Preparation method of tin-carbon composite negative electrode material and application thereof

Abstract

The application discloses a preparation method of tin-carbon composite negative material and application thereof. A two-dimensional transition metal carbide and / or two-dimensional transition metal carbonitride and tin salt are subjected to one-step hydrothermal reaction in the presence of water and sodium borohydride to prepare tin-carbon composite material coated with pre-sodiumized carbon with a porous structure. The tin-carbon composite material has the advantages that tin ions are adsorbed by the MXene sheet structure and the negative charge on the surface, and the tin ions are reduced in situ by sodium borohydride and anchored carbon in the MXene at high temperature to form a tin-carbon composite; meanwhile, sodium borohydride reacts with water at high temperature to generate hydrogen, so that the prepared tin-carbon composite negative material has a porous structure, and sodium ions introduced by sodium borohydride can be combined with functional groups on the surface of MXene through electrostatic adsorption, thereby playing a pre-sodiumization role. The tin-carbon composite material has good electric conductivity and ion conductivity, can inhibit volume expansion in the alloying process, reduce the contact between tin-carbon and electrolyte, and improve the cycle performance and first-cycle coulomb efficiency of the battery.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a method for preparing a tin-carbon composite anode material and its application. Background Technology

[0002] With the widespread adoption of electric vehicles and the promotion of clean energy and carbon neutrality, various energy storage and power batteries are playing an increasingly indispensable role in people's daily lives. Consequently, the requirements for the energy density and cycle life of lithium-ion batteries are also becoming increasingly stringent. As a crucial component of the battery, the capacity and cycle life of the anode material also significantly impact the overall capacity, lifespan, and other key performance characteristics of the battery. Sodium-ion batteries, possessing a similar energy storage mechanism to lithium-ion batteries, hold promise as a potential replacement for lithium-ion battery products due to their advantages of abundant resources and low cost.

[0003] Currently, sodium-ion batteries primarily use hard carbon as the anode material, but this material has low sodium storage capacity and low initial efficiency. Therefore, developing novel high-rate and long-life anode materials has significant research and application value. Research on anode materials has revealed that tin and sodium can form a metallic compound with a capacity far exceeding the theoretical capacity of graphite, attracting widespread attention in the battery materials field. However, this type of material exhibits a significant volume effect during alloying, leading to pulverization and shedding during charge and discharge, which reduces battery efficiency and cycle performance.

[0004] Therefore, constructing tin-containing composite materials that can maintain structural integrity during rapid sodium ion insertion / extraction and long-term cycling is key to promoting the application of tin-containing anode materials in sodium-ion batteries and effectively improving the electrochemical performance of sodium-ion batteries. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for preparing a tin-carbon composite anode material and its application. Using carbon-containing MXene material and tin salt as raw materials, a pre-sodium-coated tin-carbon composite material with a porous structure is prepared through a hydrothermal reaction in the presence of water and sodium borohydride. This tin-carbon composite material exhibits excellent electrical and ion-conducting properties, effectively suppresses volume expansion during alloying, and reduces the contact between tin-carbon and the electrolyte, thereby improving the battery's cycle performance and first-cycle coulombic efficiency.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] The first aspect of this invention provides a method for preparing a tin-carbon composite anode material, comprising the following steps:

[0008] (1) Disperse MXene material in water to obtain MXene dispersion; dissolve tin salt in water to obtain tin salt solution; the MXene material is a two-dimensional transition metal carbide and / or a two-dimensional transition metal carbonitride;

[0009] (2) Mix the tin salt solution with the MXene dispersion prepared in step (1) and stir to obtain a tin-carbon suspension;

[0010] (3) Add sodium borohydride solution to the tin-carbon suspension prepared in step (2) and carry out hydrothermal reaction in a closed reaction vessel to prepare the tin-carbon composite anode material.

[0011] Further, in step (1), the MXene material is preferably a single-layer or few-layer MXene material, and the number of layers of the few-layer MXene material does not exceed 5.

