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CN119038528B - Preparation method and application of silicon-carbon composite anode material - Google Patents

Preparation method and application of silicon-carbon composite anode material Download PDF

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CN119038528B
CN119038528B CN202411536112.9A CN202411536112A CN119038528B CN 119038528 B CN119038528 B CN 119038528B CN 202411536112 A CN202411536112 A CN 202411536112A CN 119038528 B CN119038528 B CN 119038528B
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silicon
carbon
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organic acid
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CN119038528A (en
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李阁
牛文斌
许迪新
赵玉明
岳风树
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Shanxi Fuji New Energy Material Technology Co ltd
Beijing One Gold Amperex Technology Ltd
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Beijing One Gold Amperex Technology Ltd
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
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    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/22—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
    • C23C16/24—Deposition of silicon only
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
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    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/22—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
    • C23C16/26—Deposition of carbon only
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    • H01—ELECTRIC ELEMENTS
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    • H01M10/00—Secondary cells; Manufacture thereof
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    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
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    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
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    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
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    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Abstract

本发明涉及一种硅碳复合负极材料的制备方法，包括以下步骤：（P1）共聚：将不饱和有机酸、丙烯酸盐类单体、丙烯酰胺类单体以特定比例共同溶解于水中，在牺牲剂饱和有机酸和引发剂的作用下共聚，得到含丙烯酸类共聚物的悬浊液；（P2）碱处理：悬浊液经碱处理、过滤，得到共聚物颗粒；（P3）原位聚合：在共聚物颗粒的表面进行酚醛的原位聚合，得到酚醛包覆丙烯酸类共聚物的复合树脂；（P4）热处理：将复合树脂在氧化性气体氛围中热处理，得到多孔碳；（P5）多孔碳经硅沉积和碳包覆，得到硅碳复合负极材料。本发明制得的硅碳复合负极材料用锂电池时，能有效缓解硅的体积膨胀，提高锂离子电池的循环性能和充放电容量。

The present invention relates to a method for preparing a silicon-carbon composite negative electrode material, comprising the following steps: (P1) copolymerization: unsaturated organic acid, acrylate monomer, and acrylamide monomer are dissolved in water in a specific ratio, and copolymerized under the action of sacrificial agent saturated organic acid and initiator to obtain a suspension containing acrylic copolymer; (P2) alkali treatment: the suspension is treated with alkali and filtered to obtain copolymer particles; (P3) in-situ polymerization: phenolic formaldehyde is polymerized in-situ on the surface of the copolymer particles to obtain a composite resin of phenolic formaldehyde coated acrylic copolymer; (P4) heat treatment: the composite resin is heat treated in an oxidizing gas atmosphere to obtain porous carbon; (P5) the porous carbon is subjected to silicon deposition and carbon coating to obtain a silicon-carbon composite negative electrode material. When the silicon-carbon composite negative electrode material prepared by the present invention is used in a lithium battery, it can effectively alleviate the volume expansion of silicon and improve the cycle performance and charge and discharge capacity of the lithium ion battery.

Description

Preparation method and application of silicon-carbon composite anode material
Technical Field
The invention belongs to the technical field of battery anode materials, and particularly relates to a preparation method and application of a silicon-carbon composite anode material.
Background
The porous carbon material has the advantages of high specific surface area, developed pore structure, excellent conductivity and the like, so that the porous carbon material has a huge application prospect in the field of electrochemical energy storage. However, the theoretical specific capacity of carbon is limited, while the theoretical specific capacity of silicon is up to 4200mAh/g, but because the volume expansion of silicon is large, the material structure is collapsed and the electrode is peeled off and pulverized, thereby influencing the cycle performance of the battery, so that the preparation of the silicon-carbon composite anode material by compositing silicon and porous carbon is the main development trend at present. The silicon-carbon composite anode material in the prior art is generally realized by preparing porous silicon-carbon with a core-shell structure and a capsule structure or vapor depositing silicon on the porous carbon. The preparation method is complex and has poor structural controllability, and the preparation method is relatively simple and has controllable structure, but the performance of the silicon-carbon anode material depends on the structural performance of porous carbon. The porous carbon used as the silicon-carbon composite anode needs to have higher specific surface area and stable and developed pore structure, so that higher capacity space and diffusion channel can be provided for the lithium ion battery, and the volume expansion of silicon is relieved in the adsorption-deintercalation process, so that the cycling stability of the battery is better. The traditional porous carbon material has the defects of complicated preparation process, high energy consumption in the activation process, high acid and alkali consumption, high corrosiveness to equipment and easy collapse of a pore structure, namely the pore structure is not stable enough, and the pore size distribution uniformity of the porous carbon prepared by carbonization and reactivation is still to be further improved.
