High-rate and high-capacity MXene-based composite negative electrode material as well as preparation method and application of high-rate and high-capacity MXene-based composite negative electrode material

Abstract

The invention belongs to the technical field of negative electrode materials for sodium-ion batteries, and particularly relates to a high-rate and high-capacity MXene-based composite negative electrode material as well as a preparation method and application of the high-rate and high-capacity MXene-based composite negative electrode material. The nano silicon distributed in the pore channels of the MXene-based composite negative electrode material can effectively increase sodium storage active sites, so that the sodium storage capacity of the MXene-based composite negative electrode material is improved; the MXene-based composite negative electrode material has a large interlayer spacing, which is beneficial to shuttle of sodium ions among MXene layers, and can improve sodium ion intercalation / deintercalation kinetics; the nitrogen-containing nanocarbon embedded between the layers of the MXene-based composite negative electrode material has high conductivity, so that the accumulation phenomenon between the MXene layers can be effectively relieved, a stable and continuous electron transport network is formed, and electron transport kinetics is improved; and due to the synergistic improvement of ion transmission and electron transmission, the MXene-based composite negative electrode material is ensured to have good rate capability.

Description

Technical Field

[0001] The present invention belongs to the technical field of anode materials for sodium-ion batteries, and particularly relates to a high-rate and high-capacity MXene-based composite anode material, a preparation method thereof, and an application thereof. Background Art

[0002] With the rapid development of the electric vehicle market, the demand for lithium-ion batteries has also increased sharply. However, the lithium resources in the earth's crust are limited, which results in the high cost of lithium-ion batteries. At the same time, the working principle of sodium-ion batteries is similar to that of lithium-ion batteries, with an energy density close to that of lithium-ion batteries. Moreover, sodium-ion resources are abundant, evenly distributed, and low-cost, and are expected to be applied to large-scale energy storage devices.

[0003] In recent years, two-dimensional materials have shown great advantages in the energy storage field due to their large specific surface area, short ion transport path, etc. MXene is a type of two-dimensional layered transition metal carbide with a graphene-like structure, having a high specific surface area, good electrical conductivity, and hydrophilicity, and showing great potential in the field of anode materials for sodium-ion batteries. However, due to the aggregation or re-stacking problem between MXene interlayer nanosheets caused by van der Waals forces, the specific surface area of MXene is greatly reduced, reducing the adsorption sites of Na + Moreover, the collapse and stacking will cause a significant increase in the resistivity in the vertical interlayer direction of MXene, further hindering the transport of Na + and affecting the rate performance of the anode material. In addition, the specific capacity of MXene is relatively low, which limits its application in sodium-ion batteries. Summary of the Invention

[0004] In order to improve the deficiencies of the prior art, the present invention provides a high-rate and high-capacity MXene-based composite anode material, a preparation method thereof, and an application thereof. The MXene-based composite anode material includes porous MXene, nitrogen-containing nanocarbon, and nanosilicon; the porous MXene has a large interlayer spacing, and the interlayer spacing of the porous MXene is 1.2 - 1.5 nm; the nitrogen-containing nanocarbon is embedded in the interlayer of the porous MXene, and the nanosilicon is distributed in the pores of the porous MXene. The MXene-based composite anode material can effectively alleviate the problem of aggregation or re-stacking between MXene interlayer nanosheets. The sodium-ion battery assembled from the MXene-based composite anode material has a high specific capacity and rate performance, and also has a high initial Coulomb efficiency and cycle performance.

[0005] Specifically, the present invention provides the following technical solutions:

[0006] A preparation method of an MXene-based composite anode material, the method comprising the following steps:

[0007] (1) Add hydrogen peroxide to an aqueous solution containing MXene, react, centrifuge, and wash to prepare MXene with a porous structure;

[0008] (2) Mix the MXene with a porous structure obtained in step (1), melamine, cyanuric acid, and deionized water, and perform a hydrothermal reaction to prepare modified porous MXene1;

[0009] (3) Heat-treat the modified porous MXene1 obtained in step (2) to prepare modified porous MXene2;

[0010] (4) Use chemical vapor deposition to deposit nanosilicon in the pores of the modified porous MXene2 obtained in step (3) to prepare the MXene-based composite anode material.

