Silicon-carbon composite materials, their preparation methods, and lithium-ion batteries

Abstract

This invention relates to the field of secondary battery technology, specifically to a silicon-carbon composite material, its preparation method, and a lithium-ion battery. The preparation method of the silicon-carbon composite material includes: reacting an organometallic framework ZIF-8 in a saturated metal salt solution and then evaporating and crystallizing it to obtain a metal salt-coated organometallic framework Salt@ZIF-8; pulverizing a silicon-copper alloy precursor and the Salt@ZIF-8 at a mass ratio of 1:0.05-0.7 to obtain a mixed powder; and subjecting the mixed powder to a pyrolysis reaction and acid leaching treatment to obtain the silicon-carbon composite material. The silicon-carbon composite material obtained by this invention exhibits excellent structural stability and electrochemical performance, effectively mitigating the volume expansion of the silicon anode and improving cycle performance and rate performance.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, specifically to a silicon-carbon composite material, its preparation method, and a lithium-ion battery. Background Technology

[0002] As lithium-ion batteries strive for higher energy densities, there is an urgent need to find alternatives to graphite anodes to overcome the limitation of their theoretical specific capacity of only 372 mAh / g. Therefore, silicon anodes have attracted widespread attention due to their theoretical specific capacity of 3589 mAh / g and their good abundance in the Earth's crust.

[0003] Currently, the most significant challenge facing silicon anodes is the approximately 383% volume expansion that silicon undergoes during lithium insertion / extraction. This phenomenon is primarily related to the lithium storage mechanism of silicon anodes. Research indicates that the lithiation reaction in silicon anodes is a complex, step-by-step process, and the main reason for this volume expansion is the irreversible crystalline Li. 15 The gradual formation of Si4 leads to a continuous increase in volume.

[0004] To address the problems associated with silicon anodes, existing technologies have employed various improvement strategies, which can be broadly categorized into two types: First, direct improvements to the silicon anode itself, encompassing structural design, surface modification, silicon alloy preparation, and composites with other materials. Second, system-wide improvements to the entire battery system, including optimization of binder composition, enhancement of electrolyte performance, optimization of electrode structure, and design of artificial SEI films. The aim is to improve the overall performance and stability of silicon anode lithium-ion battery systems. Among these, direct optimization of the silicon anode material addresses the problem at its root. Therefore, overcoming the tendency for silicon anodes to expand in volume and providing a high-performance silicon anode material is a pressing issue that needs to be addressed. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems existing in the prior art and provide a silicon-carbon composite material, its preparation method, and a lithium-ion battery. This silicon-carbon composite material exhibits excellent structural stability and electrochemical performance, effectively mitigating the volume expansion of the silicon anode and improving cycle performance and rate performance.

[0006] To achieve the above objectives, the present invention provides a method for preparing a silicon-carbon composite material, the method comprising: conducting a contact reaction and evaporation crystallization of an organometallic framework ZIF-8 in a saturated metal salt solution to obtain a metal salt-coated organometallic framework Salt@ZIF-8; pulverizing a silicon-copper alloy precursor and the Salt@ZIF-8 at a mass ratio of 1:0.05-0.7 to obtain a mixed powder; and subjecting the mixed powder to a pyrolysis reaction and acid leaching treatment to obtain the silicon-carbon composite material.

[0007] A second aspect of the present invention provides a silicon-carbon composite material prepared by the above method.

[0008] A third aspect of the present invention provides a lithium-ion battery comprising the above-described silicon-carbon composite material.

[0009] This invention yields a high-performance silicon-carbon composite material by combining a metal salt-coated organometallic framework (Salt@ZIF-8) with a silicon-copper alloy precursor and then performing pyrolysis and acid leaching. This silicon-carbon composite material exhibits excellent structural stability; through its regular carbon structure and strong bond bonds within the framework, it effectively suppresses volume fluctuations in silicon during lithium insertion / extraction, significantly improving the volume expansion problem of silicon anodes and enhancing service life and safety. Simultaneously, this silicon-carbon composite material also possesses excellent electrochemical performance, further enhancing the cycle performance and rate capability of lithium-ion batteries. Attached Figure Description

[0010] Figure 1 SEM image (scanning electron microscope) of the silicon-carbon composite material prepared in Example 1;

[0011] Figure 2 Here is a SEM image of NaCl@ZIF-8 prepared in Example 1;

[0012] Figure 3 Here is a SEM image of the silicon-copper alloy precursor obtained in Example 1;

[0013] Figure 4 The images show a comparison of the silicon-carbon composite material prepared in Example 1 before and after 50 cycles under 0.5C / 3C charge-discharge conditions. (a) is the SEM image before cycling, and (b) is the SEM image after cycling. Detailed Implementation

[0014] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0015] This invention provides a method for preparing a silicon-carbon composite material, comprising: reacting an organometallic framework ZIF-8 in a saturated metal salt solution and evaporating and crystallizing it to obtain a metal salt-coated organometallic framework Salt@ZIF-8; pulverizing a silicon-copper alloy precursor and the Salt@ZIF-8 at a mass ratio of 1:0.05-0.7 to obtain a mixed powder; and subjecting the mixed powder to a pyrolysis reaction and acid leaching treatment to obtain the silicon-carbon composite material.

