Silicon-based composite material, preparation method and application thereof

Abstract

The application relates to the technical field of batteries, in particular to a silicon-based composite material and a preparation method and application thereof. The silicon-based composite material comprises a core and a coating layer, and a cavity structure exists between the core and the coating layer; the core comprises a silicon-based material; the coating layer comprises a metal layer and a conductive polymer layer, wherein the conductive polymer layer is arranged on at least part of the surface of the metal layer far away from the cavity structure. Compared with the prior art, the silicon-based material is combined with the metal layer and the conductive polymer layer to form a special structure with a cavity, so that uniform deposition of lithium ions is promoted on the basis of ensuring that the material as a whole has good stability, the conductive property is good, and the silicon-based composite material is suitable for application on a negative electrode current collector.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to a silicon-based composite material, its preparation method, and its application. Background Technology

[0002] The core performance indicators of lithium batteries mainly include energy density, cycle life, charging speed, safety, and temperature adaptability. Among them, energy density refers to the electrical energy stored per unit mass or volume, which determines the battery life of electrical devices. The current mainstream lithium batteries (such as ternary and lithium iron phosphate batteries) have an energy density of 160~300Wh / kg, while cutting-edge technologies (such as solid-state batteries and lithium metal batteries) can reach 400~600Wh / kg.

[0003] To improve the energy density of lithium-ion batteries, increasing research efforts are focused on weight reduction design for battery cells. Anode-less structures, because they eliminate the need for negative electrode active materials, can significantly reduce battery weight and thus increase energy density. However, anode-less structures currently face a serious problem: without the lithium intercalation of negative electrode active materials, the fate of lithium ions extracted from the positive electrode remains a concern. While conventional copper foil anodes can deposit lithium, they suffer from uneven lithium deposition, which can easily lead to lithium dendrite formation, puncturing the separator and causing short circuits between the positive and negative electrodes, posing a safety risk. Therefore, solving the problem of uneven lithium deposition in anode-less battery structures is a key focus and challenge for their application. Summary of the Invention

[0004] In view of this, the present invention aims to at least partially solve one of the technical problems in the related art. To this end, the present invention provides a silicon-based composite material, its preparation method, and its application. By combining the silicon-based material with a functional layer to form a special structure, it can promote the uniform deposition of lithium ions while ensuring good overall material stability, and also exhibits good conductivity, making it suitable for application in electrodeless current collectors.

[0005] To solve the above-mentioned technical problems, the present invention is implemented as follows: According to one aspect of the present invention, a silicon-based composite material is provided, comprising a core and a coating layer, wherein a cavity structure exists between the core and the coating layer; The core comprises a silicon-based material; the covering layer comprises a metal layer and a conductive polymer layer, wherein the conductive polymer layer is disposed on at least a portion of the surface of the metal layer on the side away from the cavity structure.

[0006] In some embodiments, the ratio of the inner diameter of the cavity structure to the particle size of the silicon-based material is (1.5~3):1.

[0007] In some of these embodiments, the silicon-based material includes one or more of silicon, silicon suboxide, and silicon carbon.

[0008] In some of these embodiments, the particle size of the silicon-based material is 200 nm to 1000 nm.

[0009] In some of these embodiments, the material of the metal layer includes one or more of copper, silver, and tin.

[0010] In some of these embodiments, the thickness of the metal layer is 50 nm to 200 nm.

[0011] In some embodiments, the material of the conductive polymer layer includes one or more of conductive polyimide, conductive polyaniline, and conductive polypyrrole.

[0012] In some embodiments, the thickness of the conductive polymer layer is 2 μm to 5 μm.

[0013] According to another aspect of the present invention, a method for preparing a silicon-based composite material is provided, comprising the following steps: a) Mix the binder, polyethylene, and a first solvent to obtain a first slurry; then coat the first slurry onto the surface of a silicon-based material, and after drying, obtain polyethylene-coated silicon-based material particles; b) Mix the pore-forming agent, binder, and first solvent to obtain a second slurry; then coat the second slurry onto the surface of the polyethylene-coated silicon-based material particles obtained in step a), dry them, perform a first grinding, then immerse them in a metal salt solution, and then add a reducing agent to react and obtain silicon-based material particles coated with a metal layer. c) After drying the silicon-based material particles coated with the metal layer obtained in step b), immerse them in the second solvent to dissolve the polyethylene and form a cavity structure. After cleaning and drying, the dried product is obtained. d) Coat the surface of the dried product obtained in step c) with a slurry containing a conductive polymer, and after drying, form a conductive polymer layer to obtain a silicon-based composite material.

[0014] In some embodiments, the adhesive includes one or more of polytetrafluoroethylene, styrene-butadiene rubber, and sodium carboxymethyl cellulose.

[0015] In some of these embodiments, the first solvent includes one or more of water, N-methylpyrrolidone, and N,N-dimethylformamide.

[0016] In some of these embodiments, the mass ratio of the adhesive to the polyethylene in step a) is (5~10):(90~95).

[0017] In some embodiments, before coating the silicon-based material in step a), the process further includes: performing a second grinding; the second grinding is performed at a rotation speed of 500 r / min to 1000 r / min for a time of 1 h to 2 h; preferably, after the second grinding, the particle size of the silicon-based material is 200 nm to 1000 nm.

[0018] In some embodiments, the particle size of the polyethylene-coated silicon-based material particles is 500 nm to 4000 nm.

[0019] In some embodiments, the pore-forming agent includes one or more of ammonium bicarbonate, ammonium chloride, and ammonium nitrate.

[0020] In some of these embodiments, the mass ratio of the pore-forming agent to the adhesive in step b) is (80~90):(5~10).

[0021] In some of these embodiments, the particle size of the product from the first grinding process is required to be 300 nm to 3000 nm.

[0022] In some embodiments, the metal salt solution includes one or more of tin sulfate solution, tin nitrate solution, tin chloride solution, silver nitrate solution, silver sulfate solution, silver chloride solution, copper sulfate solution, copper nitrate solution, and copper chloride solution.

[0023] In some of these embodiments, the immersion time in the metal salt solution in step b) is 1 h to 4 h.

[0024] In some of these embodiments, the reducing agent includes one or more of iron, zinc, and hydrazine hydrate.

[0025] In some embodiments, the drying temperature is 100°C to 150°C and the drying time is 2 hours to 4 hours.

[0026] In some of these embodiments, the second solvent includes one or more of benzene, toluene, dichloromethane, and chloroform.

