High-rate mxene-based composite negative electrode material, 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 MXene-based composite negative electrode material and a preparation method and application thereof. The hard carbon distributed on the surface and in the pores of the MXene-based composite negative electrode material can effectively increase sodium storage active sites, thereby improving the sodium storage capacity and the initial coulombic efficiency of the MXene-based composite negative electrode material. The MXene-based composite negative electrode material has a large interlayer spacing, which is conducive 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 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 in 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 problem of aggregation or restacking between the interlayer nanosheets of MXene 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 will cause the resistivity of MXene in the vertical interlayer direction to increase greatly, further hindering the transmission of Na + , and affecting the rate performance of the negative electrode material. SUMMARY

[0004] In order to improve the deficiencies of the prior art, the application provides a high-rate 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 hard carbon; 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 hard carbon is distributed on the surface and in the pores of the MXene with a porous structure. The MXene-based composite negative electrode material can effectively alleviate the problem of aggregation or restacking between the interlayer nanosheets of MXene, and the sodium ion battery assembled from the MXene-based composite negative electrode material has high rate performance and cycle performance.

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

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

[0007] (1) adding hydrogen peroxide into an aqueous solution containing MXene, reacting, centrifuging, washing, and preparing the 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 prepare modified porous MXene 1;

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

[0010] (4) adding the modified porous MXene 2 of step (3) into a reaction kettle, vacuumizing the reaction kettle, adding an organic resin solution, performing pressure impregnation, after the pressure impregnation is completed, reducing the pressure inside and outside the reaction kettle to make the pressure the same, introducing nitrogen, and heating to remove the organic solvent to obtain modified MXene 3;

[0011] (5) performing carbonization treatment on the modified MXene 3 of step (4) to prepare the MXene-based composite negative electrode material.

[0012] According to an embodiment of the present application, in step (1), the MXene can be prepared by a method well known to those skilled in the art; for example, the MXene can be prepared by acid etching and washing after a MAX phase material, which includes one or more of Ti3AlC2, Ti2AlC and Ti3AlCN.

[0013] According to an embodiment of the present application, in step (1), the MXene includes at least one of Ti3C2 and Ti2C.

[0014] 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.

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

[0016] 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.

[0017] According to an embodiment of the present application, in step (1), the volume ratio of the hydrogen peroxide and 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 application, in step (1), the reaction is carried out under stirring.

[0019] 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, the hydrogen peroxide and the MXene carry out an oxidation reaction, realizing the increase of the interlayer spacing of the MXene, and at the same time, the size of the MXene sheet is reduced, realizing the preparation of the MXene with large interlayer spacing.

[0020] According to an embodiment of the present application, in step (1), the washing is carried out by sequentially using hydrochloric acid with a concentration of 10-25% and deionized water to wash the solid component obtained after centrifugal separation, and the purpose of the washing is to remove the by-products (such as TiO2) generated by the reaction of the hydrogen peroxide and the MXene, thereby realizing the preparation of the MXene with porous structure.

[0021] According to an embodiment of the present application, in step (1), the median particle size D 50 of the MXene with porous structure 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 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.

[0023] According to an embodiment of the present application, in step (1), the pores are distributed on each MXene sheet layer of the MXene with porous structure, and the pore size of the pores 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 application, in step (2), the mass / volume ratio of the MXene with porous structure and deionized water is 2-3 mg / mL, that is, 2-3 mg of the MXene with porous structure is dispersed in 1 mL of deionized water.

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

[0026] According to an embodiment of the present application, in step (2), the temperature of the hydrothermal reaction is 180-220℃, for example, 180℃, 190℃, 200℃, 210℃ or 220℃; 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.

[0027] 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.

[0028] According to an embodiment of the present application, in step (2), the MXene with a porous structure of step (1) is dispersed into deionized water, and ultrasonic treatment is performed for 10-30 minutes; then melamine and cyanuric acid are added into the dispersion of the MXene with a porous structure, and after mixing uniformly, hydrothermal reaction is performed.

[0029] According to an embodiment of the present application, in step (3), the temperature of the heat treatment is 300-500℃, for example, 300℃, 320℃, 330℃, 350℃, 360℃, 380℃, 400℃, 420℃, 440℃, 450℃, 460℃, 480℃ or 500℃; the time of the heat treatment is 1-3 hours, for example, 1 hour, 2 hours or 3 hours.

