Low-strain silicon-carbon negative electrode material and preparation method thereof

Abstract

The application discloses a low-strain silicon-carbon negative electrode material and a preparation method thereof. The preparation method comprises the following steps: S100, synthesizing MgV2O6 products from a magnesium source and a vanadium source; S200, mixing porous carbon and the MgV2O6 products to obtain a base material; and S300, performing vapor deposition on the outer surface and the pores of the base material by using a silane gas source and a carbon gas source in an inert gas to obtain a silicon-carbon negative electrode material. The MgV2O6 with a stable crystal structure is prepared from the magnesium source and the vanadium source, and rigid support is provided in the subsequent preparation process, so that the use stability and the thermal stability are improved. The silane gas source and the carbon gas source are vapor-deposited on the base material to generate silicon-carbon active substances in situ, so that the silicon atoms, the carbon atoms and the carbon atoms on the surface of the base material form firm chemical bonds, the stress generated when the silicon expands is absorbed by the internal structure of the silicon-carbon negative electrode material, and thus the silicon-carbon negative electrode material with high use stability is prepared.

Description

Technical Field

[0001] This application relates to the field of anode materials, and in particular to a low-strain silicon-carbon anode material and its preparation method. Background Technology

[0002] Currently, lithium-ion batteries, as high-efficiency energy storage devices, are widely used in electric vehicles, portable electronic devices, and renewable energy storage. To further expand the application range of lithium-ion batteries, continuously improving their energy density is a core research direction in the industry. As a key component of lithium-ion batteries, the anode material directly affects the battery's energy storage capacity, charging speed, lifespan, and safety; therefore, breakthroughs in anode material performance are a major limiting factor.

[0003] The theoretical specific capacity of traditional graphite anodes is nearing its physical limit (approximately 372 mAh / g), making it difficult to meet future demands. In contrast, silicon-based anodes offer advantages such as ultra-high theoretical specific capacity (4200 mAh / g) and suitable low lithium intercalation potential (<0.5 V vs. Li / Li). + With its advantages such as abundant element reserves, it is regarded as an ideal choice for the next generation of anode materials.

[0004] However, the large-scale commercialization of silicon-based anodes faces two major challenges: first, the severe volume effect, where silicon undergoes up to 300% volume expansion and contraction during charging and discharging, i.e., lithium insertion / extraction, which easily leads to the breakage of active particles, pulverization of the electrode structure, and damage to the conductive network; second, severe interfacial instability, where continuous volume changes cause the solid electrolyte interfacial film on the particle surface to repeatedly rupture and regenerate, continuously consuming electrolyte and active lithium, and increasing interfacial impedance, thus triggering severe capacity decay and reduced cycle life. Therefore, to improve the quality and stability of anode materials, it is urgent to optimize a preparation process that can produce anode materials with high stability and long service life. Summary of the Invention

[0005] One objective of this application is to provide a low-strain silicon-carbon anode material and its preparation method, which is beneficial to improving the service life of silicon-carbon anode materials and further enhancing the structural stability and long-term cycling stability of silicon-carbon anode materials.

[0006] To achieve the above objectives, the technical solution adopted in this application is as follows: a method for preparing a low-strain silicon-carbon anode material, comprising the following steps: S100, synthesizing MgV2O6 product from magnesium source and vanadium source; S200, mixing porous carbon with the MgV2O6 product to obtain a matrix material; S300, performing vapor phase deposition on the outer surface and pores of the matrix material in an inert gas using a silane gas source and a carbon gas source to obtain the silicon-carbon anode material.

[0007] In some embodiments, the preparation method satisfies at least one of the following conditions: the magnesium source is one or more of magnesium acetate, magnesium nitrate, magnesium chloride, magnesium sulfate, magnesium isopropoxide, and magnesium acetylacetonate; the vanadium source is one or more of vanadium pentoxide, ammonium metavanadate, vanadic acid, vanadium oxysulfate, and vanadium oxyacetylacetonate; and the porous carbon is one or more of bio-based porous carbon, petroleum coke-based porous carbon, or resin-based porous carbon.

[0008] In some embodiments, the molar ratio of the magnesium source to the vanadium source is (1~10):(1~10), and the mass ratio of the porous carbon to the MgV2O6 product is 1:(0.02~0.1).

[0009] In some embodiments, the preparation method satisfies at least one of the following conditions: the silane gas source is one or more of methane and silane; the carbon gas source is one or more of methane, ethane, propane, acetylene, and propyne; and the inert gas is one or more of nitrogen, argon, and helium.

[0010] In some embodiments, step S100 includes the following sub-steps: S110, dissolving a magnesium source, a vanadium source, and a complexing agent in water and heating and stirring for the first time to obtain a first mixture, wherein the complexing agent is one or more of citric acid, oxalic acid, tartaric acid, acetic acid, ethylene glycol, polyacrylamide alcohol, ethylenediaminetetraacetic acid, and glucose, wherein the temperature of the first heating is 60℃~90℃ and the time of the first heating is 0.1h~3h, and the molar ratio of the magnesium source, the vanadium source, and the complexing agent is (1~10):(1~10):(1~10); S120, heating the first mixture for the second time to obtain a second solid, wherein the temperature of the second heating is 400℃~500℃ and the time of the second heating is 0.1h~3h; S130, calcining the second solid in air to obtain a MgV2O6 product, wherein the calcination temperature is 500℃~700℃ and the calcination time is 1h~10h.

