electrode material, which helps to greatly improve the cycle performance of the all-solid-state battery. It can be seen from this that only by constructing the inner coating layer and the outer coating layer on the surface of the silicon substrate in sequence according to the present invention, and controlling the difference α, β of the coating layer on the surface of the silicon-based substrate to satisfy 0<α<4, -1<β<0, can the synergistic effect between the inner and outer coating layers be brought into play, which is beneficial to reducing the lithium ion transmission barrier, significantly improving the lithium ion transmission kinetics, giving full play to the electrochemical properties of the material, and improving the first efficiency, rate performance and cycle performance of the battery.

[0200] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A silicon-based negative electrode material, characterized in that: The material comprises a silicon-based substrate, an inner coating layer disposed on the silicon-based substrate, and an outer coating layer disposed on the inner coating layer; Among them, the Young's modulus of the silicon-based substrate is recorded as A, the Young's modulus of the inner coating layer is recorded as B, and the Young's modulus of the outer coating layer is recorded as C; wherein A, B, and C satisfy the relationship B>A>C; the difference in Young's modulus between the inner coating layer and the silicon-based substrate is defined as α, α=(BA) / A; the difference in Young's modulus between the outer coating layer and the silicon-based substrate is defined as β, β=(CA) / A; α, β satisfy, 0<α<4, -1<β<0.

2. The silicon-based negative electrode material according to claim 1, wherein: The Young's modulus A of the silicon-based substrate is 2-80 GPa, preferably 5-50 GPa; Preferably, the Young's modulus B of the inner coating layer is 20-160 GPa, preferably 50-135 GPa; Preferably, the Young's modulus C of the outer coating layer is 0.5-30 GPa, preferably 5-25 GPa; Preferably, the α satisfies, 0.5≤α≤3.8; Preferably, the β satisfies, -0.8≤β≤-0.

1.

3. The silicon-based negative electrode material according to claim 1 or 2, wherein: The inner coating layer comprises an inner ion-conducting medium and an inner electron-conducting medium, wherein the mass ratio of the inner ion-conducting medium to the inner electron-conducting medium is 0.5:1-10:1, preferably 2:1-8:1; Preferably, the Young's modulus of the inner ion conducting medium is 30-180 GPa, and the ionic conductivity is ≥10 -10 S / cm; Preferably, the inner ion conducting medium is selected from lithium-containing oxides, and more preferably selected from LiNbO3, Li2CO3, Li2SiO3, Li3PO4, LiAlO2, Li4Ti5O 12 , LiTaO3, Li2O, Li3VO4, Li2ZrO3 or more; Preferably, the electronic conductivity of the internal conductive electronic medium is 10-5000 S / cm; Preferably, the internal conductive electronic medium is selected from conductive carbon and / or nano conductive metal; wherein the conductive carbon is selected from carbon nanotubes and / or conductive carbon black, preferably carbon nanotubes, and further preferably aqueous single-walled carbon nanotubes; the nano conductive metal is selected from one or more of Ag, Sn, and Cu, preferably Ag.

4. The silicon-based negative electrode material according to any one of claims 1 to 3, wherein: The outer coating layer comprises an outer ion-conducting medium and an outer electron-conducting medium; wherein the mass ratio of the outer ion-conducting medium to the outer electron-conducting medium is 0.5:1-4.5:1, preferably 1:1-2.5:1; Preferably, the Young's modulus of the external ion conducting medium is 0.5-30 GPa, and the ionic conductivity is ≥10 -8 S / cm; Preferably, the external ion-conducting medium is selected from a sulfide electrolyte doped with a modifying element, and the chemical formula is LiXPSCl; wherein the doping modifying element X is selected from one or more of transition metals, group IIIA, group IVA, and group VA elements, preferably selected from one or more of Si, Sn, Ge, As, Y, In, Al, and Zn; further preferably, the external ion-conducting medium is one or more of LiSiPSCl, LiSnPSCl, LiGePSCl, LiYPSCl, LiInPSCl, and LiAlPSCl, more preferably one or more of LiSiPSCl, LiSnPSCl, and LiGePSCl; Preferably, the electronic conductivity of the external conductive medium is 10-5000 S / cm; Preferably, the external conductive electronic medium is selected from conductive carbon and / or nano conductive metal; wherein the conductive carbon is selected from carbon nanotubes and / or conductive carbon black, preferably carbon nanotubes, and further preferably oil-based single-walled carbon nanotubes; the nano conductive metal is selected from one or more of Sn, In, and Ga, preferably Sn and / or In.

5. The silicon-based negative electrode material according to any one of claims 1 to 4, wherein: The median particle size of the silicon-based negative electrode material is 100nm-16μm, preferably 200nm-12μm; Preferably, the thickness of the inner coating layer is 1-10 nm, preferably 2-5 nm; Preferably, the thickness of the outer coating layer is 5-100 nm, preferably 10-50 nm; Preferably, the mass ratio of the silicon-based substrate, the inner coating layer and the outer coating layer is 100:0.2:2-100:10:40, preferably 100:1:5-100:8:

20.

