Preparation method of silicon-carbon negative electrode material and application thereof as lithium ion battery electrode

Abstract

The present application utilizes the two abilities of dispersing fused ring aromatic hydrocarbon and assisting reduction of silicon in a molten salt system, concentrates the reduction of silicon and the coating of carbon in one step, and finally obtains silicon-carbon negative electrode material through carbonization. The whole process is simple, and only needs to mix raw materials of pitch, inorganic salt, reducing agent and silicon source in a certain proportion, and then generates silicon-carbon precursor through a certain heating procedure. After washing with deionized water and acid washing, the solidified salt and silicon-carbon precursor can be separated. Finally, the silicon-carbon precursor is carbonized at a certain temperature to obtain the silicon-carbon negative electrode material. In addition, the prepared silicon-carbon negative electrode can coat the reduced silicon particles in the carbon film to block the contact between silicon and electrolyte, thereby reducing the side reaction, improving the conductivity and cycle stability. After 100 cycles at a current density of 50 mA / g, the specific capacity can be maintained at 750-900 mAh / g, and after 1000 cycles at a current density of 1 A / g, the specific capacity can be maintained at 500-600 mAh / g.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery anode materials, and particularly to a method for preparing silicon-carbon anode materials in a molten salt system and their application as electrode materials for lithium-ion batteries. Technical Background

[0002] The rapid development of electric vehicles and the huge demand for energy storage power stations necessitate higher energy density and cycle stability in lithium-ion batteries. Silicon-based anode materials, with their high specific capacity (3600 mAh / g), are considered one of the most commercially promising next-generation lithium-ion anode materials. However, silicon-based anode materials suffer from volume expansion during charge and discharge, leading to SEI film rupture and material pulverization. SEI film rupture causes the electrolyte to react with the exposed silicon, continuously generating new SEI films, resulting in irreversible lithium consumption. Material pulverization causes the material to lose contact with the current collector, leading to rapid capacity degradation. Furthermore, material expansion generates significant stress, causing safety issues in battery devices.

[0003] Currently, the preparation methods for silicon-carbon anodes include high-energy ball milling, spray drying, vapor deposition, and liquid-phase coating. High-energy ball milling involves mixing silicon particles or silicon suboxide particles with a carbon precursor, ball milling to refine the particles and uniformly dispersing them, and finally carbonizing them to obtain silicon-carbon anodes. The carbon embedded between the silicon particles can buffer the volume expansion of silicon, but high-energy ball milling cannot effectively prevent the reaction between silicon and electrolyte, so its long-cycle stability still needs to be improved. [Lee DJ, Lee H, Ryou MH, et al. Electrospun three-dimensional mesoporous silicon nanofibers as an anode material for high-performance lithium secondary batteries[J].ACS Applied Material S&Interfaces,2013,5(22):12005-12010.] Spray drying involves dispersing silicon particles or silicon oxide particles in a solution of a carbon precursor, and then pyrolyzing them at high temperature to obtain carbon-coated silicon-carbon anode materials. Spray drying can effectively reduce side reactions between silicon and electrolyte by coating silicon with carbon, but in actual production, its thermal efficiency is often not high enough and it has high requirements for gas separation. [Hu Y,Qiao Y,Xie Z,et al.Water-SolublePolymer Assists Multisize Three-Dimensional Microspheres as a High-Performance Si Anode for Lithium-Ion Batteries[J].ACS Applied EnergyMaterials,2021,4(9):9673-9681.] Vapor deposition is an effective means of preparing high-performance silicon-carbon anodes, but it has high requirements for production equipment, resulting in high production costs and difficulty in commercialization.[Jia H,Li X,Song J,etal. Hierarchical porous silicon structures with extraordinary mechanical strength as high-performance lithium-ion battery anodes[J].Nature communications,2020,11(1):1474.] The liquid-phase coating method involves coating a carbon source onto silicon particles in a liquid phase, then separating the coated particles by centrifugation or filtration, and finally carbonizing the separated particles to obtain a silicon-carbon anode. However, the utilization rate of the carbon source in liquid-phase coating is often not high. [Kim SY,Lee J,Kim BH,etal.Facile synthesis of carbon-coated silicon / graphite spherical composites for high-performance lithium-ion batteries[J].ACS applied materials&interfaces,2016,8(19):12109-12117.] The above methods all use silicon or silicon suboxide as raw materials. In other words, the above methods are methods of combining two materials together, without involving the reduction of silicon. However, in actual production, micron-sized and nano-sized silicon are expensive, accounting for a significant portion of production costs. Therefore, it is necessary to provide a method for preparing silicon-carbon anodes that uses inexpensive raw materials such as silica and diatomaceous earth as silicon sources and inexpensive raw materials such as coal tar pitch and petroleum pitch as carbon sources, while simultaneously achieving coating and reduction, to promote the commercialization of silicon-carbon anodes.

