Negative electrode material, preparation method thereof, negative electrode sheet and sodium ion battery

Abstract

This application relates to the field of battery technology, specifically to a negative electrode material, its preparation method, a negative electrode sheet, and a sodium-ion battery. The negative electrode material includes WO x -W2C heterojunction nanoparticles and MXene material; the MXene material has an accordion-like layered structure, and the WO x -W2C heterojunction nanoparticles are loaded on the surface of the MXene material and between its layered structures. The negative electrode material of the present invention exhibits high reversible specific capacity and excellent ultra-long cycle stability, and can significantly improve the electrochemical performance of sodium-ion batteries.

Description

Technical Field

[0001] This application relates to the technical field of batteries, and particularly to anode materials, their preparation methods, anode sheets, and sodium-ion batteries. Background Art

[0002] With the growing global demand for sustainable energy storage solutions, sodium-ion batteries have received extensive attention due to their abundant resources, low cost, and rocking-chair working principle similar to that of lithium-ion batteries. However, due to the larger radius of sodium ions than lithium ions, their diffusion rate in electrode materials is slower, which may cause serious collapse of the electrode structure. Currently, various carbon materials, phosphides, and sulfides have been studied as anode materials for sodium-ion batteries, but they usually face problems such as poor electronic conductivity, slow kinetics, and large volume changes, which limit their reversible specific capacity and cycling stability. Therefore, it is necessary to develop an anode material for sodium-ion batteries with excellent rate performance and cycling stability. Summary of the Invention

[0003] In view of this, the present invention provides an anode material, its preparation method, an anode sheet, and a sodium-ion battery. This anode material exhibits high reversible specific capacity and excellent ultra-long cycling stability, which can significantly improve the electrochemical performance of sodium-ion batteries.

[0004] To achieve the above-mentioned invention objectives, the present invention provides the following technical solutions:

[0005] In a first aspect, the present invention provides an anode material, which includes WO x -W2C heterojunction nanoparticles and MXene material;

[0006] The MXene material has an accordion-like layered structure, and the WO x -W2C heterojunction nanoparticles are loaded on the surface of the MXene material and between its layered structures.

[0007] Preferably, the WO x -W2C heterojunction nanoparticles have an amorphous / crystalline heterojunction interface.

[0008] In an embodiment of the present invention, the WO x -W2C heterojunction nanoparticles include tungsten oxide (WO x ), where x is 0.5 to 2.

[0009] In an embodiment of the present invention, the chemical formula of the MXene material is M n+1 X n T y, wherein M is at least one of transition metal elements Ti, V, Nb, Cr, Sc, Mo, Y, Zr, Ta, W, Hf, X is C and / or N element, T y is at least one of surface functional groups -O, -Cl, -OH, -F, n is the number of layers, and n is selected from 1, 2 or 3.

[0010] Preferably, the molar ratio of WO x -W2C heterojunction nanoparticles to MXene material is (2-6):(4-8).

[0011] Preferably, in the WO x -W2C heterojunction nanoparticles, the molar ratio of WO x to W2C is (1.5-5):(3.5-5).

[0012] Preferably, the crystallinity of WO x -W2C heterojunction nanoparticles is 55%-85%.

[0013] In a second aspect, the present invention provides a method for preparing the above-mentioned anode material, comprising the following steps:

[0014] S1, in an inert gas atmosphere, mix a pH regulator, a first reducing agent and water to obtain solution A;

[0015] In an inert gas atmosphere, mix MXene material, tungsten source, a second reducing agent and water to obtain solution B;

[0016] Mix solution A and solution B to obtain a mixed solution;

[0017] Introduce methane into the mixed solution to carry out a hydrothermal reaction, wash and dry the obtained precipitate to obtain precursor C;

[0018] S2, in an inert gas atmosphere, subject precursor C to Joule heating treatment to obtain MXene material loaded with amorphous WO x -W2C heterojunction nanoparticles, denoted as A-WO x -W2C / MXene.

[0019] Preferably, the molar ratio of the pH regulator, the first reducing agent, the MXene material, the tungsten source to the second reducing agent is (1.5-3.5):(6-10):(2-4):(1-4):(0.5-2).

[0020] In the embodiment of the present invention, the pH regulator includes at least one of sodium sulfite (Na2SO3), sodium bisulfite (NaHSO3), sodium carbonate (Na2CO3), sodium bicarbonate (NaHCO3), acetic acid (CH3COOH).

[0021] In an embodiment of the present invention, the first reducing agent includes at least one of sodium borohydride (NaBH4), lithium aluminum hydride (LiAlH4), potassium borohydride (KBH4), and triethylsilane ((Et)3SiH).

[0022] In an embodiment of the present invention, the tungsten source includes at least one of ammonium tungstate ((NH4)2WO4), ammonium metatungstate ((NH4)6H2W 12 O 40 ), ammonium paratungstate ((NH4) 10 W 12 O 41 ), sodium tungstate (Na2WO4), and potassium tungstate (K2WO4).

[0023] In an embodiment of the present invention, the second reducing agent includes at least one of hydroxylamine hydrochloride (NH2OH·HCl), sodium bisulfite (NaHSO3), ascorbic acid (C6H8O6), hydroxylamine sulfate (H8N2O6S), and hydroxylamine nitrate (NH2OH·HNO3).

[0024] Preferably, in step S1, the temperature of the hydrothermal reaction is 200 - 400 °C, and the time of the hydrothermal reaction is 10 - 20 h.

[0025] Preferably, in step S2, the holding temperature of the Joule heating treatment is 1600 - 2000 K, the holding time of the Joule heating treatment is 3 - 8 s, and the heating rate of the Joule heating treatment is 800 - 1200 K s -1 .

[0026] Preferably, the preparation method further includes step S3: annealing A-WO x -W2C / MXene in an inert gas atmosphere to obtain an MXene material loaded with amorphous / crystalline WO x -W2C heterojunction nanoparticles, denoted as A / C-WO x -W2C / MXene.

[0027] Preferably, in step S3, the holding temperature of the annealing treatment is 300 - 400 °C, the holding time of the annealing treatment is 3 - 7 h, the heating rate of the annealing treatment is 1 - 5 °C min -1 , and the cooling rate of the annealing treatment is 1 - 5 °C min -1 .

[0028] In a third aspect, the present invention provides a negative electrode sheet, which includes the above-mentioned negative electrode material and / or the negative electrode material prepared by the above-mentioned preparation method.

