Graphite silicon carbon composite negative electrode material, negative electrode plate and lithium ion battery

Abstract

The invention relates to a graphite silicon carbon composite negative electrode material, a negative electrode plate and a lithium ion battery, and belongs to the technical field of battery negative electrode materials. The graphite silicon carbon composite negative electrode material comprises a graphite inner core and a composite shell layer, the composite shell layer coats the surface of the inner core, the composite shell layer comprises a continuous carbon layer, the carbon layer is of a porous structure, and the porous structure is filled with nano silicon particles. According to the core-shell structure, through a three-stage synergistic mechanism of graphite inner core conductive supporting, porous carbon layer expansion buffering and nanometer silicon capacity contribution, the cycling stability of the negative electrode material is remarkably improved while the high specific capacity is maintained.

Description

Technical Field

[0001] The present application relates to the technical field of battery negative electrode materials, and in particular to a graphite silicon-carbon composite negative electrode material, a negative electrode sheet and a lithium-ion battery. Background Art

[0002] With the rapid development of electric vehicles and portable electronic devices, lithium-ion batteries, as core energy storage devices, have an increasing demand for energy density. Silicon-based negative electrode materials are considered to be an ideal choice to break through the energy bottleneck of traditional graphite negative electrodes (372mAh / g) due to their theoretical specific capacity of up to 4200mAh / g. However, the volume expansion of silicon of up to 300% during the charge and discharge process leads to problems such as particle rupture, peeling of active materials and current collectors, and continuous reconstruction of SEI films, which seriously limit its cycle stability and practical application. To this end, researchers have proposed a strategy to composite silicon with carbon materials, using the conductivity and mechanical stability of the carbon matrix to buffer the volume change of silicon, thereby deriving an important research direction of silicon-carbon composite materials. The current mainstream technology focuses on the design of porous structures, by reserving expansion space around silicon particles to maintain electrode integrity, but existing preparation methods generally face the dual challenges of process complexity and environmental sustainability.

[0003] Patent CN112038600A uses metal catalytic etching to prepare porous silicon, which is then compounded with graphite and carbon nanotubes. Although it can construct buffer pores, the chemical corrosion process that relies on oxidants and etchants not only increases the corrosion resistance requirements of the equipment, but also brings about the environmental problem of toxic waste liquid treatment.

[0004] Patent CN112366294A prepares porous silicon-carbon composite materials by combining acid treatment of graphite surface with magnesium thermal reduction of silica. Although direct etching of silicon is avoided, the strong acid pretreatment and high-temperature reduction process lead to increased equipment loss, and the fluctuation of silica reduction efficiency can easily lead to uneven pore distribution, affecting the consistency of material batches.

[0005] Patent CN114122371A uses sodium chloride as a template and achieves the mixing of silicon, graphite and carbon source through three rounds of ball milling. Although it avoids the use of acid and alkali, repeated mechanical ball milling is not only energy-intensive and time-consuming, but may also introduce metal impurities into the material, reducing the electrochemical performance. Summary of the Invention

[0006] In view of the deficiencies in the prior art, the purpose of the embodiments of the present application includes providing a graphite silicon-carbon composite negative electrode material, a negative electrode plate and a lithium-ion battery to improve the cycle performance of the graphite silicon-carbon negative electrode material.

[0007] In a first aspect, an embodiment of the present application provides a graphite silicon-carbon composite negative electrode material, comprising: a graphite core and a composite shell layer, wherein the composite shell layer is coated on the surface of the core, and the composite shell layer comprises a continuous carbon layer, the carbon layer is a porous structure, and the porous structure is filled with nano-silicon particles.

