Negative electrode material, preparation method thereof and lithium ion battery

Abstract

The invention discloses a negative electrode material, a preparation method thereof and a lithium ion battery, and relates to the technical field of lithium ion batteries. The negative electrode material comprises a porous carbon matrix and silicon, wherein the silicon is dispersed and distributed in pores and / or the surface of the porous carbon matrix. The preparation method of the negative electrode material comprises the following steps: mixing porous carbon powder and a binder, and processing to obtain a porous carbon matrix; and compounding silicon nanoparticles on the porous carbon matrix to obtain the negative electrode material. By adjusting and selecting process parameters and the like, the porosity among the porous carbon is reduced, filling of pores of the porous carbon by silicon is also realized, the high-density negative electrode material is further formed, the compaction density and the volume specific capacity are greatly improved, and the related electrochemical performance of the negative electrode material in the lithium ion battery is improved.

Description

Negative electrode material, preparation method thereof, and lithium ion battery

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on December 28, 2022, with application number 2022117004432 and application name “Negative electrode material, preparation method thereof and lithium-ion battery”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present invention relates to the technical field of lithium ion batteries, and in particular to a negative electrode material and a preparation method thereof, and a lithium ion battery. Background Art

[0003] At present, the vast majority of commercial lithium-ion batteries still use graphite with low theoretical specific capacity as the negative electrode material, which seriously limits the application prospects of lithium-ion batteries. Compared with graphite, silicon negative electrode materials have an ultra-high theoretical specific capacity (4200mAh / g), which can significantly improve the energy density of lithium-ion batteries. However, silicon has low electronic conductivity, which affects the rate performance as an electrode material, and the huge volume change during the charge and discharge process can cause the active material to pulverize, fragment, lose effective electrical contact with the current collector, etc., and ultimately cause the capacity to decay rapidly. In this regard, by combining silicon and carbon, the application of silicon negative electrode materials can be greatly improved.

[0004] Generally speaking, negative electrode materials can be manufactured in a reactor by chemical vapor infiltration (CVI). Specifically, a porous carbon matrix is ​​placed in a reactor and is infiltrated with a thermally decomposable Si-containing compound at a temperature higher than the decomposition temperature of the compound, so that Si can be deposited on the surface and inside of the porous carbon. The Si-containing compound in the infiltrating gas is usually a silane gas, which first nucleates on the surface of the porous carbon, and then the infiltrating gas is continuously introduced to allow the Si nuclei to grow. However, in the reactor, there are usually two competing deposition forms, namely heterogeneous deposition and homogeneous decomposition deposition. If the process parameters are more conducive to heterogeneous deposition, the Si particles are mostly deposited on the surface of the porous carbon matrix, and if the process parameters are more conducive to homogeneous decomposition deposition, the Si particles are decomposed into new, very small amorphous particles and distributed in the pores of the porous carbon matrix. In other words, different process parameters affect the proportion of these two depositions in the product, thereby affecting the performance of the negative electrode material.

[0005] In existing processes, when using silane as a precursor to prepare negative electrode materials, there are several disadvantages: (1) Compared with carbon source gas, silane gas has a larger molecular weight, a smaller penetration depth, and a low Si deposition efficiency; (2) If the process parameters are not set properly, CVI is likely to form a crust on the surface of the carbon-based material when it is dense, which requires further machining, extending the preparation cycle and increasing the preparation cost. Obviously, the silicon in the negative electrode materials prepared by these processes is difficult to be evenly distributed throughout the system, and the porosity of the system is too large, making it difficult to fully fill, which in turn makes the electrochemical performance of the prepared negative electrode material poor during the battery's charge and discharge process. Therefore, it is necessary to research and develop a high-density negative electrode material to improve the electrochemical performance of lithium-ion batteries.

[0006] Application Contents

[0007] In view of this, the present application proposes a negative electrode material and a preparation method thereof and a lithium-ion battery, which can reduce volume expansion and improve cycle stability.

[0008] In the first aspect, the present application provides a negative electrode material, which includes an active substance, wherein the active substance includes a porous carbon matrix and silicon, and the silicon is distributed in the pores and / or surface of the porous carbon matrix; the adsorption constant C value of the negative electrode material is C<200, and the open porosity of the material after etching the negative electrode material is 50% to 70%.

[0009] In the second aspect, the present application provides a negative electrode material, which includes an active substance, and the active substance includes a porous carbon matrix and silicon, and the silicon is distributed in the pores and / or surface of the porous carbon matrix; the adsorption constant C value of the negative electrode material is C<200, the density of the material after etching of the negative electrode material is ρ1, and the density of the negative electrode material is ρ2, 50%≤(ρ2-ρ1) / ρ1≤80%.

[0010] In some embodiments, the silicon has a particle size of 1 nm to 100 nm.

[0011] In some embodiments, the pores of the negative electrode material after etching have a pore diameter of 0 to 1 μm.

[0012] In some embodiments, the filling degree of silicon in the porous carbon matrix is ​​≥80%.

[0013] In some embodiments, the density of the negative electrode material is 1.8 g / cm 3 ~2.3g / cm 3 The density of the negative electrode material after etching is 1g / cm 3 ~1.5g / cm 3 .

[0014] In some embodiments, the negative electrode material has a pore structure, which includes mesopores, micropores and macropores, wherein the volume proportion of the mesopores in all pore structures is >75%, the volume proportion of the micropores in all pore structures is <25%, and the volume proportion of the macropores in all pore structures is <10%.

[0015] In some embodiments, the negative electrode material has a pore structure, and the total pore volume of the pore structure measured by nitrogen adsorption method is less than 0.05 cm 3 / g.

[0016] In some embodiments, the volume of closed pores in the negative electrode material is ≤ 0.2 cm 3 / g.

[0017] In some embodiments, the adsorption constant C value of the material after etching the negative electrode material is 200 <C<500。

[0018] In some embodiments, in the nuclear magnetic resonance test of the negative electrode material, there is a Si-C resonance peak between -10ppm and 20ppm, whose intensity is D1, and there is a Si resonance peak between -90ppm and -110ppm, whose intensity is D2, and D2 / D1≥100.

[0019] In some embodiments, the particle size of the negative electrode material after etching is 1 μm to 50 μm.

[0020] In some embodiments, the silicon includes nanosilicon.

[0021] In some embodiments, the negative electrode material further includes a carbon coating layer located on at least a portion of the surface of the active material.

[0022] In some embodiments, the carbon coating layer has a thickness of 1 nm to 100 nm.

[0023] In some embodiments, the mass percentage of silicon in the negative electrode material is 10% to 90%.

[0024] In some embodiments, the specific surface area of ​​the negative electrode material is 0.5 m 2 / g~50m 2 / g.

[0025] In some embodiments, the average particle size of the negative electrode material is 1 μm to 25 μm.

[0026] In a second aspect, the present application provides a method for preparing a negative electrode material, comprising:

[0027] N porous carbon powders of different particle sizes are mixed with a binder and heat-treated to obtain a porous carbon matrix, wherein N is greater than or equal to 2;

[0028] Silicon is compounded on the porous carbon substrate to obtain the negative electrode material.

[0029] In some embodiments, the N porous carbon powders with different particle sizes are arranged in order from small to large according to the particle size, and in two adjacent porous carbon powders, the ratio of D50 of the porous carbon powder with small particle size to D50 of the porous carbon powder with large particle size is 0.25 to 0.9.

[0030] In some embodiments, the N porous carbon powders with different particle sizes are arranged in order from small to large according to the particle size, and in two adjacent porous carbon powders, the ratio of the mass of the porous carbon powder with a smaller particle size to the mass of the porous carbon powder with a larger particle size is 0.05 to 0.75.

[0031] In some embodiments, the N porous carbon powders with different particle sizes are arranged in order from small to large according to the particle size, and among two adjacent porous carbon powders, the D10 of the porous carbon powder with a larger particle size is not less than the D90 of the porous carbon powder with a smaller particle size.

[0032] In some embodiments, the N porous carbon powders with different particle sizes are arranged in order from small to large according to the particle size. When N=3, the D50 ratio of the large-sized porous carbon powder: the medium-sized porous carbon powder: the small-sized porous carbon powder is (4-7): (2-3.5):1.

[0033] In some embodiments, the N porous carbon powders with different particle sizes are arranged in order from small to large according to the particle size. When N=3, the mass ratio of the large-sized porous carbon powder: the medium-sized porous carbon powder: the small-sized porous carbon powder is (18-25): (6-12): 1.

[0034] In some embodiments, the N porous carbon powders with different particle sizes are arranged in order from small to large according to the particle size. When N=3, the D50 of the large-sized porous carbon powder, the medium-sized porous carbon powder, and the small-sized porous carbon powder are 100μm~500μm, 70μm~400μm, and 20μm~130μm, respectively.

[0035] In some embodiments, the N porous carbon powders with different particle sizes are arranged in order from small to large according to the particle size. When N=3, the average pore size of the porous carbon matrix prepared from the porous carbon powders with three different particle sizes is 2nm-50nm.

[0036] In some embodiments, the binder comprises polyvinyl butyral.

[0037] In some embodiments, the mass ratio of the N porous carbon powders of different particle sizes to the binder is (5-20):1.

[0038] In some embodiments, the heat treatment includes: heating and pressurizing the mixed material, and cooling it to obtain the porous carbon matrix.

[0039] In some embodiments, chemical vapor infiltration is used to thermally decompose the reaction gas to deposit silicon on the surface and / or in the pores of the porous carbon matrix to obtain the negative electrode material.

