Electrode material, preparation method thereof and sodium ion battery

Abstract

The application provides an electrode material, a preparation method thereof and a sodium ion battery. The electrode material comprises a carbon matrix and metal nitride doped in the carbon matrix; and the carbon matrix has closed pores, and at least part of the metal nitride is located in the closed pores. The carbon matrix of the application has closed pores, and at least part of the metal nitride is filled in the closed pores. The closed pores can limit the escape of the metal nitride from the pores, the metal nitride in the closed pores can improve the electric field in the central region of the closed pores and the storage activity, reduce the internal resistance of the closed pores filled with sodium, inhibit polarization, reduce sodium precipitation, improve the utilization rate of the central region of the closed pores for storing sodium, and further improve the capacity performance of the electrode material for storing sodium.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to an electrode material, its preparation method, and a sodium-ion battery. Background Technology

[0002] Sodium-ion batteries are characterized by high safety, fast charging, and low-temperature resistance, and can be used in conjunction with lithium-ion batteries, even replacing them in some applications. Hard carbon materials are made from inexpensive, readily available, and renewable raw materials, and when used as a negative electrode in sodium batteries, they offer advantages such as high capacity, high rate capability, and long lifespan. Currently, one of the keys to improving the energy density of sodium-ion batteries lies in enhancing the capacity performance of hard carbon materials.

[0003] In related technologies, the capacity performance of hard carbon materials is generally improved by creating pores. However, during the sodium storage process, sodium mainly fills the pore wall area, while the electric field in the pore center area is weak and the sodium storage activity is low, making it impossible to fill with sodium further. This results in a low sodium storage utilization rate in the pore center area, which affects the sodium storage capacity performance of hard carbon. Summary of the Invention

[0004] The embodiments of the present invention provide an electrode material and its preparation method, as well as a sodium-ion battery, which can improve the technical problem of poor capacity performance of hard carbon for sodium storage.

[0005] In a first aspect, embodiments of the present invention provide an electrode material, including...

[0006] A carbon matrix having closed pores;

[0007] A metal nitride, wherein the metal nitride is doped into the carbon matrix;

[0008] At least a portion of the metal nitride is located within the closed pore.

[0009] In one embodiment, the metal nitride includes any one or more combinations of iron nitride, cobalt nitride, nickel nitride, copper nitride, vanadium nitride, titanium nitride, manganese nitride, and zirconium nitride; and / or

[0010] The metal nitride in the sealed pores comprises 0.35%-2.2% by mass in the electrode material; and / or

[0011] The metal nitride in the electrode material comprises 0.5%-3.0% by mass; and / or

[0012] The particle size of the metal nitride is <1 μm; preferably, the particle size of the metal nitride is <500 nm; more preferably, the particle size of the metal nitride is <100 nm; and / or

[0013] At least a portion of the metal nitride is doped onto the surface of the carbon matrix; and / or

[0014] The carbon matrix includes a porous hard carbon layer and a carbon coating layer covering the surface of the porous hard carbon layer.

[0015] In one embodiment, the particle porosity of the electrode material is 5%-35%, preferably 10%-25%; and / or

[0016] The electrode material has an electrical conductivity of 40 S / cm-70 S / cm; preferably, it has an electrical conductivity of 46 S / cm-65 S / cm; more preferably, it has an electrical conductivity of 50 S / cm-60 S / cm; and / or

[0017] The carbon interlayer spacing of the electrode material is 0.37 nm-0.39 nm; and / or

[0018] The median particle size of the electrode material is 3μm-15μm; and / or

[0019] The electrode material has a specific surface area of ​​2.0 m². 2 / g-10.0m 2 / g.

[0020] Secondly, embodiments of the present invention provide a method for preparing the electrode material as described above, the method comprising the following steps:

[0021] The carbon source is pre-carbonized to obtain pre-carbonized material;

[0022] The pre-carbonized material is subjected to pore-forming treatment and crushed to obtain the first precursor;

[0023] The first precursor was immersed in a metal salt solution to obtain an intermediate;

[0024] The intermediate is reacted with process gas at high temperature to obtain a second precursor;

[0025] The second precursor is sintered at high temperature to obtain the electrode material.

[0026] In one embodiment, the carbon source includes any one or more combinations of plant-based carbon sources, sugar-based carbon sources, resin-based carbon sources, and polymer-based carbon sources; and / or

[0027] The pre-carbonization treatment temperature is 450℃-650℃; and / or

[0028] The pre-carbonization treatment time is 0.5h-24h; and / or

[0029] The pre-carbonization treatment is carried out in an inert gas atmosphere or an oxygen-deficient atmosphere. The inert gas atmosphere includes any one or a combination of at least two of nitrogen, argon, neon, helium, xenon, or krypton atmospheres. The oxygen-deficient atmosphere is a gas atmosphere with an oxygen content of ≤1 wt%.