[0016] According to the present invention, adding the inactive metal element copper to silicon can improve the conductivity and mechanical strength of the material to a certain extent, while also promoting ion transport and effectively releasing stress, thereby alleviating the volume expansion of silicon during the lithium extraction / intercalation process to some extent. Furthermore, the inventors of this invention have found that combining it with organometallic frameworks (MOFs) with a larger specific surface area and more controllable regularity can achieve even better results, but the performance still needs further improvement. Based on this, further research has revealed that, considering the properties of silicon-copper alloys, by combining a specific organometallic framework ZIF-8 and subjecting it to special treatment, along with a specific preparation method, a silicon-carbon composite material with excellent structural stability and electrochemical performance can be obtained, thereby significantly improving the volume expansion problem of silicon and increasing the ion migration rate and electron conduction rate of the material.

[0017] According to the present invention, when copper is introduced into the silicon-carbon anode material, ZIF-8 can achieve better compatibility with silicon-copper alloys compared to other organometallic frameworks such as ZIF-67, ZIF-5, HKUST-1, MOF-74, and JUC-1000, resulting in higher electronegativity and actual performance. Furthermore, preparing metal salt-coated ZIF-8, i.e., Salt@ZIF-8, via a template method achieves even better results. Salt@ZIF-8 not only effectively prevents nitrogen loss, thus maintaining strong electronegativity, but also possesses better coating effects and improves the pore structure of the silicon-carbon material, thereby further enhancing the overall performance of the final silicon-carbon composite material.

[0018] According to the present invention, metal salts can act as intercalating agents to promote the formation of layered porous structures and improve the overall graphitization degree of the material. The in-situ bonding of silicon-copper alloy particles with Salt@ZIF-8 can also enhance the coating effect on the silicon-copper alloy and the conductivity of the material. To obtain silicon-carbon composite materials with better performance, preferably, the saturated metal salt solution is selected from one or more saturated aqueous solutions of NaCl, ZnCl2, MgCl2, and Na2CO3, preferably a saturated aqueous solution of NaCl and / or a saturated aqueous solution of ZnCl2. Salt@ZIF-8 prepared from different metal salt solutions can be, for example, represented as NaCl@ZIF-8, ZnCl2@ZIF-8, and MgCl2@ZIF-8, etc.

[0019] According to the present invention, in order to better dissolve ZIF-8 and more fully encapsulate it with the saturated metal salt solution, thereby obtaining Salt@ZIF-8 with better properties, preferably, the amount of the saturated metal salt solution used relative to 1g of ZIF-8 is 10-30mL, more preferably 15-20mL, for example, it can be 15mL, 16mL, 18mL and 20mL and any range between these values.

[0020] According to the present invention, in order to achieve a better contact reaction effect, the contact reaction conditions preferably include: temperature 10-50℃ and time 12-36h; more preferably, temperature 20-40℃ (for example, values ​​such as 20℃, 25℃, 30℃ and 40℃ and any range thereof) and time 12-24h (for example, values ​​such as 12h, 16h, 20h and 24h and any range thereof).

[0021] According to the present invention, in order to obtain a better metal salt coating effect, the evaporation and crystallization conditions preferably include: a temperature of 60-120°C and a time of 10-16h; more preferably, a temperature of 80-100°C (for example, values ​​such as 80°C, 90°C, 95°C, and 100°C, and any range thereof) and a time of 12-14h (for example, values ​​such as 12h, 13h, 13.5h, and 14h, and any range thereof).

[0022] According to the present invention, ZIF-8 can be prepared according to existing technologies and methods provided in the literature or purchased from the market. The present invention does not have any particular limitation on this, as long as ZIF-8 with good properties can be obtained.