[0011] According to an embodiment of the present invention, in step (1), the MXene can be prepared by a method well-known to those skilled in the art; exemplarily, the MXene can be prepared by acid etching and washing of a MAX phase material, and the MAX phase material includes Ti 3 AlC 2 、Ti 2 AlC and Ti 3 One or several of AlCN.

[0012] According to an embodiment of the present invention, in step (1), the MXene includes Ti 3 C 2 And at least one of Ti 2 C.

[0013] According to an embodiment of the present invention, in step (1), the median particle size D 50 Of the MXene is 5-10 μm, for example 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm.

[0014] According to an embodiment of the present invention, in step (1), the interlayer spacing of the MXene ≤ 1 nm.

[0015] According to an embodiment of the present invention, in step (1), the concentration of the aqueous solution containing MXene is 2-3 mg / mL, for example 2 mg / mL, 2.2 mg / mL, 2.5 mg / mL, 2.6 mg / mL, 2.8 mg / mL or 3 mg / mL.

[0016] According to an embodiment of the present invention, in step (1), the volume ratio of the hydrogen peroxide to the aqueous solution containing MXene is (15 - 30):100, for example, 15:100, 18:100, 20:100, 22:100, 24:100, 25:100, 26:100, 28:100 or 30:100.

[0017] According to an embodiment of the present invention, in step (1), the reaction is carried out under stirring conditions.

[0018] According to an embodiment of the present invention, in step (1), the reaction time is 1 - 6 hours, for example, 2 hours, 3 hours, 4 hours or 5 hours; the reaction temperature is room temperature. During the reaction process, the hydrogen peroxide and MXene undergo an oxidation reaction to increase the interlayer spacing of MXene, and at the same time, the size of the MXene flakes can be reduced to achieve the preparation of MXene with a large interlayer spacing.

[0019] According to an embodiment of the present invention, in step (1), the washing is to wash the solid component obtained after centrifugation with hydrochloric acid with a concentration of 10 - 25% and deionized water in sequence. The purpose of the washing is to remove the by-products (such as TiO 2 ) generated by the reaction of hydrogen peroxide and MXene, so as to achieve the preparation of MXene with a porous structure.

[0020] According to an embodiment of the present invention, in step (1), the median particle size D 50 of the MXene with a porous structure is 3 - 8 μm, for example, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm or 8 μm.

[0021] According to an embodiment of the present invention, in step (1), the interlayer spacing of the MXene with a porous structure is 1.2 - 1.5 nm, for example, 1.2 nm, 1.3 nm, 1.4 nm or 1.5 nm.

[0022] According to an embodiment of the present invention, in step (1), the pore structure is distributed on each MXene sheet of the MXene with a porous structure, and the pore size of the pore structure is 20 - 60 nm, for example, 20 nm, 30 nm, 40 nm, 50 nm or 60 nm.

[0023] According to an embodiment of the present invention, in step (2), the mass - volume ratio of the MXene with a porous structure to deionized water is 2 - 3 mg / mL, that is, 2 - 3 mg of the MXene with a porous structure is dispersed in 1 mL of deionized water.

[0024] According to an embodiment of the present invention, in step (2), the molar ratio of the MXene with a porous structure, melamine, and cyanuric acid is 1:1:1.

[0025] According to an embodiment of the present invention, in step (2), the temperature of the hydrothermal reaction is 180 - 220 °C, such as 180 °C, 190 °C, 200 °C, 210 °C, or 220 °C; the time of the hydrothermal reaction is 20 - 28 hours, such as 20 hours, 22 hours, 24 hours, 26 hours, or 28 hours. During the hydrothermal reaction, melamine and cyanuric acid can be inserted into the interlayer of the MXene with a porous structure, and at the same time, melamine and cyanuric acid can react and form melamine cyanurate in the interlayer of the MXene with a porous structure.

[0026] According to an embodiment of the present invention, in step (2), the modified porous MXene1 includes melamine cyanurate and MXene with a porous structure, and the melamine cyanurate is inserted into the interlayer of the MXene with a porous structure; the modified porous MXene1 is a substance formed after melamine cyanurate is inserted into the interlayer of the MXene with a porous structure.