[0030] According to an embodiment of the present application, in step (3), after the heat treatment, natural cooling to room temperature is preferred.

[0031] According to an embodiment of the present application, in step (3), the heat treatment is performed in a nitrogen atmosphere or an argon atmosphere.

[0032] 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.

[0033] 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 between the layers of the MXene with a porous structure; the modified porous MXene 2 is a substance formed after melamine cyanurate is inserted between the layers of the MXene with a porous structure and then heat treated.

[0034] According to an embodiment of the present application, 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 application, in step (4), the time for the reaction kettle to be vacuumized is 10-120 min, i.e. the time for the vacuum degree to be maintained 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 application, in step (4), the organic resin is selected from at least one of petroleum-based resins (for example, petroleum-based resin C5 and / or petroleum-based resin C9), phenolic resin, epoxy resin, starch, glucose and cellulose.

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

[0038] According to an embodiment of the present application, in step (4), the mass ratio of the organic resin to the modified porous MXene 2 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 application, in step (4), the mass ratio of the organic solvent to the modified porous MXene 2 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 application, in step (4), after the organic resin solution is added, the mixing system is stirred, and the stirring speed 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 application, in step (4), the method of adding the organic resin solution is, for example, opening the suction valve of the organic resin solution, sucking the organic resin solution into the reaction kettle, closing the suction valve after the liquid is fed, and stopping vacuumizing.

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

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

[0044] According to an embodiment of the present application, in step (5), the carbonization treatment temperature is 1000-1400℃, for example, 1000℃, 1050℃, 1100℃, 1150℃, 1200℃, 1250℃, 1300℃, 1350℃ or 1400℃; and the carbonization treatment time 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 application, in step (5), the carbonization treatment is carried out in a nitrogen atmosphere or an argon atmosphere.

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

[0047] 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 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.

[0048] According to an embodiment of the present application, 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, for example, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84% or 85%.

[0049] According to an embodiment of the present application, 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 application, 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 the 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 hard carbon is uniformly distributed in the surface and channels of the MXene with a porous structure, and the introduction of the hard carbon can also effectively improve the capacity and the first coulombic efficiency of the MXene-based composite negative electrode material.

[0052] According to the embodiment of the present application, the MXene-based composite negative electrode material has a core-shell structure, including a core and a shell layer; the core includes the MXene with a porous structure, the nitrogen-containing nanocarbon and the hard carbon, the nitrogen-containing nanocarbon is embedded between the layers of the MXene with a porous structure, and the hard carbon is uniformly distributed in the channels of the MXene with a porous structure; the shell layer includes the hard carbon.

[0053] According to the embodiment of the present application, the thickness of the shell layer is 10-30 nm, for example, 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 the embodiment of the present application, the median particle size D50 of the MXene-based composite negative electrode material is 3-6 μm, for example, 3 μm, 4 μm, 5 μm or 6 μm. 50 According to the embodiment of the present application, the median particle size D50 of the MXene-based composite negative electrode material is 3-6 μm, for example, 3 μm, 4 μm, 5 μm or 6 μm.

[0055] According to the 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.

[0056] The present application also provides a use of the above-mentioned MXene-based composite negative electrode material for preparing a negative electrode of a sodium ion battery.

[0057] The present application also provides a negative electrode of a sodium ion battery, which includes the above-mentioned MXene-based composite negative electrode material.

[0058] The present application also provides a sodium ion battery, which includes the above-mentioned MXene-based composite negative electrode material or the above-mentioned negative electrode of a sodium ion battery.

[0059] The present application has the following beneficial effects:

[0060] The present application firstly realizes the increase of the interlayer spacing of MXene by the method of chemical oxidation, and reduces the size of the MXene sheet at the same time; then the oxidation product is acid washed to form pores to obtain the MXene with a porous structure; then 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 interlayers 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 interlayers of the MXene with a porous structure; finally, the air inside the modified porous MXene2 is discharged under vacuum conditions, and under high pressure, the organic resin solution can not only be coated on the surface of the modified porous MXene2, but also enter the pores of the modified porous MXene2, and the subsequent carbonization process converts the organic resin into hard carbon, thereby ensuring that the hard carbon is embedded in the pores of the MXene with a porous structure, and at the same time, a hard carbon coating layer can be formed on the surface of the MXene with a porous structure, further improving the capacity and the first coulombic efficiency of the MXene-based composite negative electrode material.

