High-rate low-expansion modified silicon-carbon composite material as well as preparation method and application thereof

Abstract

The invention discloses a high-magnification low-expansion modified silicon-carbon composite material and a preparation method and application thereof, the modified silicon-carbon composite material is of a particle structure and comprises a silicon-carbon material serving as an inner core and a fluorine-containing conductive polymer layer coating the surface of the silicon-carbon material; the silicon-carbon material is obtained by coating the surfaces of silicon particles with carbon layers; the fluorine-containing conductive polymer layer is obtained by initiating polymerization of a first monomer and a second monomer, and the first monomer is a fluorine-containing polymer monomer. The preparation method comprises the following steps: putting the silicon-carbon material, a first monomer and a second monomer into a hydrothermal reaction kettle, adding a mixed solvent of water and ethanol, heating while stirring, adding an initiator after heating to a target temperature, preserving heat, reacting, cooling, carrying out suction filtration, washing with water, and drying to obtain the fluoro-coated silicon-carbon material, namely the modified silicon-carbon composite material. According to the application, the modified silicon-carbon composite material serves as a negative electrode active component and is mixed with a conductive agent, a binding agent and a dispersing agent, so that the negative electrode coating slurry for preparing the negative electrode plate of the lithium ion battery is formed.

Description

Technical Field

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

[0002] Currently, commercially available lithium-ion batteries generally use graphite as the negative electrode material, but graphite has a low theoretical specific capacity (approximately 372 mAh / g), which is insufficient to meet the requirements of next-generation high-energy-density batteries (>500 Wh / L).

[0003] Silicon (Si) is considered an ideal material to replace graphite due to its high theoretical specific capacity (4200 mAh / g), but its industrialization faces the following key challenges: Silicon exhibits a volume expansion rate of 300–400% during lithium insertion / extraction, leading to pulverization of active particles and electrode structure collapse; simultaneously, the continuous reaction between the silicon surface and the electrolyte generates a thick and unstable solid electrolyte interface (SEI film), resulting in an initial coulombic efficiency (ICE) typically below 80%, and side reactions during cycling exacerbate capacity decay; however, silicon's electronic conductivity (<10) is also a concern. -3 The S / cm ratio is significantly lower than that of graphite (>102S / cm), requiring a complex conductive agent network to improve the electrode energy density.

[0004] Currently, silicon-carbon materials obtained by forming graphitized carbon layers on the surface of silicon particles through vapor deposition or liquid phase coating can improve conductivity, but the rigid carbon layer (elastic modulus > 50 GPa) cannot adapt to the volumetric deformation of silicon, resulting in a crack rate exceeding 40% after cycling. In addition, the difference in thermal expansion coefficients between carbon and silicon can easily lead to the peeling of the coating layer (carbon layer), thereby accelerating electrolyte penetration and triggering side reactions, resulting in poor cycling stability of the material. Summary of the Invention

[0005] The purpose of this invention is to address the problem that silicon-carbon materials obtained through current vapor deposition or liquid coating methods are prone to cracking after cycling, leading to side reactions caused by electrolyte penetration and resulting in poor material cycling stability. This invention proposes a high-rate, low-expansion modified silicon-carbon composite material to solve the above problems.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0007] The present invention provides a high-ratio, low-expansion modified silicon-carbon composite material, which has a particulate structure and includes a silicon-carbon material as a core and a fluorinated conductive polymer layer (fluorinated coating layer) covering the surface of the silicon-carbon material.

[0008] The silicon-carbon material has a particulate structure, which is obtained by coating the surface of silicon particles with a carbon layer; the fluorine-containing conductive polymer layer is obtained by polymerization initiated by a first monomer and a second monomer, wherein the first monomer is a fluorine-containing polymer monomer.