6. A method for preparing a silicon-based negative electrode material, characterized in that: The method comprises the following steps: (1) mixing a silicon-based substrate, an inner-conducting electron medium, an inner-conducting ion medium or an inner-conducting ion medium precursor with a first solvent, and stirring to obtain a first dispersion; (2) removing the first solvent in the first dispersion and performing a first heat treatment to obtain an intermediate I having an inner coating layer formed on a silicon-based substrate; (3) mixing the intermediate I, the external electron-conducting medium, the external ion-conducting medium or the external ion-conducting medium precursor with a second solvent, and stirring to obtain a second dispersion; (4) After removing the second solvent in the second dispersion, a second heat treatment is performed to obtain a silicon-based negative electrode material coated with an inner coating layer and an outer coating layer.

7. The preparation method according to claim 6, wherein: In step (1), Preferably, the silicon-based substrate is selected from one or more of silicon-oxygen materials, silicon-carbon, and pure silicon; Preferably, the internal conductive electron medium is selected from conductive carbon and / or nano conductive metal; Preferably, the inner ion conducting medium is selected from lithium-containing oxides; Preferably, the mass ratio of the silicon-based substrate, the inner electron-conducting medium, and the inner ion-conducting medium is 100:0.5:0.5-100:4.5:4.5; Preferably, the inner ion conducting medium precursor is a raw material required for synthesizing the inner ion conducting medium, and the amount of the inner ion conducting medium precursor is calculated based on the mass of the corresponding inner ion conducting medium; In step (2), Preferably, the first heat treatment conditions include: a heating rate of the first heat treatment of 1-10°C / min, a temperature of the first heat treatment of 400-1000°C, and a coating time of the first heat treatment of 1-8h; In step (3), Preferably, the external conductive electron medium is selected from conductive carbon and / or nano conductive metal; Preferably, the external ion conducting medium is selected from a sulfide electrolyte doped with a modified element, and the chemical formula is LiXPSCl; wherein the doped modified element X is selected from one or more of transition metals, group IIIA, group IVA, and group VA elements; Preferably, the mass ratio of the intermediate I, the external electron-conducting medium, and the external ion-conducting medium is 100:2:2-100:20:20; Preferably, the external ion-conducting medium precursor is a raw material required for synthesizing the external ion-conducting medium, and the amount of the external ion-conducting medium precursor is calculated based on the mass of the corresponding external ion-conducting medium; In step (4), Preferably, the operating conditions of the second heat treatment include: a heating rate of the second heat treatment of 1-10°C / min, a temperature of the second heat treatment of 300-600°C, and a time of the second heat treatment of 1-8h.

8. A negative electrode plate, characterized in that: The negative electrode plate comprises the silicon-based negative electrode material described in any one of claims 1 to 5 or the silicon-based negative electrode material prepared by the preparation method described in claim 6 or 7.

9. The negative electrode sheet according to claim 8, wherein: The negative electrode plate further includes a flexible solid electrolyte additive; wherein the Young's modulus of the flexible solid electrolyte additive is lower than the Young's modulus of the sulfide solid electrolyte; Preferably, the Young's modulus of the flexible solid electrolyte additive is ≤5 Gpa; Preferably, the flexible solid electrolyte additive is selected from halide electrolytes and / or polymer electrolytes; Preferably, the chemical formula of the halide electrolyte is LiX' m Y' n , wherein X' is a metal element selected from one or more of In, As, Ta, Y, Sr, Sn, Al, and Ti, Y' is a halogen selected from one or more of F, Cl, Br, and I, 0<m<1, 0<n<1; further preferably, the flexible solid electrolyte additive is selected from one or more of LiYCl, LiInCl, LiTaCl, LiTiCl, LiAlCl, LiAsCl, LiYI, and LiInI, preferably one or more of amorphous LiInCl, LiTaCl, LiTiCl, and LiAlCl; Preferably, the polymer electrolyte is selected from PEO-based polymer electrolyte, PAN-based polymer electrolyte, PDMA-based polymer electrolyte, PDOL-based polymer electrolyte, preferably PEO-based polymer electrolyte.

10. The negative electrode sheet according to claim 8 or 9, wherein: The negative electrode plate comprises a current collector and 50-90 parts by weight of a silicon-based negative electrode material, 0-20 parts by weight of a flexible solid electrolyte additive, 10-40 parts by weight of a sulfide solid electrolyte, 1-10 parts by weight of a conductive agent and 0.1-2 parts by weight of a binder disposed on the current collector; Preferably, the negative electrode plate includes a current collector and 60-80 parts by weight of a silicon-based negative electrode material, 5-10 parts by weight of a flexible solid electrolyte additive, 20-30 parts by weight of a sulfide solid electrolyte, 2-5 parts by weight of a conductive agent and 0.5-1 parts by weight of a binder disposed on the current collector.

11. An all-solid-state battery, characterized in that: The negative electrode sheet comprises the negative electrode sheet as described in any one of claims 8 to 10.

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