[0011] In some embodiments, step S100 includes the following sub-steps: S110, grinding the magnesium source and vanadium source and then calcining them in air for the first time to obtain a first intermediate product, wherein the first calcination temperature is 500℃~700℃, the first calcination time is 2h~24h, and the grinding time is 0.1h~2h; S120, grinding the first intermediate product and then calcining it in air for the second time to obtain the MgV2O6 product, wherein the second calcination temperature is 500℃~700℃, the second calcination time is 1h~24h, and the grinding time is 0.1h~2h.

[0012] In some embodiments, step S100 includes the following sub-steps: S110, mixing magnesium source and vanadium source evenly and pre-pressing them into sheet or block shape under normal pressure to obtain a first mixture; S120, placing the first mixture into a boron nitride tube, and then loading it into a pyrophyllite synthesis chamber to react the first mixture under high temperature and high pressure to obtain MgV2O6 product. In the pyrophyllite synthesis chamber, graphite is used as a heating tube and pyrophyllite is used as an insulating tube. The reaction temperature is 800℃~1500℃, the reaction pressure is 0.1GPa~20GPa, and the reaction time is 0.1h~2h.

[0013] In some embodiments, step S200 is as follows: ultrasonically disperse the porous carbon and the MgV2O6 product in water or ethanol and then dry them to obtain a second intermediate product. Calcine the second intermediate product in an inert gas to obtain a matrix material. The calcination temperature is 500℃~700℃ and the calcination time is 1h~4h.

[0014] In some embodiments, in step S300, the volume flow rate ratio of the silane gas source to the inert gas is 1:(1~10), and the volume flow rate ratio of the carbon gas source to the inert gas is 1:(1~10); the vapor deposition temperature is 500℃~1000℃, and the deposition time is 1h~12h.

[0015] To achieve the above objectives, this application also provides a low-strain silicon-carbon anode material prepared by the aforementioned preparation method, wherein the mass ratio of silicon to carbon in the silicon-carbon anode material is 1:(0.1~9).

[0016] Compared with the prior art, the beneficial effects of this application are as follows:

[0017] (1) This application first prepares MgV2O6 with a stable crystal structure using magnesium and vanadium sources, providing rigid support for subsequent preparation processes to restrain silicon during volume expansion, thereby improving the stability and thermal stability of the silicon-carbon anode material. When mixing porous carbon and MgV2O6, MgV2O6 is uniformly placed in the abundant pores of the porous carbon, which is conducive to building a three-dimensional conductive network in the matrix material and forming a through network that facilitates rapid electron transport, thereby enhancing the intrinsic conductivity of the prepared silicon-carbon anode material and further improving its electrochemical kinetic performance. On the other hand, by vapor-depositing silane and carbon sources on the matrix material to generate silicon-carbon active materials in situ, not only can the silicon-carbon active materials be uniformly and accurately deposited on the pores and outer surface of the matrix material, but the silicon-carbon active materials and the matrix material are also tightly intercalated. Silicon atoms and carbon atoms form strong chemical bonds with carbon atoms on the surface of the matrix material, achieving strong interfacial bonding, thereby improving the strength and conductivity of the silicon-carbon anode material itself. In other words, the silicon distributed inside the channels is rigidly constrained by the substrate material during expansion. Meanwhile, the silicon-carbon active material, grown in situ on the outer surface of the substrate and within the channels via vapor deposition, provides an elastic buffer for the expanding silicon and reduces the risk of direct contact between the silicon and the electrolyte. Thus, the stress generated during silicon expansion is absorbed by the internal structure of the silicon-carbon anode material, resulting in a low-strain silicon-carbon anode material with high stability and long service life.

[0018] (2) In this application, MgV2O6 is introduced during the preparation of silicon-carbon anode material. Due to the stable crystal structure of MgV2O6, the volume change of silicon during insertion or extraction is small. Furthermore, since a solid electrolyte interface film is generated on the surface of the anode material during the first charge, the silicon undergoes a small volume change, which is beneficial to improving the structural stability and long-term cycling stability of the solid electrolyte interface film and reducing lithium consumption. In addition, MgV2O6 has efficient transport channels and abundant active sites, which is beneficial to increasing electronic conductivity and lithium-ion diffusion coefficient, thereby improving the overall energy density. As a vanadium-based oxide, MgV2O6 combined with porous carbon provides more pathways for the rapid transport of electrons and lithium ions, improving structural stability. On the one hand, MgV2O6 has good hardness, elastic modulus and structural stability. Therefore, when silicon expands, the rigid MgV2O6 particles will inhibit the expansion of silicon and provide stable support for the pores in the porous carbon, thereby reducing the risk of pore collapse and further preventing silicon particles from squeezing and destroying the surrounding carbon network indefinitely. On the other hand, the surface of MgV2O6 particles can form strong chemical bonds with porous carbon, which is beneficial to increasing the structural and operational stability of the anode material. In other words, MgV2O6 can not only serve as a buffer matrix, but it is also an active material with lithium storage capacity, which is beneficial to compensate for initial lithium loss, improve the reversible capacity and initial coulombic efficiency of silicon-carbon anode materials, and enhance their lifespan during long-term cycling. Attached Figure Description

[0019] Figure 1 This is a process flow diagram of the preparation process of a low-strain silicon-carbon anode material in this application.