[0030] In one embodiment, during the solid-phase pore formation, the high-temperature treatment is performed at a temperature of 600°C-800°C for a duration of 0.5h-8h; and / or

[0031] The mass ratio of the pre-carbonized material to the solid pore-forming agent is 1:(0.4-3.0); and / or

[0032] The solid pore-forming agent includes at least one of sodium hydroxide, potassium hydroxide, sodium oxide, potassium oxide, sodium carbonate, potassium carbonate, potassium bicarbonate, sodium bicarbonate, calcium oxide, and zinc chloride; and / or

[0033] In the solid-phase pore formation, the inert atmosphere includes any one or a combination of at least two of the following: nitrogen atmosphere, argon atmosphere, neon atmosphere, helium atmosphere, xenon atmosphere, or krypton atmosphere; and / or

[0034] The solid-phase pore-forming treatment further includes purification treatment of the solid-phase pore-forming modification material. The purification treatment of the solid-phase pore-forming modification material includes: mixing the solid-phase pore-forming modification material, acid solution, and pure water at a mass ratio of 1:(0.5-2):(2-5) and stirring for 0.5h-24h; after stirring, performing solid-liquid separation; washing the purified product obtained from the solid-liquid separation to a pH of 2.5-4.5 and drying it; the acid solution includes one or a combination of at least two of hydrochloric acid, hydrofluoric acid, nitric acid, phosphoric acid, and sulfuric acid; and / or

[0035] In the aforementioned vapor-phase pore formation, the first temperature is 800℃-1000℃, and the holding time is 1h-8h; and / or

[0036] The pore-forming gas includes any one or a combination of at least two of the following: water vapor, carbon dioxide, chlorine, oxygen, ozone, and air; and / or

[0037] The vapor phase pore formation process further includes purification treatment of the vapor phase pore formation modifier material. The purification treatment of the vapor phase pore formation modifier material includes: mixing the vapor phase pore formation modifier material, acid solution, and pure water at a ratio of 1:(0.5-2):(1.2-5) and stirring for 0.5h-24h. After stirring, solid-liquid separation is performed. The purified product obtained from the solid-liquid separation is washed until the pH is 4-8 and then dried. The acid solution includes one or a combination of at least two of hydrochloric acid, hydrofluoric acid, nitric acid, phosphoric acid, and sulfuric acid.

[0038] In one embodiment, the step of immersing the first precursor in a metal salt solution to obtain the intermediate specifically includes:

[0039] The first precursor is immersed in the metal salt solution and stirred for 3-24 hours. After solid-liquid separation and drying, the intermediate is obtained.

[0040] In one embodiment, the concentration of the metal salt solution is 0.5 wt%-5 wt%, and the mass ratio of the first precursor to the metal salt solution is 1:(3-20); and / or

[0041] The median particle size of the first precursor is 3 μm-15 μm; and / or

[0042] The metal salt includes soluble salts of Co, Ni, Cu, V, Ti, Mn, Fe, or Zr, and the soluble salt includes one or a combination of at least two of sulfates, nitrates, and chlorides.

[0043] In one embodiment, the step of reacting the intermediate with a process gas at high temperature to obtain the second precursor specifically includes:

[0044] Under inert atmosphere conditions, the intermediate is placed in a reactor, process gas is introduced, the temperature is raised to a second temperature and then held at that temperature before cooling to obtain the second precursor.

[0045] In one embodiment, the second temperature is 1000℃-1400℃, and the heat preservation time is 3h-10h; and / or

[0046] The process gas is one or a combination of at least two of ammonia, methylamine, ethylamine, diethylamine, n-propylamine, and isopropylamine; preferably, the selected process gas includes at least one of methylamine, ethylamine, diethylamine, n-propylamine, and isopropylamine; and / or

[0047] The inert atmosphere includes any one or a combination of at least two of the following: nitrogen atmosphere, argon atmosphere, neon atmosphere, helium atmosphere, xenon atmosphere, or krypton atmosphere.

[0048] In one embodiment, in the step of high-temperature sintering the second precursor to obtain the electrode material, the high-temperature sintering is carried out under an inert atmosphere, and / or the high-temperature sintering temperature is 1200℃-1500℃, and the high-temperature sintering time is 0.5h-10h; and / or

[0049] Before the second precursor is sintered at high temperature, the following steps are also included: mixing the coated carbon source with the second precursor evenly.

[0050] In one embodiment, the mass ratio between the second precursor and the coated carbon source is 1:(0.01-0.1); and / or

[0051] The coated carbon source includes any one or more combinations of asphalt, sucrose, phenolic resin, polyacrylic resin, glucose, polystyrene, polyvinyl chloride, polytetrafluoroethylene, polyvinyl alcohol, epoxy resin, urea-formaldehyde resin, and melamine resin; and / or

[0052] The inert atmosphere is any one or a combination of at least two of the following: nitrogen atmosphere, argon atmosphere, neon atmosphere, helium atmosphere, xenon atmosphere, or krypton atmosphere.

[0053] Thirdly, embodiments of the present invention provide an electrode sheet comprising the electrode material described above or the electrode material prepared by the preparation method described above.

