Silicon carbon material as well as preparation method and application thereof

Abstract

The invention provides a silicon-carbon material and a preparation method and application thereof, the silicon-carbon material comprises a porous carbon substrate and silicon particles existing in the porous carbon substrate, and the silicon-carbon material comprises a heterostructure. The silicon-carbon material provided by the invention comprises a heterostructure, so that the problem of volume expansion of silicon can be relieved, and the cycle performance and the rate capability of the battery are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and in particular relates to a silicon-carbon material and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries are widely used in modern technology, and their performance depends largely on their anode materials. Traditional graphite anode materials are widely used due to their stability, but their capacity is limited. Silicon, as a next-generation anode material, has attracted much attention due to its high theoretical capacity. However, silicon undergoes dramatic volume expansion during charge and discharge, leading to electrode pulverization, structural collapse, and disruption of the conductive network, thus compromising the battery's cycling and rate performance.

[0003] To address these issues, researchers have attempted to combine silicon with carbon materials, leveraging carbon's stability and conductivity to mitigate silicon's volume changes. However, existing silicon-carbon materials struggle to effectively address silicon's expansion, leading to decreased battery cycle and rate performance. Therefore, developing a silicon-carbon material that can mitigate silicon's volume expansion and improve battery cycle and rate performance has become a pressing technical challenge. Summary of the Invention

[0004] The main purpose of the present invention is to provide a silicon-carbon material, which can alleviate the volume expansion problem of silicon and improve the cycle performance and rate performance of the battery when applied to the battery.

[0005] The present invention also provides a method for preparing a silicon-carbon material, which can prepare the above-mentioned silicon-carbon material, has a simple process and low cost.

[0006] The present invention also provides a negative electrode sheet comprising the above silicon-carbon material, so the negative electrode sheet has a low volume expansion rate and can be applied to a battery to improve the cycle performance and rate performance of the battery.

[0007] The present invention also provides a battery comprising the above-mentioned negative electrode sheet, so that the battery has a low expansion rate and excellent cycle performance and rate performance.

[0008] The present invention also provides an electrical device comprising the above-mentioned battery. Therefore, the performance of the battery associated with the electrical device is relatively excellent.

[0009] In a first aspect, the present invention provides a silicon-carbon material comprising a porous carbon substrate and silicon particles present in the porous carbon substrate, wherein the silicon-carbon material comprises a heterostructure.

[0010] As for the silicon-carbon material described above, the heterostructure includes a CN-Si structure and / or a CS-Si structure.

[0011] In the silicon-carbon material described above, the average pore size of the carbon material in the region of 0 μm to 2 μm from the center of the porous carbon substrate is larger than the average pore size of the carbon material in the region of 1 μm to 4 μm from the center of the porous carbon substrate.

[0012] The silicon-carbon material as described above, wherein the average pore size of the carbon material in the region 0 μm to 2 μm away from the center of the porous carbon substrate is 30 nm to 200 nm;

[0013] And / or, the average pore diameter of the carbon material in a region 1 μm to 4 μm away from the center of the porous carbon substrate is 5 nm to 30 nm.

[0014] In the silicon-carbon material as described above, the particle size Dv50 of the silicon particles is 5 nm-100 nm.

[0015] In the silicon-carbon material as described above, the mass ratio of the silicon particles to the porous carbon substrate is 1:9-3:7.

[0016] The silicon-carbon material as described above further includes a carbon coating layer present on the surface of the silicon particles.

[0017] For the silicon-carbon material as described above, the carbon coating layer accounts for 0.3%-2% of the mass of the silicon-carbon material.

[0018] In a second aspect, the present invention provides a method for preparing the silicon-carbon material as described above, comprising the following steps:

[0019] Silicon particles are loaded on a porous carbon substrate to obtain the silicon-carbon material; wherein the porous carbon substrate includes doping elements.

[0020] In the above-mentioned method for preparing silicon-carbon material, the doping element includes N element and / or S element.

[0021] The method for preparing the silicon-carbon material as described above, wherein the porous carbon substrate is prepared by a method comprising the following steps:

[0022] 1) introducing a magnetic material into an organic dual-template agent to obtain a first intermediate; the organic dual-template agent comprises a silica core and a polymer layer present on the surface of the silica core;

[0023] 2) applying a magnetic field to a first system including the first intermediate and a carbon source so that the magnetic material migrates to the surface region of the first intermediate and the carbon source is concentrated in the central region of the first intermediate, thereby obtaining a second intermediate;

[0024] 3) performing a carbonization treatment, a first activation treatment, and a second activation treatment on the second intermediate in sequence to obtain the porous carbon substrate.

[0025] The method for preparing the silicon-carbon material as described above, wherein the temperature of the carbonization treatment is 300° C.-500° C.;

[0026] And / or, the first activation treatment comprises: performing the first activation treatment using water vapor for 1 hour to 3 hours under immersion in an alkaline liquid at 500° C. to 700° C., thereby forming macropores of 30 nm to 200 nm in a region 0 μm to 2 μm away from the center of the porous carbon substrate;

[0027] And / or, the second activation treatment includes: performing the second activation treatment using carbon dioxide at 700° C.-900° C. for 0.5 h-2 h to form micropores of 5 nm-30 nm in a region 1 μm-4 μm away from the center of the porous carbon substrate.

[0028] The method for preparing the silicon-carbon material as described above, after loading silicon particles on the porous carbon substrate, further comprises: performing carbon coating treatment on the loaded product obtained by loading the silicon particles to obtain the silicon-carbon material.