[0008] The negative electrode material of the present application is a double-layer core-shell structure, including a graphite core and a composite shell, wherein the graphite core acts as a conductive skeleton, providing a stable electron transmission path by virtue of its highly ordered layered structure, while suppressing the overall deformation of the electrode through mechanical rigidity, reducing the volume change generated during the charge and discharge process, and providing a mechanical support basis for the dynamic expansion of the outer composite shell. The continuous porous carbon layer in the composite shell achieves dual functions through its three-dimensional interconnected network: first, the porous structure provides a directional buffer space for the volume expansion of nano-silicon particles, which can effectively reduce particle breakage and electrode structure collapse; second, the continuous carbon matrix forms a fully wrapped conductive network, which improves the stability of the electron transmission path during the expansion-contraction cycle. The design of nano-silicon particles filling the interior of the porous structure fully utilizes the high specific capacity characteristics of silicon (4200mAh / g), while suppressing the agglomeration of silicon particles through the physical confinement of the pores. The local Si-C chemical bonds formed on its surface and the carbon layer further strengthen the interface bonding and reduce the stripping of active substances. The core-shell structure uses a three-level synergistic mechanism of "graphite core conductive support-porous carbon layer expansion buffer-nanosilicon capacity contribution", which enables the negative electrode material to maintain high specific capacity while significantly improving the cycle stability.

[0009] In a second aspect, an embodiment of the present application provides a method for preparing a graphite silicon-carbon composite negative electrode material, comprising: mixing nano-silicon particles, graphite, an aqueous solution of sodium carboxymethyl cellulose and a water-soluble salt template to obtain a mixed solution; heating the mixed solution while stirring to obtain a viscous material; drying the viscous material, carbonizing it under an inert protective atmosphere, crushing it, and removing the water-soluble salt template to obtain a graphite silicon-carbon composite negative electrode material.

[0010] In this preparation method, a one-step solution mixing method is first used to uniformly disperse nano-silicon particles, graphite, sodium carboxymethyl cellulose (CMC) aqueous solution and water-soluble salt template, so that the nano-silicon particles are effectively wrapped by the CMC molecular chain, reducing agglomeration while ensuring uniform compounding with graphite; the subsequent heating process (60-100 ° C) induces directional crystallization of the water-soluble salt to form a porous structure with controllable pore size. Compared with the composite material prepared by the traditional ball milling method, the pore distribution obtained by this method is more uniform and avoids the metal impurities introduced by mechanical ball milling. Further, the CMC is decomposed by carbonization to generate a continuous pyrolytic carbon network. Its unique shrinkage characteristics not only strengthen the Si-OC bonding with the silicon particles, but also improve the permeability of the pores. The preparation method provided in this application integrates multiple processes such as dispersion, pore formation, and coating in the traditional process into a single continuous process. Through the controllable crystallization of the water-soluble salt template and the in-situ carbonization of CMC, the three major technical problems of uniform dispersion, pore construction and interface optimization in the preparation of silicon-carbon composite materials are simultaneously solved.

[0011] In some embodiments of the present application, the water-soluble salt template includes one or more of sodium chloride, potassium chloride, calcium chloride, sodium carbonate, potassium carbonate and ammonium chloride.

[0012] The above salts can form regular crystals and construct pores of uniform size, which can form a good size match with the nano-silicon particles.

[0013] In some embodiments of the present application, the water-soluble salt template is removed by multiple water washings.

[0014] The present application completes the removal of the water-soluble salt template by multiple water washings until the conductivity of the filtrate is close to that of deionized water.

[0015] In some embodiments of the present application, the preparation method includes: mixing nano-silicon particles and sodium carboxymethyl cellulose aqueous solution, adding graphite multiple times for mixing, and then adding a water-soluble salt template multiple times for mixing to obtain a mixed solution.

[0016] The stepwise addition of graphite ensures that the nanosilicon particles preferentially interact with the sodium carboxymethyl cellulose (CMC) aqueous solution. During the initial mixing phase, the long CMC molecular chains preferentially adsorb onto the nanosilicon surface through electrostatic interactions and hydrogen bonding, forming a stable steric barrier. This step effectively mitigates the agglomeration problem caused by the high surface energy of the nanosilicon particles. Graphite is then added in multiple, gradient steps, gradually encapsulating the graphite particles using the remaining active sites of the CMC. This gradual mixing allows the graphite and pre-dispersed silicon-CMC complex to form a uniform "core-satellite" structure, minimizing the density stratification caused by traditional all-at-once additions. Subsequently, the stepwise addition of a water-soluble salt template further optimizes the spatial distribution of the pore structure. Once the graphite-silicon-CMC system is formed, the stepwise addition of the salt solution allows the template crystals to grow in a directional manner within the established network framework: the initial addition of the salt solution preferentially nucleates in the silicon / graphite interstices, forming the foundational pores. Subsequent additions encourage the salt crystals to continue growing in the remaining spaces, ultimately forming through-hole channels. Compared with adding salt all at once, this graded pore-forming mechanism makes the pore size more uniform and is more conducive to uniformly buffering the volume expansion of silicon.