[0012] Further, in step (1), the MXene material is M n+1 X n T x Where n is any integer from 1 to 3, x > 0, M is a transition metal Sc, Ti, V, Cr, Y, Zr, Nb, Mo, Hf, Ta, W, Ni, Fe, Mn or Zn, X is C or CN, and T x These are surface terminal groups, including -OH, -O-, and -F.

[0013] Furthermore, the MXene material is preferably Ti2CT. x Nb2CT x V2CT x Ti3C2T x Ta4C3T x Ti4C3T x Ti3CNT x One or more of them.

[0014] Further, in step (1), the tin salt is preferably one or more of SnCl4, SnCl2, and SnSO4.

[0015] Further, in step (2), the tin salt solution is added dropwise to the MXene dispersion and mixed and stirred to obtain a tin-carbon suspension.

[0016] Further, in step (1), the concentration of the MXene dispersion is 0.1-1 mg / mL; the concentration of the tin salt solution is preferably 0.1-1 mol / L.

[0017] Furthermore, the mass ratio of the MXene material to the tin salt is 1:(1-30).

[0018] Furthermore, the mass ratio of sodium borohydride to tin salt is 1:(1-10).

[0019] Further, in step (3), the sodium borohydride solution is obtained by dissolving sodium borohydride in ethanol; the mass percentage of sodium borohydride in the sodium borohydride solution is 0.5%-1%.

[0020] Further, in step (3), the sodium borohydride solution is added dropwise to the tin-carbon suspension and stirred and mixed.

[0021] Furthermore, in step (3), the temperature of the hydrothermal reaction is 200-250℃, and the time of the hydrothermal reaction is 10-20h.

[0022] Furthermore, the preparation method also includes the steps of filtering, washing, and drying the hydrothermal reaction product; the drying temperature is 80-100℃.

[0023] The second aspect of the present invention provides a tin-carbon composite anode material prepared by the preparation method described in the first aspect.

[0024] A third aspect of the present invention provides a negative electrode sheet comprising the tin-carbon composite negative electrode material described in the second aspect.

[0025] A fourth aspect of the present invention provides a sodium-ion battery comprising the negative electrode sheet described in the third aspect.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] 1. This invention prepares a porous pre-sodium-coated tin-carbon composite material with MXene coating via a one-step hydrothermal method. This preparation method is simple and easy to operate, and the resulting tin-carbon composite anode material exhibits excellent electrochemical performance and structural stability. The tin-carbon composite anode material comprises a tin-carbon composite and porous pre-sodium MXene coating the tin-carbon composite. The tin-carbon composite provides high specific capacity, while the porous MXene sheets provide a continuous conductive network, thereby improving the conductivity and ion transport kinetics of the tin-carbon composite. Furthermore, the presence of the porous MXene coating effectively buffers the volume expansion problem of tin and sodium alloying during charge and discharge, while reducing direct contact between the tin-carbon composite and the electrolyte. Therefore, this tin-carbon composite anode material not only possesses high specific capacity but also high conductivity, ion conduction performance, and good structural stability. In addition, the tin-carbon composite anode material can provide surface pre-sodium coating during SEI film formation, thereby reducing the consumption of active materials and improving the coulombic efficiency of the battery.

[0028] 2. Sodium-ion batteries constructed using the above-mentioned tin-carbon anode composite material as the anode active material have high capacity, excellent cycle stability and coulombic efficiency. Under constant current charge-discharge test at a current density of 100 mA / g, the initial coulombic efficiency is not less than 90%, and under 500 charge-discharge cycles at a current density of 500 mA / g, the capacity retention rate is not less than 80%. Attached Figure Description

[0029] Figure 1 The image shows a SEM image of the tin-carbon composite anode material prepared in Example 1. Detailed Implementation

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. "Comprising" or "containing" as used herein means that it may include or contain other components in addition to the stated components. "Comprising" or "containing" as used herein may also be replaced with the closed form "is" or "consisting of".

[0031] Tin and sodium can form a metallic compound with a capacity far exceeding that of graphite. However, these materials exhibit a significant volume effect during alloying, leading to material pulverization and shedding during charge and discharge, which reduces battery efficiency and cycle performance.

