Microcrystalline silicon-carbon composite material, and preparation method and application thereof

Abstract

The application discloses a microcrystalline silicon-carbon composite material and a preparation method and application thereof. A thin sheet electrode or a solid electrode is used as a working electrode, an inorganic electrolyte is added into a strong polar solution, then alkylsilane or halogenated alkylsilane is added to configure an electrolyte, a reference electrode and a counter electrode are used to form a three-electrode electrolysis cell system for electrolysis, the voltage is-2.0 to-5.0 V, after the electrolysis is completed, the working electrode is cleaned by using an organic solvent, and the microcrystalline silicon-carbon composite material is obtained after drying and carbonization. The prepared negative electrode material is subjected to point analysis on a specific micro area of the microcrystalline silicon-carbon composite material by using a scanning electron microscope equipped with an energy dispersive X-ray spectrometer, the content of silicon deposited between the porous carbon is greater than or equal to 50%, and the content of silicon deposited in the interior of the carbon particles is less than or equal to 10%. The prepared composite material has high capacity and high first coulomb efficiency, the preparation process is safe, the cost is low, and the composite material is easy to be industrialized.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery negative electrode materials, and particularly relates to a silicon-carbon composite material and a preparation method and application thereof. BACKGROUND

[0002] The preparation methods of the silicon-carbon negative electrode material commonly used in the industry at present include sand milling and chemical vapor deposition. The former forms silicon-carbon material mainly showing the characteristics of crystalline silicon, and the latter forms material mainly showing the characteristics of amorphous silicon. Crystalline silicon as a negative electrode generally has the characteristic of high initial efficiency, and amorphous silicon has the characteristics of small expansion and good cycle.

[0003] The main material for preparing the silicon-carbon of amorphous silicon by chemical vapor deposition is silane and porous carbon. The silane has very active chemical properties, and a slight leakage will cause explosion, which is very dangerous in production. In order to solve this problem, Chinese patent application CN 119340347A discloses a porous carbon loaded nanosilicon negative electrode and a preparation method thereof. The silicon-carbon negative electrode material is prepared by using a two-stage electrochemical method, hoping to reduce the danger caused by high-temperature cracking of silane, and certain effect has been achieved. However, the method has the following disadvantages: the raw material needs to use expensive ionic liquid, which is difficult to industrialize; the supporting electrolyte uses organic ammonium salt, and the residual ammonia nitrogen will affect the initial efficiency of the material; and ultra-high voltage is needed for coating, which is difficult for the conductive metal foil to withstand. The prepared amorphous silicon-carbon negative electrode material has low capacity and initial efficiency. SUMMARY

[0004] In order to overcome the problems in the prior art, the application provides a microcrystalline silicon-carbon composite material and a preparation method and application thereof. The prepared composite material has high capacity and initial coulombic efficiency, the preparation process is safe, the cost is low, and the industrialization is easy.

[0005] To solve the above technical problems, the technical scheme provided by the application is as follows:

[0006] The application provides a preparation method of a microcrystalline silicon-carbon composite material, comprising the following steps:

[0007] S1, preparing a working electrode.

[0008] S2, adding an electrolyte into a strong polar solvent, and then adding alkylsilane or / and halogenated alkylsilane to configure an electrolyte; the strong polar solvent is a solvent capable of dissolving alkylsilane or halogenated alkylsilane and not reacting with the same.

[0009] S3, using the working electrode in S1, the electrolyte in S2, a reference electrode and a counter electrode to assemble a three-electrode electrolytic cell system for electrolysis, and the voltage is-2.0 to-5.0 V.

[0010] S4, after electrolysis, the working electrode is cleaned with organic solvent, and then microcrystalline silicon-carbon composite material is obtained after carbonization.

[0011] In the present application, alkylsilane or halogenated alkylsilane is added in strong polar solvent, which is beneficial to the dissolution of silicon source, and then electrolyte is prepared by adding electrolyte. Microcrystalline silicon is generated on the electrode of the working electrode under the voltage condition of-2.0 to-5.0V by using a three-electrode system. After carbonization, the electrolyte which is not cleaned completely and the light components which are formed during electrolysis are removed, and microcrystalline silicon-carbon composite material with high initial coulomb efficiency is obtained. If the voltage is greater than-5.0V, the strong polar solution in the electrolyte will be decomposed. If the voltage is less than-2.0V, the electrolysis power will be insufficient, and microcrystalline silicon cannot be generated on the electrode.

[0012] As an optional embodiment, in the preparation method provided by the present application, in S1, the porous material matrix is mixed with the binder, and then coated on the metal conductive plate or the carbon graphite material conductive plate to prepare the working electrode.

[0013] As an optional embodiment, in the preparation method provided by the present application, in S1, the porous material is mixed with the binder to prepare a growing strip-shaped or cylindrical working electrode.

[0014] As an optional embodiment, in the preparation method provided by the present application, in S1, the porous material is selected from one or both of porous carbon and porous graphite.

