A silicon-carbon active material, its preparation method and application in lithium-ion batteries

Abstract

This invention provides a silicon-carbon active material, its preparation method, and its application in lithium-ion batteries, belonging to the field of electrode material technology. The preparation method of the silicon-carbon active material provided by this invention includes the following steps: providing a raw material dispersion, wherein the raw material dispersion comprises silicon-carbon material, binder monomer, nitride, and dispersant; the silicon-carbon material comprises porous carbon material, silicon deposited in the pores of the porous carbon material, and a carbon layer coating the surface of the porous carbon material with deposited silicon; mixing the raw material dispersion with an initiator and carrying out a polymerization reaction to obtain the silicon-carbon active material. The silicon-carbon active material prepared by the method of this invention, when used as a negative electrode material for lithium-ion batteries, can effectively alleviate the volume expansion and pulverization of silicon-carbon materials, resulting in excellent cycle stability of lithium-ion batteries.

Description

Technical Field

[0001] This invention relates to the field of electrode materials technology, and in particular to a silicon-carbon active material, its preparation method, and its application in lithium-ion batteries. Background Technology

[0002] Compared to traditional graphite anodes, silicon-carbon anode materials have become the ideal next-generation anode material due to their high energy density. However, there are still significant obstacles to the commercial application of silicon-carbon anode materials. The volume expansion during charge and discharge causes the electrode material to pulverize, and it also suffers from poor conductivity, thus preventing its stable long-cycle application in battery systems.

[0003] Surface coating treatment of electrode materials is an effective optimization solution. For example, inorganic carbon is used as the coating layer in related technologies. However, the inorganic carbon coating layer is a rigid layer, which is prone to cracking during charging and discharging, making it difficult to alleviate the pulverization of the electrode material. Summary of the Invention

[0004] The purpose of this invention is to provide a silicon-carbon active material, its preparation method, and its application in lithium-ion batteries. The silicon-carbon active material prepared by the method of this invention, when used as a negative electrode material for lithium-ion batteries, can effectively alleviate the volume expansion and pulverization of silicon-carbon materials, thereby enabling lithium-ion batteries to have excellent cycle stability.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing silicon-carbon active materials, comprising the following steps:

[0007] A raw material dispersion is provided, the raw material dispersion comprising silicon-carbon material, binder monomer, nitride and dispersant, wherein the silicon-carbon material comprises porous carbon material, silicon deposited in the pores of the porous carbon material and a carbon layer coated on the surface of the porous carbon material on which silicon is deposited;

[0008] The raw material dispersion is mixed with an initiator and subjected to a polymerization reaction to obtain the silicon-carbon active material.

[0009] Preferably, the average particle size of the silicon-carbon material is 5-8 μm, the silicon content in the silicon-carbon material is 48-52 wt%, and the thickness of the carbon layer is 1-20 nm; the content of silicon-carbon material in the raw material dispersion is 5-15 wt%.

[0010] Preferably, the binder monomer comprises a mixture of butadiene and styrene, acrylic acid, or acrylonitrile, and the mass of the binder monomer is 0.5-10% of the mass of the silicon carbide material; the initiator is persulfate, and the mass of the initiator is 2-15% of the mass of the binder monomer.

[0011] Preferably, the nitride includes one or more of silicon nitride, carbon nitride, titanium nitride, and lithium nitride, the particle size of the nitride is 80-200 nm, and the mass of the nitride is 0.1-5% of the mass of the silicon-carbon material.

[0012] Preferably, the method for preparing the raw material dispersion includes the following steps:

[0013] A silicon-carbon material and a dispersant are first mixed to obtain a first dispersion; the mass ratio of the dispersant to the silicon-carbon material in the first dispersion is 5 to 10:1, and the first mixing is a stirring mixture.

[0014] The binder monomer, nitride, and dispersant are mixed in a second process to obtain a second dispersion; the second mixing is ultrasonic mixing, wherein the ultrasonic mixing power is 90-180W, the frequency is 30-50kHz, and the time is 1-3h.

[0015] The first dispersion and the second dispersion are mixed in a third mixture to obtain the raw material dispersion.

[0016] Preferably, the raw material dispersion further includes an electrostatic adsorbent, which includes one or more of polydiallyldimethylammonium chloride, protonated chitosan, and stearylamine, and the mass of the electrostatic adsorbent is 1 to 20% of the mass of the silicon carbide material.

[0017] Preferably, the polymerization reaction is carried out at a temperature of 40–120°C for 0.5–2 hours, and under stirring conditions. The polymerization reaction is further followed by solid-liquid separation of the product liquid obtained after the polymerization reaction, and washing and drying of the obtained solid material in sequence to obtain the silicon-carbon active material.