[0032] To address the above problems, this invention provides a method for preparing a tin-carbon composite anode material, specifically including the following steps:

[0033] (1) Disperse MXene material in water to obtain MXene dispersion; dissolve tin salt in water to obtain tin salt solution; the MXene material is a two-dimensional transition metal carbide and / or a two-dimensional transition metal carbonitride;

[0034] (2) Mix the tin salt solution with the MXene dispersion prepared in step (1) and stir to obtain a tin-carbon suspension;

[0035] (3) Add sodium borohydride solution to the tin-carbon suspension prepared in step (2) and carry out hydrothermal reaction in a closed reaction vessel to prepare the tin-carbon composite anode material.

[0036] This invention uses MXene material and tin salt as raw materials to prepare a porous pre-sodiumized MXene-coated tin-carbon composite material through a hydrothermal reaction in the presence of water and sodium borohydride. Specifically, this invention utilizes the layered structure and negatively charged properties of MXene material to adsorb tin ions, allowing tin ions to adsorb onto the surface and interlayer of the MXene material. These ions are then reduced in situ by sodium borohydride and anchored to the carbon in the MXene at high temperature, forming a tin-carbon composite. Simultaneously, sodium borohydride reacts with water in the reaction system at high temperature to generate hydrogen gas, giving the MXene material coated on the surface of the tin-carbon composite a porous structure. Some of these pores are covered by other MXene layers on the surface, forming closed pores, which helps to improve the sodium storage capacity of the material. This also avoids the problem of excessive contact between the tin-carbon material and the electrolyte due to excessive open pores, thus reducing the initial efficiency. Furthermore, the sodium ions provided by sodium borohydride can combine with the surface functional groups of the MXene material through electrostatic adsorption, completing pre-sodiumization at the molecular level during the hydrothermal reaction, thereby preparing a porous, pre-sodiumized MXene-coated tin-carbon composite material.

[0037] In this invention, the MXene material is preferably a single-layer or few-layer MXene material, wherein the number of layers in a few-layer MXene material does not exceed 5. Compared to multilayer MXene materials, Sn 2+ Sn 4+ It is easier to insert between single-layer MXene materials or between layers of few carbon-containing MXene materials, thereby increasing the tin content introduced between MXene material layers.

[0038] In this invention, MXene material is M n+1 X n T x Where n is any integer from 1 to 3, x > 0, M is preferably a transition metal Sc, Ti, V, Cr, Y, Zr, Nb, Mo, Hf, Ta, W, Ni, Fe, Mn or Zn, X is C or CN, and T x The surface-capped groups include -OH, -O-, and -F; more preferably, Ti2CT. x Nb2CT x V2CT x Ti3C2T x Ta4C3T x Ti4C3T x Ti3CNT x One or more of them.

[0039] In this invention, MXene is dispersed in water to obtain an MXene dispersion. The concentration of the MXene dispersion is preferably 0.1-1 mg / mL, such as 0.1 mg / mL, 0.2 mg / mL, 0.3 mg / mL, 0.4 mg / mL, 0.5 mg / mL, 0.6 mg / mL, 0.7 mg / mL, 0.8 mg / mL, 0.9 mg / mL, 1 mg / mL, etc., including but not limited to the concentration values ​​listed above; more preferably 0.4-0.6 mg / mL, such as 0.5 mg / mL, so that tin ions can be uniformly adsorbed between the MXene layers, and MXene can be well coated on the surface of the subsequently formed tin-carbon material.

[0040] In this invention, the tin salt is preferably one or more of SnCl4, SnCl2, and SnSO4; preferably, the tin salt solution is added dropwise to the MXene dispersion and mixed and stirred so that tin ions can be uniformly adsorbed in the interlayer of MXene to obtain a tin-carbon suspension; more preferably, the concentration of the tin salt solution is 0.1-1 mol / L, such as 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, etc., including but not limited to the concentration values ​​listed above.