[0029] In the above-mentioned method for preparing silicon-carbon material, the temperature of the carbon coating treatment is 500° C.-700° C., and the time is 3 h-5 h.

[0030] In a third aspect, the present invention provides a negative electrode sheet comprising the silicon-carbon material as described above or the silicon-carbon material prepared according to the method for preparing the silicon-carbon material as described above.

[0031] In a fourth aspect, the present invention provides a battery comprising the negative electrode sheet as described above.

[0032] In a fifth aspect, the present invention provides an electrical device comprising the battery as described above.

[0033] The silicon-carbon material provided by the present invention includes a porous carbon substrate and silicon particles present in the porous carbon substrate. The silicon-carbon material includes a heterostructure. The heterostructure plays a role in anchoring the silicon particles by forming a strong connection between the silicon particles and the porous carbon substrate, ensuring that the silicon particles can still maintain a connection with the carbon substrate after multiple charge and discharge cycles, preventing the silicon particles from falling off. The combined effect of the porous carbon substrate and the heterostructure can alleviate the volume expansion problem of silicon and improve the cycle performance and rate performance of the battery. DETAILED DESCRIPTION

[0034] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0035] Lithium-ion batteries, the core of modern energy storage technology, are widely used in portable electronic devices, electric vehicles, and renewable energy storage systems. The energy density and cycle life of batteries depend heavily on the performance of their anode materials. Traditional graphite anode materials are widely used due to their stable cycling performance and mature processing technology. However, their theoretical specific capacity is only 372 mAh / g, limiting further improvements in battery energy density.

[0036] Silicon is considered one of the most promising next-generation anode materials due to its extremely high theoretical specific capacity (approximately 4200 mAh / g). However, silicon-based anode materials face significant challenges in practical application. Silicon undergoes a volume change of up to 300% during the battery's charge and discharge processes. This dramatic volume expansion and contraction can lead to pulverization, structural collapse, and exfoliation of the active material, which in turn destroys the electrode's conductive network and significantly reduces the battery's cycling performance.

[0037] In order to solve these problems, researchers have proposed a strategy to composite silicon with carbon materials. Carbon materials have small volume changes during the charge and discharge process and have good conductivity and mechanical stability. By composite silicon with carbon, attempts are made to alleviate the volume expansion problem of silicon. However, in the existing technology, silicon-carbon negative electrode materials are usually simply deposited by silicon particles on the surface or in the gaps of carbon materials. This simple physical mixing method is difficult to effectively alleviate the volume change of silicon during the charge and discharge process. The lack of strong chemical or physical connection sites between silicon particles and the carbon substrate causes silicon particles to easily detach from the carbon substrate after multiple charge and discharge cycles, resulting in rapid attenuation of battery capacity and a decrease in rate performance. Therefore, the development of silicon-carbon materials that can effectively alleviate the volume expansion of silicon and improve battery cycle performance and rate performance has become the focus of current research.

[0038] The inventors of the present application have discovered that by changing the connection mode between carbon materials and silicon particles, the volume change of silicon during the charge and discharge process can be effectively alleviated, thereby improving the cycle performance and rate performance of the battery.

[0039] Based on this, in a first aspect, the present invention provides a silicon-carbon material, comprising a porous carbon substrate and silicon particles present in the porous carbon substrate, wherein the silicon-carbon material comprises a heterogeneous structure.

[0040] It can be understood that a heterostructure is a structure formed by regions of different materials or different crystal structures contacting or interlacing with each other.

[0041] The silicon-carbon material provided by the present invention includes a heterostructure, which can alleviate the volume expansion problem of silicon and improve the cycle performance and rate performance of the battery. This is because the heterostructure plays a role in anchoring the silicon particles by forming a strong connection between the silicon particles and the porous carbon substrate, ensuring that the silicon particles can still maintain connection with the carbon substrate after multiple charge and discharge cycles, preventing the silicon particles from falling off, ensuring the continuity of the conductive network, and thus maintaining the conductivity of the electrode. The porous carbon substrate can provide enough space to buffer the volume expansion of silicon. The heterostructure can make the silicon particles have enough space to expand when expanding, without causing damage to the structure of the silicon-carbon material, and can effectively alleviate the volume expansion problem of silicon. And the heterostructure can optimize the interface characteristics between silicon and carbon, reduce the interface resistance, improve the stability of the interface, help reduce the side reactions in the electrochemical reaction, and extend the cycle life of the battery. In addition, the conductivity of the silicon particles and the porous carbon substrate works together to ensure the effective transmission of electrons during high-rate discharge and improve the rate performance of the battery. At the same time, the heterostructure reduces the stress concentration caused by the volume change of silicon by providing mechanical support, further improving the mechanical stability of the silicon-carbon material.

[0042] Therefore, the silicon-carbon material provided by the present invention includes a heterogeneous structure, which can effectively alleviate the volume expansion problem of silicon and improve the cycle performance and rate performance of the battery.

[0043] In some embodiments of the present invention, the heterostructure includes a CN-Si structure and / or a CS-Si structure, which further enhances the connection between the silicon particles and the carbon substrate, is beneficial to maintaining the stability of the silicon particles during the charge and discharge cycle, reduces the risk of silicon particles falling off, further alleviates the volume expansion problem of silicon, and improves the cycle performance and rate performance of the battery.

[0044] In some embodiments of the present invention, the average pore size of the carbon material in the area 0 μm-2 μm from the center of the porous carbon substrate, for example, 0 μm, 0.3 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm or any two thereof, is larger than the average pore size of the carbon material in the area 1 μm-4 μm from the center of the porous carbon substrate, for example, 1 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm or any two thereof.

