A high-rate and high-capacity MXene-based composite negative electrode material, a preparation method and application thereof

Abstract

The application 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 and a preparation method and application thereof. The nano-silicon distributed in the pore channel of the MXene-based composite negative electrode material can effectively increase the sodium storage active sites, and further improve the sodium storage capacity of the MXene-based composite negative electrode material. The MXene-based composite negative electrode material has a large interlayer spacing, which is beneficial to the shuttling of sodium ions between the MXene layers, and can improve the sodium ion insertion / extraction kinetics. The nitrogen-containing nanocarbon inserted between the layers of the MXene-based composite negative electrode material has high conductivity, which can effectively alleviate the accumulation phenomenon between the MXene layers, form a stable and continuous electron transmission network, and improve the electron transmission kinetics. Due to the synergistic improvement of ion transmission and electron transmission, the MXene-based composite negative electrode material has good rate performance.

Description

TECHNICAL FIELD

[0001] The application 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 and a preparation method and application thereof. BACKGROUND

[0002] With the rapid development of the electric vehicle market, the demand for lithium ion batteries has also increased dramatically. However, the lithium resource reserves in the earth's crust are limited, which has caused the cost of lithium ion batteries to remain high. At the same time, sodium ion batteries have a working principle similar to that of lithium ion batteries, have an energy density close to that of lithium ion batteries, and have abundant sodium ion resource reserves, uniform distribution 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 transmission path. MXene is a kind of two-dimensional layered transition metal carbide with a structure similar to that of graphene, has a high specific surface area, good electrical conductivity and hydrophilicity, and shows great potential in the field of sodium ion battery negative electrode materials. However, the aggregation or restacking of MXene interlayer nanosheets caused by van der Waals forces greatly reduces the specific surface area of MXene, reduces the adsorption sites of Na + , and the collapse and stacking cause a large increase in the resistivity of MXene in the vertical interlayer direction, further hindering the transmission of Na + , and affecting the rate performance of the negative electrode material. In addition, the specific capacity of MXene is low, which limits its application in sodium ion batteries. SUMMARY

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

[0005] Specifically, the application provides the following technical solutions:

[0006] A method for preparing a MXene-based composite negative electrode material, the method comprising the following steps:

[0007] (1) adding hydrogen peroxide to an aqueous solution containing MXene, reacting, centrifuging, and washing to obtain MXene with a porous structure;

[0008] (2) mixing the MXene with a porous structure of step (1), melamine, cyanuric acid, and deionized water, and performing a hydrothermal reaction to obtain modified porous MXene 1;

[0009] (3) performing heat treatment on the modified porous MXene 1 of step (2) to obtain modified porous MXene 2;

[0010] (4) depositing nano-silicon in the pores of the modified porous MXene 2 of step (3) by chemical vapor deposition to obtain the MXene-based composite negative electrode material.

[0011] According to an embodiment of the present application, in step (1), the MXene can be prepared by methods well known to those skilled in the art; for example, the MXene can be prepared by acid etching and washing of a MAX phase material, which includes one or more of Ti3AlC2, Ti2AlC, and Ti3AlCN.

[0012] According to an embodiment of the present application, in step (1), the MXene includes at least one of Ti3C2 and Ti2C.

[0013] According to an embodiment of the present application, in step (1), the MXene has a median particle size D 50 of 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 application, in step (1), the MXene has an interlayer spacing of ≤1 nm.

[0015] According to an embodiment of the present application, in step (1), the aqueous solution containing MXene has a concentration of 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 application, in step (1), the volume ratio of 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 application, in step (1), the reaction is carried out under stirring.

[0018] According to an embodiment of the present application, in step (1), the reaction time is 1-6 hours, for example 2 hours, 3 hours, 4 hours or 5 hours; and the reaction temperature is room temperature. During the reaction, hydrogen peroxide reacts with MXene to increase the interlayer spacing of MXene, while reducing the size of MXene sheets, thereby realizing the preparation of MXene with large interlayer spacing.

[0019] According to an embodiment of the present application, in step (1), the washing is carried out by sequentially washing the solid component obtained after centrifugal separation with 10-25% hydrochloric acid and deionized water, and the purpose of the washing is to remove the by-products (such as TiO2) generated by the reaction of hydrogen peroxide with MXene, thereby realizing the preparation of MXene with porous structure.

