High-rate MXene-based composite negative electrode material and preparation method and application thereof

Abstract

The invention belongs to the technical field of negative electrode materials for sodium-ion batteries, and particularly relates to a high-rate MXene-based composite negative electrode material as well as a preparation method and application thereof. The hard carbon distributed on the surface and 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 and the first coulombic efficiency of the MXene-based composite negative electrode material are 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 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 has caused the cost of lithium-ion batteries to remain high. 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, and 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 and short ion transport path. 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 direction perpendicular to the MXene interlayer, further hindering the transport of Na + and affecting the rate performance of the anode material. Summary of the Invention

[0004] In order to improve the deficiencies of the prior art, the present invention provides a high-rate 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 hard carbon; 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 hard carbon is distributed on the surface and in the pores of the porous MXene. The MXene-based composite anode material can effectively alleviate the aggregation or re-stacking problem between MXene interlayer nanosheets, and the sodium-ion battery assembled from the MXene-based composite anode material has high rate performance and cycling 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) Add the modified porous MXene2 obtained in step (3) to a reaction kettle, evacuate the reaction kettle, add an organic resin solution, perform pressure impregnation, and after the pressure impregnation is completed, reduce the pressure to make the pressure inside and outside the reaction kettle the same, then introduce nitrogen and heat to remove the organic solvent to obtain modified MXene3.

[0011] (5) Carbonize the modified MXene3 obtained in step (4) to prepare the MXene-based composite negative electrode material.

[0012] 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 more of AlCN.

[0013] According to an embodiment of the present invention, in step (1), the MXene includes Ti 3 C 2 and Ti 2 At least one of C.

[0014] 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.

[0015] According to an embodiment of the present invention, in step (1), the interlayer spacing of the MXene ≤ 1 nm.

[0016] 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.

[0017] 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.

[0018] According to an embodiment of the present invention, in step (1), the reaction is carried out under stirring conditions.

[0019] 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 undergoes an oxidation reaction with MXene to increase the interlayer spacing of MXene, and at the same time, it can also reduce the size of MXene flakes to achieve the preparation of MXene with a large interlayer spacing.

[0020] According to an embodiment of the present invention, in step (1), the washing is carried out by washing 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, thereby achieving the preparation of MXene with a porous structure.

[0021] According to an embodiment of the present invention, in step (1), the median particle size D of the MXene with a porous structure 50 is 3 - 8 μm, for example, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm or 8 μm.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] According to an embodiment of the present invention, in step (2), the molar ratio of the porous-structured MXene, melamine, and cyanuric acid is 1:1:1.

[0026] 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 porous-structured MXene, and at the same time, melamine and cyanuric acid can react and form melamine cyanurate in the interlayer of the porous-structured MXene.

[0027] According to an embodiment of the present invention, in step (2), the modified porous MXene1 includes melamine cyanurate and porous-structured MXene, and the melamine cyanurate is inserted into the interlayer of the porous-structured MXene; the modified porous MXene1 is a substance formed after melamine cyanurate is inserted into the interlayer of the porous-structured MXene.

[0028] According to an embodiment of the present invention, in step (2), the porous-structured MXene 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 porous-structured MXene, and after mixing evenly, a hydrothermal reaction is carried out.

[0029] 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.

[0030] According to an embodiment of the present invention, in step (3), after the heat treatment, it is preferably naturally cooled to room temperature.

[0031] 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.

[0032] According to an embodiment of the present invention, in step (3), during the heat treatment, melamine cyanurate is thermally decomposed into nitrogen-containing nanocarbon.

[0033] 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.

[0034] According to an embodiment of the present invention, in step (4), the vacuum degree of the reaction kettle is 0.07 - 0.09 MPa, for example, 0.07 MPa, 0.08 MPa or 0.09 MPa.

[0035] According to an embodiment of the present invention, in step (4), the time for evacuating the reaction kettle is 10 - 120 min, that is, the time for maintaining the vacuum degree is 10 - 120 min, for example, 10 min, 20 min, 30 min, 50 min, 60 min, 80 min, 100 min or 120 min.