CN110224125A discloses a porous carbon-nano silicon-carbon core-shell structure material and a preparation method thereof, the core-shell structure material uses the porous carbon material as a substrate, the middle embedded layer is composed of nano silicon, and the outer layer is coated with amorphous carbon shell. The preparation method comprises the steps of carrying out medium-temperature etching on a pre-corroded substrate carbon material in an inert gas atmosphere, then carrying out high-temperature activation and aftertreatment to obtain a porous carbon material, mixing and grinding the porous carbon material and nano silicon in a solvent to obtain a composite material, mixing and spray granulating the composite material and a carbon source in the solvent, and then carrying out heat treatment in the inert gas atmosphere. According to the preparation method, the first coulomb efficiency and the structural stability of the material are improved, and after the material is mixed with a graphite material, the high-stability silicon-carbon composite anode active material with the reversible capacity of 400-650 mAh/g can be obtained, but the porous carbon has lower porosity, limited silicon loaded in pores and lower reversible capacity.
CN115911341a discloses a porous silicon-carbon negative electrode material, which has a core-shell structure and sequentially comprises a porous silicon-carbon-repellent core, a transition layer, a dense silicon-carbon layer and a carbon coating layer from inside to outside. The porous carbon of the porous silicon carbon anode material has a porous gap structure, wherein the porous carbon of the silicon particles is distributed in gaps of the carbon skeleton structure of the porous silicon carbon anode material, so that excellent flexibility and mechanical strength can be provided, and expansion and contraction stress generated by lithium ion deintercalation can be buffered. The porous silicon-carbon anode material has the advantages that silicon particles in the porous silicon-carbon anode material are reasonably distributed in gaps between the porous carbon and the carbon particles, the porous silicon-carbon anode material has excellent comprehensive performance, the expansion of the silicon anode material in the circulation process is effectively slowed down, the capacity attenuation is controlled, and the circulation stability is improved, but the circulation performance of the porous silicon-carbon anode material prepared by the method is better, and the reversible capacity is still to be improved.
Disclosure of Invention
In order to solve the problems in the prior art, the invention firstly forms porous carbon with stable structure, high porosity and uniform pore size distribution through copolymerization of unsaturated organic acid, acrylate monomers and acrylamide monomers, alkali treatment, in-situ polymerization and heat treatment, and then forms the silicon-carbon composite anode material with good cycle performance and high reversible capacity through silicon deposition and carbon cladding.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
the preparation method of the silicon-carbon composite anode material comprises the following steps:
The method comprises the steps of (P1) copolymerizing, namely, dissolving unsaturated organic acid, acrylic acid salt monomers, acrylamide monomers, sacrificial agent saturated organic acid and an initiator in water to form a mixed solution, heating for reaction, and cooling to obtain a suspension containing acrylic acid copolymer, wherein the molar ratio of the unsaturated organic acid to the acrylic acid salt monomers to the acrylamide monomers is 1 (1.2-2) (2-3);
(P2) alkali treatment, namely adding inorganic alkali into the suspension to enable the pH value of the suspension to be 8.5-9.5, and then filtering, washing, drying and crushing to obtain acrylic copolymer particles;
(P3) in-situ polymerization, namely adding acrylic copolymer particles and a surfactant into a solvent to form a suspension, then adding a phenolic monomer, paraformaldehyde and a base catalyst into the suspension, and heating to perform polymerization reaction;
(P4) heat treatment, namely, heat treating the composite resin in an oxidizing gas atmosphere, cooling, washing and drying to obtain a porous carbon material, wherein the ratio of the amount of the oxidizing gas to the amount of the composite resin is (60-90) L:1kg;
And (P5) silicon deposition and carbon coating, namely performing chemical vapor deposition on the porous carbon material by utilizing organic silicon source gas to enable part or all of nano silicon particles to be attached in the pores of the porous carbon, and then performing vapor deposition by adopting a vapor carbon source to form a carbon coating layer to obtain the silicon-carbon composite anode material.