[0027] According to an embodiment of the present invention, in step (2), the MXene with a porous structure obtained in step (1) is dispersed in deionized water and ultrasonically treated for 10 - 30 minutes; then, melamine and cyanuric acid are added to the dispersion of the MXene with a porous structure, and after mixing evenly, a hydrothermal reaction is carried out.

[0028] According to an embodiment of the present invention, in step (3), the temperature of the heat treatment is 300 - 500 °C, such as 300 °C, 320 °C, 330 °C, 350 °C, 360 °C, 380 °C, 400 °C, 420 °C, 440 °C, 450 °C, 460 °C, 480 °C, or 500 °C; the time of the heat treatment is 1 - 3 hours, such as 1 hour, 2 hours, or 3 hours.

[0029] According to an embodiment of the present invention, in step (3), after the heat treatment, it is preferably cooled naturally to room temperature.

[0030] According to an embodiment of the present invention, in step (3), the heat treatment is carried out in a nitrogen atmosphere or an argon atmosphere.

[0031] According to an embodiment of the present invention, in step (3), during the heat treatment, melamine cyanurate is thermally decomposed into nitrogen-containing nanocarbon.

[0032] According to an embodiment of the present invention, in step (3), the modified porous MXene2 includes nitrogen-containing nanocarbon and MXene with a porous structure, and the nitrogen-containing nanocarbon is inserted into the interlayer of the MXene with a porous structure; the modified porous MXene2 is a substance formed by inserting melamine cyanurate into the interlayer of the MXene with a porous structure and then performing heat treatment.

[0033] According to an embodiment of the present invention, in step (4), the chemical vapor deposition method includes:

[0034] First, put the modified porous MXene2 of step (3) into a chemical vapor deposition furnace, introduce nitrogen gas, then raise the temperature of the chemical vapor deposition furnace and introduce silane gas at this temperature and keep it warm for a certain period of time. The silane gas decomposes into nano-silicon. After the heat preservation time is reached, stop introducing the silane gas and cool it to room temperature with the furnace, and stop introducing nitrogen gas to achieve the preparation of the MXene-based composite negative electrode material.

[0035] According to an embodiment of the present invention, in step (4), the chemical vapor deposition method includes:

[0036] First, at room temperature, put the modified porous MXene2 of step (3) into a chemical vapor deposition furnace, introduce nitrogen gas for 20 - 40 minutes to replace the air in the chemical vapor deposition furnace, then raise the temperature of the chemical vapor deposition furnace to 450 - 650 °C and introduce silane gas at this temperature and keep it warm for 1 - 3 hours. The silane gas decomposes into nano-silicon. After the heat preservation time is reached, stop introducing the silane gas and cool it to room temperature with the furnace, and stop introducing nitrogen gas to achieve the preparation of the MXene-based composite negative electrode material.

[0037] According to an embodiment of the present invention, in step (4), the flow rate of the silane gas is 100 - 200 sccm, for example, 100 sccm, 120 sccm, 130 sccm, 150 sccm, 160 sccm, 180 sccm or 200 sccm.

[0038] According to an embodiment of the present invention, in step (4), the flow rate of the nitrogen gas is 100 - 200 sccm, for example, 100 sccm, 120 sccm, 130 sccm, 150 sccm, 160 sccm, 180 sccm or 200 sccm.

[0039] According to an embodiment of the present invention, in step (4), the mass-volume ratio of the silane gas to the modified porous MXene2 of step (3) is 5 - 20 L / g, that is, 5 - 20 L of silane gas is introduced into 1 g of the modified porous MXene2 of step (3).

[0040] According to an embodiment of the present invention, in step (4), the silane gas is silane or disilane.

[0041] According to an embodiment of the present invention, in step (4), the chemical vapor deposition method is carried out in a chemical vapor deposition furnace.

[0042] According to an embodiment of the present invention, through the chemical vapor deposition method, the silane gas can enter more fully into the pores of the modified porous MXene2, which is beneficial to the uniform dispersion of nanosilicon in the pores of the modified porous MXene2.

[0043] The present invention also provides an MXene-based composite anode material prepared by the above method.

