NEGATIVE ELECTRODE MATERIAL, ITS PREPARATION PROCESS AND LITHIUM-ION BATTERY

Abstract

A negative electrode material and a preparation method therefor, and a lithium ion battery. The negative electrode material comprises an active substance; the active substance comprises a porous matrix and a silicon matrix; at least part of the silicon matrix is distributed in pores of the porous matrix; in an infrared spectrum obtained by measuring the negative electrode material by using an infrared spectrometer, there are stretching vibration peaks of SiH2 bonds at a wave number of 2090 cm-1 and stretching vibration peaks of SiH bonds at a wave number of 2000 cm-1; the ratio Z of the vibration peak area of the SiH2 bonds to the vibration peak area of the SiH bonds in the negative electrode material is 0.01-5.0; the defined range indicates that the silicon matrix in the negative electrode material is mainly present in the form of the SiH bonds, wherein because the stability of the SiH bond is greater than that of the SiH2 bond, more SiH bonds are beneficial to improving the mechanical performance of the silicon matrix, improving the structural stability of the negative electrode material, reducing by-reaction between the negative electrode material and an electrolyte, and then improving the cycle performance and the expansion performance of the negative electrode material.

Description

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

[0001] This application claims priority to the Chinese patent application filed with the State Intellectual Property Office on September 28, 2023, with application number 202311280138.7 and application name “Negative electrode material and preparation method thereof, lithium-ion battery”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the technical field of negative electrode materials, and in particular to negative electrode materials and preparation methods thereof, and lithium-ion batteries. Background Art

[0003] Silicon-based anode materials offer advantages such as high specific capacity, low voltage plateau, environmental friendliness, and abundant resources, making them promising alternatives to graphite anodes for next-generation high-energy-density lithium-ion batteries. However, silicon undergoes significant volume changes during the deintercalation / intercalation process, which can easily lead to particle pulverization and subsequent detachment from the current collector. Furthermore, the repeated volume changes of silicon materials during electrochemical cycling also cause the SEI film formed on the silicon surface to be continuously destroyed and regenerated, resulting in continuous consumption of lithium ions and ultimately rapid capacity decay.

[0004] Crystalline silicon in silicon-based negative electrode materials is the main factor causing the volume expansion change of silicon-based negative electrode materials. In order to solve these problems, researchers usually improve the crystalline silicon through processes such as nano-sizing, carbon coating, and polymer coating, which can inhibit the volume expansion of crystalline silicon to a certain extent. However, the ability of the above methods to inhibit the volume expansion of silicon is limited and cannot meet the needs of existing high-energy-density lithium-ion batteries.

[0005] Therefore, there is an urgent need for a negative electrode material with low expansion and excellent cycle performance.

[0006] Summary of the Invention

[0007] The embodiments of the present application provide a negative electrode material and a preparation method thereof, and a lithium-ion battery, which can improve the expansion performance and cycle performance of the negative electrode material.

[0008] In a first aspect, an embodiment of the present application provides a negative electrode material, wherein the negative electrode material includes an active substance, wherein the active substance includes a porous matrix and a silicon matrix, at least a portion of the silicon matrix is ​​distributed in the pores of the porous matrix, and an infrared spectrum obtained by measuring the negative electrode material using an infrared spectrometer has a wave number of 2090 cm -1 The SiH2 bond stretching vibration peak and wave number 2000cm -1 The SiH bond stretching vibration peak of the negative electrode material is 0.01 to 5.0, and the ratio Z of the vibration peak area of ​​the SiH2 bond to the vibration peak area of ​​the SiH bond in the negative electrode material is 0.01 to 5.0.

[0009] The technical solution of this application has at least the following beneficial effects:

[0010] The active material of the negative electrode material of the present application includes a porous matrix and a silicon matrix. The silicon matrix is ​​distributed in the pores of the porous matrix. The porous matrix can alleviate the volume expansion of the silicon matrix and act as an elastic conductor of the negative electrode material. It provides ion and electron transmission paths for the negative electrode material during the charge and discharge process, enhances the conductivity of the negative electrode material, and improves the rate performance of the negative electrode material. The silicon matrix is ​​embedded in the pores of the porous matrix, which can also reduce the agglomeration of the silicon matrix particles, thereby reducing the problem of structural damage to the entire negative electrode material due to stress concentration. Secondly, the silicon matrix has a higher lithium insertion voltage (~0.4V), which can inhibit the formation of lithium dendrites (lithium dendrite formation potential ~0V), thereby improving the safety performance of the negative electrode material used in batteries. In addition, the ratio Z of the vibration peak area of ​​the SiH2 bond to the vibration peak area of ​​SiH in the negative electrode material of the present application is 0.01~5.0, the stability of the SiH bond is greater than that of the SiH2 bond, and the silicon matrix with more SiH bonds is beneficial to improving the structural stability of the negative electrode material, reducing the occurrence of side reactions between the negative electrode material and the electrolyte, and thus improving the cycle performance and expansion performance of the negative electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG1 is a flow chart of the preparation of the negative electrode material of the present application;

[0012] FIG2 is an infrared spectrum of the negative electrode material prepared in Example 2 of the present application;

[0013] FIG3 is a Raman spectrum of the negative electrode material prepared in Example 2 of the present application. DETAILED DESCRIPTION

[0014] In order to better understand the technical solution of the present application, the embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0015] It should be clear that the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0016] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or to implicitly indicate the quantity of the technical features indicated. Thus, a feature specified as "first" or "second" may explicitly or implicitly include one or more of the features.

[0017] In order to facilitate understanding of the present application, specific terms are appropriately defined in the present application. Unless otherwise defined herein, the scientific terms and technical terms used in the present application have the meanings commonly understood by those skilled in the art to which the present application belongs.

[0018] The present invention provides a negative electrode material including an active material, wherein the active material includes a porous matrix and a silicon matrix, at least part of the silicon matrix is ​​distributed in the pores of the porous matrix, and an infrared spectrum obtained by measuring the negative electrode material using an infrared spectrometer has a wave number of 2090 cm -1 The SiH2 bond stretching vibration peak and wave number 2000cm -1 The SiH bond stretching vibration peak, the ratio Z of the vibration peak area of ​​the SiH2 bond to the vibration peak area of ​​SiH in the negative electrode material is 0.01 to 5.0.

[0019] In the above scheme, the active material of the negative electrode material of the present application includes a porous matrix and a silicon matrix. The silicon matrix is ​​distributed in the pores of the porous matrix. The porous matrix can alleviate the volume expansion of the silicon matrix and act as an elastic conductor of the negative electrode material. It provides ion and electron transmission paths for the negative electrode material during the charge and discharge process, enhances the conductivity of the negative electrode material, and improves the rate performance of the negative electrode material. The silicon matrix is ​​embedded in the pores of the porous matrix, which can also reduce the problem of agglomeration of silicon matrix particles, which leads to stress concentration and destruction of the structure of the entire negative electrode material. Secondly, the silicon matrix has a higher lithium insertion voltage (~0.4V), which can inhibit the formation of lithium dendrites (lithium dendrite formation potential ~0V), thereby improving the safety performance of the negative electrode material used in the battery. In addition, the ratio Z of the vibration peak area of ​​the SiH2 bond to the vibration peak area of ​​the SiH bond in the negative electrode material of the present application is 0.01 to 5.0. The stability of the SiH bond is greater than that of the SiH2 bond. The silicon matrix with more SiH bonds is beneficial to improving the structural stability of the negative electrode material, reducing the occurrence of side reactions between the negative electrode material and the electrolyte, and thus improving the cycle performance and expansion performance of the negative electrode material. The silane cracking process produces SiH bonds, SiH2 bonds, and SiH3 bonds. SiH3 bonds will only exist in large quantities when the silane cracking is insufficient.