The invention forms acrylic copolymer by solution polymerization of unsaturated organic acid, acrylic acid salt monomer and acrylamide monomer with the mol ratio of (1.2-2) to (2-3) under the action of initiator, and the side chain of the copolymer contains carboxylic acid, carboxylate and amide group. Because the sacrificial agent saturated organic acid is added in the solution polymerization process of the step (P1), the saturated organic acid and the amide group have stronger hydrogen bond acting force, so that the saturated organic acid and the amide group are introduced into the interior and the surface of the acrylic copolymer, in the step (P2), inorganic alkali and the saturated organic acid can generate water-soluble salt, the dissolution of the salt can form pores on the surface of the acrylic copolymer, namely acrylic copolymer particles with more active sites, and more active sites are favorable for in-situ polymerization to form phenolic aldehyde in the pores and the surface of the acrylic copolymer particles under the synergistic action of the surfactant in the following step (P3), namely the composite resin of the phenolic aldehyde-coated acrylic copolymer is formed. Meanwhile, in the step (P2), the inorganic base may also react with a part of carboxylic acid in the side chain of the acrylic copolymer to form a salt, to form an acrylic copolymer having more carboxylic acid salt in the side chain, i.e., more carboxylic acid salt in the composite resin. In the next step (P4), when the composite resin is heat-treated in an oxidizing atmosphere, the acrylic copolymer is used as a heat-labile polymer to generate a small molecular gas at a relatively low temperature, the small molecular gas escapes from the matrix to form pores, while the phenolic aldehyde is a heat-stable polymer, and the carbon residue rate after heat treatment is high to form a porous carbon skeleton, and the pores of the obtained porous carbon skeleton are more uniform because the composite resin formed by in-situ polymerization is different from physical blending. Meanwhile, as the side chain of the acrylic copolymer in the composite resin contains more carboxylate, in the step (P4), the carboxylate reacts under the oxidizing atmosphere to form metal oxide and metal hydroxide which are activated pore-expanding agents, namely the acrylic copolymer in the composite resin is the pore-forming agent and the activated pore-expanding agent in the step (P4), and the carbonization pore-forming can be carried out and the activation can be carried out at the same time, so that the method is more beneficial to the structural stability of the pores. Finally, the porous carbon material with uniformly distributed holes, high porosity and stable structure is prepared, and the porous carbon material is subjected to chemical vapor silicon deposition and carbon coating to form the silicon-carbon composite anode material.
In the step (P1), the molar ratio of the unsaturated organic acid, the acrylic acid salt monomer and the acrylamide monomer is 1 (1.4-1.8) (2.2-2.4). In the present invention, not all of the unsaturated organic acid, the acrylic acid salt monomer and the acrylamide monomer in any ratio may be copolymerized to obtain the composite resin required to satisfy the step (P4). The unsaturated organic acid is one of main comonomers, the reaction activity is high, the copolymer is difficult to form due to the excessively low proportion, carboxylate in the acrylate monomer can play a main role in activating and reaming in the step (P4), and after the acrylamide monomer is copolymerized, amide groups of side chains of the acrylamide monomer have stronger hydrogen bonding effect with the sacrificial saturated organic acid, so that part of the saturated organic acid is introduced into the acrylic copolymer, and pores are formed on the surfaces of acrylic copolymer particles due to the dissolution of the salt after the salt is formed by alkali treatment, so that more active sites are provided for facilitating the subsequent in-situ polymerization. That is, the three monomers each act differently, and it is necessary to fall within the above-mentioned range to obtain a copolymer satisfying the requirements.