[0020] Figure 2 This is a process flow diagram for the preparation of another low-strain silicon-carbon anode material in this application. Detailed Implementation

[0021] The present application will be further described below with reference to specific embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0022] As used herein, the terms “prepared from” and “comprising” are synonymous. The terms “comprising,” “including,” “having,” “containing,” or any other variation thereof, as used herein, are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements and may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0023] When a quantity, concentration, or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range is disclosed as “1 to 5”, the described range should be interpreted as including ranges “1 to 4”, “1 to 3”, “1 to 2 and 4 to 5”, “1 to 3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range includes its endpoints and all integers and fractions within that range.

[0024] Approximate terms used in the specification and claims to modify quantities indicate that the invention is not limited to that specific quantity, but also includes acceptable modifications close to that quantity that do not alter the relevant essential function. Correspondingly, the use of "about," "approximately," etc., to modify a numerical value means that the invention is not limited to that precise value. In some instances, approximate terms may correspond to the precision of the instrument used to measure the value. In this application's specification and claims, scope definitions can be combined and / or interchanged, unless otherwise stated, these scopes include all subscopes contained therein.

[0025] like Figure 1 and Figure 2 It is understood that this application provides a method for preparing a low-strain silicon-carbon anode material, including the following steps: S100, synthesizing MgV2O6 product from magnesium source and vanadium source; S200, mixing porous carbon and MgV2O6 product to obtain a matrix material; S300, performing vapor deposition on the outer surface and pores of the matrix material in an inert gas using silane gas source and carbon gas source to obtain silicon-carbon anode material.

[0026] It is worth mentioning that this application first prepares MgV2O6 with a stable crystal structure using magnesium and vanadium sources, providing rigid support for subsequent preparation processes to restrain silicon during volume expansion, thereby improving the stability of the silicon-carbon anode material in use and its thermal stability. When mixing porous carbon and MgV2O6, the MgV2O6 is uniformly placed within the abundant pores of the porous carbon, which facilitates the construction of a three-dimensional conductive network in the matrix material, forming a through-network conducive to rapid electron transport. This enhances the intrinsic conductivity of the prepared silicon-carbon anode material and further improves its electrochemical kinetics performance. On the other hand, by vapor-depositing silane and carbon sources on the matrix material to generate silicon-carbon active materials in situ, not only can the silicon-carbon active materials be uniformly and precisely deposited on the pores and outer surface of the matrix material, but the silicon-carbon active materials and the matrix material are also tightly intercalated. Silicon atoms and carbon atoms form strong chemical bonds with carbon atoms on the matrix material surface, achieving strong interfacial bonding, thereby improving the strength and conductivity of the silicon-carbon anode material itself. In other words, the silicon distributed inside the channels is rigidly constrained by the substrate material during expansion. Meanwhile, the silicon-carbon active material, grown in situ on the outer surface of the substrate and within the channels via vapor deposition, provides an elastic buffer for the expanding silicon and reduces the risk of direct contact between the silicon and the electrolyte. Thus, the stress generated during silicon expansion is absorbed by the internal structure of the silicon-carbon anode material, resulting in a low-strain silicon-carbon anode material with high stability and long service life.

[0027] Furthermore, this application introduces MgV2O6 into the preparation process of silicon-carbon anode materials. Because MgV2O6 has a stable crystal structure, the volume change of silicon during insertion or extraction is small. Additionally, during the first charge, the anode material reduces the electrolyte on the anode surface to form a solid electrolyte interface film, resulting in a small volume change in silicon. This is beneficial for improving the structural stability and long-term cycling stability of the solid electrolyte interface film, and reducing lithium consumption. Furthermore, MgV2O6 possesses efficient transport channels and abundant active sites, which helps increase electronic conductivity and lithium-ion diffusion coefficient, improving overall energy density. As a vanadium-based oxide, MgV2O6, combined with porous carbon, provides more pathways for the rapid transport of electrons and lithium ions, enhancing structural stability. On the one hand, MgV2O6 has good hardness, elastic modulus, and structural stability. Therefore, when silicon expands, the rigid MgV2O6 particles inhibit silicon expansion and provide stable support for the pores in the porous carbon, reducing the risk of pore collapse and further preventing silicon particles from indiscriminately compressing and destroying the surrounding carbon network. On the other hand, the surface of MgV₂O₆ particles can form strong chemical bonds with porous carbon, which is beneficial to increasing the structural and operational stability of the anode material. In other words, MgV₂O₆ not only serves as a buffer matrix but is also an active material with lithium storage capacity, which helps compensate for initial lithium loss and improves the reversible capacity, initial coulombic efficiency, and lifespan of silicon-carbon anode materials during long-term cycling. Furthermore, the lithium intercalation potential plateau of MgV₂O₆ is typically higher than that of silicon. This means that in the initial stages of charging, MgV₂O₆ will reversibly store lithium ions in larger quantities than silicon. This not only helps reduce the runaway electrolyte decomposition reaction that accompanies violent lithium intercalation on the silicon surface but also reduces the total amount of active lithium consumed in the formation of irreversible solid electrolyte interfacial films and side reactions, thus enhancing the operational stability and initial coulombic efficiency of silicon-carbon anode materials.