[0020] Compared with the negative electrode material containing crystalline silicon, crystalline silicon is converted into an amorphous phase Li-Si during the lithium insertion process, and a two-phase reaction occurs. In this application, due to the disordered structure of the silicon matrix, a homogeneous reaction occurs during the lithium insertion process. Therefore, the volume expansion of the silicon matrix in this application is lower than that of crystalline silicon. The volume expansion of the silicon matrix in this application is small, which can improve the expansion performance of the negative electrode material.

[0021] In this application, the value of Z can be 0.01, 0.05, 0.1, 0.3, 0.8, 1.0, 2.0, 3.0, 4.0 or 5.0, etc., and of course it can also be other values ​​within the above range, and this application is not limited here. Within the above-mentioned limited range, the smaller the Z value, the more SiH bonds there are in the silicon matrix, the more stable the silicon matrix is, and the more conducive it is to improving the cycle performance and expansion performance of the negative electrode material. If the Z value is greater than 5, it means that there are too many SiH2 bonds in the silicon matrix in the negative electrode material, and SiH3 bonds may also appear, resulting in an unstable structure of the negative electrode material, resulting in a decrease in the cycle performance and expansion performance of the negative electrode material. Preferably, the value of Z is 0.05 to 3.0, and further preferably, the value of Z is 0.05 to 0.5.

[0022] In some embodiments, the silicon matrix includes silicon particles.

[0023] In some embodiments, the porosity of the negative electrode material is 0.01% to 10%, for example, 0.01%, 1%, 3%, 5%, 8%, or 10%, and other values ​​within the above range are also possible, and this application is not limited thereto. Within the above-defined range, the energy density of the negative electrode material can be increased while suppressing volume expansion.

[0024] In this application, the negative electrode material is added to concentrated nitric acid with a concentration of 1M and soaked for 4 hours. Then, a 20% mass fraction HF acid solution is dripped into the negative electrode material drop by drop, which will produce yellow smoke. The dripping is repeated many times until no yellow smoke is produced in the solution. Finally, the residue is digested with concentrated nitric acid with a concentration of 1M, and then washed and dried to obtain the negative electrode material after removing the silicon matrix, that is, the porous matrix.

[0025] In some embodiments, the porosity of the negative electrode material after removing the silicon matrix is ​​30% to 70%, for example, 30%, 40%, 50%, 55%, 60%, or 70%, and of course other values ​​within the above range are also possible, and this application is not limited thereto. Within the above-defined range, the negative electrode material after removing the silicon matrix has sufficient space to disperse the silicon matrix and has sufficient crushing resistance, which can improve the energy density of the negative electrode material while suppressing the volume expansion of the negative electrode material.

[0026] In some embodiments, the average pore size of the negative electrode material after removing the silicon matrix is ​​0.2nm to 10nm, for example, it can be 0.2nm, 0.5nm, 2nm, 5nm, 8nm or 10nm, etc. Of course, it can also be other values ​​within the above range, and this application does not limit it here.

[0027] In some embodiments, the average particle size of the silicon matrix is ​​1 nm to 10 nm, for example, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, or 10 nm, etc. Of course, other values ​​within the above range are also possible, and this application is not limited thereto. Within the above particle size range, the silicon matrix is ​​facilitated to embed into the pores of the porous matrix. Preferably, the average particle size of the silicon matrix is ​​1 nm to 5 nm.

[0028] In some embodiments, the mass proportion of the silicon matrix in the negative electrode material is 5% to 90%, for example, 5%, 10%, 20%, 50%, 70%, 80%, or 90%, etc., and of course other values ​​within the above range are also possible, and this application is not limited thereto. Within the above-mentioned limit range, it is shown that the negative electrode material of the present application has a relatively high silicon matrix load, which is beneficial to improving the capacity performance of the negative electrode material.

[0029] In some embodiments, at least a portion of the silicon matrix is ​​distributed on the surface of the porous matrix. It can be understood that in order to improve the rate performance of the negative electrode material, the silicon matrix of the present application is mainly distributed inside the porous matrix.

[0030] In some embodiments, the negative electrode material further includes a coating layer disposed on at least a portion of the surface of the active material. On the one hand, the presence of the coating layer can reduce the side reactions caused by the electrolyte entering the negative electrode material, which can lead to reduced initial efficiency and capacity. On the other hand, the coating layer can also alleviate the volume expansion of silicon to a certain extent, reducing the volume expansion of the entire negative electrode material and reducing the swelling of the electrode sheet made of the negative electrode material.

[0031] In some embodiments, the coating layer includes at least one of a carbon material, a metal oxide, and a metal sulfide.

[0032] In some embodiments, the coating layer may be at least one of a carbon layer, a metal oxide layer, and a metal sulfide layer. In some embodiments, the carbon material includes at least one of graphene, soft carbon, hard carbon, and a conductive polymer. Specifically, the conductive polymer includes at least one of polyaniline, polyacetylene, polypyrrole, polythiophene, poly-3-hexylthiophene, poly(p-phenylene vinylene), polypyridine, and poly(phenylene vinylene).

[0033] In some embodiments, the metal oxide includes at least one of titanium oxide, aluminum oxide, lithium oxide, cobalt oxide, and vanadium oxide.

[0034] In some embodiments, the metal sulfide includes at least one of tin sulfide, molybdenum sulfide, titanium sulfide, iron sulfide, and copper sulfide.

[0035] In some embodiments, the thickness of the coating layer is 5nm to 500nm, for example, it can be 5nm, 10nm, 30nm, 80nm, 120nm, 200nm, 300nm, 400nm or 500nm, etc., of course, it can also be other values ​​within the above range, which is not limited here. Preferably, the thickness of the coating layer is 10nm to 100nm. The coating layer can reduce the contact between silicon and the electrolyte, reduce the formation of passivation film, and improve the reversible capacity of the battery. If the thickness of the coating layer is greater than 500nm, the lithium ion transmission efficiency is reduced, which is not conducive to high-rate charge and discharge of the negative electrode material and reduces the overall performance of the negative electrode material; if the thickness of the coating layer is less than 5nm, it is not conducive to increasing the conductivity of the negative electrode material and has a weak performance in inhibiting the volume expansion of the negative electrode material, resulting in poor cycle performance.

[0036] In some embodiments, the median particle size D50 of the negative electrode material is 5 μm to 10 μm, for example, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm, and of course, other values ​​within the above range are also possible, and this application is not limited thereto. Preferably, the median particle size D50 of the negative electrode material is 5 μm to 8 μm, and more preferably, the median particle size D50 of the negative electrode material is 7 μm to 8 μm.