[0041] In this invention, the mass ratio of MXene material to tin salt is 1:(1-30), for example 1:1, 1:2, 1:3, 1:5, 1:10, 1:12, 1:15, 1:18, 1:20, 1:22, 1:25, 1:27, 1:30, etc., including but not limited to the mass ratios listed above; the mass ratio of sodium borohydride to tin salt is 1:(1-10), for example 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9. The mass ratios, such as 1:10, etc., are not limited to those listed above. In the hydrothermal reaction, sodium borohydride is required to reduce the tin ions adsorbed between the MXene layers and to react with water to generate hydrogen gas to prepare a porous structure. In order to ensure that the tin ions can be fully reduced and a porous composite material can be formed, the amount of sodium borohydride fed into the reaction system needs to be controlled. For example, by controlling the mass ratio of sodium borohydride to tin salt in the range of 1:(1-10), a tin-carbon composite anode material with a porous structure can be prepared.

[0042] In this invention, the sodium borohydride solution is obtained by dissolving sodium borohydride in ethanol, and the mass percentage of sodium borohydride in the sodium borohydride solution is 0.5%-1%, such as 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, etc., including but not limited to the mass percentages listed above; preferably, the sodium borohydride solution is added dropwise to the tin intercalated MXene suspension for mixing under magnetic stirring.

[0043] In this invention, the hydrothermal reaction is carried out in a high-pressure reactor. The preferred temperature for the hydrothermal reaction is 200-250°C, and the preferred reaction time is 10-20 hours, for example, maintaining the hydrothermal reaction at 200°C for 20 hours, or maintaining the hydrothermal reaction at 220°C for 10 hours. By carrying out a one-step hydrothermal reaction in the above reaction system, on the one hand, hydrogen gas is generated by the reaction of sodium borohydride and water at high temperature, forming a porous structure; on the other hand, the hydrothermal reaction can complete the pre-sodiumization of sodium ions introduced by sodium borohydride at the molecular level; and at this temperature, Sn ions adsorbed between the Mxene layers can be anchored with carbon to form Sn-C bonds and stabilized between the layers.

[0044] In this invention, after the hydrothermal reaction, the product is further subjected to steps of filtration, washing, and drying; the drying temperature can be 80-100℃.

[0045] The present invention provides a tin-carbon composite anode material in the embodiment section, which is prepared by the above preparation method.

[0046] The tin-carbon composite anode material provided by this invention consists of a tin-carbon composite and a pre-sodiumized MXene with a porous structure coating the tin-carbon composite. This tin-carbon composite anode material not only possesses high specific capacity, but its porous pre-sodiumized MXene coating layer effectively buffers the volume expansion problem during the charging and discharging process of tin and sodium alloying. Simultaneously, the porous and layered structure of MXene provides a fast channel for sodium ion transport between layers, improving the conductivity and ion transport kinetics of the tin-carbon composite. Furthermore, the pre-sodiumized sodium on the surface of the tin-carbon composite anode material can be consumed during the formation of the SEI film, thereby reducing the consumption of active material.

[0047] The present invention also provides a negative electrode sheet in the embodiment section, comprising the above-mentioned tin-carbon composite negative electrode material.

[0048] The present invention also provides a sodium-ion battery in the embodiment section, comprising the above-mentioned negative electrode sheet.

[0049] Sodium-ion batteries constructed using the tin-carbon anode composite material prepared by this invention as the anode active material have high capacity while also exhibiting excellent cycle stability and coulombic efficiency.

[0050] The present invention will be further described below with reference to embodiments, so that those skilled in the art can better understand and implement the present invention, but the embodiments are not intended to limit the present invention.

[0051] Example 1

[0052] This embodiment relates to the preparation of a tin-carbon composite anode material, specifically including the following steps:

[0053] (1) Weigh 100mg of monolayer Ti3C2T x The powder was added to 200 mL of deionized water and sonicated in an ice bath for 1 h to obtain Ti3C2T. x Monolayer dispersion;

[0054] (2) Measure 100 mL of 0.1 mol / L SnCl4 solution and add it slowly to the Ti3C2T solution in step (1) above using a pear-shaped separatory funnel under magnetic stirring. x In a monolayer dispersion, a tin-carbon suspension was obtained by stirring at a constant speed and controlling the temperature at 25℃ for 2 hours.