[0020] According to an embodiment of the present application, in step (1), the median particle size D 50 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 application, in step (1), the interlayer spacing of the MXene with 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 application, in step (1), the MXene sheet of the MXene with porous structure is distributed with a pore 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 application, in step (2), the mass / volume ratio of the MXene with porous structure and deionized water is 2-3 mg / mL, i.e. 2-3 mg of the MXene with porous structure is dispersed in 1 mL of deionized water.

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

[0025] According to an embodiment of the present application, in step (2), the temperature of the hydrothermal reaction is 180-220°C, for example, 180°C, 190°C, 200°C, 210°C or 220°C; the time of the hydrothermal reaction is 20-28 hours, for example, 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 generate melamine cyanuric acid in the interlayer of the MXene with a porous structure.

[0026] According to an embodiment of the present application, in step (2), the modified porous MXene 1 comprises melamine cyanuric acid and 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 MXene 1 is a substance formed after the melamine cyanuric acid is inserted into the interlayer of the MXene with a porous structure.

[0027] According to an embodiment of the present application, in step (2), the MXene with a porous structure of step (1) is dispersed in deionized water, and ultrasonic treatment is performed for 10-30 minutes; then melamine and cyanuric acid are added to the dispersion of the MXene with a porous structure, and after uniform mixing, a hydrothermal reaction is performed.

[0028] According to an embodiment of the present application, in step (3), the temperature of the heat treatment is 300-500°C, for example, 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, for example, 1 hour, 2 hours or 3 hours.

[0029] According to an embodiment of the present application, in step (3), after the heat treatment, natural cooling to room temperature is preferably performed.

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

[0031] According to an embodiment of the present application, in step (3), during the heat treatment, the melamine cyanuric acid is decomposed and converted into nitrogen-containing nanocarbon.

[0032] According to an embodiment of the present application, in step (3), the modified porous MXene 2 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 MXene 2 is a substance formed after the melamine cyanuric acid is inserted into the interlayer of the MXene with a porous structure and then heat treated.

[0033] According to embodiments of the present application, in step (4), the chemical vapor deposition method comprises:

[0034] The modified porous MXene 2 of step (3) is first placed into a chemical vapor deposition furnace, nitrogen is introduced, the temperature of the chemical vapor deposition furnace is then raised and silane gas is introduced at this temperature and kept for a certain time, the silane gas decomposes into nanosilicon, after the time of keeping, the introduction of silane gas is stopped and the furnace is cooled to room temperature, the introduction of nitrogen is stopped, and the preparation of the MXene-based composite negative electrode material is achieved.

[0035] According to embodiments of the present application, in step (4), the chemical vapor deposition method comprises:

[0036] The modified porous MXene 2 of step (3) is first placed into a chemical vapor deposition furnace at room temperature, nitrogen is introduced for 20-40 minutes to achieve replacement of air in the chemical vapor deposition furnace, the temperature of the chemical vapor deposition furnace is then raised to 450-650℃ and silane gas is introduced at this temperature and kept for 1-3 hours, the silane gas decomposes into nanosilicon, after the time of keeping, the introduction of silane gas is stopped and the furnace is cooled to room temperature, the introduction of nitrogen is stopped, and the preparation of the MXene-based composite negative electrode material is achieved.

[0037] According to embodiments of the present application, 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 embodiments of the present application, in step (4), the flow rate of the nitrogen is 100-200 sccm, for example 100 sccm, 120 sccm, 130 sccm, 150 sccm, 160 sccm, 180 sccm or 200 sccm.

[0039] According to embodiments of the present application, in step (4), the mass to volume ratio of the silane gas to the modified porous MXene 2 of step (3) is 5-20 L / g, i.e. 5-20 L of silane gas is introduced into 1 g of the modified porous MXene 2 of step (3).

[0040] According to embodiments of the present application, in step (4), the silane gas is monosilane or disilane.

[0041] According to embodiments of the present application, 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 application, the silane gas can be more fully introduced into the pores of the modified porous MXene 2 by the chemical vapor deposition method, which is conducive to the uniform dispersion of the nanosilicon in the pores of the modified porous MXene 2.

[0043] The present application also provides a MXene-based composite negative electrode material prepared by the above method.

[0044] According to an embodiment of the present application, the MXene-based composite negative electrode material comprises 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.

[0045] According to an embodiment of the present application, 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, for example 60%, 62%, 65%, 68%, 70%, 72%, 75%, 78% or 80%.

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

[0047] According to an embodiment of the present application, the mass of the nanosilicon accounts for 5%-20% of the total mass of the MXene-based composite negative electrode material, for example 5%, 6%, 8%, 10%, 12%, 15%, 16%, 18% or 20%. When the mass of the nanosilicon is less than 5%, the capacity of the battery will be low, and when the mass of the nanosilicon is more than 20%, the cycle performance of the battery will decrease.