[0037] In some embodiments, the minimum particle size D00 of the negative electrode material is 1 μm to 3 μm, for example, 1 μm, 1.5 μm, 2 μm, 2.5 μm, or 3 μm, and of course other values ​​within the above range are also possible, and this application is not limited thereto. Preferably, the minimum particle size D00 of the negative electrode material is 1 μm to 2 μm.

[0038] In some embodiments, the D90 of the negative electrode material is 14 μm to 25 μm, for example, 14 μm, 17 μm, 20 μm, 23 μm, or 25 μm, and of course other values ​​within the above range are also possible, and this application is not limited thereto. Preferably, the D90 of the negative electrode material is 18 μm to 20 μm.

[0039] A laser particle size analyzer was used to test the negative electrode material, revealing a symmetrical distribution similar to a normal distribution. In this symmetrical distribution, D90 is the particle size at which the cumulative number of material particles in the distribution reaches 90%, D00 is the minimum size of the material particles, referring to the smallest diameter that can be measured in this distribution, and D50 is the particle size at which the cumulative number of material particles in the distribution reaches 50%, also known as the median particle size. Ideal battery materials require a narrow particle size distribution. Studies have shown that overly small particles make silicon deposition difficult, leading to continuous electrolyte consumption during cycling and poor capacity retention. Overly large particles, on the other hand, deposit excessive silicon matrix. Excessive silicon matrix increases the negative electrode material's expansion rate, making it more susceptible to particle pulverization during cycling, which can lead to continuous thickening of the SEI. Therefore, by controlling the particle size distribution, the cycling performance of the negative electrode material can be improved. In the negative electrode material of this application, the particle size distribution of the material is relatively concentrated, which reduces the aforementioned problems while also having a higher packing density, thereby improving the electrochemical and cycling performance of the negative electrode material.

[0040] In some embodiments, the porous matrix comprises porous carbon.

[0041] In some embodiments, the negative electrode material has a Raman spectrum at 1310 cm-1 as shown in a Raman spectrum obtained by Raman spectroscopy using a measuring light source with a wavelength of 633 nm. -1 ~1350cm -1 Characteristic peak I D and at 1580cm -1 ~1620cm -1 Characteristic peak I G , I D / I G The value is 1.6 to 2.5, for example, 1.6, 1.8, 2.0, 2.2, 2.3 or 2.5, and of course other values ​​within the above range can also be used. This application does not limit this. In the Raman spectrum of this application, the D peak corresponds to the pores and defects of the porous carbon, and the G peak corresponds to the E2g stacking mode of the graphite sheets of the porous carbon. This application uses I D / I G Indicates the ease of silicon deposition on porous carbon. Within the above-defined range, it indicates that the porous carbon has more pores and defects, and has more silicon nucleation sites on its surface and interior, which is conducive to the deposition of silicon, and can greatly increase the silicon loading in the negative electrode material, thereby improving the effective utilization rate of the silicon source, and then increasing the tap density and specific capacity of the entire negative electrode material, and improving the energy density of the battery material made of the entire negative electrode material. Preferably, I D / I G is 1.6 to 2.3, more preferably, I D / I GIt is 1.8 to 2.2.

[0042] In some embodiments, the specific surface area of ​​the negative electrode material is 1.0 m 2 / g~10.0m 2 / g, for example, it can be 1.0m 2 / g, 2.0m 2 / g, 3.0m 2 / g, 4.0m 2 / g, 5.0m 2 / g, 6.0m 2 / g, 7.0m 2 / g, 8.0m 2 / g, 9.0m 2 / g or 10.0m 2 / g, etc., and of course other values ​​within the above range can also be used, and this application does not limit this. It can be understood that controlling the specific surface area of ​​the negative electrode material within the above range can reduce the formation of the SEI film of the negative electrode material and improve the electrochemical performance of the negative electrode material.

[0043] In some embodiments, the powder conductivity of the negative electrode material is 0.1 S / cm to 10.0 S / cm, for example, 0.1 S / cm, 1.0 S / cm, 3.0 S / cm, 5.0 S / cm, 7.0 S / cm, 9.0 S / cm, or 10.0 S / cm, etc. Of course, other values ​​within the above range are also possible, and this application is not limited thereto. It can be understood that controlling the powder conductivity of the negative electrode material within the above range can improve the rate performance of the negative electrode material.

[0044] The present invention also provides a method for preparing a negative electrode material, as shown in FIG1 , comprising the following steps:

[0045] S100, placing the carbon-based raw material and the activating agent in a certain proportion in a VC mixer with a processing capacity of 10L-50L, stirring at a frequency of 5-30HZ and a stirring time of 30-90min, after uniform mixing, transferring the mixture to a rotary kiln, and performing a first heat treatment on the mixture. During the heat treatment, the oxygen content of the rotary kiln is less than 100ppm, and the pressure of the rotary kiln is 10-100Pa. The heat-treated sample is mechanically crushed to obtain a first precursor with a particle size D50 of 5-15μm;

[0046] S200, placing the first precursor under an inert gas atmosphere, performing a second heat treatment on the first precursor, the deviation of the reaction system temperature from the set value is less than 10°C, the reactor needs to maintain a constant temperature for 10-60 minutes after reaching the reaction temperature, the total reaction gas velocity is 15-50L / min, the silane concentration is 10%-60%, the reaction system pressure is 0-30Kpa, and an active substance is obtained after the reaction is completed. The negative electrode material includes the active substance, and the temperature of the second heat treatment is 420°C~800°C.

[0047] In the above technical solution, the present application performs a first heat treatment on a mixture of a carbon-based raw material and an activator to form pores on the surface and inside of the carbon-based raw material to obtain porous carbon, which is a first precursor. Silane gas is further introduced into the porous carbon for a second heat treatment. By controlling the temperature of the second heat treatment to 420°C to 800°C, the silane can be fully decomposed to generate a large amount of silicon matrix in the form of SiH bonds. The silicon matrix is ​​deposited inside and / or on the surface of the first precursor, thereby obtaining a core in which at least part of the silicon matrix is ​​distributed in the pores of the porous carbon. Among them, the large amount of silicon matrix in the form of SiH bonds is beneficial to improving the structural stability of the negative electrode material, improving the mechanical properties of the negative electrode material, reducing the occurrence of side reactions between the negative electrode material and the electrolyte, and can alleviate the volume expansion of the negative electrode material during the lithium insertion stage and improve the cycle stability of the negative electrode material. The porous carbon is coated on the surface of at least part of the silicon matrix. On the one hand, the porous carbon can act as an elastic conductor, providing a transmission path for ions and electrons during the charge and discharge process of the negative electrode material, increasing the conductivity between the silicon matrix and the outside world, thereby improving the rate performance of the negative electrode material. On the other hand, the silicon matrix embedded in the porous carbon can improve the conductivity of the silicon matrix, thereby improving the rate performance of the material and meeting the requirements of the battery to achieve fast charging characteristics.