[0029] Fourthly, the present invention provides a sodium-ion battery, which includes the above-mentioned negative electrode sheet.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] 1. The MXene material in the negative electrode material of the present invention is a novel two-dimensional material with excellent electrical conductivity, outstanding mechanical properties and adjustable layer spacing. Its layered structure serves as a conductive support, significantly enhancing electron conductivity and restricting the volume change of WO x -W2C, and preventing the pulverization and attenuation of WO x -W2C. The two-dimensional structure of MXene is beneficial to the rapid diffusion of ions and the effective transmission of charges, improving the ion diffusion rate and charge-discharge performance of the battery.

[0032] 2. The surface of WO x in the negative electrode material of the present invention is rich in oxygen vacancies, defects and tungsten ions with different valence states. These characteristics enable WO x to have a strong adsorption capacity for Na + . When Na + migrates to the electrode surface in the electrolyte, WO x can quickly and effectively capture these ions, forming a stable heterogeneous interface, thereby improving the cycle stability and rate performance of the battery;

[0033] The W2C material has high electrical conductivity, which not only provides a fast channel for electron transport, but also enhances the overall structural stability of the composite material. This enables electrons to be quickly transported throughout the electrode material during charge and discharge, reducing resistance loss and improving energy conversion efficiency.

[0034] When the present invention combines WO x and W2C, the interfacial effect between the two will generate a large number of binding sites, which can serve as both adsorption centers for Na + and channels for electron transfer. In addition, due to the difference in electronic structure between WO x and W2C, an internal built-in electric field may be formed at the interface, further promoting the migration and insertion / extraction process of Na + .

[0035] Moreover, by designing an amorphous / crystalline (A / C) heterogeneous interface, the present invention can optimize the electronic structure, improve the adsorption capacity of Na + ; in addition, it also induces the generation of a rich local built-in electric field, significantly improving the charge transfer ability and promoting the reaction kinetics.

[0036] 3. The negative electrode material of the present invention combines WO x- The complementary advantages of W2C and MXene exhibit a high reversible specific capacity (673.3 mA h g -1 after 500 cycles at 0.5 A g -1 ), and excellent ultra-long cycle stability (492.4 mA h g -1 after 10,000 cycles at 8 A g -1 with a capacity decay of only 0.002% per cycle), which can significantly improve the electrochemical performance of sodium-ion batteries.

[0037] 4. The negative electrode material was successfully prepared by the hydrothermal, rapid Joule heating and annealing techniques in the present invention. This process effectively optimized the crystallinity of WO x -W2C by finely regulating the annealing temperature, opening up a simple and effective way to improve its electrochemical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 : SEM image of A / C-WO x -W2C / MXene material (Example 1).

[0039] Figure 2 : TEM image of A-WO x -W2C / MXene material (Example 6).

[0040] Figure 3 : TEM image of C-WO x -W2C / MXene material (Example 7). DETAILED DESCRIPTION OF THE INVENTION

[0041] The present invention discloses a negative electrode material, a preparation method thereof, a negative electrode sheet and a sodium-ion battery. Those skilled in the art can draw on the content of this article and appropriately improve the process parameters to achieve. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art, and they are all regarded as included in the present invention. The methods and applications of the present invention have been described through preferred embodiments, and those skilled in the art can obviously make changes or appropriate modifications and combinations to the methods and applications described herein without departing from the content, spirit and scope of the present invention to implement and apply the technical solution of the present invention.

[0042] In the description of the present invention, it should be noted that the terms "first", "second", etc. are only used for descriptive purposes, and do not indicate or imply relative importance.

[0043] In the description of the present invention, a list of items connected by the term "at least one of" or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A, B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may include a single element or multiple elements. Item B may include a single element or multiple elements. Item C may include a single element or multiple elements.

[0044] The endpoints and any values within the ranges disclosed herein are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values and individual point values of each range, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0045] If there is no special indication, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0046] If there is no special indication, all technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

[0047] If there is no special indication, the "including" and "comprising" mentioned in the present application mean open-ended, and can also be closed-ended. For example, the "including" and "comprising" can mean that other components not listed can also be included or comprised, or can only include or comprise the listed components.

[0048] Specifically, the present invention adopts the following technical solutions:

[0049] In a first aspect, the present invention provides a negative electrode material, which includes WO x -W2C heterojunction nanoparticles and MXene material;

[0050] The MXene material has an accordion-like layered structure, and the WO x -W2C heterojunction nanoparticles are loaded on the surface of the MXene material and between its layered structures.

[0051] In the present invention, the MXene material in the negative electrode material is a novel two-dimensional material, which has excellent electrical conductivity, excellent mechanical properties and adjustable layer spacing. Its layered structure is used as a conductive support, significantly enhancing the electron conductivity, restricting the volume change of WO x -W2C, and preventing WOx -W2C pulverization attenuation. The two-dimensional structure of MXene is beneficial to the rapid diffusion of ions and the effective transport of charges, improving the ion diffusion rate and charge-discharge performance of the battery.

[0052] WO in the anode material x The surface contains abundant oxygen vacancies, defects, and tungsten ions with different valence states. These characteristics make WO x have a strong adsorption capacity for Na + . When Na + migrates to the electrode surface in the electrolyte, WO x can quickly and effectively capture these ions, forming a stable heterointerfacial layer, thereby improving the cycle stability and rate performance of the battery; the W2C material has high conductivity, which not only provides a fast channel for electron transport but also enhances the overall structural stability of the composite material. This enables electrons to be quickly transported throughout the electrode material during charge and discharge, reducing resistance losses and improving energy conversion efficiency. When the WO x and W2C are combined in the present invention, the interfacial effect between them will generate a large number of binding sites, which can serve as both the adsorption centers for Na + and the channels for electron transfer. In addition, due to the difference in the electronic structures between WO x and W2C, an internal built-in electric field may be formed at the interface, further promoting the migration and insertion / extraction processes of Na + .

[0053] The anode material of the present invention combines the complementary advantages of WO x -W2C and MXene, showing a high reversible specific capacity (the capacity is 673.3 mA h g -1 after 500 cycles at 0.5 A g -1 ) and excellent ultra-long cycle stability (the capacity is 492.4 mA h g -1 after 10,000 cycles at 8 A g -1 , and the capacity decay per cycle is only 0.002%), which can significantly improve the electrochemical performance of sodium-ion batteries.