[0045] The porous carbon substrate of the present invention forms a gradient pore structure, which effectively limits the volume expansion of silicon particles, preventing excessive expansion that could lead to fatigue and breakage of the material. This helps maintain the structural integrity of the material and extend the battery's cycle life. Maintaining structural integrity and reducing particle shedding also helps maintain the continuity of the conductive network, improving the battery's rate performance.

[0046] The average pore size of the carbon material of the present invention can be obtained by calculating the pore size distribution using a transmission electron microscope and a nitrogen adsorption-desorption curve BJH.

[0047] In some embodiments of the present invention, the average pore size of the carbon material in a region 0 μm to 2 μm from the center of the porous carbon substrate is 30 nm to 200 nm, for example, 30 nm, 50 nm, 80 nm, 100 nm, 150 nm, 200 nm, or a range consisting of any two thereof. This provides sufficient space to accommodate the volume expansion of silicon particles, allowing silicon to expand during charging without causing excessive stress on the overall structure, thereby reducing material cracking and pulverization.

[0048] In some embodiments, the average pore size of the carbon material in a region 1 μm to 4 μm from the center of the porous carbon substrate is 5 nm to 30 nm, for example, 5 nm, 8 nm, 10 nm, 20 nm, 30 nm, or any combination thereof. This provides physical constraints on the expansion of the silicon particles, preventing them from overexpanding, facilitating the dispersion and alleviation of stress concentration caused by volume change, and reducing material fatigue.

[0049] In some embodiments of the present invention, the particle size Dv50 of the silicon particles is 5 nm-100 nm, for example, it can be 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 100 nm or a range consisting of any two thereof.

[0050] In the present invention, the silicon particles have a particle size Dv50 within the above range, which helps reduce stress concentration and material fracture caused by volume expansion, thereby improving the material's mechanical stability. Furthermore, the silicon particles have a large specific surface area, which increases the contact area with the electrolyte, thereby improving the efficiency of the electrochemical reaction and contributing to the improvement of the battery's capacity and rate performance. Furthermore, the silicon particles can minimize structural damage to the silicon-carbon material during multiple charge and discharge cycles, thereby improving the battery's cycle life.

[0051] In the present invention, the particle size Dv50 of the silicon particles can be obtained by transmission electron microscopy.

[0052] In some embodiments of the present invention, the mass ratio of silicon particles to porous carbon substrate is 1:9-7:3, for example, it can be 1:9, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3 or any two thereof.

[0053] In the present invention, the mass ratio of silicon particles to porous carbon substrate is within the above range, which ensures that the silicon-carbon material has a good conductive network, which is beneficial to improving the rate performance of the battery. The carbon substrate provides a buffering effect, which is beneficial to the volume expansion of silicon during the charge and discharge process, and silicon can provide a higher capacity without significantly affecting the structural integrity of the material. In addition, the carbon content is beneficial to improving the mechanical strength and cycle stability of the material. The carbon substrate can effectively anchor the silicon particles, reduce particle shedding and material pulverization, thereby extending the cycle life of the battery.

[0054] In some embodiments of the present invention, the silicon-carbon material further includes a carbon coating layer present on the surface of the silicon particles.

[0055] The carbon coating layer in the present invention can form a flexible protective layer around the silicon particles, absorbing and alleviating the volume expansion of silicon during the charge and discharge process, which is beneficial to reducing the breakage and pulverization of silicon particles, thereby improving the mechanical stability of the material. The carbon coating layer can also improve the conductivity of the silicon-carbon material, ensuring the rapid transmission of electrons in the electrode, thereby improving the rate performance of the battery. In addition, the carbon coating layer can improve the interfacial stability between the silicon particles and the electrolyte, reduce the occurrence of side reactions, and help improve the cycle life of the battery. At the same time, the carbon coating layer can improve the structural integrity of the silicon-carbon material, reduce the shedding of silicon particles during the charge and discharge cycle, and help maintain the conductive network and overall structure of the electrode.

[0056] In some embodiments of the present invention, the mass percentage of the carbon coating layer to the silicon-carbon material is 0.3%-2%, for example, it can be 0.3%, 0.5%, 0.8%, 1%, 1.5%, 2% or any two thereof.

[0057] In the present invention, the mass percentage of the carbon coating layer in the silicon-carbon material is within the above range. The carbon coating layer is sufficient to form a continuous conductive network on the surface of the silicon particles, which is beneficial to improving the overall conductivity of the material and ensuring the rapid transmission of electrons in the electrode, thereby improving the rate performance of the battery. In addition, an appropriate amount of carbon coating layer can effectively alleviate the volume expansion of the silicon particles. The carbon coating layer provides flexible protection, reduces stress concentration caused by volume change, and prevents particle breakage and pulverization. In addition, the carbon coating layer can significantly improve the interfacial stability between the silicon particles and the electrolyte, reduce the occurrence of side reactions, and help to improve the cycle life of the battery.

[0058] In a second aspect, the present invention provides a method for preparing the silicon-carbon material as described above, comprising the following steps:

[0059] Silicon particles are loaded on a porous carbon substrate to obtain a silicon-carbon material; wherein the porous carbon substrate includes a doping element.

[0060] The present invention loads silicon particles onto a porous carbon substrate containing doping elements, forming a heterostructure between the silicon particles and the porous carbon substrate. The heterostructure can provide an excellent electron transfer path, reduce interfacial resistance, and improve the conductivity of the material, thereby enhancing the rate performance of the battery. The doping elements enhance the interfacial bonding between the silicon particles and the carbon substrate through chemical bonding, reducing electrochemical instability at the interface and improving the cycle life of the battery. The heterostructure also helps alleviate the volume expansion problem of the silicon particles, reduce material pulverization and cracking, and maintain the structural integrity of the electrode.