[0004] Currently silicon and SiO x Methods for preparing (x<2) include carbothermic reduction, aluminothermic (magnesian) reduction, and reduction in molten salts. Carbothermic reduction involves removing oxygen from silicon dioxide at high temperatures using coke or similar reducing agents to obtain elemental silicon or SiO2. x(x<2). [Chen Z, Zhang H, Ma W, et al. High efficient and clean utilization of coal for the carbothermic reduction of silica[J].Sustainable Energy Technologies and Assessments,2022,53:102602.] Aluminum or magnesium thermal reduction is the process of replacing silicon in silica with aluminum or magnesium powder as a reducing agent at a temperature higher than the melting point of the reducing agent. [Zhou ZW, Liu YT, Xie XM, et al. Aluminothermic reduction enabled synthesis of silicon hollow microspheres from commercialized silica nanoparticles for superior lithium storage[J].Chemical Communications,2016,52(54):8401-8404.] The molten salt reduction method for preparing silicon is the process of reducing silicon in a molten salt system with magnesium or aluminum powder as a reducing agent and with the help of the molten salt medium. [Lin N, Han Y, Zhou J, et al. A low temperature molten salt process for aluminothermic reduction of silicon oxides to crystalline Si for Li-ion batteries[J]. Energy & Environmental Science, 2015, 8(11):3187-3191.] However, the preparation method that can simultaneously reduce silicon in molten salt and achieve carbon coating can only use expensive organosilicon as raw material. [Fan Xiaoming, Wang Zihan, Yang Yongsan, et al. A two-dimensional silicon oxide / carbon composite lithium-ion battery anode material and its preparation method: 202011175571.0[P]2021-01-15.]

[0005] The method for preparing silicon-carbon anodes described in this patent invention is characterized by utilizing the ability of polycyclic aromatic hydrocarbons such as pitch to achieve uniform dispersion in some molten salts, and the ability of silica to be reduced to SiO in molten salts. xThe fact that (x<2) allows for the combination of two methods, achieving silicon reduction and carbon coating of silicon in a single reaction. The entire process is simple: raw materials such as pitch, inorganic salts, reducing agents, and silicon sources are mixed in a certain proportion and heated to generate a silicon-carbon precursor. The solidified salt and silicon-carbon precursor can be separated by washing the obtained product with deionized water and acid leaching. Finally, the silicon-carbon precursor is carbonized at a certain temperature to obtain the silicon-carbon anode material. Summary of the Invention

[0006] To address the aforementioned problems in the prior art, the present invention aims to provide a method for preparing a silicon-carbon anode material, which is obtained by the following method:

[0007] Step 1: Mix appropriate amounts of carbon source, composite inorganic salt, reducing agent and silicon source in a certain mass ratio to obtain a mixture, and load the mixture into the reaction vessel under an inert atmosphere;

[0008] Step 2: Heat the reaction vessel prepared in Step 1 to a certain reaction temperature and maintain the temperature for a certain time; then remove the reaction product.

[0009] Step 3: Wash the reaction product obtained in Step 2 with deionized water and acid for a certain period of time, then filter, wash to remove the mixed salt, and then dry to obtain the silicon-carbon precursor.