[0054] Preferably, the WO x -W2C heterojunction nanoparticles have an amorphous / crystalline heterointerfacial layer. The amorphous / crystalline (A / C) heterointerfacial layer can achieve the optimization of the electronic structure, improve the adsorption capacity of Na + ; in addition, it induces the generation of abundant local built-in electric fields, significantly improving the charge transfer ability and promoting the reaction kinetics.

[0055] In the embodiment of the present invention, WO x-W2C heterojunction nanoparticles include tungsten oxide (WO x ), and tungsten carbide (W2C), where x is from 0.5 to 2. Exemplarily, x is any value among 0.5, 1, 1.5, 2 or any value within the range formed by any two of the above values.

[0056] In the embodiments of the present invention, the chemical formula of the MXene material is M n+1 X n T y , where M is at least one of the transition metal elements Ti, V, Nb, Cr, Sc, Mo, Y, Zr, Ta, W, Hf, X is the element C and / or N, and T y is at least one of the surface functional groups -O, -Cl, -OH, -F, and n is the number of layers, and n is selected from 1, 2 or 3.

[0057] In the specific embodiments of the present invention, the MXene material can be Ti3C2T y , V4C3T y , Ta4C3T y , Nb4C3T y , Mo2C3T y at least one of them.

[0058] Preferably, the molar ratio of WO x -W2C heterojunction nanoparticles to the MXene material is (2 - 6):(4 - 8). Exemplarily, the molar ratio of WO x -W2C heterojunction nanoparticles to the MXene material is any value among 1:4, 3:7, 1:2, 2:3, 3:4, 1:1, 3:2 or any value within the range formed by any two of the above values. When the proportion of WO x -W2C heterojunction nanoparticles is too small, the heterojunction effect is not significant. At the same time, the insufficient addition of WO x -W2C nanoparticles results in the inability to exert the modification effect on the MXene material; when the proportion of WO x -W2C heterojunction nanoparticles is too large, WO x -W2C nanoparticles cause the overall dispersibility of the material to deteriorate, affecting the uniformity and stability of the material.

[0059] Preferably, in the WO x -W2C heterojunction nanoparticles, the molar ratio of WO x to W2C is (1.5 - 5):(3.5 - 5). Exemplarily, the molar ratio of WO x to W2C is any value among 1.5:5, 1:2, 1:1, 1.5:3.5, 5:3.5 or any value within the range formed by any two of the above values. When WOx When the proportion is too small, the heterojunction is not completely formed, affecting the catalytic and stability of the material. At the same time, too little WO x affects the antioxidant property of the material; when the proportion of WO x is too large, the conductivity of the material decreases, affecting the electrochemical performance of the material.

[0060] Preferably, the crystallinity of the WO x -W2C heterojunction nanoparticles is 55% - 85%. Exemplarily, the crystallinity of the WO x -W2C heterojunction nanoparticles is any value among 55%, 60%, 65%, 70%, 75%, 80%, 85% or any value within the range formed by any two of the above values. When the crystallinity is lower than 55%, the hardness and strength of the material become poor; when the crystallinity is higher than 85%, the material becomes brittle and hard, reducing the toughness and plasticity of the composite material.

[0061] In a second aspect, the present invention provides a method for preparing the above-mentioned negative electrode material, including the following steps:

[0062] S1. In an inert gas atmosphere, mix a pH regulator, a first reducing agent, and water to obtain solution A;

[0063] In an inert gas atmosphere, mix an MXene material, a tungsten source, a second reducing agent, and water to obtain solution B;

[0064] Mix solution A and solution B to obtain a mixed solution;

[0065] Introduce methane into the mixed solution to carry out a hydrothermal reaction, wash and dry the obtained precipitate to obtain precursor C;

[0066] S2. In an inert gas atmosphere, subject precursor C to Joule heating treatment to obtain an MXene material loaded with amorphous WO x -W2C heterojunction nanoparticles, denoted as A-WO x -W2C / MXene.

[0067] In step S1, under the action of the reducing agent, the tungsten source undergoes a reduction reaction to generate low-valence tungsten oxides (WO x ), carbides (W2C); among them, MXene participates in the reaction as a carrier or catalyst, and forms a new complex with the above reduction reaction products. The reaction equations of WO x and W2C are as follows:

[0068] (NH4)2WO4 + reducing agent → WO x

[0069] (NH4)2WO4 + reducing agent + CH4 → W2C. (Condition: high-temperature heating)

[0070] Preferably, the molar ratio of the pH regulator, the first reducing agent, the MXene material, the tungsten source, and the second reducing agent is (1.5 - 3.5):(6 - 10):(2 - 4):(1 - 4):(0.5 - 2). Exemplarily, the molar ratio of the pH regulator, the first reducing agent, the MXene material, the tungsten source, and the second reducing agent is any value among 2.5:10:4:1:1, 1.5:10:2:4:0.5, 3.5:6:4:1:2, 2:5:3:2:1 or any value within the range formed by any two of the above values.

[0071] In the embodiments of the present invention, the pH regulator includes at least one of sodium sulfite (Na2SO3), sodium bisulfite (NaHSO3), sodium carbonate (Na2CO3), sodium bicarbonate (NaHCO3), acetic acid (CH3COOH). Preferably Na2SO3 because Na2SO3 is relatively stable, not easily decomposed, and has a certain solubility in water, which can be conveniently used to adjust the pH value of the solution.

[0072] In the embodiments of the present invention, the first reducing agent includes at least one of sodium borohydride (NaBH4), lithium aluminum hydride (LiAlH4), potassium borohydride (KBH4), triethylsilane ((Et)3SiH). The above first reducing agent is used for the reduction of tungsten-containing acid root ions (such as WO4 2- ) in the tungsten source. Preferably NaBH4 because NaBH4 has moderate reactivity and good selectivity, can effectively reduce various functional groups under mild conditions, and avoid unnecessary side reactions.

[0073] In the embodiments of the present invention, the tungsten source includes at least one of ammonium tungstate ((NH4)2WO4), ammonium metatungstate ((NH4)6H2W 12 O 40 ), ammonium paratungstate ((NH4) 10 W 12 O 41 ), sodium tungstate (Na2WO4), potassium tungstate (K2WO4). Preferably (NH4)2WO4 because (NH4)2WO4 has more excellent reactivity and selectivity, can better meet the process requirements, and improve the yield and purity of the product.