[0040] In some embodiments, the reaction gas includes silane gas, hydrogen gas, and an inert gas.

[0041] In some embodiments, the reaction gas includes silane gas, and the silane gas includes Si n H (2n+2) and Si n H (2n+2) Z (2n+2)-m At least one of the following, wherein n≥1, m<2n+2, and Z includes at least one halogen element selected from F, Cl, Br, and I.

[0042] In some embodiments, the reaction temperature of the thermal decomposition is 400°C to 800°C.

[0043] In some embodiments, the deposition time is 5 hours to 500 hours.

[0044] In some embodiments, the heating curve includes: first heating to a temperature 10°C to 20°C lower than the reaction temperature of the thermal decomposition at a heating rate of 1°C / min to 50°C / min, and then continuing to heat to the reaction temperature of the thermal decomposition at a heating rate of 0.05°C / min to 0.5°C / min.

[0045] In some embodiments, the pressure of the reaction system before the reaction gas is introduced is 1 Pa to 20 Pa.

[0046] In some embodiments, after the reaction gas is introduced, the total pressure of the reaction system is 0.5 kPa to 50 kPa.

[0047] In some embodiments, the oxygen content in the reaction gas is ≤0.5%.

[0048] In some embodiments, the step of thermally decomposing the reaction gas by chemical vapor infiltration to deposit silicon on the surface and / or pores of the porous carbon matrix further includes: when the reaction gas flows from the front end to the end of the porous carbon matrix, the end of the porous carbon matrix is ​​heated to the reaction temperature of the thermal decomposition by a movable heating coil, so that the reaction gas undergoes densification infiltration deposition on the porous carbon matrix at the end, and then the movable heating coil is gradually moved from the end to the front end, so that each part of the porous carbon matrix undergoes densification infiltration deposition.

[0049] In some embodiments, the reaction gas includes silane gas, hydrogen gas, and an inert gas, and the molar ratio of the hydrogen gas to the silane gas is (5-20):1.

[0050] In some embodiments, the reaction gas includes silane gas, hydrogen gas, and an inert gas, and the gas flow rate of the hydrogen gas is 100 mL / min to 500 mL / min.

[0051] In some embodiments, the reaction gas includes silane gas, hydrogen gas, and an inert gas, and the gas flow rate of the inert gas is 200 mL / min to 500 mL / min.

[0052] In some embodiments, the reaction gas includes silane gas, hydrogen gas and inert gas, wherein the hydrogen gas includes hydrogen gas as a dilution gas and hydrogen gas as a carrier gas, wherein the gas flow ratio between the hydrogen gas as a dilution gas and the hydrogen gas as a carrier gas is (3 to 10):1.

[0053] In a third aspect, the present application provides a lithium-ion battery, comprising the negative electrode material as described in the first aspect or the negative electrode material prepared according to the preparation method of the negative electrode material as described in the second aspect.

[0054] Compared with the existing technology, the technical solution of this application has at least the following technical effects:

[0055] The negative electrode material of the present application contains silicon and a porous carbon matrix, and the silicon is uniformly distributed in the skeleton of the porous carbon matrix. The open porosity of the material after etching is 50% to 70%. These open pores provide space for silicon to accommodate the volume expansion of silicon. The adsorption constant of the negative electrode material is controlled to be less than 200. The smaller the adsorption constant C, the smaller the proportion of micropores in the negative electrode material. This shows that the negative electrode material is mainly composed of mesopores and macropores. A small amount of mesopores and macropores can provide buffer space for Si expansion during charging and discharging, and on the other hand, ensure stress diffusion distribution. When the negative electrode material is used in lithium-ion batteries, the silicon filling degree can be controlled to increase the specific capacity of the negative electrode material. It can also alleviate the volume expansion of silicon, improve the particle strength of the negative electrode material, and reduce the collapse and breakage of the material structure during the electrode rolling or cycling process. Therefore, the synergistic effect of the above-mentioned overall structure improves the cycling performance and electrochemical performance of the material.

[0056] The negative electrode material of the present application contains silicon and a porous carbon matrix, and silicon is evenly distributed in the skeleton of the porous carbon matrix. The density of the material after etching of the negative electrode material is ρ1, and the density of the negative electrode material is ρ2, 50%≤(ρ2-ρ1) / ρ1≤80%. On the one hand, the adsorption constant of the negative electrode material is controlled to be less than 200. The smaller the adsorption constant C, the smaller the proportion of micropores in the negative electrode material. It can be seen that the negative electrode material is mainly composed of mesopores and macropores; a small amount of mesopores and macropores can provide a buffer space for the expansion of Si during charging and discharging, ensuring the stress diffusion distribution; on the other hand, the density increase range of the negative electrode material is controlled, thereby regulating the filling degree of silicon, improving the specific capacity of the negative electrode material, alleviating the volume expansion of silicon, improving the particle strength of the negative electrode material, reducing the collapse and breakage of the material structure during the rolling or cycling of the electrode sheet, and achieving a balance between high specific capacity, low expansion performance and high cycle performance of the negative electrode material.

[0057] This application processes porous carbon powders of various particle sizes to obtain a porous carbon matrix, then composites silicon in the pores and / or surface of the porous carbon matrix, filling the large pores in the porous carbon matrix with smaller pores to form a high-density negative electrode material, greatly improving the compaction density and volumetric capacity of the negative electrode material. At the same time, by using porous carbon powders of various particle sizes, small-particle porous carbon powders can be filled between the pores of large-particle porous carbon powders, thereby increasing the density of the porous carbon matrix and, in turn, the density of the negative electrode material.

[0058] The negative electrode material and lithium ion battery of the present application use the above-mentioned negative electrode material, and therefore also have ultra-high compaction density and volume specific capacity, thereby improving the reversible specific capacity and cycle stability of the lithium ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope of the present invention.

[0060] Figure 1 is a flow chart of the preparation process of negative electrode materials. DETAILED DESCRIPTION

[0061] As used herein:

[0062] "Prepared from" is synonymous with "comprising." As used herein, the terms "comprising," "including," "having," "containing," or any other variations thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0063] The conjunction "consisting of" excludes any unspecified element, step, or component. If used in a claim, this phrase renders the claim closed, excluding materials other than those described, except for conventional impurities associated therewith. When the phrase "consisting of" appears in a clause of the body of a claim, rather than immediately following the subject matter, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0064] When an amount, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper preferred values ​​and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value with any range lower limit or preferred value, regardless of whether the range is disclosed alone. For example, when a range of "1 to 5" is disclosed, the described range should be interpreted as including the range "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5", etc. When a numerical range is described herein, unless otherwise stated, the range is intended to include its end values ​​and all integers and fractions within the range.

[0065] In these examples, parts and percentages are by mass unless otherwise indicated.

[0066] "Parts by mass" refers to the basic unit of measurement used to express the mass ratio of multiple components. One part can represent any unit of mass, such as 1g or 2.689g. If we say that the mass of component A is a parts and the mass of component B is b parts, this means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, we could say that the mass of component A is aK and the mass of component B is Bk (K is an arbitrary number representing a multiplication factor). It's important to note that, unlike parts by mass, the sum of the mass of all components is not limited to 100 parts.

[0067] "And / or" is used to indicate that one or both of the stated situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0068] In the first aspect, the present application provides a negative electrode material, which includes an active substance, and the active substance includes a porous carbon matrix and silicon, wherein silicon is distributed in the pores and / or surface of the porous carbon matrix; the adsorption constant C value of the negative electrode material is C<200, and the open porosity of the material after etching the negative electrode material is 50% to 70%.

[0069] It should be noted that the adsorption constant C value is mainly obtained by setting the adsorption temperature (RT), which is generally 25 ° C, the saturated vapor pressure of the adsorbate gas N2 as p0 (unit: kPa), the saturated multilayer adsorption capacity when the gas equilibrium pressure is p as Q (unit: mmol / g), and ... and the saturated multilayer adsorption capacity when the gas equilibrium pressure is p as Q (unit: mmol / g). As the vertical axis, p / p 0 By plotting the horizontal axis, a linear result can be obtained by fitting. The intercept of the fitted straight line is set to a and the slope is b, and the adsorption constant C = b / a + 1 is defined.

[0070] Generally, the C value of strong adsorbents such as activated carbon and molecular sieves is greater than 200, and the C value of the negative electrode material in this application is less than 200. The smaller the adsorption constant C, the smaller the proportion of micropores in the negative electrode material. It can be seen that the negative electrode material is mainly composed of mesopores and macropores. During the deposition process, since most of the micropores have been filled with silicon, the remaining pores of the porous carbon matrix are mainly unfilled mesopores and macropores. These mesopores and macropores are located inside the porous carbon matrix or are closed pores, as well as micropores / smaller micropores formed by the conversion of mesopores / micropores after being partially filled with silicon. This makes the adsorption constant of the negative electrode material less than 200, so that a certain amount of space can be reserved to buffer the volume expansion during the insertion and extraction of lithium, and the amount of Si filling can be guaranteed (that is, the proportion of Si in the negative electrode material is higher). At this time, on the one hand, the negative electrode material can have a higher specific capacity, and on the other hand, the particle strength is higher, and it will not break during the process of preparing the pole piece rolling.