[0015] As an optional embodiment, in the preparation method provided by the present application, in S2, the electrolyte is selected from one or more of LiCl, NaCl, KCl, LiClO, NaClO, KClO, LiClO4, NaClO4, KClO4, LiBr, NaBr and KBr.

[0016] The electrolyte in the prior art is an organic ammonium salt electrolyte, such as tetrabutylammonium chloride, tetrabutylammonium bromide, etc. The organic electrolyte and its decomposition products of this type will remain in the sample and cannot be cleaned completely, thereby affecting the initial efficiency. At the same time, the residual organic ammonium salt is an impurity which will react with the electrolyte of the lithium ion battery, thereby producing gas and affecting the cycle. In the present technology, all inorganic electrolytes are used. This type of electrolyte will not leave organic light components, and in the later application of silicon-carbon material, it can also be used as the electrolyte of the lithium ion battery, which is a beneficial additive, and thus the initial efficiency can be improved.

[0017] Further, LiCl is preferred.

[0018] As an optional embodiment, in the preparation method provided by the application, the concentration of the electrolyte in the electrolyte solution in S2 is 0.01-0.3 mol / L.

[0019] In the application, the concentration of the electrolyte is controlled to be 0.01-0.3 mol / L, which is beneficial to the dissolution of the electrolyte.

[0020] Further, the concentration is preferably 0.1 mol / L.

[0021] As an optional embodiment, in the preparation method provided by the application, in S2, the chemical formula of the alkylsilane is R n SiH 4-n wherein R represents an alkyl group, n represents the number of the alkyl groups connected to the silicon atom, and n is 1-4.

[0022] Further, the alkylsilane is preferably propylsilane or tetramethylsilane.

[0023] As an optional embodiment, in the preparation method provided by the application, in S2, the chemical formula of the halogenated alkylsilane is R a X b SiH 4-(a+b) wherein R represents an alkyl group, X represents a halogen atom, a represents the number of the alkyl groups, b represents the number of the halogen atoms, and a≥0, b≥1, and a+b≤4 are required.

[0024] Further, the halogenated alkylsilane is preferably SiCl4 or SiHCl3.

[0025] As an optional embodiment, in the preparation method provided by the application, in S2, the concentration of the alkylsilane or halogenated alkylsilane in the solution is 0.1-0.8 mol / L.

[0026] In the application, the concentration of the alkylsilane or halogenated alkylsilane is controlled to be 0.1-0.8 mol / L, which is beneficial to the dissolution of the silicon source. Further, the concentration of the alkylsilane or halogenated alkylsilane is preferably 0.5 mol / L.

[0027] As an optional implementation, in the preparation method provided by the present application, in S2, the strong polar solvent is selected from one or more of propylene carbonate solution (PC), N-methyl pyrrolidone solution (NMP), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), ethylene glycol dimethyl ether (DME), ethyl acetate (EA), methyl propionate (MP), 1,3-dioxolane (DOL), dimethyl formamide (DMF), dimethylacetamide (DMAc), acetonitrile (CH3CN), dimethyl sulfoxide (DMSO), hexamethylphosphoramide (HMPA), methyl ethyl ketone (MEK), dichloromethane (CH2Cl2), chloroform (CHCl3) or tetrahydrofuran (THF).

[0028] The strong polar solvent in the present application is beneficial to the dissolution of the silicon source and is more conducive to the generation of microcrystalline silicon.

[0029] As an optional implementation, in the preparation method provided by the present application, in S4, the carbonization temperature is 200-400℃.

[0030] In the present application, the carbonization temperature is controlled to be 200-400℃, and the residual organic solvent and light components will decompose and escape at this temperature range, thereby further improving the initial efficiency of the material. If the temperature is lower than this range, the light components and the organic solvent cannot be completely volatilized, and if the temperature is higher than this range, the generated microcrystalline silicon material will rapidly grow into crystalline silicon, which is not conducive to the circulation and expansion of the material.

[0031] As an optional implementation, in the preparation method provided by the present application, in S4, the working electrode is sequentially cleaned with propylene carbonate solution, alcohol and acetone.

[0032] Based on the same technical concept, the present application also provides a microcrystalline silicon-carbon composite material prepared by the above preparation method, wherein the composite material is composed of porous carbon particles and silicon, the silicon is deposited in the interior of the porous carbon particles and between the porous carbon particles, point analysis is performed on a specific micro area of the microcrystalline silicon-carbon composite material by using a scanning electron microscope equipped with an energy dispersive X-ray spectrometer, the mass content of the silicon deposited between the porous carbon particles is ≥50%, the mass content of the silicon deposited in the interior of the porous carbon particles is ≤10%, the silicon deposited between the porous carbon particles is microcrystalline silicon, and the grain size of the microcrystalline silicon is 2.0-5.1nm.