[0010] Step 4: Carbonize the silicon-carbon precursor obtained in Step 3 at a certain carbonization temperature and for a certain carbonization time to obtain the final silicon-carbon anode material.

[0011] The carbon source of this invention is selected from coal-based pitch, petroleum-based pitch, naphthyl pitch, naphthalene, anthracene, phenanthrene, and other polycyclic aromatic hydrocarbon raw materials; the composite inorganic salt is selected from one or more of aluminum chloride, lithium chloride, sodium chloride, potassium chloride, and magnesium chloride; the reducing agent is selected from one or more of aluminum, magnesium, sodium, and lithium; the silicon source is selected from one or more of silicon dioxide-containing raw materials such as silica, diatomaceous earth, and silica gel; in step one), the mass ratio of silicon source to reducing agent is 1:(0.5-3), the mass ratio of silicon source to carbon source is 1:(0.1-10), and the mass ratio of silicon source to inorganic salt is 1:(5-20); in step two), the reaction temperature is 200℃-800℃; the holding time is 2-36h; the acid is selected from hydrochloric acid, nitric acid, and sulfuric acid; in step four), the carbonization temperature is 800-1300℃; and the carbonization time is 0.5-4h.

[0012] A further preferred embodiment of the present invention is as follows: Suitable reaction temperature, reaction time, carbonization temperature, and carbonization time are determined. Too low a temperature will prevent the silicon source from being reduced to silicon, thus reducing the specific capacity; too high a temperature will cause the reducing agent to biodegrade, reducing the reduction effect and thus reducing the specific capacity; too short a reaction time will result in too low a degree of reduction and poor coating effect, thus reducing the specific capacity and cycle stability; too low a carbonization temperature will result in an incomplete carbon film, thus reducing cycle stability; too high a carbonization temperature will lead to the formation of silicon carbide, thus reducing the specific capacity; too short a carbonization time will lead to an unstable carbon film, thus reducing cycle stability. Therefore, a reaction temperature of 200–800°C, a reaction time of 2–36 h, a carbonization temperature of 800–1300°C, and a carbonization time of 0.5–4 h are selected.

[0013] In addition, the purpose of this invention is to provide a silicon-carbon anode material prepared by the aforementioned preparation method.

[0014] This invention utilizes the dual capabilities of a molten salt system—dispersing polycyclic aromatic hydrocarbons and reducing silicon—to perform silicon reduction and carbon coating in a single step, followed by carbonization to obtain a silicon-carbon anode material. This allows for the preparation of silicon-carbon anode materials using two inexpensive raw materials: silica and pitch. The silicon-carbon anode prepared by this method eliminates the need for expensive silicon or silicon suboxide as raw materials, significantly reducing preparation costs. Furthermore, the silicon-carbon anode prepared by this invention encapsulates the reduced silicon particles within a carbon film, preventing contact between silicon and the electrolyte and reducing side reactions. This suppresses silicon volume expansion, improving conductivity and cycle stability. After 100 cycles at a current density of 50 mA / g, it maintains a specific capacity of 750–900 mAh / g, and after 1000 cycles at a current density of 1 A / g, it maintains a specific capacity of 500–600 mAh / g. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Appendix Figure 1 The data represents the rate capability of the silicon-carbon anode material obtained in Example 1.

[0017] Appendix Figure 2 The data represents the cycling data of the silicon-carbon anode material obtained in Example 1.

[0018] Appendix Figure 3 This is a TEM image of the silicon-carbon anode material obtained in Example 1.

[0019] Appendix Figure 4 This is a SEM image of the silicon-carbon anode material obtained in Example 1. Detailed Implementation

[0020] The present invention will now be described in detail with reference to the accompanying drawings and embodiments:

[0021] Example 1

[0022] 1 gram of medium-temperature coal tar pitch, 1 gram of silicon dioxide, 1.5 grams of magnesium powder, and 15 grams of aluminum chloride were mixed evenly and loaded into a reactor. The reactor was loaded under an inert atmosphere to ensure the atmosphere inside the reactor was also inert. The reactor was placed in a heating device with a heating rate of 5°C per minute, heated to 550°C, and held at that temperature for 12 hours. After the reaction was completed, the reaction product was removed, dissolved in deionized water, and filtered. The filtered product was then soaked in dilute hydrochloric acid for 2 hours for acid washing. After acid washing, the product was filtered again and rinsed four times with deionized water in a filtration device. The filtered product was then dried to obtain a silicon-carbon precursor. Finally, the silicon-carbon precursor was carbonized at 900°C for 2 hours under an inert atmosphere to obtain the final silicon-carbon anode material.