[0023] In this invention, ZIF-8, besides being commercially available, can be prepared, for example, by the following method: Zinc nitrate and 2-methylimidazole are separately dispersed in methanol, then mixed and stirred and allowed to stand. The resulting milky white precipitate is washed with methanol and dried to obtain the organometallic framework ZIF-8. The amounts of zinc nitrate and 2-methylimidazole can be selected within a wide range. Preferably, the molar ratio of zinc nitrate to 2-methylimidazole can be 1:5-10, more preferably 1:6-8, for example, 1:6, 1:7, 1:7.5, and 1:8, or any range thereof. Preferably, relative to 1 mol of zinc nitrate, the amount of methanol used to disperse zinc nitrate can be 6-16 mL, more preferably 8-12 mL, for example, 8 mL, 10 mL, 11 mL, and 12 mL, or any range thereof. Preferably, the amount of methanol used to disperse 2-methylimidazole relative to 1 mol of 2-methylimidazole can be 0.5-2 mL, preferably 1-1.5 mL, for example, 1 mL, 1.2 mL, 1.4 mL, and 1.5 mL, or any value between these values. Preferably, the stirring time can be 0.5-3 h, preferably 1-2 h, for example, 1 h, 1.2 h, 1.5 h, and 2 h, or any value between these values. Preferably, the standing time can be 12-36 h, preferably 18-30 h, for example, 18 h, 20 h, 24 h, and 30 h, or any value between these values.

[0024] According to the present invention, a high-performance silicon-carbon composite material can be obtained by adjusting the mass ratio of the silicon-copper alloy precursor and Salt@ZIF-8, and then combining them for treatment such as crushing, pyrolysis, and acid leaching. To further improve the various properties of the silicon-carbon composite material, preferably, the mass ratio of the silicon-copper alloy precursor to Salt@ZIF-8 is 1:0.1-0.5, for example, values ​​such as 1:0.11, 1:0.25, 1:0.43, and 1:0.5, or any range between these values.

[0025] According to the present invention, in order to fully pulverize and uniformly disperse the silicon-copper alloy precursor and Salt@ZIF-8, thereby obtaining a better reaction effect, the pulverization process is preferably ball milling, with the following conditions: rotation speed 300-800 rpm / min, time 3-8 h; preferably, rotation speed 450-550 rpm / min (e.g., values ​​such as 450 rpm / min, 480 rpm / min, 500 rpm / min, and 550 rpm / min, and any range thereof), time 5-6 h (e.g., values ​​such as 5 h, 5.2 h, 5.5 h, and 6 h, and any range thereof).

[0026] According to the present invention, the conditions of the pyrolysis reaction affect the properties and performance of the final product. Too low a temperature may lead to incomplete carbonization, while too high a temperature may cause structural collapse, thereby hindering electron transport and reducing electrical conductivity. Therefore, it is necessary to adjust the conditions of the pyrolysis reaction. Preferably, the conditions of the pyrolysis reaction include: a heating rate of 1-5 °C / min, a temperature of 600-1000 °C, and a time of 2-5 h; more preferably, a heating rate of 2-4 °C / min (e.g., values ​​such as 2 °C / min, 2.5 °C / min, 3 °C / min, and 4 °C / min, or any range thereof), a temperature of 700-900 °C (e.g., values ​​such as 700 °C, 750 °C, 800 °C, and 900 °C, or any range thereof), and a time of 3-4 h (e.g., values ​​such as 3 h, 3.5 h, 3.8 h, and 4 h, or any range thereof). Preferably, the pyrolysis reaction is carried out in a non-reactive gas atmosphere. Preferably, the non-reactive gas is nitrogen and / or argon. The initial temperature of the pyrolysis reaction can generally be 20-40℃.

[0027] According to the present invention, acid leaching can remove organic ligands and free metal ions to avoid potential adverse effects and allow the carbon structure to grow a large number of holes and vacancies. This not only improves the lithium ion extraction and insertion rate during charging and discharging, but also consolidates and further enhances the structural stability of the silicon-carbon composite material after acid leaching.

[0028] According to the present invention, in order to activate the silicon-carbon composite material, give it more active sites, and further improve its surface and pore structure, the acid solution for the acid leaching treatment is preferably selected from one or more aqueous solutions of nitric acid, hydrochloric acid, sulfuric acid, and phosphoric acid, and is more preferably an aqueous solution of nitric acid and / or an aqueous solution of hydrochloric acid.

[0029] According to the present invention, in the acid leaching treatment, the concentration of the acid solution affects the final treatment effect and needs to be adjusted to a suitable range. Preferably, the concentration of the acid solution in the acid leaching treatment is 0.05-0.6 mol / L, more preferably 0.1-0.3 mol / L, for example, it can be 0.1 mol / L, 0.2 mol / L, 0.25 mol / L and 0.3 mol / L and any range between these values.

[0030] According to the present invention, in order to obtain a better acid leaching effect and avoid adverse effects on silicon-carbon composite materials, the acid leaching time is preferably 2-12 hours, more preferably 4-8 hours, for example, it can be 4 hours, 5 hours, 6 hours and 8 hours and any range between these values.

[0031] According to the present invention, after the acid leaching treatment, the obtained silicon-carbon composite material can also be washed with water until the pH is neutral. Simultaneously, after the water washing treatment, the silicon-carbon composite material can also be dried. Preferably, the drying conditions include: temperature 60-120℃, time 8-24h; more preferably, temperature 80-100℃ (e.g., values ​​such as 80℃, 85℃, 90℃, and 100℃, or any range thereof), time 12-16h (e.g., values ​​such as 12h, 14h, 15h, and 16h, or any range thereof).