[0033] Based on the same technical concept, the present application also provides an application of the microcrystalline silicon-carbon composite material prepared by the above preparation method in a lithium battery negative electrode material.

[0034] Compared with the prior art, the present application has the following beneficial effects:

[0035] (1) The present invention provides a method for preparing microcrystalline silicon-carbon composite material. Compared with the existing process, the preparation process does not use silane gas, has no risk of explosion, and is highly safe.

[0036] (2) The strong polar solvent added during the preparation process of this invention is a substance contained in the electrolyte during the preparation of lithium-ion batteries. It has good adaptability and good downstream compatibility. More importantly, this strong polar solvent is conducive to the dissolution of silicon source and makes it easier to promote the formation of microcrystalline silicon.

[0037] (3) In the prior art, crystalline silicon has fewer lattice defects, resulting in more efficient lithium-ion bonding and generally higher capacity and initial efficiency, but poor cycling and expansion performance. The microcrystalline silicon prepared in this invention is the opposite, producing carbon composite materials with high capacity and initial efficiency. The preparation process is environmentally friendly, without the use of organic ammonium salts or the need for extensive solution cleaning. It has good industrialization prospects, as it does not require expensive ionic liquids. Attached Figure Description

[0038] 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 some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 The XRD pattern of the microcrystalline silicon-carbon composite material prepared in Example 1;

[0040] Figure 2 SEM image of the microcrystalline silicon-carbon composite material prepared in Example 1;

[0041] Figure 3 The image shows a cross-sectional SEM image of the microcrystalline silicon-carbon composite material prepared in Example 1.

[0042] Figure 4 for Figure 3 The cross-sectional SEM image corresponds to the EDS image. Detailed Implementation

[0043] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0044] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0045] Unless otherwise specifically indicated, all materials, reagents, and equipment used in the present application are commercially available or are prepared by known methods.

[0046] Example 1

[0047] The microcrystalline silicon-carbon composite material of the present example is prepared by the following method:

[0048] A three-electrode electrolytic cell is constructed using graphite as the counter electrode and platinum as the reference electrode. The porous carbon mixed binder is coated on a copper foil as the working electrode. Lithium chloride and propylsilane are added to dimethyl sulfoxide solution to configure a 0.1 mol / L LiCl, 0.5 mol / L propylsilane solution. The solution is poured into the three-electrode electrolytic cell, and a voltage of -4.0 V is applied using an electrochemical workstation for constant potential electrolysis for 2 h, after which the electrode is removed and sequentially cleaned with propylene carbonate (PC), alcohol, and acetone and dried, and low-temperature carbonization is performed at 350°C. The microcrystalline silicon-carbon composite material of the present example is obtained.

[0049] Example 2

[0050] The microcrystalline silicon-carbon composite material of the present example is prepared by the following method:

[0051] A three-electrode electrolytic cell is constructed using graphite as the counter electrode and platinum as the reference electrode. The porous carbon mixed binder is coated on a copper foil as the working electrode. Lithium chloride and silicon tetrachloride are added to N-methyl pyrrolidone solution to configure a 0.1 mol / L LiCl, 0.5 mol / L SiCl4 solution. The solution is poured into the three-electrode electrolytic cell, and a voltage of -4.0 V is applied using an electrochemical workstation for constant potential electrolysis for 2 h, after which the electrode is removed and sequentially cleaned with propylene carbonate (PC), alcohol, and acetone and dried, and low-temperature carbonization is performed at 350°C. The microcrystalline silicon-carbon composite material of the present example is obtained.

[0052] Example 3

[0053] The microcrystalline silicon-carbon composite material of the present example is prepared by the following method:

[0054] A three-electrode electrolytic cell was constructed using graphite as the counter electrode and platinum sheet as the reference electrode. Porous carbon mixed with binder was coated on a copper foil as the working electrode. Lithium chloride and silicon tetrachloride were added to a 1:1 mixed solution of propylene carbonate and N-methyl pyrrolidone to configure a 0.1 mol / L LiCl, 0.5 mol / L SiCl4solution. The solution was poured into the three-electrode electrolytic cell, and a voltage of -4.0 V was applied using an electrochemical workstation for constant potential electrolysis for 2 h, after which the electrode was taken out, washed with propylene carbonate (PC), alcohol, and acetone in sequence, and dried, and low-temperature carbonization was performed at 350°C. The microcrystalline silicon-carbon composite material of the present example was obtained.

[0055] Example 4

[0056] The microcrystalline silicon-carbon composite material of the present example was prepared by the following method:

[0057] A three-electrode electrolytic cell was constructed using graphite as the counter electrode and platinum sheet as the reference electrode. Porous carbon mixed with binder was coated on a copper foil as the working electrode. Lithium chloride and silicon tetrachloride were added to a 1:1 mixed solution of propylene carbonate and N-methyl pyrrolidone to configure a 0.1 mol / L LiCl, 0.5 mol / L SiCl4solution. The solution was poured into the three-electrode electrolytic cell, and a voltage of -4.0 V was applied using an electrochemical workstation for constant potential electrolysis for 2 h, after which the electrode was taken out, washed with propylene carbonate (PC), alcohol, and acetone in sequence, and dried, and low-temperature carbonization was performed at 350°C. The microcrystalline silicon-carbon composite material of the present example was obtained.