[0027] In some of these embodiments, the immersion time in the second solvent in step c) is 4 h to 12 h.

[0028] In some of these embodiments, in step d): the conductive polymer includes one or more of conductive polyimide, conductive polyaniline, and conductive polypyrrole.

[0029] In some of these embodiments, in step d), the particle size of the conductive polymer is 100 nm to 500 nm.

[0030] In some of these embodiments, in step d), the slurry comprising the conductive polymer further comprises a binder and a first solvent; preferably, the mass ratio of the binder to the conductive polymer is (10~20):(80~90).

[0031] According to another aspect of the present invention, the present invention provides a negative electrode-free current collector, comprising the silicon-based composite material described in the above technical solution or the silicon-based composite material prepared by the preparation method described in the above technical solution.

[0032] According to another aspect of the present invention, the present invention provides a battery comprising the negative electrode-free current collector described in the above technical solution.

[0033] Implementing the technical solution of the present invention has at least the following beneficial effects: 1. The silicon-based composite material provided by this invention, by setting a conductive polymer layer, adsorbs lithium ions, promotes the transfer of lithium ions to the metal layer and the core, and inhibits the growth of lithium dendrites deposited on the metal layer; furthermore, by setting a metal layer inside the conductive polymer layer, the metal layer and lithium ions attract each other, promoting the deposition of lithium ions; at the same time, by setting a core inside the metal layer, the silicon-based material in the core promotes the alloying and embedding of lithium ions, reducing the amount of lithium ions deposited on the surface of the metal layer and inhibiting the growth of lithium ion dendrites; more importantly, by setting a cavity structure between the core and the metal layer, the expansion of the silicon-based material in the core after lithium embedding is prevented from damaging the silicon-based composite material, further improving the safety performance.

[0034] 2. The preparation method provided by this invention, based on traditional silicon-based materials, first performs pre-formed pores and then forms a metal layer and a conductive polymer layer, which can effectively alleviate the huge volume effect generated by traditional silicon-based materials during lithium insertion / extraction. Moreover, the preparation method is simple, the raw materials are readily available and the cost is low, it is suitable for large-scale production, has a high degree of practicality, and has broad application prospects.

[0035] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0036] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0037] Figure 1 This is a schematic diagram of the structure of the silicon-based composite material provided in an embodiment of the present invention.

[0038] Figure 2 This is a TEM image of the silicon-based composite material provided in Embodiment 1 of the present invention.

[0039] Figure label: 1. Core; 2. Cavity structure; 3. Metal layer; 4. Conductive polymer layer.

[0040] The accompanying drawings have illustrated specific embodiments of the invention, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0041] The present application will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0042] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges or individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0043] In the description of this application, "same chemical composition" should be interpreted broadly, that is, the main components of the two have the same chemical composition, or the two have substantially the same chemical composition, but may have errors or impurities within the acceptable range that can be understood by those skilled in the art.

[0044] In the description of this application, "A and / or B" can include any of the cases of A alone, B alone, or A and B, where A and B are merely examples and can be any technical feature connected by "and / or" in this application.

[0045] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0046] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0047] Unless otherwise specified, all technical features and optional technical features of this invention can be combined to form new technical solutions.

[0048] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0049] Currently, anode-less structures, by eliminating the need for negative electrode active materials, can significantly reduce battery weight and increase the energy density of lithium batteries. However, anode-less structures present a problem: without lithium intercalation in the negative electrode active material, the fate of lithium ions extracted from the positive electrode remains a concern. While conventional copper foil anodes can deposit lithium, uneven lithium deposition is a problem, easily leading to the formation of lithium dendrites that can puncture the separator, causing a short circuit between the positive and negative electrodes and posing a safety risk. Therefore, solving the problem of uneven lithium deposition in anode-less battery structures is a key focus and challenge for their application.

[0050] Based on this, the present invention, by setting a metal layer and a core encapsulating it, allows the metal layer and lithium ions to attract each other, promoting lithium ion deposition. The silicon-based material of the core promotes lithium ion alloying and intercalation, reducing the amount of lithium ion deposited on the surface of the metal layer and inhibiting the growth of lithium ion dendrites. By setting a cavity structure between the metal layer and the core, it ensures that the expansion of the core after lithium intercalation will not damage the silicon-based composite material. Furthermore, by setting a conductive polymer layer on the outermost layer, it adsorbs lithium ions while inhibiting the growth of lithium dendrites on the metal layer, further improving safety performance. Specifically, the present invention adopts the following technical solution: According to one aspect of the present invention, a silicon-based composite material is provided, comprising a core and a coating layer, wherein a cavity structure exists between the core and the coating layer; The core comprises a silicon-based material; the covering layer comprises a metal layer and a conductive polymer layer, wherein the conductive polymer layer is disposed on at least a portion of the surface of the metal layer on the side away from the cavity structure.

[0051] In this invention, the silicon-based material of the core is in at least point contact with the metal layer. Through the composite structure of the silicon-based material of the core, the metal layer, and the conductive polymer layer, the physical adsorption of lithium ions by the conductive polymer layer and the electronic adsorption of lithium ions by the silicon-based material and the metal layer jointly promote the deposition of lithium ions while inhibiting the growth of lithium ion dendrites.

[0052] In a specific embodiment of the present invention, the ratio of the inner diameter of the cavity structure to the particle size of the silicon-based material is preferably (1.5~3):1, specifically 1.5:1, 2:1, 2.5:1, 3:1, etc.; wherein, the particle size of the silicon-based material is preferably 200nm~1000nm, specifically 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, 1000nm, etc. The present invention selects the above-mentioned ratio of the inner diameter of the cavity structure to the particle size of the silicon-based material in conjunction with the coefficient of thermal expansion of the silicon-based material. This ensures that the expansion after lithium intercalation in the core will not damage the material, while preventing the inner diameter of the cavity structure from being too large and the particle size of the silicon-based material from being too small, thus ensuring the formation of a stable structure and further improving the stability and safety of the silicon-based composite material.

[0053] In specific embodiments of the present invention, the silicon-based material preferably includes one or more of silicon, silicon suboxide, and silicon-carbon; the present invention does not have special restrictions on the source of the silicon-based material, and commercially available products well known to those skilled in the art can be used. In the present invention, the silicon-based material attracts some lithium ions, reducing the amount of lithium ion deposition on the surface of the metal layer, and further reducing the growth of lithium ion dendrites.

