Co-coated silicon-based negative electrode material, preparation method thereof, negative electrode sheet and lithium ion battery

Abstract

The present application relates to the technical field of lithium ion batteries, and particularly relates to a co-coated silicon-based negative electrode material and a preparation method, a negative electrode sheet and a lithium ion battery. The negative electrode material comprises a silicon-based material and a coating layer, wherein the coating layer is a composite containing fluoride M x F α and nitride M' y N β ; wherein M and M' are each independently selected from non-lithium metal elements, and x, y, alpha and beta are each independently selected from natural numbers of 1-4; wherein the melting point of the composite is < the melting point of the fluoride, and the melting point of the composite is < the melting point of the nitride. The negative electrode material provided by the present application not only realizes continuous and uniform coating, but also generates LiF and Li3N in situ, as well as non-lithium metal and / or lithium alloy, after pre-lithiation or formation treatment, effectively improving the electrical conductivity, lithium ion transmission and interface stability, thereby effectively improving the electrochemical performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a co-coated silicon-based anode material, a method for preparing the co-coated silicon-based anode material, an anode sheet, and a lithium-ion battery. Background Technology

[0002] Silicon, as a preferred anode material for high-energy-density lithium-ion batteries, has attracted increasing attention due to its advantages such as high specific capacity, low lithium intercalation platform, abundant reserves, and low cost. However, silicon still faces challenges in practical applications, including interface instability and slow lithium-ion transport, hindering its use in liquid and solid-state lithium-ion batteries. To enable silicon anodes to enter the high-energy-density lithium-ion battery market as soon as possible, many interface design strategies for silicon anodes have been proposed.

[0003] CN109286014A discloses a surface-modified silicon-carbon composite material and its preparation method, which combines silicon oxide and fluoride through mechanical ball milling to obtain a modified silicon-based composite material. However, the above-mentioned fluoride coating for silicon anode materials still has the following problems: On the one hand, single fluorides have high melting points and are distributed discontinuously as dots or islands on the silicon surface, failing to form a complete coating interface layer; on the other hand, during the electrochemical lithium intercalation process, the LiF phase generated by this fluoride coating layer still suffers from slow lithium-ion transport speed and insufficient electronic conductivity, which causes charge accumulation at the interface, increased polarization inside the electrode, and ultimately poor rate performance and short cycle life.

[0004] CN109841817A discloses a modified lithium-based composite anode material for solid-state batteries and its preparation. The modified lithium metal composite anode is obtained by heating and melting metallic lithium and mixing it with one or more of nitride or fluoride additives. This prior art uses metallic lithium as the main component and nitride or fluoride as additives, with the metallic lithium and nitride or fluoride physically heated and melted to generate lithium nitride and / or lithium fluoride. In addition, this technology cannot be directly used as a surface coating technology for anode materials. The main problems are as follows: (1) The reaction of nitrides or fluorides with molten lithium needs to be carried out in an inert atmosphere. This method of pre-reaction with lithium is not suitable for the surface coating of silicon anode materials and cannot obtain environmentally stable silicon anode materials; (2) During the thermal reaction, the formed products will nucleate and grow, often resulting in coarse grains and poor conductivity; (3) In the lithium metal anode system, there is no limitation on the melting point or ratio of fluorides or nitrides. There can be one or multiple types. Therefore, fluorides and nitrides are still solid particles. So the final effect is that lithium-containing fluorides or nitrides are dispersed in the liquid lithium metal in the form of bulk particles. It is not a uniform continuous phase and cannot achieve uniform coating of silicon anode materials. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of uneven / discontinuous / single coating, poor conductivity, and high melting point of existing silicon-based anode materials. This invention provides a co-coated silicon-based anode material, a method for preparing the co-coated silicon-based anode material, an anode electrode containing the anode material, and a lithium-ion battery containing the anode electrode. The anode material uses a fluoride and nitride composite as the coating layer, achieving not only continuous and uniform coating, but also, through pre-lithiation or formation treatment, in-situ generation of LiF and Li3N, as well as non-lithium metals and / or lithium alloys, effectively improving conductivity, lithium-ion transport, and interface stability, thereby effectively improving electrochemical performance.

[0006] To achieve the above objectives, a first aspect of the present invention provides a co-coated silicon-based anode material, the anode material comprising: a silicon-based material and a coating layer, wherein the coating layer is a fluoride-containing M... x F α and nitride M' y N β The complex; wherein M and M' are each independently selected from non-lithium metal elements, and x, y, α and β are each independently selected from natural numbers from 1 to 4;

[0007] Wherein, the melting point of the composite is less than the melting point of the fluoride, and the melting point of the composite is less than the melting point of the nitride.

[0008] The inventors of this invention have discovered that the key problem limiting the application of silicon anodes in lithium-ion batteries lies in the fact that lithium ions do not have a fast desolvation rate and interface migration ability at the electrolyte-anode interface, resulting in obstructed transport and severe capacity decay.

[0009] To address this issue, this invention aims to modify the interfacial dynamics of silicon-based materials by constructing a stable fluoride and nitride composite interfacial layer on their surface, thereby improving the electrode / electrolyte interfacial dynamics and optimizing the full-cell performance. However, current fluoride coatings for silicon materials are all point-like and discontinuous coatings, which lead to exposed surfaces, unstable interfaces, and insufficient interfacial lithium-ion diffusion capacity.

[0010] Based on this, this application uses fluoride M x F α and nitride M' y N βThe composite material, in particular, by optimizing the types and ratios of fluorides and nitrides, thereby controlling the melting point of the composite material, constructs a thin and dense multi-component composite interface on the surface of silicon-based material particles under low-temperature conditions. It can exist stably in air and can be produced and transported under normal conditions. At the same time, the composite material can undergo a lithium intercalation reaction during the battery formation stage by means of electrochemical in-situ conversion technology, which can generate a nanoscale mixed ion / electron conductor with high ion and electron transport capacity, thereby improving lithium ion transport and interface stability at the silicon anode interface.

[0011] In this invention, unless otherwise specified, the co-coated silicon-based anode material is simply referred to as the anode material; this anode material uses a silicon-based material as its core and contains fluoride M. x F α and nitride M' y N β The complex is used as a coating layer.

[0012] Preferably, in the composite, the mass ratio of fluoride to nitride is 1:9-4:1, and more preferably 3:7-7:3.