[0048] It can be understood that sufficient silane cracking generates a large amount of silicon matrix in the form of SiH bonds, that is, the chemical bonds in the silicon matrix contain a large number of SiH bonds. In the silicon matrix generated by insufficient silane cracking, the silicon matrix exists in the form of SiH, SiH2 bonds, and SiH3 bonds. The silicon matrix prepared by the preparation method of the present application can fully crack the silane into amorphous silicon without generating polycrystalline silicon. At the same time, the silicon matrix exists in the form of SiH bonds, so that the ratio Z of the vibration peak area of ​​the SiH2 bond to the vibration peak area of ​​the SiH bond in the negative electrode material satisfies Z = 0.01 to 5.0, thereby improving the cycle performance and expansion performance of the negative electrode material.

[0049] The preparation method of the present application is described in detail below with reference to the examples. The preparation method of the negative electrode material of the present application comprises the following steps:

[0050] S100, placing the carbon-based raw material and the activating agent in a certain proportion in a VC mixer with a processing capacity of 10L-50L, stirring at a frequency of 5-30HZ and a stirring time of 30-90min, after uniform mixing, transferring the mixture to a rotary kiln, and performing a first heat treatment on the mixture. During the heat treatment, the oxygen content of the rotary kiln is less than 100ppm, and the pressure of the rotary kiln is 10-100Pa. The heat-treated sample is mechanically crushed to obtain a first precursor with a particle size D50 of 5-15μm;

[0051] In some embodiments, the carbon-based raw material includes at least one of nut shell carbon, straw carbon, resin carbon, pitch carbon and sugar.

[0052] In some embodiments, the activator includes at least one of water vapor, an alkaline substance, and a template. The activator is activated by contacting the carbon-based material at a certain temperature. The activator can erode the surface of the carbon-based material at high temperature, causing previously blocked pores in the carbon-based material to reopen and further expand. In some structures, new pores are generated due to selective oxidation.

[0053] In some embodiments, the alkaline substance includes at least one of potassium hydroxide and sodium hydroxide.

[0054] In some embodiments, the template comprises at least one of calcium hydroxide, calcium oxide, magnesium oxide, magnesium hydroxide, melamine, aluminum oxide, and a polymer template. Exemplarily, the polymer template comprises polyurethane, melamine resin, cellulose, polystyrene, polymethyl methacrylate, and the like.

[0055] In some embodiments, the temperature of the first heat treatment is 600°C to 2000°C, for example, it can be 600°C, 800°C, 1000°C, 1100°C, 1500°C, 1800°C or 2000°C, etc., of course, it can also be other values ​​within the above range, which is not limited here. It can be understood that the temperature of the first heat treatment is controlled within the above range, which is conducive to the activation of carbon-based raw materials into pores and the improvement of the porosity of porous carbon. Preferably, the temperature of the first heat treatment is 800°C to 1500°C, and further preferably, the temperature of the first heat treatment is 800°C to 1100°C.

[0056] In some embodiments, the heating rate of the first heat treatment is 5°C / min to 20°C / min, for example, it can be 5°C / min, 10°C / min, 15°C / min, 18°C / min or 20°C / min, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0057] In some embodiments, the time of the first heat treatment is 2 hours to 10 hours, for example, 2 hours, 3 hours, 5 hours, 8 hours or 10 hours, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0058] In some embodiments, the first heat treatment further comprises the steps of washing and drying the material obtained by the first heat treatment.

[0059] In some embodiments, washing includes: first pickling the material obtained from the first heat treatment and then washing it with water, wherein the pickling acid is at least one of hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, phosphoric acid, perchloric acid, acetic acid and benzoic acid. The concentration of the acid is 1 mol / L to 5 mol / L, for example, it can be 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L or 5 mol / L, etc., and of course it can also be other values ​​within the above range, which is not limited here. It can be understood that the purpose of pickling is to remove excess activator in the material. After the first precursor is pickled, it is washed with deionized water to wash the product to neutrality.

[0060] In some embodiments, the drying temperature is 80°C to 150°C, and the specific temperature can be 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C and 150°C, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0061] In some embodiments, the drying time is 24 hours to 72 hours. The specific time can be 24 hours, 30 hours, 36 hours, 42 hours, 48 ​​hours, 52 hours, 60 hours, 72 hours, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0062] In some embodiments, the drying equipment is any one of an oven, a box furnace, and a double-cone dryer.

[0063] In some embodiments, after the first heat treatment, the method further comprises the steps of crushing and screening the material obtained by the first heat treatment.

[0064] In some embodiments, the pulverization is performed by at least one of ball milling, air flow milling, and mechanical milling, preferably mechanical milling.

[0065] In some embodiments, the median particle size of the first precursor after crushing and sieving is 5μm to 10μm, for example, it can be 5μm, 6μm, 7μm, 8μm, 9μm or 10μm, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0066] S200 , subjecting the first precursor to a second heat treatment in a silane gas atmosphere to obtain a negative electrode material, wherein the temperature of the second heat treatment is 420° C. to 800° C.

[0067] In some embodiments, the silane flow rate is 1 L / min to 10 L / min, for example, 1 L / min, 3 L / min, 5 L / min, 7 L / min, 9 L / min, or 10 L / min, and other values ​​within this range are also possible and are not limited herein. Within this limited range, the silane is effectively cracked to produce a large amount of silicon matrix in the form of SiH bonds.

[0068] In some embodiments, the temperature of the second heat treatment is 420°C to 800°C, for example, it can be 420°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C or 800°C, etc. Of course, it can also be other values ​​within the above range, which is not limited here. Preferably, the temperature of the second heat treatment is 550°C to 650°C. Within the above-defined range, it is conducive to the full decomposition of the silane gas to generate more silicon matrix in the form of SiH bonds, which is conducive to improving the structural stability of the negative electrode material, thereby improving the cycle performance and expansion performance of the negative electrode material. If the temperature is higher than 800°C, it is easy to convert the amorphous silicon generated by the decomposition of the silane gas into crystalline silicon, resulting in poor expansion performance of the negative electrode material; if the second heat treatment temperature is lower than 420°C, the silane gas is not fully decomposed, the silane decomposition conversion rate is low, and the silicon matrix decomposed by the silane mainly exists in the coexistence form of SiH bonds, SiH2 bonds, and SiH3 bonds, which reduces the structural stability of the negative electrode material.

[0069] In some embodiments, the heating rate of the second heat treatment is 3°C / min to 20°C / min, specifically 3°C / min, 5°C / min, 8°C / min, 10°C / min, 13°C / min, 16°C / min, 18°C / min or 20°C / min, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0070] In some embodiments, the second heat treatment is performed in a protective gas atmosphere comprising at least one of nitrogen, argon, and helium.

[0071] In some embodiments, the second heat treatment time is 100 min to 600 min, for example, 100 min, 200 min, 300 min, 400 min, 500 min or 600 min, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0072] In some embodiments, the second heat treatment equipment includes at least one of a kiln, a chemical vapor deposition equipment, and a chemical vapor infiltration equipment.

[0073] In some embodiments, after the second heat treatment, the method further includes: mixing the coating material with the material obtained by the second heat treatment and then performing a third heat treatment.

