Preparation method for silicon-carbon composite negative electrode material and use thereof

Abstract

The present invention relates to a preparation method for a silicon-carbon composite negative electrode material, comprising the following steps: (P1) co-polymerization: co-dissolving an unsaturated organic acid, an acrylate monomer and an acrylamide monomer in water at a specific ratio, and co-polymerizing same under the action of a sacrificial agent of a saturated organic acid and an initiator to obtain a suspension containing an acrylic copolymer; (P2) alkali treatment: performing an alkali treatment and filtration on the suspension to obtain copolymer particles; (P3) in-situ polymerization: performing in-situ polymerization of phenolic aldehyde on the surfaces of the copolymer particles to obtain a composite resin of a phenolic aldehyde-coated acrylic copolymer; (P4) heat treatment: performing a heat treatment on the composite resin in an oxidizing gas atmosphere to obtain porous carbon; and (P5) performing silicon deposition and carbon coating on the porous carbon to obtain the silicon-carbon composite negative electrode material. When the silicon-carbon composite negative electrode material prepared in the present invention is used in a lithium battery, the volume expansion of silicon can be effectively relieved, and the cycling performance and charge-discharge capacity of a lithium-ion battery are improved.

Description

Preparation method and application of silicon-carbon composite anode material Technical Field

[0001] This invention belongs to the field of battery anode material technology, specifically relating to a method for preparing and applying a silicon-carbon composite anode material. Background Technology

[0002] Porous carbon materials have shown great promise in the field of electrochemical energy storage due to their high specific surface area, well-developed pore structure, and excellent conductivity. However, carbon has a limited theoretical specific capacity, while silicon boasts a theoretical specific capacity as high as 4200 mAh / g. However, silicon's significant volume expansion can cause material structure collapse and electrode flaking and pulverization, thus affecting battery cycle performance. Therefore, the preparation of silicon-carbon composite anode materials by combining silicon with porous carbon is currently a major development trend. Existing technologies generally achieve silicon-carbon composite anode materials by preparing core-shell or capsule-structured porous silicon-carbon materials, or by vapor-depositing silicon onto porous carbon. The former generally involves more complex preparation methods and less structural controllability; the latter is relatively simpler and offers structural control, but the performance of silicon-carbon anode materials depends on the structural properties of the porous carbon. Porous carbon used as a silicon-carbon composite anode needs to have a higher specific surface area and a stable and well-developed pore structure to provide lithium-ion batteries with greater capacity space and diffusion channels, and to mitigate silicon volume expansion during the adsorption-deintercalation process, resulting in better battery cycle stability. Traditional porous carbon material preparation processes are cumbersome and energy-intensive. To achieve the required pore volume, carbonization followed by activation and pore expansion is often necessary. Activation processes are energy-intensive, require large amounts of acids and alkalis, and are highly corrosive to equipment. Over-activation can also easily cause the pore structure to collapse, resulting in insufficient pore structure stability. Furthermore, the uniformity of pore size distribution in porous carbon prepared by the carbonization-activation method needs further improvement.

[0003] CN110224125A discloses a porous carbon-nano silicon-carbon core-shell structure material and its preparation method. This core-shell structure material uses porous carbon material as a substrate, with an intermediate embedded layer composed of nano silicon, and an outer layer encapsulating an amorphous carbon shell. The preparation method includes: pre-etching the substrate carbon material in an inert gas atmosphere, first subjecting it to medium-temperature etching, then high-temperature activation, and post-treatment to obtain the porous carbon material; mixing the porous carbon material and nano silicon in a solvent and grinding them to obtain a composite material; mixing the composite material with a carbon source in a solvent and spray granulating it, followed by heat treatment in an inert gas atmosphere. This invention improves the initial coulombic efficiency and structural stability of the material. When mixed with graphite, it can yield a highly stable silicon-carbon composite anode active material with a reversible capacity of 400–650 mAh / g. However, the porous carbon in this invention has a low porosity, resulting in limited silicon loading within the pores and a low reversible capacity.