[0071] The negative electrode material of the present application contains silicon and a porous carbon matrix, and silicon is uniformly distributed in the skeleton of the porous carbon matrix. The pores in these porous carbon matrices can accommodate silicon, and the remaining pores in the negative electrode material after filling with silicon can accommodate the volume expansion of silicon; and, before compounding with silicon, the pores of the porous carbon matrix are mainly micropores (within the range of <2nm), and the open porosity of the material after etching the negative electrode material is 50% to 70%, which is conducive to the dispersed filling of silicon. After compounding with silicon, since most of the micropores have been filled with silicon, the remaining pores of the porous carbon matrix are mainly unfilled mesopores and macropores. These mesopores and macropores are located inside the porous carbon matrix or are closed pores, as well as micropores / smaller micropores formed by the conversion of mesopores / micropores after partial filling with silicon, so that the adsorption constant of the negative electrode material is less than 200. The smaller the adsorption constant of the negative electrode material, the smaller the proportion of micropores in the negative electrode material. It can be seen that the negative electrode material is mainly composed of mesopores and macropores. A small amount of mesopores and macropores can provide buffer space for the expansion of Si during charging and discharging, and on the other hand, ensure the stress diffusion distribution of silicon. When the negative electrode material is used in lithium-ion batteries, the filling degree of silicon can be controlled to improve the specific capacity of the negative electrode material. It can also alleviate the volume expansion of Si, improve the particle strength of the negative electrode material, and reduce the collapse and breakage of the material structure during the rolling or cycling of the electrode sheet, thereby improving the cycle performance and electrochemical performance of the material under the synergistic effect of the above-mentioned overall structure.

[0072] In some embodiments, the density of the negative electrode material after etching is ρ1, the density of the negative electrode material is ρ2, and 50%≤(ρ2-ρ1) / ρ1≤80%.

[0073] In the above scheme, the negative electrode material contains silicon and a porous carbon matrix, and silicon is evenly distributed in the skeleton of the porous carbon matrix. The density of the material after etching of the negative electrode material is ρ1, and the density of the negative electrode material is ρ2, and 50%≤(ρ2-ρ1) / ρ1≤80%. On the one hand, the adsorption constant of the negative electrode material is controlled to be less than 200. The smaller the adsorption constant C, the smaller the proportion of micropores in the negative electrode material. This shows that the negative electrode material is mainly composed of mesopores and macropores. A small amount of mesopores and macropores can provide buffer space for Si expansion during charge and discharge, ensuring stress diffusion distribution. On the other hand, controlling the range of increase in the density of the negative electrode material can regulate the filling degree of silicon, improve the specific capacity of the negative electrode material, alleviate the volume expansion of silicon, improve the particle strength of the negative electrode material, and reduce the collapse and breakage of the material structure during electrode rolling or cycling. This can achieve a balance between high specific capacity, low expansion performance, and high cycle performance in the negative electrode material.

[0074] In some optional embodiments, the particle size of silicon in the negative electrode material is 1 nm to 100 nm, specifically 1 nm, 10 nm, 20 nm, 50 nm, 70 nm, 100 nm, or any value between 1 nm and 100 nm.

[0075] In some optional embodiments, the open porosity of the material after etching the negative electrode material is 50% to 70%, specifically 50%, 52%, 54%, 56%, 58%, 60%, 70% or any value between 50% and 70%.

[0076] In some optional embodiments, the pore size of the pores of the negative electrode material after etching is 0-1 μm, specifically 0.001 μm, 0.01 μm, 0.05 μm, 0.1 μm, 0.3 μm, 0.5 μm, 1 μm or any value greater than 0 and between 0 and 1 μm.

[0077] In some optional embodiments, the silicon filling rate within the pores of the porous carbon matrix is ​​≥80%, and specifically can be 80%, 85%, 90%, 95%, or any value between 80% and 100%. Filling the porous carbon matrix with silicon increases the material density. By controlling the density increase range of the negative electrode material, a good balance can be achieved between high specific capacity, low expansion performance, and high cycle performance.

[0078] In some optional embodiments, the density of the negative electrode material is 1.8 g / cm 3 ~2.3g / cm 3 , specifically 1.8g / cm 3 , 2.0g / cm 3 , 2.2g / cm 3 , 2.3g / cm 3 Or 1.8g / cm 3 -2.3g / cm 3 Any value between; the density of the material after etching the negative electrode material is 1g / cm 3 ~1.5g / cm 3 , specifically 1g / cm 3 , 1.2g / cm 3 , 1.4g / cm 3 , 1.5g / cm 3 Or 1g / cm 3 ~1.5g / cm 3 Any value in between.

[0079] In some optional embodiments, the negative electrode material has a pore structure, which includes mesopores, micropores and macropores, wherein the volume proportion of mesopores in all pore structures is greater than 75%, the volume proportion of micropores in all pore structures is less than 25%, and the volume proportion of macropores in all pore structures is less than 10%.

[0080] It should be noted that the volume fraction of mesopores with pore diameters of 2 nm - 50 nm refers to the percentage of the pore volume of mesopores in the total pore volume of the entire anode material. The volume fraction of micropores with pore diameters < 2 nm refers to the percentage of the pore volume of micropores in the total pore volume of the entire anode material. The volume fraction of macropores with pore diameters > 50 nm refers to the percentage of the pore volume of macropores in the total pore volume of the entire anode material. Controlling the proportion of mesopores and macropores in the finally prepared anode material within the above range can provide a buffer space for the expansion of Si during charge and discharge. On the other hand, it ensures the dispersion of stress distribution, improves the particle strength of the anode material, and reduces the collapse and fragmentation of the material structure during pole piece rolling or cycling. Therefore, the cycling performance, electrochemical performance, etc. of the material are improved under the synergistic effect of the above overall structure.

[0081] In some optional embodiments, the anode material has a pore structure, and the total pore volume of the anode material measured by the nitrogen adsorption method < 0.05 cm 3 / g, specifically it can be 0.04 cm 3 / g, 0.035 cm 3 / g, 0.032 cm 3 / g, 0.030 cm 3 / g, 0.028 cm 3 / g, 0.025 cm 3 / g, 0.024 cm 3 / g or 0.02 cm 3 / g, etc., which are not limited herein.

[0082] In some optional embodiments, the volume of closed pores in the anode material ≤ 0.2 cm 3 / g. It can be understood that the closed pore volume is the volume that nitrogen cannot enter when tested by the nitrogen adsorption method. The porous carbon matrix includes closed pores, and the closed pores are mainly mesopores according to their pore diameter sizes, which ensures the dispersion of stress distribution, helps to accommodate the increased volume during lithium insertion, and will not damage the structure of the porous carbon or significantly increase the overall size of the anode material, and can further strengthen the stability of the silicon-carbon interface; on the one hand, the closed pores of the porous carbon reserve a buffer space for the volume expansion of Si during lithium insertion, and on the other hand, because there is no opening connected to the outside, it is difficult for the electrolyte to penetrate, so there is no problem of continuous thickening of the SEI layer.

[0083] In some optional embodiments, after testing by the gas adsorption BET method, the adsorption constant C value of the etched material of the anode material is 200 < C < 500, specifically it can be 200, 250 or 300, 400, 499, etc., which are not limited herein.

[0084] It should be noted that the calculation method of the adsorption constant C value of the etched material of the anode material is the same as the calculation method of the adsorption constant C value of the above anode material.

[0085] In a specific example, the particle size of the material after etching the negative electrode material is 1 μm to 50 μm, preferably 2 μm to 20 μm. It is understandable that the particle size of the material after etching the negative electrode material can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 17 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm or 50 μm. The particle size of the porous carbon can also be other values ​​between 1 μm and 50 μm.

[0086] In some optional embodiments, the negative electrode material is subjected to nuclear magnetic resonance testing. 29 In the Si NMR spectrum, there is a Si-C resonance peak between -10ppm and 20ppm, whose intensity is D1, and there is a Si resonance peak between -90ppm and -110ppm, whose intensity is D2, and D2 / D1≥100.

[0087] It should be noted that there is a trace amount of SiC in the negative electrode material of this embodiment. Since SiC is an inactive substance, when the content of SiC increases, the specific capacity will decrease. When D2 / D1≥100, it means that there is a certain binding force between Si and C in the negative electrode material, and an atomic-level binding force is formed between Si and C. At the same time, there is only a trace amount of crystalline SiC. Therefore, the negative electrode material of the present application can maintain structural stability during the charge and discharge process and show excellent cycle performance. It can be understood that D2 / D1 can be 100, 110, 120, 130, 140 or 150, etc., which is not limited here. The larger the value of D2 / D1, the less the content of inactive SiC, which is beneficial to improving the electrochemical performance of the negative electrode material.

[0088] It is understandable that although Si-C bonds are present in the nuclear magnetic resonance results of the negative electrode material, the Si-Si bond is dominant and its strength is much greater than that of the Si-C bond, so D2 / D1 ≥ 100. As some optional embodiments of the present application, the outermost layer of the negative electrode material further includes a carbon coating layer. Further preferably, the thickness of the carbon coating layer is 1nm-100nm, specifically 1nm, 10nm, 20nm, 50nm, 70nm, 100nm or any value between 1nm-100nm.

[0089] It is understandable that the introduction of the carbon coating layer is mainly to improve the electronic conductivity of the negative electrode material in the negative electrode, further buffer the volume change of silicon and reduce the excessive generation of SEI film on the surface of the negative electrode material.