[0009] Furthermore, a high-ratio, low-expansion modified silicon-carbon composite material: the fluorinated polymer monomer is selected from one or more of fluorinated acrylic acid, tetrafluoroethylene, trifluorochloroethylene, vinylidene fluoride, hexafluoropropylene, hexafluorobutyl methacrylate, perfluorooctyl ethyl acrylate, trifluoroethyl methacrylate, pentafluorostyrene, trifluoromethylstyrene, perfluoroalkoxy vinyl ether, hexafluoropropylene oxide, octafluorocyclobutane, trifluoropropylmethylcyclotrisiloxane, and fluorinated carbon nanotubes. Preferably, the fluorinated polymer monomer is fluorinated acrylic acid.

[0010] Furthermore, a high-ratio, low-expansion modified silicon-carbon composite material: the second monomer is acrylic acid.

[0011] Furthermore, a high-ratio, low-expansion modified silicon-carbon composite material: the initiator used for polymerization is ammonium persulfate.

[0012] This invention also provides a method for preparing a high-ratio, low-expansion modified silicon-carbon composite material, the method comprising the following steps:

[0013] The silicon-carbon material, the first monomer, and the second monomer are added to a hydrothermal reactor. A mixed solvent of water and ethanol is then added to the reactor, and the mixture is heated while stirring. Once the target temperature is reached, an initiator is added, and the reaction is maintained at this temperature. After the reaction, the mixture is cooled, filtered, washed with water, and dried to obtain a fluorinated silicon-carbon material, which is a modified silicon-carbon composite material.

[0014] Furthermore, a method for preparing a high-ratio, low-expansion modified silicon-carbon composite material: the mass ratio between the silicon-carbon material, the first monomer, and the second monomer is 1:(0.1-0.2):(0.02-0.05).

[0015] Furthermore, a method for preparing a high-ratio, low-expansion modified silicon-carbon composite material is provided: the mass ratio between the silicon-carbon material and the mixed solvent is 1:(5-15); the mixed solvent is obtained by mixing water and ethanol in a volume ratio of (1-2):(1-2).

[0016] Furthermore, a method for preparing a high-ratio, low-expansion modified silicon-carbon composite material is provided: the stirring rate is 100–600 rpm; during the preparation of the modified silicon-carbon composite material, the temperature is increased to 50–80°C at a rate of 1–3°C / min, and then 1.0–5.0% of the mass of the second monomer as an initiator is added, and the reaction is maintained at this temperature for 3–6 hours to complete the preparation.

[0017] The present invention also provides a use of a high-rate, low-expansion modified silicon-carbon composite material, wherein the modified silicon-carbon composite material is mixed with a conductive agent, a binder and a dispersant as a negative electrode active component to form a negative electrode coating slurry for preparing a negative electrode sheet for lithium-ion batteries.

[0018] The mass ratio of the modified silicon-carbon composite material, the conductive agent, and the binder is (75-85):(8-15):(8-12).

[0019] Furthermore, the application of a high-ratio, low-expansion modified silicon-carbon composite material is as follows: the conductive agent is selected from Super-P and / or carbon nanotubes; the binder is selected from at least one of LA136D, polyvinylidene fluoride, and polyacrylonitrile; the dispersant is deionized water; the preparation process of the negative electrode sheet is as follows: the negative electrode coating slurry is coated on the negative electrode current collector, dried under vacuum, and rolled to obtain the negative electrode sheet.

[0020] The beneficial effects of this invention are:

[0021] The modified silicon-carbon composite material with fluorinated coating of the present invention can construct an artificial SEI layer on the surface of the material, which can reduce the contact between the material and the electrolyte, thereby reducing the occurrence of side reactions and improving the cycling stability and structural robustness of the material; at the same time, the fluorinated coating also facilitates the high-flux transport of lithium ions, thus further improving the rate performance of the material.

[0022] This invention uses a cross-linked network formed by the polymerization reaction of fluorine-containing polymer monomers as the main body of the coating layer. It has elastic deformation ability to adapt to changes in silicon volume. After polymerization, some carboxylic acid groups are decarboxylated to form a conjugated structure, which can improve intrinsic conductivity. The undecarboxylated fluorinated regions maintain structural stability, and the decarboxylated carbon chains contribute to conductivity.