[0004] CN115911341A discloses a porous silicon-carbon anode material. This anode material has a core-shell structure, comprising, from the inside out: a porous, sparse silicon-carbon core, a transition layer, a dense silicon-carbon layer, and a carbon coating layer. The porous carbon in the carbon skeleton structure of this invention, with its porous interstitial structure of silicon particles, provides excellent flexibility and mechanical strength, and can buffer the expansion and contraction stresses caused by lithium-ion insertion / extraction. In this porous silicon-carbon anode material, silicon particles are rationally distributed within the porous carbon and the interstitial spaces, exhibiting excellent comprehensive performance. It effectively mitigates the expansion of the silicon anode material during cycling, controls capacity decay, and improves cycle stability. However, while the cycle performance of the porous silicon-carbon anode material prepared by this invention is good, its reversible capacity still needs improvement. Summary of the Invention

[0005] To address the problems in the prior art, the present invention first forms porous carbon with a stable structure, high porosity, and uniform pore size distribution by copolymerizing unsaturated organic acids, acrylate monomers, and acrylamide monomers, followed by alkali treatment, in-situ polymerization, and heat treatment. Then, silicon deposition and carbon coating are used to form a silicon-carbon composite anode material with excellent cycle performance and high reversible capacity.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing a silicon-carbon composite anode material includes the following steps:

[0008] (P1) Copolymerization: Unsaturated organic acid, acrylate monomer, acrylamide monomer, sacrificial saturated organic acid, and initiator are dissolved together in water to form a mixed solution; then the reaction is heated and cooled to obtain a suspension containing acrylic copolymer; the molar ratio of the unsaturated organic acid, acrylate monomer, and acrylamide monomer is 1:(1.2~2):(2~3);

[0009] (P2) Alkali treatment: Add inorganic alkali to the suspension to make the pH of the suspension 8.5-9.5, then filter, wash, dry and crush to obtain acrylic copolymer particles;

[0010] (P3) In-situ polymerization: Acrylic copolymer particles and surfactants are added to a solvent to form a suspension. Then, phenolic monomers, paraformaldehyde, and an alkaline catalyst are added to the suspension, and the temperature is raised to carry out the polymerization reaction. After the reaction is completed, the mixture is filtered, dried and cured to obtain a phenolic-coated acrylic copolymer composite resin.

[0011] (P4) Heat treatment: The composite resin is heat-treated in an oxidizing gas atmosphere, cooled, washed and dried to obtain porous carbon material; the ratio of the amount of oxidizing gas to the amount of composite resin is (60-90) L: 1 kg.

[0012] (P5) Silicon deposition and carbon coating: Chemical vapor deposition is performed on porous carbon materials using organosilicon source gas, so that some or all of the nano-silicon particles are attached to the pores of the porous carbon; then, a carbon coating layer is formed by vapor deposition using a gas-phase carbon source, thus obtaining silicon-carbon composite anode material.

[0013] This invention utilizes solution polymerization of unsaturated organic acids, acrylate monomers, and acrylamide monomers in a molar ratio of 1:(1.2-2):(2-3) under the action of an initiator to form an acrylic copolymer. The side chains of this copolymer contain carboxylic acid, carboxylate, and amide groups. Because a sacrificial saturated organic acid is added during the solution polymerization in step (P1), the saturated organic acid and amide groups have strong hydrogen bonding forces, thus being introduced into the interior and surface of the acrylic copolymer. In step (P2), the inorganic base can react with the saturated organic acid to form a water-soluble salt. The dissolution of the salt creates pores on the surface of the acrylic copolymer, resulting in acrylic copolymer particles with more active sites. These numerous active sites facilitate in-situ polymerization of phenolic resin within the pores and on the surface of the acrylic copolymer particles in the subsequent step (P3) under the synergistic effect of a surfactant, forming a phenolic resin-coated acrylic copolymer composite resin. Simultaneously, in step (P2), the inorganic base can also react with some of the carboxylic acids in the side chains of the acrylic copolymer to form salts, resulting in acrylic copolymers with more carboxylic acids in the side chains, meaning the composite resin contains more carboxylic acids. In the next step (P4), when the composite resin is heat-treated in an oxidizing atmosphere, the acrylic copolymer, as a thermally unstable polymer, undergoes thermal decomposition at a relatively low temperature, generating small molecule gases. These small molecule gases escape from the matrix, thus forming pores. Phenolic resin, on the other hand, is a thermally stable polymer, resulting in a high char residue after heat treatment, thus forming a porous carbon skeleton. Because the composite resin is formed by in-situ polymerization, unlike physical blending, the resulting porous carbon skeleton has more uniform pores. Furthermore, since the side chains of the acrylic copolymer in the composite resin contain a large amount of carboxylic acids, in step (P4), these carboxylic acids react in an oxidizing atmosphere to form metal oxides and metal hydroxides. These metal oxides and metal hydroxides are also activating pore-expanding agents. Therefore, the acrylic copolymer in the composite resin acts as both a pore-forming agent and an activating pore-expanding agent in step (P4), simultaneously carbonizing and pore-forming, thus improving the structural stability of the pores. Finally, a porous carbon material with uniform pore distribution, high porosity and stable structure was obtained. The porous carbon material was then subjected to chemical vapor deposition of silicon and carbon coating to form a silicon-carbon composite anode material.