[0054] Fourthly, embodiments of the present invention provide a sodium-ion battery, comprising the electrode material as described above or the electrode material prepared by the preparation method described above.

[0055] The beneficial effects of the embodiments of the present invention are as follows:

[0056] In embodiments of the present invention, the electrode material comprises a carbon matrix and a metal nitride doped in the carbon matrix. The carbon matrix has closed pores, and at least a portion of the metal nitride is located within these closed pores. On one hand, the metal nitride exhibits high stability, is less prone to side reactions with other components in the battery, and is less likely to decompose under an electric field. Furthermore, the metal nitride possesses high electronic conductivity; doping the carbon matrix with metal nitride increases the overall electronic conductivity of the carbon matrix. On the other hand, the closed pores filled with metal nitride restrict the escape of the metal nitride from the pores. The metal nitride within the closed pores can enhance the electric field and storage activity in the central region of the closed pores, reduce the internal resistance of sodium filling the closed pores, suppress polarization, reduce sodium deposition, and improve the utilization rate of sodium storage in the central region of the closed pores, thereby improving the sodium storage capacity performance of the electrode material. Attached Figure Description

[0057] To more clearly illustrate the solutions in this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0058] Figure 1 A flowchart illustrating the preparation process of one embodiment of the electrode material provided in this application;

[0059] Figure 2This is a SEM image of the electrode material prepared in Example 1 of this application;

[0060] Figure 3 The first charge-discharge curves of the electrode materials prepared in Example 1, Comparative Example 1, and Comparative Example 4 provided for this application;

[0061] Figure 4 The electrode material prepared in Example 1 of this application has a room temperature 1C / 1C@500 cycle performance curve. Detailed Implementation

[0062] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Furthermore, it should be understood that the specific embodiments described herein are only for illustration and explanation of the present invention and are not intended to limit the present invention. In the present invention, unless otherwise stated, directional terms such as "upper" and "lower" generally refer to the upper and lower positions of the device in actual use or operation, specifically the drawing directions in the accompanying drawings; while "inner" and "outer" refer to the outline of the device.

[0063] Among related technologies, hard carbon sodium storage has poor capacity performance and needs further improvement.

[0064] To address the aforementioned issues, this application provides an electrode material comprising a carbon matrix and a metal nitride doped in the carbon matrix; the carbon matrix has closed pores, and at least a portion of the metal nitride is located within the closed pores.

[0065] The sealed pore is a partially closed pore with a gap, allowing sodium ions to enter and exit through the gap, while preventing solid-state metal nitrides within the sealed pore from escaping through the gap. The formation of the gap is not limited; it can be formed by interlayer spacing between carbon layers, or by notches, channels, or other structures on the carbon matrix that communicate with the sealed pore.

[0066] In this embodiment, on the one hand, metal nitrides have high stability and are not prone to side reactions with other components in the battery; in addition, metal nitrides have high electronic conductivity, and doping the carbon matrix with metal nitrides can increase the overall electronic conductivity of the carbon matrix. On the other hand, the carbon matrix has closed pores filled with metal nitrides. The closed pores can restrict the escape of metal nitrides from the pores. Furthermore, the metal nitrides in the closed pores can improve the electric field and storage activity in the central region of the closed pores, reduce the internal resistance of sodium filling in the closed pores, suppress polarization, reduce sodium deposition, improve the utilization rate of sodium storage in the central region of the closed pores, and thus improve the sodium storage capacity performance of the electrode material.

[0067] In one embodiment, the metal nitride includes any one or more combinations of iron nitride, cobalt nitride, nickel nitride, copper nitride, vanadium nitride, titanium nitride, manganese nitride, and zirconium nitride.

[0068] In one embodiment, the mass percentage of the metal nitride in the electrode material is 0.5%-3%. Optionally, the mass percentage of the metal nitride in the electrode material can be any one or any two of 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, etc., and is not limited herein.

[0069] In one embodiment, the mass percentage of metal nitride in the closed pores in the electrode material is 0.35%-2.2%; optionally, the mass percentage of metal nitride in the closed pores in the electrode material can be any one or any two of 0.35%, 0.6%, 1.0%, 1.4%, 1.8%, 2.0%, 2.2%, etc., and is not limited herein. In this embodiment, if the metal nitride content in the closed pores is too low, it is easy to lead to insufficient or absent metal nitride content distributed in the closed pore area of ​​the electrode material, thereby reducing the sodium storage activity of the closed pores of the electrode material, resulting in low sodium storage utilization in the closed pore area, and increasing the internal resistance of sodium ion diffusion in the pore area, thereby reducing the capacity performance, rate performance, and cycle performance of the electrode material; if the metal nitride content in the closed pores is too high, it is easy to lead to excessive metal nitride occupying the closed pore volume, reducing the closed pore volume that can be used for sodium storage, resulting in a decrease in the capacity performance of the electrode material.