[0044] According to an embodiment of the present invention, the MXene-based composite anode material includes MXene with a porous structure, nitrogen-containing nanocarbon, and nanosilicon. Preferably, the MXene-based composite anode material is a composite of MXene with a porous structure, nitrogen-containing nanocarbon, and nanosilicon.

[0045] According to an embodiment of the present invention, the mass of the MXene with a porous structure accounts for 60%-80% of the total mass of the MXene-based composite anode material, such as 60%, 62%, 65%, 68%, 70%, 72%, 75%, 78%, or 80%.

[0046] According to an embodiment of the present invention, the mass of the nitrogen-containing nanocarbon accounts for 1%-10% of the total mass of the MXene-based composite anode material, such as 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%.

[0047] According to an embodiment of the present invention, the mass of the nanosilicon accounts for 5%-20% of the total mass of the MXene-based composite anode material, such as 5%, 6%, 8%, 10%, 12%, 15%, 16%, 18%, or 20%. When the mass fraction of the nanosilicon is less than 5%, the capacity of the battery will be low. When the mass fraction of the nanosilicon is higher than 20%, the cycling performance of the battery will decline.

[0048] According to an embodiment of the present invention, the nitrogen-containing nanocarbon is embedded between the layers of the MXene with a porous structure, which can effectively alleviate the stacking phenomenon between the MXene sheets and improve the rate performance of the MXene-based composite anode material; the nanosilicon is distributed in the pores of the MXene with a porous structure, which can effectively improve the capacity of the MXene-based composite anode material.

[0049] According to an embodiment of the present invention, the median particle size D of the MXene-based composite anode material 50It is 3-6 μm, for example, 3 μm, 4 μm, 5 μm or 6 μm.

[0050] According to an embodiment of the present invention, the interlayer spacing of the MXene-based composite anode material is 1.2-1.5 nm, for example, 1.2 nm, 1.3 nm, 1.4 nm or 1.5 nm.

[0051] The present invention also provides a use of the above MXene-based composite anode material, which is used to prepare the anode of a sodium-ion battery.

[0052] The present invention also provides an anode of a sodium-ion battery, which includes the above MXene-based composite anode material.

[0053] The present invention also provides a sodium-ion battery, which includes the above MXene-based composite anode material or the anode of the above sodium-ion battery.

[0054] Advantages of the present invention:

[0055] The present invention first uses a chemical oxidation method to increase the interlayer spacing of MXene and at the same time reduce the size of MXene flakes; then pickling and pore-forming are carried out on the oxidation product to obtain porous MXene; subsequently, melamine and cyanuric acid are inserted into the layers of porous MXene under hydrothermal conditions to obtain a modified material with melamine cyanurate inserted into the interlayers of porous MXene, and then the melamine cyanurate is calcined into nitrogen-containing nanocarbon by a heat treatment process to obtain a modified material with nitrogen-containing nanocarbon inserted into the interlayers of porous MXene; finally, silane gas is used as a silicon source, and the gas-phase chemical deposition method of the present invention is used to make the silicon source fully infiltrate into the pores of the modified material with nitrogen-containing nanocarbon inserted into the interlayers of porous MXene; the obtained MXene-based composite anode material has high rate performance and high capacity.

[0056] The MXene-based composite anode material has the following advantages:

[0057] (1) High sodium storage capacity. The nano-silicon distributed in the pores of the MXene-based composite anode material can effectively increase the sodium storage active sites, thereby improving the sodium storage capacity of the MXene-based composite anode material;

[0058] (2) Excellent electrochemical performance. The MXene-based composite anode material has a large interlayer spacing, which is beneficial for the shuttling of sodium ions between MXene layers and can improve the kinetics of sodium ion insertion / extraction. The nitrogen-containing nanocarbon embedded between the layers of the MXene-based composite anode material has high conductivity, which can effectively alleviate the stacking phenomenon between MXene layers, form a stable and continuous electron transport network, and improve the electron transport kinetics. Due to the synergistic improvement of ion transport and electron transport, the MXene-based composite anode material has good rate performance. Detailed implementation mode

[0059] The preparation method of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are only illustrative explanations of the present invention and should not be construed as limiting the protection scope of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0060] Unless otherwise specified, the experimental methods used in the following embodiments are all conventional methods; the reagents, materials, etc. used in the following embodiments can be obtained from commercial channels unless otherwise specified.