[0036] According to an embodiment of the present invention, in step (4), the organic resin is selected from at least one of petroleum-based resins (such as petroleum-based resin C5 and / or petroleum-based resin C9), phenolic resins, epoxy resins, starches, glucose, and cellulose.

[0037] According to an embodiment of the present invention, in step (4), the organic solvent is selected from hydrocarbon solvents, for example, at least one of wash oil, naphthalene oil, and phenol oil.

[0038] According to an embodiment of the present invention, in step (4), the mass ratio of the organic resin to the modified porous MXene2 is (10 - 30):100, preferably (15 - 25):100, for example, 10:100, 15:100, 20:100, 25:100 or 30:100.

[0039] According to an embodiment of the present invention, in step (4), the mass ratio of the organic solvent to the modified porous MXene2 is (10 - 50):100, preferably (20 - 40):100, for example, 10:100, 15:100, 20:100, 25:100, 30:100, 35:100, 40:100, 45:100 or 50:100.

[0040] According to an embodiment of the present invention, in step (4), after adding the organic resin solution, the mixing system is stirred, and the rotation speed of the stirring is 20 - 80 r / min, for example, 20 r / min, 30 r / min, 40 r / min, 50 r / min, 60 r / min, 70 r / min or 80 r / min.

[0041] According to an embodiment of the present invention, in step (4), the method of adding the organic resin solution is, for example: open the suction valve of the organic resin solution, suck the organic resin solution into the reaction kettle, close the suction valve after the liquid feeding is completed, and stop vacuum pumping.

[0042] According to an embodiment of the present invention, in step (4), the pressure of the pressure impregnation is 1 MPa - 3 MPa, and the time of the pressure impregnation is 1 - 5 hours, for example, 2 hours, 3 hours, or 4 hours.

[0043] According to an embodiment of the present invention, in step (4), the temperature of the heating is 200 - 300 °C; the time of the heating is not particularly defined, and it is sufficient until the organic solvent is completely removed.

[0044] According to an embodiment of the present invention, in step (5), the temperature of the carbonization treatment is 1000 - 1400 °C, for example, 1000 °C, 1050 °C, 1100 °C, 1150 °C, 1200 °C, 1250 °C, 1300 °C, 1350 °C, or 1400 °C; the time of the carbonization treatment is 4 - 10 hours, for example, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, or 10 hours.

[0045] According to an embodiment of the present invention, in step (5), the carbonization treatment is carried out in a nitrogen atmosphere or an argon atmosphere.

[0046] The present invention also provides an MXene-based composite negative electrode material prepared by the above method.

[0047] According to an embodiment of the present invention, the MXene-based composite negative electrode material includes porous MXene, nitrogen-containing nanocarbon, and hard carbon. Preferably, the MXene-based composite negative electrode material is a composite of porous MXene, nitrogen-containing nanocarbon, and hard carbon.

[0048] According to an embodiment of the present invention, the mass of the porous MXene accounts for 75% - 85% of the total mass of the MXene-based composite negative electrode material, for example, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, or 85%.

[0049] According to an embodiment of the present invention, the mass of the nitrogen-containing nanocarbon accounts for 1% - 5% of the total mass of the MXene-based composite negative electrode material, for example, 1%, 2%, 3%, 4%, or 5%.

[0050] According to an embodiment of the present invention, the mass of the hard carbon accounts for 3% - 10% of the total mass of the MXene-based composite negative electrode material, for example, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%.

[0051] According to an embodiment of the present invention, the nitrogen-containing nanocarbon is embedded between the layers of the MXene having 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 hard carbon is uniformly distributed on the surface and in the pores of the MXene having a porous structure, and at the same time, the introduction of the hard carbon can also effectively improve the capacity and initial Coulomb efficiency of the MXene-based composite anode material.

[0052] According to an embodiment of the present invention, the MXene-based composite anode material has a core-shell structure, including a core and a shell layer; the core includes MXene having a porous structure, nitrogen-containing nanocarbon, and hard carbon, the nitrogen-containing nanocarbon is embedded between the layers of the MXene having a porous structure, and the hard carbon is uniformly distributed in the pores of the MXene having a porous structure; the shell layer includes hard carbon.