[0028] In other words, porous carbon constructs an electron transport network that runs through the electrode. The MgV2O6 product, which has a certain intrinsic conductivity, forms an interfacial bond with the porous carbon, further enhancing the electron transport path and transport rate. Furthermore, the MgV2O6 product acts as a rigid support point in the matrix material. The matrix material made from MgV2O6 and porous carbon provides rigid constraint on silicon expansion, reducing the risk of plastic deformation or collapse of the matrix material under stress. Based on this, the silicon-carbon active material generated in situ on the outer surface and within the internal channels of the matrix material acts as a flexible buffer layer. This helps reduce the risk of drastic volume changes in silicon during charging and discharging, and also helps reduce the structural stress of the silicon-carbon anode material, reduce electrode pulverization, and enhance the cycle stability of the silicon-carbon anode material. On the other hand, the silicon-carbon active material formed by vapor deposition acts as a flexible buffer layer, providing physical isolation to the internal matrix material. This confines the volume change of silicon within the matrix material and the flexible buffer layer, thereby reducing the risk of damaging the solid electrolyte interfacial film.

[0029] In some embodiments, the preparation method satisfies at least one of the following conditions: the magnesium source is one or more of magnesium acetate, magnesium nitrate, magnesium chloride, magnesium sulfate, magnesium isopropoxide, and magnesium acetylacetonate. It should be understood that magnesium nitrate, magnesium chloride, and magnesium sulfate have good solubility, are inexpensive, and are easy to prepare silicon-carbon anode materials with high purity. When using magnesium acetate, magnesium isopropoxide, and magnesium acetylacetonate as magnesium sources to prepare MgV2O6 via the sol-gel method, magnesium acetate, magnesium isopropoxide, and magnesium acetylacetonate can synergistically interact with the complexing agent to form a uniform MgV2O6 product, which is beneficial for obtaining silicon-carbon anode materials with high stability and high uniformity.

[0030] In some embodiments, the vanadium source is one or more of vanadium pentoxide, ammonium metavanadate, vanadate, vanadium sulfate, and vanadium acetylacetonate. By selecting a suitable vanadium source, uniform MgV₂O₆ can be obtained, which further facilitates the preparation of silicon-carbon anode materials with high performance stability and high uniformity.

[0031] In some embodiments, the porous carbon is one or more of bio-based porous carbon, petroleum coke-based porous carbon, or resin-based porous carbon. It should be understood that bio-based porous carbon has a wide range of readily available and inexpensive raw materials, and possesses interconnected channels ranging from micrometer to nanometer scales, which is beneficial for improving the permeability of reactant gases and the uniform loading of silicon during vapor deposition. Petroleum coke-based porous carbon exhibits high electrical conductivity, good structural density, and performance stability. Resin-based porous carbon allows for precise control of pore size, distribution, shape, and channel connectivity using template methods or self-assembly methods.

[0032] In some embodiments, the molar ratio of magnesium source to vanadium source is (1~10):(1~10), and the mass ratio of porous carbon to MgV2O6 product is 1:(0.02~0.1). The molar ratio of magnesium source to vanadium source can be 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, or 10:1. The mass ratio of porous carbon to MgV2O6 product can be 1:0.02, 1:0.03, 1:0.04, 1:0.05, 1:0.06, 1:0.07, 1:0.08, 1:0.09, or 1:0.1. It is understandable that when the amount of MgV2O6 product is too large, the excessive MgV2O6 particles will severely occupy and block the internal channels and surface of porous carbon. Furthermore, the conductivity of MgV2O6 is much lower than that of porous carbon, and excessive MgV2O6 will block the direct contact between carbon particles, thereby increasing the overall resistance. Conversely, when the amount of MgV2O6 product is too small, the insufficient number of rigid MgV2O6 particles cannot form a penetrating support network, causing irreversible plastic deformation, channel collapse, or breakage of the carbon network, thus reducing its stability in use.

[0033] On the one hand, excessive magnesium source content can easily lead to the formation of magnesium-containing impurities, disrupting the structural uniformity and electrochemical stability of silicon-carbon anode materials. Insufficient magnesium source content results in excess vanadium, generating vanadium oxide impurities and triggering severe chemical and electrochemical side reactions. On the other hand, excessive vanadium source content can easily lead to the formation of free vanadium pentoxide, initiating electrochemical side reactions and reducing operational stability. Insufficient vanadium source content results in excess magnesium, generating inert impurities such as magnesium oxide, reducing the overall mass specific capacity and volume specific capacity of the material.

[0034] In some embodiments, the preparation method satisfies at least one of the following conditions: the silane gas source is one or more of silane and disilane; the carbon gas source is one or more of methane, ethane, propane, acetylene, and propyne; and the inert gas is one or more of nitrogen, argon, and helium. It should be understood that the silicon-hydrogen bonds (Si-H) in silane and disilane have low bond energies and moderate thermal decomposition temperatures, allowing them to cleave under relatively mild conditions to generate highly active silicon atoms or silicon clusters, which are easily nucleated and grown on the surface of the substrate material. Alkanes and alkynes have high deposition rates, which is beneficial for forming uniformly distributed silicon-carbon active materials.