[0014] Further, in step (P1), the molar ratio of the unsaturated organic acid, acrylate monomer, and acrylamide monomer is 1:(1.4-1.8):(2.2-2.4). In this invention, unsaturated organic acid, acrylate monomer, and acrylamide monomer in any proportion can be copolymerized to obtain the composite resin required in step (P4). Unsaturated organic acid is one of the main comonomers, with high reactivity; if its proportion is too low, the copolymer is difficult to form. The carboxylate in the acrylate monomer plays a major role in activating and expanding pores in step (P4). After copolymerization, the amide groups on the side chains of the acrylamide monomer have strong hydrogen bonding with the sacrificial saturated organic acid, thereby introducing some of the saturated organic acid into the acrylic copolymer. After alkali treatment to form a salt, the salt dissolves and forms pores on the surface of the acrylic copolymer particles, thus providing more active sites for subsequent in-situ polymerization. That is, the three monomers each have different functions, and a copolymer that meets the requirements needs to be obtained within the above-mentioned range.

[0015] Further, in step (P1), the unsaturated organic acid is at least one of acrylic acid, methacrylic acid, 3,3-dimethacrylic acid, 4-pentenoic acid, and 5-hexenoic acid; the acrylate monomer is a sodium or potassium salt of an acrylic acid monomer, such as sodium acrylate, potassium acrylate, potassium methacrylate, and sodium methacrylate; and the acrylamide monomer is at least one of acrylamide, N-hydroxymethylacrylamide, and N-isopropylacrylamide.

[0016] Further, in step (P1), the sacrificial saturated organic acid is a C3-C6 saturated organic dicarboxylic acid or polycarboxylic acid, such as adipic acid, glutaric acid, succinic acid, malonic acid, or citric acid; the initiator is at least one of benzoyl peroxide (BPO) and azobisisobutyronitrile (AIBN).

[0017] Further, in step (P1), the amount of the sacrificial saturated organic acid is 6-10% of the total mass of the unsaturated organic acid, acrylate monomers, and acrylamide monomers; the amount of the initiator is 4-8% of the total mass of the unsaturated organic acid, acrylate monomers, and acrylamide monomers. The amount of initiator affects the molecular weight of the copolymer. The purpose of controlling the amount of initiator within the above range in this invention is to prevent the molecular weight of the copolymer from becoming too high.

[0018] Furthermore, in step (P1), the reaction conditions are: temperature 75–90°C, time 1.5–4 h.

[0019] Further, in step (P2), the inorganic alkali is potassium hydroxide or sodium hydroxide; the crushing is crushing to 200-1000 mesh.

[0020] Further, in step (P3), the mass ratio of acrylic copolymer particles, surfactant, and phenolic monomer is 1:(0.02-0.04):(10-15); the molar ratio of phenolic monomer to paraformaldehyde is 1:(1.5-1.6), and the molar amount of paraformaldehyde is based on the formaldehyde monomer; the amount of alkaline catalyst is 1.5-3 wt% of the phenolic monomer.

[0021] Further, in step (P3), the surfactant is an organic sodium salt, such as sodium dodecyl sulfonate, sodium succinate sulfonate, or sodium fatty alcohol polyoxyethylene ether sulfate; the solvent is an alcohol-water mixture, wherein the alcohol concentration is 15-30 wt%, and the alcohol is ethanol or propanol; the phenolic monomer is at least one of phenol, cresol, and xylenol; and the alkaline catalyst is an inorganic base, such as potassium hydroxide or sodium hydroxide.

[0022] Furthermore, in step (P3), the conditions for the polymerization reaction are: temperature of 70–90°C and time of 3–6 hours.