[0048] According to an embodiment of the present application, 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 layers and improve the rate performance of the MXene-based composite negative electrode 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 negative electrode material.

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

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

[0051] The application also provides a use of the MXene-based composite negative electrode material for preparing a negative electrode of a sodium ion battery.

[0052] The application also provides a negative electrode of a sodium ion battery, which comprises the MXene-based composite negative electrode material.

[0053] The application also provides a sodium ion battery, which comprises the MXene-based composite negative electrode material or the negative electrode of the sodium ion battery.

[0054] The application has the following beneficial effects:

[0055] The application first realizes the increase of the interlayer spacing of MXene by adopting a chemical oxidation method, and reduces the size of the MXene sheet at the same time; then pores are formed in the oxidation product by acid washing to obtain MXene with a porous structure; subsequently, melamine and cyanuric acid are inserted into the layers of the MXene with a porous structure under hydrothermal conditions to obtain a modified material with melamine cyanuric acid inserted into the layers of the MXene with a porous structure, and then the melamine cyanuric acid is calcined into nitrogen-containing nanocarbon by using a heat treatment process to obtain a modified material with nitrogen-containing nanocarbon inserted into the layers of the MXene with a porous structure; finally, the silane gas is used as a silicon source, and the pores of the modified material with nitrogen-containing nanocarbon inserted into the layers of the MXene with a porous structure are fully infiltrated with the silicon source by using the gas-phase chemical deposition method of the application; thus, the MXene-based composite negative electrode material obtained has high rate performance and high capacity.

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

[0057] (1) High sodium storage capacity, the nanosilicon distributed in the pores of the MXene-based composite negative electrode material can effectively increase the sodium storage active sites, thereby improving the sodium storage capacity of the MXene-based composite negative electrode material;

[0058] (2) Excellent electrochemical performance, the MXene-based composite negative electrode material has a large interlayer spacing, which is conducive to the shuttling of sodium ions between the layers of MXene, and can improve the sodium ion intercalation / deintercalation kinetics; the nitrogen-containing nanocarbon intercalated between the layers of the MXene-based composite negative electrode material has high electrical conductivity, which can effectively alleviate the accumulation phenomenon between the layers of MXene, 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 negative electrode material has good rate performance. DETAILED DESCRIPTION

[0059] The preparation method of the present application will be further described in detail below in connection with specific examples. It should be understood that the following examples are only illustratively described and explained, and should not be interpreted as limiting the scope of protection of the present application. Any technology achieved based on the above description of the present application is covered within the scope intended to be protected by the present application.

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

[0061] The MXene in the following examples and comparative examples is Ti3C2, the interlayer spacing is 0.92 nm, D 50 8 μm, and the concentration of the aqueous solution containing MXene is 2.2 mg / mL.

[0062] Example 1

[0063] (1) 15 mL of hydrogen peroxide was added to 100 mL of an aqueous solution containing MXene, and after continuous stirring at room temperature for 3 h, centrifugation, washing with 15% hydrochloric acid and deionized water in sequence, MXene with a porous structure (interlayer spacing of 1.25 nm, D 50 8 μm, and a pore size of 50 nm) was obtained;

[0064] (2) 64 g of the MXene with a porous structure of step (1) was dispersed into 26 L of deionized water, ultrasonic treatment for 15 minutes, 126 g of melamine and 129 g of cyanuric acid were added, stirred uniformly, hydrothermal treatment at 200 ℃ for 20 hours, centrifugation, washing with deionized water, and modified porous MXene 1 was obtained;

[0065] (3) After the modified porous MXene 1 of step (2) was heat-treated at 380 ℃ for 1.5 hours under a nitrogen atmosphere, it was cooled to room temperature to obtain modified porous MXene 2;

[0066] (4) 10 g of the modified porous MXene 2 of step (3) was placed in the reaction chamber of a gas-phase chemical deposition furnace at room temperature, nitrogen gas was introduced into the reaction chamber (flow rate of 150 sccm) for 30 minutes to replace the air in the chemical vapor deposition furnace, then the temperature of the reaction chamber was increased to 500 ℃ and silane gas was introduced at a flow rate of 150 sccm, and the temperature was maintained for 1 hour. After the temperature was maintained, the silane gas was stopped and the furnace was cooled to room temperature, and the nitrogen gas was stopped to obtain the MXene-based composite negative electrode material.