[0013] A second aspect of the present invention provides a method for preparing a co-coated silicon-based anode material, the method comprising the following steps:

[0014] (1) Fluoride M x F α and nitride M' y N β The first mixing is performed to obtain a complex;

[0015] (2) In an inert atmosphere, the composite and the silicon-based material are mixed and heat-treated in sequence to coat the surface of the silicon-based material with the composite, thereby obtaining a co-coated silicon-based anode material.

[0016] Wherein, M and M' are each independently selected from non-lithium metal elements, and x, y, α and β are each independently selected from natural numbers from 1 to 4.

[0017] A third aspect of the present invention provides a negative electrode sheet, the negative electrode sheet comprising the negative electrode material provided in the first aspect, or the negative electrode material prepared by the preparation method provided in the second aspect.

[0018] A fourth aspect of the present invention provides a lithium-ion battery, the lithium-ion battery comprising: a positive electrode, an electrolyte, and a negative electrode provided in the third aspect.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] (1) The negative electrode material provided by the present invention uses a fluoride M xF α and nitride M' y N β The composite material can be used to coat silicon-based materials in a multi-element manner. This not only solves the problem of single fluoride or single nitride coating being dot-like and discontinuous, but also constructs a uniform and dense multi-element fluoride or nitride interface on the surface of silicon-based materials. Furthermore, it can solve the problem of high melting point of single fluoride or single nitride. In particular, by controlling the type and mass ratio of fluoride or nitride, the melting point of the composite material can be controlled, enabling uniform coating of silicon-based materials at low temperature conditions.

[0021] Furthermore, some of the composites can form continuous crystalline LiF and Li3N, as well as non-lithium metals and / or lithium alloys in situ during lithium intercalation. Specifically, LiF and Li3N maintain a higher affinity for lithium ions, effectively promoting the formation of lithium-ion intercalation. + The desolvation and migration of lithium metals into the solid electrolyte interface (SEI) form a stable SEI interface and create a uniform ion flow channel. Non-lithium metals and / or lithium alloys retain a certain electronic conductivity, thereby forming a uniform dual-particle flow transport channel at the interface, effectively improving the ionic conductivity and electronic conductivity of the negative electrode.

[0022] (2) When the negative electrode sheet provided by the present invention is used in a lithium-ion battery, the rate performance and cycle stability of the battery can be further improved due to the synergistic effect of multi-metal fluorides and nitrides, ultimately realizing the development and application of high energy density lithium-ion batteries. Attached Figure Description

[0023] Figure 1 The image shows a scanning electron microscope (SEM) image of the negative electrode material S1 prepared in Example 1.

[0024] Figure 2 Scanning electron microscope image of the negative electrode material DS1 prepared for Comparative Example 1;

[0025] Figure 3 This is a graph showing the first charge-discharge curve of a lithium-ion battery assembled from the negative electrode material S1 prepared in Example 1.

[0026] Figure 4 The graph shows the rate and cycle performance of a lithium-ion battery assembled from the negative electrode material S1 prepared in Example 1. Detailed Implementation

[0027] The endpoints and any values ​​of the ranges disclosed herein 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 the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0028] In this invention, unless otherwise specified, "first" and "second" do not indicate a sequence or limit the specific materials or steps; they are merely used to distinguish or indicate that these are not the same material or step. For example, "first" and "second" in "first mixture" and "second mixture" are only used to indicate that these are not the same mixture.

[0029] The first aspect of this invention provides a co-coated silicon-based anode material, the anode material comprising: a silicon-based material and a coating layer, wherein the coating layer is a fluoride-containing material M x F α and nitride M' y N β The complex, wherein M and M' are each independently selected from non-lithium metal elements, and x, y, α and β are each independently selected from natural numbers from 1 to 4;

[0030] Wherein, the melting point of the composite is less than the melting point of the fluoride, and the melting point of the composite is less than the melting point of the nitride.

[0031] In this invention, compared to coatings with a single fluoride or a single nitride, the simultaneous presence of both offers the following advantages: ① The multiphase, multi-compound composite structure, with the retention of low-melting-point fluorides, solves the problem of poor coating effects of high-melting-point nitrides at the process stage. Simultaneously, it retains the high mechanical strength advantage of LiF generated in situ during electrochemical processes, adapting to the large volume expansion of silicon; ② The introduction of nitrides, with the high ionic conductivity Li3N generated in situ during electrochemical processes, can compensate for the LiF converted during fluoride coating, improving the Li... + The problem of insufficient transmission capacity.

[0032] Therefore, simultaneous coating with fluorides and nitrides is significantly more effective than coating with either a single fluoride or nitride. The synergistic effect of both further promotes the growth of Li. + Migration within the SEI forms a high-mechanical-strength SEI interface, creating a uniform ion flow channel. Simultaneously, non-lithium metals and / or lithium alloys are generated as electronically conductive phases, enhancing electronic conductivity. This results in a uniform dual-particle flow transport channel at the interface, which can be applied to high-energy-density liquid and solid-state lithium-ion batteries with excellent rate performance and good cycle stability.

[0033] In this invention, unless otherwise specified, non-lithium metal elements refer to metal elements other than lithium.

[0034] In some embodiments of the present invention, preferably, M and M' are each independently selected from metallic elements that form alloys with lithium, or from metallic elements that do not form alloys with lithium.

[0035] In this invention, M and M' can be the same or different.

[0036] In this invention, more preferably, M and M' are each independently selected from at least one of Na, K, Mg, Ca, Al, Sr, Ba, Cu, Fe, Ni, Co, Mn, Ge, W, Zn, In, Mo, Nb, Sn, Ag and W.

[0037] In this invention, the metal elements that form alloys with lithium include, but are not limited to, Sn, Na, Ge, Al, Mg, In, Zn, etc.; the metal elements that do not form alloys with lithium include, but are not limited to, Fe, Ni, Cu, Co, Mn, etc.

[0038] In this invention, more preferably, M is selected from at least one of Na, K, Mg, Al, Cu and Fe, and more preferably from at least one of Na, K, Mg and Cu; M' is selected from at least one of Ge, Cu, Mg, Ag, Mo, Zn, Sn, Co, Ni and W, and more preferably from at least one of Cu, Mg and Mo.

[0039] In this invention, by controlling the types of M and M', the melting point of the composite is controlled, thereby achieving low-temperature melting coating of the composite on the surface of the silicon-based material, forming a dense, continuous and uniform coating layer.

[0040] In some embodiments of the present invention, preferably, the melting point of the fluoride is ≤1300℃, more preferably 800-1300℃, for example, 800℃, 900℃, 1000℃, 1100℃, 1200℃, 1300℃, and any value within a range of any two values.

[0041] In this invention, unless otherwise specified, the melting point parameter is measured using differential scanning calorimetry.