Further, in the step (P1), the unsaturated organic acid is at least one of acrylic acid, methacrylic acid, 3-dimethyl acrylic acid, 4-pentenoic acid and 5-hexenoic acid, the acrylic acid salt monomer is sodium salt or potassium salt of acrylic acid monomer, such as sodium acrylate, potassium methacrylate and sodium methacrylate, and the acrylamide monomer is at least one of acrylamide, N-methylolacrylamide and N-isopropylacrylamide.
Further, in the step (P1), the sacrificial saturated organic acid is a C3-C6 saturated organic dibasic acid or polybasic acid, such as adipic acid, glutaric acid, succinic acid, malonic acid and citric acid, and the initiator is at least one of dibenzoyl peroxide (BPO) and Azobisisobutyronitrile (AIBN).
Further, in the step (P1), the amount of the saturated organic acid serving as the sacrificial agent is 6-10% of the total mass of the unsaturated organic acid, the acrylic acid salt monomer and the acrylamide monomer, and the amount of the initiator is 4-8% of the total mass of the unsaturated organic acid, the acrylic acid salt monomer and the acrylamide monomer. The amount of the initiator used affects the molecular weight of the copolymer, and the purpose of controlling the amount of the initiator used in the present invention within the above-mentioned range is to make the molecular weight of the copolymer not too high.
Further, in the step (P1), the reaction condition is that the temperature is 75-90 ℃ and the time is 1.5-4 hours.
Further, in the step (P2), the inorganic base is potassium hydroxide or sodium hydroxide, and the crushing is carried out until the granularity is 200-1000 meshes.
In the step (P3), the mass ratio of the acrylic copolymer particles to the surfactant to the phenolic monomer is 1 (0.02-0.04): 10-15), the molar ratio of the phenolic monomer to the paraformaldehyde is 1 (1.5-1.6), the molar amount of the paraformaldehyde is calculated by the monomer formaldehyde, and the amount of the base catalyst is 1.5-3 wt% of the phenolic monomer.
Further, in the 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 mixed solution, wherein the concentration of alcohol is 15-30wt%, the alcohol is ethanol or propanol, the phenolic monomer is at least one of phenol, cresol and xylenol, and the alkali catalyst is an inorganic alkali, such as potassium hydroxide or sodium hydroxide.
Further, in the step (P3), the polymerization reaction is carried out under the conditions that the temperature is 70-90 ℃ and the time is 3-6 hours.
Further, in the step (P4), the oxidizing gas is CO 2 and/or O 2, preferably mixed gas of CO 2 and O 2 according to the volume ratio of 1 (1-2), and the heat treatment condition is that the temperature is kept at 700-900 ℃ for 2-4 hours. The control of the amount of the oxidizing gas is important, and in the invention, the ratio of the amount of the oxidizing gas to the amount of the composite resin is (60-90) L:1kg, and when the amount is more than the value, the composite resin is easy to burn and the carbon residue rate is low, and when the amount is too low, the activation reaming effect is poor.
Further, in the step (P4), the washing is performed by acidic washing and then water washing to be neutral, and the acid is at least one of acetic acid, oxalic acid and citric acid.
In step (P5), the process of vapor depositing silicon and carbon coatings is well known to those skilled in the art. If the organic silicon source gas is adopted for carrying out vapor deposition on silicon, the dosage ratio of the porous carbon to the organic silicon source gas is 1 kg:150L-300L, the organic silicon source gas is at least one of silane, disilane, trichlorosilane, silicon tetrachloride and silicon tetrafluoride, and if the gas phase carbon source is adopted for carrying out carbon coating, the dosage ratio of the porous carbon to the gas phase carbon source is 1 kg:250L-500L, and the gas phase carbon source is at least one of C1-4 alkane, C2-4 alkene and C2-4 alkyne.