[0053] According to an embodiment of the present invention, the thickness of the shell layer is 10-30 nm, such as 10 nm, 12 nm, 15 nm, 18 nm, 20 nm, 22 nm, 24 nm, 25 nm, 26 nm, 28 nm or 30 nm.

[0054] According to an embodiment of the present invention, the median particle size D of the MXene-based composite anode material 50 is 3-6 μm, such as 3 μm, 4 μm, 5 μm or 6 μm.

[0055] According to an embodiment of the present invention, the interlayer spacing of the MXene-based composite anode material is 1.2-1.5 nm, such as 1.2 nm, 1.3 nm, 1.4 nm or 1.5 nm.

[0056] 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.

[0057] The present invention also provides an anode of a sodium-ion battery, which includes the above MXene-based composite anode material.

[0058] 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.

[0059] Advantages of the present invention:

[0060] The present invention first increases the interlayer spacing of MXene and reduces the size of MXene flakes by means of chemical oxidation; 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 lamellae of the porous MXene under hydrothermal conditions to obtain a modified material with melamine cyanurate inserted into the interlayer of the porous MXene, and then the melamine cyanurate is calcined into nitrogen-containing nanocarbon by means of a heat treatment process to obtain a modified material with nitrogen-containing nanocarbon inserted into the interlayer of the porous MXene; finally, the air inside the modified porous MXene2 is discharged under vacuum conditions. Under high pressure, the organic resin solution can not only coat the surface of the modified porous MXene2, but also enter the pores of the modified porous MXene2. The subsequent carbonization process converts the organic resin into hard carbon, thereby ensuring that the hard carbon is embedded in the pores of the porous MXene, and at the same time, a hard carbon coating layer can be formed on the surface of the porous MXene, further improving the capacity and initial Coulomb efficiency of the MXene-based composite anode material.

[0061] The MXene-based composite anode material has the following advantages:

[0062] (1) High sodium storage capacity and initial Coulomb efficiency. The hard carbon distributed on the surface and in the pores of the MXene-based composite anode material can effectively increase the sodium storage active sites, thereby improving the sodium storage capacity and initial Coulomb efficiency of the MXene-based composite anode material;

[0063] (2) Excellent electrochemical performance. The MXene-based composite anode material has a large interlayer spacing, which is conducive to the shuttle of sodium ions between the MXene layers and can improve the sodium ion insertion / extraction kinetics; the nitrogen-containing nanocarbon embedded in the interlayer of the MXene-based composite anode material has high conductivity, which can effectively alleviate the stacking phenomenon between the 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. Specific Embodiments

[0064] 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 used to illustrate and explain the present invention exemplarily 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.

[0065] The experimental methods used in the following embodiments are all conventional methods unless otherwise specified; the reagents, materials, etc. used in the following embodiments can all be obtained from commercial channels unless otherwise specified.

[0066] In the following examples and comparative examples, the MXene is Ti 3 C 2 , with an interlayer spacing of 0.92 nm, D 50 is 8 μm, and the concentration of the aqueous solution containing MXene is 2.2 mg / mL.

[0067] Example 1

[0068] (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 MXene with a porous structure (interlayer spacing of 1.25 nm, D 50 is 8 μm, and pore size is 50 nm);

[0069] (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;

[0070] (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;

[0071] (4) Put 10 g of the modified porous MXene2 obtained in step (3) into a reaction kettle, evacuate for 60 min. When the vacuum degree of the reaction kettle reaches 0.07 MPa, open the suction valve of the phenolic resin wash oil solution (formed by dissolving 1.5 g of phenolic resin in 3 g of wash oil), suck all the solution into the reaction kettle. After the liquid inlet is completed, close the suction valve and stop evacuating. At the same time, stir the mixed liquid at a high speed (20 r / min) for 40 min, impregnate under pressure (1.5 MPa). After impregnation is completed, reduce the pressure to make the pressure inside and outside the reaction kettle the same, and then introduce nitrogen and heat to 230 °C to remove the wash oil to obtain modified MXene3;

[0072] (5) Carbonize the modified MXene3 obtained in step (4) under nitrogen protection at a temperature of 1000 °C for 5 hours, and then cool to room temperature to obtain the MXene-based composite negative electrode material.