[0042] In this invention, a wide range of types of fluorides can be selected, as long as the above-mentioned limitations are met. Preferably, the fluoride is selected from at least one of NaF, KF, MgF2, AlF3, CuF2, CuF, FeF3, and FeF2, and more preferably from at least one of NaF, MgF2, and AlF3.

[0043] In this invention, the melting point of NaF is 993℃, the melting point of KF is 858℃, the melting point of MgF2 is 1261℃, the melting point of AlF3 is 1040℃, the melting point of CuF2 is 908℃, the melting point of CuF is 950℃, the melting point of FeF3 is 1000℃, and the melting point of FeF2 is >1000℃.

[0044] In some embodiments of the present invention, preferably, the melting point of the nitride is ≤1100℃, more preferably 200-1100℃, for example, 200℃, 300℃, 400℃, 500℃, 800℃, 1000℃, 1100℃, and any value within a range of any two values.

[0045] In this invention, the types of nitrides can be selected from a wide range, as long as they meet the above-mentioned limitations. Preferably, the nitride is selected from at least one of Ge3N4, Cu3N, Cu3N3, Zn3N2, Mg3N2, Ag3N, Sn4N3, CoN, Ni3N, MoN2, and WN2, and more preferably from at least one of Cu3N, Mg3N2, and MoN2.

[0046] In this invention, the melting point of Ge3N4 is 850℃, the melting point of Cu3N is 300℃, the melting point of Mg3N2 is 800℃, the melting point of Ag3N is 175℃, the melting point of MoN2 is 790℃, and the melting point of WN2 is 600℃.

[0047] In some embodiments of the present invention, preferably, the average particle size of the fluoride and nitride is independently 10-200 nm, for example, 10 nm, 20 nm, 25 nm, 30 nm, 40 nm, 50 nm, 80 nm, 100 nm, 150 nm, 200 nm, and any value within any range of any two values, preferably 20-50 nm. Reducing the average particle size to the nanometer level can, on the one hand, increase the surface energy of the fluoride and nitride, which is beneficial for adsorption onto the surface of silicon-based materials, achieving a better mixing effect; on the other hand, during heat treatment, nano-sized fluorides and nitrides have higher activity and higher heat transfer efficiency, enabling rapid co-coating.

[0048] In this invention, the average particle size parameter was measured using a Malvern 3000 laser particle size analyzer.

[0049] In this invention, the average particle size of the fluoride and the nitride can be the same or different.

[0050] In some embodiments of the present invention, it is further preferred that the melting point of the composite is ≤800℃, for example, 800℃, 700℃, 600℃, 550℃, 500℃, 450℃, 400℃, 350℃, 300℃, 250℃, 200℃, and any value within the range of any two values, preferably 200-600℃, more preferably 400-600℃.

[0051] In some embodiments of the present invention, preferably, the composite consists of at least one fluoride and at least one nitride.

[0052] In some embodiments of the present invention, more preferably, the complex consists of one fluoride and two nitrides, or the complex consists of two fluorides and one nitride.

[0053] In this invention, the composite composition that meets the above-defined requirements utilizes the characteristic of a significantly reduced melting point of multiphase mixtures. This not only lowers the melting point of the composite but also achieves dense and uniform coating of silicon-based materials at relatively low temperatures, resulting in superior coating performance.

[0054] In some embodiments of the present invention, preferably, the mass ratio of fluoride to nitride in the composite is 1:9-4:1, for example, 1:9, 1:8, 3:7, 1:2, 4:7, 4:6, 1:1, 6:4, 2:1, 7:3, 8:3, 3:1, 4:1, and any value within any range of any two values, preferably 3:7-7:3. In the present invention, the mass ratio satisfying the above range controls the melting point of the composite, thereby controlling the performance of the negative electrode material.

[0055] In this invention, by controlling the type and mass ratio of fluorides and nitrides in the composite, not only can the melting point of the composite be reduced, but also a dense and uniform coating of silicon-based materials can be achieved at a relatively low temperature, forming a complete and continuous coating layer.

[0056] In some embodiments of the present invention, preferably, based on the total mass of the silicon-based material, the content of the composite is ≤2wt%, for example, 0.01wt%, 0.02wt%, 0.05wt%, 0.1wt%, 0.2wt%, 0.5wt%, 0.8wt%, 1wt%, 1.5wt%, 2wt%, and any value within any range of any two values, preferably 0.05-2wt%, more preferably 0.05-1wt%.

[0057] In this invention, the negative electrode material is composed of a silicon-based material as the core and a composite of fluoride and nitride as the coating layer.

[0058] In some embodiments of the present invention, preferably, the average particle size of the silicon-based material is 0.05-12 μm, for example, 0.05 μm, 0.1 μm, 0.5 μm, 1 μm, 2 μm, 5 μm, 8 μm, 10 μm, 12 μm, and any value within the range of any two values, preferably 2-12 μm.

[0059] In some embodiments of the present invention, preferably, the silicon-based material is selected from silicon materials and / or silicon-carbon materials, and more preferably from at least one of zero-dimensional silicon particles, one-dimensional silicon nanowires, two-dimensional silicon wafers, three-dimensional porous silicon particles and silicon carbide particles.

[0060] In some embodiments of the present invention, preferably, the thickness of the coating layer is ≤10 nm, for example, 10 nm, 8 nm, 5 nm, 4 nm, 3 nm, 2 nm, 1 nm, and any value within the range of any two values, preferably 1-5 nm. In the present invention, the thickness parameter is measured using a high-resolution transmission electron microscope.

[0061] In some embodiments of the present invention, preferably, in the negative electrode material, the first lithium intercalation potential of F and N is 0.8-1.5V; and the second lithium intercalation potential of M and / or M' is 0.001-0.6V. In the present invention, the first and second lithium intercalation potentials are only related to the element species.

[0062] In this invention, the first lithium intercalation potential refers to the potential at which the F element of the fluoride and the N element of the nitride in the composite are converted in situ into LiF and Li3N; the second lithium intercalation potential refers to the potential at which the M element of the fluoride and / or the M' element of the nitride in the composite are converted in situ into lithium alloy (i.e., M-Li and / or M'-Li).

[0063] During the initial lithium intercalation process of the negative electrode material provided by this invention, the fluorides and nitrides in the coating layer first undergo a conversion reaction. The F and N elements can be converted in situ into the LiF phase with excellent mechanical strength and the Li3N phase with higher lithium-ion conductivity, as well as the M metal phase and the M' metal phase. As the lithium intercalation potential continues to decrease, the M metal phase and / or the M' metal phase further alloy with lithium to form a lithium metal alloy dispersed therein, increasing the electronic conductivity of the interface layer.