[0017] In some embodiments of the present application, the carbonization temperature is 500-1000° C., and the carbonization time is 3-8 hours.

[0018] Carbonization at 500-1000℃ can promote the carbonization of CMC to form a highly conductive network and stabilize the Si-OC interface, thereby improving the degree of graphitization; carbonization for 3-5h can form through pores with a dense pore structure.

[0019] In some embodiments of the present application, the carbonization temperature is 600-800° C., and the carbonization time is 4-6 hours.

[0020] Carrying out carbonization within the above-mentioned temperature and time range is more conducive to improving the cycle performance of the negative electrode material.

[0021] In some embodiments of the present application, the mass ratio of nano-silicon particles to graphite is 1:(1-10).

[0022] By controlling the mass ratio of nano-silicon particles to graphite to 1:(1-10), the capacity of the negative electrode material can be improved.

[0023] In some embodiments of the present application, the mass ratio of nano-silicon particles to graphite is 1:(4-9).

[0024] Within the above ratio range, it is more conducive to improving the capacity and cycle performance of the negative electrode material.

[0025] In some embodiments of the present application, the mass ratio of the sum of the mass of the nano-silicon particles and the graphite to the mass of the water-soluble salt template is 10:(1-10).

[0026] Within the above-mentioned ratio range, different silicon loading requirements can be adapted, and the porosity can be controlled by adjusting the template dosage, thereby improving the cycling performance of the material.

[0027] In some embodiments of the present application, the mass ratio of the sum of the mass of the nano-silicon particles and the graphite to the mass of the water-soluble salt template is 10:(2-5).

[0028] Within the above ratio range, it is more conducive to improving the recycling performance of the material.

[0029] In some embodiments of the present application, the heating temperature is 60-100°C.

[0030] Within the above heating temperature range, the water-soluble salt template can be evaporated and crystallized, and then dissolved to produce regular pores, so that the nano-silicon can expand and contract in the pores, avoiding the rupture of the carbon coating due to the expansion of silicon.

[0031] In some embodiments of the present application, the drying temperature is 70-120°C.

[0032] In a third aspect, an embodiment of the present application provides a negative electrode plate comprising the above-mentioned graphite silicon-carbon composite negative electrode material.

[0033] This negative electrode inherits the inherent advantages of core-shell structural materials: the continuous conductive network constructed by the graphite core reduces the resistivity of the electrode, and the porous structure formed after the template agent is dissolved in the composite shell can effectively buffer the silicon expansion stress and reduce the thickness expansion rate of the electrode after multiple cycles. The chemical bonding between nano-silicon particles and pyrolytic carbon (Si-OC) inhibits the stripping of active materials, giving the electrode a higher capacity. At the same time, the pyrolytic carbon coating blocks direct contact between silicon and the electrolyte, reducing the capacity decay of the electrode at high temperatures.

[0034] In a fourth aspect, an embodiment of the present application provides a lithium-ion battery comprising the above-mentioned negative electrode plate.

[0035] Thanks to the high capacity characteristics and excellent structural stability of the graphite silicon-carbon composite negative electrode material in the negative electrode sheet, the energy density of the assembled lithium-ion battery is significantly improved. This is also attributed to the effective buffering of silicon expansion by the porous structure and the stability of the Si-OC bonding interface, which improves the battery's cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0037] Figure 1 Schematic diagram of the structure of the graphite silicon-carbon composite negative electrode material provided in an embodiment of the present application.