[0054] In specific embodiments of the present invention, the material of the metal layer preferably includes one or more of copper, silver, and tin; the present invention does not have special restrictions on the source of the material of the metal layer, and commercially available products well known to those skilled in the art can be used. In the present invention, the material of the metal layer can attract lithium ions, promote the transfer of lithium ions from the conductive polymer layer to the metal layer, thereby promoting the deposition of lithium ions in the metal layer.

[0055] In a specific embodiment of the present invention, the thickness of the metal layer is preferably 50nm~200nm, specifically 50nm, 100nm, 150nm, 200nm, etc. The present invention selects the above-mentioned metal layer thickness to achieve the composite effect of the core, the metal layer and the conductive polymer layer, which together promote the deposition of lithium ions and ensure that a silicon-based composite material with expected performance is obtained.

[0056] In specific embodiments of the present invention, the material of the conductive polymer layer preferably includes one or more of conductive polyimide, conductive polyaniline, and conductive polypyrrole; the present invention does not have special restrictions on the source of the material of the conductive polymer layer, and commercially available products well known to those skilled in the art can be used. In the present invention, the material of the conductive polymer layer has the ability to conduct electricity and ions, which can promote the transfer of lithium ions to the metal layer and the core, while inhibiting the growth of lithium dendrites deposited on the metal layer, thereby further improving safety performance.

[0057] In a specific embodiment of the present invention, the thickness of the conductive polymer layer is preferably 2μm to 5μm, specifically 2μm, 3μm, 4μm, 5μm, etc. The present invention selects the above-mentioned conductive polymer layer thickness to achieve the combined effect of the core, metal layer and conductive polymer layer, which jointly promote the deposition of lithium ions. At the same time, it can maintain the integrity of the material during the lithiation and delithiation of silicon-based materials without generating new interfaces that come into contact with the electrolyte, reducing the continuous growth of SEI, and improving the coulombic efficiency and cycle life of the material.

[0058] The silicon-based composite material provided by this invention features a conductive polymer layer that adsorbs lithium ions, promoting lithium ion transfer to the metal layer and core while inhibiting the growth of lithium dendrites deposited on the metal layer. Furthermore, by incorporating a metal layer within the conductive polymer layer, the metal layer and lithium ions attract each other, promoting lithium ion deposition. Simultaneously, by incorporating a core within the metal layer, the silicon-based material in the core promotes lithium ion alloying and embedding, reducing the amount of lithium ion deposited on the metal layer surface and inhibiting lithium ion dendrite growth. More importantly, by creating a cavity structure between the core and the metal layer, the expansion of the silicon-based material in the core after lithium embedding prevents damage to the silicon-based composite material, further improving safety performance.

[0059] According to another aspect of the present invention, a method for preparing a silicon-based composite material is provided, comprising the following steps: a) Mix the binder, polyethylene, and a first solvent to obtain a first slurry; then coat the first slurry onto the surface of a silicon-based material, and after drying, obtain polyethylene-coated silicon-based material particles; b) Mix the pore-forming agent, binder, and first solvent to obtain a second slurry; then coat the second slurry onto the surface of the polyethylene-coated silicon-based material particles obtained in step a), dry them, perform a first grinding, then immerse them in a metal salt solution, and then add a reducing agent to react and obtain silicon-based material particles coated with a metal layer. c) After drying the silicon-based material particles coated with the metal layer obtained in step b), immerse them in the second solvent to dissolve the polyethylene and form a cavity structure. After cleaning and drying, the dried product is obtained. d) Coat the surface of the dried product obtained in step c) with a slurry containing a conductive polymer, and after drying, form a conductive polymer layer to obtain a silicon-based composite material.

[0060] The present invention first mixes an adhesive, polyethylene, and a first solvent to obtain a first slurry; then coats the first slurry onto the surface of a silicon-based material, and after drying, obtains polyethylene-coated silicon-based material particles.

[0061] In specific embodiments of the present invention, the binder preferably includes one or more of polytetrafluoroethylene, styrene-butadiene rubber, and sodium carboxymethyl cellulose; the present invention does not have special restrictions on the source of the binder, and commercially available products well known to those skilled in the art can be used. The use of the above-mentioned binder in the present invention ensures that the subsequently obtained first slurry has good performance, thereby further obtaining polyethylene-coated silicon-based material particles that meet the performance requirements of the present invention.

[0062] In a specific embodiment of the present invention, the first solvent preferably includes one or more of water, N-methylpyrrolidone, and N,N-dimethylformamide; the present invention does not have any special restrictions on the source of the first solvent, and commercially available products well known to those skilled in the art can be used. The use of the above-mentioned first solvent in the present invention facilitates the full dispersion of the binder and polyethylene, ensuring that the subsequently obtained first slurry has good performance, thereby further obtaining polyethylene-coated silicon-based material particles that meet the performance requirements of the present invention.

[0063] In a specific embodiment of the present invention, the preferred mass ratio of the binder to the polyethylene in step a) is (5~10):(90~95). By selecting the above-mentioned suitable mass ratio, the present invention can ensure that the volume of the formed cavity structure effectively alleviates the huge volume effect generated by the silicon-based material during the lithium insertion / extraction process, thereby further obtaining silicon-based material particles that meet the performance requirements of the present invention.

[0064] In a preferred embodiment of the present invention, the binder, polyethylene, and a first solvent are mixed and vacuum stirred to obtain a first slurry; then, the first slurry is sprayed onto the surface of a silicon-based material by spray drying. The present invention uses spray drying for coating, which has advantages such as fast drying speed, good coating uniformity, and easy control, and also has strong process continuity, making it suitable for industrial production.

[0065] In a specific embodiment of the present invention, before coating the silicon-based material in step a), it is preferable to further include: performing a second grinding; the second grinding is preferably performed using a ball mill, and the grinding speed is preferably 500 r / min to 1000 r / min, specifically 500 r / min, 750 r / min, 1000 r / min, etc.; the grinding time is preferably 1 h to 2 h, specifically 1 h, 1.5 h, 2 h, etc. The present invention performs a second grinding on the untreated silicon-based material under the above specific conditions, ultimately obtaining a silicon-based material with uniform particle size; the particle size of the silicon-based material is preferably 200 nm to 1000 nm, specifically 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, etc.