[0064] In some embodiments of the present invention, preferably, the specific surface area of ​​the negative electrode material is 0.1-30 m². 2 / g, for example, 0.1m 2 / g, 0.5m 2 / g、1m 2 / g、2m 2 / g、5m 2 / g、6m 2 / g、8m 2 / g, 10m 2 / g、20m 2 / g、30m 2 / g, and any value within the range of any two values, preferably 1-10m. 2 / g, more preferably 1-6m 2 / g. In this invention, the specific surface area parameter is measured using the BJH equation based on nitrogen isothermal adsorption-desorption curves.

[0065] In some embodiments of the present invention, preferably, the specific surface area of ​​the negative electrode material is such that the tap density is 0.2-1 g / cc, for example, 0.2 g / cc, 0.5 g / cc, 0.6 g / cc, 0.65 g / cc, 0.7 g / cc, 0.75 g / cc, 0.8 g / cc, 1 g / cc, or any value within a range of any two values, preferably 0.6-0.8 g / cc. In the present invention, the tap density parameter is measured using a tap density meter.

[0066] A second aspect of the present invention provides a method for preparing a co-coated silicon-based anode material, the method comprising the following steps:

[0067] (1) Fluoride M x F α and nitride M' y N β The first mixing is performed to obtain a complex;

[0068] (2) In an inert atmosphere, the composite and the silicon-based material are mixed and heat-treated in sequence to coat the surface of the silicon-based material with the composite, thereby obtaining a co-coated silicon-based anode material.

[0069] Wherein, M and M' are each independently selected from non-lithium metal elements, and x, y, α and β are each independently selected from natural numbers from 1 to 4.

[0070] In this invention, the types and parameters of the fluorides, nitrides and silicon-based materials are limited in accordance with the above-mentioned limitations, and will not be elaborated upon further in this invention.

[0071] In some embodiments of the present invention, preferably, in step (1), the mass ratio of the fluoride to the nitride is 1:9-4:1, for example, 1:9, 1:8, 3:7, 1:2, 4:7, 4:6, 1:1, 6:4, 2:1, 7:3, 8:3, 3:1, 4:1, and any value within any range of any two values, preferably 3:7-7:3. Satisfying the above mass ratio range is more conducive to controlling the melting point of the composite.

[0072] In this invention, the first mixing is intended to uniformly mix the fluoride and nitride. Preferably, the conditions for the first mixing are: temperature of 10-40°C, more preferably 20-30°C; rotation speed of 200-500 rpm; and time of 5-30 min.

[0073] In one specific embodiment of the present invention, fluorides and nitrides with a particle size of 20-200 nm are weighed according to a certain mass ratio, and mixed in a dry environment with an acoustic resonance device at a temperature of 10-40°C and a rotation speed of 200-500 rpm for 5-30 minutes to obtain a composite.

[0074] In this invention, the inert atmosphere includes, but is not limited to, nitrogen atmosphere, helium atmosphere, argon atmosphere, neon atmosphere, etc., and is preferably nitrogen atmosphere.

[0075] In some embodiments of the present invention, preferably, in step (2), the mass ratio of the composite to the silicon-based material is ≤2:100, for example, 2:100, 1.5:100, 1:100, 0.8:100, 0.6:100, 0.5:100, 0.2:100, 0.15:100, 0.1:100, 0.08:100, 0.06:100, 0.05:100, 0.02:100, 0.01:100, and any value within the range of any two values, preferably 0.05-2:100, more preferably 0.05-1:100.

[0076] In this invention, the second mixing is intended to uniformly mix the composite and the silicon-based material. Preferably, the conditions for the second mixing are: a temperature of 10-40°C, more preferably 20-30°C; a rotation speed of 200-800 rpm; and a time of 10-60 min.

[0077] In some embodiments of the present invention, preferably, the temperature difference T between the heat treatment temperature and the melting point of the composite satisfies: -100℃≤T≤100℃, for example, -100℃, -80℃, -60℃, -50℃, -20℃, -10℃, 0℃, 10℃, 20℃, 50℃, 60℃, 80℃, 100℃, and any value within a range of any two values.

[0078] In some embodiments of the present invention, it is further preferred that the temperature of the heat treatment is 200-900°C, for example, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, 700°C, 800°C, 900°C, and any value within the range of any two values, preferably 200-600°C, more preferably 400-600°C.

[0079] In some embodiments of the present invention, more preferably, the heat treatment conditions further include: a heating rate of 2-10℃ / min, preferably 2-5℃ / min; a rotation speed of 100-500rpm, preferably 200-400rpm; and a time of 1-10h, preferably 2-8h.

[0080] In one specific embodiment of the present invention, a suitable mass of silicon-based material with an average particle size of 0.05-12 μm and a certain proportion of composite material are taken and stirred in an inert protective atmosphere using a high-power mixer at a speed of 200-800 rpm for 10-60 min. After uniform mixing, the composite powder is transferred to a high-temperature fusion machine for reaction, and heated to 200-800℃ at a heating rate of 2-10℃ / min, not exceeding the melting point of the composite material. At this temperature, the mixture is stirred at a speed of 100-500 rpm for 1-10 h to achieve low-temperature melting coating of the silicon-based material.

[0081] A third aspect of the present invention provides a negative electrode sheet, the negative electrode sheet comprising the negative electrode material provided in the first aspect, or the negative electrode material prepared by the preparation method provided in the second aspect.

[0082] In this invention, unless otherwise specified, the negative electrode sheet includes: a negative electrode current collector and a negative electrode coating loaded on the negative electrode current collector, wherein the negative electrode coating contains a negative electrode material, a conductive agent, and a binder provided by this invention, wherein the mass ratio of the negative electrode material, the conductive agent, and the binder is 90-99:0.5-5:0.5-5.

[0083] In this invention, the conductive agent is selected from at least one of fumed carbon nanotubes, conductive carbon black, carbon fibers, carbon nanotubes, acetylene black, Ketjen black, graphite, and graphene; the binder is selected from at least one of polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), polytetrafluoroethylene (PTFE), nitrile rubber (NBR), polyacrylonitrile (PAN), polyacrylic acid (PAA), and polyacrylate. In this invention, polyacrylate includes, but is not limited to, polymethyl acrylate, polyethyl acrylate, and polypropyl acrylate.