[0070] In one embodiment, the particle size of the metal nitride is <1 μm, preferably <500 nm; more preferably, the particle size is <100 nm. The smaller the particle size of the metal nitride, the wider its distribution on the surface and in the closed-pore region of the electrode material. This facilitates better contact between the metal nitride and the carbon matrix, better modification of the modification sites, better reduction of the diffusion resistance of sodium ions on the surface and in the closed-pore region of the electrode material, reduction of the polarization of the electrode material, and improvement of the uniformity of current and voltage distribution during charge and discharge, further enhancing the capacity performance, rate performance, and cycle performance of the electrode material.

[0071] In one embodiment, at least a portion of the metal nitride is doped onto the surface of the carbon matrix. In this embodiment, the metal nitride on the carbon matrix surface can improve the electronic conductivity of the carbon matrix surface, reduce the contact resistance between carbon matrix particles, suppress polarization, reduce sodium deposition, and improve the rate performance and cycling performance of the carbon matrix.

[0072] In one embodiment, the carbon matrix includes porous hard carbon and a carbon coating layer covering the surface of the porous hard carbon. In this embodiment, the carbon coating layer can transform the open pores in the porous hard carbon into closed pores with sodium storage activity, increasing the number of closed pores, and at the same time, facilitating the fixation of metal nitrides in the closed pores.

[0073] In one embodiment, the particle porosity of the electrode material is 5%-35%, preferably 10%-25%. In this embodiment, the particle porosity of the electrode material can be any one or any two of 5%, 10%, 15%, 20%, 25%, 30%, and 35%, and is not limited herein. In this embodiment, if the particle porosity is too large, the pores in the carbon matrix will be too large, resulting in unsatisfactory effects from carbon coating, high-temperature sintering, and other processes in forming closed pores. If the particle porosity is too small, the pore volume in the carbon matrix will be too small, resulting in insufficient volume of closed pores formed by carbon coating, high-temperature sintering, and other processes, reducing the sodium storage capacity of the pores and hindering the improvement of the electrode material's capacity performance.

[0074] In one embodiment, the conductivity of the electrode material is 40 S / cm-70 S / cm; preferably, the conductivity is 46 S / cm-65 S / cm; more preferably, the conductivity is 50 S / cm-60 S / cm. In this embodiment, the conductivity of the electrode material can be any one or any two of 40 S / cm, 45 S / cm, 50 S / cm, 55 S / cm, 60 S / cm, 65 S / cm, and 70 S / cm, and is not limited herein. In this embodiment, if the conductivity is too low, the internal resistance to sodium ion migration in the electrode material increases, and the kinetic performance deteriorates; if the conductivity is too high, a larger amount of metal nitride is required to modify the electrode material, which can easily lead to a waste of the pore volume of the electrode material and a reduction in capacity performance.

[0075] In one embodiment, the carbon interlayer spacing of the electrode material is 0.37nm-0.39nm; in this embodiment, the carbon interlayer spacing of the electrode material can be any one or any two of 0.37nm, 0.375nm, 0.38nm, 0.385nm, 0.39nm, etc., and is not limited here.

[0076] In one embodiment, the median particle size of the electrode material is 3μm-15μm; optionally, the median particle size of the electrode material can be any one or any two of 3μm, 6μm, 9μm, 11μm, 13μm, 15μm, etc., and is not limited herein. In this embodiment, if the median particle size of the electrode material is too small, it is easy to cause the specific surface area of ​​the electrode material to be too high, reducing the first efficiency of the battery; in addition, if the median particle size of the electrode material is too small, more binder is required in the process of making the negative electrode sheet, and excessive binder can easily lead to a decrease in the power performance of the battery; if the median particle size of the electrode material is too large, the interparticle gap of the electrode material increases, which can easily lead to a lower compaction density of the negative electrode sheet, and the distance for sodium ions to diffuse from the surface of the electrode material particles to the center of the electrode material particles is too large, resulting in a decrease in kinetic performance. In addition, the edges and corners of large-particle electrode materials are sharper, which can easily puncture the current collector when making the negative electrode sheet, resulting in a decrease in yield.

[0077] In one embodiment, the electrode material has a specific surface area of ​​2.0 m². 2 / g-10.0m 2 / g. Optionally, the specific surface area of ​​the electrode material can be 2.0m². 2 / g, 4.0m 2 / g, 6.0m 2 / g, 8.0m 2 / g, 10.0m 2The range between any one or any two of / g, etc., is not limited here. In this embodiment, if the specific surface area is too small, it indicates that the coating layer is too thick, which increases the steric hindrance for sodium ions to enter the closed pores from the electrolyte, and the battery polarization becomes larger; if the specific surface area is too large, it indicates that the effect of converting the open pores into closed pores is not ideal, the activity of the sodium storage sites in the pores is low, and the effect of metal nitride modification of the closed pores is not ideal.

[0078] This application also provides a method for preparing an electrode material, such as... Figure 1 As shown, it includes the following steps:

[0079] S1. The carbon source is pre-carbonized to obtain pre-carbonized material;

[0080] S2. The pre-carbonized material is subjected to pore-forming treatment and crushed to obtain the first precursor.