[0061] The present invention can deposit silicon particles (loaded silicon particles) on the porous carbon substrate by a vapor deposition method.

[0062] The method for preparing the silicon-carbon material of the present invention can prepare the above-mentioned silicon-carbon material. The silicon-carbon material includes a heterogeneous structure, which can alleviate the volume expansion problem of silicon and improve the cycle performance and rate performance of the battery.

[0063] In some embodiments of the present invention, the doping element includes N element and / or S element.

[0064] Doping with N and / or S elements is beneficial to the formation of a heterogeneous structure between silicon particles and the porous carbon substrate, namely, a CN-Si structure and / or a CS-Si structure, which can further alleviate the volume expansion problem of silicon and improve the cycle performance and rate performance of the battery.

[0065] In some embodiments of the present invention, the porous carbon substrate is prepared by a method comprising the following steps:

[0066] 1) introducing a magnetic material into an organic dual-template agent to obtain a first intermediate; the organic dual-template agent comprises a silica core and a polymer layer on the surface of the silica core;

[0067] 2) applying a magnetic field to a first system including a first intermediate and a carbon source so that the magnetic material migrates to the surface region of the first intermediate and the carbon source is concentrated in the central region of the first intermediate, thereby obtaining a second intermediate;

[0068] 3) The second intermediate is subjected to a carbonization treatment, a first activation treatment, and a second activation treatment in sequence to obtain a porous carbon substrate.

[0069] Specifically, in step 1), the magnetic material can be Fe3O4 nanoparticles (particle size Dv50 is 10nm-50nm), and the magnetic material can be loaded in the silica core by a sol-gel method.

[0070] In one embodiment, the organic dual template can be prepared by the following process:

[0071] Silica microspheres are prepared using a silicon source and a template, and the particle size Dv50 of the microspheres can be 4μm-10μm with a deviation of less than 3%. The silicon source can be tetraethyl orthosilicate (TEOS), and the template can be cetyltrimethylammonium bromide (CTAB).

[0072] A polymer is grafted onto the surface of silica to form a polymer layer, wherein the thickness of the polymer layer can be 2 μm-4 μm, and the polymer can be a polyethylene oxide-polypropylene oxide-polyethylene oxide (P123) triblock copolymer.

[0073] In step 2), the carbon source can be formed by dissolving resorcinol and thiourea in a solution of ethanol and water in a volume ratio of 3:1-5:1. The carbon source is added to the first intermediate, and a radial magnetic field gradient (0→1.5T) is then established in the reaction vessel. Specifically, the magnetic field can be generated using an electromagnetic field generator (adjustable from 0 to 1.5T with an accuracy of ±0.1T). Helmholtz coils generate a spatially varying magnetic field with a radial gradient, from a weak central magnetic field (0T) to a strong peripheral magnetic field (1.5T). The magnetic force pulls the magnetic material toward the surface of the first intermediate, forcing the carbon source to concentrate in the center. The reaction mixture is then stirred at 300-500 rpm and 40-70°C for 5-12 hours, allowing a resin layer to form in the center of the first intermediate and silica and polymer layers to form on the surface. At this point, the magnetic material will separate from the first intermediate, forming a second intermediate.

[0074] In step 3), the second intermediate can be carbonized under an inert gas, such as nitrogen, to maintain its template structure. The resin layer and the polymer layer are carbonized to form an amorphous carbon core. A first activation treatment is then performed to form macropores in the central region. A second activation treatment is then performed to form micropores in the surface region. The silica template is then removed to obtain a porous carbon substrate. Specifically, the silica can be etched away using a hydrofluoric acid solution, the concentration of which can be 2% to 5%. At the same time, the hydrofluoric acid solution removes the magnetic material on the surface.

[0075] The preparation method of the porous carbon substrate provided by the present invention can form a gradient pore structure in the prepared porous carbon substrate, further alleviate the volume expansion problem of silicon, and improve the cycle performance and rate performance of the battery.

[0076] In some embodiments of the present invention, the temperature of the carbonization treatment is 300°C-500°C, for example, 300°C, 350°C, 400°C, 450°C, 500°C or a range consisting of any two thereof.

[0077] The heating rate of the carbonization treatment of the present invention can be 1° C. / min-3° C. / min, and the temperature of the carbonization treatment can effectively convert organic matter into carbon material while maintaining the structural integrity of the material.

[0078] In some embodiments, the first activation treatment includes: performing a first activation treatment using water vapor for 1 hour to 3 hours at 500°C to 700°C and immersing in an alkaline liquid to form macropores of 30nm to 200nm in a region 0μm to 2μm away from the center of the porous carbon substrate.

[0079] Exemplarily, the temperature of the first activation treatment can be 500°C, 550°C, 600°C, 650°C, 700°C or a range consisting of any two thereof; the time can be 1h, 1.5h, 2h, 2.5h, 3h or a range consisting of any two thereof; the distance can be 0μm, 0.3μm, 0.5μm, 1μm, 1.5μm, 2μm or a range consisting of any two thereof; the pore diameter of the macropore can be 30nm, 50nm, 80nm, 100nm, 150nm, 200nm or a range consisting of any two thereof.