[0084] In some embodiments of the present invention, preferably, the negative electrode sheet is pre-lithiated or formed to obtain a modified negative electrode sheet, wherein the composite in the negative electrode material is in situ generated to form a modified negative electrode material containing LiF and Li3N, as well as non-lithium metals and / or lithium alloys.

[0085] In this invention, LiF and Li3N serve as ion-conducting phases to improve the ion conductivity of the modified anode material, while non-lithium metals and / or lithium alloys serve as electronically conductive phases to improve the electronic conductivity of the modified anode material.

[0086] In some embodiments of the present invention, preferably, the modified negative electrode sheet has an ionic conductivity of (0.1-10)×10⁻⁶. -8 S / cm, for example, 0.1×10 -8 S / cm, 0.2×10 -8 S / cm, 0.6×10-8 S / cm, 1×10 -8 S / cm, 2×10 - 8 S / cm, 3×10 -8 S / cm, 5×10 -8 S / cm, 8×10 -8 S / cm, 9×10 -8 S / cm, 10×10 -8 S / cm, and any value within the range of any two values, preferably (0.2-10)×10 -8 S / cm, more preferably (0.6-10)×10 -8 S / cm.

[0087] In this invention, unless otherwise specified, the ionic conductivity parameter is measured using the AC impedance method. The specific test includes: clamping the sample between two stainless steel disc electrodes, measuring the ionic conductivity (σ) using electrochemical impedance spectroscopy (EIS) within a frequency range of 1Hz-7MHz with an AC amplitude of 10mV, and applying the formula σ = L / (R). b The calculation is performed using ×S); where R b The volume resistivity (R) of the sample to be tested b (Determined by impedance spectroscopy), where L and S are the thickness and area of ​​the sample to be tested.

[0088] In some embodiments of the present invention, preferably, the electronic conductivity of the modified negative electrode sheet is 0.01-10 S / cm, for example, 0.01 S / cm, 0.02 S / cm, 0.05 S / cm, 0.08 S / cm, 0.1 S / cm, 0.2 S / cm, 0.3 S / cm, 0.4 S / cm, 0.5 S / cm, 0.6 S / cm, 0.8 S / cm, 1 S / cm, 2 S / cm, 5 S / cm, 8 S / cm, 10 S / cm, and any value within any range of any two values, preferably 0.1-10 S / cm, more preferably 0.1-1 S / cm.

[0089] In this invention, unless otherwise specified, the electronic conductivity parameter is measured using the four-probe method. The specific test includes: cutting the sample to be tested into a 4cm × 8cm square, placing the sample under two probes, which are connected to a ohmmeter via two terminals, rotating the handle of the testing device, and applying stable pressure to the probes to compress the electrode. The pressure is controlled by a pressure gauge. Once a certain pressure is reached, the resistance data from the ohmmeter is read; this data is the relative resistance value R of the sample. The electronic conductivity σ' of the electrode is then calculated using the formula σ' = l / (R × s), where l and s are the thickness and area of ​​the sample.

[0090] In some embodiments of the present invention, preferably, the modified negative electrode sheet has a lithium-ion diffusion coefficient ≥ 1.2 × 10⁻⁶. -12 cm 2 / s, preferably (1.2-20)×10 -12 cm 2 / s, for example, 1.2×10 -12 cm 2 / s, 1.4×10 -12 cm 2 / s, 1.8×10 -12 cm 2 / s, 2×10 -12 cm 2 / s, 5×10 -12 cm 2 / s, 8×10 -12 cm 2 / s, 10×10 -12 cm 2 / s, 12×10 -12 cm 2 / s, 15×10 -12 cm 2 / s, 18×10 -12 cm 2 / s, 20×10 -12 cm 2 / s, and any value within a range of any two values. In this invention, the lithium-ion diffusion coefficient parameter is measured using the galvanostatic gap titration (GITT) method.

[0091] In some embodiments of the present invention, preferably, the mechanical strength of the modified negative electrode sheet is ≥2 GPa, for example, 2 GPa, 3 GPa, 5 GPa, 6 GPa, 8 GPa, 8.2 GPa, 8.5 GPa, 8.8 GPa, 9 GPa, 9.2 GPa, 9.5 GPa, 9.8 GPa, 10 GPa, or any value within any range of two such values, preferably 5-10 GPa, more preferably 8-10 GPa. In the present invention, the above mechanical strength parameters are measured using the QNM (Quantitative Nanomechanical Measurement) method.

[0092] In this invention, unless otherwise specified, the ionic conductivity, electronic conductivity, and lithium-ion diffusion coefficient were all measured at room temperature (25 ± 2 °C).

[0093] A fourth aspect of the present invention provides a lithium-ion battery, the lithium-ion battery comprising: a positive electrode, an electrolyte, and a negative electrode provided in the third aspect.

[0094] In this invention, unless otherwise specified, the positive electrode sheet includes: a positive current collector and a positive electrode coating loaded on the positive current collector, wherein the positive electrode coating contains a positive electrode material, a conductive agent, and a binder, wherein the mass ratio of the positive electrode material, the conductive agent, and the binder is 90-99:0.5-5:0.5-5.

[0095] In this invention, the positive electrode material is selected from lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, and lithium nickel cobalt manganese oxide (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (abbreviated as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (abbreviated as NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2 (abbreviated as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi) 0.80 Co 0.15 Al 0.05 At least one of O2 and its modified compounds.

[0096] In this invention, preferably, the electrolyte is selected from at least one of liquid electrolytes, sulfide electrolytes, halide electrolytes, and polymer electrolytes, including but not limited to zLi2S·(100-z)P2S5 (0≤z≤100), Li3PS4, and Li7P3S. 11 Li6PS5X (X = Cl, Br, I) and its derivatives, Li 10 M”P2S 12 (M” = Ge and / or Sn), Li 3.25 Ge 0.25 P 0.75 S4, Li4GeS4, Li 11 Sn2PS 12 Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 Li3InCl6 and its derivative systems, Li 0.388 Ta 0.238 La 0.475Cl3 and its derivative systems, Li5X3M"'2O 12 (M”'=Ta and / or Nb), Li7La3Zr2O 12 and its derivative systems, La 2 / 3-γ Li 3γ At least one of TiO3 (0 < γ < 2 / 3) and its derivatives, NaZr2(PO4)3 and its derivatives, polyethylene oxide (PEO) group and its derivatives, polymethyl ethylene carbonate (PPC), polyacrylonitrile (PAN), polydimethylsiloxane (PDMS), polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA) and its derivatives, and LiBH4.