[0023] As attached Figure 1 The rate performance data shown indicates that the obtained silicon-carbon anode material has a specific capacity of 430 mAh / g at a current density of 1 A / g and a specific capacity of 340 mAh / g at a current density of 2 A / g, demonstrating good rate performance.

[0024] As attached Figure 2 The results show that the silicon-carbon anode material retains a specific capacity of 550 mAh / g after 1000 cycles at a current density of 1 A / g, indicating that the obtained silicon-carbon anode material has stable cycling performance.

[0025] As attached Figure 3 The TEM image shown indicates that the obtained silicon-carbon anode material structure consists of secondary particles composed of primary particles, in which nano-silicon has been successfully encapsulated by a carbon shell.

[0026] As attached Figure 4 The SEM image shown indicates that the obtained silicon-carbon anode material exhibits a granular structure with particle sizes ranging from 10 to 70 μm.

[0027] Example 2

[0028] 1 gram of petroleum asphalt, 1 gram of silica, 1.5 grams of aluminum powder, and 15 grams of aluminum chloride were mixed evenly and loaded into a reaction vessel. The vessel was loaded under an inert atmosphere to ensure the atmosphere inside the vessel was also inert. The reaction vessel was placed in a heating device with a heating rate of 5°C per minute, heated to 550°C, and held at that temperature for 12 hours. After the reaction was completed, the reaction product was removed, dissolved in deionized water, and filtered. The filtered product was then soaked in dilute hydrochloric acid for 2 hours for acid washing. After acid washing, the product was filtered again and rinsed four times with deionized water in a filtration device. The filtered product was then dried to obtain a silicon-carbon precursor. Finally, the silicon-carbon precursor was carbonized at 900°C for 2 hours under an inert atmosphere to obtain the final silicon-carbon anode material.

[0029] Example 3

[0030] 1 gram of petroleum asphalt, 1 gram of diatomaceous earth, 1.5 grams of aluminum powder, and 15 grams of aluminum chloride were mixed evenly and loaded into a reaction vessel. The vessel was loaded under an inert atmosphere to ensure the atmosphere inside the vessel was also inert. The reaction vessel was placed in a heating device with a heating rate of 5°C per minute, heated to 550°C, and held at that temperature for 24 hours. After the reaction was completed, the reaction product was removed, dissolved in deionized water, and filtered. The filtered product was then soaked in dilute hydrochloric acid for 2 hours for acid washing. After acid washing, the product was filtered again and rinsed four times in a filtration device with deionized water. The filtered product was then dried to obtain a silicon-carbon precursor. Finally, the silicon-carbon precursor was carbonized at 1000°C for 2 hours under an inert atmosphere to obtain the final silicon-carbon anode material.

[0031] Example 4

[0032] 2 g of medium-temperature coal tar pitch, 1 g of silicon dioxide, 1.5 g of magnesium powder, and 10 g of aluminum chloride were mixed evenly and loaded into a reactor. The reactor was loaded under an inert atmosphere to ensure the atmosphere inside the reactor was also inert. The reactor was placed in a heating device with a heating rate of 5°C per minute, heated to 650°C, and held at that temperature for 12 hours. After the reaction was completed, the reaction product was removed, dissolved in deionized water, and filtered. The filtered product was then soaked in dilute sulfuric acid for 2 hours for acid washing. After acid washing, the product was filtered again and rinsed four times with deionized water in a filtration device. The filtered product was then dried to obtain a silicon-carbon precursor. Finally, the silicon-carbon precursor was carbonized at 900°C for 2 hours under an inert atmosphere to obtain the final silicon-carbon anode material.