[0080] The alkaline liquid can be a potassium hydroxide solution, where the mass ratio of potassium hydroxide to water is 1:3-1:5. The central region is formed by polymer bonding. In this bonding region, the polymer reacts with carbon at high temperature, etching the carbon skeleton to form larger voids, forming macropores. This macroporous structure helps increase the specific surface area and porosity of the material, facilitating the rapid transport of large molecules or ions. It also provides sufficient space to accommodate the volume expansion of silicon particles, allowing silicon to expand during charging without causing excessive stress on the overall structure, thereby reducing material cracking and pulverization.

[0081] In some embodiments, the second activation treatment includes performing a second activation treatment using carbon dioxide at 700° C.-900° C. for 0.5 h-2 h to form micropores of 5 nm-30 nm in a region 1 μm-4 μm away from the center of the porous carbon substrate.

[0082] Exemplarily, the temperature of the second activation treatment can be 700°C, 750°C, 800°C, 850°C, 900°C or a range consisting of any two thereof; the time can be 0.5h, 1h, 1.2h, 1.5h, 2h or a range consisting of any two thereof; the distance can be 1μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm or a range consisting of any two thereof; the pore diameter of the micropores can be 5nm, 8nm, 10nm, 20nm, 30nm or a range consisting of any two thereof.

[0083] A second activation treatment using carbon dioxide is performed at a higher temperature. At high temperatures, carbon dioxide reacts with carbon surface functional groups (e.g., hydroxyl and carboxyl groups), preferentially etching the carbon material's surface and forming micropores. These micropores provide a larger surface area, helping to improve the material's adsorption capacity and reactivity. They also physically restrict the expansion of silicon particles, preventing them from overexpanding. This helps disperse and alleviate stress concentration caused by volume change, reducing material fatigue.

[0084] In some embodiments of the present invention, after loading silicon particles on the porous carbon substrate, the method further comprises: performing carbon coating treatment on the loaded product obtained by loading the silicon particles to obtain a silicon-carbon material.

[0085] In the present invention, the carbon source used for carbon coating treatment can be asphalt. Specifically, the loaded product can be mixed with the carbon source and then ball milled. The ball milling time can be 1h-3h, and the rotation speed can be 300rpm-500rpm. After ball milling, the material is carbon coated and heated to a certain temperature at a heating rate of 1°C / min-3°C / min under the protection of an inert gas, such as nitrogen, to obtain a carbon-coated silicon-carbon material.

[0086] The carbon coating layer can provide a continuous conductive network, improve the conductivity of the silicon-carbon material, and enhance the overall electrochemical performance of the material. The carbon coating layer acts as a flexible protective shell, which can effectively alleviate the volume expansion of silicon particles during the charge and discharge process, reducing the breakage and pulverization of particles. In addition, the carbon coating layer improves the interfacial stability between silicon particles and the electrolyte, reduces the occurrence of side reactions, and extends the cycle life of the battery. At the same time, the presence of the carbon coating layer improves the bonding force between silicon particles and the porous carbon substrate, reduces the shedding of silicon particles during the cycle, and maintains the structural integrity of the electrode.

[0087] In some embodiments of the present invention, the temperature of the carbon coating treatment is 500°C-700°C, for example, it can be 500°C, 550°C, 600°C, 650°C, 700°C or a range consisting of any two thereof; the time is 1h-3h, for example, it can be 1h, 1.5h, 2h, 2.5h, 3h or a range consisting of any two thereof.

[0088] The carbon coating treatment temperature within the above range allows the carbon source to fully decompose and evenly deposit on the surface of the silicon particles, forming a dense and uniform carbon coating layer, which helps improve the conductivity and mechanical stability of the material. It also promotes the decomposition of the carbon source and the formation of the carbon layer without causing excessive crystallization or structural damage to the silicon particles.

[0089] The carbon coating treatment time is within the above range, which can ensure the sufficient formation of the carbon layer and avoid the problem of excessively thick or uneven carbon layer that may be caused by too long a time.

[0090] In a third aspect, the present invention provides a negative electrode sheet comprising the silicon-carbon material as described above or the silicon-carbon material prepared according to the method for preparing the silicon-carbon material as described above.

[0091] The negative electrode sheet of the present invention can be prepared by conventional technical means in the field. Specifically, the above-mentioned silicon-carbon material, conductive agent, and binder can be uniformly dispersed in a solvent to obtain a negative electrode slurry, and then the negative electrode slurry is coated on at least one functional surface of the negative electrode collector. After drying, the negative electrode sheet of the present invention can be obtained.

[0092] The present invention does not particularly limit the specific type of the negative electrode current collector, which may include at least one of copper foil, nickel foil, stainless steel, and composite materials.

[0093] The present invention does not particularly limit the specific types of the conductive agent and the adhesive. The conductive agent, the adhesive and other components can be selected from conventional substances in the field. For example, the conductive agent can be selected from one or more of conductive carbon black, carbon nanotubes, conductive graphite, graphene, and conductive polymers, and the adhesive can be selected from one or more of polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), and polyvinyl alcohol (PVA).

[0094] The present invention does not specifically limit the coating method, and the negative electrode slurry can be coated by any coating method such as gravure coating, extrusion coating, spraying, screen printing, etc.

[0095] The negative electrode sheet provided by the present invention includes the above-mentioned silicon-carbon material. Therefore, the negative electrode sheet has a low volume expansion rate and can be applied to a battery to improve the cycle performance and rate performance of the battery.

[0096] In a fourth aspect, the present invention provides a battery comprising the negative electrode sheet as described above. The battery has advantages corresponding to the above negative electrode sheet, which will not be described in detail.