[0061] The MXene in the following embodiments and comparative examples is Ti 3 C 2 , the interlayer spacing is 0.92 nm, D 50 is 8 μm, and the concentration of the aqueous solution containing MXene is 2.2 mg / mL.

[0062] Example 1

[0063] (1) Add 15 mL of hydrogen peroxide to 100 mL of the aqueous solution containing MXene. After continuously stirring at room temperature for 3 h, centrifuge and wash successively with 15% hydrochloric acid and deionized water to obtain porous MXene (interlayer spacing is 1.25 nm, D 50 is 8 μm, and the pore diameter is 50 nm);

[0064] (2) Disperse 64 g of the porous MXene obtained in step (1) into 26 L of deionized water, ultrasonically treat for 15 minutes, add 126 g of melamine and 129 g of cyanuric acid, stir evenly, perform hydrothermal treatment at 200 °C for 20 hours, centrifuge, and wash with deionized water to obtain modified porous MXene1;

[0065] (3) Heat-treat the modified porous MXene1 obtained in step (2) in a nitrogen atmosphere at 380 °C for 1.5 hours, and then cool to room temperature to obtain modified porous MXene2;

[0066] (4) At room temperature, place 10 g of the modified porous MXene2 from step (3) into the reaction chamber of a chemical vapor deposition furnace. Introduce nitrogen gas (flow rate: 150 sccm) into the reaction chamber for 30 minutes to displace the air in the chemical vapor deposition furnace. Then, raise the temperature of the reaction chamber to 500 °C and introduce silane gas at this temperature with a silane flow rate of 150 sccm. Keep the temperature for 1 hour. After the holding time, stop introducing silane gas and cool it to room temperature with the furnace, and then stop introducing nitrogen gas to obtain the MXene-based composite anode material.

[0067] Example 2

[0068] (1) Add 20 mL of hydrogen peroxide to 100 mL of an aqueous solution containing MXene. Continuously stir at room temperature for 4 h, then centrifuge and wash successively with 20% hydrochloric acid and deionized water to obtain porous MXene (interlayer spacing: 1.3 nm, D 50 is 7 μm, pore diameter is 45 nm);

[0069] (2) Disperse 64 g of the porous MXene from step (1) into 26 L of deionized water, ultrasonically treat for 15 minutes, add 126 g of melamine and 129 g of cyanuric acid, stir evenly, perform hydrothermal treatment at 180 °C for 28 hours, centrifuge, and wash with deionized water to obtain modified porous MXene1;

[0070] (3) Heat-treat the modified porous MXene1 from step (2) in a nitrogen atmosphere at 350 °C for 2 hours, then cool to room temperature to obtain modified porous MXene2;

[0071] (4) At room temperature, place 10 g of the modified porous MXene2 from step (3) into the reaction chamber of a chemical vapor deposition furnace. Introduce nitrogen gas (flow rate: 100 sccm) into the reaction chamber for 30 minutes to displace the air in the chemical vapor deposition furnace. Then, raise the temperature of the reaction chamber to 550 °C and introduce silane gas at this temperature with a silane flow rate of 100 sccm. Keep the temperature for 1.5 hours. After the holding time, stop introducing silane gas and cool it to room temperature with the furnace, and then stop introducing nitrogen gas to obtain the MXene-based composite anode material.

[0072] Example 3

[0073] (1) Add 25 mL of hydrogen peroxide to 100 mL of an aqueous solution containing MXene. Continuously stir at room temperature for 3 h, then centrifuge and wash successively with 25% hydrochloric acid and deionized water to obtain porous MXene (interlayer spacing: 1.4 nm, D 50 is 6 μm, pore diameter is 40 nm);

[0074] (2) Disperse 64 g of the MXene with a porous structure obtained in step (1) into 26 L of deionized water, ultrasonically treat for 15 minutes, add 126 g of melamine and 129 g of cyanuric acid, stir evenly, perform hydrothermal treatment at 180 °C for 20 hours, centrifuge, and wash with deionized water to obtain modified porous MXene1;

[0075] (3) After heat-treating the modified porous MXene1 obtained in step (2) in a nitrogen atmosphere at 380 °C for 1.5 hours, cool it to room temperature to obtain modified porous MXene2;

