Negative electrode material, electrochemical device, and method for producing negative electrode material

Abstract

This invention provides an anode material, an electrochemical device, and a method for preparing the anode material, belonging to the field of secondary battery technology. The anode material includes a substrate, a first coating layer, and a second coating layer. The substrate comprises tin; the first coating layer is attached to the surface of the substrate and comprises a carbon material; the second coating layer is at least partially attached to the surface of the first coating layer and comprises MXene material. This invention utilizes the synergistic effect of the double-layer coating structure to confine and suppress the volume expansion of substrate particles during the alloying / dealloying process during charging and discharging, improving the structural stability of the anode sheet. Furthermore, it forms a three-dimensional conductive network within the anode material, effectively enhancing its conductivity in the electrolyte and reducing its charge transport impedance. Consequently, the anode material possesses both considerable lithium storage capacity and stable, excellent electrochemical performance.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, specifically to a negative electrode material, an electrochemical device, and a method for preparing the negative electrode material. Background Technology

[0002] With the widespread use of electronic products and the popularization of electric vehicles, people have placed higher demands on batteries, and energy density is a key indicator for determining battery range. In the field of next-generation battery technology, lithium-ion batteries are now widely used in electronic products such as mobile phones and computers due to their advantages such as long cycle life, high power density, high energy density, and high voltage platform.

[0003] The negative electrode is a crucial component of battery materials, and its capacity directly affects the battery's energy density. Graphite, currently the most widely used negative electrode material, has already reached a practical capacity close to its theoretical value (372 mAh / g), which is insufficient to meet the requirements of high-energy-density batteries.

[0004] Compared to traditional graphite materials, metallic tin (Sn) possesses advantages such as a higher theoretical lithium storage capacity (994 mAh / g) and a lower lithium-ion insertion / extraction plateau voltage, making it a highly promising non-carbon anode material. Tin anode materials are considered one of the ideal alternatives to commercially available graphite-based carbon materials to meet the demands of next-generation high-capacity lithium-ion batteries.

[0005] However, tin materials, similar to other alloy types of anode materials, cause the anode sheet to undergo a volume change of more than 300% during the charging and discharging process. The internal stress generated by the volume expansion will cause the anode material to pulverize and peel off, resulting in a decrease in battery capacity and a rapid decline in cycle performance.

[0006] Therefore, it is necessary to design a negative electrode material, an electrochemical device, and a method for preparing the negative electrode material to solve the above problems. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the present invention provides a negative electrode material, an electrochemical device, and a method for preparing the negative electrode material, in order to improve the technical problem that tin-based negative electrode materials are prone to volume expansion during charging and discharging, resulting in a decrease in battery capacity and degradation of cycle performance.

[0008] To achieve the above and other related objectives, the present invention provides a negative electrode material comprising a matrix, a first coating layer, and a second coating layer.

[0009] The substrate comprises tin; a first coating layer is attached to the surface of the substrate, the first coating layer comprising a carbon material; and a second coating layer is at least partially attached to the surface of the first coating layer, the second coating layer comprising an MXene material.

[0010] In one example of the present invention, the surface potential of the negative electrode material particles is greater than or equal to -5mV.

[0011] In one example of the present invention, the surface of the first coating layer and / or the surface of the substrate and the first coating layer are modified with a silane coupling agent.

[0012] In one example of the present invention, the negative electrode material includes secondary particles with a particle size of 200-400 nm.

[0013] In one example of the present invention, the particle size of the substrate is 50-200 nm; the mass of the first coating layer is 10%-50% of the mass of the substrate; and the mass of the second coating layer is 5%-50% of the mass of the substrate.

[0014] The present invention also provides a method for preparing the negative electrode material according to any of the above examples, the method comprising:

[0015] A substrate is provided, the substrate comprising tin;

[0016] A first coating layer is attached to the surface of the substrate to obtain a composite material; the first coating layer comprises a carbon material.

[0017] A second coating layer is attached to the surface of the composite material to obtain a negative electrode material; the second coating layer includes MXene material.

[0018] In one example of the present invention, the step of attaching and forming a second coating layer on the surface of the composite material includes:

[0019] The composite material is then surface-modified;

[0020] After surface modification of the composite material, a second coating layer is attached to the surface of the composite material to obtain a negative electrode material.

[0021] In one example of the present invention, the preparation method further includes a step of surface modification of the substrate before the first coating layer is attached to the substrate surface, comprising: dispersing the substrate in a solvent to obtain a first mixture; dispersing a silane coupling agent in the first mixture such that the silane coupling agent adheres to the particle surface of the substrate to obtain the surface-modified substrate; wherein the mass of the silane coupling agent mixed in the first mixture is 5%-10% of the mass of the substrate.

[0022] In one example of the present invention, the step of surface modification of the composite material includes: dispersing the composite material in a solvent to obtain a second mixture; dispersing a silane coupling agent in the second mixture such that the silane coupling agent adheres to the particle surface of the composite material to obtain the surface-modified composite material; wherein the mass of the silane coupling agent mixed in the second mixture is 5%-10% of the mass of the matrix.

[0023] In one example of the present invention, the step of attaching and forming a first coating layer on the surface of the substrate after surface modification includes:

[0024] A carbon source is dispersed into the first mixture, allowing the carbon source to interact with the silane coupling agent and adsorb onto the particle surface of the matrix. Under a protective atmosphere, the first mixture is dried and sintered, causing the carbon source adhering to the matrix surface to carbonize, thereby forming the first coating layer on the matrix surface.

[0025] In one example of the present invention, the step of attaching and forming a second coating layer on the surface of the composite material after surface modification includes:

[0026] MXene material is dispersed in the second mixture, so that MXene interacts with the silane coupling agent and adsorbs onto the surface of the composite material to form the second coating layer on the surface of the composite material; wherein, the MXene material is dispersed in the second mixture in the form of an MXene dispersion, and the concentration of the MXene material in the MXene dispersion is 2-15 mg / mL.

[0027] The present invention also provides an electrochemical device, the electrochemical device comprising a negative and a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the negative electrode comprises a negative current collector and a negative active material layer, and the negative active material layer comprises the negative electrode material described in any of the above examples, or the negative electrode material prepared by the preparation method described in any of the above examples.

[0028] This invention provides a negative electrode material in which a first coating layer (carbon coating layer) and a second coating layer (MXene coating layer) are sequentially formed on the outside of tin matrix particles. This negative electrode material utilizes the synergistic effect of the double-layer coating structure to restrain and suppress the volume expansion of the matrix particles during the alloying / dealloying process during charging and discharging, thereby improving the structural stability of the negative electrode sheet. Furthermore, it forms a three-dimensional conductive network within the negative electrode material, effectively enhancing its conductivity in the electrolyte and reducing its charge transport impedance. Consequently, the negative electrode material possesses both considerable lithium storage capacity and stable, excellent electrochemical performance. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other embodiments can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a scanning electron microscope (SEM) image of the negative electrode material in one embodiment of the present invention;

[0031] Figure 2 This is the XPS spectrum of nitrogen element in the negative electrode material in one embodiment of the present invention;

[0032] Figure 3 This is a schematic flowchart of a method for preparing a negative electrode material in one embodiment of the present invention;

[0033] Figure 4 This is a flowchart illustrating step S1 in one embodiment of the present invention;

[0034] Figure 5 This is a flowchart illustrating step S2 in one embodiment of the present invention; Figure 6 This is a flowchart illustrating step S3 in one embodiment of the present invention. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0037] In this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. Furthermore, the terms "first" and "second" are used only for descriptive and distinguishing purposes and should not be construed as indicating or implying relative importance.

[0038] The negative electrode material is one of the key materials determining the performance of a rechargeable battery, directly affecting its energy density, cycle life, rate performance, and safety performance. Tin (Sn) material has excellent application prospects as a negative electrode material for rechargeable batteries due to its high theoretical specific capacity (994 mAh / g), suitable operating voltage (0.4V~1.2V), and good conductivity. However, as an alloy-type negative electrode material, tin material undergoes significant volume expansion during alloying / dealloying with lithium ions. Severe volume expansion can lead to pulverization and detachment of the negative electrode material, compromising the structural stability of the negative electrode and reducing the actual capacity of the battery in application.