[0035] Depend on Figure 2It is known that in some embodiments, step S100 includes the following sub-steps: S110, dissolving a magnesium source, a vanadium source, and a complexing agent in water and heating and stirring for the first time to obtain a first mixture, wherein the complexing agent is one or more of citric acid, oxalic acid, tartaric acid, acetic acid, ethylene glycol, polyacryl alcohol, ethylenediaminetetraacetic acid, and glucose, the temperature of the first heating is 60℃~90℃, the heating time is 0.1h~3h, and the molar ratio of magnesium source, vanadium source, and complexing agent is (1~10):(1~10):(1~10); S120, heating the first mixture for the second time to obtain a second solid, the temperature of the second heating is 400℃~500℃, and the heating time is 0.1h~3h; S130, calcining the second solid in air to obtain the MgV2O6 product, the calcination temperature is 500℃~700℃, and the calcination time is 1h~10h. Understandably, in step S110, magnesium atoms, vanadium ions, and a complexing agent are first uniformly mixed. The complexing agent facilitates the complexation of metal ions, preventing hydrolysis and precipitation, and promoting the formation of a uniform and stable sol or gel. The first heating step further promotes the complexation reaction and sol formation. The longer duration of this first heating step allows for gradual removal of moisture, promoting the transformation of the sol into a gel, while avoiding bumping or excessively high local concentrations, thus ensuring gel uniformity. In step S120, the organic components undergo slow decomposition, forming a loose, porous intermediate, and avoiding the risk of product splashing or agglomeration due to violent gas release during subsequent high-temperature calcination. In step S130, the second solid is converted into well-crystallized, phase-pure MgV₂O₆. In other words, MgV2O6 products are prepared by the sol-gel method, in which the complexing agent promotes the formation of a uniform and stable sol system, so that the magnesium source and vanadium source can be uniformly mixed at the molecular level, and a porous and loose MgV2O6 product can be obtained to enrich the multi-scale pore system.

[0036] It is worth noting that when the amount of complexing agent increases, the metal ions are effectively complexed by the complexing agent molecules, forming a homogeneous and stable sol-like first mixture. However, when the amount of complexing agent is insufficient, some ions cannot be effectively bound, leading to segregation during evaporation and gelation. Excessive complexing agent increases the solubility of the system, prolonging the gelation time or even making gel formation difficult, thereby reducing the uniformity and stability of the prepared silicon-carbon anode material. Therefore, selecting an appropriate amount of complexing agent is beneficial for obtaining silicon-carbon anode materials with good electrical and performance characteristics.

[0037] In some embodiments, step S100 includes the following sub-steps: S110, grinding the magnesium source and vanadium source and then calcining them in air for the first time to obtain a first intermediate product. The first calcination temperature is 500℃~700℃, the first calcination time is 2h~24h, and the grinding time is 0.1h~2h; S120, grinding the first intermediate product and then calcining it in air for the second time to obtain the MgV2O6 product. The second calcination temperature is 500℃~700℃, the second calcination time is 1h~24h, and the grinding time is 0.1h~2h. It is understood that MgV2O6 products with complete crystal structures and few defects can be obtained under high temperature and long reaction time. In other words, the solid-state reaction method is advantageous for obtaining MgV2O6 with high crystallinity and high stability.

[0038] In some embodiments, step S100 includes the following sub-steps: S110, mixing magnesium source and vanadium source uniformly and pre-pressing them into sheets or blocks under normal pressure to obtain a first mixture; S120, placing the first mixture into a boron nitride tube, and then loading it into a pyrophyllite synthesis chamber to react the first mixture under high temperature and high pressure to obtain MgV2O6 product. In the pyrophyllite synthesis chamber, graphite is used as the heating tube, and pyrophyllite is used as the insulating tube. The reaction temperature is 800℃~1500℃, the reaction pressure is 0.1GPa~20GPa, and the reaction time is 0.1h~2h. It is understood that under high temperature and high pressure reaction conditions, rapid chemical reactions can occur in the first mixture, which is beneficial for the formation of well-crystallized MgV2O6 in subsequent reactions.

[0039] Furthermore, the MgV2O6 product obtained by the high temperature and high pressure method can be ball-milled before step S200, or the magnesium source and / or vanadium source can be ball-milled before step S110. This is beneficial to obtain MgV2O6 products with small particle size to increase the contact area between the MgV2O6 product and the porous carbon, thereby enhancing the mixing uniformity of the MgV2O6 product and the porous carbon, and thus obtaining a uniform matrix material.

[0040] In some embodiments, step S200 involves: ultrasonically dispersing porous carbon and MgV2O6 products in water or ethanol, followed by drying to obtain a second intermediate product; calcining the second intermediate product in an inert gas atmosphere to obtain a matrix material; the calcination temperature being 500℃~700℃; and the calcination time being 1h~4h. It is worth noting that calcining the porous carbon and MgV2O6 products allows the MgV2O6 products to be uniformly embedded, attached, or loaded onto the inner walls and outer surfaces of the porous carbon pores, forming a highly uniform, interwoven three-dimensional structure, which is beneficial for enhancing the interfacial bonding performance between the porous carbon and the MgV2O6 products.