[0066] In a specific embodiment of the present invention, the particle size of the polyethylene-coated silicon-based material particles is preferably 500 nm to 4000 nm, specifically 500 nm, 1000 nm, 1500 nm, 2000 nm, 2500 nm, 3000 nm, 3500 nm, 4000 nm, etc. By selecting the above-mentioned suitable particle size, the present invention can ensure that the volume of the subsequently formed cavity structure effectively mitigates the huge volume effect generated by the silicon-based material during the lithium insertion / extraction process, thereby further obtaining a silicon-based composite material that meets the performance requirements of the present invention.

[0067] After obtaining the polyethylene-coated silicon-based material particles, the present invention mixes the pore-forming agent, the binder, and the first solvent to obtain a second slurry; then the second slurry is coated onto the surface of the polyethylene-coated silicon-based material particles obtained in step a), dried, and then subjected to a first grinding, and then immersed in a metal salt solution, and then a reducing agent is added to react to obtain silicon-based material particles with a metal layer.

[0068] In specific embodiments of the present invention, the pore-forming agent preferably includes one or more of ammonium bicarbonate, ammonium chloride, and ammonium nitrate; the present invention does not have special restrictions on the source of the pore-forming agent, and commercially available products well known to those skilled in the art can be used. The pore-forming agent selected in the present invention decomposes upon heating to generate a large amount of small molecule gas, forming pores, providing a channel for the permeation of the metal salt solution, and ensuring that the subsequently obtained metal layer meets the performance requirements of the present invention.

[0069] In this invention, the adhesive and the first solvent are the same as those in the above technical solutions, and will not be repeated here.

[0070] In a specific embodiment of the present invention, the preferred mass ratio of the pore-forming agent to the binder in step b) is (80~90):(5~10); the present invention selects the above-mentioned mass ratio of the pore-forming agent to the binder to ensure that a second slurry that meets the requirements for subsequent use is obtained.

[0071] In a preferred embodiment of the present invention, the second slurry is preferably sprayed onto the surface of the polyethylene-coated silicon-based material particles obtained in step a) by spray drying.

[0072] In a specific embodiment of the present invention, the particle size of the first grinding product is preferably 300nm to 3000nm, specifically 300nm, 500nm, 1000nm, 1500nm, 2000nm, 2500nm, 3000nm, etc. By selecting the aforementioned particle size of the first grinding product, the present invention can ensure the acquisition of silicon-based material particles coated with a metal layer that meet the expected performance requirements.

[0073] In a specific embodiment of the present invention, the metal salt solution preferably includes one or more of the following: tin sulfate solution, tin nitrate solution, tin chloride solution, silver nitrate solution, silver sulfate solution, silver chloride solution, copper sulfate solution, copper nitrate solution, and copper chloride solution. The present invention does not impose any special restrictions on the source of the metal salt solution; commercially available products well-known to those skilled in the art can be used. The immersion time in the metal salt solution is preferably 1 hour to 4 hours, specifically 1 hour, 2 hours, 3 hours, 4 hours, etc. By selecting the above-mentioned metal salt solution and immersion time, the present invention precisely controls the metal ion deposition process, ensuring that the subsequently obtained metal layer is uniform, dense, and has a controllable thickness.

[0074] In specific embodiments of the present invention, the reducing agent preferably includes one or more of iron, zinc, and hydrazine hydrate; the present invention does not have special restrictions on the source of the reducing agent, and commercially available products well known to those skilled in the art can be used. The present invention uses the above-mentioned reducing agent to reduce metal ions in metal salts to elemental metals, forming a uniform and dense metal layer.

[0075] After obtaining the silicon-based material particles coated with the metal layer, the present invention dries the obtained silicon-based material particles coated with the metal layer, immerses them in a second solvent to dissolve polyethylene to form a cavity structure, and then cleans and dries them to obtain the dried product.

[0076] In a specific embodiment of the present invention, the drying temperature is preferably 100℃~150℃, specifically 100℃, 125℃, 150℃, etc.; the drying time is preferably 2h~4h, specifically 2h, 3h, 4h, etc. The present invention selects the above drying temperature and time to remove residual metal salt solution and reducing agent, reduce the moisture content of the material, inhibit oxidation reaction, and ensure that the conductivity and mechanical strength of the obtained metal layer meet the performance requirements of the present invention.

[0077] In specific embodiments of the present invention, the second solvent preferably includes one or more of benzene, toluene, dichloromethane, and chloroform; the present invention does not have special restrictions on the source of the second solvent, and commercially available products well known to those skilled in the art can be used. The present invention uses the above-mentioned second solvent, which can dissolve polyethylene without reacting with the metal layer or silicon-based material, and other structures are not damaged during the formation of the cavity structure.

[0078] In a specific embodiment of the present invention, the immersion time in the second solvent is preferably 4h to 12h, specifically 4h, 6h, 8h, 10h, 12h, etc. The present invention selects the above immersion time to completely dissolve the polyethylene layer, avoid the cavity being too large, which would prevent the core from being unable to intercalate lithium, or the cavity being too small, which would not be able to effectively buffer the expansion of the core volume, and further obtain a silicon-based composite material that meets the performance requirements of the present invention.

[0079] The present invention does not impose any special limitations on the cleaning and drying process; conventional cleaning and drying techniques known to those skilled in the art can be used.

[0080] After obtaining the dried product, the present invention coats the surface of the dried product with a slurry including a conductive polymer, and after drying, forms a conductive polymer layer to obtain a silicon-based composite material.

[0081] In specific embodiments of the present invention, the conductive polymer preferably includes one or more of conductive polyimide, conductive polyaniline, and conductive polypyrrole; the present invention does not have special restrictions on the source of the conductive polymer, and commercially available products well known to those skilled in the art can be used. The particle size of the conductive polymer is preferably 100nm~500nm, specifically 100nm, 200nm, 300nm, 400nm, 500nm, etc.; the present invention selects the above-mentioned conductive polymer and its particle size to ensure that the subsequently obtained conductive polymer layer has conductive and ion-conducting capabilities, avoiding uneven coating caused by excessively large particle size or slurry agglomeration caused by excessively small particle size, and further obtaining a silicon-based composite material that meets the performance requirements of the present invention.

[0082] In a specific embodiment of the present invention, the slurry comprising the conductive polymer preferably further includes: a binder and a first solvent; the mass ratio of the binder to the conductive polymer is preferably (10~20):(80~90); the present invention uses the above-mentioned conductive polymer slurry, which is beneficial to the uniform dispersion of the conductive polymer and ensures that the subsequently obtained conductive polymer layer is uniform and stable on the surface of the metal layer.