[0032] According to the present invention, the silicon-copper alloy precursor described herein can be prepared by the following method: nano-silicon and copper powder are subjected to a second pulverization to obtain mixed particles, and the mixed particles, dispersant, carbon source and acid catalyst are subjected to a hydrothermal reaction in water to obtain the silicon-copper alloy precursor.

[0033] According to the present invention, in order to obtain a silicon-copper alloy precursor with better performance, and further to obtain a silicon-carbon composite material with better performance, preferably, the mass ratio of the nano-silicon to the copper powder is 1:0.05-0.7, more preferably 1:0.1-0.5, for example, it can be 1:0.11, 1:0.25, 1:0.43 and 1:0.5 and any range between these values.

[0034] According to the present invention, in order to better pulverize and more uniformly mix nano-silicon and copper powder, preferably, the second pulverization method is ball milling, with conditions including: rotation speed of 200-800 rpm / min and time of 1-10 h; preferably, rotation speed of 300-500 rpm / min (e.g., values ​​such as 300 rpm / min, 350 rpm / min, 400 rpm / min and 500 rpm / min and any range thereof), and time of 2-6 h (e.g., values ​​such as 2 h, 4 h, 5 h and 6 h and any range thereof).

[0035] According to the present invention, in order to obtain a silicon-copper alloy precursor with better performance and meeting the requirements, preferably, the mass ratio of the mixed particles, the dispersant, the carbon source and the acid catalyst is 1:1-4:2-6:1-4, more preferably 1:2-3:3-5:2-3, for example, it can be 1:2:4:2, 1:3:3:2, 1:2:5:3 and 1:2:4:3 and any range between these values.

[0036] According to the present invention, in order to ensure more adequate contact between the components, preferably, the amount of water used is 20-40 mL relative to 1 g of the mixed particles, more preferably 28-32 mL, for example, values ​​such as 28 mL, 29 mL, 30 mL and 32 mL and any range between these values.

[0037] According to the present invention, in order to better carry out the hydrothermal reaction and obtain a better silicon-copper alloy precursor, the hydrothermal reaction conditions preferably include: temperature 80-180℃, time 6-14h, and pressure 1-10MPa; more preferably, temperature 100-150℃ (e.g., values ​​such as 100℃, 120℃, 140℃, and 150℃, and any range thereof), time 8-12h (e.g., values ​​such as 8h, 9h, 10h, and 12h, and any range thereof), and pressure 3-5MPa (e.g., values ​​such as 3MPa, 3.5MPa, 4MPa, and 5MPa, and any range thereof).

[0038] According to the present invention, the selection of raw materials has a significant impact on the reaction, and thus on the properties of the obtained silicon-copper alloy precursor. To obtain a silicon-copper alloy precursor with better performance and meeting the requirements, preferably, the dispersant is selected from one or more of hexadecyltrimethylammonium bromide, sodium polyacrylate, polyvinylpyrrolidone, and sodium dodecyl sulfate, preferably hexadecyltrimethylammonium bromide and / or polyvinylpyrrolidone. Preferably, the carbon source is selected from one or more of sucrose, glucose, fructose, lactose, starch, and cellulose, preferably sucrose and / or glucose. Preferably, the acidic catalyst is selected from one or more of oxalic acid, citric acid, and potassium dihydrogen phosphate, preferably oxalic acid and / or citric acid.

[0039] According to the present invention, after the hydrothermal reaction is completed, the reaction product can be post-processed. The post-processing method can be selected within a wide range, as long as a silicon-copper alloy precursor with good properties can be obtained. For better post-processing results, preferably, the post-processing includes centrifugation, washing, and a second drying.

[0040] Preferably, the centrifugation conditions include a rotation speed of 5000-10000 rpm / min and a time of 3-10 min; more preferably, the rotation speed is 7000-9000 rpm / min (for example, values ​​such as 7000 rpm / min, 7500 rpm / min, 8000 rpm / min, and 9000 rpm / min, or any range thereof), and the time is 5-8 min (for example, values ​​such as 5 min, 6 min, 7 min, and 8 min, or any range thereof).

[0041] Preferably, the solvent used for washing can be selected from one or more of water, methanol, ethanol, ethylene glycol, propanol, acetonitrile, tetrahydrofuran, dimethyl sulfoxide, N,N-dimethylformamide and N-methylpyrrolidone, and is more preferably one or more of water, ethanol, acetonitrile and N,N-dimethylformamide.