[0076] (4) At room temperature, place 10 g of the modified porous MXene2 obtained in step (3) in the reaction chamber of a chemical vapor deposition furnace. Introduce nitrogen gas (flow rate: 200 sccm) into the reaction chamber for 30 minutes to replace the air in the chemical vapor deposition furnace. Then raise the temperature of the reaction chamber to 650 °C and introduce silane gas at this temperature. The flow rate of silane gas is 200 sccm, keep it warm for 1 hour. After the holding time, stop introducing silane gas and cool it to room temperature with the furnace, and stop introducing nitrogen gas to obtain the MXene-based composite negative electrode material.

[0077] Comparative Example 1

[0078] (1) Add 15 mL of hydrogen peroxide to 100 mL of an aqueous solution containing MXene. Continuously stir at room temperature for 3 h, then centrifuge, and wash successively with 15% hydrochloric acid and deionized water to obtain MXene with a porous structure (interlayer spacing is 1.25 nm, D 50 is 8 μm, pore size is 50 nm);

[0079] (2) Disperse 64 g of the MXene with a porous structure obtained in step (1) into 26 L of deionized water, ultrasonically treat for 15 minutes, add 126 g of melamine and 129 g of cyanuric acid, stir evenly, perform hydrothermal treatment at 200 °C for 20 hours, centrifuge, and wash with deionized water to obtain modified porous MXene1;

[0080] (3) After heat-treating the modified porous MXene1 obtained in step (2) in a nitrogen atmosphere at 380 °C for 1.5 hours, cool it to room temperature to obtain the MXene-based composite negative electrode material.

[0081] Comparative Example 2

[0082] (1) Add 15 mL of hydrogen peroxide to 100 mL of an aqueous solution containing MXene. Continuously stir at room temperature for 3 h, then centrifuge, and wash successively with 15% hydrochloric acid and deionized water to obtain MXene with a porous structure (interlayer spacing is 1.25 nm, D 50 is 8 μm, pore size is 50 nm);

[0083] (2) At room temperature, place 10 g of the MXene with a porous structure obtained in step (1) into the reaction chamber of a chemical vapor deposition furnace. Introduce nitrogen gas (flow rate: 150 sccm) into the reaction chamber for 30 minutes to displace the air in the chemical vapor deposition furnace. Then, raise the temperature of the reaction chamber to 500 °C and introduce silane gas at this temperature with a flow rate of 150 sccm. Keep the temperature for 1 hour. After the holding time, stop introducing silane gas and cool it to room temperature with the furnace, and then stop introducing nitrogen gas to obtain the MXene-based composite anode material.

[0084] Comparative Example 3

[0085] (1) Disperse 64 g of MXene into 26 L of deionized water, ultrasonically treat for 15 minutes, add 126 g of melamine and 129 g of cyanuric acid, stir evenly, perform hydrothermal treatment at 200 °C for 20 hours, centrifuge, and wash with deionized water to obtain modified MXene1.

[0086] (2) After heat-treating the modified MXene1 obtained in step (1) in a nitrogen atmosphere at 380 °C for 1.5 hours, cool it to room temperature to obtain modified MXene2.

[0087] (3) At room temperature, place 10 g of the modified MXene2 obtained in step (2) into the reaction chamber of a chemical vapor deposition furnace. Introduce nitrogen gas (flow rate: 150 sccm) into the reaction chamber for 30 minutes to displace the air in the chemical vapor deposition furnace. Then, raise the temperature of the reaction chamber to 850 °C and introduce silane gas at this temperature with a flow rate of 150 sccm. Keep the temperature for 1 hour. After the holding time, stop introducing silane gas and cool it to room temperature with the furnace, and then stop introducing nitrogen gas to obtain the MXene-based composite anode material.