[0097] The lithium-ion battery provided by this invention has an initial coulombic efficiency (ICE) between 80-87% and a capacity retention rate of 76-83% at 1C.

[0098] The present invention will be described in detail below through embodiments.

[0099] Example 1

[0100] (1) MgF2 (average particle size of 25 nm), Cu3N (average particle size of 25 nm) and Mg3N2 (average particle size of 25 nm) were mixed in a mass ratio of 3:4:3 (300 rpm for 30 min) to obtain composite A1.

[0101] (2) In a nitrogen atmosphere, the above composite A1 and silicon-based material (micron silicon with an average particle size of 3 μm) are mixed in a second mixing process at a mass ratio of 0.5:100 (500 rpm for 60 min) and then heat-treated (500 °C at a heating rate of 3 °C / min, 300 rpm for 4 h) so that the above composite is coated on the surface of the silicon-based material in a molten state to obtain the negative electrode material S1.

[0102] The scanning electron microscope image of the aforementioned negative electrode material S1 is shown below. Figure 1 As shown, a continuous, uniform, and dense coating layer is formed on the surface of the negative electrode material S1.

[0103] Example 2

[0104] The method is the same as in Example 1, except that...

[0105] In step (1), KF (average particle size of 25 nm), NaF (average particle size of 25 nm) and Mg3N2 (average particle size of 25 nm) are mixed in a mass ratio of 3:4:3 to obtain complex A2;

[0106] Under the same conditions, the negative electrode material S2 was obtained.

[0107] Example 3

[0108] The method is the same as in Example 1, except that...

[0109] In step (1), MgF2 (average particle size of 20 nm) and Mg3N2 (average particle size of 25 nm) are mixed in a mass ratio of 3:7 to obtain composite A3;

[0110] Under the same conditions, the negative electrode material S3 was obtained.

[0111] Example 4

[0112] The method is the same as in Example 1, except that...

[0113] In step (1), CuF2 (average particle size of 25 nm) and Cu3N (average particle size of 25 nm) are mixed in a mass ratio of 3:7 to obtain composite A4;

[0114] Under the same conditions, the negative electrode material S4 was obtained.

[0115] Example 5

[0116] The method is the same as in Example 1, except that...

[0117] In step (1), NaF (average particle size of 40 nm) and Cu3N (average particle size of 25 nm) are mixed in a mass ratio of 3:7 to obtain composite A5;

[0118] Under the same conditions, the negative electrode material S5 was obtained.

[0119] Example 6

[0120] The method is the same as in Example 1, except that...

[0121] In step (1), the mass ratio of MgF2, Cu3N and Mg3N2 is replaced with 4:4:3 to obtain complex A6;

[0122] Under the same conditions, the negative electrode material S6 was obtained.

[0123] Example 7

[0124] The method is the same as in Example 1, except that...

[0125] In step (1), the mass ratio of MgF2, Cu3N and Mg3N2 is replaced with 7:4:3 to obtain complex A7;

[0126] Under the same conditions, the negative electrode material S7 was obtained.

[0127] Example 8

[0128] The method is the same as in Example 1, except that...

[0129] In step (1), the mass ratio of MgF2, Cu3N and Mg3N2 is replaced with 8:2:1 to obtain complex A8;

[0130] Under the same conditions, the negative electrode material S8 was obtained.

[0131] Example 9

[0132] The method is the same as in Example 1, except that...

[0133] In step (1), the mass ratio of MgF2, Cu3N and Mg3N2 is replaced with 9:1:1 to obtain complex A9;

[0134] Under the same conditions, the negative electrode material S9 was obtained.

[0135] Example 10

[0136] The method is the same as in Example 1, except that...

[0137] In step (1), the mass ratio of MgF2, Cu3N and Mg3N2 is replaced with 1:5:5 to obtain the complex A10;

[0138] Under the same conditions, the negative electrode material S10 was obtained.

[0139] Example 11

[0140] The method is the same as in Example 1, except that...

[0141] In step (2), the mass ratio of the above composite A1 to the silicon-based material is replaced with 0.2:100; the other conditions are the same, and the negative electrode material S11 is obtained.

[0142] Example 12

[0143] The method is the same as in Example 1, except that...

[0144] In step (2), the mass ratio of the above composite A1 to the silicon-based material is replaced with 1:100; the other conditions are the same, and the negative electrode material S12 is obtained.

[0145] Example 13

[0146] The method is the same as in Example 1, except that...

[0147] In step (2), the mass ratio of the above composite A1 to the silicon-based material is replaced with 2:100; the other conditions are the same, and the negative electrode material S13 is obtained.

[0148] Example 14

[0149] The method is the same as in Example 1, except that...

[0150] In step (2), the heat treatment temperature is replaced with 400℃;

[0151] Under the same conditions, the negative electrode material S14 was obtained.

[0152] Example 15

[0153] The method is the same as in Example 1, except that...

[0154] In step (2), the heat treatment temperature is replaced with 600℃;

[0155] Under the same conditions, the negative electrode material S15 was obtained.

[0156] Example 16

[0157] The method is the same as in Example 1, except that...

[0158] In step (2), the heat treatment time is replaced with 2 hours;

[0159] Under the same conditions, the negative electrode material S16 was obtained.

[0160] Example 17

[0161] The method is the same as in Example 1, except that...

[0162] In step (2), the heat treatment time is replaced with 8 hours;

[0163] Under the same conditions, the negative electrode material S17 was obtained.

[0164] Comparative Example 1

[0165] In a nitrogen atmosphere, MgF2 (average particle size of 25 nm) and silicon-based material (micron-sized silicon with an average particle size of 3 μm) were mixed sequentially at a mass ratio of 0.5:100 (300 rpm for 30 min) and then heat-treated (500 °C at a heating rate of 3 °C / min, 300 rpm for 4 h) to obtain the negative electrode material DS1.

[0166] The scanning electron microscope image of the aforementioned negative electrode material DS1 is shown below. Figure 2 As shown, a discontinuous, island-like coating layer is formed on the surface of the negative electrode material DS1.

[0167] Comparative Example 2

[0168] The method is the same as in Example 1, except that...

[0169] In step (1), MgF2 and CuF2 are mixed in a mass ratio of 5:5 to obtain the complex DA2;

[0170] Under the same conditions, the negative electrode material DS2 was obtained.

[0171] Comparative Example 3

[0172] In a nitrogen atmosphere, Mg3N2 (average particle size of 25 nm) and silicon-based material (micron-sized silicon with an average particle size of 3 μm) were mixed sequentially at a mass ratio of 0.5:100 (300 rpm for 30 min) and then heat-treated (500 °C at a heating rate of 3 °C / min, 300 rpm for 4 h) to obtain the negative electrode material DS3.