[0042] Preferably, the second drying conditions include a temperature of 60-120°C and a time of 8-24 hours; more preferably, a temperature of 80-100°C (e.g., values ​​such as 80°C, 85°C, 90°C, and 100°C, or any range thereof) and a time of 12-16 hours (e.g., values ​​such as 12 hours, 14 hours, 15 hours, and 16 hours, or any range thereof).

[0043] According to the present invention, the silicon-carbon composite material obtained by the preparation method of the present invention has a good surface structure and pore structure, thereby further improving the various properties of the silicon-carbon composite material. Specifically, the silicon-carbon composite material obtained by the present invention has a suitable specific surface area; preferably, the specific surface area of ​​the silicon-carbon composite material is 100-350 m². 2 / g, preferably 230-300m 2 / g, for example, can be 230m 2 / g、250m 2 / g、280m 2 / g and 300m 2 / g and other numerical values ​​and the range between any of these values. Furthermore, the silicon-carbon composite material prepared by this invention also has a high pore volume; preferably, the pore volume (<10nm) of the silicon-carbon composite material is 0.2-1.2cm³. 3 / g, preferably 0.8-0.95cm 3 / g, for example, can be 0.8cm 3 / g, 0.85cm 3 / g, 0.9cm 3 / g and 0.95cm 3 / g and other values ​​and the range between any of these values. Among them, pore volume (<10nm) refers to the volume of pores with a particle size of less than 10nm.

[0044] According to the present invention, the silicon-carbon composite material obtained by the specific preparation method can not only have excellent structural stability and electrochemical performance, but also have good surface reactivity. In addition, it can also generate a stable solid electrolyte interphase (SEI) film when in contact with electrolyte.

[0045] A second aspect of the present invention provides a silicon-carbon composite material prepared by the above method.

[0046] A third aspect of the present invention provides a lithium-ion battery comprising the above-described silicon-carbon composite material.

[0047] This invention yields a high-performance silicon-carbon composite material by combining a metal salt-coated organometallic framework (Salt@ZIF-8) with a silicon-copper alloy precursor and then performing pyrolysis and acid leaching. This silicon-carbon composite material exhibits excellent structural stability; through its regular carbon structure and strong bond bonds within the framework, it effectively suppresses volume fluctuations in silicon during lithium insertion / extraction, significantly improving the volume expansion problem of silicon anodes and enhancing service life and safety. Simultaneously, this silicon-carbon composite material also possesses excellent electrochemical performance, further enhancing the cycle performance and rate capability of lithium-ion batteries.

[0048] The present invention will be described in detail below through embodiments.

[0049] In the following examples, the apparatus used is conventional experimental equipment in the field, the experimental procedures employed are conventional procedures in the field, and the raw materials and reagents used are commercially available.

[0050] The organometallic framework ZIF-8 was purchased from Beijing Beike New Materials Co., Ltd., with the grade name 59061-53-9.

[0051] Polyvinylpyrrolidone was purchased from Wuhan Shuer Biotechnology Co., Ltd., with brand name 9003-39-8;

[0052] The conductive carbon black SP was purchased from Dongguan Hailong New Materials Co., Ltd., and its grade is DENKA HS-100.

[0053] Carboxymethyl cellulose was purchased from Shanghai Haiyi Science & Trade Co., Ltd., and its brand name was BVH8.

[0054] Styrene-butadiene latex was purchased from Huaming Power (Shenzhen) Co., Ltd., with the brand name SN-307R.

[0055] The carbon nanotubes were purchased from Zhongke Leiming (Beijing) Technology Co., Ltd., with the grade name 308068-56-6.

[0056] The polyvinylidene fluoride was purchased from Shenzhen Taineng New Materials Co., Ltd., and its grade was Solef5130.

[0057] The ceramic diaphragm was purchased from Hebei Jinli New Energy Technology Co., Ltd., with the grade SC14-S2-B(12LD+2).

[0058] Example 1

[0059] (1) Preparation of silicon-copper alloy precursor: Nano-silicon and copper powder were ball-milled at 500 rpm / min for 6 h at a mass ratio of 1:0.11 to obtain mixed particles. The mixed particles, hexadecyltrimethylammonium bromide, sucrose and oxalic acid were added to water (30 mL relative to 1 g of mixed particles) at a mass ratio of 1:2:4:2 and stirred evenly. The mixture was reacted in a reactor at 150 °C and 4 MPa for 10 h. The reaction product was centrifuged at 8000 rpm / min for 6 min, washed with water, and vacuum dried at 80 °C for 12 h to obtain the silicon-copper alloy precursor.

[0060] (2) Preparation of NaCl@ZIF-8: The organometallic framework ZIF-8 was added to a saturated aqueous solution of NaCl (the amount of saturated aqueous solution of NaCl was 20 mL relative to 1 g of ZIF-8), and the reaction was carried out at 30 °C for 12 h. Then, it was evaporated and crystallized at 80 °C for 12 h to obtain NaCl@ZIF-8.