[0090] In a specific example, the mass percentage of silicon in the negative electrode material is 10% to 90%, preferably 20% to 80%. It is understood that the mass percentage of silicon in the negative electrode material can be 10%, 12%, 14%, 16%, 18%, 20%, 25%, 30%, 35%, 40%, 50%, 60%, 70%, 80% or 90%. The mass percentage of silicon in the negative electrode material can also be other values ​​between 10% and 90%.

[0091] In a specific example, the specific surface area of ​​the negative electrode material is 0.5 m 2 / g~50m 2 / g. It can be understood that the specific surface area of ​​the negative electrode material can be 0.5m 2 / g, 1.0m 2 / g, 5.0m 2 / g、10m 2 / g、13m 2 / g、16m 2 / g, 20m 2 / g、23m 2 / g、26m 2 / g、30m 2 / g、33m 2 / g、36m 2 / g, 40m 2 / g、43m 2 / g、46m 2 / g or 50m 2 / g. The specific surface area of ​​the negative electrode material can also be 0.5m 2 / g~50m 2 Other values ​​between / g.

[0092] In a specific example, the average particle size D50 of the negative electrode material is 1 μm to 25 μm, preferably 2 μm to 15 μm, and more preferably 3 μm to 10 μm. It should be explained that when the average particle size of the negative electrode material is ≥1 μm, the tap density of the electrode can be reduced, thereby seriously affecting its processing performance as a negative electrode of a lithium-ion battery, reducing the problem of too low compaction density of the pole piece and low energy density, and obtaining a suitable volumetric capacity. In addition, when the average particle size of the negative electrode material is ≤25 μm, the slurry forming the electrode can be appropriately coated to a uniform thickness. Optionally, the average particle size D 50 The average particle size D of the negative electrode material may be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 12 μm, 14 μm, 15 μm, 17 μm, 19 μm, 21 μm, 23 μm or 25 μm. 50 Other values ​​between 1 μm and 25 μm are also possible.

[0093] In one specific example, the negative electrode material further includes a carbon coating located on at least a portion of the surface of the active material. It is understood that the carbon coating, as a shell, can mechanically constrain the active material, improving the electronic conductivity of the negative electrode material within the negative electrode. Furthermore, the carbon coating allows lithium ions to pass through while reducing the interaction between the electrolyte and the internal active material, further buffering the volume change of silicon and reducing the excessive formation of the SEI film on the surface of the negative electrode material.

[0094] In a specific example, the carbon coating layer has a thickness of 1 nm to 100 nm. It is understood that the average thickness of the coating layer can be 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, or 100 nm. The average thickness of the coating layer can also be other values ​​between 1 nm and 100 nm.

[0095] In a second aspect, the present application further provides a method for preparing a negative electrode material, as shown in FIG1 , the preparation method comprises:

[0096] S1. Mixing N porous carbon powders of different particle sizes with a binder and heat-treating them to obtain a porous carbon matrix, where N ≥ 2;

[0097] S2. Composite silicon on a porous carbon matrix to obtain a negative electrode material.

[0098] By selecting this preparation process, the present application controls the relevant physical characteristics of the obtained porous carbon matrix, including the pore distribution, porosity, pore shape, etc. of the porous carbon matrix; on the other hand, controls the subsequent silicon composite process, and further prepares the negative electrode material on the skeleton of the prepared porous carbon matrix by adjusting the process parameters, so that the micropores in the negative electrode material dominate, thereby alleviating the volume expansion during the battery cycle, ensuring the strength of the negative electrode material particles, and reducing the chance of particle collapse and damage during the cycle.

[0099] The N porous carbon powders with different particle sizes in S1 are arranged in order from small to large according to the particle size, and then numbered as C1, C2, C3..., CN, among which the average particle size of the C1 porous carbon powder is the smallest, and the average particle size of the CN porous carbon powder is the largest.

[0100] In some optional embodiments, in two adjacent porous carbon powders, the ratio of D50 of the porous carbon powder with a smaller particle size to the D50 of the porous carbon powder with a larger particle size is 0.25-0.9. For example, the ratio of the D50 particle size of the C1 porous carbon powder to the D50 particle size of the C2 porous carbon powder is 0.25-0.9. Specifically, it can be 0.25, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or any value between 0.25-0.9.

[0101] In some optional embodiments, in two adjacent porous carbon powders, the ratio of the mass of the porous carbon powder with a smaller particle size to the mass of the porous carbon powder with a larger particle size is 0.05-0.75. For example, the ratio of the mass of the C2 porous carbon powder to the mass of the C3 porous carbon powder is 0.05-0.75. Specifically, it can be 0.05, 0.15, 0.25, 0.35, 0.45, 0.55, 0.65, 0.75 or any value between 0.05-0.75.

[0102] In some optional embodiments, in two adjacent porous carbon powders, the D10 of the porous carbon powder with a larger particle size is not smaller than the D90 of the porous carbon powder with a smaller particle size. For example, the D10 particle size of the C2 porous carbon powder is not smaller than the D90 particle size of the C1 porous carbon powder, and the D10 particle size of the C3 porous carbon powder is not smaller than the D90 particle size of the C2 porous carbon powder.

[0103] In a preferred embodiment, the raw materials of the porous carbon matrix include three types of porous carbon powders with different particle sizes. The three types of porous carbon powders with different particle sizes are divided into C1, C2, and C3 in order of particle size from small to large.

[0104] Preferably, the D50 particle size ratio of C3:C2:C1 is (4-7):(2-3.5):1, specifically 4:2:1, 4:3.5:1, 5:2:1, 5:3.5:1, 6:2:1, 6:3:1, 6:3.5:1, 7:2:1, 7:3.5:1 or any value between (4-7):(2-3.5):1.

[0105] Preferably, the mass ratio of C3:C2:C1 is (18-25):(6-12):1, specifically 18:6:1, 18:12:1, 20:6:1, 20:10:1, 20:12:1, 23:6:1, 23:12:1, 25:6:1, 25:12:1 or any value between (18-25):(6-12):1.

[0106] Preferably, the average particle sizes of C3, C2 and C1, i.e., D50, are 100 μm to 500 μm, 70 μm to 400 μm and 20 μm to 130 μm, respectively.

[0107] Preferably, the average pore size of the porous carbon matrix prepared using three porous carbon powders with different particle sizes is 2nm to 50nm, specifically 2nm, 10nm, 20nm, 30nm, 40nm, 50nm or any value between 2nm and 50nm.

[0108] The particle gradation of the porous carbon powder of the present application is preferably a three-level gradation method, that is, porous carbon powders of three different particle sizes are used as raw materials for the porous carbon matrix. In this way, during the forming process of the porous carbon matrix, the porous carbon particles of medium particle size will fill the gaps between the porous carbon particles of large particle size, and the porous carbon particles of small particle size will further fill the pores between the porous carbon particles of large particle size and the porous carbon particles of medium particle size. If only a porous carbon powder raw material of one particle size is used to prepare the porous carbon matrix, there will be large pores between these porous carbon particles, that is, the pores of the porous carbon matrix are large. Even if silicon is subsequently infiltrated therein, it will affect the densification of the negative electrode material, so that the porosity and pore size of the obtained negative electrode material are too high, which has a negative effect on the volumetric capacity and compaction density of the composite material. Therefore, the use of porous carbon powders of multiple different particle sizes as the raw material for the porous carbon matrix is ​​conducive to improving the density of the prepared negative electrode material.

[0109] In some optional implementations, the binder in S1 may be polyvinyl butyral.

[0110] In some optional embodiments, the ratio of the total mass of N porous carbon powders of different particle sizes in S1 to the mass of the binder is (5-20):1, specifically 5:1, 10:1, 15:1, 20:1 or any value between (5-20):1. An appropriate amount of binder can mix and adhere the porous carbon particles together. Too much binder may cause the conductivity of the material to decrease, and too little binder may reduce the particle stability of the negative electrode material. By controlling the amount of binder added, the specific capacity of the negative electrode material can be increased while ensuring that the porous carbon particles are effectively bonded and pressed together, thereby improving the electrochemical properties of the material.

[0111] In some optional embodiments, the mixing method in S1 includes at least one of VC mixing, manual mixing, normal temperature film pressing, and spray drying.

[0112] In some optional embodiments, the heat treatment in S1 includes: heating and pressurizing the mixed material, and cooling it to obtain a porous carbon matrix.

[0113] Specifically, the mixed material after the first mixing step can be spread flatly in a mold, which is then heated and pressurized, cooled, and demolded to obtain a porous carbon matrix. Furthermore, before the mixed material is spread flatly in the mold, a release agent is applied to the inner surface of the mold to facilitate rapid removal of the porous carbon matrix.

[0114] In some optional embodiments, the mold comprises a steel mold.

[0115] In some optional embodiments, the heating treatment temperature is 50°C to 500°C, specifically 50°C, 100°C, 200°C, 300°C, 400°C, 500°C or any value between 50°C and 500°C; the time is 0.5h to 5h, specifically 0.5h, 1h, 2h, 3h, 4h, 5h or any value between 0.5h and 5h.

[0116] In some optional embodiments, the pressure of the pressurization treatment is 5 MPa to 50 MPa, specifically 5 MPa, 10 MPa, 20 MPa, 30 MPa, 40 MPa, 50 MPa, or any value between 5 MPa and 50 MPa. The time is 0.2 h to 10 h, specifically 0.5 h, 1 h, 2 h, 3 h, 4 h, 5 h, or any value between 0.5 h and 5 h.