[0083] In a preferred embodiment of the present invention, a slurry comprising a conductive polymer is spray-dried onto the surface of the dried product obtained in step c), and after drying, a conductive polymer layer is formed to obtain a silicon-based composite material. The present invention uses spray drying for coating, which has advantages such as fast drying speed, good coating uniformity, and ease of control, and also offers strong process continuity, making it suitable for industrial production.

[0084] The preparation method provided by this invention, based on traditional silicon-based materials, first performs pre-forming of holes and then forms a metal layer and a conductive polymer layer, which can effectively alleviate the huge volume effect generated by traditional silicon-based materials during lithium insertion / extraction. Moreover, the preparation method is simple, the raw materials are readily available and low in cost, suitable for large-scale production, highly practical, and has broad application prospects.

[0085] According to another aspect of the present invention, a negative electrode-free current collector is provided, comprising the silicon-based composite material described in the above-described technical solutions or the silicon-based composite material prepared by the preparation method described in the above-described technical solutions. Therefore, the negative electrode-free current collector possesses all the features and advantages of the silicon-based composite material described in the above-described technical solutions, which will not be repeated here.

[0086] In a specific embodiment of the present invention, the negative electrode-free current collector is preferably obtained by coating a negative electrode slurry onto at least one side of the negative electrode current collector, followed by drying and pressing. The present invention does not impose any special restrictions on the preparation method of the negative electrode-free current collector; wherein, the negative electrode slurry includes the silicon-based composite material described in the above technical solution or the silicon-based composite material prepared by the preparation method described in the above technical solution.

[0087] In a specific embodiment of the present invention, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode slurry is coated on either or both of the two opposite surfaces of the negative electrode current collector. In a preferred embodiment of the present invention, the negative electrode current collector is a copper foil.

[0088] In a specific embodiment of the present invention, the negative electrode slurry, in addition to the above-mentioned silicon-based composite material, preferably also includes conventional components such as binders and solvents used to prepare the negative electrode slurry, with the aim of obtaining the above-mentioned negative electrode slurry that can be used for coating. The present invention does not have any special limitations in this regard.

[0089] In a preferred embodiment of the present invention, the preparation method of the negative electrode-free current collector includes the following steps: mixing silicon-based composite material and binder in a solvent at a mass ratio of (80~90):(10~20) to prepare a negative electrode slurry, coating the negative electrode slurry onto the negative electrode current collector, drying, cold pressing, and slitting to obtain the negative electrode-free current collector.

[0090] According to another aspect of the present invention, a battery is provided, comprising the negative electrode-free current collector described in the above-described technical solution. Thus, the battery possesses all the features and advantages of the negative electrode-free current collector described in the above-described technical solution, which will not be repeated here.

[0091] In a specific embodiment of the present invention, the battery is preferably formed by stacking a positive electrode, a separator, a current collector without a negative electrode, and the separator, and then winding them together. In a preferred embodiment of the present invention, the battery preparation process includes: sequentially stacking the positive electrode, separator, current collector without a negative electrode, and separator together, and then winding them together to form an electrode assembly; packaging with a polymer; filling with electrolyte; and performing formation and other processes to form the battery. The specific conditions and parameters for each step in the above preparation process can be achieved using battery preparation techniques well known to those skilled in the art, and the present invention does not impose any special limitations on them.

[0092] In a specific embodiment of the present invention, the positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector along the thickness direction; wherein, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode active material layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0093] In a specific embodiment of the present invention, the positive electrode active material layer includes a positive electrode active material, a binder, and a conductive agent; wherein, the positive electrode active material includes, but is not limited to, lithium iron phosphate, high-nickel ternary positive electrode materials, preferably NCM811; the binder includes, but is not limited to, one or more of polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS), preferably PVDF; the conductive agent includes, but is not limited to, one or more of conductive carbon, acetylene black, conductive carbon black (SP), Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers, preferably carbon nanotubes. The present invention does not impose any special restrictions on the source of the above-mentioned positive electrode active material, binder, and conductive agent; commercially available products well known to those skilled in the art can be used.

[0094] In a specific embodiment of the present invention, the method for preparing the positive electrode includes: thoroughly mixing a positive electrode active material, a binder, and a conductive agent to prepare a positive electrode slurry; coating the positive electrode slurry onto a positive electrode current collector; and drying, cold pressing, and slitting to obtain the positive electrode. The positive electrode current collector can be a metal foil such as aluminum foil.

[0095] The present invention does not impose any special restrictions on the type and source of the separator; commercially available separators known to those skilled in the art for the preparation of batteries may be used.

[0096] In a specific embodiment of the present invention, the electrolyte comprises an organic solvent, an electrolyte lithium salt, and additives. The electrolyte lithium salt may be LiPF6 and / or LiBOB used in high-temperature electrolytes; or one or more of LiBF4, LiBOB, and LiPF6 used in low-temperature electrolytes; or one or more of LiBF4, LiBOB, LiPF6, and LiTFSI used in overcharge-resistant electrolytes; or one or more of LiClO4, LiAsF6, LiCF3SO3, and LiN(CF3SO2)2. The organic solvent may be a cyclic carbonate, including propylene carbonate (PC) and / or ethylene carbonate (EC); or a chain carbonate, including at least one of diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC); or a carboxylic acid ester, including at least one of methyl formate, methyl acetate, ethyl acetate, and methyl propionate. The additives include, but are not limited to, at least one of the following: film-forming additives, conductive additives, flame-retardant additives, overcharge prevention additives, additives for controlling the H2O and HF content in the electrolyte, additives for improving low-temperature performance, and multifunctional additives. In a preferred embodiment of the present invention, the electrolyte is a LiPF6 electrolyte, and the solvent is a mixed solvent of ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate.

[0097] The present application will be described in detail below with reference to the accompanying drawings and embodiments. However, the implementation and protection of the present invention are not limited thereto. The following embodiments are only some embodiments of the present application and are not intended to limit the present application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0098] Example 1 (1) The original silica particles were ground at a speed of 500 r / min for 1 h using a ball mill to obtain silica particles with a particle size of 500 nm. Then, polytetrafluoroethylene and polyethylene were mixed in N-methylpyrrolidone (NMP) at a mass ratio of 5:95 and stirred under vacuum to obtain the first slurry. The first slurry was then sprayed onto the surface of the silica particles by spray drying until the thickness of the polyethylene coating layer was 1000 nm. After drying, the polyethylene-coated silicon-based material particles were obtained.