[0039] To address the inherent technical shortcomings of tin as an anode material, this application provides an anode material with a tin substrate. A carbon coating layer is in-situ coated onto the substrate surface, and MXene nanosheets are coupled and adsorbed onto the carbon coating layer to form an MXene coating layer, resulting in a double-layer coated tin anode material. This anode material utilizes the synergistic effect of the carbon and MXene coating layers to better adapt to and suppress the volume expansion and contraction of the substrate during charging and discharging, thereby reducing the probability of pulverization and detachment of the anode material on the anode sheet. Simultaneously, based on the layer-by-layer enhanced mechanical ductility of the double coating layer on the outer side of the substrate, a structurally stable three-dimensional conductive network is constructed between the anode material particles, reducing the charge transport impedance in the anode material and effectively improving the conductivity and electrochemical stability of the tin anode material.

[0040] The aforementioned negative electrode material includes a substrate, a first coating layer, and a second coating layer. The substrate includes tin. The first coating layer is attached to the surface of the substrate particles and includes a carbon material, which is in-situ coated on the surface of the substrate particles. The second coating layer coats the outer layer of the negative electrode material particles. The second coating layer is attached to at least the surface of the first coating layer and includes MXene material. The MXene material is coupled and attached in a two-dimensional form to the surface of the first coating layer and even to the surface of the substrate particles not covered by the first coating layer. Figure 1The image shows the bonding pattern between the matrix particles and the MXene material; the randomly arranged MXene nanosheets are uniformly coated on the tin-carbon composite particles. Figure 1 The outer layer of the white particles in the middle forms a three-dimensional conductive network with MXene nanosheets as the conductive substrate between the negative electrode material particles. Figure 1 (Medium-transparent fibers). This three-dimensional conductive network structure can enhance the electronic / ionic conductivity of the anode material, regulate the current distribution, and reduce the local current density, thereby improving the electrochemical performance of the anode material.

[0041] In the anode material, a first coating layer is sintered onto the surface of the matrix particles. By modifying the surface of this first coating layer, MXene nanosheets are adsorbed and coupled to it through intermolecular forces (such as electrostatic forces and hydrogen bonds) to form a second coating layer. This anode material utilizes surface modification to enhance the bonding strength between different material interfaces, thereby forming a uniform, layered, and structurally stable double-coating structure on the surface of the matrix particles. The double-coating structure formed outside the matrix particles through at least one surface modification exhibits strong structural stability and mechanical ductility, better adapting to and suppressing the volume expansion and contraction of the matrix during charging and discharging. It can reduce the probability of matrix pulverization while maintaining the integrity of the conductive network formed by the double coating layers, thus effectively extending the lifespan of the anode material and further improving the battery's capacity and cycle performance.

[0042] Optionally, the aforementioned negative electrode material undergoes a first modification on the surface of the substrate particles, resulting in the formation of reactive groups on the surface of the substrate particles. The carbon material interacts with these groups and adsorbs onto the surface of the substrate particles, forming a first coating layer. In the first coating layer, the carbon material is adsorbed and connected to the groups on the surface of the substrate particles. For example, the carbon material can be attached to the surface of the substrate particles at least through covalent bonds. The covalent bond connection between the carbon material and the uniformly modified groups on the surface of the substrate particles enables in-situ coating of the substrate particles by the first coating layer, improving the uniformity of the coating. Simultaneously, this covalent bond structure greatly enhances the bonding strength between the first coating layer and the substrate surface, thereby effectively suppressing the volume expansion of the substrate and improving the structural and electrochemical stability of the negative electrode sheet.

[0043] The negative electrode material undergoes a second modification on the surface of the first coating layer, resulting in the formation of reactive groups on its surface. The end-face groups of the MXene material interact with these reactive groups and adsorb onto the first coating layer surface, forming a second coating layer. In the second coating layer, the surface groups of the MXene material interact with the reactive groups of the first coating layer surface to form hydrogen bonds and electrostatic adsorption. The MXene material utilizes adsorption to form a structurally stable interfacial connection structure on the first coating layer surface. This results in a well-defined and structurally stable double-coating structure on the outside of the substrate. The strong bonding strength between the second and first coating layers ensures the sustainability of the performance improvement effect of the double-coating structure on the negative electrode material, effectively enhancing the cycle performance of the battery in practical applications.

[0044] In this invention, through two surface modification processes, a layered and structurally stable double-coating structure is formed on the outer side of the substrate. On the one hand, the double-coated structure has the structural characteristic of increasing mechanical extensibility layer by layer. Utilizing the strong elasticity provided by the outer MXene material, it can better adapt to and suppress the volume expansion and contraction of the substrate during charging and discharging, and buffer between the negative electrode material particles, thereby reducing the probability of pulverization of the negative electrode material. On the other hand, based on the interfacial bonding structure between the layers in the negative electrode material, the double-coated structure can avoid interlayer separation when suppressing and adapting to changes in substrate volume. It can effectively maintain the structural stability of the double-coated negative electrode material during charging and discharging, avoiding material structure collapse and side reactions caused by pulverization of negative electrode material particles. Furthermore, the double-coated structure also has the physical property of increasing electronic / ionic conductivity layer by layer, which can form a three-dimensional conductive network between negative electrode material particles, improve the electron and ion migration efficiency on the surface of negative electrode material particles, enhance the conductivity of the negative electrode material, and avoid lithium plating due to insufficient ion migration rate on the surface of the negative electrode material, thereby improving the cycle and rate performance of the assembled secondary battery.

[0045] In this invention, the MXene material is M n+1 X n T y n = 1-3; M is a transition metal element, such as Ti, Zr, V, Mo, etc.; X is C or N; T yThe terminal groups are typically -OH, -O, -F, and -Cl. The MXene material is prepared using methods well-known to those skilled in the art, obtained from MAX phase powder material through acid etching and washing. The MXene material obtained after acid washing exhibits an overall negative charge due to the presence of negative ion groups on its terminal faces. The MAX phase material includes at least one of Ti3AlC2, Ti2AlC, Ti3AlCN, V2AlC, V4AlC, Nb2AlC, Nb3AlC2, TiNbAlC, Zr3AlC2, and Mo3AlC2. The MXene material corresponds to at least one of Ti3C2, Ti2C, Ti3CN, V2C, V4C, Nb2C, Nb3C2, TiNbC, Zr3C2, and Mo3C2. Optionally, the MXene material can be selected from at least one of Ti3C2, Ti2C, and V2C; for example, the MXene material can be V2C or a combination of Ti3C2 and Ti2C.

[0046] In the negative electrode material, the reactive groups on the surface of the first coating layer interact with the anionic groups on the end face of the MXene material to neutralize some of the anionic groups in the MXene material, thereby making the surface potential of the negative electrode material higher than that of the MXene raw material. Specifically, the surface potential of the MXene material is usually less than -10mV, while the surface potential of the negative electrode material is greater than or equal to -5mV. When the surface potential of the negative electrode material is greater than or equal to -5mV, it indicates that the surface of the negative electrode material is coated with an appropriate amount of MXene material, and the adsorption effect of MXene material on the surface of the negative electrode material is good, and the interfacial bonding strength between the second coating layer and the first coating layer is high. If the surface potential of the negative electrode material is less than -5mV, it may indicate that the surface modification effect of the first coating layer is poor. A large number of negative ion groups of MXene material fail to combine with the reactive groups on the surface of the first coating layer and remain on the surface of the negative electrode material, resulting in a low bonding strength between the second coating layer and the first coating layer, which manifests as a low surface potential of the negative electrode material. Alternatively, it may indicate that there is too much MXene material coated on the surface of the negative electrode material. A large number of negative ion groups of MXene material fail to combine with the reactive groups on the surface of the first coating layer and remain on the surface of the negative electrode material. Excessive MXene material causes the second coating layer to be too thick, which may reduce the capacity of the negative electrode material.

[0047] It should be noted that, based on the above structural characteristics, the connection structure between the second coating layer and the first coating layer can be characterized by testing the surface potential of the negative electrode material. When the surface potential of the negative electrode material is higher than that of the MXene material used, it can be proven that the negative ion groups on the end face of the MXene material interact with the reactive groups on the surface of the first coating layer, and the negative ion groups on the end face of the MXene material are neutralized to form the interface connection structure between the first coating layer and the second coating layer.