[0023] Further, in step (P4), the oxidizing gas is CO2 and / or O2, preferably a mixture of CO2 and O2 at a volume ratio of 1:(1-2); the heat treatment conditions are: holding at 700-900℃ for 2-4 hours. Controlling the amount of oxidizing gas is crucial. In this invention, the ratio of oxidizing gas to composite resin is (60-90) L:1 kg. If the amount exceeds this value, the composite resin is easily combusted, resulting in a low carbon residue rate; if the amount is too low, the activation and pore-expanding effect is poor.

[0024] Further, in step (P4), the washing is first acidic and then water-washed until neutral, and the acid is at least one of acetic acid, oxalic acid, and citric acid.

[0025] In step (P5), the processes of vapor-phase silicon deposition and carbon coating are well known to those skilled in the art. If an organosilicon source gas is used for vapor-phase silicon deposition, the ratio of porous carbon to organosilicon source gas is 1 kg: 150 L to 300 L, and the organosilicon source gas is selected from at least one of silane, silane, trichlorosilane, silicon tetrachloride, and silicon tetrafluoride. If a gaseous carbon source is used for carbon coating, the ratio of porous carbon to gaseous carbon source is 1 kg: 250 L to 500 L, and the gaseous carbon source is selected from at least one of C1-4 alkanes, C2-4 alkenes, and C2-4 alkynes.

[0026] Secondly, the present invention provides a silicon-carbon anode material, which is prepared by the aforementioned preparation method.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] (1) This invention uses unsaturated organic acids, acrylate monomers, and acrylamide monomers in a specific ratio to form acrylic copolymers. During the copolymerization process, the sacrificial saturated organic acid is introduced into the interior and surface of the copolymer due to its strong hydrogen bonding with the amide groups. After alkali treatment, acrylic copolymer particles with porous surfaces and numerous carboxylates in their side chains are formed. These copolymer particles are then polymerized in situ to form a phenolic resin-coated acrylic copolymer composite resin. The composite resin is finally heat-treated under a trace amount of oxidizing gas, where the acrylic copolymers decompose and escape from the matrix to form pores. Simultaneously, the carboxylates in the side chains of the acrylic copolymers form activators under the oxidizing gas atmosphere. That is, the composite resin achieves carbonization and pore formation and activation during heat treatment under a trace amount of oxidizing gas, resulting in a porous carbon material with uniform pore distribution, high porosity, and stable structure. This porous carbon material is then coated with silicon by chemical vapor deposition and carbon to finally obtain a silicon-carbon composite anode material.

[0029] (2) When the silicon-carbon composite anode material of the present invention is used in lithium batteries, it can effectively alleviate the volume expansion of silicon, improve the cycle performance and charge-discharge capacity of lithium-ion batteries, and its first reversible capacity is more than 1800mAh / g, the first coulombic efficiency is more than 90%, and the capacity retention rate after 100 cycles at 0.1C is more than 88%. Attached Figure Description

[0030] Figure 1 shows the first charge-discharge curve of the lithium battery assembled from the silicon-carbon composite anode material of Example 1 at a rate of 0.1C. Detailed Implementation

[0031] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to the following embodiments.

[0032] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; unless otherwise specified, the reagents and materials are commercially available.

[0033] Example 1

[0034] (P1) Copolymerization: First, 4-pentenoic acid, sodium acrylate, and acrylamide are prepared into a monomer mixture with a total mass of 100g by molar ratio of 1:1.2:2. Then, 100g of the monomer mixture, 7g of adipic acid, and 5g of initiator BPO are dissolved together in pure water to form a mixed solution. Then, the temperature is raised to 85℃ and reacted for 2.5h. After cooling to room temperature, a suspension containing acrylic copolymer is obtained.

[0035] (P2) Alkali treatment: Sodium hydroxide was added to the suspension and stirred for 20 min to make the pH of the suspension 9.0. Then, the suspension was filtered, washed twice with pure water, dried in an oven at 80℃ for 24 h, and crushed to 800 mesh to obtain acrylic copolymer particles.

[0036] (P3) In-situ polymerization: 10g of acrylic copolymer particles and 0.3g of fatty alcohol polyoxyethylene ether sodium sulfate were added to 1000g of ethanol-water mixture (ethanol concentration of 20wt%) under stirring to form a suspension. Then, 120g of phenol, 60g of paraformaldehyde and 2.5g of sodium hydroxide were added to the suspension, and the temperature was raised to 75℃ and reacted for 5h. After the reaction was completed, the mixture was filtered and dried and cured in an oven at 90℃ for 24h to obtain a phenol-coated acrylic copolymer composite resin (weighed as 136.4g).