[0074] In an embodiment of the present invention, the second reducing agent includes at least one of hydroxylamine hydrochloride (NH2OH·HCl), sodium bisulfite (NaHSO3), ascorbic acid (C6H8O6), hydroxylamine sulfate (H8N2O6S), and hydroxylamine nitrate (NH2OH·HNO3). The above-mentioned second reducing agent has strong reducibility and nucleophilicity and can participate in various chemical reactions to help promote the reduction of tungstate ions (such as WO4 2- ), and stabilize the dispersion of MXene. NH2OH·HCl is preferred because NH2OH·HCl has the characteristics of stable chemical properties, strong reducibility, high reactivity, good solubility, and easy preparation and purification.

[0075] Preferably, in step S1, the temperature of the hydrothermal reaction is 200 - 400 °C. Exemplarily, the temperature of the hydrothermal reaction is any value among 200 °C, 250 °C, 300 °C, 350 °C, 400 °C or any value within the range formed by any two of the above values.

[0076] Preferably, in step S1, the time of the hydrothermal reaction is 10 - 20 h. Exemplarily, the time of the hydrothermal reaction is any value among 10 h, 12 h, 14 h, 16 h, 18 h, 20 h or any value within the range formed by any two of the above values.

[0077] Preferably, in step S2, the holding temperature of the Joule heating treatment is 1600 - 2000 K. Exemplarily, the holding temperature of the Joule heating treatment is any value among 1600 K, 1700 K, 1800 K, 1900 K, 2000 K or any value within the range formed by any two of the above values.

[0078] Preferably, in step S2, the holding time of the Joule heating treatment is 3 - 8 s. Exemplarily, the holding time of the Joule heating treatment is any value among 3 s, 4 s, 5 s, 6 s, 7 s, 8 s or any value within the range formed by any two of the above values.

[0079] Preferably, in step S2, the heating rate of the Joule heating treatment is 800 - 1200 K s -1 . Exemplarily, the heating rate of the Joule heating treatment is 800 K s -1 , 900 K s -1 , 1000 K s -1 , 1100 K s -1 , 1200 K s -1 or any value within the range formed by any two of the above values.

[0080] Preferably, the preparation method further includes step S3: Under an inert gas atmosphere, A-WO x -W2C / MXene is annealed to obtain a MXene material loaded with amorphous / crystalline WO x -W2C heterojunction nanoparticles, denoted as A / C-WO x -W2C / MXene.

[0081] Preferably, in step S3, the holding temperature of the annealing treatment is 300-400 °C. Exemplarily, the holding temperature of the annealing treatment is any value among 300 °C, 320 °C, 340 °C, 360 °C, 380 °C, 400 °C or any value within the range formed by any two of the above values.

[0082] Preferably, in step S3, the holding time of the annealing treatment is 3-7 h. Exemplarily, the holding time of the annealing treatment is any value among 3 h, 4 h, 5 h, 6 h, 7 h or any value within the range formed by any two of the above values.

[0083] Preferably, in step S3, the heating rate of the annealing treatment is 1-5 °C min -1 . Exemplarily, the heating rate of the annealing treatment is 1 °C min -1 , 2 °C min -1 , 3 °C min -1 , 4 °C min -1 , 5 °C min -1 or any value within the range formed by any two of the above values.

[0084] Preferably, in step S3, the cooling rate of the annealing treatment is 1-5 °C min -1 . Exemplarily, the cooling rate of the annealing treatment is 1 °C min -1 , 2 °C min -1 , 3 °C min -1 , 4 °C min -1 , 5 °C min -1 or any value within the range formed by any two of the above values.

[0085] In the embodiment of the present invention, the preparation method of the MXene material includes: mixing the MAX phase material and the etching solution evenly to obtain a mixture; stirring the mixture, collecting the precipitate, and after washing and drying, obtaining the MXene material.

[0086] In the embodiment of the present invention, the chemical formula of the MAX phase material is M n+1 AX n, wherein M is at least one of transition metal elements Ti, V, Nb, Cr, Sc, Mo, Y, Zr, Ta, W, Hf; A is at least one of Al, Ga, Zn, Si, P, S, Ge, As, Cd, In, Sn, Tl, Pb; X is C and / or N element; n is the number of layers, and n is selected from 1, 2 or 3.

[0087] In the embodiments of the present invention, the MAX phase material can be at least one of Ti3AlC2, V4AlC3, Ta4AlC3, Nb4AlC3, Mo2AlC3.

[0088] In the embodiments of the present invention, the etching solution includes at least one of hydrofluoric acid (HF) solution, zinc chloride (ZnCl2) solution, copper chloride (CuCl2) solution, cadmium chloride (CdCl2) solution, hydrochloric acid (HCl) solution, nitric acid (HNO3) solution, perchloric acid (HClO4) solution. HF is preferred because HF has selectivity for the etching of the MAX phase and can preferentially select the M—A bond with weaker bond energy, so that the M-X layer connected by A atoms is gradually separated to generate the corresponding MXenes material; in addition, the HF etching method has been widely used in the etching of various MAX phases.

[0089] Preferably, the mass percentage concentration of the etching solution is 20% - 60%. If the concentration range is too low (less than 20%), the etching effect is insufficient and the etching rate becomes slow, increasing the preparation cost and time; if the concentration is too high (more than 60%), the etching effect is too strong, which may lead to over-etching of MXene and damage its crystal structure and properties. The optimal choice is 40%. After the concentration exceeds 40%, HF will start to evaporate and form gas, which not only increases the volatile loss during the preparation process, but also may cause corrosion and pollution to the experimental environment and equipment.

[0090] In the embodiments of the present invention, based on g / mL, the ratio of the MAX phase material to the etching solution is (2 - 5):(40 - 60).

[0091] In the embodiments of the present invention, the stirring time is 12 - 24 h to ensure that the MAX phase fully reacts with the etchant in the etching solution and is converted into MXene material.

[0092] In the third aspect, the present invention provides a negative electrode sheet, which includes the above-mentioned negative electrode material and / or the negative electrode material prepared by the above-mentioned preparation method.

[0093] In the embodiments of the present invention, the negative electrode sheet further includes a conductive agent and a binder. The present application does not particularly limit the types of the conductive agent and the binder, and those skilled in the art can select according to actual needs as long as the purpose of the present application can be achieved. The dosages of the conductive agent and the binder are conventional dosages in the art, and the present invention will not elaborate herein.