[0074] In this step, the coating material is mixed with the material obtained from the second heat treatment and then subjected to a third heat treatment to form a coating layer. On the one hand, it can reduce the side reactions caused by the electrolyte entering the negative electrode material, resulting in a decrease in the first effect and capacity. On the other hand, it can cooperate with the core material to alleviate the volume expansion of the silicon matrix, reduce the volume expansion of the entire negative electrode material, and reduce the swelling of the electrode sheet made of the negative electrode material.

[0075] In some embodiments, the coating material includes at least one of a carbon source, a metal oxide, and a metal sulfide.

[0076] In some embodiments, the carbon source includes at least one of a gaseous carbon source and a solid carbon source.

[0077] In some embodiments, the gaseous carbon source includes at least one of acetylene, methane, propylene, benzene, ethanol, methanol, ethylene, propane, and butane.

[0078] In some embodiments, the flow rate of the gaseous carbon source is 1 L / min to 15 L / min, for example, it can be 1 L / min, 3 L / min, 5 L / min, 8 L / min, 10 L / min, 12 L / min or 15 L / min, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0079] In some embodiments, the solid carbon source includes at least one of sucrose, fructose, glucose, pitch, phenolic resin, polyimide, citric acid, epoxy resin, amino resin, polystyrene, polyacrylic acid, carboxymethyl cellulose, and cellulose acetate butyrate.

[0080] In some embodiments, the mass ratio of the solid carbon source and the material obtained by the second heat treatment is (0.2-2):1, for example, it can be 0.2:1, 0.5:1, 0.8:1, 1.5:1, 1.8:1 or 2:1, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0081] In some embodiments, the metal oxide includes at least one of iron oxide, zinc oxide, tin oxide, copper oxide, and titanium oxide.

[0082] In some embodiments, the metal sulfide includes at least one of tin sulfide, molybdenum sulfide, titanium sulfide, iron sulfide, and copper sulfide.

[0083] In some embodiments, the mass ratio of the metal oxide and the material obtained by the second heat treatment is (0.2-2):1, for example, it can be 0.2:1, 0.5:1, 0.8:1, 1.5:1, 1.8:1 or 2:1, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0084] In some embodiments, the mass ratio of the metal sulfide to the material obtained by the second heat treatment is (0.2-2):1, for example, it can be 0.2:1, 0.5:1, 0.8:1, 1.5:1, 1.8:1 or 2:1, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0085] In some embodiments, the temperature of the third heat treatment is 300°C to 1100°C, for example, 300°C, 400°C, 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C, and 1100°C, etc., and of course, other values ​​within the above range are also possible and are not limited herein. Within the above-defined range, it is possible to ensure that the coating material is completely carbonized while not significantly affecting the silicon matrix of the core. In order to reduce changes in the silicon matrix during the third heat treatment, the temperature of the third heat treatment is preferably 400°C to 800°C, and more preferably, the temperature of the third heat treatment is 500°C to 700°C.

[0086] In some embodiments, the third heat treatment time is 2 hours to 5 hours, for example, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours or 5 hours, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0087] In a third aspect, the present application provides a lithium-ion battery, which comprises a negative electrode material prepared by the above preparation method.

[0088] While the embodiments of the present application are described, the present application is not limited to these examples unless it exceeds the gist of the present application.

[0089] Example 1

[0090] (1) 400 g of coal tar, 120 g of calcium hydroxide and 50 g of potassium hydroxide were mixed in a VC mixer at a stirring frequency of 20 Hz for 30 min. The purpose of mixing was to prepare a precursor with uniform pore size distribution. After uniform mixing, the precursor was placed in a rotary kiln with an oxygen content of less than 100 ppm and a pressure of 10-100 Pa. The temperature was raised to 700 ° C at a rate of 10 ° C / min and kept constant for 5 h. The obtained material was soaked in 2 mol / L hydrochloric acid for 1 h, filtered, washed with pure water until neutral, and dried in a 100 ° C oven for 4 h. After that, it was crushed and passed through a 325 mesh sieve.

[0091] (2) 200 g of the material obtained in step (1) was placed in a CVD reactor, and the temperature was raised to 550°C at a rate of 5°C / min and kept constant for 60 min to ensure the stability of the temperature of the CVD reactor. 0.6 L / min SiH4 and 0.6 L / min nitrogen were introduced, the reaction system pressure was 0-30 KPa, and the reaction was carried out for 300 min to obtain the first precursor.

[0092] (3) The first precursor was placed in a CVD reactor, heated to 700°C at a rate of 10°C / min, and 1 L / min of C3H6 and 2 L / min of nitrogen were introduced, and the reaction was continued for 150 min.

[0093] (4) The material obtained in step (3) was placed in a VC mixer, crushed, and passed through a 325-mesh sieve to obtain a negative electrode material.

[0094] The negative electrode material obtained in this embodiment includes a core and a coating layer covering the surface of the core. The core includes porous carbon and a silicon matrix located inside and / or on the surface of the porous carbon. The silicon matrix exists mostly in the form of SiH bonds, and the coating layer is a carbon layer.

[0095] Example 2

[0096] (1) 400 g of coal tar, 120 g of calcium hydroxide and 50 g of potassium hydroxide were mixed in a VC mixer at a stirring frequency of 20 Hz for 30 min. The purpose of mixing was to prepare a precursor with uniform pore size distribution. After uniform mixing, the precursor was placed in a rotary kiln with an oxygen content of less than 100 ppm and a pressure of 10-100 Pa. The temperature was raised to 900 ° C at a rate of 10 ° C / min and kept constant for 5 h. The obtained material was soaked in 2 mol / L hydrochloric acid for 1 h, filtered, washed with pure water until neutral, and dried in a 100 ° C oven for 4 h. After that, it was crushed and passed through a 325 mesh sieve.

[0097] (2) 200 g of the material obtained in step (1) was placed in a CVD reactor, and the temperature was raised to 550°C at a rate of 5°C / min and kept constant for 60 min to ensure the stability of the temperature of the CVD reactor. 0.6 L / min SiH4 and 0.6 L / min nitrogen were introduced, the reaction system pressure was 0-30 KPa, and the reaction was carried out for 300 min to obtain the first precursor.

[0098] (3) The first precursor was placed in a CVD reactor, heated to 700°C at a rate of 10°C / min, and 1 L / min of C3H6 and 2 L / min of nitrogen were introduced, and the reaction was continued for 150 min.

[0099] (4) The material obtained in step (3) was placed in a VC mixer, crushed, and passed through a 325-mesh sieve to obtain a negative electrode material.

[0100] The negative electrode material obtained in this embodiment includes a core and a coating layer covering the surface of the core. The core includes porous carbon and a silicon matrix located inside and / or on the surface of the porous carbon. The silicon matrix exists mostly in the form of SiH bonds, and the coating layer is a carbon layer.

[0101] The infrared spectrum of the negative electrode material prepared in this embodiment is shown in FIG2 . As shown in FIG2 , the negative electrode material prepared in Example 2 has a wave number of 2090 cm -1 The SiH2 bond stretching vibration peak and wave number 2000cm-1 The SiH bond stretching vibration peak was imported into Origin software and the wave number was 2000 cm -1 The SiH bond stretching vibration peak at wave number 2090 cm -1 The SiH2 bond stretching vibration peak at the position of the double peak fitting is the Gauss fitting optimization method. The two peaks obtained by fitting are the fitting variance R 2 In the range of 0.6-0.95, the peak area ratio Z value represents the ratio of SiH bond to SiH2 bond, and also represents the degree of silane cracking reaction. -1 No vibration peak of SiH3 bond was found, indicating that SiH3 bond does not exist in silicon-based carbon materials, further indicating that silane cracking is relatively sufficient.