[0041] In some embodiments, in step S300, the volumetric flow rate ratio of silane gas source to inert gas is 1:(1~10), and the volumetric flow rate ratio of carbon gas source to inert gas is 1:(1~10); the vapor deposition temperature is 500℃~1000℃, and the deposition time is 1h~12h. Specifically, the volumetric flow rate ratio of silane gas source to inert gas can be 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, or 1:10; the vapor deposition temperature can be 500℃, 600℃, 700℃, 800℃, 900℃, or 1000℃; and the deposition time can be 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, or 12h. By selecting suitable vapor deposition processing conditions and gas flow rate ratios, it is beneficial to obtain silicon-carbon anode materials with good stability.

[0042] This application also provides a low-strain silicon-carbon anode material prepared by the aforementioned method, wherein the mass ratio of silicon to carbon in the silicon-carbon anode material is 1:(0.1~9). Specifically, the mass ratio of silicon to carbon can be 1:0.1, 1:0.5, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, or 1:10. It should be understood that the silicon-carbon anode material prepared by the method provided in this application has good stability and service life, further improving the intrinsic conductivity of the silicon-carbon anode material.

[0043] Example 1

[0044] A method for preparing a low-strain silicon-carbon anode material includes the following steps:

[0045] (1) Citric acid, magnesium nitrate hexahydrate and ammonium metavanadate were dissolved in pure water in a molar ratio of 1:1:2. The resulting solution was stirred and heated at 80°C for 10 min. The mixed solution was then placed in an electric resistance furnace and heated to 450°C for 30 min. Finally, the solid product was annealed at 550°C for 2 h to obtain MgV2O6 product.

[0046] (2) The resin-based porous carbon and MgV2O6 product were placed in a ball mill and ball-milled until homogeneous to obtain the matrix material. The mass ratio of resin-based porous carbon to MgV2O6 product was 95:5, the ball milling time was 5 hours, the ball milling speed was 400 rpm, and the ball-to-material ratio was 10:1.

[0047] (3) The matrix material is placed in a rotary furnace, and silane is introduced under an argon atmosphere, wherein the silane flow rate: nitrogen flow rate = 1:1, and the deposition temperature is 500℃. After silane deposition, propyne is introduced under argon protection, wherein the propyne flow rate: argon flow rate = 1:1. After deposition, the furnace is cooled to obtain silicon-carbon anode material. The silicon-carbon anode material has a silicon mass fraction of 90 wt.% and a carbon mass fraction of 10 wt.% (based on a total silicon-carbon mass content of 100 wt.%).

[0048] (4) The silicon-carbon anode material, conductive carbon black, carbon nanotubes and binder LA132 were made into a negative electrode sheet with a mass ratio of 94:1:1:4 and the electrical performance was tested.

[0049] Example 2

[0050] The difference between Example 2 and Example 1 is that step (2) is: the resin-based porous carbon and MgV2O6 product are ultrasonically dispersed in water and then dried to obtain a second intermediate product. The second intermediate product is calcined in an inert gas to obtain a matrix material. The calcination temperature is 600℃ and the calcination time is 2h.

[0051] Example 3

[0052] The difference between Example 3 and Example 1 is that step (1) is as follows: magnesium nitrate hexahydrate and ammonium metavanadate are placed in a ball mill at a molar ratio of 1:2 and ball-milled until homogeneous, wherein the ball milling time is 3 hours, the ball milling speed is 400 rpm, and the ball-to-material ratio is 10:1; the dried material is annealed at 550°C for 2 hours to obtain the first intermediate product. The first intermediate product is then ball-milled again for 3 hours, the ball milling speed is 400 rpm, the ball-to-material ratio is 10:1, and then annealed at 550°C for 2 hours to obtain the MgV2O6 product.

[0053] Example 4

[0054] The difference between Example 4 and Example 1 is that step (1) is as follows: magnesium nitrate hexahydrate and ammonium metavanadate are placed in a ball mill at a molar ratio of 1:1:2 and ball-milled until uniform. After being pre-pressed into sheets under normal pressure, the sheets are placed in a boron nitride tube and then loaded into a pyrophyllite synthesis chamber. Graphite is used as a heating tube and pyrophyllite is used as an insulating tube in the pyrophyllite synthesis chamber. The reaction temperature is 900℃, the reaction pressure is 5GPa, and the reaction time is 1h to obtain the MgV2O6 product.

[0055] Example 5

[0056] The difference between Example 5 and Example 1 is that the mass ratio of resin-based porous carbon to MgV2O6 product in step (2) is 90:10.

[0057] Example 6

[0058] The difference between Example 6 and Example 1 is that the mass ratio of resin-based porous carbon to MgV2O6 product in step (2) is 1:0.02.

[0059] Example 7

[0060] The difference between Example 7 and Example 1 is that the molar ratio of citric acid, magnesium nitrate hexahydrate and ammonium metavanadate in step (1) is 1:5:2.

[0061] Example 8

[0062] The difference between Example 8 and Example 1 is that the molar ratio of citric acid, magnesium nitrate hexahydrate and ammonium metavanadate in step (1) is 1:0.5:2.