[0094] Fourthly, the present invention provides a sodium-ion battery, which includes the above-mentioned negative electrode sheet.

[0095] In the embodiments of the present invention, the battery structure includes but is not limited to coin cells, soft-pack batteries, cylindrical batteries, and the like.

[0096] The present application places no particular restrictions on the positive electrode sheet, separator, and electrolyte in the battery. Those skilled in the art can select according to actual needs as long as the purpose of the present application can be achieved.

[0097] The reagents, instruments, materials, etc. used in the present invention can all be obtained through commercial channels.

[0098] The following further elaborates the present invention in conjunction with embodiments:

[0099] Example 1:

[0100] The preparation of the negative electrode material (A / C-WO x -W2C / MXene) in this example includes the following steps:

[0101] S1: First, using the stepwise feeding method, 3 g of MAX (Ti3AlC2) powder is slowly added to 60 mL of an HF solution containing 40%. Subsequently, the magnetic stirrer is used to continuously stir the mixed system for 24 hours to ensure that MAX fully reacts with HF and is converted into MXene (Ti3C2T x ) precursor.

[0102] S2: The reaction mixture is centrifuged at a speed of 3000 rpm for 5 minutes by a centrifuge to collect the generated MXene precipitate. The obtained precipitate needs to be washed with deionized water multiple times to thoroughly remove residual HF and other impurities. Finally, the washed MXene precipitate is dried at 60 °C for 12 hours to obtain a pure MXene product.

[0103] S3: Under an argon atmosphere, 2.5 mmol of Na2SO3 powder is added to 10 mL of deionized water, and then 10 mmol of NaBH4 powder is dissolved in the above solution, named solution A.

[0104] S4: Meanwhile, 4 mmol of MXene, 1 mmol (NH4)2WO4, and 1 mmol of NH2OH·HCl are added to 30 mL of deionized water and stirred for 2 hours, named solution B.

[0105] S5: Mix solution A and solution B together and transfer them to a 50 mL reactor. Introduce methane gas and react at 200 °C for 20 hours. Collect the resulting precipitate, wash it thoroughly by centrifugation with deionized water, and dry it in a vacuum oven at 60 °C for 12 hours to obtain precursor C.

[0106] S6: In a nitrogen environment, convert precursor C compound into A-WO x -W2C / MXene by Joule heating with instantaneous high temperature (about 1800 K).

[0107] S7: Place the prepared A-WO x -W2C / MXene in a quartz tube and heat it to 300 °C at a heating rate of 1 °C min -1 in an argon atmosphere and maintain sintering for 3 hours. Then cool it to room temperature at a cooling rate of 1 °C min -1 . Name the obtained product A / C-WO x -W2C / MXene.

[0108] Figure 1 is the SEM image of A / C-WO x -W2C / MXene material. It can be seen that it presents a typical accordion-like structure. In the A / C-WO x -W2C / MXene composite material, WO x and W2C are attached between the MXene lamellae. It can be seen that the overall composite material maintains the accordion-like structure of MXene, indicating that the introduction of WO x and W2C does not destroy the two-dimensional layered structure of MXene.

[0109] Example 2:

[0110] The preparation of the negative electrode material (A / C-WO x -W2C / MXene) in this example includes the following steps:

[0111] S1: First, adopt the stepwise feeding method and slowly add 3 g of MAX (V4AlC3) powder to 60 mL of HF solution containing 40%. Subsequently, continuously stir the mixed system with a magnetic stirrer for 24 hours to ensure that MAX fully reacts with HF and is converted into MXene (V4C3T x ).

[0112] S2: Centrifuge the reaction mixture at 3000 rpm for 5 minutes to collect the resulting MXene precipitate. The obtained precipitate needs to be washed multiple times with deionized water to thoroughly remove residual HF and other impurities. Finally, place the washed MXene precipitate in an oven at 60 °C for drying for 12 hours to obtain a pure MXene product.

[0113] S3: Under an argon atmosphere, add 2.5 mmol of Na2SO3 powder to 10 mL of deionized water, and then dissolve 10 mmol of NaBH4 powder in the above solution, named solution A.

[0114] S4: Meanwhile, add 4 mmol of MXene, 1 mmol of (NH4)2WO4, and 1 mmol of NH2OH·HCl to 30 mL of deionized water and stir for 2 hours, named solution B.

[0115] S5: Mix solution A and solution B together and transfer them to a 50 mL autoclave, introduce methane gas, and react at 200 °C for 20 hours. Collect the resulting precipitate, wash it clean by centrifugation with deionized water, and dry it in a vacuum oven at 60 °C for 12 hours to obtain precursor C.

[0116] S6: In a nitrogen environment, convert the precursor C compound into A-WO x -W2C / MXene by instantaneous high-temperature (about 1800 K) Joule heating.

[0117] S7: Place the prepared A-WO x -W2C / MXene in a quartz tube, and under an argon atmosphere, heat it to 320 °C at a heating rate of 2 °C min -1 and maintain sintering for 4 hours, and then cool it to room temperature at a cooling rate of 2 °C min -1 to obtain a product named A / C-WO x -W2C / MXene.

[0118] Example 3:

[0119] The preparation of the negative electrode material (A / C-WO x -W2C / MXene) in this example includes the following steps:

[0120] S1: First, using the stepwise feeding method, slowly add 3 g of MAX (Ta4AlC3) powder to 60 mL of an HF solution containing 40%. Subsequently, continuously stir the mixed system with a magnetic stirrer for 24 hours to ensure that MAX fully reacts with HF and is converted into MXene (Ta4C3Tx )Precursor.

[0121] S2: Centrifuge the reaction mixture at 3000 rpm for 5 minutes using a centrifuge to collect the generated MXene precipitate. The obtained precipitate needs to be washed multiple times with deionized water to thoroughly remove residual HF and other impurities. Finally, place the washed MXene precipitate in an oven at 60 °C for drying for 12 hours to obtain a pure MXene product.

[0122] S3: Add 2.5 mmol of Na2SO3 powder to 10 mL of deionized water under an argon atmosphere, and then dissolve 10 mmol of NaBH4 powder in the above solution, named solution A.

[0123] S4: Meanwhile, add 4 mmol of MXene, 1 mmol of (NH4)2WO4, and 1 mmol of NH2OH·HCl to 30 mL of deionized water and stir for 2 hours, named solution B.