[0037] (P4) Heat treatment: 100g of composite resin was placed in a tube furnace and a mixture of CO2 and O2 with a volume ratio of 1:1 was introduced. The volume of the mixed gas was 6L and the mixture was heat treated at 800℃ for 3h. After the heat treatment was completed, the mixture was cooled to room temperature, then washed with acetic acid for 60min, washed with deionized water until neutral, and then placed in an oven to dry at 90℃ for 12h to obtain porous carbon material.

[0038] (P5) Silicon deposition and carbon coating: 50g of porous carbon material was placed in a CVD furnace at a rotation speed of 20rpm. Helium gas was introduced at a flow rate of 5L / min. After heating to 600℃ in a helium environment, the helium flow rate was maintained and silane gas was introduced at a flow rate of 0.2L / min for chemical vapor deposition for 1h, so that the silicon particles formed were partially or completely attached to the pores of the porous carbon. After the silane deposition was completed, the silane gas was stopped, and helium gas was continuously introduced at a flow rate of 5L / min to remove excess silane gas. Then, acetylene gas was introduced at a flow rate of 0.4L / min and the temperature was maintained at 600℃ for vapor deposition for 1h. The carbon particles formed after the decomposition of acetylene gas were deposited on the surface of multiple carbon particles, thus forming a carbon coating layer, and finally obtaining a silicon-carbon composite anode material.

[0039] Example 2

[0040] The rest is the same as in Example 1, except that in step (P1), the molar ratio of 4-pentenoic acid, sodium acrylate, and acrylamide is 1:1.4:2.2.

[0041] Example 3

[0042] The rest is the same as in Example 1, except that in step (P1), the molar ratio of 4-pentenoic acid, sodium acrylate, and acrylamide is 1:1.6:2.2.

[0043] Example 4

[0044] The rest is the same as in Example 1, except that in step (P1), the molar ratio of 4-pentenoic acid, sodium acrylate, and acrylamide is 1:1.8:2.4.

[0045] Example 5

[0046] The rest is the same as in Example 1, except that in step (P1), the molar ratio of 4-pentenoic acid, sodium acrylate, and acrylamide is 1:1.8:2.6.

[0047] Example 6

[0048] The rest is the same as in Example 1, except that in step (P1), the molar ratio of 4-pentenoic acid, sodium acrylate, and acrylamide is 1:2:2.8.

[0049] Example 7

[0050] The rest is the same as in Example 1, except that in step (P1), the molar ratio of 4-pentenoic acid, sodium acrylate, and acrylamide is 1:2:3.

[0051] Example 8

[0052] The rest is the same as in Example 1, except that in step (P1), acrylic acid is used instead of 4-pentenoic acid, sodium methacrylate is used instead of sodium acrylate, and citric acid is used instead of adipic acid.

[0053] Example 9

[0054] The rest is the same as in Example 1, except that in step (P4), the amount of mixed gas used is 9L.

[0055] Comparative Example 1

[0056] The rest is the same as in Example 1, except that in step (P1), the molar ratio of 4-pentenoic acid, sodium acrylate, and acrylamide is 1:0.5:1.5.

[0057] Comparative Example 2

[0058] The rest is the same as in Example 1, except that in step (P1), the molar ratio of 4-pentenoic acid, sodium acrylate, and acrylamide is 1:2.5:4.

[0059] Comparative Example 3

[0060] The rest is the same as in Example 1, except that step (P3) is omitted and replaced with: the acrylic copolymer obtained in step (P2) is mixed with commercially available phenolic resin at a mass ratio of 1:12.6 to form a mixture, and then the heat treatment in step (P4) is performed.

[0061] Comparative Example 4

[0062] The rest is the same as in Example 1, except that in step (P4), the amount of mixed gas used is 4L.