[0048] In anode materials, by controlling the number of reactive groups on the surface of the first coating layer in the anode material particles, the number of bonds formed by the end-face groups of the MXene material on the surface of the first coating layer can be adjusted, thereby adjusting the interfacial bonding strength between the second coating layer and the first coating layer. This structural adjustment results in a change in the surface potential of the anode material. Only by adjusting the surface potential of the anode material to a suitable range can the stability of the coating layer structure be ensured while also considering the interfacial ion migration efficiency.

[0049] If the surface potential of the negative electrode material is too low (e.g., below -5mV), it indicates that the amount of surface modifier used in the first coating layer is too small or that there is too much MXene material coated in the second coating layer. Specifically, when there is too little surface modifier in the first coating layer, there are fewer negative ion groups in the MXene material that bond and neutralize with the first coating layer, resulting in a low interfacial bonding strength between the second and first coating layers and an unstable double-coating structure on the substrate surface. Conversely, when there is too much MXene material in the second coating layer, it will result in an excessively thick second coating layer, reducing the mass content of the substrate in the negative electrode material and potentially decreasing its capacity.

[0050] If the surface potential of the negative electrode material is too high (e.g., above 5mV), it indicates that the amount of surface modifier on the surface of the first coating layer is too large or the amount of MXene material coated in the second coating layer is too small. While excessive surface modifier on the first coating layer can enhance the interfacial bonding strength between the second and first coating layers, too much modifier can also easily form an isolation layer on the outside of the substrate, hindering ion migration within the negative electrode material. Conversely, insufficient MXene material in the second coating layer results in poor coating performance of the negative electrode material.

[0051] Therefore, in some embodiments, the surface potential of the negative electrode material is -5mV to 5mV. Within this surface potential range, the interfacial bonding strength between the second coating layer and the first coating layer in the negative electrode material is good, and it does not have a negative impact on ion migration within the negative electrode material.

[0052] Furthermore, in some embodiments, the surfaces of the matrix particles, the first coating layer, or both are modified with a silane coupling agent. The silane coupling agent hydrolyzes the hydroxyl groups on the matrix and first coating layer surfaces, replacing the hydroxyl groups with reactive groups; for example, amino groups may be attached to the surfaces of the matrix and first coating layer modified with the silane coupling agent. It should be noted that the negative electrode material modified with the silane coupling agent can be characterized using X-ray photoelectron spectroscopy (XPS). Figure 2 As shown, Figure 2 This is the XPS spectrum of nitrogen in the negative electrode material. Figure 2The presence of characteristic peaks corresponding to graphitic N (graphitic nitrogen) and -NH2 groups indicates that the first coating layer carbon material contains N element groups, while the characteristic peak corresponding to the -NH2 group proves that the surface of the negative electrode material has been modified by a silane coupling agent.

[0053] In some embodiments, the mass of the silane coupling agent used to modify the substrate surface accounts for 5% to 10% of the mass of the substrate raw material. When the mass content of the silane coupling agent used to modify the substrate surface is within the above range, the modification effect on the substrate surface is guaranteed, the bonding strength of the first coating layer on the substrate surface is enhanced, and the formation of an isolation layer by the silane coupling agent on the substrate surface is avoided, which would hinder the migration and transport of ions between the coating layer and the substrate, negatively affect the ionic conductivity of the negative electrode material, and cause the battery capacity to be unable to be realized.

[0054] In some embodiments, the mass of the silane coupling agent used to modify the surface of the first coating layer accounts for 5% to 10% of the mass of the matrix raw material. When the mass content of the silane coupling agent used to modify the surface of the first coating layer is within the above range, the surface modification effect of the first coating layer is guaranteed, the bonding strength of the second coating layer on the surface of the first coating layer is enhanced, and the formation of an isolation layer by the silane coupling agent on the surface of the composite material particles is avoided, which would hinder the migration and transport of ions between the coating layer and the matrix, negatively affect the ionic conductivity of the negative electrode material, and cause the battery capacity to be unable to be realized.

[0055] In some embodiments, the carbon material may be selected from at least one of amorphous carbon, graphite and carbon nanotubes, and optionally, the carbon material may be amorphous carbon.

[0056] In some embodiments, the particle size of the matrix particles is 50–200 nm; within this particle size range, the coating effect of the negative electrode material can be optimized. If the particle size of the matrix particles is too small, they are prone to agglomeration during the coating process, resulting in uneven coating on the outer side of the matrix; if the particle size of the matrix particles is too large, the coating effect may be poor due to the excessively large surface area of ​​the particles to be coated.

[0057] In some embodiments, the mass of the first coating layer is 10% to 50% of the matrix mass, for example, the mass content of the first coating layer relative to the matrix can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%. Further, the mass of the first coating layer can be 10% to 30% of the matrix mass, for example, the mass content of the first coating layer relative to the matrix can be 10%, 12%, 15%, 17%, 20%, 23%, 25%, 27%, or 30%. Within the above range, the mass content of the first coating layer relative to the matrix can optimize both the coating effect and energy density of the negative electrode material. If the mass content of the first coating layer is too low, the coating effect on the matrix will be poor; if the mass content of the first thin layer is too high, over-coating will negatively impact the energy density of the negative electrode material. It should be noted that the mass content of the first coating layer in the negative electrode material can be obtained by measuring the mass loss of the negative electrode material using thermogravimetric analysis.

[0058] In some embodiments, the mass of the second coating layer is 5% to 50% of the mass of the substrate. For example, the mass content of the second coating layer relative to the substrate can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%. When the mass content of the second coating layer relative to the substrate is within the above range, it can optimize both the coating effect and energy density of the anode material. If the mass content of the second coating layer is too low, the coating effect on the substrate will be poor; if the mass content of the second thin layer is too high, over-coating will negatively impact the energy density of the anode material.

[0059] In some embodiments, a first coating layer is applied in situ to the surface of the matrix particles, and the first coating layer fully covers the matrix particles (full coverage means that the area of ​​the matrix particle surface covered by the first coating layer is greater than 90%). A second coating layer is attached at least to the first coating layer to achieve partial coating on the outermost layer of the matrix particles. In addition to being attached to the surface of the first coating layer, the second coating layer can also be attached to the surface of the matrix particles not covered by the first coating layer.

[0060] In some embodiments, the negative electrode material includes, in addition to discrete primary particles, secondary particles formed by the aggregation of primary particles. The primary particles are matrix particles and a first coating layer and a second coating layer covering the matrix particles. The particle size of the secondary particles is 200–400 nm. In the secondary particles, the second coating layer is at least partially embedded between the primary particles to form a three-dimensional conductive network within the secondary particles. Furthermore, the second coating layer also covers the outside of the secondary particles to form conductive networks between the secondary particles and between the secondary particles and the discrete primary particles.

[0061] In another aspect, the present invention also provides a method for preparing a negative electrode material. For example... Figure 3 As shown, the preparation method of this negative electrode material includes the following steps:

[0062] S1. Provide a substrate, the substrate comprising tin;

[0063] S2. A first coating layer is attached to the surface of the matrix to obtain a composite material; the composite material is a tin-carbon composite material, which includes matrix particles and a first coating layer covering the outside of the matrix particles, the first coating layer including carbon material.

[0064] S3. A second coating layer is attached to the surface of the composite material to obtain a negative electrode material; the second coating layer includes MXene material. The MXene material is attached at least to the surface of the first coating layer; it should be noted that if the first coating layer fails to completely cover the surface of the matrix particles, the MXene material is attached to the exposed surface of the matrix particles.

[0065] like Figure 6 As shown, in some embodiments, step S3 includes the following steps:

[0066] S31. Surface modification of the composite material to give the surface of the composite material reactive groups; it should be noted that if the first coating layer fails to completely cover the surface of the matrix particles, the reactive groups will not only adhere to the surface of the first coating layer, but also to the surface of the matrix particles not covered by the first coating layer.

[0067] S32. After surface modification of the composite material, a second coating layer is attached to the surface of the composite material to obtain the negative electrode material. MXene material is coupled and adsorbed on the surface of the first coating layer by interacting with the reactive groups modified on the surface of the first coating layer to form the second coating layer. It should be noted that if the first coating layer fails to completely cover the surface of the matrix particles, the MXene material can interact with the reactive groups on the exposed surface of the matrix particles, thereby adhering to the exposed surface of the matrix particles.