[0081] S3. The first precursor is immersed in a metal salt solution to obtain an intermediate;

[0082] S4. The intermediate is reacted with the process gas at high temperature to obtain the second precursor;

[0083] S5. The second precursor is sintered at high temperature to obtain the electrode material.

[0084] In the above scheme, this application prepares a first precursor with abundant open pores through pre-carbonization and pore-forming treatment. Then, metal salts are loaded onto the surface and pores of the first precursor through solution impregnation. The metal salts are then converted into nano-metal oxides at high temperature, and process gases further convert the nano-metal oxides into stable metal nitrides. Finally, high-temperature sintering transforms the open pores of the second precursor into closed pores, restricting the escape of metal nitrides from the pores, thereby obtaining a metal nitride-modified electrode material. In this embodiment, through metal salt solution impregnation, secondary conversion (metal salt first converts to metal oxide, then to metal nitride), and high-temperature sintering, metal nitrides are nano-sized and uniformly loaded onto the surface and closed pores of the electrode material, improving the electronic conductivity of the closed pore region and providing a prerequisite for improving the sodium storage activity of the electrode material. Furthermore, converting open pores into closed pores provides a structural basis for improving the sodium storage capacity of the negative electrode and facilitates the fixation of metal nitrides within the closed pores.

[0085] The preparation method of this application is described in detail below with reference to the embodiments:

[0086] S1. The carbon source is pre-carbonized to obtain pre-carbonized material.

[0087] In some embodiments, the carbon source includes any one or more combinations of plant-based carbon sources, sugar-based carbon sources, resin-based carbon sources, and polymer-based carbon sources. Preferably, plant-based carbon sources include any one or more combinations of coconut shells, almond shells, pistachio shells, macadamia nut shells, date pit shells, chestnut shells, hazelnut shells, peanut shells, walnut shells, peach pit shells, cotton, wood, bamboo, sugarcane bagasse, straw, and lignin; preferably, sugar-based carbon sources include any one or more combinations of sucrose, maltose, lactose, fructose, starch, and cellulose; preferably, resin-based carbon sources include any one or more combinations of phenolic resins, polyimide resins, polyester resins, polyaldehyde resins, polyolefin resins, and polyacrylic acid resins; preferably, polymer-based carbon sources include any one or more combinations of polyfurfuryl alcohol, polyaniline, polyethylene glycol, polyethylene oxide, polyvinylidene fluoride, natural rubber, and polyacrylonitrile.

[0088] In some embodiments, the pre-carbonization temperature is 450°C-650°C. Optionally, the pre-carbonization temperature can be any one or any two of 450°C, 500°C, 550°C, 600°C, 650°C, etc., and is not limited herein.

[0089] In some embodiments, the pre-carbonization treatment time is 0.5h-24h. Optionally, the pre-carbonization treatment time can be any one or any two of 0.5h, 1h, 4h, 8h, 12h, 16h, 20h, 24h, etc., and is not limited here.

[0090] In some embodiments, the pre-carbonization treatment is carried out in an inert gas atmosphere or an oxygen-deficient atmosphere. The inert gas atmosphere includes any one or a combination of at least two of nitrogen, argon, neon, helium, xenon, or krypton atmospheres, and the oxygen-deficient atmosphere is a gas atmosphere with an oxygen content ≤1 wt%.

[0091] S2. The pre-carbonized material is subjected to pore-forming treatment and crushed to obtain the first precursor.

[0092] In some embodiments, the pulverization process includes pulverizing the pore-forming product to a median particle size of 3μm-15μm. Optionally, the pulverization process includes one or more combinations of ball milling, air jet milling, mechanical milling, and roller milling.

[0093] In some embodiments, the pore-forming process includes solid-phase pore-forming, which includes the following steps: uniformly mixing a pre-carbonized material with a solid-phase pore-forming agent under an inert atmosphere and subjecting the mixture to high-temperature treatment to obtain a solid-phase pore-forming modified material.

[0094] In some embodiments, during the solid-phase pore-forming step, the high-temperature treatment temperature is 600℃-800℃, and the high-temperature treatment time is 0.5h-8h. Optionally, the high-temperature treatment temperature can be any one or any two of 600℃, 650℃, 700℃, 740℃, 780℃, 800℃, etc., and is not limited herein; the high-temperature treatment time can be any one or any two of 0.5h, 1h, 2h, 4h, 6h, 8h, etc., and is not limited herein.

[0095] In some embodiments, the mass ratio of the pre-carbonized material to the solid-phase pore-forming agent is 1:(0.4-3.0). Optionally, the mass ratio of the pre-carbonized material to the solid-phase pore-forming agent can be any one or any two of 1:0.4, 1:0.8, 1:1, 1:1.5, 1:2.0, 1:2.5, 1:3.0, etc., and is not limited here. In this embodiment, if the amount of solid-phase pore-forming agent added is too small, it is easy to cause the pore volume of the first precursor to be too small, and the effect of loading metal nitrides on the electrode material is not ideal; if the amount of solid-phase pore-forming agent added is too large, it is easy to cause the pore size generated during the pore-forming process to be too large, the specific surface area of ​​the first precursor to be too high, and the excessively large pore size is not conducive to the adsorption of metal salts by the first precursor, resulting in a reduction in the amount of metal nitrides loaded on the electrode material.