In a second aspect, the present invention provides a silicon-carbon negative electrode material prepared by the aforementioned preparation method.
Compared with the prior art, the invention has the following beneficial effects:
(1) The method comprises the steps of copolymerizing unsaturated organic acid, acrylic acid salt monomers and acrylamide monomers according to a specific proportion to form an acrylic copolymer, introducing the sacrificial agent saturated organic acid into the copolymer and the surface of the copolymer due to strong hydrogen bond action with an amide group in the copolymerization process, then forming acrylic copolymer particles with pores on the surface and more carboxylate in side chains after alkali treatment, and forming the composite resin of the phenolic aldehyde coated acrylic copolymer through in-situ polymerization of the copolymer particles. The composite resin is finally subjected to heat treatment under a trace amount of oxidizing gas, wherein acrylic copolymer is decomposed and escapes from a matrix to form pores, and simultaneously carboxylate of a side chain in the acrylic copolymer forms an activating agent under an oxidizing gas atmosphere, namely carbonization pore-forming and activation pore expansion are synchronously realized when the composite resin is subjected to heat treatment under the trace amount of oxidizing gas, so that a porous carbon material with uniformly distributed pores, high porosity and stable structure is prepared, and a silicon-carbon composite anode material is finally prepared by coating more carbon with chemical vapor deposition silicon and carbon.
(2) When the lithium battery for the silicon-carbon composite anode material is prepared by the invention, the volume expansion of silicon can be effectively relieved, the cycle performance and the charge-discharge capacity of the lithium ion battery are improved, the first reversible capacity is more than 1800 mAh/g, the first coulomb efficiency is more than 90%, and the 100-cycle capacity retention rate at 0.1C is more than 88%.
Drawings
Fig. 1 is a first-turn charge-discharge curve of a lithium battery assembled from the silicon-carbon composite anode material of example 1 at a 0.1C rate.
Detailed Description
The present invention will be further illustrated with reference to the following specific examples, but the present invention is not limited to the following examples.
The experimental methods described in the examples below, unless otherwise indicated, are conventional, and the reagents and materials, unless otherwise indicated, are commercially available.
Example 1
(P1) copolymerizing, namely preparing a monomer mixture with the total mass of 100g by using 4-pentenoic acid, sodium acrylate and acrylamide according to a molar ratio of 1:1.2:2, then dissolving 100g of the monomer mixture, 7g of adipic acid and 5g of an initiator BPO in pure water together to form a mixed solution, then heating to 85 ℃ for reacting for 2.5 hours, and cooling to room temperature to obtain a suspension containing acrylic copolymer;
(P2) alkali treatment, namely adding sodium hydroxide into the suspension, stirring and reacting for 20min to enable the pH value of the suspension to be 9.0, sequentially filtering, washing with pure water for 2 times, drying in an 80 ℃ oven for 24h, and crushing to 800 meshes to obtain acrylic copolymer particles;
(P3) in-situ polymerization, namely, 10g of acrylic copolymer particles and 0.3g of fatty alcohol polyoxyethylene ether sodium sulfate are added into 1000g of ethanol water mixed solution (the ethanol concentration is 20 wt%) with stirring to form a suspension, 120g of phenol, 60g of paraformaldehyde and 2.5g of sodium hydroxide are added into the suspension, the mixture is heated to 75 ℃ to react for 5 hours, the reaction is filtered, and the mixture is dried and cured in an oven at 90 ℃ for 24 hours to obtain a phenolic-coated acrylic copolymer composite resin (136.4 g is weighed);
(P4) heat treatment, namely placing 100g of composite resin into a tube furnace, introducing mixed gas of CO 2 and O 2 in a volume ratio of 1:1, wherein the amount of the mixed gas is 6L, and heat treating for 3 hours at 800 ℃, cooling to room temperature after heat treatment, then washing with acetic acid for 60 minutes, washing with deionized water to be neutral, and then placing into an oven to dry for 12 hours at 90 ℃ to obtain a porous carbon material;
And (P5) silicon deposition and carbon coating, namely placing 50g of porous carbon material in a CVD furnace, introducing helium at the rotating speed of the CVD furnace of 20rpm and at the flow rate of 5L/min, heating to 600 ℃ in a helium environment, then maintaining the flow rate of helium, introducing monosilane gas at the flow rate of 0.2L/min, performing chemical vapor deposition for 1h to enable part or all of formed silicon particles to be attached in porous carbon pores, stopping introducing monosilane gas after the silane deposition, continuously introducing helium at the flow rate of 5L/min to remove redundant monosilane gas, introducing acetylene gas at the flow rate of 0.4L/min, performing vapor deposition for 1h at the temperature of 600 ℃, and depositing carbon particles formed after the decomposition of the acetylene gas on the surfaces of a plurality of carbon blocks to form a silicon-carbon composite anode material.