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

[0062] (1) High sodium storage capacity and first coulombic efficiency; the hard carbon distributed on the surface and 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 and the first coulombic efficiency of the MXene-based composite negative electrode material;

[0063] (2) Excellent electrochemical performance; 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 intercalation / deintercalation 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 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

[0064] The preparation method of the present application will be further described in detail below in conjunction with specific examples. It should be understood that the following examples are only illustratively and explain the present application, and should not be interpreted as limiting the scope of protection of the present application. Any technology realized based on the above description of the present application is covered within the scope intended to be protected by the present application.

[0065] 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.

[0066] 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.

[0067] Example 1

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

[0069] (2) 64 g of the MXene with a porous structure in step (1) was dispersed into 26 L of deionized water, ultrasonic treatment for 15 min, 126 g of melamine and 129 g of cyanuric acid were added, stirred uniformly, hydrothermal treatment at 200 ℃ for 20 h, centrifugation, and deionized water washing to obtain modified porous MXene 1;

[0070] (3) After the modified porous MXene 1 in step (2) was heat-treated at 380 ℃ for 1.5 h under a nitrogen atmosphere, it was cooled to room temperature to obtain modified porous MXene 2;

[0071] (4) 10 g of the modified porous MXene 2 in step (3) was placed in a reaction kettle, vacuumized for 60 min, when the vacuum degree of the reaction kettle reached 0.07 MPa, the suction valve of the phenolic resin oil solution (1.5 g of phenolic resin dissolved in 3 g of oil to form) was opened, and the solution was completely sucked into the reaction kettle. After the liquid feeding was completed, the suction valve was closed, the vacuumization was stopped, and the mixed solution was stirred at high speed (20 r / min) for 40 min. After the impregnation was completed under pressure (1.5 MPa), the pressure inside and outside the reaction kettle was equalized, and nitrogen was introduced to heat to 230 ℃ to remove the oil, thereby obtaining modified MXene 3;

[0072] (5) The modified MXene 3 in step (4) was carbonized at a temperature of 1000 ℃ for 5 h under nitrogen protection, and cooled to room temperature to obtain the MXene-based composite negative electrode material.

[0073] Example 2

[0074] (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, and washing with 20% hydrochloric acid and deionized water in sequence, MXene with a porous structure (interlayer spacing: 1.3 nm, D 50 7 μm, and the pore size is 45 nm);

[0075] (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 minutes, 126 g of melamine and 129 g of cyanuric acid were added, stirring was performed until uniform, hydrothermal treatment was performed at 180 °C for 28 hours, centrifugation was performed, deionized water washing was performed, and modified porous MXene 1 was obtained;

[0076] (3) After the modified porous MXene 1 of step (2) was heat treated at 350 °C for 2 hours under a nitrogen atmosphere, cooling was performed to room temperature, and modified porous MXene 2 was obtained;

[0077] (4) 10 g of the modified porous MXene 2 of step (3) was placed into a reaction kettle, vacuumization was performed for 60 min, when the vacuum degree of the reaction kettle reached 0.07 MPa, a phenolic aldehyde resin naphthalene oil solution (1.5 g of phenolic aldehyde resin was dissolved in 3 g of naphthalene oil to form) suction valve was opened, the solution was completely sucked into the reaction kettle, after the liquid was completely introduced, the suction valve was closed, vacuumization was stopped, and high-speed stirring (20 r / min) of the mixed solution was performed for 40 min, after impregnation was completed under pressure (2 MPa), the pressure inside and outside the reaction kettle was made the same, and naphthalene oil was removed by heating to 250 °C under the introduction of nitrogen, and modified MXene 3 was obtained;

[0078] (5) The modified MXene 3 of step (4) was carbonized at a temperature of 1200 °C for 5 hours under the protection of nitrogen, and cooling was performed to room temperature, and the MXene-based composite negative electrode material was obtained.