[0063] Example 9

[0064] The difference between Example 9 and Example 1 is that the molar ratio of citric acid, magnesium nitrate hexahydrate and ammonium metavanadate in step (1) is 1:1:8.

[0065] Example 10

[0066] The difference between Example 10 and Example 1 is that the molar ratio of citric acid, magnesium nitrate hexahydrate and ammonium metavanadate in step (1) is 1:1:0.5.

[0067] Example 11

[0068] The difference between Example 11 and Example 1 is that magnesium nitrate hexahydrate in step (1) is replaced with magnesium acetate.

[0069] Example 12

[0070] The difference between Example 12 and Example 1 is that magnesium nitrate hexahydrate in step (1) is replaced with magnesium sulfate.

[0071] Example 13

[0072] The difference between Example 13 and Example 1 is that ammonium metavanadate in step (1) is replaced with vanadium pentoxide.

[0073] Example 14

[0074] The difference between Example 14 and Example 1 is that ammonium metavanadate in step (1) is replaced with vanadium acetylacetonate.

[0075] Example 15

[0076] The difference between Example 15 and Example 1 is that the molar ratio of citric acid, magnesium nitrate hexahydrate and ammonium metavanadate in step (1) is 3:1:2.

[0077] Example 16

[0078] The difference between Example 16 and Example 1 is that the molar ratio of citric acid, magnesium nitrate hexahydrate and ammonium metavanadate in step (1) is 10:1:2.

[0079] Example 17

[0080] The difference between Example 17 and Example 1 is that the molar ratio of citric acid, magnesium nitrate hexahydrate and ammonium metavanadate in step (1) is 0.5:1:2.

[0081] Example 18

[0082] The difference between Example 18 and Example 1 is that the resin-based porous carbon in step (1) is replaced with coconut shell-based porous carbon.

[0083] Example 19

[0084] The difference between Example 19 and Example 1 is that the resin-based porous carbon in step (1) is replaced with needle-shaped coke-based porous carbon.

[0085] Comparative Example 1

[0086] The difference between Comparative Example 1 and Example 1 is that step (1) was not performed and MgV2O6 product was not added in step (2).

[0087] Comparative Example 2

[0088] The difference between Comparative Example 2 and Example 1 is that step (1) was not performed, and the MgV2O6 product in step (2) was replaced with lithium titanate.

[0089] Comparative Example 3

[0090] The difference between Comparative Example 3 and Example 1 is that step (1) was not performed, and the MgV2O6 product in step (2) was replaced with magnesium oxide.

[0091] Comparative Example 4

[0092] The difference between Comparative Example 4 and Example 1 is that step (1) was not performed, and the MgV2O6 product in step (2) was replaced with vanadium pentoxide.

[0093] Comparative Example 5

[0094] The difference between Comparative Example 5 and Example 1 is that step (1) was not performed, and the MgV2O6 product in step (2) was replaced with titanium nitride.

[0095] Performance testing

[0096] The silicon-carbon anode plates prepared in Examples 1-19 and Comparative Examples 1-5 were tested using the test methods provided in GB / T 24533-2019, and the performance results are shown in Table 1.

[0097] Table 1: Performance Testing of Silicon-Carbon Anode Sheets

[0098]

[0099] As shown in Examples 1-4, 11-14, and 18-19, silicon-carbon anode materials with good performance stability and electrical properties can be prepared by selecting suitable magnesium sources, vanadium sources, porous carbon, or MgV2O6 products prepared by different methods. As shown in Examples 1 and 5-6, when the amount of MgV2O6 product is too large, the excessive MgV2O6 particles will severely occupy and block the internal pores and surface of the porous carbon. Furthermore, the conductivity of MgV2O6 is much lower than that of porous carbon, and excessive MgV2O6 will block the direct contact between carbon particles, thereby increasing the overall resistance. When the amount of MgV2O6 product is too small, the insufficient number of rigid MgV2O6 particles cannot form a penetrating support network, causing irreversible plastic deformation, pore collapse, or breakage of the carbon network, thus reducing performance stability. As shown in Examples 1 and 7-8, when the amount of magnesium source is too large, magnesium-containing impurities are easily generated, which damages the structural uniformity and electrochemical stability of the silicon-carbon anode material. When the amount of magnesium source is too small, vanadium is excessive, resulting in the generation of vanadium oxide impurities, which triggers serious chemical and electrochemical side reactions. As shown in Examples 1 and 9-10, when the amount of vanadium source is too large, free vanadium pentoxide is easily generated, triggering electrochemical side reactions and reducing the stability in use. When the amount of vanadium source is too small, magnesium is excessive, resulting in the generation of inert impurities such as magnesium oxide, which reduces the overall mass specific capacity and volume specific capacity of the material. As shown in Examples 1 and 15-17, when the amount of citric acid increases, the metal ions are effectively complexed by the citric acid molecules to form a uniform and stable first mixture with a sol. However, when the amount of citric acid is small, some ions cannot be effectively bound, and segregation easily occurs during evaporation and gelation. When citric acid is in excess, it increases the solubility of the system, prolonging the gelation time and even making gel formation difficult, thereby reducing the uniformity and stability of the prepared silicon-carbon anode material. Comparative Examples 1 and 1-5 show that selecting appropriate reaction conditions is beneficial for obtaining silicon-carbon anode materials with good electrical performance and operational stability. When MgV₂O₆ is replaced with lithium titanate, lithium titanate can achieve near-zero strain, but the resulting side reactions reduce the overall capacity. Magnesium oxide and titanium nitride have no lithium storage capacity and low capacity. Vanadium pentoxide is easily soluble in the electrolyte, its structure is rapidly destroyed, and its capacity decays extremely quickly.