Example 2
The remainder is the same as in example 1, except that in step (P1), the molar ratio of 4-pentenoic acid, sodium acrylate, acrylamide is 1:1.4:2.2.
Example 3
The remainder is the same as in example 1, except that in step (P1), the molar ratio of 4-pentenoic acid, sodium acrylate, acrylamide is 1:1.6:2.2.
Example 4
The remainder is the same as in example 1, except that in step (P1), the molar ratio of 4-pentenoic acid, sodium acrylate, acrylamide is 1:1.8:2.4.
Example 5
The remainder is the same as in example 1, except that in step (P1), the molar ratio of 4-pentenoic acid, sodium acrylate, acrylamide is 1:1.8:2.6.
Example 6
The remainder is the same as in example 1, except that in step (P1), the molar ratio of 4-pentenoic acid, sodium acrylate, acrylamide is 1:2:2.8.
Example 7
The remainder is the same as in example 1, except that in step (P1), the molar ratio of 4-pentenoic acid, sodium acrylate, acrylamide is 1:2:3.
Example 8
The remainder was the same as in example 1, except that in step (P1), acrylic acid was used instead of 4-pentenoic acid, sodium methacrylate was used instead of sodium acrylate, and citric acid was used instead of adipic acid.
Example 9
The remainder was the same as in example 1 except that in step (P4), the amount of the mixed gas was 9L.
Comparative example 1
The remainder is the same as in example 1, except that in step (P1), the molar ratio of 4-pentenoic acid, sodium acrylate, acrylamide is 1:0.5:1.5.
Comparative example 2
The remainder is the same as in example 1, except that in step (P1), the molar ratio of 4-pentenoic acid, sodium acrylate, acrylamide is 1:2.5:4.
Comparative example 3
The remainder was the same as in example 1 except that step (P3) was omitted and instead the acrylic copolymer obtained in step (P2) was mixed with a commercially available phenolic resin at a mass ratio of 1:12.6 to form a mixture, followed by the heat treatment of step (P4).
Comparative example 4
The rest is the same as in example 1, except that in step (P4), the amount of the mixed gas used was 4L.
Application example 1
The silicon-carbon composite anode material prepared in example 1 was applied to an anode of a lithium ion battery, assembled into a lithium battery, and its electrochemical properties were tested. The preparation method comprises the steps of mixing a silicon-carbon negative electrode material, super P, a carbon nano tube, carboxymethyl cellulose and a styrene-butadiene rubber composite binder according to a mass ratio of 80:9.8:0.2:10 to prepare slurry (CMC and SBR are 1:1), coating the slurry on a copper foil by using a200 mu m thick scraper, drying in the air, placing the copper foil in a vacuum drying mode for 12 h hours to prepare a silicon-based negative electrode piece, then taking metallic lithium as a counter electrode, polyolefin as a diaphragm, taking 1 mol/L LiPF6 (a mixed solution of ethylene carbonate and dimethyl carbonate with a volume ratio of 1:1) as an electrolyte, adding VC with a volume fraction of 2% and FEC with a volume fraction of 5% into the electrolyte, and assembling the composite battery in a German Braun inert gas glove box in an argon atmosphere. And (3) carrying out charge and discharge tests on the assembled battery on a LAND charge and discharge tester, wherein the charge and discharge interval is 50 mV-1.5V, the compaction density is 1.1 g/cm 3, and after three times of charge and discharge under the current density of 0.1C (1C =1500 mA/g), the multiplying power charge and discharge tests are respectively carried out under the current densities of 1C and 5C.