[0079] Example 3

[0080] (1) 25 mL of hydrogen peroxide was added to 100 mL of an aqueous solution containing MXene, and continuous stirring was performed at room temperature for 3 h, centrifugation was performed, and washing was performed with 25% hydrochloric acid and deionized water in sequence, and MXene with a porous structure (interlayer spacing of 1.4 nm, D 50 of 6 μm, and pore size of 40 nm) was obtained;

[0081] (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 minutes, 126 g of melamine and 129 g of cyanuric acid were added, stirring was performed until uniform, hydrothermal treatment was performed at 180 °C for 28 hours, centrifugation was performed, deionized water washing was performed, and modified porous MXene 1 was obtained;

[0082] (3) After the modified porous MXene 1 of step (2) was heat treated at 350 °C for 2 hours under a nitrogen atmosphere, cooling was performed to room temperature, and modified porous MXene 2 was obtained;

[0083] (4) Put 10 g of modified porous MXene 2 from step (3) into a reaction kettle, vacuumize for 60 min, when the vacuum degree of the reaction kettle reaches 0.07 MPa, open the suction valve of the phenolic resin oil solution (1.5 g of phenolic resin dissolved in 3 g of oil after washing to form), suck the solution into the reaction kettle, close the suction valve after the liquid is completely fed, stop vacuumizing, and at the same time, high-speed stirring (20 r / min) of the mixture is carried out for 40 min, then impregnation is completed after pressurization (1.5 MPa), the pressure inside and outside the reaction kettle is equalized after depressurization, nitrogen is introduced, and heating to 230°C is carried out to remove the oil, and modified MXene 3 is obtained;

[0084] (5) Carbonize the modified MXene 3 from step (4) at a temperature of 1000°C for 5 hours under nitrogen protection, and cool to room temperature to obtain the MXene-based composite negative electrode material.

[0085] Comparative Example 1

[0086] (1) 15 mL of hydrogen peroxide is added to 100 mL of an aqueous solution containing MXene, continuously stirred at room temperature for 3 h, centrifuged, and then washed with 15% hydrochloric acid and deionized water in sequence to obtain MXene with a porous structure (interlayer spacing of 1.25 nm, D 50 of 8 μm, and a pore size of 50 nm);

[0087] (2) 64 g of the MXene with a porous structure from step (1) is dispersed into 26 L of deionized water, ultrasonically treated for 15 min, 126 g of melamine and 129 g of cyanuric acid are added, stirred uniformly, hydrothermally treated at 200°C for 20 h, centrifuged, and washed with deionized water to obtain modified porous MXene 1;

[0088] (3) The modified porous MXene 1 from step (2) is heat-treated at 380°C for 1.5 h under a nitrogen atmosphere, and then cooled to room temperature to obtain modified porous MXene 2;

[0089] (4) The modified porous MXene 2 from step (3) is carbonized at a temperature of 1000°C for 5 hours under nitrogen protection, and then cooled to room temperature to obtain the MXene-based composite negative electrode material.

[0090] Comparative Example 2

[0091] (1) 15 mL of hydrogen peroxide is added to 100 mL of an aqueous solution containing MXene, continuously stirred at room temperature for 3 h, centrifuged, and then washed with 15% hydrochloric acid and deionized water in sequence to obtain MXene with a porous structure (interlayer spacing of 1.25 nm, D 50 of 8 μm, and a pore size of 50 nm);

[0092] (2) Put 10 g of the MXene with a porous structure of step (1) into a reaction kettle, vacuumize for 60 min, when the vacuum degree of the reaction kettle reaches 0.07 MPa, open the suction valve of the phenolic resin oil solution (1.5 g of phenolic resin dissolved in 3 g of oil after forming), suck the solution into the reaction kettle, close the suction valve after the liquid is completely fed, stop vacuumizing, and at the same time, high-speed stir (20 r / min) the mixture for 40 min, then impregnate after pressurizing (1.5 MPa), reduce the pressure to make the pressure inside and outside the reaction kettle the same, then introduce nitrogen to heat to 230℃ to remove the oil, and obtain modified MXene 1;