[0068] This preparation method, through two coating processes, can form a distinct double-coating structure with a first coating layer and a second coating layer on the outside of the matrix. At the same time, reactive groups are attached to the surface of the first coating layer of the composite material, so that when the second coating layer coats the first coating layer, it can form a strong adsorption structure at the interface through chemical bonding with the groups, thereby enhancing the interfacial bonding strength between different material layers in the negative electrode material and forming a structurally stable double-coating structure on the outside of the matrix particles.

[0069] like Figure 4 As shown, in some embodiments, step S1 of the preparation method further includes a step of surface modification of the provided substrate, which specifically includes the following steps:

[0070] S11. Disperse the matrix particles in a solvent to obtain a first mixture; specifically, add the matrix raw material to the solvent and disperse it to ensure that the matrix particles are fully dispersed in the solvent, thereby obtaining the first mixture.

[0071] S12. The silane coupling agent is dispersed in the first mixture, allowing it to adhere to the surface of the matrix particles to obtain a surface-modified matrix. Specifically, the silane coupling agent is added to the first mixture and dispersed, allowing it to fully mix with the matrix particles in the solvent. The hydrolytic groups of the silane coupling agent react with the hydroxyl groups on the matrix surface, resulting in the replacement of the hydroxyl groups on the matrix surface with reactive groups (such as amino groups).

[0072] In some embodiments, in step S11, the particle size of the matrix material used is 50–200 nm. Using a particle size within this range allows for optimal coating of the negative electrode material. If the particle size of the matrix material is too small, it is prone to agglomeration during the coating process, resulting in uneven coating on the outer side of the matrix. If the particle size of the matrix material is too large, the coating effect may be poor due to the excessively large surface area of ​​the particles to be coated.

[0073] In some embodiments, in step S12, the mass of the silane coupling agent added to the first mixture accounts for 5% to 10% of the mass of the matrix raw material. When the mass content of the silane coupling agent used to modify the matrix surface is within the above range, the modification effect on the matrix surface is guaranteed, the bonding strength of the first coating layer on the matrix surface is enhanced, and the formation of an isolation layer by the silane coupling agent on the matrix surface is avoided, which would hinder the migration and transport of ions between the coating layer and the matrix, negatively affecting the ionic conductivity of the negative electrode material and causing the battery capacity to be unrealized.

[0074] like Figure 5 As shown, in some embodiments, step S2 specifically includes the following steps:

[0075] S21. Disperse the carbon source into the first mixture, so that the carbon source interacts with the silane coupling agent and is adsorbed on the particle surface of the matrix.

[0076] S22. Under a protective atmosphere, the first mixture is dried and sintered to carbonize the carbon source attached to the substrate surface to form amorphous carbon, thereby forming a first coating layer on the substrate surface.

[0077] In the above embodiments, the preparation method utilizes a surface modification process before the two coatings to attach reactive groups to the surface of the substrate and the tin-carbon composite material coating the first coating layer, respectively. This allows the coating material and the reactive groups to interact with each other at the interface when the first coating layer coats the substrate and when the second coating layer coats the first coating layer, thereby forming a strong adsorption structure at the interface. This enhances the interfacial bonding strength between different material layers in the negative electrode material and forms a layered and structurally stable double coating layer structure on the outside of the substrate particles.

[0078] In some embodiments, the carbon source used in step S21 may be selected from at least one of sucrose, glucose, maltose, lactose, starch, formaldehyde, acetaldehyde, propionaldehyde, phenolic resin, epoxy resin, polyethylene glycol, cellulose, lignin, polyvinyl alcohol, polyvinyl chloride, polyethylene oxide, polyurethane, polyfurfural, citric acid, and cyclodextrin; optionally, the carbon source may be at least one of starch, sucrose, and polyvinyl alcohol. The above-mentioned carbon source contains small organic molecules or polymers containing elements such as oxygen and hydrogen. After sintering and carbonization, this carbon source can form a porous carbon layer on the surface of the matrix, which buffers the volume expansion of the matrix particles during charging and discharging.

[0079] In some embodiments, in step S21, the mass fraction of the carbon source relative to the matrix is ​​10% to 50%. For example, the mass fraction of the added carbon source can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%. In step S21, when the mass fraction of the carbon source added to the first mixture is within the above-mentioned range, the coating effect and energy density of the prepared anode material can be optimized. If the mass fraction of the carbon source is too low, the coating effect on the matrix will be poor; if the mass fraction of the carbon source is too high, over-coating will negatively affect the energy density of the anode material.

[0080] In some embodiments, in step S21, in addition to adding a carbon source, a dispersant is also added to the first mixture. The dispersant in the solvent can assist the carbon source and the matrix particles in being fully mixed, thereby helping the carbon source to adhere to the surface of the matrix particles. The mass fraction of the dispersant relative to the matrix is ​​1%-5%, for example, the mass fraction of the dispersant can be 1%, 2%, 3%, 4%, or 5%. Optionally, the mass fraction of the dispersant used can be 2%-3%. If too little dispersant is added to the first mixture, it will affect the uniform mixing of the carbon source and the matrix in the first mixture; if too much dispersant is added to the first mixture, it will affect the coating effect of the carbon source on the matrix.

[0081] In some embodiments, in step S21, the dispersant used may be selected from one or more combinations of polyvinylpyrrolidone, polyvinyl alcohol, polyethylene oxide, polyacrylic acid, LA132, and LA135. Optionally, polyvinylpyrrolidone may be selected as the dispersant.

[0082] In some embodiments, step S22 specifically includes drying the first mixture to obtain a core-shell structured tin-carbon composite material precursor powder; sintering the composite material precursor powder under a protective atmosphere to carbonize the carbon source attached to the surface of the matrix particles to form a first coating layer, thereby obtaining the composite material. The composite material has a core-shell structure, with the core being the matrix particles and the outer shell being the first coating layer. The first coating layer includes amorphous carbon, which is adsorbed and attached to the surface of the matrix particles through intermolecular forces and covalent bonds.

[0083] In step S22, the sintering treatment of the composite material precursor powder includes: placing the composite material precursor powder in a tube furnace filled with a protective atmosphere, raising the furnace temperature from room temperature to the sintering temperature, and sintering at the sintering temperature for 8 to 16 hours, for example, the sintering time can be 8, 10, 12, 14, or 16 hours; wherein the heating rate is 3 to 10 °C / min, the above heating rate taking into account both carbonization efficiency and effect. Optionally, the heating rate can be 5 °C / min. The sintering temperature is 600 °C to 1200 °C, optionally, the sintering temperature is 600 °C to 700 °C, for example, the sintering temperature can be 600 °C, 620 °C, 640 °C, 650 °C, 660 °C, 680 °C, or 700 °C.

[0084] It should be noted that the protective atmosphere in step S22 is one or a combination of at least two of argon, nitrogen, hydrogen, and helium. Optionally, the protective atmosphere is a mixture of nitrogen, argon, and hydrogen.

[0085] In some embodiments, step S31 specifically includes the following steps: dispersing the composite material in a solvent to obtain a second mixture; dispersing a silane coupling agent in the second mixture so that the silane coupling agent adheres to the particle surface of the composite material to obtain a surface-modified composite material. Specifically, the silane coupling agent is added to the second mixture and dispersed to ensure that the silane coupling agent is fully mixed with the composite material particles in the solvent. The hydrolytic groups of the silane coupling agent react with the hydroxyl groups on the surface of the composite material and combine, thereby replacing the hydroxyl groups on the surface of the composite material with reactive groups.

[0086] In some embodiments, in step S31, the mass of the silane coupling agent added to the second mixture accounts for 5% to 10% of the mass of the matrix raw material. When the mass content of the silane coupling agent used to modify the surface of the composite material is within the above range, the surface modification effect of the composite material is guaranteed, the bonding strength of the second coating layer on the surface of the first coating layer is enhanced, and the formation of an isolation layer by the silane coupling agent on the surface of the composite material particles is avoided, which would hinder the migration and transport of ions between the coating layer and the matrix, negatively affecting the ionic conductivity of the negative electrode material and causing the battery capacity to be unrealized.