[0102] The Raman spectrum of the negative electrode material prepared in this embodiment is shown in FIG3 . As shown in FIG3 , the negative electrode material of Example 2 has a Raman spectrum at 480 cm - 1 There is a characteristic peak at , which is identified as a characteristic peak of amorphous silicon, indicating that the silane is fully cracked to generate amorphous silicon in this embodiment.

[0103] Example 3

[0104] (1) 400 g of coal tar, 120 g of calcium hydroxide and 50 g of potassium hydroxide were mixed in a VC mixer at a stirring frequency of 20 Hz for 30 min. The purpose of mixing was to prepare a precursor with uniform pore size distribution. After uniform mixing, the precursor was placed in a rotary kiln with an oxygen content of less than 100 ppm and a pressure of 10-100 Pa. The temperature was raised to 1100 ° C at a rate of 10 ° C / min and kept constant for 5 h. The obtained material was soaked in 2 mol / L hydrochloric acid for 1 h, filtered, washed with pure water until neutral, and dried in a 100 ° C oven for 4 h. After that, it was crushed and passed through a 325 mesh sieve.

[0105] (2) 200 g of the material obtained in step (1) was placed in a CVD reactor, and the temperature was raised to 550°C at a rate of 5°C / min and kept constant for 60 min to ensure the stability of the temperature of the CVD reactor. 0.6 L / min SiH4 and 0.6 L / min nitrogen were introduced, the reaction system pressure was 0-30 KPa, and the reaction was carried out for 300 min to obtain the first precursor.

[0106] (3) The first precursor was placed in a CVD reactor, heated to 700°C at a rate of 10°C / min, and 1 L / min of C3H6 and 2 L / min of nitrogen were introduced, and the reaction was continued for 150 min.

[0107] (4) The material obtained in step (3) was placed in a VC mixer, crushed, and passed through a 325-mesh sieve to obtain a negative electrode material.

[0108] The negative electrode material obtained in this embodiment includes a core and a coating layer covering the surface of the core. The core includes porous carbon and a silicon matrix located inside and / or on the surface of the porous carbon. The silicon matrix exists mostly in the form of SiH bonds, and the coating layer is a carbon layer.

[0109] Example 4

[0110] The difference from Example 2 is step (2): heating to 420°C at 5°C / min, introducing 0.6L / min SiH4 and 0.6L / min nitrogen, and reacting for 300min.

[0111] The negative electrode material obtained in this embodiment includes a core and a coating layer covering the surface of the core. The core includes porous carbon and a silicon matrix located inside and / or on the surface of the porous carbon. The silicon matrix exists mostly in the form of SiH bonds, and the coating layer is a carbon layer.

[0112] Example 5

[0113] The difference from Example 2 is step (2): heating to 450°C at 5°C / min, introducing 0.6L / min SiH4 and 0.6L / min nitrogen, and reacting for 300min.

[0114] The negative electrode material obtained in this embodiment includes a core and a coating layer covering the surface of the core. The core includes porous carbon and a silicon matrix located inside and / or on the surface of the porous carbon. The silicon matrix exists mostly in the form of SiH bonds, and the coating layer is a carbon layer.

[0115] Example 6

[0116] The difference from Example 2 is step (2): heating to 480°C at 5°C / min, introducing 0.6L / min SiH4 and 0.6L / min nitrogen, and reacting for 300min.

[0117] The negative electrode material obtained in this embodiment includes a core and a coating layer covering the surface of the core. The core includes porous carbon and a silicon matrix located inside and / or on the surface of the porous carbon. The silicon matrix exists mostly in the form of SiH bonds, and the coating layer is a carbon layer.

[0118] Example 7

[0119] The difference from Example 2 is step (2): heating to 510°C at 5°C / min, introducing 0.6L / min SiH4 and 0.6L / min nitrogen, and reacting for 300min.

[0120] The negative electrode material obtained in this embodiment includes a core and a coating layer covering the surface of the core. The core includes porous carbon and a silicon matrix located inside and / or on the surface of the porous carbon. The silicon matrix exists mostly in the form of SiH bonds, and the coating layer is a carbon layer.

[0121] Example 8

[0122] The difference from Example 2 is step (2): heating to 600°C at 5°C / min, introducing 0.6L / min SiH4 and 0.6L / min nitrogen, and reacting for 300min.

[0123] The negative electrode material obtained in this embodiment includes a core and a coating layer covering the surface of the core. The core includes porous carbon and a silicon matrix located inside and / or on the surface of the porous carbon. The silicon matrix exists mostly in the form of SiH bonds, and the coating layer is a carbon layer.

[0124] Example 9

[0125] The difference from Example 2 is step (2): heating to 650°C at 5°C / min, introducing 0.6L / min SiH4 and 0.6L / min nitrogen, and reacting for 300min.

[0126] The negative electrode material obtained in this embodiment includes a core and a coating layer covering the surface of the core. The core includes porous carbon and a silicon matrix located inside and / or on the surface of the porous carbon. The silicon matrix exists mostly in the form of SiH bonds, and the coating layer is a carbon layer.

[0127] Example 10

[0128] The difference from Example 2 is step (2): heating to 800°C at 5°C / min, introducing 0.6L / min SiH4 and 0.6L / min nitrogen, and reacting for 300min.

[0129] The negative electrode material obtained in this embodiment includes a core and a coating layer covering the surface of the core. The core includes porous carbon and a silicon matrix located inside and / or on the surface of the porous carbon. The silicon matrix exists mostly in the form of SiH bonds, and the coating layer is a carbon layer.

[0130] Example 11

[0131] The difference from Example 4 is step (2): heating to 420°C at 5°C / min, introducing 0.6 L / min SiH4 and 0.6 L / min nitrogen, and reacting for 350 min.

[0132] The negative electrode material obtained in this embodiment includes a core and a coating layer covering the surface of the core. The core includes porous carbon and a silicon matrix located inside and / or on the surface of the porous carbon. The silicon matrix exists mostly in the form of SiH bonds, and the coating layer is a carbon layer.

[0133] Example 12

[0134] The difference from Example 8 is step (2): heating to 650°C at 5°C / min, introducing 0.6L / min SiH4 and 0.6L / min nitrogen, and reacting for 270min.

[0135] The negative electrode material obtained in this embodiment includes a core and a coating layer covering the surface of the core. The core includes porous carbon and a silicon matrix located inside and / or on the surface of the porous carbon. The silicon matrix exists mostly in the form of SiH bonds, and the coating layer is a carbon layer.

[0136] Example 13

[0137] (1) 500 g of coconut shell charcoal was placed in a reactor, heated to 900 °C at 10 °C / min, and steam was introduced at 30 g / min for 120 min. The resulting material was then soaked in 2 mol / L hydrochloric acid for 1 h, filtered, and washed with pure water until neutral. After being dried in a 100 °C oven for 4 h, it was crushed and passed through a 325 mesh sieve.