[0018] The present invention provides a silicon-carbon active material prepared by the preparation method described above, comprising a silicon-carbon material and a composite polymer layer coated on the surface of the silicon-carbon material; the silicon-carbon material comprises a porous carbon material, silicon deposited in the pores of the porous carbon material, and a carbon layer coated on the surface of the porous carbon material; the composite polymer layer comprises a binder-type polymer formed by the polymerization reaction of nitrides and binder monomers.

[0019] This invention provides the application of the silicon-carbon active material described in the above technical solution in lithium-ion battery anode materials.

[0020] The present invention provides a lithium-ion battery, comprising a negative electrode, a positive electrode, an electrolyte, and a separator. The negative electrode comprises a substrate and a negative electrode material loaded on the surface of the substrate. The negative electrode material comprises the silicon-carbon active material described in the above technical solution.

[0021] This invention provides a method for preparing a silicon-carbon active material, comprising the following steps: providing a raw material dispersion, wherein the raw material dispersion comprises a silicon-carbon material, a binder monomer, a nitride, and a dispersant, wherein the silicon-carbon material comprises a porous carbon material, silicon deposited in the pores of the porous carbon material, and a carbon layer coating the surface of the porous carbon material coated with silicon; mixing the raw material dispersion with an initiator and carrying out a polymerization reaction to obtain the silicon-carbon active material. In this invention, although the surface of the silicon-carbon material is coated with a carbon layer, this carbon layer is brittle and prone to cracking during material processing or electrode cycling. This invention uses a binder monomer to generate a binder-type polymer through in-situ polymerization, thereby forming a polymer layer in-situ coated on the surface of the silicon-carbon material. This polymer layer has stronger adhesion and better integrity to the silicon-carbon material, and the polymer is flexible, which can alleviate the volume expansion of the material during charging and discharging. Simultaneously, this invention introduces a nitride, which has high mechanical strength and is an inactive phase that can suppress the volume change of the material during charging and discharging, and can act as a mechanical protective layer to reduce the formation of SEI. Its reduction in the amorphous region can also accelerate Li… + Rapid conduction. Therefore, in this invention, the composite polymer layer formed by the binder-type polymer and nitride on the surface of silicon-carbon material can effectively alleviate the volume expansion and pulverization problems of the material and improve cycle stability.

[0022] Furthermore, the binder monomers of this invention include a mixture of butadiene and styrene, acrylic acid, or acrylonitrile. The binder monomers used in this invention contain unsaturated bonds and carboxyl groups, which allow for a tighter bond with silicon-carbon materials, thus improving the integrity of the polymer layer (for example, if the surface of a silicon-carbon material is not completely covered by a carbon layer, some silicon may be exposed and combine with moisture in the air to form Si-OH; the carboxyl groups in the binder monomer, such as acrylic acid, can form hydrogen bonds with the hydroxyl groups on the surface of the silicon-carbon material, thereby achieving a tight bond). Simultaneously, using the binder-type polymer formed by the polymerization reaction of the binder monomers as the binder in the preparation of electrodes for silicon-carbon anode materials enhances the adhesion between the silicon-carbon anode material and the electrode sheet, exhibits high stability in the electrolyte, and avoids side reactions with the electrolyte that could affect the performance of the lithium-ion battery.

[0023] Furthermore, related technologies involve high-temperature CVD carbon coating treatment on the surface of silicon-carbon materials to further form a carbon coating layer. This high-temperature treatment process increases the silicon grain size of the silicon-carbon material. The present invention prepares a composite polymer layer on the surface of silicon-carbon materials without high-temperature carbonization treatment. Therefore, the silicon grain size of the silicon-carbon material is small and controllable, essentially in an amorphous state. Small silicon grain size is beneficial to improving the cycle stability of the material. Therefore, the silicon-carbon active material provided by the present invention exhibits excellent cycle stability as a negative electrode material for lithium-ion batteries. Attached Figure Description

[0024] Figure 1Scanning electron microscope image of silicon carbide material;

[0025] Figure 2 This is a scanning electron microscope image of the silicon-carbon active material prepared in Example 1;

[0026] Figure 3 The image shows the XRD pattern of the silicon-carbon active material prepared in Example 1.

[0027] Figure 4 This is a graph showing the first charge-discharge curve of a coin cell assembled using the silicon-carbon active material described in Example 1. Detailed Implementation

[0028] This invention provides a method for preparing silicon-carbon active materials, comprising the following steps:

[0029] A raw material dispersion is provided, the raw material dispersion comprising silicon-carbon material, binder monomer, nitride and dispersant, wherein the silicon-carbon material comprises porous carbon material, silicon deposited in the pores of the porous carbon material and a carbon layer coated on the surface of the porous carbon material on which silicon is deposited;

[0030] The raw material dispersion is mixed with an initiator and subjected to a polymerization reaction to obtain the silicon-carbon active material.