[0038] Icon: 100 - core; 201 - nanosilicon; 202 - pores; 203 - carbon layer. DETAILED DESCRIPTION

[0039] To make the purpose, technical solutions and advantages of the examples of the present application clearer, the technical solutions in the examples of the present application will be described clearly and completely below. Where specific conditions are not specified in the examples, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0040] The following is a detailed description of a graphite silicon-carbon composite negative electrode material, a negative electrode plate, and a lithium-ion battery in an embodiment of the present application.

[0041] An embodiment of the present application provides a graphite silicon-carbon composite negative electrode material, comprising: a graphite core 100 and a composite shell layer, wherein the composite shell layer is coated on the surface of the core 100, and the composite shell layer comprises a continuous carbon layer 203, wherein the carbon layer 203 is a porous structure filled with nano-silicon particles.

[0042] The preparation method of the graphite silicon-carbon composite negative electrode material of the present application is described below.

[0043] A method for preparing a graphite silicon-carbon composite negative electrode material comprises the following steps:

[0044] S1. Mixing nano-silicon 201 particles, graphite, sodium carboxymethyl cellulose aqueous solution and a water-soluble salt template to obtain a mixed solution.

[0045] As another embodiment, after the nano-silicon 201 particles and the sodium carboxymethyl cellulose aqueous solution are mixed, graphite is added in multiple times and mixed, and then a water-soluble salt template is added in multiple times and mixed to obtain a mixed solution.

[0046] The water-soluble salt template includes one or more of sodium chloride, potassium chloride, calcium chloride, sodium carbonate, potassium carbonate and ammonium chloride.

[0047] The mass ratio of nano-silicon 201 particles to graphite is 1:(1-10). As an example, the mass ratio of nano-silicon 201 particles to graphite includes but is not limited to 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, and 1:10.

[0048] The mass ratio of the sum of the mass of the nano-silicon 201 particles and the graphite to the mass of the water-soluble salt template is 10:(1-10). As an example, the mass ratio of the sum of the mass of the nano-silicon 201 particles and the graphite to the mass of the water-soluble salt template includes but is not limited to 10:1, 10:2, 10:3, 10:4, 10:5, 10:6, 10:7, 10:8, 10:9, and 1:1.

[0049] The mass of the sodium carboxymethyl cellulose aqueous solution is 5-20 times the mass of the nano-silicon 201 particles.

[0050] S2. The mixed solution in step S1 is heated while being stirred to obtain a viscous material.

[0051] The heating temperature is 60-100° C. For example, the heating temperature includes but is not limited to 60° C., 70° C., 80° C., 90° C., and 100° C.

[0052] S3. After drying the viscous material in step S2, carbonizing it under an inert protective atmosphere to remove the water-soluble salt template agent to obtain a graphite silicon-carbon composite negative electrode material.

[0053] The template is removed by washing with water, i.e., washing with deionized water and filtering, and this process is repeated at least three times until the conductivity of the filtrate is close to that of deionized water. The material is then taken out and placed in a vacuum oven to dry at 60-120°C.

[0054] The inert protective atmosphere includes at least one of nitrogen and argon.

[0055] The carbonization temperature is 500-1000° C., and the carbonization time is 3-8 hours. For example, the carbonization temperature includes, but is not limited to, 500° C., 600° C., 700° C., 800° C., 900° C., and 1000° C. The carbonization time includes, but is not limited to, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, and 8 hours.