[0023] This invention achieves uniform coating of silicon-carbon materials with precisely controllable coating thickness through a controlled polymerization process. The designed fluorine-containing coating interface facilitates the formation of an artificial SEI layer, allowing for in-situ generation of lithium fluoride during lithiation, thus enhancing Li-carbon performance. + High-throughput transmission accelerates the desolvation process of lithium ions, thereby improving rate performance. Detailed Implementation

[0024] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0025] Example 1

[0026] This embodiment 1 provides a high-ratio, low-expansion modified silicon-carbon composite material. The modified silicon-carbon composite material has a particulate structure and includes a silicon-carbon material as the core and a fluorinated conductive polymer layer (fluorinated coating layer) covering the surface of the silicon-carbon material.

[0027] The silicon-carbon material is prepared by chemical vapor deposition and has a particulate structure, specifically by coating a carbon layer onto the surface of silicon particles; the fluorinated conductive polymer layer is obtained by polymerization initiated by a first monomer and a second monomer, wherein the first monomer is a fluorinated polymer monomer, specifically fluorinated acrylic acid; and the second monomer is acrylic acid.

[0028] The specific preparation process of this high-ratio, low-expansion modified silicon-carbon composite material is as follows:

[0029] (1) Add 1000.0g of silicon carbide material, 100.0g of fluoroacrylic acid and 20.0g of acrylic acid to a hydrothermal reactor;

[0030] (2) Add 10.0 kg of mixed solvent (made of water and ethanol in a volume ratio of 1:1) to the reactor and stir at a rate of 200 rpm. At the same time, raise the temperature from room temperature to 70°C at a rate of 2°C / min. After the temperature reaches 70°C, slowly add 0.5 g of ammonium persulfate as an initiator to the reactor and keep the reaction at the temperature for 6 hours. After the reaction, cool, filter, wash with water, and dry to obtain fluorinated coated silicon carbon material, which is the modified silicon carbon composite material.

[0031] Application: The modified silicon-carbon composite material of Example 1 is mixed with a conductive agent, binder and dispersant as the negative electrode active component to form a negative electrode coating slurry for preparing a negative electrode sheet for lithium-ion batteries; wherein, the mass ratio between the modified silicon-carbon composite material, the conductive agent and the binder is 80:10:10; the conductive agent is Super-P, the binder is LA136D and the dispersant is deionized water; the preparation process of the negative electrode sheet is as follows: the negative electrode coating slurry is coated on the negative electrode current collector (copper foil), vacuum dried and rolled to obtain the negative electrode sheet.

[0032] Example 2

[0033] The difference between Example 2 and Example 1 is that the choice of fluorinated polymer monomers is different. In Example 2, the fluorinated acrylic acid in Example 1 is replaced with tetrafluoroethylene, and the other conditions are the same as in Example 1.

[0034] Example 3

[0035] The difference between Example 3 and Example 1 is that Example 3 and Example 1 have different choices of fluorinated polymer monomers. In Example 3, the fluorinated acrylic acid in Example 1 is replaced with trifluoroethylene, and the other conditions are the same as in Example 1.

[0036] Example 4

[0037] The difference between Example 4 and Example 1 is that the choice of fluorinated polymer monomers is different. In Example 4, the fluorinated acrylic acid in Example 1 is replaced with vinylidene fluoride, and the other conditions are the same as in Example 1.

[0038] Example 5

[0039] The difference between Example 5 and Example 1 is that the choice of fluorinated polymer monomers is different. In Example 5, the fluorinated acrylic acid in Example 1 is replaced with perfluorooctyl ethyl acrylate, and the other conditions are the same as in Example 1.

[0040] Example 6

[0041] The difference between Example 6 and Example 1 is that the choice of fluorinated polymer monomers is different. In Example 6, the fluorinated acrylic acid in Example 1 is replaced with hexafluoropropylene, and the other conditions are the same as in Example 1.

[0042] Example 7

[0043] The difference between Example 7 and Example 1 is that the choice of fluorinated polymer monomers is different. In Example 7, the fluorinated acrylic acid in Example 1 is replaced with 100.0g of hexafluorobutyl methacrylate and 0.8g of fluorinated carbon nanotubes, and the other conditions are the same as in Example 1.