[0067] Example 2

[0068] (1) 20 mL of hydrogen peroxide was added to 100 mL of an aqueous solution containing MXene, and after continuous stirring at room temperature for 4 h, centrifugation, washing with 20% hydrochloric acid and deionized water in sequence, a MXene with a porous structure was obtained (interlayer spacing was 1.3 nm, D 50 was 7 pm, and the pore size was 45 nm);

[0069] (2) 64 g of the MXene with a porous structure of step (1) was dispersed into 26 L of deionized water, ultrasonic treatment was performed for 15 min, 126 g of melamine and 129 g of cyanuric acid were added, stirring was uniformly performed, hydrothermal treatment was performed at 180 °C for 28 h, centrifugation was performed, and deionized water washing was performed to obtain modified porous MXene 1;

[0070] (3) After the modified porous MXene 1 of step (2) was heat-treated at 350 °C for 2 h under a nitrogen atmosphere, cooling was performed to room temperature to obtain modified porous MXene 2;

[0071] (4) 10 g of the modified porous MXene 2 of step (3) was placed in a reaction chamber of a chemical vapor deposition furnace at room temperature, nitrogen was introduced into the reaction chamber (flow rate was 100 sccm) for 30 min to replace air in the chemical vapor deposition furnace, then the temperature of the reaction chamber was increased to 550 °C, and at this temperature, silane gas was introduced, the flow rate of the silane was 100 sccm, and heat preservation was performed for 1.5 h, after the heat preservation, the introduction of the silane was stopped, and the furnace was cooled to room temperature, the introduction of the nitrogen was stopped, and the MXene-based composite negative electrode material was obtained.

[0072] Example 3

[0073] (1) 25 mL of hydrogen peroxide was added to 100 mL of an aqueous solution containing MXene, and after continuous stirring at room temperature for 3 h, centrifugation, washing with 25% hydrochloric acid and deionized water in sequence, a MXene with a porous structure was obtained (interlayer spacing was 1.4 nm, D 50 was 6 pm, and the pore size was 40 nm);

[0074] (2) 64 g of the MXene with a porous structure of step (1) was dispersed into 26 L of deionized water, ultrasonic treatment was performed for 15 min, 126 g of melamine and 129 g of cyanuric acid were added, stirring was uniformly performed, hydrothermal treatment was performed at 180 °C for 20 h, centrifugation was performed, and deionized water washing was performed to obtain modified porous MXene 1;

[0075] (3) After the modified porous MXene 1 of step (2) was heat-treated at 380 °C for 1.5 h under a nitrogen atmosphere, cooling was performed to room temperature to obtain modified porous MXene 2;

[0076] (4) 10 g of the modified porous MXene 2 of step (3) was placed in the reaction chamber of a chemical vapor deposition furnace at room temperature, nitrogen gas was introduced into the reaction chamber (flow rate was 200 sccm) for 30 minutes to replace the air in the chemical vapor deposition furnace, then the temperature of the reaction chamber was increased to 650 °C, and at this temperature, silane gas was introduced, the flow rate of silane was 200 sccm, and the temperature was kept for 1 hour. After the temperature was kept for 1 hour, the introduction of silane gas was stopped and the furnace was cooled to room temperature. The nitrogen gas was stopped, and the MXene-based composite negative electrode material was obtained.

[0077] Comparative Example 1

[0078] (1) 15 mL of hydrogen peroxide was added to 100 mL of an aqueous solution containing MXene, and after continuous stirring at room temperature for 3 h, centrifugation, and washing with 15% hydrochloric acid and deionized water in sequence, a MXene with a porous structure (interlayer spacing was 1.25 nm, D 50 was 8 μm, and the pore size was 50 nm) was obtained.

[0079] (2) 64 g of the MXene with a porous structure of step (1) was dispersed in 26 L of deionized water, and ultrasonic treatment was performed for 15 minutes. 126 g of melamine and 129 g of cyanuric acid were added and stirred uniformly. Hydrothermal treatment was performed at 200 °C for 20 hours. Centrifugation and washing with deionized water were performed, and a modified porous MXene 1 was obtained.

[0080] (3) The modified porous MXene 1 of step (2) was heat-treated at 380 °C for 1.5 hours under a nitrogen atmosphere, and then cooled to room temperature. The MXene-based composite negative electrode material was obtained.