[0031] In this invention, unless otherwise specified, all raw materials used are commercially available products well known to those skilled in the art or prepared using methods well known to those skilled in the art.

[0032] This invention provides a raw material dispersion comprising a silicon-carbon material, a binder monomer, a nitride, and a dispersant. The silicon-carbon material comprises a porous carbon material, silicon deposited in the pores of the porous carbon material, and a carbon layer (specifically an inorganic carbon layer) coating the surface of the silicon-deposited porous carbon material. In one embodiment of this invention, the particle size of the silicon-carbon material can be 5–10 μm; the average particle size of the silicon-carbon material can be 5–8 μm, more preferably 6–7 μm, specifically 6.5 μm; the silicon content in the silicon-carbon material can be 48–52 wt%, more preferably 49–51 wt%, specifically 49.8 wt%, and the silicon deposited in the pores of the porous carbon material is sufficient to ensure that the silicon content in the silicon-carbon material meets the above requirements; the thickness of the carbon layer can be 1–50 nm, more preferably 10–50 nm; and the porosity of the porous carbon material can be 70–80%. In one embodiment of the present invention, silicon is deposited in the pores of a porous carbon material using chemical vapor deposition (CVD), followed by carbon deposition on the surface of the silicon-coated porous carbon material using CVD to form a carbon layer. The present invention does not impose specific limitations on the specific conditions for silicon and carbon deposition, as long as the required silicon content and carbon layer thickness are obtained. In another embodiment of the present invention, the silicon-carbon material content in the raw material dispersion can be 5–15 wt%, specifically 5 wt%, 6 wt%, 7 wt%, 7.7%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, or 15 wt%.

[0033] In one embodiment of the present invention, the binder monomer may include a mixture of butadiene and styrene, acrylic acid or acrylonitrile, with acrylic acid specifically used in the embodiment; the mass of the binder monomer may be 0.5% to 10% of the mass of the silicon carbide material, specifically 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%.

[0034] In one embodiment of the present invention, the nitride may include one or more of silicon nitride, carbon nitride, titanium nitride, and lithium nitride, specifically silicon nitride, carbon nitride, titanium nitride, or lithium nitride; the particle size of the nitride may be 80–200 nm, more preferably 100–200 nm; the mass of the nitride may be 0.1–5% of the mass of the silicon-carbon material, specifically 0.1%, 0.3%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%.

[0035] This invention utilizes a binder monomer that undergoes a polymerization reaction to form a binder-type polymer that is in situ coated onto the surface of silicon-carbon materials, creating a uniform polymer coating layer. The binder monomers used in this embodiment contain unsaturated bonds and carboxyl groups, enabling a tighter bond with the silicon-carbon material surface and improving the integrity of the polymer coating layer. Furthermore, this binder-type polymer is used as a binder in the preparation of electrodes for silicon-carbon anode materials, exhibiting high stability in the electrolyte and avoiding side reactions with the electrolyte that could affect lithium-ion battery performance. In this embodiment, controlling the amount of the binder monomer within the aforementioned range ensures the formation of a uniform and complete coating layer on the silicon-carbon material surface. If the amount of binder monomer is insufficient, the coating will be incomplete, making it difficult to form a uniform and complete coating layer on the silicon-carbon material surface.

[0036] Meanwhile, this invention introduces nitrides into the binder monomer base. As an inactive phase, nitrides can suppress volume changes in silicon-carbon anode materials and possess high mechanical strength, serving as a mechanical protective layer to reduce SEI formation. Furthermore, their reduction in the amorphous region can promote Li… + Rapid conduction. Therefore, the composite polymer layer formed by the binder-type polymer and nitride in this invention can effectively alleviate the volume expansion problem of silicon-carbon anode materials and improve cycle stability. The above-mentioned types of nitrides used in the embodiments of this invention can enhance Li... + Conducting and mitigating electrode volume expansion helps improve the stability of electrode materials; controlling the amount of the nitride within the above range can reduce capacity loss and help maintain a high capacity.