[0093] (3) Carbonize the modified MXene 1 of step (2) at a temperature of 1000℃ for 5 hours under nitrogen protection, and cool 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, ultrasonic treat for 15 min, add 126 g of melamine and 129 g of cyanuric acid, stir uniformly, hydrothermal treat at 200℃ for 20 hours, centrifuge, and wash with deionized water to obtain modified MXene 1;

[0096] (2) Heat treat the modified MXene 1 of step (1) at 380℃ for 1.5 hours under a nitrogen atmosphere, and cool to room temperature to obtain modified MXene 2;

[0097] (3) Put 10 g of the modified MXene 2 of step (2) into a reaction kettle, vacuumize for 60 min, when the vacuum degree of the reaction kettle reaches 0.07 MPa, open the suction valve of the phenolic resin oil solution (1.5 g of phenolic resin dissolved in 3 g of oil after forming), suck the solution into the reaction kettle, close the suction valve after the liquid is completely fed, stop vacuumizing, and at the same time, high-speed stir (20 r / min) the mixture for 40 min, then impregnate after pressurizing (1.5 MPa), reduce the pressure to make the pressure inside and outside the reaction kettle the same, then introduce nitrogen to heat to 230℃ to remove the oil, and obtain modified MXene 3;

[0098] (4) Carbonize the modified MXene 3 of step (3) at a temperature of 1000℃ for 5 hours under nitrogen protection, and cool to room temperature to obtain the MXene-based composite negative electrode material.

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

[0100] Take MXene-based composite negative electrode material, conductive agent Super P, binder carboxymethyl cellulose sodium (CMC) and water-based binder (SBR) with a mass ratio of 95:2:1.5:1.5, grind thoroughly in a marquisan mortar, add a small amount of deionized water to mix into a uniform black paste slurry, coat the black paste slurry on a copper foil current collector as a test electrode, use a metal sodium sheet as a contrast electrode to assemble into a button cell, use 1M sodium hexafluorophosphate solution dissolved in a volume ratio of 1:1 ethylene carbonate (EC) and dimethyl carbonate (DMC) mixed solution as electrolyte, add 5wt.% fluoroethylene carbonate (FEC) as additive in the electrolyte, use glass fiber as separator, use CR2032 type stainless steel as battery shell to assemble into a button cell, test capacity and initial coulombic efficiency under a voltage range of 0.01-3.0V using 0.1C constant rate.

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

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

[0103]

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

[0105] Comparative Example 1 does not use phenolic resin wash oil solution to modify porous MXene 2, that is, the surface and pores of the obtained MXene-based composite negative electrode material do not have hard carbon, which greatly reduces the capacity, initial coulombic efficiency and cycle performance of the prepared MXene-based composite negative electrode material.

[0106] 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, which reduces the conductivity of the MXene-based composite negative electrode material and the rate performance of the battery, and the charging and discharging process is easy to cause the aggregation or restacking of the nanosheet in the interlayer of MXene, which reduces the cycle performance and rate performance of the battery.

[0107] Comparative Example 3 does not use hydrogen peroxide to expand the layer and create pores of MXene, which results in small interlayer spacing of the MXene-based composite negative electrode material, which greatly reduces the rate performance and cycle performance of the MXene-based composite negative electrode material.

[0108] 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, and the like made within the spirit and principle of the present application should be included in the scope of the present application.

Claims

1. A method for preparing an MXene-based composite anode material, the method comprising the following steps: (1) Hydrogen peroxide was added to an aqueous solution containing MXene, reacted, centrifuged, washed, and MXene with a porous structure was prepared. (2) Mix the porous MXene, melamine, cyanuric acid and deionized water from step (1) and carry out a hydrothermal reaction to prepare modified porous MXene1; wherein, the modified porous MXene1 includes melamine cyanuric acid and MXene with a porous structure, and the melamine cyanuric acid is inserted into the interlayer of the porous MXene; (3) The modified porous MXene1 from step (2) is heat-treated to prepare modified porous MXene2; wherein 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 MXene with a porous structure. (4) Add the modified porous MXene2 from step (3) into the reactor, evacuate the reactor, add the organic resin solution, and perform pressure impregnation. After the pressure impregnation is completed, reduce the pressure to make the pressure inside and outside the reactor the same, introduce nitrogen gas, heat to remove the organic solvent, and obtain modified MXene3. (5) The modified MXene3 from step (4) is carbonized to prepare the MXene-based composite anode material; the MXene-based composite anode material has a core-shell structure; hard carbon is uniformly distributed in the pores of the porous MXene; the shell layer includes hard carbon.