Application examples 2 to 9
Other conditions were the same as in application example 1, except that silicon-carbon composite anode materials were prepared in examples 2 to 9, respectively.
Comparative application examples 1 to 4
Other conditions were the same as in application example 1 except that silicon-carbon composite anode materials were prepared in comparative examples 1 to 4, respectively.
Testing and analysis
1) Performance test of porous silicon carbon composite anode materials pore size distribution measurement was performed on the porous carbon materials prepared in the above examples and comparative examples, respectively, by the following test methods, and elemental content test was performed on the silicon carbon composite anode materials, and the data are shown in table 1.
Pore size distribution measurement according to the GB/T19587-2017 gas adsorption BET method, a TRISTAR II type 3020 full-automatic specific area and pore size analyzer manufactured by U.S. Micromeritics Instrument Corporation was used for carrying out a low-temperature nitrogen adsorption experiment on the porous carbon materials prepared in the step (P4) of examples and comparative examples, and the pore size distribution was measured.
Main element content according to GB/T38823-2020, adopting a vario EL cube element analyzer of Elementar, germany to test the silicon element content in the porous silicon-carbon composite anode material, and adopting an HCS-801 infrared carbon-sulfur analyzer to test the carbon element content in the porous silicon-carbon composite material.
TABLE 1 Properties of porous silicon carbon composite negative electrode Material
。
As can be seen from Table 1, compared with the comparative example, the porous carbon material prepared by the preparation method of the invention has significantly higher specific surface area and micropore ratio, the specific surface area is as high as 1800 m 2/g or more, the pore size distribution is mainly micropores with the diameter of <2nm, and the micropore ratio is more than 90%.
In comparative examples 1 and 2, the microporosity of the porous carbon material was relatively low, and the pore volume and specific surface area were also relatively low.
In comparative example 3, the porous carbon material has a relatively large number of micropores, but the pore volume and the specific surface area are low, indicating that the overall porosity is low.
In comparative example 4, when the content of the oxidizing gas during the heat treatment is too low, the porous carbon material has relatively large micropores, but the pore volume and the specific surface area are relatively low, which means that the content of the oxidizing gas during the heat treatment is too low and the activation reaming effect is poor.
2) Electrochemical performance test the batteries assembled in the application example and the comparative example were subjected to charge and discharge tests on a LAND charge and discharge tester, the electric interval was 50 mV-1.5V, the compaction density was 1.1 g/cm 3, and the charge and discharge tests were performed three times at a current density of 0.1C (1C =1500 mA/g). The battery performance test data are shown in table 2.
Table 2 electrochemical performance test
。
As can be seen from the data in Table 2, when the silicon-carbon composite anode material prepared by the preparation method is used in a lithium battery, the first reversible capacity of the silicon-carbon composite anode material is more than 1800 mAh/g, the first coulomb efficiency is more than 90%, and the 100-cycle capacity retention rate at 0.1C is more than 88%, which indicates that the silicon-carbon composite anode material prepared by the preparation method can effectively relieve the volume expansion of silicon and improve the cycle performance and charge and discharge capacity of the lithium ion battery.
The foregoing detailed description is directed to one of the possible embodiments of the present invention, which is not intended to limit the scope of the invention, but is to be accorded the full scope of all such equivalents and modifications so as not to depart from the scope of the invention.