[0088] Test Example 1

[0089] Use the MXene-based composite anode materials prepared in the above examples and comparative examples as the anode materials of sodium-ion batteries, and conduct electrochemical performance tests. The method is as follows:

[0090] MXene-based composite negative electrode material, conductive agent SuperP, binder sodium carboxymethyl cellulose (CMC) and aqueous binder (SBR) were weighed in a mass ratio of 95:2:1.5:1.5, and after being fully ground in an agate mortar, a small amount of deionized water was added to mix to form a uniform black paste slurry. The black paste slurry was coated on a copper foil current collector as a test electrode, and a metal sodium sheet was used as a reference electrode to assemble into a button cell. The electrolyte was 1M sodium hexafluorophosphate dissolved in a mixed solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1:1, 5wt% of fluoroethylene carbonate (FEC) was added to the electrolyte as an additive, glass fiber was used as a separator, and CR2032 stainless steel was used as a battery shell to assemble into a button cell, and the capacity and first coulombic efficiency were tested at a constant rate of 0.1C in a voltage range of 0.01-3.0V.

[0091] Battery rate performance and cycle performance test: Place the sodium ion battery in an environment of 25°C, charge it to 4.0V at a constant current and constant voltage of (1C-3C), with a cut-off current of 0.05C, and discharge it to 1.5V at a constant current of 0.7C. This step of charge and discharge is recorded as one cycle. Repeat this cycle until the capacity retention rate is less than 80%, and record the number of cycles.

[0092] Table 1 Electrochemical performance of MXene-based composite anode materials

[0093]

[0094] As can be seen from Table 1, the MXene-based composite negative electrode material prepared in the present invention has high capacity, first coulombic efficiency, rate performance and cycle performance.

[0095] Comparative Example 1 did not utilize silane chemical vapor deposition to modify the porous MXene2, that is, there was no nano-silicon in the pores of the obtained MXene-based composite negative electrode material, resulting in a significant reduction in the capacity, first coulombic efficiency and cycle performance of the prepared MXene-based composite negative electrode material.

[0096] Comparative Example 2 did not use hydrothermal treatment to insert melamine and cyanuric acid into the interlayer of MXene, that is, there was no nitrogen-containing nanocarbon between the MXene layers, resulting in reduced conductivity of the MXene-based composite negative electrode material and reduced rate performance of the battery. In addition, the charge and discharge process easily caused the aggregation or restacking of the MXene interlayer nanosheets, resulting in reduced cycle performance and rate performance of the battery.

[0097] In Comparative Example 3, MXene was not exfoliated with hydrogen peroxide, resulting in a small interlayer spacing of the MXene-based composite anode material, which caused a significant reduction in the rate performance and cycling performance of the MXene-based composite anode material; at the same time, since MXene was not pore-formed with hydrogen peroxide, the pore channels of the MXene-based composite anode material were small and could not accommodate more nanosilicon, resulting in a reduction in the capacity of the MXene-based composite anode material.

[0098] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a MXene-based composite negative electrode material, the method comprising the following steps: (1) adding hydrogen peroxide to an aqueous solution containing MXene, reacting, centrifuging, and washing to prepare MXene with a porous structure; (2) mixing the MXene with a porous structure prepared in step (1), melamine, cyanuric acid and deionized water, and performing a hydrothermal reaction to prepare a modified porous MXene 1; (3) heat treating the modified porous MXene1 prepared in step (2) to obtain modified porous MXene2; (4) Using chemical vapor deposition, nano-silicon is deposited in the pores of the modified porous MXene2 in step (3) to prepare the MXene-based composite negative electrode material.

2. The method according to claim 1, wherein: In step (1), the MXene includes at least one of Ti3C2 and Ti2C; And / or, in step (1), the median particle size D of the MXene 50 5-10μm; And / or, in step (1), the interlayer spacing of the MXene is ≤1 nm; And / or, in step (1), the volume ratio of hydrogen peroxide to the aqueous solution containing MXene is (15-30):100; And / or, in step (1), the washing is washing the solid component obtained after centrifugal separation with hydrochloric acid and deionized water in a concentration of 10-25% in sequence; And / or, in step (1), the median particle size D of the MXene having a porous structure is 50 3-8μm; And / or, in step (1), the interlayer spacing of the MXene having a porous structure is 1.2-1.5 nm; And / or, in step (1), each MXene layer of the MXene having a porous structure is distributed with a pore structure, and the pore size of the pore structure is 20-60 nm.