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 It is 5-10 μm; And / or, in step (1), the interlayer spacing of the MXene is ≤1nm; 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 to wash the solid components obtained after centrifugation with hydrochloric acid and deionized water at a concentration of 10-25% in sequence; And / or, in step (1), the median particle size D of the MXene with the porous structure 50 3-8μm; And / or, in step (1), the interlayer spacing of the porous MXene is 1.2-1.5 nm; And / or, in step (1), each MXene sheet of the porous MXene has a pore structure distributed on it, and the pore size of the pore structure is 20-60 nm.

3. The method according to claim 1, wherein, In step (2), the mass-to-volume ratio of the porous MXene to deionized water is 2-3 mg / mL; And / or, in step (2), the molar ratio of the porous MXene, 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 is a substance formed by inserting melamine cyanuric acid into the interlayer of MXene with a porous structure.

4. The method according to claim 1, wherein, In step (3), the temperature of the heat treatment is 300-500℃; the time of the heat treatment is 1-3 hours. And / or, in step (3), the modified porous MXene2 is a substance formed by inserting melamine cyanuric acid into the interlayer of MXene with a porous structure and then heat-treating it; And / or, in step (4), the vacuum degree of the reactor is 0.07-0.09 MPa; And / or, in step (4), the time for evacuating the reactor is 10-120 min; And / or, in step (4), the organic resin is selected from at least one of petroleum-based resins, phenolic resins and epoxy resins; 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 organic resin solution is: open the suction valve of organic resin solution, suck the organic resin solution into the reaction vessel, close the suction valve after the liquid addition is completed, and stop the vacuuming; And / or, in step (4), the pressure of the pressure impregnation is 1MPa-3MPa, and the pressure impregnation time is 1-5 hours; And / or, in step (5), the carbonization temperature is 1000-1400℃; the carbonization time is 4-10 hours.

5. An MXene-based composite anode material prepared by the method according to any one of claims 1-4.

6. The MXene-based composite anode material according to claim 5, wherein, The MXene-based composite anode material includes MXene with a porous structure, nitrogen-containing nano-carbon, and hard carbon.

7. The MXene-based composite anode material according to claim 5, wherein, The MXene-based composite anode material is a composite of MXene with a porous structure, nitrogen-containing nano-carbon, and hard carbon.

8. The MXene-based composite anode material according to claim 6 or 7, wherein, The porous MXene accounts for 75%-85% of the total mass of the MXene-based composite anode material; the nitrogen-containing nano-carbon accounts for 1%-5% of the total mass of the MXene-based composite anode material; and the hard carbon accounts for 3%-10% of the total mass of the MXene-based composite anode material.

9. The MXene-based composite anode material according to claim 5 or 6, wherein, The nitrogen-containing nano-carbon is embedded in the interlayer of the porous MXene; the hard carbon is uniformly distributed on the surface and in the pores of the porous MXene.

10. The MXene-based composite anode material according to claim 5, wherein, The MXene-based composite anode material has a core-shell structure, including a core and a shell. The core includes MXene with a porous structure, nitrogen-containing nano-carbon, and hard carbon. The nitrogen-containing nano-carbon 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 includes hard carbon. The thickness of the shell layer is 10-30 nm; The median particle size D of the MXene-based composite anode material 50 3-6μm; The interlayer spacing of the MXene-based composite anode material is 1.2-1.5 nm.

11. Use of the MXene-based composite anode material according to any one of claims 5-10, for preparing the anode of a sodium-ion battery.

12. A negative electrode for a sodium-ion battery, comprising the MXene-based composite negative electrode material as described in any one of claims 5-10.

13. A sodium-ion battery comprising the MXene-based composite anode material according to any one of claims 5-10 or the anode of the sodium-ion battery according to claim 12.

Images