[0058] Example 5

[0059] The microcrystalline silicon-carbon composite material of the present example was prepared by the following method:

[0060] A three-electrode electrolytic cell was constructed using graphite as the counter electrode and platinum sheet as the reference electrode. Porous carbon mixed with binder was coated on a copper foil as the working electrode. Lithium chloride and silicon tetrachloride were added to a 1:1 mixed solution of propylene carbonate and N-methyl pyrrolidone to configure a 0.1 mol / L LiCl, 0.5 mol / L SiCl4solution. The solution was poured into the three-electrode electrolytic cell, and a voltage of -4.0 V was applied using an electrochemical workstation for constant potential electrolysis for 2 h, after which the electrode was taken out, washed with propylene carbonate (PC), alcohol, and acetone in sequence, and dried, and low-temperature carbonization was performed at 350°C. The microcrystalline silicon-carbon composite material of the present example was obtained.

[0061] Example 6

[0062] The microcrystalline silicon-carbon composite material of the present example was prepared by the following method:

[0063] A three-electrode electrolytic cell was constructed using graphite as the counter electrode and platinum sheet as the reference electrode. The porous carbon mixed with binder was coated on the copper foil as the working electrode. Propylene carbonate was added with lithium chloride and silicon tetrachloride to configure a 0.1 mol / L LiCl, 0.1 mol / L SiCl4solution. The solution was poured into the three-electrode electrolytic cell, and a voltage of -4.0 V was applied for constant potential electrolysis for 2 h using an electrochemical workstation, after which the electrode was taken out, sequentially cleaned with propylene carbonate (PC), alcohol, and acetone, and dried, and low-temperature carbonization was performed at 350°C. The microcrystalline silicon-carbon composite material of the present example was obtained.

[0064] Example 7

[0065] The microcrystalline silicon-carbon composite material of the present example was prepared by the following method:

[0066] A three-electrode electrolytic cell was constructed using graphite as the counter electrode and platinum sheet as the reference electrode. The porous carbon mixed with binder was coated on the copper foil as the working electrode. Propylene carbonate was added with lithium chloride and silicon tetrachloride to configure a 0.05 mol / L LiCl, 0.05 mol / L NaCl, 0.5 mol / L SiCl4solution. The solution was poured into the three-electrode electrolytic cell, and a voltage of -4.0 V was applied for constant potential electrolysis for 2 h using an electrochemical workstation, after which the electrode was taken out, sequentially cleaned with propylene carbonate (PC), alcohol, and acetone, and dried, and low-temperature carbonization was performed at 350°C. The microcrystalline silicon-carbon composite material of the present example was obtained.

[0067] Example 8

[0068] The microcrystalline silicon-carbon composite material of the present example was prepared by the following method:

[0069] A three-electrode electrolytic cell was constructed using graphite as the counter electrode and platinum sheet as the reference electrode. The porous carbon mixed with binder was coated on the copper foil as the working electrode. Propylene carbonate was added with lithium chloride and silicon tetrachloride to configure a 0.1 mol / L LiCl, 0.1 mol / L SiCl4solution. The solution was poured into the three-electrode electrolytic cell, and a voltage of -4.0 V was applied for constant potential electrolysis for 2 h using an electrochemical workstation, after which the electrode was taken out, sequentially cleaned with propylene carbonate (PC), alcohol, and acetone, and dried, and low-temperature carbonization was performed at 350°C. The microcrystalline silicon-carbon composite material of the present example was obtained.

[0070] Example 9

[0071] A three-electrode electrolytic cell was constructed using graphite as the counter electrode and platinum sheet as the reference electrode. The porous carbon mixed with binder was coated on the copper foil as the working electrode. Lithium chloride and silicon tetrachloride were added to propylene carbonate to configure a 0.1 mol / L LiCl, 0.8 mol / L SiCl4 solution. The solution was poured into the three-electrode electrolytic cell, and a voltage of -4.0 V was applied using an electrochemical workstation for constant potential electrolysis for 2 h, after which the electrode was taken out, sequentially cleaned with propylene carbonate (PC), alcohol, and acetone, and dried, and low-temperature carbonization was performed at 350°C. The microcrystalline silicon-carbon composite material of the present example was obtained.