[0073] Example 2

[0074] (1) Add 20 mL of hydrogen peroxide to 100 mL of the aqueous solution containing MXene. After continuously stirring at room temperature for 4 h, centrifuge and wash successively with 20% hydrochloric acid and deionized water to obtain MXene with a porous structure (interlayer spacing of 1.3 nm, D 50 is 7 μm, and pore size is 45 nm);

[0075] (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 180 °C for 28 hours, centrifuge, and wash with deionized water to obtain modified porous MXene1;

[0076] (3) After heat-treating the modified porous MXene1 obtained in step (2) in a nitrogen atmosphere at 350 °C for 2 hours, cool it to room temperature to obtain modified porous MXene2;

[0077] (4) Put 10 g of the modified porous MXene2 obtained in step (3) into a reaction kettle, evacuate for 60 min. When the vacuum degree of the reaction kettle reaches 0.07 MPa, open the suction valve of the phenolic resin naphthalene oil solution (formed by dissolving 1.5 g of phenolic resin in 3 g of naphthalene oil), suck all the solution into the reaction kettle. After the liquid inlet is completed, close the suction valve and stop evacuating. At the same time, stir the mixed liquid at a high speed (20 r / min) for 40 min, impregnate under pressure (2 MPa). After impregnation is completed, reduce the pressure to make the pressure inside and outside the reaction kettle the same, and then introduce nitrogen and heat to 250 °C to remove naphthalene oil to obtain modified MXene3;

[0078] (5) Carbonize the modified MXene3 obtained in step (4) under nitrogen protection at a temperature of 1200 °C for 5 hours, and cool it to room temperature to obtain the MXene-based composite negative electrode material.

[0079] Example 3

[0080] (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 (the interlayer spacing is 1.4 nm, D 50 is 6 μm, and the pore diameter is 40 nm);

[0081] (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 180 °C for 20 hours, centrifuge, and wash with deionized water to obtain modified porous MXene1;

[0082] (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;

[0083] (4) Put 10 g of the modified porous MXene2 from step (3) into a reaction kettle, evacuate for 60 min. When the vacuum degree of the reaction kettle reaches 0.07 MPa, open the suction valve of the phenolic resin wash oil solution (formed by dissolving 1.5 g of phenolic resin in 3 g of wash oil), suck all the solution into the reaction kettle. After the liquid feeding is completed, close the suction valve and stop evacuating. At the same time, stir the mixed liquid at a high speed (20 r / min) for 40 min, then impregnate under pressure (1.5 MPa). After the impregnation is completed, reduce the pressure to make the pressure inside and outside the reaction kettle the same, and then introduce nitrogen to heat to 230 °C to remove the wash oil, obtaining modified MXene3;

[0084] (5) Under the protection of nitrogen, carbonize the modified MXene3 from step (4) at a temperature of 1000 °C for 5 hours, and then cool to room temperature to obtain the MXene-based composite anode material.

[0085] Comparative Example 1

[0086] (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 porous MXene (the interlayer spacing is 1.25 nm, D 50 is 8 μm, and the pore diameter is 50 nm);

[0087] (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, and hydrothermally treat at 200 °C for 20 hours. Then centrifuge and wash with deionized water to obtain modified porous MXene1;

[0088] (3) Heat-treat the modified porous MXene1 from step (2) in a nitrogen atmosphere at 380 °C for 1.5 hours, and then cool to room temperature to obtain modified porous MXene2;

[0089] (4) Under the protection of nitrogen, carbonize the modified porous MXene2 from step (3) at a temperature of 1000 °C for 5 hours, and then cool to room temperature to obtain the MXene-based composite anode material.