[0117] It should be noted that the correct selection of a porous carbon matrix is ​​critical to achieving the infiltration and infiltration of silicon in the porous carbon matrix. If the porosity of the matrix and the size of the pores are too large, the density of the composite material obtained by silicon infiltration into the matrix is ​​low; and if they are too small, it is difficult to introduce the silicon source gas deeply into the deeper areas of the pores so that the gas forms silicon therein. Therefore, one of the research objectives of this application is to find suitable process parameters for deeply introducing silicon into the pores of the porous carbon matrix used, and to ensure that the prepared composite material has a correct balance between good mechanical strength and electrochemical properties.

[0118] In some optional embodiments, the compounding method in S2 includes: any one of chemical vapor infiltration, dry mixing process and wet mixing process, and chemical vapor infiltration is more preferred.

[0119] Among them, the dry mixing process is to dry-mix the porous carbon matrix and silicon by ball milling, and the wet mixing process is to mix the porous carbon matrix with a silicon-containing solution.

[0120] In some optional embodiments, the chemical vapor infiltration method used in the composite of the present application includes: placing the porous carbon substrate in an infiltration furnace, evacuating the infiltration furnace, then heating it to the reaction temperature, introducing silicon source gas, and performing infiltration deposition.

[0121] In some embodiments, chemical vapor infiltration is used to thermally decompose the reaction gas to deposit silicon on the surface and / or in the pores of the porous carbon matrix to obtain the negative electrode material.

[0122] In some embodiments, the reaction gas includes silane gas, hydrogen gas, and an inert gas.

[0123] In some embodiments, the reaction gas includes silane gas, which includes Si n H (2n+2) and Si n H (2n+2) Z (2n+2)-m At least one of the following, wherein n≥1, m<2n+2, and Z includes at least one halogen element selected from F, Cl, Br, and I.

[0124] In some optional embodiments, the reaction temperature of thermal decomposition is 400°C to 800°C, specifically 400°C, 500°C, 600°C, 700°C, 800°C or any value between 400°C and 800°C.

[0125] In some optional implementations, the deposition time is 5 h to 500 h, specifically 5 h, 10 h, 100 h, 250 h, 500 h or any value between 5 h and 500 h.

[0126] In some optional embodiments, the pressure of the reaction system before the reaction gas is introduced is 1Pa to 20Pa, specifically 1Pa, 5Pa, 10Pa, 15Pa, 20Pa or any value between 1Pa and 20Pa.

[0127] In some optional embodiments, the oxygen content in the reaction system is ≤0.5%.

[0128] Furthermore, after the reaction gas is introduced, the total pressure of the reaction system is 0.5 kPa to 50 kPa, specifically 0.5 kPa, 1 kPa, 5 kPa, 10 kPa, 20 kPa, 30 kPa, 40 kPa, 50 kPa or any value between 0.5 kPa and 50 kPa.

[0129] In some optional embodiments, the heating curve during heating includes: first heating to 10°C to 20°C below the desired reaction temperature at a heating rate of 1°C / min to 50°C / min, specifically 1°C / min, 10°C / min, 20°C / min, 30°C / min, 40°C / min, 50°C / min or any value between 1°C / min and 50°C / min, and then continuing to heat to the desired reaction temperature at a heating rate of 0.05°C / min to 0.5°C / min, more preferably continuing to heat at a heating rate of 0.1°C / min.

[0130] It should be noted that the key to increasing the densification rate of chemical vapor infiltration (CVI) is to ensure that the silane gas does not decompose and deposit before entering the pores of the porous carbon, but rather decomposes and deposits rapidly once inside. However, increasing the reaction temperature during infiltration and the flow and pressure of the reactive silicon source gas only increase the silicon infiltration rate simultaneously, making it more likely for silicon to penetrate the material's surface rather than the pores. Therefore, these commonly used methods are not conducive to improving the densification rate.

[0131] In this application, in order to increase the CVI densification speed, vacuum is first performed to make the air pressure inside and outside the porous carbon matrix close to zero, and then the temperature in the infiltration furnace is quickly heated to about 10°C-20°C below the temperature of gas decomposition at a heating rate of 1°C / min-50°C / min, and then slowly heated to the decomposition temperature of the gas at a heating rate of 0.1°C / min, thereby ensuring that the temperature inside and outside the porous carbon matrix remains consistent and the stability of the thermodynamic conditions is ensured. Then, silane gas diluted with inert gases such as H2 and argon is introduced into the infiltration furnace to ensure uniform diffusion of silane gas inside the porous carbon, which is conducive to its uniform penetration.

[0132] In some optional embodiments, performing infiltration deposition also includes: when the silicon source gas flows from the front end to the end of the porous carbon matrix, using a movable heating coil to heat the end of the porous carbon matrix to the reaction temperature of the gas, so that the silicon source gas undergoes a densification reaction on the porous carbon matrix at the end, and infiltration deposition is performed; thereafter, the movable heating coil is gradually moved from the end to the front end, so that each part of the porous carbon matrix undergoes densification infiltration deposition.

[0133] It can be understood that the method of using a movable coil to heat and infiltrate the porous carbon matrix in an infiltration furnace ensures that every part of the porous carbon matrix can undergo a densification reaction as much as possible, so that the negative electrode material finally prepared has a high density and silicon is evenly distributed on the porous carbon matrix.

[0134] In some optional embodiments, the molar ratio of hydrogen to silane gas is (5-20):1, and specifically can be 5:1, 10:1, 15:1, 20:1, or any value between (5-20):1. It is understood that, in the silicon source gas, argon is primarily a diluent gas, while hydrogen serves as both a diluent gas and a carrier gas.

[0135] In some optional embodiments, the gas flow ratio of hydrogen as a diluent gas and hydrogen as a carrier gas is (3-10):1, specifically 3:1, 5:1, 8:1, 10:1 or any value between (3-10):1.

[0136] In some optional embodiments, the hydrogen gas flow rate is 100 mL / min to 500 mL / min, specifically 100 mL / min, 200 mL / min, 300 mL / min, 400 mL / min, 500 mL / min or any value between 100 mL / min and 500 mL / min.

[0137] In some optional embodiments, the gas flow rate of argon is 200 mL / min to 500 mL / min, specifically 200 mL / min, 300 mL / min, 400 mL / min, 500 mL / min or any value between 200 mL / min and 500 mL / min.

[0138] In some optional embodiments, after the infiltration deposition is completed, the process further includes: stopping the power supply and the introduction of the silicon source gas, closing the vacuum system used for vacuum extraction, and continuously introducing argon into the infiltration furnace until the pressure in the infiltration furnace reaches normal pressure, then opening the vent valve to allow the temperature of the infiltration furnace to cool to room temperature, and then stopping the introduction of argon and taking out the prepared product.

[0139] It should be noted that the negative electrode material prepared by the chemical vapor infiltration method has a porosity of about 10%-15%, wherein silicon is dispersed and embedded in the porous carbon matrix.

[0140] In some embodiments, the method further comprises: coating the intermediate product prepared after the composite with the carbon source using a solid phase carbon coating treatment, a liquid phase carbon coating treatment, or a gas phase carbon coating treatment method.

[0141] In some embodiments, the coating process comprises the following steps: mixing the intermediate product with a carbon source, and controlling the thermal decomposition of the carbon source in a protective atmosphere to form a carbon coating layer on the surface of the intermediate product.

[0142] In some embodiments, the carbon source comprises a gaseous carbon source.

[0143] In some embodiments, the carbon source comprises a gaseous carbon source, and the gaseous carbon source comprises a gaseous hydrocarbon carbon source.

[0144] In some embodiments, the carbon source comprises a gaseous carbon source, and the gaseous carbon source comprises at least one of methane, acetylene, ethylene, ethane, propane, propylene, propyne, acetone, and benzene.

[0145] In some embodiments, the carbon source comprises a solid-phase carbon source.

[0146] In some embodiments, the carbon source comprises a solid-phase carbon source, and the solid-phase carbon source comprises a solid-phase organic carbon source.

[0147] In some embodiments, the carbon source comprises a solid carbon source, and the solid carbon source comprises at least one of citric acid, glucose, asphalt, phenolic resin, and furfural resin.

[0148] In some embodiments, the carbon source comprises a liquid carbon source.

[0149] In some embodiments, the carbon source comprises a liquid carbon source, and the liquid carbon source comprises a liquid organic carbon source.

[0150] In some embodiments, the carbon source comprises a liquid carbon source, and the liquid carbon source comprises at least one of n-hexane, toluene, benzene, xylene, methanol, ethanol, propanol, butanol, pentanol, acetone, butanone, 2-pentanone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate and pentyl acetate.

[0151] In some embodiments, the temperature of thermal cracking is 600°C to 1200°C.

[0152] In some embodiments, the heating rate of thermal cracking is 0.1°C / min to 50°C / min.

[0153] The negative electrode material prepared in this application can be used as a negative electrode material in lithium-ion batteries. Specifically, after the negative electrode material is used in a lithium-ion battery, its initial reversible specific capacity is ≥2000mAh / g, the expansion rate after 50 cycles is <38%, and the capacity retention rate is >87%. According to in-situ XRD data, the negative electrode material is initially discharged to 0.05V vs Li / Li + When the Si characteristic peaks (111), (220), and (311) are always present; 0.01V vs Li / Li + When c-Li 15 Si4 peak. According to in-situ TEM and selected area electron diffraction, the surface of silicon is lithiated to form Li x Si, the interior is crystalline silicon. After one cycle, the Li x Si delithiation forms amorphous Si (a-Si), while the interior is still crystalline silicon.