[0096] In some embodiments, the solid pore-forming agent includes at least one selected from sodium hydroxide, potassium hydroxide, sodium oxide, potassium oxide, sodium carbonate, potassium carbonate, potassium bicarbonate, sodium bicarbonate, calcium oxide, and zinc chloride.

[0097] In some embodiments, during the solid-phase pore-forming step, the inert atmosphere includes any one or a combination of at least two of nitrogen, argon, neon, helium, xenon, or krypton atmospheres.

[0098] In some embodiments, the solid-phase pore-forming treatment further includes purification of the solid-phase pore-forming modified material. This purification process involves uniformly mixing the solid-phase pore-forming modified material, acid, and pure water, stirring for 0.5-24 hours, performing solid-liquid separation after stirring, washing the purified product obtained from the solid-liquid separation to a pH of 2.5-4.5, and then drying. In this embodiment, without purification of the solid-phase pore-forming modified material, residual pore-forming agents or impurities may occupy the pore volume of the first precursor. When the first precursor is subsequently immersed in a metal salt solution, the amount of metal salt adsorbed by the first precursor decreases, resulting in a lower content of loaded metal nitrides in the electrode material, a reduced pore volume with sodium storage activity, and a decrease in the conductivity of the electrode material. This, in turn, leads to a decrease in the specific capacity, rate performance, and cycle performance of the electrode material. Furthermore, residual pore-forming agents and impurities in the first precursor are prone to side reactions with the electrolyte during battery charging and discharging, catalyzing self-discharge and causing a decrease in the battery's initial efficiency and lifespan.

[0099] In some embodiments, the mass ratio of the solid-phase pore-forming modifier, acid, and pure water is 1:(0.5-2):(2-5). Optionally, the mass ratio of the solid-phase pore-forming modifier, acid, and pure water can be any one or any two of 1:0.5:2, 1:1:3, 1:2:4, 1:2:5, 1:0.5:5, etc., and is not limited here.

[0100] In some embodiments, the acid solution may be one or a combination of at least two of hydrochloric acid, hydrofluoric acid, nitric acid, phosphoric acid, and sulfuric acid.

[0101] In some embodiments, the pore-forming process includes gas-phase pore-forming, which includes the following steps: placing the pre-carbonized material in a reactor, introducing pore-forming gas, heating to a first temperature and then holding it at that temperature to obtain a gas-phase pore-forming modified material.

[0102] In some embodiments, during the vapor phase pore-forming step, the first temperature is 800℃-1000℃, and the holding time is 1h-8h. Optionally, the first temperature can be any one or any two of 800℃, 850℃, 900℃, 950℃, 1000℃, etc., and is not limited here; the holding time can be any one or any two of 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, etc., and is not limited here.

[0103] In some embodiments, the pore-forming gas includes any one or a combination of at least two of water vapor, carbon dioxide, chlorine, oxygen, ozone, and air.

[0104] In some embodiments, the vapor-phase pore-forming treatment further includes purification of the vapor-phase pore-forming modified material, specifically including: mixing the vapor-phase pore-forming modified material, acid, and pure water at a mass ratio of 1:(0.5-2):(1.2-5) and stirring for 0.5h-24h; after stirring, performing solid-liquid separation; washing the purified product obtained from the solid-liquid separation to a pH of 4-8; and drying. Optionally, the mass ratio between the vapor-phase pore-forming modified material, acid, and pure water can be any one or any two of 1:0.5:1.2, 1:1:3, 1:2:1.2, 1:2:5, 1:0.5:5, etc., and is not limited here.

[0105] S3. The first precursor is immersed in a metal salt solution to obtain an intermediate.

[0106] In some embodiments, step S3 specifically includes: immersing the first precursor in a metal salt solution, stirring for 3-24 hours, separating the solid and liquid, drying, and obtaining an intermediate.

[0107] In some embodiments, the concentration of the metal salt solution is 0.5wt%-5wt%, and the mass ratio of the first precursor to the metal salt solution is 1:(3-20). Optionally, the concentration of the metal salt solution can be any one or any two of 0.5wt%, 1.0wt%, 1.5wt%, 2.0wt%, 2.5wt%, 3.0wt%, 3.5wt%, 4.0wt%, 4.5wt%, 5.0wt%, etc., and is not limited herein; the mass ratio of the first precursor to the metal salt solution can be any one or any two of 1:3, 1:5, 1:10, 1:12, 1:15, 1:18, 1:20, etc., and is not limited herein.

[0108] In this embodiment, if the content of the metal salt solution is too low, the content of the metal nitride doped on the electrode material will be too low, which will lead to a decrease in the specific capacity, rate performance and cycle performance of the electrode material. If the content of the metal salt solution is too high, the content of the metal nitride on the final electrode material will be too high, the pore volume of the electrode material that can be used for sodium storage will decrease, the number of sodium storage sites in the pores will decrease, and the capacity performance will decrease.