[0099] (2) Ammonium bicarbonate and styrene-butadiene rubber are mixed in water at a mass ratio of 90:10 to obtain a second slurry. The second slurry is then sprayed onto the surface of the polyethylene-coated silicon-based material particles obtained in step (1) by spray drying. After low-temperature drying, the particles are ground into particles with a particle size of 2000 nm. The particles are then immersed in copper sulfate solution for 1 hour. After that, hydrazine hydrate is added to react and a metal-coated silicon-based material particle is obtained. The thickness of the metal layer is 100 nm.

[0100] (3) The silicon-based material particles coated with the metal layer obtained in step (2) are dried at 100°C for 2 hours. After drying, they are immersed in toluene for 8 hours to dissolve the polyethylene and form a cavity structure. After cleaning and drying, the dried product is obtained.

[0101] (4) Conductive polyimide with a particle size of 200 nm and styrene-butadiene rubber are mixed evenly in water at a mass ratio of 90:10 to obtain a slurry containing the conductive polymer. The slurry containing the conductive polymer is then sprayed onto the surface of the dried product obtained in step (3) by spray drying. The spray thickness is 3 μm. After drying, a conductive polymer layer is formed to obtain a silicon-based composite material. See the schematic diagram of its structure. Figure 1 As shown; the TEM image of this silicon-based composite material is shown below. Figure 2 As shown.

[0102] (5) The silicon-based composite material and styrene-butadiene rubber are uniformly mixed in NMP at a mass ratio of 80:20 to prepare a negative electrode slurry. The negative electrode slurry is coated on copper foil, dried, and cold-pressed to obtain a negative electrode current collector.

[0103] A cathode slurry was prepared by thoroughly mixing NCM811, SP, carbon nanotubes, and PVDF5130 in NMP at a mass ratio of 97:1.5:0.5:1. The cathode slurry was then coated onto a 13 μm aluminum foil with a coating density of 195 g / m². 2 The positive electrode is obtained by drying and cold pressing, and its compaction density is 3.4 g / m³. 3 .

[0104] An electrolyte with a LiPF6 concentration of 1.2 mol / L was obtained by dissolving LiPF6 in a mixed solvent of ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate in a volume ratio of 1:1:1.

[0105] Polypropylene membrane was selected as the base membrane for the separator, with a thickness of 9μm PE layer + 3μm ceramic layer + 3μm adhesive layer + 3μm adhesive layer.

[0106] The positive electrode, separator, current collector without negative electrode, and separator are stacked and assembled in sequence and then wound to form a battery cell. The electrolyte is injected into the dry battery cell and soaked for 24 hours. Then, it is formed at 45°C. The formation process includes charging to 3.4V at 0.05C and then charging to 3.75V at 0.2C. After aging at room temperature for 24 hours, the battery is formed.

[0107] Example 2 The silicon-based composite material, the negative electrode-free current collector, and the battery were obtained sequentially using the preparation method provided in Example 1. The difference is that in step (1), the thickness of the polyethylene coating layer is 1500 nm.

[0108] Example 3 The silicon-based composite material, the negative electrode-free current collector, and the battery were obtained sequentially using the preparation method provided in Example 1. The difference is that in step (1), the particle size of the silicon suboxide particles is 1000 nm.

[0109] Example 4 The silicon-based composite material, the negative electrode current collector and the battery were obtained sequentially by the preparation method provided in Example 1. The difference is that in step (2), the ground particles were immersed in copper sulfate solution three times, each time for 1 hour, and the thickness of the metal layer was 200 nm.

[0110] Example 5 The silicon-based composite material, the negative electrode-free current collector, and the battery were obtained sequentially using the preparation method provided in Example 1. The difference is that in step (2), the ground particles were immersed in copper sulfate solution for 0.5 h to obtain a metal layer with a thickness of 50 nm.

[0111] Example 6 The silicon-based composite material, the negative electrode current collector and the battery were obtained sequentially by the preparation method provided in Example 1. The difference is that in step (4), the thickness of the spray coating is 2 μm.

[0112] Example 7 The silicon-based composite material, the negative electrode-free current collector, and the battery were obtained sequentially using the preparation method provided in Example 1. The difference is that in step (1), the silicon suboxide particles were replaced with silicon carbon materials.

[0113] Example 8 The silicon-based composite material, the negative electrode-free current collector, and the battery were obtained sequentially using the preparation method provided in Example 1. The difference is that in step (2), the copper sulfate solution was replaced with the tin sulfate solution.

[0114] Example 9 The silicon-based composite material, the negative electrode-free current collector, and the battery were obtained sequentially using the preparation method provided in Example 1. The difference is that in step (4), the conductive polyimide was replaced with conductive polyaniline.

[0115] Comparative Example 1 The silicon-based composite material, the negative electrode-free current collector, and the battery were obtained sequentially using the preparation method provided in Example 1. The difference is that in step (1), the thickness of the polyethylene coating layer is 2500 nm.

[0116] Comparative Example 2 The silicon-based composite material, the negative electrode-free current collector, and the battery were obtained sequentially using the preparation method provided in Example 1. The difference is that in step (1), the thickness of the polyethylene coating layer is 500 nm.

[0117] Comparative Example 3 The silicon-based composite material, the negative electrode-free current collector, and the battery were obtained sequentially using the preparation method provided in Example 1. The difference is that in step (1), the particle size of the silicon suboxide particles is 2000 nm.

[0118] Comparative Example 4 The silicon-based composite material, the negative electrode current collector, and the battery were obtained sequentially using the preparation method provided in Example 1. The difference is that in step (2), the thickness of the metal layer is 30 nm.

[0119] Comparative Example 5 The silicon-based composite material, the negative electrode current collector, and the battery were obtained sequentially using the preparation method provided in Example 1. The difference is that in step (4), the thickness of the spray coating is 1 μm.

[0120] Comparative Example 6 The silicon-based composite material, the negative electrode-free current collector, and the battery were obtained sequentially using the preparation method provided in Example 1. The difference is that: in step (1), polyethylene was not added; and in step (3), toluene was not impregnated.

[0121] Comparative Example 7 The silicon-based composite material, the negative electrode-free current collector, and the battery were obtained sequentially using the preparation method provided in Example 1. The difference is that in step (1), the silicon suboxide particles were replaced with polystyrene, and the resulting silicon-based composite material had no core.