[0154] This application conducted adsorption and desorption tests on porous carbon matrices prepared using porous carbon powders of three different particle sizes. The resulting adsorption and desorption curves exhibited Type I, a typical Langmuir isotherm (including narrow microporous materials with pore widths less than 1 nm and mixtures containing narrower mesoporous materials with pore widths less than 2.5 nm). The desorption curve of the resulting negative electrode material exhibited Type IV(a), indicating capillary condensation followed by a hysteresis loop (a typical desorption curve for mesoporous materials).

[0155] In the process of studying the negative electrode material and preparation method thereof of the present application, the inventors tested the prepared porous carbon matrix and negative electrode material by the following test methods, as follows:

[0156] Porosity can be calculated by multiplying the amount of pores per unit weight of a material (cm3 / g) by the bulk density (g / cm3). Bulk density can be obtained by dividing the mass of the material by the volume of the sample. The amount of pores per unit weight can be further measured under well-known conditions using conventional equipment or a mercury porosimeter.

[0157] The oxygen content in the permeation furnace can be measured using an oxygen / carbon monoxide meter Bacharach model 0024-7341.

[0158] SEM is used to confirm the particle structure in the material, and combined with EDS, the element ratio of Si, O, and C in the material can be characterized and analyzed to determine the phase composition of the material.

[0159] Use a laser particle size analyzer to measure the D50, D90, and D10 of the material particle size, and then calculate the value of (D90-D10) / D50 to ensure that the material particle size has a symmetrical normal distribution. In the volume-based distribution, the cumulative 10% diameter is D10, the cumulative 50% diameter is D50, and the cumulative 90% diameter is D90.

[0160] The specific surface area of ​​the material was tested using the American Micromeritics TriStar 3000 specific surface area and pore size analyzer.

[0161] The XRD peak of the material was obtained using a PANalytical X'pert Pro X-ray diffractometer, and then the Si peak in the XRD was fitted using Jade 6.5 software to obtain the silicon crystallite size.

[0162] 29Si MAS NMR (29Si Magic Angle Spinning Nuclear Magnetic Resonance Spectroscopy) was used as the standard for silicon chemical shift measurements. A Bruker AV 300 NMR instrument was used. For quantitative analysis, single pulses were used rather than cross-polarization. The pulse width was 4.5 μs, theta was 54.7°, the relaxation delay (i.e., the time delay between two samples) was 5 seconds, and the rotation speed was 7 kHz. TMS was used as the chemical shift standard.

[0163] Measuring silicon particle size using SEM or TEM images: Save an SEM or TEM image of the negative electrode material. Run Nano Measurer software, open the SEM or TEM image to be analyzed, set the scale, and drag the mouse to mark the particles on the image to obtain their particle size. Randomly select five 100µm x 75µm areas and randomly select 20 nano-silicon particles within each area for particle size analysis to determine the particle size distribution range. Use Origin software to fit the obtained particle size values ​​to a normal distribution and calculate the mean and standard deviation, with the standard deviation ≤ 0.2.

[0164] Gravimetric method for testing silicon content: Use a box-type atmosphere furnace to burn in an O2 atmosphere, so that the silicon in the sample reacts into SiO2, and C is converted into CO2 after combustion and discharged. The silicon content is calculated by weighing.

[0165] C value, specific surface area, and pore volume measurement methods: Micropore and mesopore analysis was performed using the Micromeretics ASAP 2460. At liquid nitrogen temperature, the equilibrium amount of nitrogen adsorbed on a surface is related to properties such as pore size. By combining the relationship between the amount of adsorption and relative pressure during adsorption, various models can be fitted to calculate pore size. The software report uses density functional theory (DFT) to calculate pore size distribution, total pore volume, and pore volume within a specific range.

[0166] The test method for the open porosity of the material after etching the negative electrode material is as follows: weigh about 0.5g of the negative electrode material sample and place it in a platinum crucible, add a mixed acid of 5mL HNO3 and 10mL HF, and after the mixed acid reacts stably with the sample, place the platinum crucible on a 350℃ hot plate to heat the acid until the hydrofluoric acid evaporates and no white smoke is emitted; after the crucible cools down, add 6mL of HCl and heat until the residue is completely dissolved. The remaining is the negative electrode material after etching.

[0167] Open porosity is the ratio of the volume of open pores in a sample to the total volume of the sample. Open pores are pores with an open edge that can communicate with liquids or gases in the environment. In practical applications, open porosity is often used to describe the properties and performance of materials such as porous media, filtration materials, and magnetic materials.

[0168] Open porosity is typically measured using methods such as gas infiltration and liquid displacement. The gas infiltration method measures the average diameter and pore volume of open pores, which are then used to calculate the open porosity. The liquid displacement method measures the volume of open pores by immersing the sample in a liquid, and can also provide the open porosity.

[0169] Closed porosity is the ratio of the volume of closed pores in a sample to the total volume of the sample. Closed pores are pores with closed edges that are not connected to liquids or gases in the environment. They are generally used in fields such as geological exploration.

[0170] Closed-cell porosity is typically measured using methods such as density and helium measurement. For example, a volume of anhydrous ethanol (V1) is placed in a graduated cylinder. The dry material is immersed in the cylinder for 5 minutes. The ethanol is then vacuumed until no bubbles are present. The volume of the ethanol at this point is recorded as V2. The material is removed and the volume at this point is recorded as V3. The porosity is calculated as (V1 - V3) / (V2 - V3) * 100%. Three samples are measured per group, and the average value is taken.

[0171] Silicon filling rate test method: the true density of the material after etching the negative electrode material is determined to be ρ1, and the specific pore volume is V1, then the apparent density ρ2 = V1 + 1 / ρ1, the porosity of C material θ1 = 1-ρ2 / ρ1, the true density of the negative electrode material is determined to be ρ3, and the specific pore volume is V2, then the apparent density ρ4 = V2 + 1 / ρ3, the porosity of C material θ2 = 1-ρ4 / ρ3, then the silicon filling rate is (θ2-θ1) / θ1, the pore volume test method has been supplemented in the specific surface area test and will not be repeated here.

[0172] True density test method: Use the Best 3H-2000TD / Quanta 5200e true density meter, apply the Archimedean principle of gas displacement (density = mass / volume), and utilize the Bohr law of inert gases with small molecular diameters under certain conditions (PV = nRT) to accurately measure the true volume of the material being tested, thereby obtaining its true density.

[0173] Lithium-ion battery performance test: A negative electrode slurry was prepared with a mass ratio of 75:15:10 of negative electrode material, conductive carbon black Super-P(5) + conductive graphite SFG-6(10), and aqueous dispersion of acrylonitrile multipolymer (LA133 aqueous binder), coated on copper foil, and dried to form a negative electrode sheet. A button cell was assembled in an Ar-filled glove box using a metal lithium sheet as the counter electrode. The button cell was charged and discharged at a current density of 0.1C in the charge and discharge range of 0.01-5V to obtain the first reversible specific capacity and ICE of the button cell.

[0174] A negative electrode slurry was prepared using a mixture of negative electrode material and graphite, conductive carbon black Super-P, conductive carbon black KS-6, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) in a mass ratio of 92:2:2:2:2. This was then coated onto copper foil and dried to form a negative electrode plate. The proportions of negative electrode material and graphite in the mixture were determined by their initial reversible specific capacities and the required combined capacity. A button cell was assembled in an Ar-filled glove box using a metal lithium sheet as the counter electrode. The button cell was subjected to 50 cycles of charge and discharge testing at a current density of 1C in the 0.01V-5V charge and discharge range. The capacity retention and plate thickness expansion rate after 50 cycles were determined.

[0175] The embodiments of the present invention will be described in detail below with reference to specific examples, but those skilled in the art will appreciate that the following examples are intended only to illustrate the present invention and should not be construed as limiting the scope of the present invention. Where specific conditions are not specified in the examples, the methods were performed according to conventional conditions or the conditions recommended by the manufacturer. Where the manufacturers of the reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0176] Example 1

[0177] This embodiment provides a negative electrode material, the specific preparation method of which includes:

[0178] (1) According to mass percentage, 65% of porous carbon with D50 = 150 μm, 22% of porous carbon with D50 = 80 μm, 3% of porous carbon with D50 = 30 μm, and 10% of polyvinyl butyral were mixed with VC;

[0179] (2) A layer of polytetrafluoroethylene paper is attached to the working surface of the steel mold, and then the inner surface of the mold is evenly coated with dimethyl silicone oil. Then, the powder mixed in step (1) is poured into the mold. The mold is then placed in an oven and heated at 200°C for 1 hour. Finally, a pressure of 10 MPa is applied to the mold on a press to obtain a porous carbon matrix.

[0180] (3) placing the porous carbon substrate into a CVI infiltration furnace, evacuating the CVI infiltration furnace to exhaust the air in the furnace, and stopping the vacuuming when the pressure in the furnace reaches 1 Pa;

[0181] (4) The CVI infiltration furnace was powered on and heated to 400°C at a heating rate of 8°C / min, and then heated to 420°C at a heating rate of 0.1°C / min. The vacuum system was turned on again, and the furnace was evacuated to 1 Pa. Then, a mixture of silane, H2, and Ar was introduced from the bottom to the top of the vertical CVI furnace. The H2 gas flow rate was 180 mL / min, the Ar flow rate was 300 mL / min, the molar ratio of H2 to silane was 12, and the flow ratio of diluted H2 to carrier H2 was 5.