[0056] This application uses food-grade sodium carboxymethyl cellulose (CMC) as a dispersant and carbon source, and water-soluble salts such as sodium chloride as templates to form a porous structure through a physical dissolution method. The entire process is free of acid and alkali. The mild process of physical mixing (step S1) → water washing and dissolution (step S3) replaces chemical etching. The wastewater contains only inorganic salts and can be directly treated. Moreover, multiple washings with deionized water can achieve a clean standard of filtrate conductivity <5μS / cm. At the same time, this application has developed a "one-step stirring method" (step S1): a) Nano-silicon 201 and CMC aqueous solution first form a stable colloid; b) Graphite is added in batches to avoid agglomeration; c) Sodium chloride solution is evaporated at 60-100°C to induce crystallization, and simultaneously achieves: uniform dispersion of silicon / graphite (replacing ball milling), spatial positioning of the template (replacing mechanical mixing) and pre-forming of the CMC coating layer. Moreover, by controlling the heating temperature of step S2 (60-100°C), the water-soluble salt template is directionally grown into grains of a certain size to form a regular pore framework; the pores 202 are dual pores, namely: a) the template dissolves to produce macropores (to accommodate silicon expansion); b) CMC carbonizes and shrinks to form mesopores (to promote electrolyte infiltration). Traditional asphalt carbon sources have poor high-temperature fluidity and cracks in the coating layer. When the CMC of the present application is carbonized at 500-1000°C, on the one hand, it will decompose to produce oxygen-containing free radicals, forming Si-OC covalent bonds with the -OH on the silicon surface; on the other hand, the shrinkage stress generated causes the carbon layer 203 to tightly wrap the silicon particles; and the carbonized pyrolytic carbon not only coats the silicon particles, but also penetrates the pore walls to form a conductive skeleton.

[0057] In summary, the preparation method provided in this application not only overcomes the environmental risk issues of acid-base etching, the process complexity of multi-step ball milling, the uncontrollable defects of pore structure and the discontinuous interface problem of carbon coating, but also combines the three steps of "ball milling mixing + template introduction + carbon coating" in the traditional process into a one-step solution treatment, significantly reducing industrial costs.

[0058] The schematic diagram of the structure of the negative electrode material prepared by the preparation method of the present application is as follows Figure 1As shown, this material utilizes a unique core-shell structure design, with a graphite core 100 at its core and a functionalized composite shell coating the surface of the core 100, forming a highly optimized microstructure. The graphite core 100 is a regular spherical particle that effectively alleviates the anisotropic stress generated by the expansion of the outer silicon-carbon composite shell during charge and discharge. The composite shell tightly coats the surface of the graphite core 100 and consists of three key components: a continuous pyrolytic carbon matrix forming a three-dimensional network skeleton, within which is uniformly distributed a multi-level pore structure formed by the dissolution of a water-soluble salt template. Nanosilicon particles 201 are precisely embedded within these pores 202. Furthermore, the pyrolytic carbon matrix not only completely coats each nanosilicon particle 201 but also tightly bonds to the silicon surface through chemical bonding, forming a continuous conductive pathway within the pores 202, enabling efficient transmission of both electrons and lithium ions while providing an ideal buffer for the volume expansion of the silicon particles. The uniqueness of the entire core-shell structure lies in the perfect mechanical adaptation and electrochemical coupling between the spherical graphite core 100 and the composite shell, which not only maintains the excellent conductivity and structural stability of graphite, but also fully utilizes the high capacity characteristics of silicon materials. At the same time, the carefully designed porous structure solves the problem of structural damage caused by silicon expansion.

[0059] The features and performance of the present application are further described in detail below with reference to the embodiments.

[0060] Example 1

[0061] This embodiment provides a graphite silicon-carbon composite negative electrode material, the preparation method of which includes the following steps:

[0062] (1) Weigh 15 g of nano-silicon powder, 85 g of graphite powder and 100 g of 1.5% CMC aqueous solution for later use. Put the nano-silicon powder and CMC aqueous solution into a beaker together. Then put the beaker into a water bath, set the temperature at 25 ° C, turn on the magnetic stirrer, stir for 1 hour, then gradually add the graphite powder into the beaker in 5 times, stir for another 1 hour, then raise the water bath temperature to 90 ° C, and put it into a blast oven to dry at 90 ° C after the solution becomes viscous.

[0063] (2) After drying, the sample was placed in a crucible and placed in an atmosphere furnace. Under nitrogen protection, it was calcined at 750°C for 5 h. After cooling, the material was taken out and ground, and passed through a 300-mesh sieve.