[0124] S5: Mix solution A and solution B together and transfer them to a 50 mL autoclave, introduce methane gas, and react at 200 °C for 20 hours. Collect the obtained precipitate and wash it clean by centrifugation with deionized water, and dry it in a vacuum oven at 60 °C for 12 hours to obtain precursor C.

[0125] S6: In a nitrogen environment, convert precursor C compound into A-WO x -W2C / MXene by instantaneous high-temperature (about 1800 K) Joule heating.

[0126] S7: Place the prepared A-WO x -W2C / MXene in a quartz tube, and under an argon atmosphere, heat it to 340 °C at a heating rate of 3 °C / min and maintain sintering for 5 hours, and then cool it to room temperature at a cooling rate of 3 °C / min. The obtained product is named A / C-WO -1 -1 -W2C / MXene. x

[0127] Example 4:

[0128] The preparation of the negative electrode material (A / C-WO x -W2C / MXene) in this example includes the following steps:

[0129] S1: First, using the stepwise feeding method, 3 g of MAX (Nb4AlC3) powder was slowly added to 60 mL of HF solution containing 40%. Subsequently, the magnetic stirrer was used to continuously stir the mixed system for 24 hours to ensure that MAX and HF fully reacted and were converted into MXene (Nb4C3T x ) precursor.

[0130] S2: The reaction mixture was centrifuged at 3000 rpm for 5 minutes to collect the generated MXene precipitate. The obtained precipitate was washed several times with deionized water to thoroughly remove the residual HF and other impurities. Finally, the washed MXene precipitate was dried at 60 °C for 12 hours to obtain a pure MXene product.

[0131] S3: Under an argon atmosphere, 2.5 mmol of Na2SO3 powder was added to 10 mL of deionized water, and then 10 mmol of NaBH4 powder was dissolved in the above solution, named solution A.

[0132] S4: Meanwhile, 4 mmol of MXene, 1 mmol of (NH4)2WO4, and 1 mmol of NH2OH·HCl were added to 30 mL of deionized water and stirred for 2 hours, named solution B.

[0133] S5: Solution A and solution B were mixed together and transferred to a 50 mL autoclave. Methane gas was introduced, and the reaction was carried out at 200 °C for 20 hours. The obtained precipitate was collected and centrifuged and washed clean with deionized water, and dried at 60 °C in a vacuum oven for 12 hours to obtain precursor C.

[0134] S6: In a nitrogen environment, the precursor C compound was converted into A-WO x -W2C / MXene by instantaneous high-temperature (about 1800 K) Joule heating.

[0135] S7: The prepared A-WO x -W2C / MXene was placed in a quartz tube and heated to 370 °C at a heating rate of 4 °C min -1 in an argon atmosphere and sintered for 6 hours, and then cooled to room temperature at a cooling rate of 4 °C min -1 . The obtained product was named A / C-WO x -W2C / MXene.

[0136] Example 5:

[0137] The negative electrode material of this example (A / C-WO xThe preparation of A-WO-W2C / MXene) includes the following steps:

[0138] S1: First, using the stepwise feeding method, 3 g of MAX (Mo2AlC3) powder is slowly added to 60 mL of an HF solution containing 40%. Subsequently, the magnetic stirrer is used to continuously stir the mixed system for 24 hours to ensure that MAX and HF fully react and are converted into MXene (Mo2C3T x ) precursor.

[0139] S2: The reaction mixture is centrifuged at 3000 rpm for 5 minutes to collect the generated MXene precipitate. The obtained precipitate is washed multiple times with deionized water to thoroughly remove residual HF and other impurities. Finally, the washed MXene precipitate is dried at 60 °C for 12 hours to obtain a pure MXene product.

[0140] S3: Under an argon atmosphere, 2.5 mmol of Na2SO3 powder is added to 10 mL of deionized water, and then 10 mmol of NaBH4 powder is dissolved in the above solution, named solution A.

[0141] S4: Meanwhile, 4 mmol of MXene, 1 mmol of (NH4)2WO4, and 1 mmol of NH2OH·HCl are added to 30 mL of deionized water and stirred for 2 hours, named solution B.

[0142] S5: Solution A and solution B are mixed together and transferred to a 50 mL autoclave, methane gas is introduced, and the reaction is carried out at 200 °C for 20 hours. The obtained precipitate is collected and centrifuged and washed clean with deionized water, and dried at 60 °C in a vacuum oven for 12 hours to obtain precursor C.

[0143] S6: In a nitrogen environment, the precursor C compound is converted into A-WO x -W2C / MXene by instantaneous high-temperature (about 1800 K) Joule heating.

[0144] S7: The prepared A-WO x -W2C / MXene is placed in a quartz tube and heated to 400 °C at a heating rate of 5 °C min -1 and sintered for 7 hours under an argon atmosphere, and then cooled to room temperature at a cooling rate of 5 °C min -1 . The obtained product is named A / C-WO x -W2C / MXene.

[0145] Example 6:

[0146] In this embodiment, the preparation of the anode material (A-WO x -W2C / MXene) includes the following steps:

[0147] S1: First, using the stepwise feeding method, 3 g of MAX powder is slowly added to 60 mL of an HF solution containing 40%. Subsequently, the magnetic stirrer is used to continuously stir the mixed system for 24 hours to ensure that MAX and HF fully react and are converted into the MXene precursor.

[0148] S2: The reaction mixture is centrifuged at 3000 rpm for 5 minutes to collect the generated MXene precipitate. The obtained precipitate is washed several times with deionized water to completely remove the residual HF and other impurities. Finally, the washed MXene precipitate is dried at 60 °C for 12 hours to obtain a pure MXene product.

[0149] S3: Under an argon atmosphere, 2.5 mmol of Na2SO3 powder is added to 10 mL of deionized water, and then 10 mmol of NaBH4 powder is dissolved in the above solution, named solution A.

[0150] S4: Meanwhile, 4 mmol of MXene, 1 mmol of (NH4)2WO4, and 1 mmol of NH2OH·HCl are added to 30 mL of deionized water and stirred for 2 hours, named solution B.

[0151] S5: Solution A and solution B are mixed together and transferred to a 50 mL autoclave, methane gas is introduced, and the reaction is carried out at 200 °C for 20 hours. The obtained precipitate is collected and centrifuged and washed clean with deionized water, and dried at 60 °C in a vacuum oven for 12 hours to obtain the precursor C.