[0173] Comparative Example 4

[0174] The method is the same as in Example 1, except that...

[0175] In step (1), LiF and Li3N are mixed in a mass ratio of 3:7 to obtain the complex DA4;

[0176] Under the same conditions, the negative electrode material DS4 was obtained.

[0177] Table 1

[0178]

[0179] Note: 1- Mass ratio of each component in the composite; 2- Composite content (wt%) based on the total mass of silicon-based materials.

[0180] As can be seen from the results in Table 1, compared with Comparative Examples 1-4, Examples 1-17 use a coating layer containing fluorides and nitrides. In particular, by controlling the types and mass ratios of fluorides and nitrides, the composite not only has a lower melting point, but also achieves a uniform and dense coating effect when coated under low-temperature heat treatment. Furthermore, it effectively optimizes the physical properties of the negative electrode material, that is, it has both low specific surface area and high tap density.

[0181] Test case

[0182] Negative electrode preparation: 10g of negative electrode material (S1-S17 and DS1-DS4), 0.1g of VGCF, 0.1g of graphene powder, and 0.1g of conductive carbon black were added to a mixer and stirred at low speed (400rpm) for 15min to mix evenly. Then, 0.7g of polytetrafluoroethylene (PTFE) was added and stirred at low speed (400rpm) for 15min to mix evenly. The mixture was then stirred at high speed (8000rpm) for 30min to induce fibrosis. The mixed powder was placed in a roller press and hot-rolled at 150℃ to form a self-supporting film. Finally, it was combined with a current collector by hot-rolling to obtain the negative electrode sheet.

[0183] Preparation of positive electrode sheet: The positive electrode material (NCM811), conductive carbon black SP, PVDF, and (succinic acid + LiTFSI) are dissolved or dispersed in solvent NMP at a mass ratio of 97:1:1:1 and stirred thoroughly for 8 hours to obtain a positive electrode slurry. The slurry is coated and dried under vacuum at 100°C for 12 hours to obtain the positive electrode sheet.

[0184] Lithium-ion battery preparation: The above-mentioned positive electrode sheet, alumina-coated separator and negative electrode sheet are stacked in a CR2036 button stainless steel battery case and assembled into a complete battery.

[0185] The first charge-discharge curve of the lithium-ion battery assembled from the negative electrode material S1 prepared in Example 1 is shown in the figure below. Figure 3 As shown, the battery has a high 0.1C first-cycle charge-discharge specific capacity.

[0186] The rate and cycle performance of the lithium-ion battery assembled from the negative electrode material S1 prepared in Example 1 are shown in the figure below. Figure 4 As shown, this battery has excellent rate performance, with a 1C capacity retention rate of up to 82.8%.

[0187] Table 2

[0188]

[0189] Continued from Table 2

[0190]

[0191]

[0192] As shown in Table 2, compared with Comparative Examples 1-4, Examples 1-17 use the negative electrode material provided by the present invention for the first lithium intercalation process. Because the fluorides and nitrides in the coating layer are transformed in situ into the LiF phase with excellent mechanical strength and the Li3N phase with higher lithium-ion conductivity, as well as non-lithium metals and / or lithium alloys, the ionic conductivity, electronic conductivity and lithium-ion diffusion coefficient of the modified negative electrode sheet, the mechanical strength of the modified negative electrode sheet, and the rate performance and cycle stability of the battery are effectively improved.

[0193] (1) The influence of coating type on the performance of negative electrode material

[0194] Compared to Comparative Example 1, which uses a single fluoride coating, Comparative Example 2, which uses two fluorides, Comparative Example 3, which uses a single nitride coating, and Comparative Example 4, which directly uses LiF and Li3N for coating, Example 1 uses a composite of one fluoride and two nitrides for simultaneous coating, and Example 2 uses a composite of two fluorides and one nitride for simultaneous coating. This not only effectively lowers the melting point of the composite but also provides higher conductivity and lithium-ion diffusion coefficient. Furthermore, batteries containing this negative electrode material exhibit higher rate performance and cycle stability. However, coating with a single nitride, fluoride, or two fluorides cannot achieve a dense and uniform coating, thus exhibiting poor electrochemical performance. This invention, through the synergistic effect of fluorides and nitrides, generates LiF and Li3N, as well as non-lithium metals and / or lithium alloys, in situ during the electrochemical process, effectively improving conductivity, lithium-ion transport, and interface stability, thereby significantly improving electrochemical performance.

[0195] Examples 1 and 3-5 demonstrate that controlling the types of fluorides and nitrides in the composite can regulate its melting point. As the number of components in the composite increases, the melting point decreases, allowing for complete melting and coating under the same heat treatment process. This results in a smaller specific surface area and better coating effect. Furthermore, a suitable component ratio improves coating uniformity and further optimizes electrochemical performance.

[0196] (2) Effect of the mass ratio of fluoride and nitride in the coating layer on the performance of the anode material

[0197] As can be seen from Examples 1 and 6-8, the melting point of the composite can be controlled by adjusting the mass ratio of fluoride to nitride in the composite. When the content of high-melting-point fluoride increases, the melting point of the composite increases accordingly. As can be seen from Examples 1 and 9-10, when the mass ratio of fluoride to nitride is within the range defined by this invention, it is more beneficial to improve the electrochemical performance of the battery. This may be because when the mass ratio of fluoride to nitride is within the range defined by this invention, it can ensure that the mass ratio is not too low, which would cause the composite to approach the properties of only nitride, and that the mass ratio is not too high, which would cause the composite to approach the properties of only fluoride, thus preventing better co-coating, increasing the specific surface area, and deteriorating the coating effect.

[0198] (3) The effect of the mass ratio of the coating layer to the silicon-based material on the performance of the anode material

[0199] As can be seen from Examples 1 and 11-13, by adjusting the mass ratio of the composite to the silicon-based material, the electronic conductivity decreases and the rate performance deteriorates as the coating ratio increases. A suitable mass ratio is beneficial to the performance.

[0200] (4) Effects of heat treatment temperature and time on the properties of anode materials

[0201] As can be seen from Examples 1 and 14-15, the electrochemical performance changes with the temperature of the heat treatment. This is because as the heat treatment temperature increases, the melting rate of the composite accelerates, leading to a higher nucleation rate upon cooling, which in turn promotes grain growth, resulting in poor coating and the formation of island-like coatings. If the heat treatment temperature is too low, the melting effect is insufficient, and coating cannot be achieved. Therefore, selecting a suitable heat treatment temperature is more beneficial for improving the initial coulombic efficiency, specific charge capacity, and capacity retention of the battery.