[0055] (3) Measure 10g of sodium borohydride solution with a mass ratio of 0.5% and slowly add it dropwise to the tin-carbon suspension obtained in step (2) above under magnetic stirring; then transfer it to a high-pressure reactor and maintain the hydrothermal reaction at a constant temperature of 220℃ for 10h.

[0056] (4) The hydrothermal reaction product from step (3) was centrifuged and washed at 4000 r / min until the supernatant pH was 7. The supernatant was then dried at 80°C to obtain porous pre-sodiumized Ti3C2T. x Coated tin-carbon composite anode material.

[0057] The SEM image of the tin-carbon composite anode material prepared in this embodiment is shown below. Figure 1 As shown in the figure, the wrinkled material on the particle surface is pre-sodiumized two-dimensional Ti3C2T. x The material is uniformly coated on the surface of tin-carbon particles to form a tin-carbon composite material.

[0058] Example 2

[0059] This embodiment relates to the preparation of a tin-carbon composite anode material, which differs from Example 1 only in that: the single-layer Ti3C2T in step (1) is used instead of the single-layer Ti3C2T. x Powder replaced with monolayer Ni2CT x Powder; all other operations were the same, to prepare porous pre-sodiumized Ni2CT. x Coated tin-carbon composite anode material.

[0060] Example 3

[0061] This embodiment relates to the preparation of a tin-carbon composite anode material. The only difference from Example 1 is that in step (2), 10 mL of 1 mol / L SnCl4 solution is slowly titrated into the Ti3C2T in step (1) using a pear-shaped separatory funnel under magnetic stirring. x In a monolayer dispersion, the mixture was stirred at a constant speed and the temperature was controlled at 25℃ for 2 hours to obtain a tin-carbon suspension; all other operations were the same to prepare a porous pre-sodiumized Ti3C2T. x Coated tin-carbon composite anode material.

[0062] Example 4

[0063] This embodiment relates to the preparation of a tin-carbon composite anode material. The only difference from Example 1 is that the 100 mL of 0.1 mol / L SnCl4 solution in step (2) is replaced with 100 mL of 0.1 mol / L SnSO4 solution; all other operations are the same, and a porous pre-sodiumized Ti3C2T is prepared. x Coated tin-carbon composite anode material.

[0064] Example 5

[0065] This embodiment relates to the preparation of a tin-carbon composite anode material. The only difference from Example 1 is that the 0.5% sodium borohydride ethanol solution in step (3) is replaced with a 1% sodium borohydride ethanol solution; all other operations are the same, and a porous pre-sodium-treated Ti3C2T is prepared. x Coated tin-carbon composite anode material.

[0066] Example 6

[0067] This embodiment relates to the preparation of a tin-carbon composite anode material. The only difference from Example 1 is that in step (3), the hydrothermal reaction is maintained at 200°C for 20 hours; all other operations are the same, and porous pre-sodium-treated Ti3C2T is prepared. x Coated tin-carbon composite anode material.

[0068] Example 7

[0069] This embodiment relates to the preparation of a tin-carbon composite anode material, which differs from Example 1 only in that: the single-layer Ti3C2T in step (1) is used instead of the single-layer Ti3C2T. x Powder replaced with multilayer Ti3C2T x Powder; all other operations were the same, to prepare porous pre-sodiumized Ti3C2T x Coated tin-carbon composite anode material.

[0070] Comparative Example 1

[0071] This comparative example relates to the preparation of a tin-carbon composite anode material. The difference from Example 1 is that this comparative example uses tin salt and a carbon precursor (glucose) as raw materials, and synthesizes the tin-carbon composite material through sintering heat treatment. The specific preparation method is as follows:

[0072] (1) Weigh out a fixed amount of 1g glucose and 10g tin chloride and place them in a porcelain boat, then place them in a tube furnace;

[0073] (2) The temperature was increased to 1200℃ at a rate of 5℃ / min, and nitrogen was continuously filled as a protective gas during the calcination process. The holding time was 8h to obtain the tin-carbon composite material.

[0074] Comparative Example 2

[0075] This comparative example relates to the preparation of a tin-carbon composite anode material. The only difference from Example 1 is that in step (3), an equal amount and concentration of sodium chloride solution is used instead of sodium borohydride ethanol solution; all other operations are the same, and pre-sodium-treated Ti3C2T is prepared. x Coated tin-carbon composite anode material.