[0037] In one embodiment of the present invention, the raw material dispersion may further include an electrostatic adsorbent, which may include one or more of polydiallyldimethylammonium chloride, protonated chitosan, and stearylamine. Specifically, it may be polydiallyldimethylammonium chloride, protonated chitosan, or stearylamine. The mass of the electrostatic adsorbent is 1-20% of the mass of the silicon-carbon material, more specifically 1-10%, and even more specifically 1-5%, specifically 1-2%. The electrostatic adsorbent of the present invention helps to ensure sufficient contact between the binder monomer and the silicon-carbon material. In the embodiments of the present invention, the above-mentioned type of electrostatic adsorbent is used, which can be adsorbed on the surface of the silicon-carbon material, which is beneficial to the uniform dispersion and adsorption of the binder monomer on the surface of the silicon-carbon material. Controlling the amount of the electrostatic adsorbent within the above range can avoid excessive electrostatic adsorbent agglomeration and reduced capacity, which is beneficial to ensuring that the final silicon-carbon active material has excellent electrochemical performance.

[0038] In one embodiment of the present invention, the dispersant in the raw material dispersion can be water, and the water can be pure water.

[0039] As one embodiment of the present invention, the method for preparing the raw material dispersion may include the following steps:

[0040] The silicon-carbon material and the dispersant are mixed in the first step to obtain the first dispersion.

[0041] The binder monomer, nitride and dispersant are mixed a second time to obtain a second dispersion;

[0042] The first dispersion and the second dispersion are mixed in a third mixture to obtain the raw material dispersion.

[0043] In one embodiment of the present invention, when the raw material dispersion includes an electrostatic adsorbent, the electrostatic adsorbent is specifically added during the first mixing process, that is, the first dispersion includes an electrostatic adsorbent (specifically, silicon carbon material, electrostatic adsorbent, and dispersant can be first mixed to obtain a first dispersion). In one embodiment of the present invention, the mass ratio of dispersant to silicon carbon material in the first dispersion can be 5-10:1, further 7-9:1, and specifically 8:1; the first mixing method can be stirring mixing, the first mixing time can be 5-15 minutes, and the first mixing can be carried out at room temperature (25°C); the present invention does not have a special limitation on the stirring mixing rate, and a rate well known to those skilled in the art can be used.

[0044] In one embodiment of the present invention, the mass ratio of dispersant to binder monomer in the second dispersion can be 100-300:1, more preferably 150-250:1, and specifically 200:1; the second mixing method can be ultrasonic mixing, the ultrasonic mixing power can be 90-180W, more preferably 110-140W, and specifically 120W; the frequency can be 30-50kHz, more preferably 35-45kHz, and specifically 40kHz; the ultrasonic mixing time can be 1-3h, specifically 1h, 1.5h, 2h, 2.5h, or 3h; if the ultrasonic mixing time is too short, it may lead to uneven dispersion or even regional agglomeration of binder monomer and nitride, affecting the uniformity of the coating layer and the stability of the material.

[0045] In one embodiment of the present invention, the volume ratio of the first dispersion to the second dispersion is sufficient to ensure that the content of each component meets the requirements of the raw material dispersion; the third mixing specifically involves adding the second dispersion to the first dispersion.

[0046] In this invention, the silicon-carbon material is coated with a carbon layer, which has a certain degree of hydrophobicity. If the amount of dispersant is too low, the silicon-carbon material is difficult to disperse uniformly, and the uniformity of the binder monomer and nitride dispersion is also difficult to guarantee, affecting the polymerization reaction process and the uniformity of the composite polymer layer. If the amount of dispersant is too high, the mechanical operation during the mixing process may damage the carbon layer structure, causing the silicon deposited in the pores of the porous carbon material to be exposed to water, leading to gas generation, silicon oxidation, and other situations, resulting in deterioration of material performance. In the embodiments of this invention, the amount of each component is controlled within the above-mentioned range, which is conducive to ensuring uniform dispersion of each component, allowing the silicon-carbon material, binder monomer and nitride to fully contact, and a more complete and uniform composite polymer layer can be constructed on the surface of the silicon-carbon material through the polymerization reaction.

[0047] After obtaining the raw material dispersion, the present invention mixes the raw material dispersion with an initiator to carry out a polymerization reaction to obtain the silicon-carbon active material. In one embodiment of the present invention, the initiator can be a persulfate, which may include one or more of ammonium persulfate, sodium persulfate, and potassium persulfate, specifically ammonium persulfate, sodium persulfate, or potassium persulfate; the mass of the initiator can be 2-15% of the mass of the binder monomer, more preferably 8-12%, specifically 10%. Controlling the amount of initiator within the above range in the embodiments of the present invention is beneficial to ensuring the polymerization reaction proceeds fully. If the amount of initiator is too low, it is difficult to ensure the complete polymerization of the binder monomer; if the amount of initiator is too high, too many impurities will be introduced, affecting the performance of the silicon-carbon active material.