[0087] In some embodiments, step S32 specifically includes the following steps: adding MXene material to the second mixture in the form of an MXene dispersion, so that the MXene material interacts with the silane coupling agent and is adsorbed on the surface of the composite material, thereby forming a second coating layer on the particle surface of the composite material.

[0088] In some embodiments, in step S32, the mass fraction of MXene material added to the second mixture relative to the matrix is ​​5% to 10%. For example, the mass fraction of MXene material can be 5%, 6%, 7%, 8%, 9%, or 10%. Specifically, in step S32, 10 to 100 mL of MXene nanosheet dispersion is added to the second mixture, and the second mixture is dispersed for 10 to 30 minutes, followed by drying to obtain a double-layer coated negative electrode material powder. The concentration of the MXene dispersion added to the second mixture is 2-15 mg / mL. For example, the concentration of MXene material in the MXene dispersion can be 2 mg / mL, 3 mg / mL, 4 mg / mL, 5 mg / mL, 6 mg / mL, 7 mg / mL, 8 mg / mL, 9 mg / mL, 10 mg / mL, 11 mg / mL, 12 mg / mL, 13 mg / mL, 14 mg / mL, or 15 mg / mL. When the MXene dispersion added to the second mixture is within the above concentration range, the coating effect of MXene on the negative electrode material can be optimized.

[0089] In some embodiments, the MXene material may be selected from at least one of Ti3C2, Ti2C and V2C. For example, the MXene material may be V2C or a combination of Ti3C2 and Ti2C.

[0090] It should be noted that the MXene dispersion can be prepared using conventional processes in the art, involving acid etching and washing of the MAX phase powder material. For example, 0.2–2 g of MAX material is slowly added to a 5–20 mL hydrochloric acid solution containing 0.2–2 g LiF, and the solution is stirred at 35°C for 24–48 hours. The reaction product is then washed with deionized water and centrifuged for 5–20 min at 2500–4500 rpm. Once the pH of the resulting liquid reaches 5, 10–30 mL of deionized water is added, and the mixture is vigorously stirred for 30–90 min, sonicated for 10–30 min at 550–950 W, and centrifuged for 2–6 min at 2500–4500 rpm. This process is repeated three times. The supernatant is collected, vacuum filtered to obtain a black substance, which is then dried to obtain MXene nanosheet powder. Finally, MXene nanosheet powder was dispersed in deionized water, and the deionized water content was adjusted to prepare an MXene nanosheet dispersion with a concentration of 2–15 mg / mL.

[0091] In some embodiments, the solvent used in the above preparation method may be selected from at least one of water, methanol, ethanol, propanol, isopropanol, butanol, ethylene glycol, acetone, dimethylformamide, dimethyl sulfoxide, and ethyl acetate; optionally, the solvent may be selected from at least one of water, ethanol, isopropanol, and ethyl acetate; for example, in one example, a mixture of water and ethanol is selected as the solvent.

[0092] In some embodiments, the silane coupling agent used in the above preparation method may be selected from at least one of 3-aminopropyltriethoxysilane, N-2-aminoethyl-3-aminopropyltrimethoxysilane, N-2-aminoethyl-3-aminopropylmethyldimethoxysilane, 3-aminopropyltrimethoxysilane, and N-(β-aminoethyl)-γ-aminopropyltriethoxysilane.

[0093] In some embodiments, the dispersion treatment in the above preparation method can be a combination of one or more of the following methods: ultrasonication, stirring, and ball milling.

[0094] In some embodiments, the drying treatment of the first mixture and the second mixture in the above preparation method can be one or more of the following methods combined: vacuum drying, spray drying, freeze drying, and filtration drying; optionally, the drying treatment can be freeze drying.

[0095] This invention also provides an electrochemical device, which can be a solid-state lithium-ion secondary battery or a liquid lithium-ion secondary battery. Taking a liquid lithium-ion secondary battery as an example, the electrochemical device includes a positive electrode, a negative electrode, a separator disposed between the positive and negative electrode, and an electrolyte. The negative electrode includes a negative current collector and a negative active material layer disposed on the negative current collector. The negative active material layer includes a conductive agent, a thickener, a binder, and the negative electrode material described in any of the above embodiments, or the negative electrode material prepared by the preparation method described in any of the above embodiments. The positive electrode includes a positive current collector and a positive active material layer disposed on the positive current collector. The positive active material layer includes a positive electrode material, a conductive agent, and a binder. The positive and negative electrode materials can intercalate and deintercalate lithium ions to achieve energy storage and release. The electrolyte is the carrier for lithium ion transport between the positive and negative electrodes. The separator is permeable to lithium ions but non-conductive, thus separating the positive and negative electrodes to prevent short circuits.

[0096] It should be noted that the preparation of the positive electrode, negative electrode, separator, and electrolyte, as well as the assembly of the electrochemical device, can be carried out using conventional methods in this field. The preparation methods for the electrochemical device are described below with examples:

[0097] (1) Preparation of positive electrode sheet: The positive electrode material, conductive agent, and binder are mixed in a weight ratio of (90 to 99):(1 to 10):(1 to 10), optionally 95:2.5:2.5. N-methylpyrrolidone (NMP) solvent is added, and the mixture is stirred under vacuum until the system is homogeneous and transparent to obtain a positive electrode slurry. This positive electrode slurry is uniformly coated onto a positive electrode current collector aluminum foil, which is then dried at room temperature and transferred to an oven for further drying. The foil is then cold-pressed and slit to obtain the positive electrode sheet. The positive electrode material is selected from one or more of lithium cobalt oxide, ternary materials, and lithium phosphates; specifically, ternary materials include, but are not limited to, lithium nickel cobalt manganese oxide (LiNi). x Co y Mn z O2 (x+y+z=1); lithium phosphates include, but are not limited to, lithium manganese iron phosphate, lithium iron phosphate, lithium manganese phosphate, etc. Conductive agents can be selected from at least one of the following conductive materials: carbon black (Super P), acetylene black, carbon nanotubes (CNT), graphene, and carbon nanofibers (VGCF). For example, the conductive agents can be SP and CNT, with a mass ratio of SP to CNT of 2:1. Binders can be selected from at least one of the following: polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE). For example, PVDF can be used as the binder.

[0098] (2) Preparation of negative electrode sheet: The negative electrode material, conductive agent, thickener and binder are mixed in a mass ratio of 97:1:1:1, deionized water is added to adjust the slurry solid content to 55%, and then the mixture is thoroughly stirred under vacuum to obtain a negative electrode slurry. The negative electrode slurry is uniformly coated on both sides of an 8μm negative electrode current collector copper foil. After drying at room temperature, it is transferred to an oven for drying, and then the negative electrode sheet is obtained through cold pressing, slitting and other processes. The conductive agent can be selected from at least one of conductive materials such as carbon black (Super P), acetylene black, carbon nanotubes (CNT), graphene, and carbon nanofibers (VGCF). The binder is selected from at least one of the binder materials such as polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), and styrene-butadiene rubber (SBR). The thickener is selected from carboxymethyl cellulose, which can be sodium carboxymethyl cellulose (CMC-Na) or lithium carboxymethyl cellulose (CMC-Li).

[0099] (3) Electrolyte preparation: In an argon atmosphere glove box with a water content of <10ppm, ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are uniformly mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1mol / L.

[0100] (4) Preparation of membrane: The membrane is selected from conventional types in the art, such as PE porous membrane. The thickness of the membrane is 9 to 18 μm, the air permeability is 180 s / 100 mL to 380 s / 100 mL, and the porosity is 30% to 50%.

[0101] (5) Battery assembly: Battery assembly is carried out according to conventional methods. For example, after preparation, the negative electrode, separator, and positive electrode are stacked in sequence and placed in an aluminum-plastic film to obtain a dry cell. The dry cell is then baked to remove water. The prepared electrolyte is injected into the dry cell and sealed to obtain the finished lithium-ion battery.

[0102] The technical solution of the present invention will be described in detail below through several specific embodiments and comparative examples. Unless otherwise stated, the raw materials and reagents used in the following embodiments are commercially available products or can be prepared by conventional methods in the art.