[0097] The battery of the present invention includes, in addition to the negative electrode sheet, a separator, a positive electrode sheet, and an electrolyte. The composition of the positive electrode sheet can refer to conventional positive electrode sheets in the art, and the separator can also be a separator commonly used in the art, such as PP film, PE film, etc.

[0098] The battery of the present invention can be prepared by conventional methods in the field. Specifically, the positive electrode sheet, the separator and the negative electrode sheet can be stacked in sequence, and then the battery core can be obtained through a lamination or winding process, and then through baking, liquid injection, formation, packaging and other processes to obtain the above-mentioned battery.

[0099] The batteries of the present invention may be in the form of battery cells, battery modules, and battery packs. In some embodiments, battery cells may be assembled into a battery module, which may contain one or more battery cells, with the specific number selected by those skilled in the art based on the application and capacity of the battery module. In some embodiments, battery modules may also be assembled into a battery pack, which may contain one or more battery modules, with the specific number selected by those skilled in the art based on the application and capacity of the battery pack.

[0100] There are no particular restrictions on the specific type of battery of the present invention. For example, from the perspective of shape, the battery includes but is not limited to square-shell batteries, soft-pack batteries, and cylindrical batteries, etc., and this application does not impose any particular restrictions. From the perspective of the electrode core structure, the electrode core of the battery can be a wound electrode core (i.e., the positive electrode sheet, the negative electrode sheet, and the separator are stacked and then wound to form the electrode core), or a laminated electrode core (i.e., multiple positive electrode sheets, negative electrode sheets, and separators are stacked to form the electrode core). The outer shell can be a hard shell (such as a steel shell, a hard plastic shell, etc.) or a soft shell (such as an aluminum-plastic film, a bag-type soft shell, etc.). This application does not impose any particular restrictions.

[0101] In a fifth aspect, the present invention provides an electrical device comprising the battery as described above. The electrical device has advantages corresponding to those of the negative electrode sheet described above, which will not be described in detail.

[0102] The electrical equipment of the present invention can be conventional electrical equipment in the field, such as power equipment (such as electric vehicles), electronic equipment (such as computers, mobile phones, digital cameras, printers, fax machines, etc.), wearable devices (such as watches, bracelets, VR glasses, etc.), household appliances (such as air conditioners, refrigerators, washing machines, microwave ovens, etc.), etc., without special restrictions.

[0103] The technical solution of the present invention is further described below with reference to specific embodiments.

[0104] Example 1

[0105] The preparation method of the silicon-carbon material of this embodiment comprises the following steps:

[0106] 1) SiO2 microspheres with a particle size Dv50 of 6 μm were prepared using 1 mol tetraethyl orthosilicate (TEOS) as the silicon source and 50 g cetyltrimethylammonium bromide (CTAB) as the template.

[0107] Polyethylene oxide-polypropylene oxide-polyethylene oxide (P123) triblock copolymer was grafted onto the SiO2 surface to form a polymer shell with a thickness of 50 nm.

[0108] The first intermediate was obtained by loading 1 mol of Fe3O4 nanoparticles (particle size Dv50 was 50 nm) on the SiO2 core through the sol-gel method.

[0109] 2) Resorcinol (5g) and thiourea (3g) were dissolved in 500g of a mixture of ethanol and water (v / v = 3:1) to form a carbon source, which was then added to the first intermediate. An electromagnetic field generator (adjustable from 0-1.5T, accuracy ±0.1T) was used to generate a spatially varying magnetic field with a Helmholtz coil. The gradient was radial, with a weak magnetic field at the center (0T) and a strong magnetic field at the periphery (1.5T). This established a radial magnetic field gradient (0→1.5T) in the reaction vessel. The magnetic force attracted Fe₃O₄ particles to the surface of the first intermediate, forcing the resorcinol-thiourea (RF) resin to accumulate in the center of the first intermediate. The mixture was stirred at 300 rpm and 50°C for 12 hours, resulting in the formation of a resin layer in the center of the first intermediate and silica and polymer layers on the surface, forming the second intermediate.

[0110] 3) The second intermediate is heated to 400° C. at a heating rate of 1° C. / min under nitrogen protection for carbonization treatment, retaining the SiO2 template structure, and the resin layer and the polymer layer are carbonized to form an amorphous carbon core.

[0111] Then, the first activation treatment was carried out using water vapor for 2 hours at 600°C and immersion in a KOH solution (the mass ratio of KOH to water was 1:3), forming macropores with an average pore size of 100 nm in the area 0 μm-1.5 μm away from the center of the porous carbon substrate.

[0112] Then, a second activation treatment was performed using CO2 at 800°C for 1 hour to form micropores with an average pore diameter of 25 nm in a region 1.5 μm to 3.5 μm away from the center of the porous carbon substrate.

[0113] SiO2 was etched away using 4% HF solution to obtain a porous carbon substrate.

[0114] 4) Silicon particles were vapor deposited on the porous carbon substrate (loaded silicon particles) at a temperature of 700°C, a gas source of 20% SiH4+80% Ar, a gas flow velocity of 1 m / s, and a deposition time of 3 min. The mass ratio of silicon particles to the porous carbon substrate was 2:8, and the particle size Dv50 of the silicon particles was 20 nm. The doping elements N and S in the porous carbon substrate were used to form CN-Si heterostructures and CS-Si heterostructures to form loaded products.

[0115] 5) The loaded product was mixed with asphalt and then ball-milled at a mass ratio of 99:1. The ball-milling time was 2 h at a rotation speed of 500 rpm. The mixture was then heated to 500°C (at a heating rate of 1°C / min) under nitrogen protection for 3 h for carbon coating to obtain a silicon-carbon material.