[0048] In this invention, the raw material dispersion is preferably heated to the temperature required for the polymerization reaction, and then an initiator is added to carry out the polymerization reaction. As one embodiment of this invention, the polymerization reaction temperature can be 40–120°C, more preferably 50–100°C, and even more preferably 55–80°C, specifically 60°C; the time can be 0.5–2 hours, specifically 1 hour; the polymerization reaction is preferably carried out under stirring conditions. This invention does not have a particular limitation on the stirring rate; any rate well known to those skilled in the art can be used. In the polymerization process described in this invention, the binder monomers are polymerized in situ on the surface of the silicon-carbon material under the action of the initiator to form a binder-type polymer. At the same time, nitrides are doped into the binder-type polymer, thereby forming a composite polymer layer composed of the binder-type polymer and nitrides on the surface of the silicon-carbon material. If the polymerization temperature is too low, the binder monomers will have difficulty polymerizing. If the polymerization temperature is too high, the silicon-carbon material is prone to oxidation, which will affect the performance of the silicon-carbon active material. If the polymerization time is too long, the structure of the silicon-carbon material will be easily destroyed, affecting the stability of the reaction system. In addition, the silicon-carbon material is prone to oxidation during this process, which will lead to a decrease in the electrochemical performance of the silicon-carbon active material.

[0049] As one embodiment of the present invention, the polymerization reaction preferably further includes: solid-liquid separation of the product liquid obtained after the polymerization reaction, and washing and drying the obtained solid material in sequence to obtain the silicon-carbon active material; the solid-liquid separation can be centrifugation; the washing reagent can be pure water; the drying temperature can be 80-120℃, specifically 100℃, and the time can be 8-12h, specifically 10h; the drying is preferably carried out in a protective atmosphere, preferably an inert atmosphere, specifically nitrogen.

[0050] This invention improves the expansion and structural stability of silicon-carbon active materials through in-situ polymerization, while also enhancing their long-cycle capability. Moreover, the preparation process is safe and simple, which is conducive to industrial implementation. The silicon-carbon active material is a low-expansion and high-stability silicon-carbon material with broad application prospects.

[0051] The present invention provides a silicon-carbon active material prepared by the preparation method described above, comprising a silicon-carbon material and a composite polymer layer coated on the surface of the silicon-carbon material; the silicon-carbon material comprises a porous carbon material, silicon deposited in the pores of the porous carbon material, and a carbon layer coated on the surface of the porous carbon material on which silicon is deposited; the composite polymer layer comprises a binder-type polymer formed by the polymerization reaction of nitrides and binder monomers.

[0052] In one embodiment of the present invention, the material of the composite polymer layer may further include an electrostatic adsorbent; specifically, during the polymerization reaction, the electrostatic adsorbent in the raw material dispersion adsorbs onto the surface of the silicon-carbon material. When the binder monomer is added, it is more easily and uniformly dispersed and adsorbed on the surface of the silicon-carbon material, which is beneficial for forming a uniform composite polymer layer and ultimately retaining some of the electrostatic adsorbent in the composite polymer layer. In one embodiment of the present invention, the thickness of the composite polymer layer can be 1–20 nm, and more preferably 2–10 nm.

[0053] This invention provides the application of the silicon-carbon active material described in the above technical solution in lithium-ion battery anode materials.

[0054] The present invention provides a lithium-ion battery, comprising a negative electrode, a positive electrode, an electrolyte, and a separator. The negative electrode comprises a substrate and a negative electrode material loaded on the surface of the substrate. The negative electrode material comprises the silicon-carbon active material described in the above technical solution.

[0055] The negative electrode of this invention comprises a substrate and a negative electrode material loaded on the surface of the substrate. In one embodiment of this invention, the substrate may be a copper foil current collector; the raw materials for preparing the negative electrode material may include silicon-carbon active material, carbon black, and a binder, wherein the mass ratio of the silicon-carbon active material, carbon black, and binder may be 80:10:10, and the binder may be an aqueous solution of polyacrylic acid with a concentration of 3.4 wt%. In a specific embodiment of this invention, the silicon-carbon active material, carbon black, and binder are mixed, the resulting mixture is coated onto the surface of the substrate, and dried to obtain the negative electrode.

[0056] In one embodiment of the present invention, the positive electrode is specifically a lithium metal sheet.

[0057] In one embodiment of the present invention, the electrolyte may be LBC3425A26 (purchased from Shenzhen Xinzhoubang Technology Co., Ltd.).

[0058] In one embodiment of the present invention, the diaphragm may be a ceramic diaphragm.