[0072] Example 10

[0073] The microcrystalline silicon-carbon composite material of the present example was prepared by the following method:

[0074] A three-electrode electrolytic cell was constructed using graphite as the counter electrode and platinum sheet as the reference electrode. The porous carbon mixed with binder was coated on the copper foil as the working electrode. Lithium chloride and silicon tetrachloride were added to propylene carbonate to configure a 0.1 mol / L LiCl, 0.5 mol / L SiHCl3 solution. The solution was poured into the three-electrode electrolytic cell, and a voltage of -4.0 V was applied using an electrochemical workstation for constant potential electrolysis for 2 h, after which the electrode was taken out, sequentially cleaned with propylene carbonate (PC), alcohol, and acetone, and dried, and low-temperature carbonization was performed at 350°C. The microcrystalline silicon-carbon composite material of the present example was obtained.

[0075] Example 11

[0076] The microcrystalline silicon-carbon composite material of the present example was prepared by the following method:

[0077] A three-electrode electrolytic cell was constructed using graphite as the counter electrode and platinum sheet as the reference electrode. The porous carbon mixed with binder was coated on the copper foil as the working electrode. Lithium chloride and silicon tetrachloride were added to propylene carbonate to configure a 0.1 mol / L LiCl, 0.25 mol / L SiCl4 solution, 0.25 mol / L SiHCl3 solution. The solution was poured into the three-electrode electrolytic cell, and a voltage of -4.0 V was applied using an electrochemical workstation for constant potential electrolysis for 2 h, after which the electrode was taken out, sequentially cleaned with propylene carbonate (PC), alcohol, and acetone, and dried, and low-temperature carbonization was performed at 350°C. The microcrystalline silicon-carbon composite material of the present example was obtained.

[0078] Example 12

[0079] The microcrystalline silicon-carbon composite material of the present example was prepared by the following method:

[0080] A three-electrode electrolytic cell was constructed using graphite as the counter electrode and platinum sheet as the reference electrode. Porous carbon mixed with binder was coated on a copper foil as the working electrode. Lithium chloride and silicon tetrachloride were added to propylene carbonate to configure a 0.1 mol / L LiCl, 0.5 mol / L SiCl4 solution. The solution was poured into the three-electrode electrolytic cell, and a voltage of -2.0 V was applied using an electrochemical workstation for potentiostatic electrolysis for 2 h, after which the electrode was taken out, sequentially cleaned with propylene carbonate (PC), alcohol, and acetone, and dried, and low-temperature carbonization was performed at 350°C. The microcrystalline silicon-carbon composite material of this example was obtained.

[0081] Example 13

[0082] The microcrystalline silicon-carbon composite material of this example was prepared by the following method:

[0083] A three-electrode electrolytic cell was constructed using graphite as the counter electrode and platinum sheet as the reference electrode. Porous carbon mixed with binder was coated on a copper foil as the working electrode. Lithium chloride and silicon tetrachloride were added to propylene carbonate to configure a 0.1 mol / L LiCl, 0.5 mol / L SiCl4 solution. The solution was poured into the three-electrode electrolytic cell, and a voltage of -5.0 V was applied using an electrochemical workstation for potentiostatic electrolysis for 2 h, after which the electrode was taken out, sequentially cleaned with propylene carbonate (PC), alcohol, and acetone, and dried, and low-temperature carbonization was performed at 350°C. The microcrystalline silicon-carbon composite material of this example was obtained.

[0084] Example 14

[0085] The microcrystalline silicon-carbon composite material of this example was prepared by the following method:

[0086] A three-electrode electrolytic cell was constructed using graphite as the counter electrode and platinum sheet as the reference electrode. Porous carbon mixed with binder was coated on a copper foil as the working electrode. Lithium chloride and silicon tetrachloride were added to propylene carbonate to configure a 0.1 mol / L LiCl, 0.5 mol / L SiCl4 solution. The solution was poured into the three-electrode electrolytic cell, and a voltage of -4.0 V was applied using an electrochemical workstation for potentiostatic electrolysis for 4 h, after which the electrode was taken out, sequentially cleaned with propylene carbonate (PC), alcohol, and acetone, and dried, and low-temperature carbonization was performed at 350°C. The microcrystalline silicon-carbon composite material of this example was obtained.

[0087] Example 15

[0088] The microcrystalline silicon-carbon composite material of this example was prepared by the following method:

[0089] A three-electrode electrolytic cell was constructed using graphite as the counter electrode and platinum as the reference electrode. Porous carbon mixed with a binder was coated on a copper foil as the working electrode. Lithium chloride and silicon tetrachloride were added to propylene carbonate to form a 0.1 mol / L LiCl, 0.5 mol / L SiCl4 solution. The solution was poured into the three-electrode electrolytic cell, and a voltage of -4.0 V was applied using an electrochemical workstation for potentiostatic electrolysis for 2 h. The electrode was then removed, washed with propylene carbonate (PC), alcohol, and acetone in sequence, and dried, and low-temperature carbonization was performed at 200°C. The microcrystalline silicon-carbon composite material of this example was obtained.