[0064] (3) The sieved material and water in step (2) are then added to deionized water in a ratio of 1:10, stirred for 10 minutes, and the mixture is vacuum filtered. The filter residue is mixed with water again, stirred, and filtered. This is repeated three times. The conductivity of the filtrate is close to that of deionized water. The filter residue after the last filtration is placed in a blast drying oven, dried at 80°C, and then transferred to a vacuum oven and continued to dry at 100°C for 5 hours. After cooling, it is taken out, ground, and passed through a 300-mesh sieve to obtain a graphite silicon-carbon composite negative electrode material.

[0065] Example 2

[0066] This embodiment provides a graphite silicon-carbon composite negative electrode material, the preparation method of which includes the following steps:

[0067] (1) Weigh 15 g of nano-silicon powder, 85 g of graphite powder, 20 g of sodium chloride and 100 g of 1.5% CMC aqueous solution for later use. Put the nano-silicon powder and CMC aqueous solution into a beaker together. Then put the beaker into a water bath, set the temperature at 25 ° C, turn on the magnetic stirrer, stir for 1 hour, then gradually add the graphite powder into the beaker in 5 times, stir for another 1 hour, then raise the water bath temperature to 90 ° C, and put it into a blast oven to dry at 90 ° C after the solution becomes viscous.

[0068] (2) After drying, the sample was placed in a crucible and placed in an atmosphere furnace. Under nitrogen protection, it was calcined at 750°C for 5 hours. After cooling, the material was taken out and ground, and then passed through a 300-mesh sieve to obtain a graphite silicon-carbon composite material.

[0069] (3) The sieved material and water in step (2) are then added to deionized water in a ratio of 1:10, stirred for 10 minutes, and the mixture is vacuum filtered. The filter residue is mixed with water again, stirred, and filtered. This is repeated three times. The conductivity of the filtrate is close to that of deionized water. The filter residue after the last filtration is placed in a blast drying oven, dried at 80°C, and then transferred to a vacuum oven and continued to dry at 100°C for 5 hours. After cooling, it is taken out, ground, and passed through a 300-mesh sieve to obtain a graphite silicon-carbon composite negative electrode material.

[0070] Example 3

[0071] This embodiment provides a graphite silicon-carbon composite negative electrode material, the preparation method of which includes the following steps:

[0072] (1) Weigh 15 g of nano-silicon powder, 85 g of graphite powder, 40 g of sodium chloride and 100 g of 1.5% CMC aqueous solution for later use. Put the nano-silicon powder and CMC aqueous solution into a beaker together. Then put the beaker into a water bath, set the temperature at 25 ° C, turn on the magnetic stirrer, stir for 1 hour, then gradually add the graphite powder into the beaker in 5 times, stir for another 1 hour, then raise the water bath temperature to 90 ° C, and put it into a blast oven to dry at 90 ° C after the solution becomes viscous.

[0073] (2) After drying, the sample was placed in a crucible and placed in an atmosphere furnace. Under nitrogen protection, it was calcined at 750°C for 5 hours. After cooling, the material was taken out and ground, and then passed through a 300-mesh sieve to obtain a graphite silicon-carbon composite material.

[0074] (3) The sieved material and water in step (2) are then added to deionized water in a ratio of 1:10, stirred for 10 minutes, and the mixture is vacuum filtered. The filter residue is mixed with water again, stirred, and filtered. This is repeated three times. The conductivity of the filtrate is close to that of deionized water. The filter residue after the last filtration is placed in a blast drying oven, dried at 80°C, and then transferred to a vacuum oven and continued to dry at 100°C for 5 hours. After cooling, it is taken out, ground, and passed through a 300-mesh sieve to obtain a graphite silicon-carbon composite negative electrode material.

[0075] Example 4

[0076] This embodiment provides a graphite silicon-carbon composite negative electrode material, the preparation method of which includes the following steps:

[0077] (1) Weigh 15 g of nano-silicon powder, 85 g of graphite powder, 20 g of sodium chloride and 100 g of 1.5% CMC aqueous solution for later use. Put the nano-silicon powder and CMC aqueous solution into a beaker together. Then put the beaker into a water bath, set the temperature at 25 ° C, turn on the magnetic stirrer, stir for 1 hour, then gradually add the graphite powder into the beaker in 5 times, stir for another 1 hour, then raise the water bath temperature to 90 ° C, and put it into a blast oven to dry at 90 ° C after the solution becomes viscous.