3. The method according to claim 1 or 2, wherein: In step (2), the mass volume ratio of the MXene having a porous structure to deionized water is 2-3 mg / mL; And / or, in step (2), the molar ratio of the MXene having a porous structure, melamine and cyanuric acid is 1:1:1; And / or, in step (2), the temperature of the hydrothermal reaction is 180-220° C.; the time of the hydrothermal reaction is 20-28 hours; And / or, in step (2), the modified porous MXene1 includes melamine cyanuric acid and a MXene with a porous structure, and the melamine cyanuric acid is inserted into the interlayer of the MXene with a porous structure; the modified porous MXene1 is a substance formed after melamine cyanuric acid is inserted into the interlayer of the MXene with a porous structure. Preferably, in step (3), the temperature of the heat treatment is 300-500° C.; the time of the heat treatment is 1-3 hours; And / or, in step (3), the modified porous MXene2 includes nitrogen-containing nanocarbon and MXene with a porous structure, and the nitrogen-containing nanocarbon is inserted into the interlayer of the MXene with a porous structure; the modified porous MXene2 is a substance formed by inserting melamine cyanuric acid into the interlayer of the MXene with a porous structure and then subjecting it to heat treatment.

4. The method according to any one of claims 1 to 3, wherein: In step (4), the chemical vapor deposition method comprises: First, the modified porous MXene2 of step (3) is placed in a chemical vapor deposition furnace, and nitrogen is introduced. Then, the temperature of the chemical vapor deposition furnace is increased and silane gas is introduced at this temperature and kept warm for a certain period of time. The silane gas is decomposed into nano-silicon. After the insulation time is reached, the introduction of silane gas is stopped and the furnace is cooled to room temperature. The introduction of nitrogen is stopped to achieve the preparation of the MXene-based composite negative electrode material. Preferably, in step (4), the chemical vapor deposition method comprises: First, the modified porous MXene2 of step (3) is placed in a chemical vapor deposition furnace at room temperature, and nitrogen is introduced for 20-40 minutes to replace the air in the chemical vapor deposition furnace. Then, the temperature of the chemical vapor deposition furnace is increased to 450-650°C and silane gas is introduced at this temperature and kept warm for 1-3 hours. The silane gas is decomposed into nano-silicon. After the insulation time is up, the introduction of silane gas is stopped and the furnace is cooled to room temperature. The introduction of nitrogen is stopped to achieve the preparation of the MXene-based composite negative electrode material. Preferably, in step (4), the flow rate of the silane gas is 100-200 sccm; And / or, in step (4), the mass volume ratio of the silane gas to the modified porous MXene2 of step (3) is 5-20 L / g; And / or, in step (4), the silane gas is monosilane or disilane.

5. A MXene-based composite negative electrode material prepared by the method according to any one of claims 1 to 4.

6. The MXene-based composite negative electrode material according to claim 5, wherein: The MXene-based composite negative electrode material includes MXene with a porous structure, nitrogen-containing nanocarbon and nanosilicon. Preferably, the MXene-based composite negative electrode material is a composite of MXene with a porous structure, nitrogen-containing nanocarbon and nanosilicon. Preferably, the mass of the MXene with a porous structure accounts for 60%-80% of the total mass of the MXene-based composite negative electrode material; the mass of the nitrogen-containing nanocarbon accounts for 1%-10% of the total mass of the MXene-based composite negative electrode material; the mass of the nano-silicon accounts for 5%-20% of the total mass of the MXene-based composite negative electrode material.

7. The MXene-based composite negative electrode material according to claim 5 or 6, wherein: The nitrogen-containing nano-carbon is embedded in the interlayers of the MXene with a porous structure; and the nano-silicon is distributed in the pores of the MXene with a porous structure. Preferably, the median particle size D of the MXene-based composite negative electrode material is 50 3-6μm. Preferably, the interlayer spacing of the MXene-based composite negative electrode material is 1.2-1.5 nm.

8. A use of the MXene-based composite negative electrode material according to any one of claims 5 to 7 for preparing a negative electrode for a sodium ion battery.

9. A negative electrode for a sodium ion battery, comprising the MXene-based composite negative electrode material according to any one of claims 5 to 7.

10. A sodium ion battery, comprising the MXene-based composite negative electrode material according to any one of claims 5 to 7 or the negative electrode of the sodium ion battery according to claim 9.

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