[0090] Example 16

[0091] The microcrystalline silicon-carbon composite material of this example was prepared by the following method:

[0092] A three-electrode electrolytic cell was constructed using graphite as the counter electrode and platinum as the reference electrode. Porous carbon mixed with a binder was coated on a copper foil as the working electrode. Lithium chloride and silicon tetrachloride were added to propylene carbonate to form a 0.1 mol / L LiCl, 0.5 mol / L SiCl4 solution. The solution was poured into the three-electrode electrolytic cell, and a voltage of -4.0 V was applied using an electrochemical workstation for potentiostatic electrolysis for 2 h. The electrode was then removed, washed with propylene carbonate (PC), alcohol, and acetone in sequence, and dried, and low-temperature carbonization was performed at 400°C. The microcrystalline silicon-carbon composite material of this example was obtained.

[0093] Example 17

[0094] The microcrystalline silicon-carbon composite material of this example was prepared by the following method:

[0095] A three-electrode electrolytic cell was constructed using graphite as the counter electrode and platinum as the reference electrode. Porous carbon mixed with a binder was prepared into a vertical strip-shaped solid-state electrode as the working electrode. Lithium chloride and silicon tetrachloride were added to N-methyl pyrrolidone solution to form a 0.1 mol / L LiCl, 0.5 mol / L SiCl4 solution. The solution was poured into the three-electrode electrolytic cell, and a voltage of -4.0 V was applied using an electrochemical workstation for potentiostatic electrolysis for 2 h. The electrode was then removed, washed with PC, alcohol, and acetone in sequence, and dried, and low-temperature carbonization was performed at 350°C. The microcrystalline silicon-carbon composite material of this example was obtained.

[0096] Example 18

[0097] A three-electrode electrolytic cell was constructed using graphite as the counter electrode and platinum sheet as the reference electrode. The porous carbon mixed with binder was coated on the copper foil as the working electrode. Lithium chloride and silicon tetrachloride were added to the propylene carbonate solution to configure a 0.1 mol / L LiCl, 1.5 mol / L SiCl4solution. The solution was poured into the three-electrode electrolytic cell, and a voltage of -4.0 V was applied for constant potential electrolysis for 2 h using an electrochemical workstation. After that, the electrode was taken out, washed with propylene carbonate (PC), alcohol, and acetone in sequence, and dried, and low-temperature carbonization was performed at 100°C. A microcrystalline silicon-carbon composite material was obtained.

[0098] Example 19

[0099] A three-electrode electrolytic cell was constructed using graphite as the counter electrode and platinum sheet as the reference electrode. The porous carbon mixed with binder was coated on the copper foil as the working electrode. Lithium chloride and silicon tetrachloride were added to the propylene carbonate solution to configure a 0.1 mol / L LiCl, 1.5 mol / L SiCl4solution. The solution was poured into the three-electrode electrolytic cell, and a voltage of -4.0 V was applied for constant potential electrolysis for 2 h using an electrochemical workstation. After that, the electrode was taken out, washed with propylene carbonate (PC), alcohol, and acetone in sequence, and dried, and low-temperature carbonization was performed at 600°C. A silicon-carbon composite material was obtained.

[0100] Comparative Example 1

[0101] A three-electrode electrolytic cell was constructed using graphite as the counter electrode and platinum sheet as the reference electrode. The porous carbon mixed with binder was coated on the copper foil as the working electrode. Lithium chloride and silicon tetrachloride were added to the propylene carbonate solution to configure a 0.1 mol / L LiCl, 1.5 mol / L SiCl4solution. The solution was poured into the three-electrode electrolytic cell, and a voltage of -4.0 V was applied for constant potential electrolysis for 2 h using an electrochemical workstation. After that, the electrode was taken out, washed with propylene carbonate (PC), alcohol, and acetone in sequence, and dried, and low-temperature carbonization was performed at 600°C. A silicon-carbon composite material was obtained.

[0102] Comparative Example 2

[0103] A three-electrode electrolytic cell was constructed using graphite as the counter electrode and platinum sheet as the reference electrode. The porous carbon mixed with binder was coated on the copper foil as the working electrode. Lithium chloride and silicon tetrachloride were added to the propylene carbonate solution to configure a 0.1 mol / L LiCl, 1.5 mol / L SiCl4solution. The solution was poured into the three-electrode electrolytic cell, and a voltage of -4.0 V was applied for constant potential electrolysis for 2 h using an electrochemical workstation. After that, the electrode was taken out, washed with propylene carbonate (PC), alcohol, and acetone in sequence, and dried, and low-temperature carbonization was performed at 600°C. A silicon-carbon composite material was obtained.