Claims (10)

1. The preparation method of the silicon-carbon composite anode material is characterized by comprising the following steps of:
The method comprises the steps of (P1) copolymerizing, namely, dissolving unsaturated organic acid, acrylic acid salt monomers, acrylamide monomers, sacrificial agent saturated organic acid and an initiator in water to form a mixed solution, heating for reaction, and cooling to obtain a suspension containing acrylic acid copolymer, wherein the molar ratio of the unsaturated organic acid to the acrylic acid salt monomers to the acrylamide monomers is 1 (1.2-2) (2-3);
(P2) alkali treatment, namely adding inorganic alkali into the suspension to enable the pH value of the suspension to be 8.5-9.5, and then filtering, washing, drying and crushing to obtain acrylic copolymer particles;
(P3) in-situ polymerization, namely adding acrylic copolymer particles and a surfactant into a solvent to form a suspension, then adding a phenolic monomer, paraformaldehyde and a base catalyst into the suspension, and heating to perform polymerization reaction;
(P4) heat treatment, namely, heat treating the composite resin in an oxidizing gas atmosphere, cooling, washing and drying to obtain a porous carbon material, wherein the ratio of the amount of the oxidizing gas to the amount of the composite resin is (60-90) L:1kg;
And (P5) silicon deposition and carbon coating, namely performing chemical vapor deposition on the porous carbon material by utilizing organic silicon source gas to enable part or all of nano silicon particles to be attached in the pores of the porous carbon, and then performing vapor deposition by adopting a vapor carbon source to form a carbon coating layer to obtain the silicon-carbon composite anode material.
2. The preparation method of claim 1, wherein in the step (P1), the molar ratio of the unsaturated organic acid, the acrylic acid salt monomer and the acrylamide monomer is 1 (1.4-1.8): 2.2-2.4.
3. The process according to claim 1, wherein in the step (P1), the unsaturated organic acid is at least one of acrylic acid, methacrylic acid, 3-dimethylacrylic acid, 4-pentenoic acid, 5-hexenoic acid, the acrylic acid salt monomer is sodium salt or potassium salt of an acrylic acid monomer, the acrylamide monomer is at least one of acrylamide, N-methylolacrylamide, N-isopropylacrylamide, and/or
The sacrificial agent saturated organic acid is C3-C6 saturated organic dibasic acid or polybasic acid, and the initiator is at least one of dibenzoyl peroxide and azodiisobutyronitrile.
4. The preparation method of claim 1, wherein in the step (P1), the amount of the sacrificial agent saturated organic acid is 6-10% of the total mass of the unsaturated organic acid, the acrylate monomer and the acrylamide monomer, and the amount of the initiator is 4-8% of the total mass of the unsaturated organic acid, the acrylate monomer and the acrylamide monomer.
5. The preparation method according to claim 1, wherein in the step (P1), the reaction condition is that the temperature is 75-90 ℃ and the time is 1.5-4 hours.
6. The preparation method of claim 1, wherein in the step (P2), the inorganic base is potassium hydroxide or sodium hydroxide, and the crushing is carried out to 200-1000 meshes.
7. The method according to claim 1, wherein in the step (P3), the mass ratio of the acrylic copolymer particles, the surfactant and the phenolic monomer is 1 (0.02-0.04): 10-15, the molar ratio of the phenolic monomer to the paraformaldehyde is 1 (1.5-1.6), the molar amount of the paraformaldehyde is calculated as the monomer formaldehyde, and the amount of the base catalyst is 1.5-3 wt% of the phenolic monomer.
8. The method according to claim 1, wherein in the step (P3), the surfactant is an organic sodium salt, the solvent is an aqueous alcohol mixture, wherein the concentration of the alcohol is 15-30wt%, the alcohol is ethanol or propanol, the phenolic monomer is at least one of phenol, cresol and xylenol, and the base catalyst is an inorganic base.
9. The method according to claim 1, wherein in the step (P3), the polymerization reaction is carried out at a temperature of 70 to 90 ℃ for 3 to 6 hours.
10. The preparation method according to claim 1, wherein in the step (P4), the oxidizing gas is CO 2 and/or O 2, and the heat treatment is carried out under the condition of 700-900 ℃ for 2-4 hours.
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