[0090] Comparative Example 2

[0091] (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 porous MXene (the interlayer spacing is 1.25 nm, D 50 is 8 μm, and the pore diameter is 50 nm);

[0092] (2) Put 10 g of the MXene with a porous structure obtained in step (1) into a reaction kettle, evacuate it for 60 min. When the vacuum degree of the reaction kettle reaches 0.07 MPa, open the suction valve of the phenolic resin wash oil solution (formed by dissolving 1.5 g of phenolic resin in 3 g of wash oil), suck all the solution into the reaction kettle. After the liquid inlet is completed, close the suction valve and stop evacuating. At the same time, stir the mixed liquid at a high speed (20 r / min) for 40 min, then impregnate it under pressure (1.5 MPa). After impregnation is completed, reduce the pressure to make the pressure inside and outside the reaction kettle the same, and then introduce nitrogen to heat to 230 °C to remove the wash oil, obtaining modified MXene 1;

[0093] (3) Under the protection of nitrogen, carbonize the modified MXene 1 obtained in step (2) at a temperature of 1000 °C for 5 hours, and then cool it to room temperature to obtain the MXene-based composite negative electrode material.

[0094] Comparative Example 3

[0095] (1) Disperse 64 g of MXene into 26 L of deionized water, ultrasonically treat it 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 MXene 1;

[0096] (2) Under a nitrogen atmosphere, heat-treat the modified MXene 1 obtained in step (1) at 380 °C for 1.5 hours, and then cool it to room temperature to obtain modified MXene 2;

[0097] (3) Put 10 g of the modified MXene 2 obtained in step (2) into a reaction kettle, evacuate it for 60 min. When the vacuum degree of the reaction kettle reaches 0.07 MPa, open the suction valve of the phenolic resin wash oil solution (formed by dissolving 1.5 g of phenolic resin in 3 g of wash oil), suck all the solution into the reaction kettle. After the liquid inlet is completed, close the suction valve and stop evacuating. At the same time, stir the mixed liquid at a high speed (20 r / min) for 40 min, then impregnate it under pressure (1.5 MPa). After impregnation is completed, reduce the pressure to make the pressure inside and outside the reaction kettle the same, and then introduce nitrogen to heat to 230 °C to remove the wash oil, obtaining modified MXene 3;

[0098] (4) Under the protection of nitrogen, carbonize the modified MXene 3 obtained in step (3) at a temperature of 1000 °C for 5 hours, and then cool it to room temperature to obtain the MXene-based composite negative electrode material.

[0099] Use the MXene-based composite negative electrode materials prepared in the above Examples 1-3 and Comparative Examples 1-3 as the negative electrode materials of sodium-ion batteries, and conduct electrochemical performance tests. The method is as follows:

[0100] Weigh the MXene-based composite anode material, conductive agent Super P, binder sodium carboxymethyl cellulose (CMC), and aqueous binder (SBR) at a mass ratio of 95:2:1.5:1.5. After thoroughly grinding them in an agate mortar, add a small amount of deionized water and mix to form a uniform black paste-like slurry. Coat the black paste-like slurry on a copper foil current collector as a test electrode, use a sodium metal sheet as a counter electrode to assemble a button cell, and use an electrolyte of 1 M sodium hexafluorophosphate dissolved in a mixed solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) with a volume ratio of 1:1. Add 5 wt.% of fluoroethylene carbonate (FEC) as an additive to the electrolyte, use glass fiber as the separator, and assemble a button cell with a CR2032 type stainless steel as the battery case. Test the capacity and initial Coulombic efficiency at a constant rate of 0.1C in the voltage range of 0.01 - 3.0V.

[0101] Battery rate performance and cycle performance test: Place the sodium-ion battery in an environment of 25°C, charge it at a constant current and constant voltage of (1C - 3C) to 4.0V, with a cut-off current of 0.05C, and discharge it at a constant current of 0.7C to 1.5V. This one-step charge and discharge is recorded as one cycle. Repeat this cycle until the capacity retention rate is lower than 80%, and record the number of cycles.