[0104] Comparative Example 3

[0105] A three-electrode electrolytic cell was constructed using graphite as the counter electrode and platinum sheet as the reference electrode. The porous carbon mixed with binder was coated on the copper foil as the working electrode. Lithium chloride and ethyl silicate (TEOS) were added to the propylene carbonate solution to configure a 0.1 mol / L LiCl, 0.5 mol / L TEOS solution. The solution was poured into the three-electrode electrolytic cell, and a voltage of -4.0 V was applied for 2 h using an electrochemical workstation for constant potential electrolysis, after which the electrode was taken out and sequentially cleaned with propylene carbonate (PC), alcohol, and acetone and dried, and low-temperature carbonization was performed at 350°C. A microcrystalline silicon-carbon composite material was obtained.

[0106] Comparative Example 4

[0107] A three-electrode electrolytic cell was constructed using graphite as the counter electrode and platinum sheet as the reference electrode. The porous carbon mixed with binder was coated on the copper foil as the working electrode. Lithium chloride and silicon tetrachloride were added to the propylene carbonate solution to configure a 0.1 mol / L LiCl, 0.5 mol / L SiCl4 solution. The solution was poured into the three-electrode electrolytic cell, and a voltage of -8.0 V was applied for 2 h using an electrochemical workstation for constant potential electrolysis, after which the electrode was taken out and sequentially cleaned with propylene carbonate (PC), alcohol, and acetone and dried, and low-temperature carbonization was performed at 350°C. A microcrystalline silicon-carbon composite material was obtained.

[0108] Comparative Example 5

[0109] A three-electrode electrolytic cell was constructed using graphite as the counter electrode and platinum sheet as the reference electrode. The porous carbon mixed with binder was coated on the copper foil as the working electrode. Lithium chloride and silicon tetrachloride were added to the propylene carbonate solution to configure a 0.1 mol / L LiCl, 0.5 mol / L SiCl4 solution. The solution was poured into the three-electrode electrolytic cell, and a voltage of -8.0 V was applied for 2 h using an electrochemical workstation for constant potential electrolysis, after which the electrode was taken out and sequentially cleaned with propylene carbonate (PC), alcohol, and acetone and dried, and low-temperature carbonization was performed at 350°C. A microcrystalline silicon-carbon composite material was obtained.

[0110] Comparative Example 6

[0111] A three-electrode electrolytic cell was constructed using graphite as the counter electrode and platinum sheet as the reference electrode. The porous carbon mixed with binder was coated on the copper foil as the working electrode. Lithium chloride and silicon tetrachloride were added to the propylene carbonate solution to configure a 0.1 mol / L LiCl, 0.5 mol / L SiCl4 solution. The solution was poured into the three-electrode electrolytic cell, and a voltage of -4.0 V was applied for 2 h using an electrochemical workstation for constant potential electrolysis, after which the electrode was taken out and sequentially cleaned with propylene carbonate (PC), alcohol, and acetone and dried, and low-temperature carbonization was performed at 350°C. A microcrystalline silicon-carbon composite material was obtained.

[0112] The microcrystalline silicon-carbon composite material prepared in Example 1 was subjected to performance detection, and the XRD pattern is as shown inFigure 1 As shown, by Figure 1 It can be seen that a weak characteristic peak of silicon appears at the position of 2Theta 28.6°, indicating that microcrystalline silicon has been formed. According to the Scherrer formula, the grain size of the microcrystalline silicon is 3.6 nm.

[0113] SEM images of the microcrystalline silicon-carbon composite material prepared in Example 1 are attached. Figure 2 As shown, by Figure 2 It can be seen that the generated silicon is uniformly distributed between the electrode particles. A cross-sectional SEM image of the microcrystalline silicon-carbon composite material prepared in Example 1 is attached. Figure 3 As shown, by Figure 3 It was found that silicon was deposited both inside and between the porous carbon particles. Point analysis of specific micro-regions of the sample was performed using a scanning electron microscope equipped with an energy-dispersive X-ray spectrometer. Figure 3 The cross-sectional SEM image corresponds to the EDS image as follows: Figure 4 As shown, one point between porous carbon particles was selected for EDS spot scanning. The energy dispersive spectroscopy data showed that Si accounted for 90.13% of the elemental composition at this point. Two points inside the porous carbon particles were selected for EDS spot scanning. The energy dispersive spectroscopy data showed that Si accounted for only 3.97% of the elemental composition at this point. This indicates that most of the silicon is deposited between the particles, with the silicon content between the particles reaching more than 50%, while the silicon content inside the particles is relatively low.

[0114] The silicon-carbon materials prepared in the examples and comparative examples were tested according to GB / T 38823-2020 Silicon-Carbon, and the test results are shown in Table 1 below.