[0078] (2) After drying, the sample was placed in a crucible and placed in an atmosphere furnace. Under nitrogen protection, it was calcined at 650°C for 5 hours. After cooling, the material was taken out and ground, and then passed through a 300-mesh sieve to obtain a graphite silicon-carbon composite material.

[0079] (3) The sieved material and water in step (2) are then added to deionized water in a ratio of 1:10, stirred for 10 minutes, and the mixture is vacuum filtered. The filter residue is mixed with water again, stirred, and filtered. This is repeated three times. The conductivity of the filtrate is close to that of deionized water. The filter residue after the last filtration is placed in a blast drying oven, dried at 80°C, and then transferred to a vacuum oven and continued to dry at 100°C for 5 hours. After cooling, it is taken out, ground, and passed through a 300-mesh sieve to obtain a graphite silicon-carbon composite negative electrode material.

[0080] Example 5

[0081] This embodiment provides a graphite silicon-carbon composite negative electrode material, the preparation method of which includes the following steps:

[0082] (1) Weigh 15 g of nano-silicon powder, 85 g of graphite powder, 40 g of sodium chloride and 100 g of 1.5% CMC aqueous solution for later use. Put the nano-silicon powder and CMC aqueous solution into a beaker together. Then put the beaker into a water bath, set the temperature at 25 ° C, turn on the magnetic stirrer, stir for 1 hour, then gradually add the graphite powder into the beaker in 5 times, stir for another 1 hour, then raise the water bath temperature to 90 ° C, and put it into a blast oven to dry at 90 ° C after the solution becomes viscous.

[0083] (2) After drying, the sample was placed in a crucible and placed in an atmosphere furnace. Under nitrogen protection, it was calcined at 650°C for 5 hours. After cooling, the material was taken out and ground, and then passed through a 300-mesh sieve to obtain a graphite silicon-carbon composite material.

[0084] (3) The sieved material and water in step (2) are then added to deionized water in a ratio of 1:10, stirred for 10 minutes, and the mixture is vacuum filtered. The filter residue is mixed with water again, stirred, and filtered. This is repeated three times. The conductivity of the filtrate is close to that of deionized water. The filter residue after the last filtration is placed in a blast drying oven, dried at 80°C, and then transferred to a vacuum oven and continued to dry at 100°C for 5 hours. After cooling, it is taken out, ground, and passed through a 300-mesh sieve to obtain a graphite silicon-carbon composite negative electrode material.

[0085] Example 6

[0086] This embodiment provides a graphite silicon-carbon composite negative electrode material, the preparation method of which includes the following steps:

[0087] (1) Weigh 20 g of nano-silicon powder, 80 g of graphite powder, 20 g of sodium chloride and 100 g of 1.5% CMC aqueous solution for later use. Put the nano-silicon powder and CMC aqueous solution into a beaker together. Then put the beaker into a water bath, set the temperature at 25 ° C, turn on the magnetic stirrer, stir for 1 hour, then gradually add the graphite powder into the beaker in 5 times, stir for another 1 hour, then raise the water bath temperature to 90 ° C, and put it into a blast oven to dry at 90 ° C after the solution becomes viscous.

[0088] (2) After drying, the sample was placed in a crucible and placed in an atmosphere furnace. Under nitrogen protection, it was calcined at 650°C for 5 hours. After cooling, the material was taken out and ground, and then passed through a 300-mesh sieve to obtain a graphite silicon-carbon composite material.

[0089] (3) The sieved material and water in step (2) are then added to deionized water in a ratio of 1:10, stirred for 10 minutes, and the mixture is vacuum filtered. The filter residue is mixed with water again, stirred, and filtered. This is repeated three times. The conductivity of the filtrate is close to that of deionized water. The filter residue after the last filtration is placed in a blast drying oven, dried at 80°C, and then transferred to a vacuum oven and continued to dry at 100°C for 5 hours. After cooling, it is taken out, ground, and passed through a 300-mesh sieve to obtain a graphite silicon-carbon composite negative electrode material.