[0103] Example 1

[0104] This embodiment provides a negative electrode material, which includes a substrate, a first coating layer, and a second coating layer. The substrate is tin; the first coating layer includes amorphous carbon, and the mass fraction of the first coating layer relative to the substrate is 30%; the second coating layer includes MXene nanosheets, and the mass fraction of the second coating layer relative to the substrate is 10%. During the preparation process, the negative electrode material is modified only on the surface of the substrate particles. The preparation method of this negative electrode material is as follows:

[0105] S1. Under an air atmosphere, 1g of matrix powder is placed in methanol for ultrasonic dispersion to obtain a first mixture, wherein the matrix raw material is tin powder; 5% by mass of silane coupling agent (3-aminopropyltriethoxysilane) is added to the first mixture and dispersed for 30 minutes, so that the silane coupling agent in the first mixture adheres to the surface of the matrix particles.

[0106] S2. A carbon source (citric acid) with a mass fraction of 30% relative to the matrix and a dispersant (polyvinylpyrrolidone) with a mass fraction of 2% are added to the first mixture, and stirred and ultrasonically dispersed to allow the carbon source and silane coupling agent to interact and couple to the particle surface of the matrix. The first mixture is freeze-dried to obtain a core-shell structured tin-carbon composite precursor powder. The composite precursor powder is placed in a tube furnace and carbonized at 900°C for 12 hours under an argon atmosphere (heating rate 5°C / min) to obtain a composite material with a core-shell structure, the core being tin and the outer shell being amorphous carbon.

[0107] S3. Add 20 mL of MXene dispersion with a concentration of 5 mg / mL to the second mixture and ultrasonically disperse for 20 minutes. After drying, the negative electrode material is obtained. The MXene material is a combination of Ti3C2 and Ti2C.

[0108] Example 2

[0109] This embodiment provides a negative electrode material, which includes a matrix, a first coating layer, and a second coating layer. The matrix is ​​tin; the first coating layer includes amorphous carbon, and the mass fraction of the first coating layer relative to the matrix is ​​30%; the second coating layer includes MXene nanosheets, and the mass fraction of the second coating layer relative to the matrix is ​​10%. During the preparation process, the negative electrode material is modified only on the surface of the tin-carbon composite material. The preparation method of this negative electrode material is as follows:

[0110] S1. Under an air atmosphere, 1g of matrix powder is placed in methanol and ultrasonically dispersed to obtain a first mixture, wherein the matrix raw material is tin powder.

[0111] S2. A carbon source (citric acid) with a mass fraction of 30% relative to the matrix and a dispersant (polyvinylpyrrolidone) with a mass fraction of 2% are added to the first mixture, and stirred and ultrasonically dispersed to allow the carbon source to adhere to the particle surface of the matrix. The first mixture is freeze-dried to obtain a core-shell structured tin-carbon composite material precursor powder. The composite material precursor powder is placed in a tube furnace and carbonized at 900°C for 12 hours under an argon atmosphere (heating rate 5°C / min) to obtain a composite material with a core-shell structure, the core being tin and the outer shell being amorphous carbon.

[0112] S3. Place the composite material powder in methanol to obtain a second mixed solution; add 5% by mass of silane coupling agent (3-aminopropyltriethoxysilane) to the second mixed solution and perform ultrasonic dispersion treatment for 30 minutes to allow the silane coupling agent to adhere to the particle surface of the composite material; then, add 20 mL of MXene dispersion with a concentration of 5 mg / mL to the second mixed solution and perform ultrasonic dispersion treatment for 20 minutes, and dry to obtain the negative electrode material; the MXene material is a combination of Ti3C2 and Ti2C.

[0113] Example 3

[0114] This embodiment provides a negative electrode material, which includes a matrix, a first coating layer, and a second coating layer. The matrix is ​​tin; the first coating layer includes amorphous carbon, and the mass fraction of the first coating layer relative to the matrix is ​​10%; the second coating layer includes MXene nanosheets, and the mass fraction of the second coating layer relative to the matrix is ​​10%. During the preparation process, the surfaces of the matrix particles and the tin-carbon composite material are modified. The preparation method of this negative electrode material is as follows:

[0115] S1. Under an air atmosphere, 1g of matrix powder is placed in methanol for ultrasonic dispersion to obtain a first mixture, wherein the matrix raw material is tin powder; 5% by mass of silane coupling agent (3-aminopropyltriethoxysilane) is added to the first mixture and dispersed for 30 minutes, so that the silane coupling agent in the first mixture adheres to the surface of the matrix particles.

[0116] S2. A carbon source (citric acid) with a mass fraction of 10% relative to the matrix and a dispersant (polyvinylpyrrolidone) with a mass fraction of 2% are added to the first mixture, and stirred and ultrasonically dispersed to allow the carbon source and silane coupling agent to interact and couple to the particle surface of the matrix. The first mixture is freeze-dried to obtain a core-shell structured tin-carbon composite precursor powder. The composite precursor powder is placed in a tube furnace and carbonized at 900°C for 12 hours under an argon atmosphere (heating rate 5°C / min) to obtain a composite material with a core-shell structure, the core being tin and the outer shell being amorphous carbon.

[0117] S3. Place the composite material powder in methanol to obtain a second mixed solution; add 5% by mass of silane coupling agent (3-aminopropyltriethoxysilane) to the second mixed solution and perform ultrasonic dispersion treatment for 30 minutes to allow the silane coupling agent to adhere to the particle surface of the composite material; then, add 20 mL of MXene dispersion with a concentration of 5 mg / mL to the second mixed solution and perform ultrasonic dispersion treatment for 20 minutes, and dry to obtain the negative electrode material; the MXene material is a combination of Ti3C2 and Ti2C.

[0118] Example 4

[0119] This embodiment prepares a negative electrode material with the same system as in Example 3. The negative electrode material includes a substrate, a first coating layer, and a second coating layer. The substrate is tin; the first coating layer includes amorphous carbon, and the mass fraction of the first coating layer relative to the substrate is 10%; the second coating layer includes MXene nanosheets, and the mass fraction of the second coating layer relative to the substrate is 10%. The difference between this embodiment and Example 3 is that, in step S1, a 10% mass fraction of silane coupling agent (3-aminopropyltriethoxysilane) is added to the first mixture.

[0120] Example 5

[0121] This embodiment prepares a negative electrode material with the same system as in Example 4. The negative electrode material includes a substrate, a first coating layer, and a second coating layer. The substrate is tin; the first coating layer includes amorphous carbon, and the mass fraction of the first coating layer relative to the substrate is 30%; the second coating layer includes MXene nanosheets, and the mass fraction of the second coating layer relative to the substrate is 10%. The difference between this embodiment and Example 4 is that in step S2, a carbon source (citric acid) with a mass fraction of 30% is added to the first mixture.

[0122] Example 6

[0123] This embodiment prepares a negative electrode material with the same system as in Example 4. The negative electrode material includes a substrate, a first coating layer, and a second coating layer. The substrate is tin; the first coating layer includes amorphous carbon, and the mass fraction of the first coating layer relative to the substrate is 50%; the second coating layer includes MXene nanosheets, and the mass fraction of the second coating layer relative to the substrate is 10%. The difference between this embodiment and Example 4 is that in step S2, a carbon source (citric acid) with a mass fraction of 50% is added to the first mixture.

[0124] Example 7

[0125] This embodiment prepares a negative electrode material with the same system as in Example 5. The negative electrode material includes a matrix, a first coating layer, and a second coating layer. The matrix is ​​tin; the first coating layer includes amorphous carbon, and the mass fraction of the first coating layer relative to the matrix is ​​30%; the second coating layer includes MXene nanosheets, and the mass fraction of the second coating layer relative to the matrix is ​​10%. The difference between this embodiment and Example 5 is that in step S2, a dispersant (polyvinylpyrrolidone) with a mass fraction of 3% is added to the first mixture.

[0126] Example 8

[0127] This embodiment prepares a negative electrode material with the same system as in Example 5. The negative electrode material includes a matrix, a first coating layer, and a second coating layer. The matrix is ​​tin; the first coating layer includes amorphous carbon, and the mass fraction of the first coating layer relative to the matrix is ​​30%; the second coating layer includes MXene nanosheets, and the mass fraction of the second coating layer relative to the matrix is ​​5%. The difference between this embodiment and Example 5 is that in step S3, 10 mL of MXene dispersion with a concentration of 5 mg / mL is added to the second mixture.