[0116] Example 2

[0117] The preparation method of the silicon-carbon material in Example 2 is basically the same as that in Example 1, except that the temperature of the first activation treatment is changed to 500°C and the time is 1 hour, so that the average pore size of the carbon material in the area 2000 nm away from the center of the porous carbon substrate is 30 nm.

[0118] Example 3

[0119] The preparation method of the silicon-carbon material in Example 3 is basically the same as that in Example 1, except that the temperature of the first activation treatment is changed to 700°C and the time is changed to 3 hours, so that the average pore size of the carbon material in the area 4000 nm away from the center of the porous carbon substrate is 200 nm.

[0120] Example 4

[0121] The preparation method of the silicon-carbon material in Example 4 is basically the same as that in Example 1, except that the temperature of the second activation treatment is changed to 700°C and the time is changed to 0.5h, so that the average pore size of the carbon material in the area 2000nm away from the center of the porous carbon substrate is 5nm.

[0122] Example 5

[0123] The preparation method of the silicon-carbon material in Example 5 is basically the same as that in Example 1, except that the temperature of the second activation treatment is changed to 900°C and the time is changed to 2 hours, so that the average pore size of the carbon material in the area 3500 nm away from the center of the porous carbon substrate is 30 nm.

[0124] Example 6

[0125] The preparation method of the silicon-carbon material in Example 6 is basically the same as that in Example 1, except that the vapor deposition gas source is 10% SiH4+90% Ar, and the mass ratio of silicon particles to porous carbon substrate is 1:9.

[0126] Example 7

[0127] The preparation method of the silicon-carbon material in Example 7 is basically the same as that in Example 1, except that the vapor deposition gas source is 30% SiH4+70% Ar, and the mass ratio of silicon particles to porous carbon substrate is 3:7.

[0128] Example 8

[0129] The preparation methods of the silicon-carbon material in Example 8 are basically the same as those in Example 1, except that the vapor deposition time is 0.5 min and the particle size Dv50 of the silicon particles is 5 nm.

[0130] Example 9

[0131] The preparation method of the silicon-carbon material in Example 9 is basically the same as that in Example 1, except that the vapor deposition time is 10 min and the particle size Dv50 of the silicon particles is 100 nm.

[0132] Example 10

[0133] The preparation method of the silicon-carbon material in Example 10 is basically the same as that in Example 1, except that the mass ratio of the loaded product to the asphalt is 99.7:0.3.

[0134] Example 11

[0135] The preparation method of the silicon-carbon material in Example 11 is basically the same as that in Example 1, except that the mass ratio of the loaded product to the asphalt is 98:2.

[0136] Comparative Example 1

[0137] The preparation method of the silicon-carbon material of Comparative Example 1 comprises the following steps:

[0138] 1) The porous carbon substrate of Example 1, silicon particles with a particle size Dv50 of 20 nm, and asphalt were placed in a ball mill at a mass ratio of 79:20:1 and ball milled for 2 h at a speed of 500 rpm. After the ball milling, the mixture was heated to 500°C (heating rate of 1°C / min) under nitrogen protection and carbon-coated for 3 h to obtain a silicon-carbon material.

[0139] Test example:

[0140] At 25°C and normal pressure (0.1 MPa), the silicon-carbon material, conductive carbon black, and binder polyvinylidene fluoride (PVDF) of each embodiment and comparative example were respectively stirred and mixed in N-methylpyrrolidone (NMP) at a mass percentage ratio of 95:3:2 to obtain a slurry. The slurry was coated on a copper foil, dried, and cold-pressed to obtain an electrode. A 2025 button battery case was used, a lithium sheet was used as the counter electrode, and conventional lithium-ion battery electrolyte was used to assemble the button battery.

[0141] 1. Average pore size: The pore size distribution can be calculated by transmission electron microscopy and nitrogen adsorption-desorption curve BJH method to obtain the average pore size of the inner and outer layers of the carbon material.

[0142] 2. Particle size Dv50: can be obtained through transmission electron microscopy testing.

[0143] 3. Expansion rate: For button-type full-electric in-situ expansion test, calculate the ratio of the thickness of the negative electrode at full charge to the thickness after rolling, that is, expansion rate = (full charge thickness - thickness after rolling) / full charge thickness.

[0144] 4. Rate performance: According to the method in the withholding capacity test, the silicon-carbon material is coated into the negative electrode sheet, the positive active material is NCM811, and the diaphragm polyethylene and the electrolyte (the electrolyte is LiPF6 and the solvent is EC / DMC) form a full battery. It is charged at a constant current rate of 0.1C to a voltage of 4.2V, and then charged at a constant voltage at a voltage of 4.2V to a current equal to 0.05C. After standing for 5 minutes, it is discharged at a constant current rate of 0.1C to a voltage of 2.5V. The capacity at this time is recorded as the discharge capacity at 0.1C rate; after standing for 10 minutes, it is charged at a constant current rate of 1C to a voltage of 4.2V, and then charged at a constant voltage at a voltage of 4.2V to a current equal to 0.05C. After standing for 5 minutes, it is discharged at a constant current rate of 1C to a voltage of 2.5V. The capacity at this time is recorded as the discharge capacity at 1C rate. The ratio of the discharge capacity at 1C rate to the discharge capacity at 0.1C rate is the 1C rate performance.