[0033] Example 5

[0034] 1 gram of medium-temperature coal tar pitch, 1 gram of silica, 2 grams of aluminum powder, and 15 grams of aluminum chloride-sodium chloride were mixed evenly and loaded into a reactor. The reactor was loaded under an inert atmosphere to ensure the atmosphere inside the reactor was also inert. The reactor was placed in a heating device with a heating rate of 5°C per minute, heated to 550°C, and held at that temperature for 6 hours. After the reaction was completed, the reaction product was removed, dissolved in deionized water, and filtered. The filtered product was then soaked in dilute hydrochloric acid for 2 hours for acid washing. After acid washing, the product was filtered again and rinsed four times with deionized water in a filtration device. The filtered product was then dried to obtain a silicon-carbon precursor. Finally, the silicon-carbon precursor was carbonized at 850°C for 2.5 hours under an inert atmosphere to obtain the final silicon-carbon anode material.

[0035] Example 6

[0036] 1 gram of medium-temperature coal tar pitch, 1 gram of diatomaceous earth, 1.5 grams of aluminum powder, and 15 grams of aluminum chloride were mixed evenly and loaded into a reactor. The reactor was loaded under an inert atmosphere to ensure the atmosphere inside the reactor was also inert. The reactor was placed in a heating device with a heating rate of 10°C per minute, heated to 750°C, and held at that temperature for 12 hours. After the reaction was completed, the reaction product was removed, dissolved in deionized water, and filtered. The filtered product was then soaked in dilute hydrochloric acid for 2 hours for acid washing. After acid washing, the product was filtered again and rinsed four times in a filtration apparatus with deionized water. The filtered product was then dried to obtain a silicon-carbon precursor. Finally, the silicon-carbon precursor was carbonized at 900°C for 2 hours under an inert atmosphere to obtain the final silicon-carbon anode material.

[0037] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the embodiments described. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention, and these equivalent modifications or substitutions are all included within the scope defined by the claims of this application.

Claims

1. A method for preparing a silicon-carbon anode material, characterized in that... It is prepared by the following method: Step 1: Mix a certain amount of carbon source, composite inorganic salt, reducing agent and silicon source in a certain mass ratio to obtain a mixture, and load the mixture into a reaction vessel under an inert atmosphere; Step 2: Heat the reaction vessel prepared in Step 1 to a certain reaction temperature and maintain the temperature for a certain time; then remove the reaction product. Step 3: Wash the reaction product obtained in Step 2 with deionized water and acid for a certain period of time, then filter, wash to remove the mixed salt, and then dry to obtain the silicon-carbon precursor. Step 4: The silicon-carbon precursor obtained in Step 3 is treated at a certain temperature for a certain time to obtain the final silicon-carbon anode material; In step one, the carbon source is selected from one of coal-based pitch, petroleum-based pitch, naphthyl pitch, naphthalene, anthracene, and phenanthrene; one of the composite inorganic salts is aluminum chloride, and the other is one of lithium chloride, sodium chloride, potassium chloride, and magnesium chloride.

2. The method for preparing the silicon-carbon anode material as described in claim 1, characterized in that: The reducing agent is selected from one or more of aluminum, magnesium, sodium, and lithium.

3. The method for preparing the silicon-carbon anode material as described in claim 1, characterized in that: The silicon source is selected from one or more of silicon dioxide, diatomaceous earth, and silica gel.

4. The method for preparing the silicon-carbon anode material as described in claim 1, characterized in that: In step one), the mass ratio of silicon source to reducing agent is 1:(0.5~3); the mass ratio of silicon source to carbon source is 1:(0.1~10); and the mass ratio of silicon source to inorganic salt is 1:(5~20).

5. The method for preparing the silicon-carbon anode material as described in claim 1, characterized in that: In step two), the reaction temperature is 200℃~800℃; the holding time is 2~36h.

6. The method for preparing the silicon-carbon anode material as described in claim 1, characterized in that: The carbonization temperature in step four is 800~1300℃; the carbonization time is 0.5~4h.

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