[0182] (5) The vacuum pump speed was adjusted to control the infiltration pressure in the CVI furnace at 0.5 kPa, and the infiltration time was 60 h. At this time, the induction coil first heated the range of 25% of the working interval from the top of the furnace body. After the reaction time reached 36 h, it gradually moved downward to complete the densification process of the entire porous carbon matrix. The porosity of the composite material was 13%;

[0183] (6) After the CVI chemical vapor densification treatment is completed, the power and reaction gas are turned off, the vacuum system is closed, Ar gas is introduced into the CVI furnace until the pressure reaches normal pressure, and the vent valve is opened. After the temperature in the CVI furnace cools to room temperature, the introduction of Ar gas is stopped;

[0184] (7) The material was taken out, ultrasonically cleaned with ethanol for 30 minutes, and dried at 80° C. to obtain a negative electrode material, wherein the size of silicon was 2-100 nm.

[0185] Example 2

[0186] This embodiment provides a negative electrode material, the specific preparation method of which includes:

[0187] (1) According to mass percentage, 63% of porous carbon with D50 = 250 μm, 26.5% of porous carbon with D50 = 190 μm, 3.5% of porous carbon with D50 = 60 μm, and 7% of PVB and VC were mixed;

[0188] (2) A layer of polytetrafluoroethylene paper is attached to the working surface of the steel mold, and then the inner surface of the mold is evenly coated with dimethyl silicone oil. The mixed powder is then poured into the mold. The mold is then placed in an oven and heated at 150°C for 2 hours. Finally, a pressure of 20 MPa is applied to the mold on a press to obtain a porous carbon matrix.

[0189] (3) The porous carbon substrate is placed in a CVI furnace, and the CVI furnace is evacuated to exhaust the air in the CVI furnace. When the pressure in the CVI furnace reaches 5 Pa, the evacuation is stopped;

[0190] (4) The CVI furnace was powered on and heated to 400°C at a heating rate of 6°C / min, and then to 420°C at a heating rate of 0.1°C / min. The vacuum system was re-opened and evacuated to 6 Pa. Then, a mixture of silane, H2, and Ar was introduced from the bottom to the top of the vertical CVI furnace. The H2 gas flow rate was 350 mL / min, the Ar flow rate was 380 mL / min, the molar ratio of H2 to silane was 3, and the flow ratio of diluted H2 to carrier H2 was 8;

[0191] (5) The vacuum pump speed was adjusted to control the infiltration pressure in the CVI furnace at 5 kPa, and the infiltration time was 80 h. At this time, the induction coil first heated the range of 25% of the working interval from the top of the furnace body. After the reaction time reached 36 h, it gradually moved downward to complete the densification process of the entire porous carbon matrix. The porosity of the composite material was 12%;

[0192] (6) After the CVI chemical vapor densification treatment is completed, the power and reaction gas are turned off, the vacuum system is closed, Ar gas is introduced into the CVI furnace until the pressure reaches normal pressure, and the vent valve is opened. After the temperature in the CVI furnace cools to room temperature, the introduction of Ar gas is stopped;

[0193] (7) The composite material was taken out, ultrasonically cleaned with anhydrous ethanol for 35 minutes, and then dried in a drying oven at 100° C. to obtain a negative electrode material, wherein the size of silicon was 5-80 nm.

[0194] Example 3

[0195] This embodiment provides a negative electrode material, the specific preparation method of which includes:

[0196] (1) According to mass percentage, 65% of porous carbon with D50 = 370 μm, 24% of porous carbon with D50 = 250 μm, 3% of porous carbon with D50 = 90 μm, and 8% of PVB and VC were mixed;

[0197] (2) A layer of polytetrafluoroethylene paper is attached to the working surface of the steel mold, and then the inner surface of the mold is evenly coated with dimethyl silicone oil. The mixed powder is then poured into the mold. The mold is then placed in an oven and heated at 250°C for 0.5 hours. Finally, a pressure of 25 MPa is applied to the mold on a press to obtain a porous carbon matrix.

[0198] (3) The porous carbon substrate is placed in a CVI furnace, and the CVI furnace is evacuated to exhaust the air in the CVI furnace. When the pressure in the deposition furnace reaches 5 Pa, the evacuation is stopped;

[0199] (4) The CVI furnace was powered on and heated to 400°C at a heating rate of 10°C / min, and then to 450°C at a heating rate of 0.2°C / min. The vacuum system was turned on again, and the furnace was evacuated to 10 Pa. Then, a mixture of silane, H2, and Ar was introduced from the bottom to the top of the vertical CVI furnace. The H2 gas flow rate was 300 mL / min, the Ar flow rate was 380 mL / min, the molar ratio of H2 to silane was 4, and the flow ratio of diluted H2 to carrier H2 was 8;

[0200] (5) The vacuum pump speed was adjusted to control the deposition pressure in the CVI furnace at 2.5 kPa, and the infiltration time was 300 h. At this time, the induction coil first heated the range of 25% of the working interval from the top of the furnace body. After the reaction time reached 36 h, it gradually moved downward to complete the densification process of the entire porous carbon matrix. The porosity of the composite material was 15%;

[0201] (6) After the CVI chemical vapor densification treatment is completed, the power and reaction gas are turned off, the vacuum system is closed, Ar gas is introduced into the CVI furnace until the pressure reaches normal pressure, and the vent valve is opened. After the temperature in the CVI furnace cools to room temperature, the introduction of Ar gas is stopped;

[0202] (7) The composite material was taken out, ultrasonically cleaned with ethanol for 60 minutes, and then dried in a drying oven at 90° C. to obtain a negative electrode material, wherein the size of silicon was 10-90 nm.

[0203] Example 4:

[0204] This embodiment provides a negative electrode material, the specific preparation method of which includes:

[0205] (1) According to mass percentage, 64% of porous carbon with D50 = 500 μm, 27% of porous carbon with D50 = 350 μm, 3% of porous carbon with D50 = 120 μm, and 6% of PVB and VC were mixed;

[0206] (2) A layer of polytetrafluoroethylene paper is attached to the working surface of the steel mold, and then the inner surface of the mold is evenly coated with dimethyl silicone oil. The mixed powder is then poured into the mold. The mold is then placed in an oven and heated at 350°C for 3 hours. Finally, a pressure of 5 MPa is applied to the mold on a press to obtain a porous carbon matrix.

[0207] (3) The porous carbon substrate is placed in a CVI furnace, and the CVI furnace is evacuated to exhaust the air in the CVI furnace. When the pressure in the CVI furnace reaches 5 Pa, the evacuation is stopped;

[0208] (4) The CVI furnace was powered on and heated to 420°C at a heating rate of 8°C / min, and then to 450°C at a heating rate of 0.1°C / min. The vacuum system was re-opened and evacuated to 10 Pa. Then, a mixture of silane, H2, and Ar was introduced from the bottom to the top of the vertical CVI furnace. The H2 gas flow rate was 300 mL / min, the Ar flow rate was 380 mL / min, the molar ratio of H2 to silane was 2.5, and the flow ratio of diluted H2 to carrier H2 was 10.

[0209] (5) Adjust the vacuum pump speed to control the deposition pressure in the CVI furnace at 0.9 kPa, and the infiltration time is 60 h. At this time, the induction coil first heats the range of 25% of the working range from the top of the furnace body. After the reaction time reaches 40 h, it gradually moves downward to complete the densification process of the entire porous carbon. The porosity of the composite material is 15%;

[0210] (6) After the CVI chemical vapor densification treatment is completed, the power and reaction gas are turned off, the vacuum system is closed, Ar gas is introduced into the CVI furnace until the pressure reaches normal pressure, and the vent valve is opened. After the temperature in the CVI furnace cools to room temperature, the introduction of Ar gas is stopped;

[0211] (7) The composite material was taken out, ultrasonically cleaned with ethanol for 30 minutes, and then dried in a drying oven at 100° C. to obtain a negative electrode material, wherein the size of silicon was 20-90 nm.

[0212] Example 5

[0213] This embodiment provides a negative electrode material, the specific preparation method of which includes:

[0214] (1) According to mass percentage, 63.5% of porous carbon with D50 = 300 μm, 24% of porous carbon with D50 = 235 μm, 3.5% of porous carbon with D50 = 75 μm, and 9% of PVB and VC were mixed;

[0215] (2) A layer of polytetrafluoroethylene paper is attached to the working surface of the steel mold, and then the inner surface of the mold is evenly coated with dimethyl silicone oil. The mixed powder is then poured into the mold. The mold is then placed in an oven and heated at 280°C for 2 hours. Finally, a pressure of 30 MPa is applied to the mold on a press to obtain a porous carbon matrix.

[0216] (3) The porous carbon substrate is placed in a CVI furnace, and the CVI furnace is evacuated to exhaust the air in the CVI furnace. When the pressure in the CVI furnace reaches 5 Pa, the evacuation is stopped;

[0217] (4) The CVI furnace was powered on and heated to 420°C at a heating rate of 10°C / min, and then to 440°C at a heating rate of 0.1°C / min. The vacuum system was re-opened and evacuated to 5 Pa. Then, a mixture of silane, H2, and Ar was introduced from the bottom to the top of the vertical CVI furnace. The H2 gas flow rate was 320 mL / min, the Ar flow rate was 360 mL / min, the molar ratio of H2 to silane was 2.5, and the flow ratio of diluted H2 to carrier H2 was 5;

[0218] (5) The vacuum pump speed was adjusted to control the infiltration pressure in the CVI furnace at 1.1 kPa, and the infiltration time was 300 h. At this time, the induction coil first heated the range of 25% of the working interval from the top of the furnace body. After the reaction time reached 36 h, it gradually moved downward to complete the densification process of the entire porous carbon matrix. The porosity of the composite material was 13%;

[0219] (6) After the CVI chemical vapor densification treatment is completed, the power and reaction gas are turned off, the vacuum system is closed, Ar gas is introduced into the CVI furnace until the pressure reaches normal pressure, and the vent valve is opened. After the temperature in the CVI furnace cools to room temperature, the introduction of Ar gas is stopped;

[0220] (7) The composite material was taken out, ultrasonically cleaned with ethanol for 70 minutes, and then dried in a drying oven at 100° C. to obtain a negative electrode material, wherein the size of silicon was 20-70 nm.