[0081] Comparative Example 2

[0082] (1) 15 mL of hydrogen peroxide was added to 100 mL of an aqueous solution containing MXene, and after continuous stirring at room temperature for 3 h, centrifugation, and washing with 15% hydrochloric acid and deionized water in sequence, a MXene with a porous structure (interlayer spacing was 1.25 nm, D 50 was 8 μm, and the pore size was 50 nm) was obtained.

[0083] (2) 10 g of the MXene with a porous structure of step (1) was placed in the reaction chamber of a chemical vapor deposition furnace at room temperature, nitrogen gas was introduced into the reaction chamber (flow rate was 150 sccm) for 30 minutes to replace the air in the chemical vapor deposition furnace, then the temperature of the reaction chamber was increased to 500 °C, and at this temperature, silane gas was introduced, the flow rate of silane was 150 sccm, and the temperature was kept for 1 hour. After the temperature was kept for 1 hour, the introduction of silane gas was stopped and the furnace was cooled to room temperature. The nitrogen gas was stopped, and the MXene-based composite negative electrode material was obtained.

[0084] Comparative Example 3

[0085] (1) 64 g MXene was dispersed into 26 L deionized water, ultrasonic treatment for 15 minutes, 126 g melamine, 129 g cyanuric acid were added, stirred uniformly, hydrothermal treatment at 200 ℃ for 20 hours, centrifugation, deionized water washing, to obtain modified MXene 1;

[0086] (2) After the modified MXene 1 of step (1) was heat treated at 380 ℃ for 1.5 hours under nitrogen atmosphere, it was cooled to room temperature to obtain modified MXene 2;

[0087] (3) 10 g of modified MXene 2 of step (2) was placed in the reaction chamber of a chemical vapor deposition furnace at room temperature, nitrogen gas was introduced into the reaction chamber (flow rate was 150 sccm) for 30 minutes to replace the air in the chemical vapor deposition furnace, then the temperature of the reaction chamber was increased to 850 ℃ and silane gas was introduced at this temperature, the flow rate of silane was 150 sccm, and the temperature was kept for 1 hour. After the temperature was kept, the silane gas was stopped and the furnace was cooled to room temperature. The nitrogen gas was stopped, and the MXene-based composite negative electrode material was obtained.

[0088] Test Example 1

[0089] The MXene-based composite negative electrode material prepared in the above examples and comparative examples was used as a negative electrode material of a sodium ion battery, and electrochemical performance test was carried out, and the method was as follows:

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

[0091] Battery rate performance and cycle performance test: the sodium ion battery was placed in an environment of 25 ℃, charged to 4.0V at (1C-3C) constant current and constant voltage, the cutoff current was 0.05C, discharged to 1.5V at 0.7C constant current, which was recorded as one cycle, and the cycle was repeated until the capacity retention rate was less than 80%, and the cycle number was recorded.

[0092] Table 1 Electrochemical performance of MXene-based composite negative electrode material

[0093]

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

[0095] Comparative Example 1 does not use silyl chemical vapor deposition to modify the porous MXene 2, that is, there is no nano-silicon in the pore channel 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 does not use hydrothermal treatment to insert melamine and cyanuric acid into the interlayer of MXene, that is, there is no nitrogen-containing nanocarbon in the interlayer of MXene, resulting in a reduction in the conductivity of the MXene-based composite negative electrode material, a decrease in the rate performance of the battery, and the aggregation or restacking of the nanosheet in the interlayer of MXene during the charging and discharging process, leading to a reduction in the cycle performance and rate performance of the battery.

[0097] Comparative Example 3 does not use hydrogen peroxide to expand the MXene, resulting in a small interlayer spacing of the MXene-based composite negative electrode material, a significant reduction in the rate performance and cycle performance of the MXene-based composite negative electrode material, and a small pore channel of the MXene-based composite negative electrode material due to the lack of pore-forming by hydrogen peroxide, which cannot accommodate more nano-silicon, resulting in a reduction in the capacity of the MXene-based composite negative electrode material.

[0098] The above describes the embodiments of the present application. However, the present application is not limited to the above-described embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

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 obtain MXene with a porous structure; (2) mixing the MXene with a porous structure of step (1), melamine, cyanuric acid, and deionized water, and performing a hydrothermal reaction to obtain modified porous MXene 1; the modified porous MXene 1 comprises melamine cyanuric acid and MXene with a porous structure, and the melamine cyanuric acid is inserted between layers of the MXene with a porous structure; (3) performing heat treatment on the modified porous MXene 1 of step (2) to obtain modified porous MXene 2; the modified porous MXene 2 comprises nitrogen-containing nanocarbon and MXene with a porous structure, and the nitrogen-containing nanocarbon is inserted between layers of the MXene with a porous structure; (4) depositing nanosilicon in the pores of the modified porous MXene 2 of step (3) by using a chemical vapor deposition method to obtain the MXene-based composite negative electrode material.