[0061] (3) Preparation of silicon-carbon composite material: The prepared silicon-copper alloy precursor and NaCl@ZIF-8 were ball-milled at a mass ratio of 1:0.11 at a speed of 500 rpm / min for 6 h. The mixed powder was transferred to a tube furnace and heated to 800 °C at a heating rate of 3 °C / min under a nitrogen atmosphere. The mixture was pyrolyzed at 800 °C for 4 h. The pyrolysis product was acid-leached in 0.1 mol / L nitric acid aqueous solution for 5 h. The acid-leached product was washed with water until the pH was neutral and then vacuum-dried at 80 °C for 12 h to obtain silicon-carbon composite material.

[0062] The specific surface area of ​​the prepared silicon-carbon composite material was measured to be 253 m² using a BSD-660A6S BET specific surface area analyzer and pore size analyzer. 2 / g, pore volume (<10nm) is 0.897cm 3 / g.

[0063] The prepared silicon-carbon composite material, NaCl@ZIF-8, and silicon-copper alloy precursor were characterized by scanning electron microscopy, and the results are as follows: Figure 1 , Figure 2 and Figure 3 As shown. By Figure 1 It can be seen that the silicon-carbon composite material has a multilayer structure, with silicon-copper alloy distributed between the layers and encapsulated by carbon. Figure 2 It can be seen that NaCl@ZIF-8 prepared using NaCl as a template adheres to each other, and NaCl, as an intercalating agent, can promote the formation of porous structures. Figure 3 It can be seen that when silicon and copper are completely mixed, the resulting silicon-copper alloy is in the form of microspheres.

[0064] Example 2

[0065] (1) Preparation of silicon-copper alloy precursor: Nano-silicon and copper powder were ball-milled at 300 rpm / min for 4 h at a mass ratio of 1:0.25 to obtain mixed particles. The mixed particles, polyvinylpyrrolidone, glucose and citric acid were added to water (28 mL relative to 1 g of mixed particles) at a mass ratio of 1:3:5:2 and stirred evenly. The reaction was carried out at 0 °C and 3 MPa for 8 h. The reaction product was centrifuged at 7000 rpm / min for 6 min, washed with 10 g of water in a reaction vessel, and then vacuum dried at 100 °C for 16 h to obtain the silicon-copper alloy precursor.

[0066] (2) Preparation of ZnCl2@ZIF-8: The organometallic framework ZIF-8 was added to a saturated aqueous solution of ZnCl2 (the amount of saturated aqueous solution of ZnCl2 was 15 mL relative to 1 g of ZIF-8), and the reaction was carried out at 40 °C for 24 h. Then, it was evaporated and crystallized at 100 °C for 14 h to obtain ZnCl2@ZIF-8.

[0067] (3) Preparation of silicon-carbon composite material: The prepared silicon-copper alloy precursor and ZnCl2@ZIF-8 were ball-milled at a mass ratio of 1:0.43 at a speed of 450 rpm / min for 5 h. The mixed powder was transferred to a tube furnace and heated to 700 °C at a heating rate of 2 °C / min under a nitrogen atmosphere. The mixture was pyrolyzed at 700 °C for 4 h. The pyrolysis product was acid-leached in 0.3 mol / L hydrochloric acid aqueous solution for 8 h. The acid-leached product was washed with water until the pH was neutral and then vacuum-dried at 80 °C for 14 h to obtain silicon-carbon composite material.

[0068] The specific surface area of ​​the prepared silicon-carbon composite material was measured to be 128 m² using a BSD-660A6S BET specific surface area analyzer and pore size analyzer. 2 / g, pore volume (<10nm) is 0.55cm 3 / g.

[0069] Example 3

[0070] (1) Preparation of silicon-copper alloy precursor: Nano-silicon and copper powder were ball-milled at 500 rpm / min for 2 h at a mass ratio of 1:0.25 to obtain mixed particles. The mixed particles, sodium dodecyl sulfate, sucrose and oxalic acid were added to water (32 mL relative to 1 g of mixed particles) at a mass ratio of 1:2:3:2 and stirred evenly. The mixture was reacted in a reactor at 120 °C and 5 MPa for 8 h. The reaction product was centrifuged at 9000 rpm / min for 5 min, washed with water, and vacuum dried at 80 °C for 12 h to obtain the silicon-copper alloy precursor.

[0071] (2) Preparation of Na2CO3@ZIF-8: The organometallic framework ZIF-8 was added to a saturated aqueous solution of Na2CO3 (the amount of saturated aqueous solution of Na2CO3 was 18 mL relative to 1 g of ZIF-8), and the reaction was carried out at 20 °C for 16 h. Then, it was evaporated and crystallized at 100 °C for 12 h to obtain Na2CO3@ZIF-8.