[0128] Example 9

[0129] This embodiment prepares a negative electrode material with the same system as in Example 5. The negative electrode material includes a matrix, a first coating layer, and a second coating layer. The matrix is ​​tin; the first coating layer includes amorphous carbon, and the mass fraction of the first coating layer relative to the matrix is ​​30%; the second coating layer includes MXene nanosheets, and the mass fraction of the second coating layer relative to the matrix is ​​50%. The difference between this embodiment and Example 5 is that in step S3, 100 mL of MXene dispersion with a concentration of 5 mg / mL is added to the second mixture.

[0130] Example 10

[0131] This embodiment prepares a negative electrode material with the same system as in Example 5. The negative electrode material includes a substrate, a first coating layer, and a second coating layer. The substrate is tin; the first coating layer includes amorphous carbon, and the mass fraction of the first coating layer relative to the substrate is 30%; the second coating layer includes MXene nanosheets, and the mass fraction of the second coating layer relative to the substrate is 10%. The difference between this embodiment and Example 5 is that in step S4, the MXene nanosheet material used is a combination of Nb2C and Nb3C2.

[0132] Comparative Example 1

[0133] This comparative example prepares a negative electrode material coated only with a first coating layer. The negative electrode material includes a substrate and a first coating layer. The substrate is tin. The first coating layer includes amorphous carbon, and the mass fraction of the first coating layer relative to the substrate is 30%. The preparation method of this comparative example differs from that of Example 5 in that step S3 is omitted.

[0134] Comparative Example 2

[0135] This comparative example provides a negative electrode material comprising a substrate, a first coating layer, and a second coating layer. The substrate is tin. The first coating layer comprises MXene nanosheets, and the mass fraction of the first coating layer relative to the substrate is 10%. The second coating layer comprises amorphous carbon, and the mass fraction of the second coating layer relative to the substrate is 30%. The preparation method of this negative electrode material is as follows:

[0136] S1. Under an air atmosphere, 1g of matrix powder is placed in methanol and ultrasonically dispersed to obtain a first mixture, wherein the matrix raw material is tin powder.

[0137] S2. Add 20 mL of MXene dispersion with a concentration of 5 mg / mL to the first mixture and ultrasonically disperse for 20 minutes. After drying, a composite material is obtained. The composite material has a core-shell structure, with the core being tin and the shell being MXene material. The MXene material is a combination of Ti3C2 and Ti2C.

[0138] S3. Place the composite material powder in methanol to obtain a second mixed solution; then, add a carbon source (citric acid) with a mass fraction of 30% relative to the matrix and a dispersant (polyvinylpyrrolidone) with a mass fraction of 2% to the second mixed solution, and stir and ultrasonically disperse it to allow the carbon source to adhere to the particle surface of the matrix; freeze-dry the second solution, and place the dried powder in a tube furnace and carbonize it at 900°C for 12 hours under an argon atmosphere (heating rate 5°C / min) to carbonize the carbon source on the surface of the composite material into amorphous carbon, thereby obtaining the negative electrode material.

[0139] The process parameters for preparing the anode materials in Examples 1 to 10 and Comparative Examples 1 to 2 are shown in Table 1.

[0140] It should be noted that the carbon source used in the preparation methods of the above embodiments and comparative examples is not limited to citric acid. Other commercially available carbon sources can also be used, such as graphite, sucrose, glucose, maltose, lactose, starch, formaldehyde, acetaldehyde, propionaldehyde, phenolic resin, epoxy resin, polyethylene glycol, cellulose, lignin, polyvinyl alcohol, polyvinyl chloride, polyethylene oxide, polyurethane, polyfurfural, citric acid, cyclodextrin, etc. Similarly, the silane coupling agent used in the preparation methods of the above embodiments and comparative examples is not limited to 3-aminopropyltriethoxysilane. Other commercially available silane coupling agents can also be used, such as N-2-aminoethyl-3-aminopropyltrimethoxysilane, N-2-aminoethyl-3-aminopropylmethyldimethoxysilane, 3-aminopropyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltriethoxysilane, etc.

[0141] To further verify the efficacy of the present invention, the surface potential, initial discharge performance, and cycle discharge performance of the negative electrode materials prepared in Examples 1 to 8 and Comparative Examples 1 to 3 were tested. The test results are shown in Table 2.

[0142] Surface potential test: The surface potential of the negative electrode materials prepared in Examples 1 to 8 and Comparative Examples 1 to 3 was tested using the Zeta potential test method. Specifically, 50 mg of negative electrode material powder sample was dispersed in water, ensuring that the pH value of the water was 7, sonicated for 5 minutes, and then dried. The sample powder was then placed in the Malvern Zetasizer Nano ZS90 instrument. The Zeta potential was obtained by indirectly measuring the particle electrophoresis velocity by measuring the change in the frequency or phase of light using the Doppler electrophoresis light scattering principle.

[0143] Then, the negative electrode materials prepared in Examples 1 to 10 and Comparative Examples 1 to 2 were assembled into coin cells, and the discharge capacity and negative electrode volume expansion rate of the negative electrode materials prepared in Examples 1 to 10 and Comparative Examples 1 to 2 were tested using coin cells to verify the improvement effect of the negative electrode materials on their own volume expansion, battery capacity and cycle performance. The test results are shown in Table 2.

[0144] The preparation process of the coin cell is as follows: The negative electrode material prepared above, the conductive agent carbon black (Super P), and the binder polyacrylic acid are mixed in a weight ratio of 8:1:1 to prepare a negative electrode slurry; the negative electrode slurry is coated on copper foil and dried in a vacuum drying oven at 110°C for 12 hours. After drying, it is rolled into a negative electrode sheet with a diameter of φ12mm; lithium metal is used as the positive electrode sheet, and Celgard 2400 polypropylene (PP) membrane is used as the separator; an electrolyte with a LiPF6 concentration of 1.0 mol / L is prepared using ethylene carbonate and diethyl carbonate in a volume ratio of 1:1 as solvents and LiPF6 as the lithium salt; 35 μL of electrolyte is dropped onto each side of the separator; the positive electrode shell, positive electrode sheet, separator, negative electrode sheet, and negative electrode shell are assembled in sequence in a glove box to form a half cell (CR2032 type). After being placed at room temperature for 24 hours to allow the electrolyte to fully wet the electrode sheet, subsequent battery testing is performed.

[0145] Battery discharge specific capacity and initial coulombic efficiency test: At room temperature of 25°C, within the test voltage range of 0.01V (discharge cutoff voltage) to 1.5V (charge cutoff voltage), a one-week charge-discharge test was conducted on the coin cell half-cell at a current rate of 0.5A / g. The initial charge capacity and initial discharge capacity of the battery were recorded. The initial discharge specific capacity is obtained by dividing the initial discharge capacity by the mass of the negative electrode, and the initial coulombic efficiency is obtained by dividing the initial discharge capacity by the initial charge capacity.

[0146] Battery cycle capacity retention density test: At room temperature of 25℃, within the test voltage range of 0.01V (discharge cutoff voltage) to 1.5V (charge cutoff voltage), 100 cycles of charge-discharge test were performed on the coin cell half-cell at a current rate of 0.5A / g. The discharge capacity of the battery on the first cycle and the discharge capacity on the 100th cycle were recorded, and the capacity retention rate of the battery after 100cls cycles was calculated (capacity retention rate of 100cls = discharge capacity of 100cls / discharge capacity of 1cls).

[0147] Table 1: Composition parameters of the anode materials prepared in Examples 1 to 10 and Comparative Examples 1 to 2

[0148]

[0149] Table 2: Battery performance test results of the negative electrode materials prepared in Examples 1 to 10 and Comparative Examples 1 to 2

[0150]

[0151]

[0152] Comparing the test results of Examples 1, 2, 5 and Comparative Example 1, it can be seen that, compared with conventional carbon-coated tin anode materials, coating the outermost layer of tin anode material particles with an additional MXene coating layer can effectively suppress the volume expansion of the anode sheet during charging and discharging while ensuring that the battery's initial coulombic efficiency and initial discharge specific capacity do not decay. This significantly improves the cycle stability of the battery and extends its service life.