[0109] In some embodiments, the median particle size of the first precursor is 3 μm-15 μm. Optionally, the median particle size of the first precursor can be any one or any two of 3 μm, 5 μm, 7 μm, 9 μm, 11 μm, 13 μm, 15 μm, etc., and is not limited herein.

[0110] In some embodiments, the metal salt includes soluble salts of Co, Ni, Cu, V, Ti, Mn, Fe, or Zr, and the soluble salt includes one or a combination of at least two of sulfates, nitrates, chlorides, etc.

[0111] S4. The intermediate is reacted with the process gas at high temperature to obtain the second precursor.

[0112] In step S4, during the reaction of the intermediate with the process gas at high temperature, the metal salt on the intermediate is converted into nano-metal oxide at high temperature, and the process gas then converts the nano-metal oxide into stable metal nitride.

[0113] In some embodiments, step S4 specifically includes: placing the intermediate in a reactor under an inert atmosphere, introducing process gas, heating to a second temperature, holding at that temperature, and cooling to obtain a second precursor.

[0114] In some embodiments, the second temperature is 1000℃-1400℃, and the holding time is 3h-10h. In this embodiment, if the second temperature is too low, the metal oxide may not be converted or may only be partially converted into metal nitride; if the second temperature is too high, the generated metal nitride may partially or completely sublimate, resulting in an unsatisfactory effect of the metal nitride on the modification of closed pores. Optionally, the second temperature can be any one or any two of 1000℃, 1100℃, 1200℃, 1300℃, 1400℃, etc., without limitation; the holding time can be any one or any two of 3h, 4h, 6h, 7h, 8h, 9h, 10h, etc., without limitation.

[0115] In some embodiments, the inert atmosphere includes any one or a combination of at least two of nitrogen, argon, neon, helium, xenon, or krypton atmospheres.

[0116] In some embodiments, the process gas is one or a combination of at least two of ammonia, methylamine, ethylamine, diethylamine, n-propylamine, and isopropylamine. In this embodiment, the process gas contains ammonia or is produced by cracking, and the ammonia can react with metal oxides at high temperatures to form metal nitrides.

[0117] Preferably, the process gas includes at least one of methylamine, ethylamine, diethylamine, n-propylamine, and isopropylamine. In this embodiment, methylamine, ethylamine, diethylamine, n-propylamine, and isopropylamine are all process gases containing carbon atoms and amino groups. In step S4, the above-mentioned process gas can generate ammonia, which can react with metal oxides at high temperature to generate metal nitrides. At the same time, the above-mentioned process gas contains carbon atoms, which can serve as a carbon source for carbon coating of intermediates, reducing the pore size of the open pores in the intermediates, facilitating the conversion of the open pores in the intermediates into closed pores, inhibiting the escape of the generated metal nitrides from the pore structure, and ensuring the effectiveness of the metal nitride modification of the closed pores.

[0118] S5. The second precursor is sintered at high temperature to obtain the electrode material.

[0119] In some embodiments, in step S5, high-temperature sintering is carried out under an inert atmosphere, with a sintering temperature of 1200℃-1500℃ and a sintering time of 0.5h-10h. In this embodiment, if the high-temperature sintering temperature is too low, the open pores may not be effectively converted into closed pores, and the open pores will not have sodium storage activity, thus reducing the sodium storage utilization rate of the electrode material pore volume. If the high-temperature sintering temperature is too high, the metal nitride may sublimate and all or part of the closed pores may collapse, resulting in a decrease in the porosity of the electrode material particles and a reduction in the carbon layer spacing, thus making the effect of the metal nitride in improving the electric field and storage activity in the central region of the closed pores unsatisfactory. Optionally, the high-temperature sintering temperature can be any one or any two of 1200℃, 1300℃, 1400℃, 1500℃, etc., without limitation; the high-temperature sintering time can be any one or any two of 0.5h, 1h, 3h, 5h, 7h, 9h, 10h, etc., without limitation.

[0120] In some embodiments, before high-temperature sintering of the second precursor, the following step is further included: uniformly mixing the coated carbon source with the second precursor. In this embodiment, uniformly mixing the coated carbon source with the second precursor allows the coated carbon source to transform open pores into closed pores during high-temperature sintering, restricting the escape of metal nitrides from the pores, effectively fixing the metal nitrides in the pore structure, increasing the sodium storage sites in the pores, thereby improving the sodium storage capacity, rate performance, and cycle performance of the electrode material.

[0121] In some embodiments, the mass ratio between the second precursor and the coated carbon source is 1:(0.01-0.1). Optionally, the mass ratio between the second precursor and the coated carbon source can be any one or any two of 1:0.01, 1:0.02, 1:0.04, 1:0.06, 1:0.08, 1:0.1, etc., and is not limited here.