[0102] Table 1 Electrochemical performance of MXene-based composite anode material

[0103]

[0104] As can be seen from Table 1, the MXene-based composite anode material prepared by the present invention has high capacity, initial Coulombic efficiency, rate performance, and cycle performance.

[0105] In Comparative Example 1, the modified porous MXene2 was not treated with a phenolic resin wash oil solution, that is, there is no hard carbon on the surface and in the pores of the obtained MXene-based composite anode material, resulting in a significant reduction in the capacity, initial Coulombic efficiency, and cycle performance of the prepared MXene-based composite anode material.

[0106] In Comparative Example 2, hydrothermal treatment was not used to insert melamine and cyanuric acid into the interlayer of MXene, that is, there is no nitrogen-containing nanocarbon in the MXene interlayer, resulting in a decrease in the conductivity of the MXene-based composite anode material, a decline in the rate performance of the battery, and it is easy to cause aggregation or re-stacking of the nanosheets in the MXene interlayer during the charge and discharge process, leading to a decrease in the cycle performance and rate performance of the battery.

[0107] In Comparative Example 3, MXene was not expanded and pore-formed with hydrogen peroxide, resulting in a small interlayer spacing of the MXene-based composite anode material, causing a significant reduction in the rate performance and cycle performance of the MXene-based composite anode material.

[0108] 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) adding the modified porous MXene2 of step (3) into a reactor, evacuating the reactor, adding an organic resin solution, and performing pressure impregnation. After the pressure impregnation is completed, the pressure is reduced to make the pressure inside and outside the reactor the same, nitrogen is introduced, and the organic solvent is removed by heating to obtain modified MXene3; (5) Carbonizing the modified MXene3 obtained in step (4) 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.

4. The method according to any one of claims 1 to 3, wherein: In step (3), the heat treatment temperature is 300-500° C. and the heat treatment time is 1-3 hours; And / or, in step (3), the modified porous MXene2 comprises 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; And / or, in step (4), the vacuum degree of the reactor is 0.07-0.09 MPa; And / or, in step (4), the reaction kettle is evacuated for 10-120 min; And / or, in step (4), the organic resin is selected from at least one of petroleum resin, phenolic resin, epoxy resin, starch, glucose and cellulose; And / or, in step (4), the mass ratio of the organic resin to the modified porous MXene2 is (10-30):100; And / or, in step (4), the mass ratio of the organic solvent to the modified porous MXene2 is (10-50):100; And / or, in step (4), the method of adding the organic resin solution is: opening the suction valve of the organic resin solution to suck the organic resin solution into the reaction kettle, and closing the suction valve after the liquid is added to stop vacuuming; And / or, in step (4), the pressure of the pressurized impregnation is 1 MPa-3 MPa, and the time of the pressurized impregnation is 1-5 hours; Preferably, in step (5), the temperature of the carbonization treatment is 1000-1400° C.; and the time of the carbonization treatment is 4-10 hours.

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 hard carbon. Preferably, the MXene-based composite negative electrode material is a composite of MXene with a porous structure, nitrogen-containing nanocarbon and hard carbon. Preferably, the mass of the MXene with a porous structure accounts for 75%-85% of the total mass of the MXene-based composite negative electrode material; the mass of the nitrogen-containing nanocarbon accounts for 1%-5% of the total mass of the MXene-based composite negative electrode material; the mass of the hard carbon accounts for 3%-10% 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 nanocarbon is embedded in the interlayer of the MXene with a porous structure; and the hard carbon is evenly distributed on the surface and in the pores of the MXene with a porous structure. Preferably, the MXene-based composite negative electrode material has a core-shell structure, including a core and a shell layer; the core includes MXene with a porous structure, nitrogen-containing nanocarbon and hard carbon, the nitrogen-containing nanocarbon is embedded in the interlayer of the MXene with a porous structure, and the hard carbon is uniformly distributed in the pores of the MXene with a porous structure; the shell layer includes hard carbon. Preferably, the shell layer has a thickness of 10-30 nm. 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. 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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