[0076] Comparative Example 3

[0077] This comparative example relates to the preparation of a tin-carbon composite anode material. The difference from Example 1 is that this comparative example uses tin salt and a carbon precursor (glucose) as raw materials, and synthesizes a porous pre-sodium-modified tin-carbon composite material through sintering heat treatment in the presence of sodium borohydride. The specific preparation method is as follows:

[0078] (1) Mix 100 mL each of 2 mg / mL glucose solution, 1 mg / mL sodium borohydride solution and 0.1 mol / L SnCl4 solution evenly, pour into a reaction vessel and maintain a constant temperature of 220℃ for hydrothermal reaction for 10 h;

[0079] (2) After the hydrothermal reaction, the mixture was washed and dried and then transferred to a ceramic boat. The ceramic boat was placed in a tube furnace and heated to 1200°C at a heating rate of 5°C / min. Nitrogen gas was continuously filled as a protective gas during the calcination process and the holding time was 8h to obtain a porous pre-sodium tin carbon composite material.

[0080] Comparative Example 4

[0081] This comparative example relates to the preparation of a tin-carbon composite anode material. The only difference from Example 1 is that in step (3), an equal amount and concentration of potassium borohydride ethanol solution is used instead of sodium borohydride ethanol solution; all other operations are the same, and porous Ti3C2T is prepared. x Coated tin-carbon composite anode material.

[0082] Application and performance testing

[0083] The tin-carbon composite anode material prepared in the above embodiments and comparative examples was used as the anode active material to prepare the anode sheet, and then a CR2032 button cell was assembled. The specific operation is as follows:

[0084] Preparation of negative electrode sheet: Tin-carbon composite negative electrode material, SuperP conductive agent, CMC thickener and SBR binder are mixed with water in a mass ratio of 90:5:1:4 to prepare negative electrode slurry, which is coated on aluminum foil current collector, dried at 80°C and cut into sheets for later use.

[0085] Positive electrode: Sodium metal sheet;

[0086] Electrolyte: 1.0 mol / L LiPF6, solvent is a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC) and fluoroethylene carbonate (FEC) (EC, DMC and FEC volume ratio 4.5:4.5:1);

[0087] Different CR2032 button cells were assembled in an argon glove box using different negative electrode sheets.

[0088] The initial charge-discharge capacity, cycle performance, and initial coulombic efficiency of CR2032 button cells assembled with different negative electrode plates were tested using the following methods:

[0089] First charge-discharge capacity test: Constant current charge-discharge test was performed at a current density of 100mA / g, with a voltage range of 0 to 2V, to test the first charge-discharge capacity;

[0090] Initial coulombic efficiency = (initial charge capacity / initial discharge capacity) × 100%;

[0091] Cyclic performance test: Constant current charge and discharge test was conducted at a current density of 500mA / g, with a voltage range of 0 to 2V, for 500 cycles to test the battery capacity retention rate.

[0092] The performance test results are shown in Table 1 below:

[0093] Table 1

[0094]

[0095] As shown in Table 1, the performance test results indicate that the button cell batteries prepared using the porous pre-sodium-coated MXene-coated tin-carbon composite anode material prepared in Examples 1-7 as the anode active material exhibit high reversible charging capacity, initial coulombic efficiency, and excellent cycle stability. Furthermore, Examples 1-7 demonstrate that the batteries constructed using anode materials prepared with monolayer MXene have higher charge-discharge capacity. This is because monolayer MXene is more conducive to the introduction of tin atoms compared to multilayer MXene, increasing the tin content in the tin-carbon composite anode material and thus resulting in a higher specific capacity.