[0063] Application Example 1

[0064] The silicon-carbon composite anode material prepared in Example 1 was applied to the anode of a lithium-ion battery, assembled into a lithium battery, and its electrochemical performance was tested. Specific method: The silicon-carbon anode material, Super P, carbon nanotubes, and carboxymethyl cellulose with styrene-butadiene rubber composite binder were mixed at a mass ratio of 80:9.8:0.2:10 to prepare a slurry (CMC and SBR mass ratio of 1:1). The slurry was coated onto copper foil using a 200 μm thick scraper, dried in a drying room, and then vacuum dried for 12 hours to prepare a silicon-based anode sheet. Then, lithium metal was used as the counter electrode, polyolefin as the separator, and 1 mol / L LiPF6 (solvent being a 1:1 volume ratio mixture of ethylene carbonate and dimethyl carbonate) as the electrolyte. 2% VC and 5% FEC were added to the electrolyte. A coin cell was assembled in an argon-atmosphere Braun inert gas glove box in Germany. The assembled battery was subjected to charge-discharge tests on a LAND charge-discharge tester, with a charge-discharge range of 50mV to 1.5V and a compaction density of 1.1g / cm³. 3 After three charge-discharge cycles at a current density of 0.1C (1C = 1500mA / g), rate charge-discharge tests were performed at current densities of 1C and 5C, respectively.

[0065] Application Example 2-9

[0066] The other conditions are the same as in Application Example 1, except that the silicon-carbon composite anode materials were prepared in Examples 2-9 respectively.

[0067] Compare and contrast examples 1-4

[0068] The other conditions are the same as in Application Example 1, except that the silicon-carbon composite anode materials were prepared in Comparative Examples 1-4 respectively.

[0069] Testing and Analysis

[0070] 1) Performance testing of porous silicon-carbon composite anode materials: The pore size distribution of the porous carbon materials prepared in the above examples and comparative examples was determined by the following test methods, and the elemental content of the silicon-carbon composite anode materials was tested. The data are shown in Table 1.

[0071] Pore ​​size distribution determination: According to GB / T 19587-2017 Gas Adsorption BET Method, a Tristar II 3020 fully automatic specific area and pore size analyzer manufactured by Micromeritics Instrument Corporation, USA, was used to conduct low-temperature nitrogen adsorption experiments on the porous carbon materials prepared in step (P4) of the examples and comparative examples to determine their pore size distribution.

[0072] Main element content: In accordance with GB / T 38823-2020, the silicon content in the porous silicon-carbon composite anode material was tested using a vario EL cube elemental analyzer from Elementar GmbH, Germany, and the carbon content in the porous silicon-carbon composite material was tested using an HCS-801 infrared carbon-sulfur analyzer.

[0073] Table 1 Performance of porous silicon-carbon composite anode materials

[0074] As shown in Table 1, compared with the comparative example, the porous carbon material prepared by the method of the present invention has a significantly higher specific surface area and micropore ratio, with a specific surface area as high as 1800 m². 2 The pore size distribution is mainly composed of micropores <2nm, accounting for more than 90%.

[0075] In Comparative Examples 1 and 2, the microporosity of the porous carbon materials was relatively low, and the pore volume and specific surface area were also relatively low.

[0076] In Comparative Example 3, although the porous carbon material has a relatively large proportion of micropores, its pore volume and specific surface area are relatively low, indicating that the overall porosity is relatively low.

[0077] In Comparative Example 4, when the content of oxidizing gas during heat treatment was too low, although the micropores of the porous carbon material accounted for a large proportion, the pore volume and specific surface area were low, indicating that the content of oxidizing gas during heat treatment was too low and the activation and pore expansion effect was poor.

[0078] 2) Electrochemical performance testing: The batteries assembled in the application examples and comparative examples were subjected to charge-discharge tests on a LAND charge-discharge tester. The charge range was 50mV to 1.5V, and the compaction density was 1.1g / cm³. 3 Three charge-discharge tests were conducted at a current density of 0.1C (1C = 1500 mA / g). The battery performance test data are shown in Table 2.

[0079] Table 2 Electrochemical Performance Tests

[0080] As can be seen from the data in Table 2, when the silicon-carbon composite anode material prepared by the method of the present invention is used in lithium batteries, its initial reversible capacity is above 1800 mAh / g, its initial coulombic efficiency is above 90%, and its capacity retention rate after 100 cycles at 0.1C is above 88%. This indicates that the silicon-carbon composite anode material prepared by the method of the present invention can effectively alleviate the volume expansion of silicon and improve the cycle performance and charge / discharge capacity of lithium-ion batteries.