[0044] Example 8

[0045] This embodiment 8 provides a high-ratio, low-expansion modified silicon-carbon composite material. The modified silicon-carbon composite material has a particulate structure and includes a silicon-carbon material as the core and a fluorinated conductive polymer layer (fluorinated coating layer) covering the surface of the silicon-carbon material.

[0046] The silicon-carbon material is prepared by chemical vapor deposition and has a particulate structure, specifically obtained by coating a carbon layer onto the surface of silicon particles; the fluorinated conductive polymer layer is obtained by polymerization initiated by a first monomer and a second monomer, wherein the first monomer is a fluorinated polymer monomer, specifically trifluoroethyl methacrylate; and the second monomer is acrylic acid.

[0047] The specific preparation process of this high-ratio, low-expansion modified silicon-carbon composite material is as follows:

[0048] (1) Add 1000.0g of silicon carbide material, 150.0g of trifluoroethyl methacrylate and 30.0g of acrylic acid to a hydrothermal reactor;

[0049] (2) Add 12.0 kg of mixed solvent (made of water and ethanol in a volume ratio of 1:2) to the reactor and stir at a rate of 400 rpm. At the same time, raise the temperature from room temperature to 65°C at a rate of 2°C / min. After the temperature reaches 65°C, slowly add 0.6 g of ammonium persulfate as an initiator to the reactor and keep the reaction at the temperature for 4 hours. After the reaction, cool, filter, wash with water, and dry to obtain fluorinated coated silicon carbon material, which is the modified silicon carbon composite material.

[0050] Example 9

[0051] This embodiment 9 provides a high-ratio, low-expansion modified silicon-carbon composite material. The modified silicon-carbon composite material has a particulate structure and includes a silicon-carbon material as the core and a fluorinated conductive polymer layer (fluorinated coating layer) covering the surface of the silicon-carbon material.

[0052] The silicon-carbon material is prepared by chemical vapor deposition and has a particulate structure, specifically obtained by coating a carbon layer on the surface of silicon particles; the fluorinated conductive polymer layer is obtained by polymerization initiated by a first monomer and a second monomer, wherein the first monomer is a fluorinated polymer monomer, specifically hexafluoropropylene oxide; and the second monomer is acrylic acid.

[0053] The specific preparation process of this high-ratio, low-expansion modified silicon-carbon composite material is as follows:

[0054] (1) Add 1000.0g of silicon carbide material, 185.0g of hexafluoropropylene oxide and 45.0g of acrylic acid to a hydrothermal reactor;

[0055] (2) Add 7.0 kg of mixed solvent (made of water and ethanol in a volume ratio of 1:2) to the reactor and stir at a rate of 400 rpm. At the same time, raise the temperature from room temperature to 75°C at a rate of 2°C / min. After the temperature reaches 75°C, slowly add 1.5 g of ammonium persulfate as an initiator to the reactor and keep the reaction at the temperature for 5 hours. After the reaction, cool, filter, wash with water, and dry to obtain fluorinated coated silicon carbon material, which is the modified silicon carbon composite material.

[0056] Comparative Example 1

[0057] Comparative Example 1 uses silicon-carbon materials prepared by chemical vapor deposition as a direct comparison, as described in Examples 1-9.

[0058] test:

[0059] The specific capacity, initial coulombic efficiency (ICE), expansion rate, and Li were measured in Examples 1-7 and Comparative Example 1. + The diffusion coefficient was tested, and the specific results are as follows:

[0060]

[0061]

[0062] As can be seen from the test results of the above embodiments and comparative examples, the high-ratio, low-expansion modified silicon-carbon composite material provided by this invention has an improved initial coulombic efficiency (ICE) compared to existing silicon-carbon materials. More importantly, it reduces the material's expansion rate, which can effectively avoid the problem of coating layer cracking, thereby reducing the occurrence of side reactions and improving the material's cycle stability. Furthermore, the test results also show that the modified silicon-carbon composite material provided by this invention can further improve Li... + Diffusion coefficient helps Li + High-throughput transmission improves rate performance.