2. The method of claim 1, wherein, In step (1), the MXene comprises at least one of Ti 3C 2 and Ti 2C; And / or, in step (1), the MXene has a median particle size D 50 of 5-10 pm; and / or, in step (1), the interlayer spacing of the MXene is ≤1 nm; and / or, in step (1), the volume ratio of the 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 with a concentration of 10-25% and deionized water in sequence; And / or, in step (1), the MXene with a porous structure has a median particle size D 50 of 3-8 pm; and / or, in step (1), the interlayer spacing of the MXene with a porous structure is 1.2-1.5 nm; and / or, in step (1), each MXene sheet layer of the MXene with a porous structure is distributed with a pore structure, and the pore size of the pore structure is 20-60 nm.

3. The method of claim 1, wherein, In step (2), the mass / volume ratio of the MXene with a porous structure to deionized water is 2-3 mg / mL; and / or, in step (2), the molar ratio of the MXene with 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 ℃; and the time of the hydrothermal reaction is 20-28 hours; and / or, in step (2), the modified porous MXene 1 is a substance formed after melamine cyanuric acid is inserted between layers of the MXene with a porous structure.

4. The method of claim 1, wherein, In step (3), the temperature of the heat treatment is 300-500 ℃; and the time of the heat treatment is 1-3 hours; and / or, in step (3), the modified porous MXene 2 is a substance formed after melamine cyanuric acid is inserted between layers of the MXene with a porous structure and then heat treated.

5. The method according to any one of claims 1 to 4, wherein, In step (4), the chemical vapor deposition method comprises: Firstly, the modified porous MXene 2 of step (3) is placed into a chemical vapor deposition furnace, nitrogen is introduced, then the temperature of the chemical vapor deposition furnace is raised and silane gas is introduced at this temperature and kept for a certain time, the silane gas decomposes into nano-silicon, after keeping for a certain time, the introduction of silane gas is stopped and the furnace is cooled to room temperature, the introduction of nitrogen is stopped, and the preparation of the MXene-based composite negative electrode material is realized.

6. The method of claim 5, wherein, In step (4), the chemical vapor deposition method comprises: Firstly, the modified porous MXene 2 of step (3) is placed into a chemical vapor deposition furnace at room temperature, 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 raised to 450-650℃ and silane gas is introduced at this temperature and kept for 1-3 hours, the silane gas decomposes into nano-silicon, after keeping for a certain time, the introduction of silane gas is stopped and the furnace is cooled to room temperature, the introduction of nitrogen is stopped, and the preparation of the MXene-based composite negative electrode material is realized.

7. The method of claim 6, wherein, 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 MXene 2 of step (3) is 5-20 L / g; And / or, in step (4), the silane gas is monosilane or disilane.

8. A MXene-based composite negative electrode material prepared by the method of any one of claims 1-7.

9. The MXene-based composite anode material of claim 8, wherein, The MXene-based composite negative electrode material comprises MXene with a porous structure, nitrogen-containing nanocarbon, and nano-silicon.

10. The MXene-based composite anode material of claim 8, wherein, The MXene-based composite negative electrode material is a composite of MXene with a porous structure, nitrogen-containing nanocarbon, and nano-silicon.

11. The MXene-based composite anode material of claim 8, wherein, 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; and the mass of the nano-silicon accounts for 5%-20% of the total mass of the MXene-based composite negative electrode material.

12. The MXene-based composite anode material of claim 9 or 10, wherein, The nitrogen-containing nanocarbon is embedded between the layers of the MXene with a porous structure; and the nano-silicon is distributed within the pores of the MXene with a porous structure.

13. The MXene-based composite anode material of claim 9 or 10, wherein, The MXene-based composite negative electrode material has a median particle size D 50 of 3-6 pm; The interlayer spacing of the MXene-based composite negative electrode material is 1.2-1.5 nm.

14. Use of the MXene-based composite negative electrode material of any one of claims 8-13 for preparing a negative electrode of a sodium ion battery.

15. A negative electrode of a sodium ion battery, comprising the MXene-based composite negative electrode material of any one of claims 8-13.

16. A sodium ion battery, comprising the MXene-based composite negative electrode material of any one of claims 8-13 or the negative electrode of a sodium ion battery of claim 15.

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