[0059] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0060] Unless otherwise specified, the operating methods used in the following experiments are all conventional methods. Unless otherwise specified, the raw materials and reagents used in the following experiments can be obtained commercially or prepared using methods well known to those skilled in the art; the protonated chitosan used was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., model C766421; the silicon-carbon material used was from Jiangxi Yijin New Energy Technology Co., Ltd., specifically, silicon was deposited in the pores of porous carbon material (porosity 75%) using chemical vapor deposition, followed by carbon deposition on the surface of the silicon-deposited porous carbon material using chemical vapor deposition to form a carbon layer, thus obtaining the silicon-carbon material. The silicon content in the silicon-carbon material is 49.8% by mass, the thickness of the carbon layer is 10–50 nm, the particle size of the silicon-carbon material is 5–10 μm, and the average particle size is 6.5 μm.

[0061] Example 1

[0062] (1) Mix 10g of silicon carbide material, 0.1g of electrostatic adsorbent (specifically protonated chitosan) with 80mL of pure water, and stir and disperse at room temperature (25℃) for 10min to obtain the first dispersion;

[0063] (2) Mix 0.2g acrylic monomer, 0.1g silicon nitride powder (particle size 100-200nm) with 40mL pure water, and ultrasonically disperse for 2h under ultrasonic power of 120W and frequency of 40kHz to obtain a second dispersion.

[0064] (3) The second dispersion is added to the first dispersion (the mass of acrylic monomer is 2% of the mass of silicon carbon material, and the mass of silicon nitride powder is 1% of the mass of silicon carbon material). The resulting raw material dispersion is heated to 60°C, and 0.02g of initiator (specifically ammonium persulfate) is added. The polymerization reaction is carried out under the heat preservation condition by stirring for 1h to form a composite polymer layer on the surface of the silicon carbon material. The resulting product liquid is centrifuged, the solid material is collected and washed with pure water, and then dried at 100°C for 10h in an inert atmosphere (specifically nitrogen) to obtain silicon carbon active material (the thickness of the composite polymer layer is 2-10nm).

[0065] Figure 1 The image shows a scanning electron microscope (SEM) image of silicon-carbon material. The results show that the silicon-carbon material particles have a smooth and dense surface and a particle size of 5–10 μm.

[0066] Figure 2 The image shows a scanning electron microscope (SEM) image of the silicon-carbon active material prepared in Example 1. The results show that the silicon-carbon active material prepared in Example 1 has a smooth and dense surface with no obvious pores and a particle size of 5–10 μm.

[0067] Figure 3 The image shows the XRD pattern of the silicon-carbon active material prepared in Example 1. The results show that the silicon-carbon active material prepared in Example 1 has no obvious impurity peaks, indicating that the morphology and crystal form of the silicon-carbon material do not change significantly after polymer coating treatment, and the initial morphology is retained.

[0068] Example 2

[0069] The method is operated according to Example 1, except that the volume of pure water in step (1) is 50 mL, which is 5 times the mass of silicon carbon material.

[0070] Example 3

[0071] The method is operated according to Example 1, except that the volume of pure water in step (1) is 100 mL, which is 10 times the mass of silicon carbon material.

[0072] Example 4

[0073] The procedure is the same as in Example 1, except that in step (2), the mass of the acrylic monomer is 0.05 g, which is 0.5% of the mass of the silicon carbide material.

[0074] Example 5

[0075] The procedure is the same as in Example 1, except that in step (2), the mass of the acrylic monomer is 0.1g, which is 1% of the mass of the silicon carbide material.

[0076] Example 6

[0077] The procedure is the same as in Example 1, except that in step (2), the mass of the acrylic monomer is 0.3g, which is 3% of the mass of the silicon carbide material.

[0078] Example 7

[0079] The procedure is the same as in Example 1, except that in step (2), the mass of the acrylic monomer is 0.5g, which is 5% of the mass of the silicon carbide material.

[0080] Example 8

[0081] The method is operated according to Example 1, except that the mass of silicon nitride powder in step (2) is 0.05g, that is, the mass of silicon nitride powder is 0.5% of the mass of silicon carbon material.

[0082] Example 9

[0083] The procedure is the same as in Example 1, except that the mass of silicon nitride powder in step (2) is 0.2g, which is 2% of the mass of silicon carbon material.

[0084] Example 10

[0085] The procedure is the same as in Example 1, except that the ultrasonic dispersion time in step (2) is 0.5 h.

[0086] Example 11

[0087] The procedure is the same as in Example 1, except that the ultrasonic dispersion time in step (2) is 1 hour.

[0088] Example 12

[0089] The procedure is the same as in Example 1, except that the ultrasonic dispersion time in step (2) is 3 hours.

[0090] Example 13

[0091] The method is operated according to Example 1, except that the polymerization reaction time in step (3) is 0.5 h.

[0092] Example 14

[0093] The method is operated according to Example 1, except that the polymerization reaction time in step (3) is 2 hours.