[0138] (2) 200 g of the material obtained in step (1) was placed in a CVD reactor, and the temperature was raised to 550°C at a rate of 5°C / min and kept constant for 60 min to ensure the stability of the temperature of the CVD reactor. 0.6 L / min SiH4 and 0.6 L / min nitrogen were introduced, the reaction system pressure was 0-30 KPa, and the reaction was carried out for 300 min to obtain the first precursor.

[0139] (3) Place the first precursor in a CVD reactor, raise the temperature to 700°C at 10°C / min, introduce 1L / min C3H6 and 2L / min nitrogen, and react for 150 minutes.

[0140] (4) The material obtained in step (3) was placed in a VC mixer, crushed, and passed through a 325-mesh sieve to obtain a negative electrode material.

[0141] The negative electrode material obtained in this embodiment includes a core and a coating layer covering the surface of the core. The core includes porous carbon and a silicon matrix located inside and / or on the surface of the porous carbon. The silicon matrix exists mostly in the form of SiH bonds, and the coating layer is a carbon layer.

[0142] Comparative Example 1

[0143] Step (1): 400g coal tar, 120g calcium hydroxide, and 50g potassium hydroxide are mixed in a VC mixer at a stirring frequency of 20HZ for 30min. The purpose of mixing is to prepare a precursor with uniform pore size distribution. After mixing evenly, the mixture is placed in a rotary kiln with an oxygen content of less than 100ppm and a pressure of 10-100pa. The temperature is raised to 700℃ at a rate of 10℃ / min and kept constant for 5h. The obtained material is soaked in 2mol / L hydrochloric acid for 1h, filtered, washed with pure water until neutral, and then dried in a 100℃ oven for 4h. It is then crushed and passed through a 325-mesh sieve.

[0144] Step (2): Place 200 g of the material obtained in step (1) in a CVD reactor, raise the temperature to 400 ° C at 5 ° C / min, and keep the temperature constant for 60 minutes to ensure the stability of the temperature of the CVD reactor. 0.6 L / min SiH4 and 0.6 L / min nitrogen are introduced, the reaction system pressure is 0-30 KPa, and the reaction is carried out for 300 minutes to obtain the first precursor.

[0145] Step (3): Place the first precursor in a CVD reactor, raise the temperature to 700°C at 10°C / min, introduce 1L / min C3H6 and 2L / min nitrogen, and react for 150 minutes.

[0146] Step (4): The material obtained in step (3) was placed in a VC mixer, crushed, and passed through a 325-mesh sieve to obtain a negative electrode material.

[0147] The negative electrode material obtained in this comparative example includes a core and a coating layer covering the surface of the core, the core includes porous carbon and a silicon matrix located inside and / or on the surface of the porous carbon, the silicon matrix exists in the form of SiH bonds, SiH2 bonds and SiH3 bonds, and the coating layer is a carbon layer.

[0148] Comparative Example 2

[0149] Step (1): 400g coal tar, 120g calcium hydroxide, and 50g potassium hydroxide are mixed in a VC mixer at a stirring frequency of 20HZ for 30min. The purpose of mixing is to prepare a precursor with uniform pore size distribution. After mixing evenly, the mixture is placed in a rotary kiln with an oxygen content of less than 100ppm and a pressure of 10-100pa. The temperature is raised to 700℃ at a rate of 10℃ / min and kept constant for 5h. The obtained material is soaked in 2mol / L hydrochloric acid for 1h, filtered, washed with pure water until neutral, and then dried in a 100℃ oven for 4h. It is then crushed and passed through a 325-mesh sieve.

[0150] Step (2): Place 200 g of the material obtained in step (1) in a CVD reactor, raise the temperature to 900 ° C at 5 ° C / min, and keep the temperature constant for 60 minutes to ensure the stability of the temperature of the CVD reactor. 0.6 L / min SiH4 and 0.6 L / min nitrogen are introduced, the reaction system pressure is 0-30 KPa, and the reaction is carried out for 300 minutes to obtain the first precursor.

[0151] Step (3): Place the first precursor in a CVD reactor, raise the temperature to 700°C at 10°C / min, introduce 1L / min C3H6 and 2L / min nitrogen, and react for 150 minutes.

[0152] Step (4): The material obtained in step (3) was placed in a VC mixer, crushed, and passed through a 325-mesh sieve to obtain a negative electrode material.

[0153] The negative electrode material obtained in this comparative example includes a core and a coating layer covering the surface of the core, the core includes porous carbon and polysilicon located inside and / or on the surface of the porous carbon, and the coating layer is a carbon layer.

[0154] Performance testing:

[0155] 1. Porosity, Pore Size, and Pore Fraction Test Method: Porosity can be calculated by multiplying the amount of pores per unit weight of a material (cm3 / g) by the bulk density (g / cm3). Therefore, porosity can be expressed based on volume as (volume / volume). 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 nitrogen adsorption (micropores and mesopores) or a mercury porosimeter (macroporous).

[0156] 2. The D50, D00, and D90 of the negative electrode material were measured using a laser particle size analyzer. They exhibit a symmetrical, normal-like distribution. D90 is the particle size at which the cumulative distribution of the material particles reaches 90%, and D00 is the minimum particle size, referring to the smallest diameter that can be measured in the distribution. D50 is the particle size at which the cumulative distribution of the material particles reaches 50%, also known as the median particle size.

[0157] 3. The mass proportion of the silicon matrix in the negative electrode material can be determined by the specific weight method. Specifically, the silicon matrix can be burned at high temperature in air to generate silicon dioxide. The mass of the silicon matrix can be deduced by calculating the mass of silicon dioxide, and then the mass proportion of the silicon matrix in the negative electrode material can be calculated.

[0158] 4. The test instrument is a Renishaw confocal Raman spectrometer from the United Kingdom, model inVia. Test conditions: 633 nm laser, test range 800 cm -1 ~2000cm -1 .

[0159] 5. Fourier transform infrared spectroscopy was performed using the American Thermo Scientific iN10 instrument, with a spectral range of 4000 cm -1 -400cm -1 The infrared test data were imported into the Origin software, and the SiH bond stretching vibration peak at the wave number 1985cm-1 and the SiH2 bond stretching vibration peak at the wave number 2080cm-1 were used as the double peak fitting positions. The Gauss fitting optimization method was used for the infrared spectrum of the wave number 1750-2220cm-1. The ratio Z value of the peak area of ​​the two fitted peaks represents the ratio of the SiH bond to the SiH2 bond.

[0160] 6. A lithium-ion battery was prepared using the negative electrode materials obtained in Comparative Examples 1 to 2 and Examples 1 to 13 as active materials. The preparation process was as follows:

[0161] Binder Preparation: Mix polyacrylic acid and sodium carboxymethyl cellulose in a 1:1 mass ratio, add a certain amount of pure water, and magnetically stir for 6-12 hours. Add the silicon composite material and conductive agent to the binder in a mass ratio of 70:15:15, and magnetically stir for 6-12 hours to obtain a slurry. Electrode Preparation: Apply the slurry evenly onto copper foil, let it dry, slice it, and dry it to obtain the silicon composite electrode sheet.