[0081] The above detailed description is a specific description of one of the feasible embodiments of the present invention. This embodiment is not intended to limit the patent scope of the present invention. All equivalent implementations or modifications that do not depart from the present invention should be included within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a silicon-carbon composite anode material, characterized in that, Includes the following steps: (P1) Copolymerization: Unsaturated organic acid, acrylate monomer, acrylamide monomer, sacrificial saturated organic acid, and initiator are dissolved together in water to form a mixed solution; then the reaction is heated and cooled to obtain a suspension containing acrylic copolymer; the molar ratio of the unsaturated organic acid, acrylate monomer, and acrylamide monomer is 1:(1.2~2):(2~3); (P2) Alkali treatment: Add inorganic alkali to the suspension to make the pH of the suspension 8.5-9.5, then filter, wash, dry and crush to obtain acrylic copolymer particles; (P3) In-situ polymerization: Acrylic copolymer particles and surfactants are added to a solvent to form a suspension. Then, phenolic monomers, paraformaldehyde, and an alkaline catalyst are added to the suspension, and the temperature is raised to carry out the polymerization reaction. After the reaction is completed, the mixture is filtered, dried and cured to obtain a phenolic-coated acrylic copolymer composite resin. (P4) Heat treatment: The composite resin is heat-treated in an oxidizing gas atmosphere, cooled, washed and dried to obtain porous carbon material; the ratio of the amount of oxidizing gas to the amount of composite resin is (60-90) L: 1 kg. (P5) Silicon deposition and carbon coating: Chemical vapor deposition is performed on porous carbon materials using organosilicon source gas, so that some or all of the nano-silicon particles are attached to the pores of the porous carbon; then, a carbon coating layer is formed by vapor deposition using a gas-phase carbon source, thus obtaining silicon-carbon composite anode material.

2. The preparation method according to claim 1, characterized in that, In step (P1), the molar ratio of the unsaturated organic acid, acrylate monomer, and acrylamide monomer is 1:(1.4-1.8):(2.2-2.4).

3. The preparation method according to claim 1, characterized in that, In step (P1), the unsaturated organic acid is at least one selected from acrylic acid, methacrylic acid, 3,3-dimethacrylic acid, 4-pentenoic acid, and 5-hexenoic acid; the acrylate monomer is a sodium or potassium salt of an acrylic acid monomer; the acrylamide monomer is at least one selected from acrylamide, N-hydroxymethylacrylamide, and N-isopropylacrylamide; and / or The sacrificial agent saturated organic acid is a C3-C6 saturated organic dicarboxylic acid or polycarboxylic acid; the initiator is at least one of benzoyl peroxide and azobisisobutyronitrile.

4. The preparation method according to claim 1, characterized in that, In step (P1), the amount of the sacrificial agent saturated organic acid is 6-10% of the total mass of the unsaturated organic acid, acrylate monomers and acrylamide monomers; the amount of the initiator is 4-8% of the total mass of the unsaturated organic acid, acrylate monomers and acrylamide monomers.

5. The preparation method according to claim 1, characterized in that, In step (P1), the reaction conditions are: temperature 75-90℃, time 1.5-4h.

6. The preparation method according to claim 1, characterized in that, In step (P2), the inorganic alkali is potassium hydroxide or sodium hydroxide; the crushing is crushing to 200-1000 mesh.

7. The preparation method according to claim 1, characterized in that, In step (P3), the mass ratio of acrylic copolymer particles, surfactant and phenolic monomer is 1:(0.02-0.04):(10-15); the molar ratio of phenolic monomer to paraformaldehyde is 1:(1.5-1.6), and the molar amount of paraformaldehyde is based on the formaldehyde monomer; the amount of alkaline catalyst is 1.5-3 wt% of phenolic monomer.

8. The preparation method according to claim 1, characterized in that, In step (P3), the surfactant is an organic sodium salt; the solvent is an alcohol-water mixture, wherein the concentration of the alcohol is 15-30 wt%, and the alcohol is ethanol or propanol; the phenolic monomer is at least one of phenol, cresol, and xylenol; and the alkaline catalyst is an inorganic base.

9. The preparation method according to claim 1, characterized in that, In step (P3), the conditions for the polymerization reaction are: temperature 70-90℃ and time 3-6h.

10. The preparation method according to claim 1, characterized in that, In step (P4), the oxidizing gas is CO2 and / or O2; the heat treatment conditions are: holding at 700-900℃ for 2-4 hours.

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