[0094] Example 15

[0095] The procedure is the same as in Example 1, except that no electrostatic adsorbent is used.

[0096] Example 16

[0097] The procedure is the same as in Example 1, except that the electrostatic adsorbent in step (1) is polydiallyldimethylammonium chloride (0.1g).

[0098] Comparative Example 1

[0099] Mix 10g of silicon-carbon material with 120mL of pure water, stir and disperse at room temperature for 10min, then heat to 60℃ and stir and disperse for 1h; centrifuge the resulting liquid, collect the solid material, wash with pure water, and then dry at 100℃ for 10h in an inert atmosphere (specifically nitrogen) to obtain silicon-carbon active material.

[0100] Comparative Example 2

[0101] The procedure is the same as in Example 1, except that no acrylic monomer is used.

[0102] Comparative Example 3

[0103] The procedure is the same as in Example 1, except that no silicon nitride powder is used.

[0104] Application Example 1

[0105] The electrochemical performance of the silicon-carbon active materials prepared in the examples and comparative examples was tested according to the following method: The prepared silicon-carbon active material was used as the negative electrode material and mixed with carbon black and polyacrylic acid (PAA) aqueous solution at a mass ratio of 80:10:10 to form a slurry, wherein the polyacrylic acid aqueous solution was used as a binder and the concentration of the polyacrylic acid aqueous solution was 3.4 wt%; the slurry was uniformly coated onto a copper foil current collector and dried under vacuum for 12 h to obtain the working electrode; a lithium sheet was used as the counter electrode, a ceramic separator was used, and LBC3425A26 electrolyte (purchased from Shenzhen Xinzhoubang Technology Co., Ltd.) was used to assemble a coin cell in an argon atmosphere in a Microna inert gas glove box.

[0106] Charge and discharge test: The assembled button cell battery was charged and discharged on the LAND charge and discharge tester. The charge and discharge range was 0.005 to 1.5V. A three-stage discharge method was adopted, with discharge current densities of 0.1C, 0.02C and 0.01C, and a charging current density of 0.1C. Figure 4 This is a graph showing the first charge-discharge curve of a coin cell assembled using the silicon-carbon active material described in Example 1.

[0107] Expansion Test: The working electrode prepared by the above process is used to measure the initial electrode thickness. The electrode is then assembled into a coin cell according to the above process and charged and discharged for one week. After lithium insertion to 70% SOC, the battery is disassembled, the electrode is allowed to dry, and the electrode thickness after lithium insertion is measured. The unit expansion is calculated based on the formula: (lithium-inserted electrode thickness - initial electrode thickness) / lithium insertion amount. A smaller unit expansion indicates better material stability.

[0108] High-temperature gas generation test: The silicon-carbon active material prepared in the examples and comparative examples was used as the negative electrode material and mixed with carbon black and composite binder at a mass ratio of 90:5:5 to form a slurry. The composite binder was a binder formed by sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR), and the mass ratio of CMC to SBR in the composite binder was 2:3. The slurry was sealed in an aluminum-plastic bag to remove air, and the density value of the freshly prepared slurry was tested using a solid density meter. Then, the density value was tested again after storing it at 45°C for 24 hours. The gas generation of the material was calculated according to v = m / ρ. The higher the gas generation value, the more serious the material damage and the worse the material stability.

[0109] The results of electrochemical performance testing, expansion testing, and high-temperature gas generation testing of silicon-carbon active materials are shown in Table 1 below.

[0110] Table 1 Performance test results of silicon-carbon active materials

[0111]

[0112]

[0113] from Figure 4 As can be seen from the data in Table 1, the initial reversible specific capacity of the silicon-carbon active material prepared in Example 1 of this invention is above 1800 mAh / g, the initial coulombic efficiency is above 92%, the capacity retention rate after 100 cycles is above 82%, the material expansion per unit is less than 5 μm / mAh, and the gas production of the slurry is low during the preparation of the negative electrode slurry, indicating that the composite polymer layer in this invention can effectively alleviate the volume expansion and particle breakage of silicon-carbon materials during the charging and discharging process.

[0114] Furthermore, according to Table 1, in Comparative Example 1, the silicon-carbon material with carbon layer was not subjected to in-situ polymerization of binder monomers and modification with silicon nitride. Although the initial coulombic efficiency of the electrode was not significantly reduced, its initial reversible specific capacity was low, its cycle performance was poor, and its gas production was high, indicating that an effective polymer coating layer was not formed.

[0115] In Comparative Example 2, the silicon-carbon material containing the carbon layer was not polymerized in situ with binder monomers, but only modified with silicon nitride. It had a low initial reversible specific capacity, low cycle performance, and high gas production.