[0063] The above-described preferred embodiments of the present invention are for illustrative purposes only and are not intended to limit the scope of the invention. Any obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A high-ratio, low-expansion modified silicon-carbon composite material, characterized in that, The modified silicon-carbon composite material has a particulate structure, comprising a silicon-carbon material as the core and a fluorinated conductive polymer layer coating the surface of the silicon-carbon material. The silicon-carbon material has a particulate structure, which is obtained by coating the surface of silicon particles with a carbon layer; the fluorine-containing conductive polymer layer is obtained by polymerization initiated by a first monomer and a second monomer, wherein the first monomer is a fluorine-containing polymer monomer.

2. The high-ratio, low-expansion modified silicon-carbon composite material according to claim 1, characterized in that, The fluorinated polymer monomer is selected from one or more of the following: fluorinated acrylic acid, tetrafluoroethylene, trifluorochloroethylene, vinylidene fluoride, hexafluoropropylene, hexafluorobutyl methacrylate, perfluorooctyl ethyl acrylate, trifluoroethyl methacrylate, pentafluorostyrene, trifluoromethylstyrene, perfluoroalkoxy vinyl ether, hexafluoropropylene oxide, octafluorocyclobutane, trifluoropropylmethylcyclotrisiloxane, and fluorinated carbon nanotubes.

3. The high-ratio, low-expansion modified silicon-carbon composite material according to claim 1, characterized in that, The second monomer is acrylic acid.

4. The high-ratio, low-expansion modified silicon-carbon composite material according to claim 1, characterized in that, The initiator used to initiate the polymerization is ammonium persulfate.

5. A method for preparing a high-ratio, low-expansion modified silicon-carbon composite material according to any one of claims 1 to 4, characterized in that, The method includes the following steps: The silicon-carbon material, the first monomer, and the second monomer are added to a hydrothermal reactor. A mixed solvent of water and ethanol is then added to the reactor, and the mixture is heated while stirring. Once the target temperature is reached, an initiator is added, and the reaction is maintained at this temperature. After the reaction, the mixture is cooled, filtered, washed with water, and dried to obtain a fluorinated silicon-carbon material, which is a modified silicon-carbon composite material.

6. The method for preparing a high-ratio, low-expansion modified silicon-carbon composite material according to claim 5, characterized in that, The mass ratio between the silicon-carbon material, the first monomer, and the second monomer is 1:(0.1-0.2):(0.02-0.05).

7. The method for preparing a high-ratio, low-expansion modified silicon-carbon composite material according to claim 5, characterized in that, The mass ratio between the silicon-carbon material and the mixed solvent is 1:(5-15); the mixed solvent is obtained by mixing water and ethanol in a volume ratio of (1-2):(1-2).

8. The method for preparing a high-ratio, low-expansion modified silicon-carbon composite material according to claim 5, characterized in that, The stirring rate is 100-600 rpm; during the preparation process, the temperature is increased to 50-80℃ at a rate of 1-3℃ / min, and then 1.0-5.0% of the mass of the second monomer as an initiator is added, and the reaction is maintained at this temperature for 3-6 hours to complete the preparation.

9. The use of the high-ratio, low-expansion modified silicon-carbon composite material according to any one of claims 1 to 4, characterized in that, The modified silicon-carbon composite material is mixed with a conductive agent, a binder and a dispersant as the negative electrode active component to form a negative electrode coating slurry for preparing a negative electrode sheet for lithium-ion batteries. The mass ratio of the modified silicon-carbon composite material, the conductive agent, and the binder is (75-85):(8-15):(8-12).

10. The use of the high-ratio, low-expansion modified silicon-carbon composite material according to claim 9, characterized in that, The conductive agent is selected from Super-P and / or carbon nanotubes; the binder is selected from at least one of LA136D, polyvinylidene fluoride, and polyacrylonitrile; the dispersant is deionized water; the preparation process of the negative electrode sheet is as follows: the negative electrode coating slurry is coated on the negative electrode current collector, dried under vacuum, and rolled to obtain the negative electrode sheet.

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