[0072] (3) Preparation of silicon-carbon composite material: The obtained silicon-copper alloy precursor and Na2CO3@ZIF-8 were ball-milled at a mass ratio of 1:0.25 at a speed of 500 rpm / min for 6 h. The mixed powder was transferred to a tube furnace and heated to 900 °C at a heating rate of 4 °C / min under a nitrogen atmosphere. The mixture was pyrolyzed at 900 °C for 4 h. The pyrolysis product was acid-leached in 0.2 mol / L phosphoric acid aqueous solution for 5 h. The acid-leached product was washed with water until the pH was neutral and then vacuum-dried at 80 °C for 12 h to obtain silicon-carbon composite material.

[0073] The specific surface area of ​​the prepared silicon-carbon composite material was measured to be 226 m² using a BSD-660A6S BET specific surface area analyzer and pore size analyzer. 2 / g, pore volume (<10nm) is 0.25cm 3 / g.

[0074] Example 4

[0075] The method is the same as in Example 1, except that in step (3), the mass ratio of the silicon-copper alloy precursor to NaCl@ZIF-8 is 1:0.05.

[0076] Example 5

[0077] The method is the same as in Example 1, except that in step (3), the mass ratio of the silicon-copper alloy precursor to NaCl@ZIF-8 is 1:0.7.

[0078] Example 6

[0079] The method is the same as in Example 1, except that in step (3), the 0.1 mol / L nitric acid aqueous solution is replaced with a 1 mol / L nitric acid aqueous solution.

[0080] Example 7

[0081] The method is the same as in Example 1, except that in step (3), the temperature of the pyrolysis reaction is 1000°C.

[0082] Comparative Example 1

[0083] The method according to Example 1 is different except that step (2) is not performed, and NaCl@ZIF-8 in step (3) is replaced with ZIF-8.

[0084] Comparative Example 2

[0085] The method of Example 1 differs in that, in step (3), acid leaching is not performed.

[0086] Comparative Example 3

[0087] The method of Example 1 differs in that, in step (1), copper powder was not used to prepare the silicon precursor. In step (3), the silicon-copper alloy precursor was replaced with the silicon precursor.

[0088] Test case

[0089] The silicon-carbon composite materials prepared in Examples 1-7 and Comparative Examples 1-3 were used as negative electrode materials and assembled into lithium-ion batteries according to the following method for testing.

[0090] Negative electrode sheet: The negative electrode material, conductive carbon black SP, carboxymethyl cellulose, styrene-butadiene latex, carbon nanotubes, and silicon material are mixed in water at a mass ratio of 86.7:1.32:1.7:2.2:0.08:8 (1.26 mL of water is used per 1 g of solid material), coated onto copper foil, and then processed through rolling, slitting, and sheet forming to achieve a compacted density of 1.53 g / cm³. 3 The negative electrode.

[0091] Positive electrode: LiNi 8.8 Co 0.7 Mn 0.5 O2, carbon nanotubes, conductive carbon black SP, and polyvinylidene fluoride were mixed in N-methylpyrrolidone at a mass ratio of 95.8:1.3:0.9:1.2 (0.43 mL of N-methylpyrrolidone per 1 g of solid material), coated onto aluminum foil, and then processed through rolling, slitting, and sheeting to achieve a compacted density of 3.32 g / cm³. 3 Positive electrode film.

[0092] A lithium-ion battery is assembled from a positive electrode, a negative electrode, a ceramic separator, and an electrolyte (1.1 mol / L LiPF6 electrolyte with ethylene carbonate as the solvent).

[0093] 3C cycle performance: At 25±2℃, 0.5C charge to 4.2V with a cutoff current of 100mA, rest for 10min, 3C discharge to 2.5V, rest for 30min.

[0094] 5C cycle performance: At 25±2℃, 0.5C charge to 4.2V with a cutoff current of 100mA, rest for 10min, 5C discharge to 2.5V, rest for 30min.

[0095] The lithium-ion battery prepared in Example 1 was cycled 50 times under 0.5C / 3C charge-discharge conditions. The silicon-carbon composite material before and after cycling was characterized by scanning electron microscopy. Figure 4 As shown, (a) is the SEM image before cycling and (b) is the SEM image after cycling. It can be seen that the silicon-carbon composite material has a stable structure before and after cycling, and the surface does not undergo significant changes, with no obvious volume expansion problem.

[0096] The test results are shown in Table 1.

[0097] Table 1

[0098]

[0099]

[0100] As shown in Table 1, the silicon-carbon composite materials prepared using the technical solutions of this invention in Examples 1-7 exhibit significantly better performance than those in Comparative Examples 1-3. Specifically, the silicon-carbon composite materials prepared by this invention achieve a 3C reversible specific capacity as high as 383.2 mAh / g and a 5C reversible specific capacity as high as 294.2 mAh / g, indicating that the material experiences minimal energy loss and high charge / discharge efficiency during charging and discharging. Furthermore, the high reversible specific capacity suggests that the internal electrode structure and chemical reactions are relatively more stable during charging and discharging, and less prone to irreversible changes.