[0116] In Comparative Example 3, the silicon-carbon material containing the carbon layer was only polymerized in situ with binder monomers without silicon nitride modification. The initial reversible specific capacity was low and the cycle performance was reduced, indicating that the ion transport effect of nitrides affected its cycle performance to a certain extent.

[0117] In summary, the binder monomer used in this invention contains unsaturated bonds and carboxyl groups, enabling it to bond more tightly to the surface of silicon-carbon materials. Through in-situ polymerization and coating, the resulting binder-type polymer forms a polymer coating layer with good uniformity and integrity on the surface of the silicon-carbon material. Furthermore, this binder-type polymer, used as a binder in the preparation of silicon-carbon anode electrodes, exhibits high stability in the electrolyte, avoiding side reactions with the electrolyte that could affect the performance of the lithium-ion battery. Additionally, this invention introduces nitrides, which are inactive phases with high mechanical strength, capable of suppressing volume changes in the anode material. Their reduction in the amorphous region can also promote the reduction of Li... + Due to the rapid conduction of the binder polymer and nitride, the composite polymer layer formed by these two materials in this invention can effectively alleviate the volume expansion problem of the silicon-carbon anode and improve cycle stability. The preparation method provided by this invention is simple to operate, highly efficient and safe, and uses inexpensive raw materials and reagents, thus having broad application prospects.

[0118] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a silicon-carbon active material, comprising the following steps: A raw material dispersion is provided, the raw material dispersion comprising silicon-carbon material, binder monomer, nitride and dispersant, wherein the silicon-carbon material comprises porous carbon material, silicon deposited in the pores of the porous carbon material, and a carbon layer coating the surface of the porous carbon material on which silicon is deposited; the nitride is one or more of silicon nitride, carbon nitride, titanium nitride and lithium nitride. The raw material dispersion is mixed with an initiator and subjected to a polymerization reaction to obtain the silicon-carbon active material; the polymerization reaction is carried out at a temperature of 40~120℃ for a time of 0.5~2h. The silicon-carbon material has an average particle size of 5-8 μm, a silicon content of 48-52 wt%, and a carbon layer thickness of 1-20 nm; the raw material dispersion contains 5-15 wt% silicon-carbon material; the binder monomer is a mixture of butadiene and styrene, acrylic acid, or acrylonitrile, and the mass of the binder monomer is 0.5-10% of the mass of the silicon-carbon material; the initiator is persulfate, and the mass of the initiator is 2-15% of the mass of the binder monomer; the nitride has a particle size of 80-200 nm, and the mass of the nitride is 0.1-5% of the mass of the silicon-carbon material.

2. The preparation method according to claim 1, characterized in that, The preparation method of the raw material dispersion includes the following steps: A silicon-carbon material and a dispersant are first mixed to obtain a first dispersion; the mass ratio of the dispersant to the silicon-carbon material in the first dispersion is 5~10:1, and the first mixing is a stirring mixture. The binder monomer, nitride, and dispersant are mixed in a second process to obtain a second dispersion; the second mixing is ultrasonic mixing, wherein the ultrasonic mixing power is 90~180W, the frequency is 30~50kHz, and the time is 1~3h. The first dispersion and the second dispersion are mixed in a third mixture to obtain the raw material dispersion.

3. The preparation method according to claim 1, characterized in that, The raw material dispersion also includes an electrostatic adsorbent, which includes one or more of polydiallyldimethylammonium chloride, protonated chitosan, and stearylamine. The mass of the electrostatic adsorbent is 1 to 20% of the mass of the silicon carbide material.

4. The preparation method according to claim 1, characterized in that, The polymerization reaction is carried out under stirring conditions; after the polymerization reaction, the product liquid obtained after the polymerization reaction is subjected to solid-liquid separation, and the obtained solid material is washed and dried in sequence to obtain the silicon-carbon active material.

5. The silicon-carbon active material prepared by the preparation method according to any one of claims 1 to 4 comprises a silicon-carbon material and a composite polymer layer coated on the surface of the silicon-carbon material; the silicon-carbon material comprises a porous carbon material, silicon deposited in the pores of the porous carbon material, and a carbon layer coated on the surface of the porous carbon material on which silicon is deposited; the composite polymer layer comprises a binder-type polymer formed by the polymerization reaction of nitrides and binder monomers.

6. The application of the silicon-carbon active material according to claim 5 in lithium-ion battery anode materials.

7. A lithium-ion battery, comprising a negative electrode, a positive electrode, an electrolyte, and a separator, wherein the negative electrode comprises a substrate and a negative electrode material loaded on the surface of the substrate, and the negative electrode material comprises the silicon-carbon active material of claim 5.

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