[0152] S6: In a nitrogen environment, the precursor C compound is converted into A-WO x -W2C / MXene by instantaneous high-temperature (about 1800 K) Joule heating.

[0153] Figure 2 The TEM image of the A-WO x -W2C / MXene material is shown, in which an amorphous structure can be seen. It means that the WO x and W2C components in the material are arranged in a disordered manner without forming an obvious crystal structure.

[0154] Example 7:

[0155] In this embodiment, the anode material (C-WO xThe preparation of (-W2C / MXene) includes the following steps:

[0156] S1: First, using the stepwise feeding method, 3 g of MAX powder is slowly added to 60 mL of an HF solution containing 40%. Subsequently, the magnetic stirrer is used to continuously stir the mixed system for 24 hours to ensure that MAX and HF fully react and are converted into the MXene precursor.

[0157] S2: The reaction mixture is centrifuged at 3000 rpm for 5 minutes to collect the generated MXene precipitate. The obtained precipitate needs to be washed several times with deionized water to thoroughly remove the residual HF and other impurities. Finally, the washed MXene precipitate is dried at 60 °C for 12 hours to obtain a pure MXene product.

[0158] S3: Under an argon atmosphere, 2.5 mmol of Na2SO3 powder is added to 10 mL of deionized water, and then 10 mmol of NaBH4 powder is dissolved in the above solution, named solution A.

[0159] S4: Meanwhile, 4 mmol of MXene, 1 mmol of (NH4)2WO4, and 1 mmol of NH2OH·HCl are added to 30 mL of deionized water and stirred for 2 hours, named solution B.

[0160] S5: Solution A and solution B are mixed together and transferred to a 50 mL autoclave, methane gas is introduced, and the reaction is carried out at 200 °C for 20 hours. The obtained precipitate is collected and centrifuged and washed clean with deionized water, and dried at 60 °C in a vacuum oven for 12 hours to obtain the precursor C.

[0161] S6: In a nitrogen environment, the precursor C compound is converted into A-WO through instantaneous high-temperature (about 1800 K) Joule heating. x -W2C / MXene.

[0162] S7: The prepared A-WO x -W2C / MXene is placed in a quartz tube and sintered at 800 °C for 2 hours under an argon atmosphere, and then naturally cooled to room temperature. The obtained product is named C-WO x -W2C / MXene.

[0163] Figure 3 The TEM image of the C-WO x -W2C / MXene material is shown, in which the crystal structure can be clearly seen. This means that WO in the material xIt forms an ordered crystal structure with the W2C component.

[0164] Comparative Example 1:

[0165] The preparation of the negative electrode material (A / C-WO x -W2C) of this comparative example includes the following steps:

[0166] S1: Under an argon atmosphere, 2.5 mmol of Na2SO3 powder was added to 10 mL of deionized water, and then 10 mmol of NaBH4 powder was dissolved in the above solution, named solution A.

[0167] S2: At the same time, 1 mmol of (NH4)2WO4 and 1 mmol of NH2OH·HCl were added to 30 mL of deionized water and stirred for 2 hours, named solution B.

[0168] S3: Solution A and solution B were mixed together and transferred to a 50 mL reaction kettle, methane gas was introduced, and the reaction was carried out at 200 °C for 20 hours. The obtained precipitate was collected and centrifugally washed with deionized water until clean, and dried in a vacuum oven at 60 °C for 12 hours to obtain the precursor C.

[0169] S4: In a nitrogen environment, the precursor C compound was converted into A-WO x -W2C by instantaneous high-temperature (about 1800 K) Joule heating.

[0170] S5: The prepared A-WO x -W2C was placed in a quartz tube and heated to 300 °C at a heating rate of 1 °C min -1 and sintered for 3 hours, and then cooled to room temperature at a cooling rate of 1 °C min -1 . The obtained product was named A / C-WO x -W2C.

[0171] Test Example:

[0172] I. Preparation of the battery:

[0173] (1) Preparation of the negative electrode sheet:

[0174] The negative electrode sheets were prepared using the negative electrode materials prepared in the examples and comparative examples. The process for fabricating the negative electrode sheets was as follows: The prepared negative electrode material, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) were mixed uniformly at a ratio of 7:2:1 to form a mixture. Solvent N-methylpyrrolidone (NMP) was added to the above mixture, and stirring was continued until a homogeneous slurry was formed. The solid content of the slurry was 50%. The slurry was uniformly coated on the current collector copper foil using a coating device, and the coating thickness was 150 nm. The coated current collector was placed in a drying device for drying treatment.

[0175] (2) Assembly of sodium-ion coin half-cells:

[0176] The prepared negative electrode sheet was used as the working electrode, a sodium metal sheet was used as the reference electrode, Whatman GF / D glass fiber was used as the separator, and 1 mol L -1 NaPF6 / DIGLYME (DIGLYME is diethylene glycol dimethyl ether, which is the solvent) was used as the electrolyte, and 100 μL was added dropwise. The half-cell was assembled in the order of the positive electrode shell, negative electrode sheet, separator, sodium sheet, gasket, spring piece, and negative electrode shell. The assembled half-cell was clamped on a sealing machine with insulating tweezers for sealing treatment. Finally, the sealed battery was taken out of the glove box and left to stand for 12 hours to allow the electrolyte to fully infiltrate before performing relevant electrochemical tests.

[0177] II. Performance testing of the battery:

[0178] (1) First-cycle capacity test:

[0179] A sodium-ion coin half-cell was taken and subjected to a first-cycle capacity test under the test conditions of a current density of 0.5 A g -1 at 26 °C, a charging cut-off voltage of 3.0 V, and a discharging cut-off voltage of 0.01 V to obtain the first-cycle discharge specific capacity and the first-cycle Coulombic efficiency.

[0180] (2) 8 A g -1 Cycle life test:

[0181] A sodium-ion coin half-cell was taken and subjected to a cyclic test at a current density of 8 A g -1 at 26 °C (charging cut-off voltage 3.0 V, discharging cut-off voltage 0.01 V) to obtain the number of cycles and the capacity retention rate at a current density of 8 A g -1

[0182] (3) Electrochemical impedance spectroscopy test:

[0183] An electrochemical impedance spectroscopy test was performed on the sodium-ion coin half-cell using a Letpub electrochemical workstation at a test frequency of 0.01 Hz to 100 kHz to obtain the charge transfer resistance of the new battery.