[0090] Comparative Example 1

[0091] This comparative example provides a graphite silicon-carbon composite negative electrode material, the preparation method of which comprises the following steps:

[0092] 15 g of nano-silicon powder and 85 g of graphite powder were mixed in a mixer for 20 minutes to obtain a graphite silicon-carbon composite negative electrode material.

[0093] Some parameters of the above examples and comparative examples are detailed in Table 1.

[0094] Table 1

[0095]

[0096]

[0097] Test example

[0098] The graphite silicon-carbon composite negative electrode materials prepared in the above Examples 1-6 and Comparative Examples 1 and 2 were respectively mixed in a ratio of negative electrode material: conductive agent (Super P): binder (PVDF) of 8:1:1 to prepare negative electrode sheets. Metallic lithium was used as the counter electrode, and a 1 mol / L LiPF6 solution (EC:DEC:DMC is 1:1:1) was used as the electrolyte to prepare 2032 button batteries. The batteries were activated three times at a rate of 0.1C using a Land test system, and the electrochemical performance was tested at a rate of 0.33C (1C = 1000 mA / g). The test results are shown in Table 2.

[0099] Table 2

[0100] sample Initial specific capacity (mAh / g) 20-week cycle capacity retention rate (%) Example 1 486 94.86 Example 2 475 93.26 Example 3 552 85.69 Example 4 549 82.51 Example 5 545 88.44 Example 6 577 87.18 Comparative Example 1 587 48.89

[0101] As can be seen from Table 2, the graphite silicon-carbon composite negative electrode material provided in this application can improve the material cycle performance.

[0102] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

Claims

1. A graphite silicon carbon composite negative electrode material, characterized in that include: Graphite core; The composite shell layer is coated on the surface of the core, and the composite shell layer includes a continuous carbon layer. The carbon layer has a porous structure, and the porous structure is filled with nano-silicon particles.

2. A method for preparing the graphite silicon-carbon composite negative electrode material according to claim 1, characterized in that: include: Mixing the nano-silicon particles, the graphite, a sodium carboxymethyl cellulose aqueous solution and a water-soluble salt template to obtain a mixed solution; The mixed solution is heated and stirred to obtain a viscous material; The viscous material is dried, carbonized under an inert protective atmosphere, crushed, and the water-soluble salt template is removed to obtain the graphite silicon-carbon composite negative electrode material.

3. The preparation method according to claim 2, characterized in that The water-soluble salt template includes one or more of sodium chloride, potassium chloride, calcium chloride, sodium carbonate, potassium carbonate and ammonium chloride; Optionally, the water-soluble salt template is removed by multiple water washings.

4. The preparation method according to claim 3, characterized in that include: After the nano-silicon particles and the sodium carboxymethyl cellulose aqueous solution are mixed, the graphite is added in multiple times and mixed, and then the water-soluble salt template is added in multiple times and mixed to obtain the mixed solution.

5. The preparation method according to claim 3, characterized in that The carbonization temperature is 500-1000°C, and the carbonization time is 3-8h; Optionally, the carbonization temperature is 600-800° C., and the carbonization time is 4-6 hours.

6. The preparation method according to any one of claims 2 to 5, characterized in that The mass ratio of the nano-silicon particles to the graphite is 1:(1-10); Optionally, the mass ratio of the nano-silicon particles to the graphite is 1:(4-9).

7. The preparation method according to any one of claims 2 to 5, characterized in that The mass ratio of the sum of the mass of the nano-silicon particles and the graphite to the mass of the water-soluble salt template is 10:(1-10); Optionally, the mass ratio of the sum of the mass of the nano-silicon particles and the graphite to the mass of the water-soluble salt template is 10:(2-5).

8. The preparation method according to any one of claims 2 to 5, characterized in that The heating temperature is 60-100° C. Optionally, the drying temperature is 70-120°C.

9. A negative electrode plate, characterized in that: It includes the graphite silicon-carbon composite negative electrode material according to claim 1 or 2.

10. A lithium ion battery, characterized in that: Including the negative electrode sheet according to claim 9.

Images