[0100] The basic principles, main features, and advantages of this application have been described above. Those skilled in the art should understand that this application is not limited to the above embodiments. The embodiments and descriptions in the specification are merely the principles of this application. Various changes and modifications can be made to this application without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claims. The scope of protection claimed by this application is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a low-strain silicon-carbon anode material, characterized in that, Including the following steps: S100, synthesize MgV2O6 product from magnesium source and vanadium source; S200: Mix porous carbon with the MgV2O6 product to obtain a matrix material, wherein the mass ratio of the porous carbon to the MgV2O6 product is 1:(0.02~0.1). S300, using a silane gas source and a carbon gas source in an inert gas environment, vapor-phase deposition is performed on the outer surface and pores of the substrate material to obtain a silicon-carbon anode material; and Step S200 is as follows: porous carbon and the MgV2O6 product are ultrasonically dispersed in water or ethanol and then dried to obtain a second intermediate product. The second intermediate product is calcined in an inert gas to obtain a matrix material. The calcination temperature is 500℃~700℃ and the calcination time is 1h~4h.

2. The preparation method according to claim 1, characterized in that, At least one of the following conditions must be met: The magnesium source is one or more of magnesium acetate, magnesium nitrate, magnesium chloride, magnesium sulfate, magnesium isopropoxide, and magnesium acetylacetonate. The vanadium source is one or more of vanadium pentoxide, ammonium metavanadate, vanadium acid, vanadium oxysulfate, and vanadium oxyacetylacetonate. The porous carbon is one or more of bio-based porous carbon, petroleum coke-based porous carbon, or resin-based porous carbon.

3. The preparation method according to claim 1, characterized in that, The molar ratio of the magnesium source to the vanadium source is (1~10):(1~10).

4. The preparation method according to any one of claims 1 to 3, characterized in that, At least one of the following conditions must be met: The silane gas source is one or more of methane and ethyl silane; The carbon source is one or more of methane, ethane, propane, acetylene, and propyne. The inert gas is one or more of argon and helium.

5. The preparation method according to claim 1, characterized in that, Step S100 includes the following sub-steps: S110. A first mixture is prepared by dissolving a magnesium source, a vanadium source, and a complexing agent in water and heating and stirring for the first time. The complexing agent is one or more of citric acid, oxalic acid, tartaric acid, acetic acid, ethylene glycol, polyacryl alcohol, ethylenediaminetetraacetic acid, and glucose. The temperature of the first heating is 60℃~90℃, and the heating time is 0.1h~3h. The molar ratio of the magnesium source, the vanadium source, and the complexing agent is (1~10):(1~10):(1~10). S120. The first mixture is heated a second time to obtain a second solid, wherein the temperature of the second heating is 400℃~500℃ and the time of the second heating is 0.1h~3h; S130. The second solid is calcined in air to obtain MgV2O6 product. The calcination temperature is 500℃~700℃ and the calcination time is 1h~10h.

6. The preparation method according to claim 1, characterized in that, Step S100 includes the following sub-steps: S110. After grinding the magnesium source and vanadium source, the first intermediate product is obtained by first calcination in air. The first calcination temperature is 500℃~700℃, the first calcination time is 2h~24h, and the grinding time is 0.1h~2h. S120. After grinding the first intermediate product, it is calcined for the second time in air to obtain the MgV2O6 product. The second calcination temperature is 500℃~700℃, the second calcination time is 1h~24h, and the grinding time is 0.1h~2h.

7. The preparation method according to claim 1, characterized in that, Step S100 includes the following sub-steps: S110. Mix the magnesium source and vanadium source evenly and pre-press them into sheets or blocks under normal pressure to obtain the first mixture; S120. The first mixture is placed in a boron nitride tube and then loaded into a pyrophyllite synthesis chamber to react the first mixture under high temperature and high pressure to obtain MgV2O6 product. In the pyrophyllite synthesis chamber, graphite is used as a heating tube and pyrophyllite is used as an insulating tube. The reaction temperature is 800℃~1500℃, the reaction pressure is 0.1GPa~20GPa, and the reaction time is 0.1h~2h.

8. The preparation method according to claim 4, characterized in that, In step S300, the volume flow rate ratio of the silane gas source to the inert gas is 1:(1~10), and the volume flow rate ratio of the carbon gas source to the inert gas is 1:(1~10); the vapor deposition temperature is 500℃~1000℃, and the deposition time is 1h~12h.

9. A low-strain silicon-carbon anode material, characterized in that, The silicon-carbon anode material is prepared by the preparation method according to any one of claims 1 to 8, wherein the mass ratio of silicon to carbon in the silicon-carbon anode material is 1:(0.1 to 9).

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