[0115] Table 1: Performance Test Results of Silicon-Carbon Materials

[0116]

[0117] As can be seen from Table 1, the microcrystalline silicon carbon negative electrode material prepared in Example 1 has a silicon grain size of 3.6 nm, a specific capacity of 2215 mAh / g, and a first efficiency of 91.6%, and has the best comprehensive performance. The silicon grain size of the remaining examples is all above 2.5 nm, and the specific capacity and first efficiency are above 1600 mAh / g and 85%, respectively. In Example 18, the silicon source concentration is too large, which causes the solution to separate, low electrolysis efficiency, low capacity, and too low carbonization temperature, resulting in incomplete volatilization of light components and low first efficiency. In Example 19, the carbonization temperature is too high, resulting in a sharp increase in silicon grain size, generating crystalline silicon instead of microcrystalline silicon. Although the capacity and first efficiency are both acceptable, the large grain size will affect the cycle and expansion performance of the silicon carbon material. In Comparative Example 1, the ethanol solvent will react with the halogenated alkylsilane, and the purity and voltage window limit will result in almost no electrolysis. In Comparative Example 2, without adding electrolyte, the capacity and first efficiency values are low. In Comparative Example 3, other ester silicon sources will also affect the capacity and first efficiency. In Comparative Example 4, the high electrolysis voltage will cause the silicon grains to abnormally grow, and the decomposition of the solution will result in a significant decrease in capacity and first efficiency. In Comparative Example 5, only soaking without electricity cannot form deposited silicon, and only shows the capacity of carbon particles. In Comparative Example 6, without carbonization, the number of heteroatoms is large, and the capacity and first efficiency are low.

[0118] The above is a further detailed description of the present application in combination with specific preferred embodiments, and cannot be considered as limiting the specific implementation of the present application to these descriptions. For ordinary skilled persons in the field to which the present application belongs, several simple deductions or substitutions can be made without departing from the concept of the present application, and all should be considered as falling within the protection scope of the present application.

Claims

1. A method for producing a microcrystalline silicon-carbon composite material, characterized by, The method comprises the following steps: S1, mixing porous carbon and a binder to prepare a working electrode coated on a conductive plate; S2, adding an inorganic electrolyte to a strong polar solvent, and then adding alkylsilane or / and halogenated alkylsilane to configure an electrolyte, wherein the concentration of the alkylsilane or halogenated alkylsilane in the electrolyte is 0.1-0.8 mol / L; the strong polar solvent is a solvent capable of dissolving the alkylsilane or halogenated alkylsilane and not reacting with the alkylsilane or halogenated alkylsilane; the electrolyte is selected from one or more of LiCl, NaCl, KCl, LiClO, NaClO, KClO, LiClO4, NaClO4, KClO4, LiBr, NaBr and KBr; S3, using the working electrode in S1, the electrolyte in S2, a reference electrode and a counter electrode to assemble a three-electrode electrolytic cell system for electrolysis, and the voltage is-2.0--5.0V; S4, after the electrolysis, cleaning the working electrode with an organic solvent, and carbonizing at 200-400 ℃ to obtain a microcrystalline silicon-carbon composite material.

2. The production method according to claim 1, characterized by, In S2, the chemical formula of the alkylsilane is R n SiH 4-n where R represents an alkyl group, n represents the number of alkyl groups attached to the silicon atom, and n has a value of 1 to 4; The halogenated alkylsilane has a general formula of R a X b SiH 4-(a+b) wherein R represents an alkyl group, X represents a halogen atom, a represents the number of alkyl groups, b represents the number of halogen atoms, and a≥0, b≥1, a+b≤4 are satisfied.

3. The preparation method according to claim 1, characterized in that, In S2, the alkylsilane is selected from one or both of propylsilane and tetramethylsilane; and the halogenated alkylsilane is selected from one or both of SiCl4 and SiHCl3.

4. The production method according to claim 1, characterized by, In S2, the strong polar solvent is selected from one or more of propylene carbonate solution, N-methylpyrrolidone solution, ethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene glycol dimethyl ether, ethyl acetate, methyl propionate, 1,3-dioxolane, dimethylformamide, dimethylacetamide, acetonitrile, dimethyl sulfoxide, hexamethylphosphoramide, methyl ethyl ketone, dichloromethane, chloroform and tetrahydrofuran.

5. The preparation method according to claim 1, characterized in that, In S2, the concentration of the electrolyte in the electrolyte is 0.01-0.3 mol / L.

6. The method of claim 1, wherein, In S4, the working electrode is sequentially cleaned with propylene carbonate solution, alcohol and acetone.

7. The microcrystalline silicon-carbon composite material produced by the production method according to any one of claims 1 to 6, characterized by The composite material is composed of porous carbon particles and silicon, the silicon is deposited in the interior of the porous carbon particles and between the porous carbon particles, point analysis of a specific micro area of the microcrystalline silicon-carbon composite material is performed by a scanning electron microscope equipped with an energy dispersive X-ray spectrometer, the mass content of the silicon deposited between the porous carbon particles is ≥50%, the mass content of the silicon deposited in the interior of the porous carbon particles is ≤10%, the silicon deposited between the porous carbon particles is microcrystalline silicon, and the grain size of the microcrystalline silicon is 2.0-5.1 nm.

8. Application of a microcrystalline silicon-carbon composite material prepared by the preparation method in any one of claims 1-6 to a lithium battery negative electrode material.

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