[0096] Comparative Example 1 synthesized a tin-carbon composite material directly through sintering heat treatment using tin salt and a carbon precursor (glucose) as raw materials. The coin cell prepared using this tin-carbon composite material as the negative electrode active material showed significantly lower initial charge capacity, initial coulombic efficiency, and capacity retention compared to the examples described above. Comparative Example 3 used glucose instead of the carbon-containing MXene in Example 1 as the precursor carbon source, first undergoing a hydrothermal reaction followed by thermal sintering to prepare a porous pre-sodiumized tin-carbon composite material. While its initial charge capacity and initial coulombic efficiency were improved compared to Comparative Example 1, its capacity retention after 500 cycles was actually lower than that of Comparative Example 1.

[0097] As shown in Example 1 and Comparative Example 2, when sodium chloride is used instead of sodium borohydride as the sodium source (Comparative Example 2), although the tin-carbon composite material can be pre-sodiumized, it cannot effectively reduce tin ions or form a porous structure, resulting in lower initial charge capacity, lower initial coulombic efficiency, and decreased cycle performance. As shown in Example 1 and Comparative Example 4, when potassium borohydride is used instead of sodium borohydride as the reducing agent (Comparative Example 4), the initial charge capacity and initial coulombic efficiency of the coin cell constructed from the tin-carbon composite material prepared by this method are significantly reduced.

[0098] In summary, this invention uses MXene material and tin salt as raw materials, and prepares a porous tin-carbon composite material pre-sodium-coated with MXene through a subsequent hydrothermal reaction in the presence of water and sodium borohydride. This tin-carbon composite anode material not only possesses high specific capacity, but its porous pre-sodium-coated MXene coating effectively buffers the volume expansion problem during the charging and discharging process of tin and sodium alloying. Simultaneously, the porous and layered structure of MXene provides a rapid channel for sodium ion transport between layers. Furthermore, the pre-sodium-coated sodium on the surface of the tin-carbon composite anode material can be consumed during SEI film formation, thereby reducing the consumption of active materials. Thus, the battery containing this tin-carbon composite anode material exhibits high capacity, high coulombic efficiency, and excellent cycle stability.

[0099] The embodiments described above are merely preferred examples to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A method for preparing a tin-carbon composite anode material, characterized in that, Includes the following steps: (1) Disperse MXene material in water to obtain an MXene dispersion; dissolve tin salt in water to obtain a tin salt solution; the MXene material is a two-dimensional transition metal carbide and / or a two-dimensional transition metal carbonitride; the MXene material is a monolayer or few-layer MXene material; the MXene material is M n+1 X n T x Where n is any integer from 1 to 3, x > 0, M is a transition metal Sc, Ti, V, Cr, Y, Zr, Nb, Mo, Hf, Ta, W, Ni, Fe, Mn or Zn, X is C or CN, and T x The tin salt is a surface terminal group, including -OH, -O-, and -F; the tin salt is selected from one or more of SnCl4, SnCl2, and SnSO4; the concentration of the MXene dispersion is 0.1-1 mg / mL; the concentration of the tin salt solution is 0.1-1 mol / L. (2) Mix the MXene dispersion prepared in step (1) with the tin salt solution and stir to obtain a tin-carbon suspension; (3) Add sodium borohydride solution to the tin-carbon suspension prepared in step (2) and carry out hydrothermal reaction in a closed reaction vessel to prepare the tin-carbon composite anode material; the temperature of the hydrothermal reaction is 200-250 ℃ and the time of the hydrothermal reaction is 10-20 h.

2. The preparation method according to claim 1, characterized in that, The MXene material is selected from Ti2CT. x Nb2CT x V2CT x Ti3C2T x Ta4C3T x Ti4C3T x Ti3CNT x One or more of them.

3. The preparation method according to claim 1, characterized in that, The mass ratio of MXene material to tin salt is 1:(1-30); the mass ratio of sodium borohydride to tin salt is 1:(1-10).

4. The preparation method according to claim 1, characterized in that, In step (3), the sodium borohydride solution is obtained by dissolving sodium borohydride in ethanol; the mass percentage of sodium borohydride in the sodium borohydride solution is 0.5%-1%.

5. A tin-carbon composite anode material prepared by the preparation method according to any one of claims 1-4.

6. A negative electrode sheet, characterized in that, It includes the tin-carbon composite anode material as described in claim 5.

7. A sodium-ion battery, characterized in that, It includes the negative electrode sheet as described in claim 6.

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