[0122] Comparative Example 8 The silicon-based composite material, the current collector without negative electrode and the battery were obtained sequentially by the preparation method provided in Example 1. The difference is that in step (4), no slurry containing conductive polymer was sprayed, and the resulting silicon-based composite material had no conductive polymer layer.

[0123] Comparative Example 9 The silicon-based composite material, the negative electrode current collector, and the battery were obtained sequentially using the preparation method provided in Example 1. The difference is that in step (2), the silicon-based composite material was not immersed in copper sulfate solution and hydrazine hydrate was not added for reaction, so the silicon-based composite material obtained had no metal layer.

[0124] Performance testing: The physicochemical properties of the silicon-based composite materials and negative electrode-free current collectors prepared in Examples 1-9 and Comparative Examples 1-9 were tested as follows: (1) Specific surface area test: Weigh 1g of sample and place it in the sample chamber of the specific surface area tester. Then, introduce N2 into the sample chamber and calculate the specific surface area of ​​the sample by the amount of nitrogen adsorption under different relative pressures.

[0125] (2) Maximum compaction density test: The above-mentioned current collector without negative electrode was passed through a roller press under different pressure conditions, and the compaction density was 3.2 g / m³ in sequence. 3 3.3g / m 3 3.4g / m 3 3.5g / m 3 3.6g / m 3 The presence or absence of breakage in the adsorption layer material can be determined by TEM and CP measurements of the cross-section.

[0126] (3) Weight test: Cut the above-mentioned negative electrode current collector into 10cm×10cm size and weigh it.

[0127] (4) Conductivity test: The conductivity is measured by powder layer resistivity test. A certain amount of silicon-based composite material is put into the test container. The same mass of silicon-based composite material is pressed into a dense block under a pressure of 3t~10t, and its resistivity is tested under this state.

[0128] The test results are shown in Table 1 below.

[0129] Table 1. Physicochemical property test data of each group of silicon-based composite materials and negative electrode-free current collectors. Table 1 shows that the compaction density (i.e., compressive strength) of the silicon-based composite material is significantly related to the thickness of the metal layer and the volume of the cavity structure. For example, if the cavity volume in Comparative Example 1 is too large or the metal layer thickness in Comparative Example 4 is too small, the compressive strength of the silicon-based composite material decreases substantially. Conversely, if the cavity structure volume in Comparative Example 2 is reduced, the compressive strength of the material can be improved. Furthermore, electrical conductivity shows a strong correlation with the thickness of the metal layer; for instance, as the metal layer thickness in Comparative Example 4 decreases, the electrical conductivity also decreases accordingly.

[0130] The data from Examples 7-9 show that changing the main materials has little impact on the physicochemical properties of the silicon-based composite material. However, the absence of the core, cavity structure, and coating layer will affect the physicochemical properties and safety. Comparative Example 6, lacking a cavity structure, has a significantly reduced specific surface area, which reduces lithium-ion deposition sites and may affect safety performance. Comparative Example 7, without a core, shows a slight decrease in the composite material's pressure resistance, but attention should be paid to whether excessive lithium-ion deposition on the metal layer could lead to safety risks. Comparative Example 8, lacking a conductive polymer layer, shows little difference in physicochemical data, but the outermost layer's role in suppressing lithium dendrites needs to be considered, as safety may be reduced. Comparative Example 9, lacking a metal layer, shows a significant decrease in conductivity, and attention should be paid to lithium plating in subsequent processes. Specifically, with the same cathode capacity, most lithium ions would normally deposit on the metal surface; the absence of a metal layer results in lithium ions depositing only on the silicon-based material, causing lithium plating and affecting safety performance.

[0131] The electrical performance of the batteries prepared in Examples 1-9 and Comparative Examples 1-9 was tested, as follows: (1) DC internal resistance ACR test: Discharge the battery to 50% SOC state according to the standard charge and discharge regime of 0.5C / 1C, and use a DC internal resistance meter to test the DC internal resistance of the battery.

[0132] (2) Capacity retention rate: The charge and discharge test was carried out according to the standard test procedure of 0.5C / 1C. At 25℃, the constant current and constant voltage of 0.5C was used to charge to 4.25V, and then left to stand for 30 minutes. The constant current of 1C was used to discharge to 2.5V, and then left to stand for 30 minutes. The above steps were repeated for 500 cycles. The discharge capacity of the first and 500th cycles was recorded. The capacity retention rate = the discharge capacity of the 500th cycle / the discharge capacity of the first cycle × 100%.

[0133] (3) 1C energy density = 1C discharge capacity × 1C discharge average voltage / total weight of battery.

[0134] (4) Rate test: At 25℃, charge to 4.25V with constant current and constant voltage using XC, let stand for 30 minutes, discharge to 2.5V with constant current using 1C, let stand for 30 minutes, repeat the above steps, and complete the rate test at charging rates of 1C, 2C, 3C, XC, etc. until the battery experiences thermal runaway. The rate at this time is the maximum safe rate of the negative electrode current collector battery, which indirectly reflects the safety performance of the negative electrode current collector structure.

[0135] The test results are shown in Table 2 below.

[0136] Table 2 Electrical performance test data for each group of batteries As shown in Table 2, compared with the other embodiments, Comparative Example 1 has an excessively large cavity structure, which significantly reduces the pressure resistance and energy density of the silicon-based composite material. This is presumably due to the reduced pressure resistance, particle breakage, and consequently, a decrease in lithium deposition sites. Furthermore, the structural damage reduces the number of lithium-ion deposition sites during high-rate charging, leading to a decrease in the maximum charging rate. Comparative Example 2 has an excessively small cavity, also resulting in a decrease in energy density. This is presumably due to the reduced cavity volume, causing lithium intercalation expansion in the core silicon-based material, leading to particle breakage and thus affecting lithium-ion deposition and safety performance. Comparative Example 3 has excessively large internal silicon particles, causing excessive volume expansion, resulting in breakage of the silicon-based composite material, affecting lithium-ion deposition sites, and consequently impacting energy density and maximum charging rate. Comparative Example 4 is similar to Comparative Example 1; the reduced metal layer thickness leads to decreased pressure resistance, causing partial material breakage, which in turn affects energy density and maximum charging rate. Comparative Example 5 shows a significant impact on cycle performance and maximum charge rate due to the reduced thickness of the conductive polymer layer. This is likely because lithium dendrites are formed during the later stages of cycling, and the thin conductive polymer layer is insufficient to suppress them, resulting in excessive self-discharge and affecting cycle performance. It also hinders the charge rate. Comparative Example 6 exhibits the most significant deterioration in energy density and maximum charge rate compared to other examples. Physicochemical parameters indicate that the reduced specific surface area limits lithium ion deposition sites, decreasing lithium ion deposition. Furthermore, the lack of a cavity structure leads to greater silicon particle expansion and breakage of the silicon-based composite material, resulting in the worst overall performance. Comparative Example 7, lacking internal silicon-based material, shows a deterioration in cycle performance and maximum charge rate, further demonstrating that silicon-based materials synergistically promote lithium ion deposition and improve safety. Comparative Example 8, lacking an outermost conductive polymer layer, suffers from uneven lithium ion deposition due to the absence of its ion-conducting ability, affecting cycle performance. Additionally, the lack of suppression of lithium dendrite growth on the metal surface and the absence of its safety-enhancing function significantly reduces the maximum charge rate. Comparative Example 9 lacks an intermediate metal layer, resulting in a significant deterioration in battery internal resistance and a substantial reduction in energy density. Combined with the decrease in maximum charging rate, it can be inferred that the absence of a metal layer should have increased energy density, but due to the lack of a site to hinder deposition, lithium ions can only be deposited, thus reducing battery capacity and affecting energy density and maximum charging rate.