[0184] (4)Galvanostatic Intermittent Titration Technique Test:

[0185] The sodium-ion button half-cell was tested using a Neware battery test system. At 26 °C, the galvanostatic intermittent titration technique test was carried out (charging cut-off voltage 3.0 V, discharging cut-off voltage 0.01 V) to obtain the sodium-ion diffusion coefficient of the new battery.

[0186] Table 1 Performance Comparison of Half-Cells

[0187]

[0188] In Examples 1-7, the addition of MXene significantly improved the conductivity of the material and reduced the resistance of the battery. Secondly, the two-dimensional structure of MXene is beneficial to the rapid diffusion of ions and the effective transmission of charges, improving the ion diffusion rate and charge-discharge performance of the battery.

[0189] Among them, in Examples 1-5, the synergistic effect of amorphous / crystalline WO x -W2C and MXene provides more active sites and a more stable structure, enabling the anode material to maintain excellent performance during the battery cycle.

[0190] In Example 6, since WO x -W2C is an amorphous material, the amorphous structure leads to slightly poor structural stability, making the material more likely to undergo structural changes during the charge-discharge cycle, and the cycle life of the battery is worse than that of Examples 1-5.

[0191] In Example 7, WO x -W2C is a crystalline material. The crystalline structure will limit the rapid diffusion of ions to a certain extent because the diffusion path of ions in the ordered structure may be restricted by the lattice. During the battery cycle, the crystalline structure may be more stable, but it may cause lattice fatigue and damage to a certain extent due to the repeated insertion and extraction of ions. In terms of resistance, the conductivity of the crystalline structure is usually high, but the resistance also increases due to the presence of grain boundaries. The cycle life of the battery is worse than that of Examples 1-6.

[0192] In Comparative Example 1, the absence of MXene will significantly reduce the conductivity of the material and increase the resistance of the battery. At the same time, as a high-performance two-dimensional conductive material, MXene can also provide structural support and stability. Its absence may cause the material to easily undergo structural changes during the battery cycle, thus affecting the cycle life of the battery. In terms of ion diffusion, the absence of MXene may also lead to a decrease in the ion diffusion rate.

[0193] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A negative electrode material, characterized in that: The negative electrode material is applied to sodium ion batteries; the negative electrode material includes WO x -W2C heterojunction nanoparticles and MXene materials; The MXene material has an accordion-like layered structure. x -W2C heterojunction nanoparticles are loaded on the surface of the MXene material and between its layered structure, wherein x is 0.5 to 2; the WO x -W2C heterojunction nanoparticles have an amorphous / crystalline heterointerface.

2. The negative electrode material according to claim 1, characterized in that The WO x -W2C heterojunction nanoparticles including WO x and W2C; And / or, the chemical formula of the MXene material is M n+1 X n T y , wherein M is at least one of the transition metal elements Ti, V, Nb, Cr, Sc, Mo, Y, Zr, Ta, W, and Hf, X is C and / or N, T y It is at least one of the surface functional groups -O, -Cl, -OH, and -F, and n is the number of layers, which is selected from 1, 2, or 3.

3. The negative electrode material according to claim 1, characterized in that The WO x -The molar ratio of W2C heterojunction nanoparticles to the MXene material is (2-6): (4-8); and / or, the WO x -W2C heterojunction nanoparticles, the WO x The molar ratio of W2C is (1.5-5): (3.5-5); and / or, the WO x -The crystallinity of W2C heterojunction nanoparticles is 55% to 85%.

4. The method for preparing the negative electrode material according to any one of claims 1 to 3, characterized in that: The steps include: S1, mixing a pH adjuster, a first reducing agent and water under an inert gas atmosphere to obtain a solution A; Under an inert gas atmosphere, MXene material, tungsten source, second reducing agent and water are mixed to obtain solution B; Mixing the solution A and the solution B to obtain a mixed solution; Passing methane into the mixed solution to carry out a hydrothermal reaction, washing and drying the obtained precipitate to obtain a precursor C; S2, in an inert gas atmosphere, subjecting the precursor C to Joule heating to obtain amorphous WO x -W2C heterojunction nanoparticle MXene material, denoted as A-WO x -W2C / MXene; S3, in an inert gas atmosphere, the A-WO x -W2C / MXene is annealed to obtain amorphous / crystalline WO x -W2C heterojunction nanoparticle MXene material, denoted as A / C-WO x -W2C / MXene.

5. The preparation method according to claim 4, characterized in that: The molar ratio of the pH regulator, the first reducing agent, the MXene material, the tungsten source and the second reducing agent is (1.5-3.5): (6-10): (2-4): (1-4): (0.5-2); And / or, the pH adjuster includes at least one of sodium sulfite, sodium bisulfite, sodium carbonate, sodium bicarbonate, and acetic acid; and / or, the first reducing agent comprises at least one of sodium borohydride, lithium aluminum hydride, potassium borohydride, and triethylsilane; And / or, the tungsten source includes at least one of ammonium tungstate, ammonium metatungstate, ammonium paratungstate, sodium tungstate, and potassium tungstate; And / or, the second reducing agent includes at least one of hydroxylamine hydrochloride, sodium bisulfite, ascorbic acid, hydroxylamine sulfate, and hydroxylamine nitrate.

6. The preparation method according to claim 4, characterized in that: In the step S1, the temperature of the hydrothermal reaction is 200-400° C., and the time of the hydrothermal reaction is 10-20 h; And / or, in step S2, the Joule heating treatment is carried out at a holding temperature of 1600 to 2000 K, a holding time of 3 to 8 s, and a heating rate of 800 to 1200 K s -1 .

7. The preparation method according to claim 4, characterized in that: In step S3, the holding temperature of the annealing treatment is 300-400°C, the holding time of the annealing treatment is 3-7 h, and the heating rate of the annealing treatment is 1-5°C min -1 The cooling rate of the annealing treatment is 1-5 °C min -1 .

8. A negative electrode sheet, characterized in that: The negative electrode sheet comprises the negative electrode material according to any one of claims 1 to 3, and / or the negative electrode material prepared by the preparation method according to any one of claims 4 to 7.

9. A sodium ion battery, characterized in that: The sodium ion battery comprises the negative electrode sheet according to claim 8.

Images