[0145] 5. Cycle performance: The full battery is charged to 4.2V at a constant current of 1C at a charge rate of 25°C, then charged to 0.05C at a constant voltage, and then discharged to 2.5V at a discharge rate of 1C. This charge and discharge cycle is repeated 300 times. The discharge capacity Q1 at the first cycle and the discharge capacity Q at the 300th cycle are measured. 300 The capacity retention rate after 300 cycles is Q=Q 300 / Q1×100%.

[0146] Table 1

[0147]

[0148] As can be seen from Table 1, compared with the comparative example, the silicon-carbon material provided by the present invention includes a porous carbon substrate and silicon particles present in the porous carbon substrate. The silicon-carbon material includes a heterogeneous structure. The heterogeneous structure plays a role in anchoring the silicon particles by forming a strong connection between the silicon particles and the porous carbon substrate, ensuring that the silicon particles can still maintain a connection with the carbon substrate after multiple charge and discharge cycles, preventing the silicon particles from falling off. The combined effect of the porous carbon substrate and the heterogeneous structure can alleviate the volume expansion problem of silicon and improve the cycle performance and rate performance of the battery.

[0149] Finally, it should be noted that those skilled in the art will readily identify other embodiments of the present invention after considering the specification and practicing the invention disclosed herein. The present invention is intended to cover any variations, uses, or adaptations of the present invention that follow the general principles of the present invention and include common knowledge or customary techniques in the art not disclosed herein. The present invention is not limited to the foregoing description and may be modified and altered in various ways without departing from the scope thereof. The scope of the present invention is limited solely by the appended claims.

Claims

1. A silicon-carbon material, characterized in that: The invention comprises a porous carbon substrate and silicon particles in the porous carbon substrate, wherein the silicon-carbon material comprises a heterostructure.

2. The silicon-carbon material according to claim 1, characterized in that The heterostructure includes a CN-Si structure and / or a CS-Si structure.

3. The silicon-carbon material according to claim 1 or 2, characterized in that: An average pore diameter of the carbon material in a region of 0 μm to 2 μm from the center of the porous carbon substrate is larger than an average pore diameter of the carbon material in a region of 1 μm to 4 μm from the center of the porous carbon substrate.

4. The silicon-carbon material according to claim 3, characterized in that The average pore size of the carbon material in a region 0 μm to 2 μm away from the center of the porous carbon substrate is 30 nm to 200 nm; And / or, the average pore diameter of the carbon material in a region 1 μm to 4 μm away from the center of the porous carbon substrate is 5 nm to 30 nm.

5. The silicon-carbon material according to any one of claims 1 to 4, characterized in that: The particle size Dv50 of the silicon particles is 5nm-100nm.

6. The silicon-carbon material according to any one of claims 1 to 5, characterized in that: The mass ratio of the silicon particles to the porous carbon substrate is 1:9-3:

7.

7. The silicon-carbon material according to any one of claims 1 to 6, characterized in that: The silicon-carbon material further includes a carbon coating layer present on the surface of the silicon particles.

8. The silicon-carbon material according to claim 7, characterized in that The mass percentage of the carbon coating layer to the silicon-carbon material is 0.3%-2%.

9. A method for preparing a silicon-carbon material according to any one of claims 1 to 8, characterized in that: The following steps are involved: Silicon particles are loaded on a porous carbon substrate to obtain the silicon-carbon material; wherein the porous carbon substrate includes doping elements.

10. The method for preparing the silicon-carbon material according to claim 9, characterized in that: The doping element includes N element and / or S element.

11. The method for preparing the silicon-carbon material according to claim 9 or 10, characterized in that: The porous carbon substrate is prepared by a method comprising the following steps: 1) introducing a magnetic material into an organic dual-template agent to obtain a first intermediate; the organic dual-template agent comprises a silica core and a polymer layer present on the surface of the silica core; 2) applying a magnetic field to a first system including the first intermediate and a carbon source so that the magnetic material migrates to the surface region of the first intermediate and the carbon source is concentrated in the central region of the first intermediate, thereby obtaining a second intermediate; 3) performing a carbonization treatment, a first activation treatment, and a second activation treatment on the second intermediate in sequence to obtain the porous carbon substrate.

12. The method for preparing the silicon-carbon material according to claim 11, characterized in that: The temperature of the carbonization treatment is 300°C-500°C; And / or, the first activation treatment comprises: performing the first activation treatment using water vapor for 1 hour to 3 hours under immersion in an alkaline liquid at 500° C. to 700° C., thereby forming macropores of 30 nm to 200 nm in a region 0 μm to 2 μm away from the center of the porous carbon substrate; And / or, the second activation treatment includes: performing the second activation treatment using carbon dioxide at 700° C.-900° C. for 0.5 h-2 h to form micropores of 5 nm-30 nm in a region 1 μm-4 μm away from the center of the porous carbon substrate.

13. The method for preparing a silicon-carbon material according to any one of claims 9 to 12, characterized in that: After the silicon particles are loaded on the porous carbon substrate, the method further comprises: performing carbon coating treatment on the loaded product obtained by loading the silicon particles to obtain the silicon-carbon material.

14. The method for preparing the silicon-carbon material according to claim 13, wherein: The temperature of the carbon coating treatment is 500° C.-700° C., and the time is 3 h-5 h.

15. A negative electrode sheet, characterized in that: The silicon-carbon material comprises the silicon-carbon material according to any one of claims 1 to 8 or the silicon-carbon material prepared according to the method for preparing the silicon-carbon material according to any one of claims 9 to 14.

16. A battery, characterized in that: Including the negative electrode sheet according to claim 15.

17. An electrical device, characterized in that: Including the battery according to claim 16.

Images