[0137] The parts of this invention not described in detail are techniques known to those skilled in the art.

[0138] The basic principles of the present invention have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in the present invention are merely examples and not limitations, and should not be considered as essential features of each embodiment of the present invention. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the present invention to the necessity of employing the aforementioned specific details.

[0139] In the foregoing description of this specification, references to terms such as "one embodiment," "another embodiment," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment is included in at least one embodiment of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples, without contradiction. Additionally, it should be noted that in this specification, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features.

[0140] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A silicon-based composite material, characterized in that, It includes a core and a cover layer, and there is a cavity structure between the core and the cover layer; The core comprises a silicon-based material; the covering layer comprises a metal layer and a conductive polymer layer, wherein the conductive polymer layer is disposed on at least a portion of the surface of the metal layer on the side away from the cavity structure.

2. The silicon-based composite material according to claim 1, characterized in that, The ratio of the inner diameter of the cavity structure to the particle size of the silicon-based material is (1.5~3):

1.

3. The silicon-based composite material according to claim 1, characterized in that, The silicon-based material includes one or more of silicon, silicon suboxide, and silicon-carbon. And / or, the particle size of the silicon-based material is 200nm~1000nm; And / or, the material of the metal layer includes one or more of copper, silver, and tin; And / or, the thickness of the metal layer is 50nm~200nm.

4. The silicon-based composite material according to claim 1, characterized in that, The material of the conductive polymer layer includes one or more of conductive polyimide, conductive polyaniline, and conductive polypyrrole. And / or, the thickness of the conductive polymer layer is 2μm~5μm.

5. A method for preparing a silicon-based composite material according to any one of claims 1 to 4, characterized in that, Includes the following steps: a) Mix the binder, polyethylene, and a first solvent to obtain a first slurry; then coat the first slurry onto the surface of a silicon-based material, and after drying, obtain polyethylene-coated silicon-based material particles; b) Mix the pore-forming agent, binder, and first solvent to obtain a second slurry; then coat the second slurry onto the surface of the polyethylene-coated silicon-based material particles obtained in step a), dry them, perform a first grinding, then immerse them in a metal salt solution, and then add a reducing agent to react and obtain silicon-based material particles coated with a metal layer. c) After drying the silicon-based material particles coated with the metal layer obtained in step b), immerse them in the second solvent to dissolve the polyethylene and form a cavity structure. After cleaning and drying, the dried product is obtained. d) Coat the surface of the dried product obtained in step c) with a slurry containing a conductive polymer, and after drying, form a conductive polymer layer to obtain a silicon-based composite material.

6. The preparation method according to claim 5, characterized in that, The preparation method satisfies at least one of the following features (1) to (5): (1) The adhesive includes one or more of polytetrafluoroethylene, styrene-butadiene rubber, and sodium carboxymethyl cellulose; (2) The first solvent includes one or more of water, N-methylpyrrolidone, and N,N-dimethylformamide; (3) The mass ratio of the adhesive to the polyethylene in step a) is (5~10):(90~95); (4) Before coating the silicon-based material described in step a), the process further includes: performing a second grinding; the rotation speed of the second grinding is 500 r / min to 1000 r / min, and the time is 1 h to 2 h; preferably, after the second grinding, the particle size of the silicon-based material is 200 nm to 1000 nm; (5) The particle size of the polyethylene-coated silicon-based material particles is 500nm~4000nm.

7. The preparation method according to claim 5, characterized in that, The preparation method satisfies at least one of the following features (1) to (9): (1) The pore-forming agent includes one or more of ammonium bicarbonate, ammonium chloride, and ammonium nitrate; (2) The mass ratio of the pore-forming agent and the adhesive in step b) is (80~90):(5~10); (3) The particle size requirement of the product from the first grinding process is 300nm~3000nm; (4) The metal salt solution includes one or more of the following: tin sulfate solution, tin nitrate solution, tin chloride solution, silver nitrate solution, silver sulfate solution, silver chloride solution, copper sulfate solution, copper nitrate solution, and copper chloride solution; (5) The immersion time in the metal salt solution described in step b) is 1h to 4h; (6) The reducing agent includes one or more of iron, zinc, and hydrazine hydrate; (7) The drying temperature is 100℃~150℃ and the time is 2h~4h; (8) The second solvent includes one or more of benzene, toluene, dichloromethane, and chloroform; (9) The immersion time in the second solvent as described in step c) is 4h~12h.

8. The preparation method according to claim 5, characterized in that, In step d): The conductive polymer includes one or more of conductive polyimide, conductive polyaniline, and conductive polypyrrole; And / or, the particle size of the conductive polymer is 100nm~500nm; And / or, the slurry comprising the conductive polymer further comprises: a binder and a first solvent; preferably, the mass ratio of the binder to the conductive polymer is (10~20):(80~90).

9. A current collector without a negative electrode, characterized in that, The silicon-based composite material includes the silicon-based composite material according to any one of claims 1 to 4 or the silicon-based composite material prepared by the preparation method according to any one of claims 5 to 8.

10. A battery, characterized in that, Includes the negative electrode-less current collector as described in claim 9.

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