[0153] Comparing the test results of Examples 1, 2, and 5 and Comparative Examples 1 and 2, it can be seen that the negative electrode material formed by sequentially coating MXene and carbon materials on tin particles in Comparative Example 2 without surface modification cannot form a stable double-coating structure after compaction. Instead, it exhibits a disordered combination of tin, carbon, and MXene, making it difficult to exert the binding and protective effect of the coating layer on the tin particles. Compared with the case of single-layer carbon coating on tin particles in Comparative Document 1, Comparative Example 2 does not significantly improve the discharge capacity and cycle stability of the battery. In contrast, the present solution, which sequentially coats carbon and MXene materials on tin particles, can form a stable double-coating structure on the outside of the tin particles. This double-coating structure can effectively utilize the MXene layer to form a conductive network on the outside of the particles, providing an electrolyte wetting structure and improving the electronic and ionic conductivity of the negative electrode material; it can also effectively utilize the carbon coating layer to provide a binding and suppressing effect on the expansion and deformation of the tin particles, improving the structural stability of the negative electrode material. This solution, with its dual-coating structure designed for tin particles, can further improve both the charge / discharge efficiency and cycle life of the battery.

[0154] Comparing the test results of Example 5 and Example 1, it can be seen that, compared with the negative electrode material in Example 1 where surface modification was only performed on the surface of the tin particles in the substrate, the negative electrode material in Example 5, with modification on both the surface of the tin particles in the substrate and the surface of the first coating layer, results in uniform coating of the first and second coating layers sequentially covering the outside of the substrate, and strong interfacial bonding strength. The double-coating effect of the negative electrode material in Example 5 is good, and its structural strength is high. It can effectively maintain its structural stability during battery charge-discharge cycles, and thus better suppress the volume expansion of the negative electrode sheet during long-term battery use, improving the cycle stability of the battery.

[0155] Comparing the test results of Examples 5 and 2, it can be seen that in Example 2, the negative electrode material was not modified on the surface of the tin particles in the substrate. This resulted in uneven coating of the first coating layer on the substrate surface, further affecting the coating effect of the second coating layer on the surface of the first coating layer. Consequently, the double-coating structure on the surface of the negative electrode material was unstable and the coating effect was poor. In contrast, in Example 5, the negative electrode material underwent modification on both the surface of the silicon particles in the substrate and the surface of the first coating layer. This resulted in uniform coating of the first and second coating layers sequentially coated on the outside of the substrate, with strong interfacial bonding strength. The double-coating effect of the negative electrode material in Example 5 was good, and the structural strength was high. It was also able to effectively maintain its structural stability during battery charge-discharge cycles, thereby suppressing the volume expansion of the negative electrode sheet during long-term battery use and improving the cycle stability performance of the battery.

[0156] Comparing the test results of Examples 4 to 6, it can be seen that when the carbon coating amount is low, the battery cycle capacity retention rate increases with the increase of the carbon coating amount of the negative electrode material. This is because when the carbon coating amount increases within a low content range, it can further suppress the volume expansion of the negative electrode material during charging and discharging, while still ensuring smooth ion exchange between the negative electrode material and the outside world, thus preventing excessive degradation of the conductivity of the negative electrode material. However, when the carbon coating amount is high, the battery cycle capacity retention rate decreases with the increase of the carbon coating amount of the negative electrode material. This is because when the carbon coating layer is too thick, further increases in carbon coating amount will block the ion transport gaps on the substrate surface, making it easy for embedded lithium ions to become trapped in the coating layer and difficult to migrate to the surface of the negative electrode material, resulting in capacity decay of the battery at high cycle counts. In addition, when the carbon coating amount is increased to 30 wt.%, the optimal balance between the structural stability of the material and the battery performance is achieved. However, as the carbon coating amount increases, the initial discharge specific capacity of the negative electrode gradually decreases. This is because the increase in the carbon coating layer reduces the proportion of the base silicon material in the negative electrode, thereby reducing the discharge specific capacity of the negative electrode.

[0157] In summary, this invention provides an anode material and its preparation method. This anode material utilizes two surface modifications to form a structurally stable and uniformly coated double-layer structure on the surface of the matrix particles. By leveraging the synergistic effect of the double-layer coating structure on the outer side of the matrix, this anode material effectively restrains and suppresses the volume expansion of the tin matrix particles during the alloying / dealloying process during charging and discharging, thereby improving the structural stability of the anode sheet. Furthermore, it forms a three-dimensional conductive network within the anode material, effectively enhancing its conductivity in the electrolyte and reducing its charge transport impedance. Consequently, the anode material possesses both considerable lithium storage capacity and excellent electrochemical performance.

[0158] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A negative electrode material, characterized in that, include: The matrix comprises tin; A first coating layer is attached to the surface of the substrate, and the first coating layer comprises a carbon material; A second coating layer is at least partially attached to the surface of the first coating layer, and the second coating layer comprises MXene material.

2. The negative electrode material according to claim 1, characterized in that, The surface potential of the negative electrode material particles is greater than or equal to -5mV.

3. The negative electrode material according to claim 1, characterized in that, The surface of the first coating layer and / or the surface of the substrate and the first coating layer are modified with a silane coupling agent.

4. The negative electrode material according to claim 1, characterized in that, The negative electrode material includes secondary particles with a particle size of 200–400 nm.

5. The negative electrode material according to claim 1, characterized in that, The particle size of the matrix is ​​50-200 nm; the mass of the first coating layer is 10%-50% of the mass of the matrix; and the mass of the second coating layer is 5%-50% of the mass of the matrix.

6. A method for preparing the negative electrode material according to any one of claims 1 to 5, characterized in that, include: A substrate is provided, the substrate comprising tin; A first coating layer is attached to the surface of the substrate to obtain a composite material; the first coating layer comprises a carbon material. A second coating layer is attached to the surface of the composite material to obtain a negative electrode material; the second coating layer includes MXene material.

7. The preparation method according to claim 6, characterized in that, The step of attaching and forming a second coating layer on the surface of the composite material includes: The composite material is then surface-modified; After surface modification of the composite material, a second coating layer is attached to the surface of the composite material to obtain a negative electrode material.

8. The preparation method according to claim 7, characterized in that, The method further includes a step of surface modification of the substrate before the first coating layer is attached to the substrate surface, comprising: dispersing the substrate in a solvent to obtain a first mixture; dispersing a silane coupling agent in the first mixture, such that the silane coupling agent is attached to the particle surface of the substrate to obtain a surface-modified substrate; wherein the mass of the silane coupling agent mixed in the first mixture is 5% to 10% of the mass of the substrate; And / or, The step of surface modification of the composite material includes: dispersing the composite material in a solvent to obtain a second mixture; dispersing a silane coupling agent in the second mixture such that the silane coupling agent adheres to the particle surface of the composite material to obtain the surface-modified composite material; wherein the mass of the silane coupling agent mixed in the second mixture is 5% to 10% of the mass of the matrix.

9. The preparation method according to claim 8, characterized in that, The step of attaching and forming a first coating layer on the surface of the substrate after surface modification includes: dispersing a carbon source into the first mixture, so that the carbon source interacts with the silane coupling agent and is adsorbed on the particle surface of the substrate; and drying and sintering the first mixture under a protective atmosphere to carbonize the carbon source attached to the substrate surface, so as to attach and form the first coating layer on the substrate surface. And / or, The step of attaching a second coating layer to the surface of the composite material after surface modification includes: dispersing MXene material into the second mixture, so that MXene interacts with the silane coupling agent and adsorbs onto the surface of the composite material to attach and form the second coating layer on the surface of the composite material; wherein the MXene material is dispersed into the second mixture in the form of an MXene dispersion, and the concentration of the MXene material in the MXene dispersion is 2 to 15 mg / mL.

10. An electrochemical device, characterized in that, The invention includes a negative electrode sheet, which comprises a negative current collector and a negative active material layer, wherein the negative active material layer comprises the negative electrode material according to any one of claims 1 to 5, or the negative electrode material prepared by the preparation method according to any one of claims 6 to 9.

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