[0221] Comparative Example 1

[0222] This embodiment provides a negative electrode material, the specific preparation method of which includes:

[0223] According to mass percentage, 90% of porous carbon with D50 = 100 μm and 10% of PVB were mixed with VC;

[0224] The subsequent steps are the same as those in Example 1.

[0225] Comparative Example 2

[0226] This embodiment provides a negative electrode material, the specific preparation method of which includes:

[0227] According to mass percentage, 50% of porous carbon with D50=100 μm, 40% of porous carbon with D50=80 μm, and 10% of PVB and VC were mixed;

[0228] The subsequent steps are the same as those in Example 1.

[0229] Comparative Example 3

[0230] This embodiment provides a negative electrode material, the specific preparation method of which includes:

[0231] According to mass percentage, 60% of porous carbon with D50=800μm, 25% of porous carbon with D50=60μm, 5% of porous carbon with D50=30μm, and 10% of PVB and VC were mixed;

[0232] The subsequent steps are the same as those in Example 1.

[0233] Comparative Example 4

[0234] This embodiment provides a negative electrode material, the specific preparation method of which includes:

[0235] According to mass percentage, 60% of porous carbon with D50 = 100 μm, 25% of porous carbon with D50 = 90 μm, 5% of porous carbon with D50 = 30 μm, and 10% of PVB and VC were mixed;

[0236] The subsequent steps are the same as those in Example 1.

[0237] Comparative Example 5

[0238] This embodiment provides a negative electrode material, the specific preparation method of which includes:

[0239] According to mass percentage, 60% of porous carbon with D50=100 μm, 25% of porous carbon with D50=60 μm, 5% of porous carbon with D50=10 μm, and 10% of PVB and VC were mixed;

[0240] The subsequent steps are the same as those in Example 1.

[0241] Comparative Example 6

[0242] This comparative example uses 90% by mass of porous carbon with D50=50μm, 10% of PVB, and VC mixed;

[0243] The subsequent steps are the same as those in Example 1.

[0244] According to the above-mentioned test method, the negative electrode materials prepared in Examples 1-5 and Comparative Examples 1-6 were used as negative electrode materials in lithium-ion batteries, and the test data shown in Tables 1 and 2 were obtained.

[0245] Table 1. Performance parameters of negative electrode materials of the examples

[0246] Table 2. Performance parameters of negative electrode materials of Examples and Comparative Examples

[0247] By analyzing the data in Tables 1 and 2, it can be found that: by using the porous carbon matrix prepared in the technical solution of the present application and the related CVI chemical vapor infiltration treatment process, the negative electrode material finally prepared has a higher density and is more uniform, and silicon can penetrate deeply into the pores of the porous carbon matrix.

[0248] Comparison of Example 1 and Comparative Examples 1 to 6 shows that it is necessary to control the proportion of various porous carbons in the material. Otherwise, the pore distribution in the material will be unreasonable, the silicon content that penetrates will be too little, and the final pore volume (micropores and mesopores) of the negative electrode material will account for too much. The C value of the negative electrode material is too high, which affects the particle strength of the material (easy to break during rolling); the silicon grains will aggregate and grow, and the cycle performance of the material will decrease.

[0249] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

[0250] Furthermore, those skilled in the art will appreciate that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of the present invention and to form different embodiments. For example, in the claims above, any of the claimed embodiments may be used in any combination. The information disclosed in this background section is intended solely to enhance understanding of the overall background of the present invention and should not be construed as an admission or any form of implication that such information constitutes prior art known to those skilled in the art.

Claims

1. A negative electrode material, characterized in that: The negative electrode material includes an active substance, which includes a porous carbon matrix and silicon, and the silicon is distributed in the pores and / or on the surface of the porous carbon matrix; the adsorption constant C value of the negative electrode material is C<200, and the open porosity of the material after etching the negative electrode material is 50% to 70%.

2. A negative electrode material, characterized in that: The negative electrode material includes an active substance, which includes a porous carbon matrix and silicon, and the silicon is distributed in the pores and / or on the surface of the porous carbon matrix; the adsorption constant C value of the negative electrode material is C<200, the density of the material after etching the negative electrode material is ρ1, the density of the negative electrode material is ρ2, 50%≤(ρ2-ρ1) / ρ1≤80%.

3. The negative electrode material according to claim 1 or 2, characterized in that At least one of the following conditions is met: (1) The particle size of the silicon is 1 nm to 100 nm; (2) The pores of the silicon material after etching of the negative electrode material have a pore diameter of 0 to 1 μm; (3) The filling degree of silicon in the porous carbon matrix is ​​≥80%; (4) The density of the negative electrode material is 1.8 g / cm 3 ~2.3g / cm 3 The density of the negative electrode material after etching is 1g / cm 3 ~1.5g / cm 3 ; (5) The negative electrode material has a pore structure, and the pore structure includes mesopores, micropores and macropores, wherein the volume proportion of the mesopores in all pore structures is greater than 75%, the volume proportion of the micropores in all pore structures is less than 25%, and the volume proportion of the macropores in all pore structures is less than 10%; (6) The negative electrode material has a pore structure, and the total pore volume of the negative electrode material measured by nitrogen adsorption method is less than 0.05 cm 3 / g; (7) The volume of the closed pores in the negative electrode material is ≤ 0.2 cm 3 / g; (8) The adsorption constant C value of the material after etching of the negative electrode material is 200 <C<500; (9) In the nuclear magnetic resonance test of the negative electrode material, there is a Si-C resonance peak between -10ppm and 20ppm, whose intensity is D1, and there is a Si-Si resonance peak between -90ppm and 110ppm, whose intensity is D2, and D2 / D1≥100; (10) The particle size of the negative electrode material after etching is 1 μm to 50 μm; (11) The silicon includes nanosilicon.

4. The negative electrode material according to any one of claims 1 to 3, characterized in that The negative electrode material further includes a carbon coating layer located on at least a portion of the surface of the active material.

5. The negative electrode material according to claim 4, characterized in that At least one of the following conditions is met: (1) The thickness of the carbon coating layer is 1 nm-100 nm; (2) The mass percentage of silicon in the negative electrode material is 10% to 90%; (3) The specific surface area of ​​the negative electrode material is 0.5 m 2 / g~50m 2 / g; (4) The average particle size of the negative electrode material is 1 μm to 25 μm.

6. A method for preparing a negative electrode material, characterized in that: include: N porous carbon powders of different particle sizes are mixed with a binder and subjected to heat treatment to obtain a porous carbon matrix, wherein N is greater than or equal to 2; Silicon is compounded on the porous carbon substrate to obtain the negative electrode material.

7. The preparation method according to claim 6, characterized in that: According to the size of the particle size, the N porous carbon powders with different particle sizes are arranged in order from small to large, and the porous carbon powders meet at least one of the following conditions: (1) In two adjacent porous carbon powders, the ratio of D50 of the porous carbon powder with a smaller particle size to D50 of the porous carbon powder with a larger particle size is 0.25 to 0.9; (2) In two adjacent porous carbon powders, the ratio of the mass of the porous carbon powder with a smaller particle size to the mass of the porous carbon powder with a larger particle size is 0.05 to 0.75; (3) Among the two adjacent porous carbon powders, D10 of the porous carbon powder with a larger particle size is not less than D90 of the porous carbon powder with a smaller particle size; (4) When N=3, the ratio of D50 of the porous carbon powder of large size: the porous carbon powder of medium size: the porous carbon powder of small size is (4-7): (2-3.5): 1; (5) When N=3, the mass ratio of the porous carbon powder of large size: the porous carbon powder of medium size: the porous carbon powder of small size is (18-25):(6-12):1; (6) When N=3, the D50 of the large-sized porous carbon powder, the medium-sized porous carbon powder, and the small-sized porous carbon powder are 100 μm to 500 μm, 70 μm to 400 μm, and 20 μm to 130 μm, respectively; (7) When N=3, the average pore size of the porous carbon matrix prepared from the porous carbon powders of three different particle sizes is 2nm to 50nm; (8) The binder comprises polyvinyl butyral; (9) The mass ratio of the N porous carbon powders of different particle sizes to the binder is (5-20):

1.

8. The preparation method according to claim 6, characterized in that: The heat treatment comprises: heating and pressurizing the mixed material, and cooling it to obtain the porous carbon matrix.

9. The preparation method according to claim 6, characterized in that: The chemical vapor infiltration method is used to thermally decompose the reaction gas so that silicon is deposited on the surface and / or in the pores of the porous carbon matrix to obtain the negative electrode material.

10. A lithium ion battery, characterized in that: The raw material includes the negative electrode material described in any one of claims 1 to 5 or the negative electrode material prepared by the preparation method of any one of claims 6 to 9.

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