[0202] As can be seen from Examples 1 and 16-17, the coating effect can be optimized by adjusting the heat treatment time. If the heat treatment time is too short, the fluidity is poor and complete coating cannot be achieved; if the heat treatment time is too long, the diffusion distance is too long, which will also cause some surface to be exposed, affecting the coating effect.

[0203] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A co-coated silicon-based anode material, characterized in that, The negative electrode material includes: a silicon-based material and a coating layer, wherein the coating layer contains fluoride M. x F α and nitride M' y N β The complex, wherein M and M' are each independently selected from non-lithium metal elements, and x, y, α and β are each independently selected from natural numbers from 1 to 4; Wherein, the melting point of the composite is less than the melting point of the fluoride, and the melting point of the composite is less than the melting point of the nitride.

2. The negative electrode material according to claim 1, wherein, M and M' are each independently selected from metallic elements that form alloys with lithium, or from metallic elements that do not form alloys with lithium; Preferably, M and M' are each independently selected from at least one of Na, K, Mg, Ca, Al, Sr, Ba, Cu, Fe, Ni, Co, Mn, Ge, W, Zn, In, Mo, Nb, Sn, Ag, and W; More preferably, M is selected from at least one of Na, K, Mg, Al, Cu and Fe; and M' is selected from at least one of Ge, Cu, Mg, Ag, Mo, Zn, Sn, Co, Ni and W.

3. The negative electrode material according to claim 1 or 2, wherein, The fluoride has a melting point ≤1300℃ and is preferably selected from at least one of NaF, KF, MgF2, AlF3, CuF2, CuF, FeF3 and FeF2, more preferably selected from at least one of NaF, MgF2 and AlF3; Preferably, the nitride has a melting point ≤1100℃, and the nitride is selected from at least one of Ge3N4, Cu3N, Cu3N3, Zn3N2, Mg3N2, Ag3N, Sn4N3, CoN, Ni3N, MoN2 and WN2, and more preferably from at least one of Cu3N, Mg3N2 and MoN2; Preferably, the average particle size of the fluoride and nitride is 10-200 nm, and more preferably 20-50 nm.

4. The negative electrode material according to any one of claims 1-3, wherein, The melting point of the composite is ≤800℃, preferably 200-600℃, and more preferably 400-600℃; Preferably, the complex consists of at least one fluoride and at least one nitride.

5. The negative electrode material according to any one of claims 1-4, wherein, In the composite, the mass ratio of fluoride to nitride is 1:9-4:1, preferably 3:7-7:3; Preferably, based on the total mass of the silicon-based material, the content of the composite is ≤2wt%, more preferably 0.05-2wt%, and more preferably 0.05-1wt%.

6. The negative electrode material according to any one of claims 1-5, wherein, The average particle size of the silicon-based material is 0.05-12 μm, preferably 2-12 μm; Preferably, the silicon-based material is selected from silicon materials and / or silicon-carbon materials, and more preferably from at least one of zero-dimensional silicon particles, one-dimensional silicon nanowires, two-dimensional silicon wafers, three-dimensional porous silicon particles, and silicon carbide particles; Preferably, the thickness of the coating layer is ≤10nm, and more preferably 1-5nm.

7. The negative electrode material according to any one of claims 1-6, wherein, In the negative electrode material, the first lithium intercalation potential of F and N is 0.8-1.5V; the second lithium intercalation potential of M and / or M' is 0.001-0.6V; Preferably, the specific surface area of ​​the negative electrode material is 0.1-30 m². 2 / g, preferably 1-10m 2 / g; Preferably, the tap density of the negative electrode material is 0.2-1 g / cc, and more preferably 0.6-0.8 g / cc.

8. A method for preparing a co-coated silicon-based anode material, characterized in that, The preparation method includes the following steps: (1) Fluoride M x F α and nitride M' y N β The first mixing is performed to obtain a complex; (2) In an inert atmosphere, the composite and the silicon-based material are mixed and heat-treated in sequence to coat the surface of the silicon-based material with the composite, thereby obtaining a co-coated silicon-based anode material. Wherein, M and M' are each independently selected from non-lithium metal elements, and x, y, α and β are each independently selected from natural numbers from 1 to 4.

9. The preparation method according to claim 8, wherein, In step (1), the mass ratio of the fluoride to the nitride is 1:9-4:1, preferably 3:7-7:3; Preferably, in step (2), the mass ratio of the composite to the silicon-based material is ≤2:100, more preferably 0.05-2:100, and more preferably 0.05-0.1:100; Preferably, the temperature difference T between the heat treatment temperature and the melting point of the composite satisfies: -100℃≤T≤100℃; Preferably, the heat treatment temperature is 200-900℃, more preferably 200-600℃, and even more preferably 400-600℃; Preferably, the heat treatment conditions further include: a heating rate of 2-10℃ / min, preferably 2-5℃ / min; a rotation speed of 100-500rpm, preferably 200-400rpm; and a time of 1-10h, preferably 2-8h.

10. A negative electrode sheet, characterized in that, The negative electrode sheet comprises the negative electrode material according to any one of claims 1-7, or the negative electrode material prepared by the preparation method according to claim 8 or 9.

11. The negative electrode sheet according to claim 10, wherein, The negative electrode sheet is pre-lithiated or formed to obtain a modified negative electrode sheet; The composite in the negative electrode material can generate in situ modified negative electrode materials containing LiF and Li3N, as well as non-lithium metals and / or lithium alloys. Preferably, the modified negative electrode has an ionic conductivity of (0.1-10)×10⁻⁶. -8 S / cm, preferably (0.2-10)×10 -8 S / cm; Preferably, the modified negative electrode has an electronic conductivity of 0.01-10 S / cm, more preferably 0.1-10 S / cm; Preferably, the modified negative electrode has a lithium-ion diffusion coefficient ≥ 1.2 × 10⁻⁶. -12 cm 2 / s, preferably (1.2-20)×10 -12 cm 2 / s; Preferably, the mechanical strength of the modified negative electrode sheet is ≥2GPa, and more preferably 5-10GPa.

12. A lithium-ion battery, characterized in that, The lithium-ion battery includes: a positive electrode, an electrolyte, and a negative electrode as described in claim 10 or 11. Preferably, the electrolyte is selected from at least one of liquid electrolytes, oxide electrolytes, sulfide electrolytes, halide electrolytes, and polymer electrolytes.

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