[0162] Button cells were assembled to test their electrochemical performance. The battery case used was CR2032, the counter electrode was a metal lithium sheet, and the electrolyte was 1M LiPF6. Examples 1 to 13 were designated S1 to 13, and Comparative Examples 1 to 2 were designated D1 to 2.

[0163] Table 1. Parameters of negative electrode materials of Examples and Comparative Examples

[0164] Table 2. Electrochemical properties of negative electrode materials prepared in experimental examples and comparative examples

[0165] From the data in Tables 1 and 2 of the results of the comparative examples and embodiment tests, it can be found that the negative electrode material of the present application includes a silicon matrix and porous carbon, at least part of the silicon matrix is ​​distributed in the pores of the porous carbon, and the ratio Z of the vibration peak area of ​​the SiH2 bond to the vibration peak area of ​​the SiH bond in the negative electrode material is 0.01 to 5.0, indicating that the silane is fully cracked during the preparation process of the negative electrode material of the present application, so that the silicon matrix in the negative electrode material exists more in the form of amorphous silicon with SiH bonds, which can alleviate the volume expansion of the negative electrode material, reduce the swelling of the electrode sheet prepared from the negative electrode material, and improve the cycle performance and rate performance of the negative electrode material.

[0166] Under the same conditions, I D / I G The larger the value of , the easier it is for silane to deposit on the carbon material. However, excessive silicon deposition will reduce the cycle performance and rate performance of the negative electrode material. In Examples 1 to 3, as the heat treatment temperature in step (1) increases, I D / I G The ratio shows a trend of gradually decreasing. The deposition amount of the silicon matrix of the negative electrode material of Example 2 in the present application is appropriate, so that the initial efficiency and expansion performance of the negative electrode material are optimized.

[0167] The temperature of silane cracking in the present application has a great influence on the performance of the negative electrode material. In Examples 2, 4, 5, 6, 7, 8, 9 and 10, as the silane cracking temperature increases, the Z value decreases, indicating that the cracking of silane is more and more complete, thereby improving the conversion rate of silane cracking. However, if the temperature of silane cracking is too high, it will lead to the conversion of amorphous silicon to crystalline silicon. Therefore, when the temperature of silane cracking into silicon matrix is ​​550°C, the negative electrode material can simultaneously obtain better cycle performance and expansion performance.

[0168] In Examples 4 and 11, at a certain temperature and with the same amount of silane deposition, the degree of silane cracking did not change much with the extension of reaction time, indicating that the influence of whether silane cracking is complete depends mainly on the temperature of silane cracking.

[0169] In the negative electrode material prepared in Comparative Example 1, the decomposition temperature of silane is low, resulting in a low silane decomposition conversion rate, a small amount of silicon loaded on the porous matrix, and the silicon matrix where silane is not fully decomposed exists in the form of SiH2 bonds, SiH3 bonds and SiH bonds, and the amount of SiH bonds is small, resulting in Z not meeting the range of 0.01 to 5.0, which greatly reduces the structural stability of the negative electrode material, and further leads to poor cycle performance, capacity and rate performance of the negative electrode material.

[0170] In the negative electrode material prepared in Comparative Example 2, the cracking temperature of silane is too high, resulting in the cracking of silane to form polysilicon. The volume expansion of polysilicon is large, resulting in poor cycle performance and expansion performance of the negative electrode material.

[0171] The above description is merely a preferred embodiment of the present application and is not intended to limit the present application. Those skilled in the art will readily appreciate that various modifications and variations are possible. Any modifications, equivalent substitutions, or improvements made within the scope of protection of the present application shall be included within the scope of protection of the present application.

Claims

1. A negative electrode material, characterized in that: The negative electrode material includes an active substance, the active substance includes a porous matrix and a silicon matrix, at least part of the silicon matrix is ​​distributed in the pores of the porous matrix, and an infrared spectrum obtained by measuring the negative electrode material using an infrared spectrometer has a wave number of 2090cm -1 The SiH2 bond stretching vibration peak and wave number 2000cm -1 The SiH bond stretching vibration peak, the ratio Z of the vibration peak area of ​​the SiH2 bond to the vibration peak area of ​​the SiH bond is 0.01 to 5.

0.

2. The negative electrode material according to claim 1, characterized in that The value of Z is 0.05 to 3.

0.

3. The negative electrode material according to claim 1, characterized in that The porosity of the negative electrode material after removing the silicon matrix is ​​30% to 70%.

4. The negative electrode material according to claim 1, characterized in that The average pore size of the negative electrode material after removing the silicon matrix is ​​0.2nm-10nm.

5. The negative electrode material according to claim 1, characterized in that The average particle size of the silicon matrix is ​​1 nm to 10 nm.

6. The negative electrode material according to claim 1, characterized in that The silicon matrix accounts for 5% to 90% by mass of the negative electrode material.

7. The negative electrode material according to claim 1, characterized in that At least a portion of the silicon matrix is ​​distributed on the surface of the porous matrix.

8. The negative electrode material according to claim 1, characterized in that The negative electrode material further includes a coating layer disposed on at least a portion of the surface of the active material, and the negative electrode material includes at least one of the following features (1) to (2): (1) The coating layer contains at least one of a carbon material, a metal oxide and a metal sulfide; (2) The thickness of the coating layer is 5 nm to 500 nm.

9. The negative electrode material according to claim 8, characterized in that The negative electrode material includes at least one of the following features (1) to (3): (1) The coating layer comprises a carbon material, wherein the carbon material comprises at least one of graphene, soft carbon, hard carbon and a conductive polymer; (2) The coating layer comprises a metal oxide, wherein the metal oxide comprises at least one of titanium oxide, aluminum oxide, lithium oxide, cobalt oxide and vanadium oxide; (3) The coating layer includes metal sulfide, and the metal sulfide includes at least one of tin sulfide, molybdenum sulfide, titanium sulfide, iron sulfide and copper sulfide.

10. The negative electrode material according to claim 1, characterized in that The negative electrode material includes at least one of the following features (1) to (3): (1) The median particle size D50 of the negative electrode material is 5 μm to 10 μm; (2) The minimum particle size D00 of the negative electrode material is 1 μm to 3 μm; (3) The D90 of the negative electrode material is 14 μm to 25 μm.

11. The negative electrode material according to claim 1, characterized in that The negative electrode material is shown in a Raman spectrum obtained by Raman spectroscopy using a measurement light source with a wavelength of 633 nm. The negative electrode material has a wavelength of 1310 cm -1 ~1350cm -1 Characteristic peak I D and at 1580cm -1 ~1620cm -1 Characteristic peak I G , I D / I G It is 1.6 to 2.

5.

12. The negative electrode material according to claim 1, characterized in that The specific surface area of ​​the negative electrode material is 1.0 m 2 / g~10.0m 2 / g.

13. The negative electrode material according to claim 1, characterized in that The powder conductivity of the negative electrode material is 0.1 S / cm to 10.0 S / cm.

14. The negative electrode material according to claim 1, characterized in that The porosity of the negative electrode material is 0.01% to 10%.

15. A lithium ion battery, characterized in that: The lithium-ion battery comprises the negative electrode material according to any one of claims 1 to 14.