[0101] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing a silicon-carbon composite material, characterized in that, The method includes: The organometallic framework ZIF-8 was subjected to a contact reaction in a saturated metal salt solution and then evaporated and crystallized to obtain a metal salt-coated organometallic framework Salt@ZIF-8. The silicon-copper alloy precursor and the Salt@ZIF-8 were pulverized at a mass ratio of 1:0.05-0.7 to obtain a mixed powder. The mixed powder was subjected to a pyrolysis reaction and acid leaching treatment to obtain a silicon-carbon composite material.

2. The method according to claim 1, wherein, The mass ratio of the silicon-copper alloy precursor to Salt@ZIF-8 is 1:0.1-0.

5.

3. The method according to claim 1 or 2, wherein, The specific surface area of ​​the silicon-carbon composite material is 100-350 m². 2 / g, preferably 230-300m 2 / g; And / or, the pore volume (<10nm) of the silicon-carbon composite material is 0.2-1.2cm. 3 / g, preferably 0.8-0.95cm 3 / g.

4. The method according to any one of claims 1-3, wherein, The saturated metal salt solution is selected from one or more saturated aqueous solutions of NaCl, ZnCl2, MgCl2 and Na2CO3, preferably a saturated aqueous solution of NaCl and / or a saturated aqueous solution of ZnCl2. And / or, relative to 1g of the ZIF-8, the amount of the saturated metal salt solution used is 10-30mL, preferably 15-20mL; And / or, the conditions for the contact reaction include: temperature 10-50°C, time 12-36h; preferably temperature 20-40°C, time 12-24h; And / or, the conditions for the evaporation crystallization include: a temperature of 60-120°C and a time of 10-16 hours; preferably, a temperature of 80-100°C and a time of 12-14 hours.

5. The method according to any one of claims 1-4, wherein, The pulverization process is ball milling, with the following conditions: rotation speed 300-800 rpm / min, time 3-8 h; preferably 450-550 rpm / min, time 5-6 h. And / or, the conditions for the pyrolysis reaction include: heating rate of 1-5℃ / min, temperature of 600-1000℃, and time of 2-5h; preferably, heating rate of 2-4℃ / min, temperature of 700-900℃, and time of 3-4h. And / or, the acid solution for the acid leaching treatment is selected from one or more aqueous solutions of nitric acid, hydrochloric acid, sulfuric acid and phosphoric acid, preferably aqueous solutions of nitric acid and / or hydrochloric acid; And / or, the concentration of the acid solution used for the acid leaching treatment is 0.05-0.6 mol / L, preferably 0.1-0.3 mol / L; And / or, the acid leaching treatment time is 2-12 hours, preferably 4-8 hours.

6. The method according to any one of claims 1-5, wherein, The silicon-copper alloy precursor is prepared by the following method: nano-silicon and copper powder are subjected to a second pulverization to obtain mixed particles, and the mixed particles, dispersant, carbon source and acid catalyst are subjected to a hydrothermal reaction in water to obtain the silicon-copper alloy precursor.

7. The method according to claim 6, wherein, The mass ratio of the nano-silicon to the copper powder is 1:0.05-0.7, preferably 1:0.1-0.5; And / or, the second pulverization method is ball milling, with conditions including: rotation speed 200-800 rpm / min, time 1-10 h; preferably 300-500 rpm / min, time 2-6 h; And / or, the mass ratio of the mixed particles, the dispersant, the carbon source and the acid catalyst is 1:1-4:2-6:1-4, preferably 1:2-3:3-5:2-3; And / or, relative to 1g of the mixed particles, the amount of water used is 20-40mL, preferably 28-32mL; And / or, the conditions for the hydrothermal reaction include: temperature 80-180℃, time 6-14h, and pressure 1-10MPa; preferably, temperature 100-150℃, time 8-12h, and pressure 3-5MPa.

8. The method according to claim 6 or 7, wherein, The dispersant is selected from one or more of hexadecyltrimethylammonium bromide, sodium polyacrylate, polyvinylpyrrolidone, and sodium dodecyl sulfate, preferably hexadecyltrimethylammonium bromide and / or polyvinylpyrrolidone; And / or, the carbon source is selected from one or more of sucrose, glucose, fructose, lactose, starch and cellulose, preferably sucrose and / or glucose; And / or, the acidic catalyst is selected from one or more of oxalic acid, citric acid and potassium dihydrogen phosphate, preferably oxalic acid and / or citric acid.

9. A silicon-carbon composite material prepared by the method according to any one of claims 1-8.

10. A lithium-ion battery comprising the silicon-carbon composite material of claim 9.

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