[0122] In some embodiments, the coated carbon source includes any one or more combinations of asphalt, sucrose, phenolic resin, polyacrylic resin, glucose, polystyrene, polyvinyl chloride, polytetrafluoroethylene, polyvinyl alcohol, epoxy resin, urea-formaldehyde resin, and melamine resin.

[0123] In some embodiments, the inert atmosphere is any one or a combination of at least two of nitrogen, argon, neon, helium, xenon, or krypton atmospheres.

[0124] This application also provides a sodium-ion battery, including the electrode material described above or the electrode material prepared by the preparation method described above.

[0125] The present application will be further described below through specific embodiments.

[0126] Example 1

[0127] (1) In a tube furnace, the coconut shell is heated to 500°C under nitrogen and kept at that temperature for 12 hours. After cooling, the resulting material is crushed using a crusher with a screen mesh size of 5 mm to obtain pre-carbonized material.

[0128] (2) The pre-carbonized material and sodium hydroxide were mixed in a mass ratio of 1:1.5 and placed in a box furnace. The mixture was heated to 700°C under a nitrogen atmosphere and kept at that temperature for 1 hour. After cooling, pure water was added and the mixture was washed until the pH reached 9. Solid-liquid separation was performed to obtain a solid-phase pore-forming modified material. The solid-phase pore-forming modified material, hydrochloric acid (concentration of 31 wt%), hydrofluoric acid (concentration of 55 wt%) and water were then mixed in a mass ratio of 1:1:0.1:5. The mixture was heated to 80°C and stirred for 12 hours. Solid-liquid separation was performed. The mixture was washed until the pH reached 3.5, dried, and ball-milled until the median particle size was 7 μm to obtain the first precursor.

[0129] (3) Prepare a cobalt nitrate solution with a concentration of 2.5 wt%. Immerse one mass of the first precursor in ten masses of cobalt nitrate solution, stir for 12 h, separate the solid and liquid, dry to obtain an intermediate, place the intermediate in a furnace, heat to 1200 °C under nitrogen atmosphere, introduce ammonia, keep warm for 5 h, cool to obtain the second precursor.

[0130] (4) The second precursor and asphalt are mixed at a mass ratio of 1:0.02. The mixture is transferred to a tube furnace and heated to 1300℃ under a nitrogen atmosphere for 3 hours. After cooling, the mixture is sieved through a 325-mesh sieve to obtain the electrode material.

[0131] Example 2

[0132] (1) The phenolic resin was heated to 650°C in a box furnace under a helium atmosphere, held for 0.5 h, cooled, and the resulting material was crushed with a crusher with a screen mesh size of 3 mm to obtain pre-carbonized material.

[0133] (2) The pre-carbonized material and sodium carbonate were mixed in a mass ratio of 1:3 and placed in a box furnace. The mixture was heated to 800°C under a nitrogen atmosphere and kept at that temperature for 0.5 hours. After cooling, pure water was added and the mixture was washed until the pH value reached 9. Solid-liquid separation was performed to obtain a solid-phase pore-forming modified material. The solid-phase pore-forming modified material, hydrochloric acid (concentration of 31wt%) and water were then mixed in a mass ratio of 1:0.5:3, heated to 60°C, stirred for 1 hour, and the mixture was separated into solid and liquid. The mixture was washed until the pH value reached 3.5, dried, and air-jet pulverized to a median particle size of 3μm to obtain the first precursor.

[0134] (3) Prepare a 0.5 wt% ferric sulfate solution, immerse one mass of the first precursor in three masses of the ferric sulfate solution, stir for 3 h, separate the solid and liquid, dry to obtain an intermediate. Place the obtained intermediate in a furnace, heat to 1400 °C under a neon atmosphere, introduce methylamine, keep at the temperature for 10 h, cool to obtain the second precursor;

[0135] (4) The second precursor is transferred to a tube furnace, heated to 1500℃ and sintered for 4 hours in a helium atmosphere, cooled, and sieved through a 325-mesh sieve to obtain the electrode material.

[0136] Example 3

[0137] (1) The sucrose is heated to 450°C in an argon atmosphere in a box furnace, kept at the temperature for 24 hours, cooled, and the resulting material is crushed with a crusher with a screen mesh size of 1 mm to obtain pre-carbonized material.

[0138] (2) The pre-carbonized material and zinc chloride were mixed at a mass ratio of 1:0.5 and placed in a box furnace. The mixture was heated to 700℃ under a nitrogen atmosphere and held for 2 hours. Then, it was cooled. Pure water was added and washed until the pH reached 9. Solid-liquid separation was performed to obtain a solid-phase pore-forming modified material. The solid-phase pore-forming modified material, hydrochloric acid (concentration of 31wt%), and water were then mixed at a mass ratio of 1:1:5 and stirred for 1 hour. Solid-liquid separation was performed, and the mixture was washed until the pH reached 3.5. The material was then dried. The resulting material was air-jet pulverized to a median particle size of 5μm to obtain the first precursor.

[0139] (3) Prepare a nickel chloride solution with a concentration of 1 wt%. Immerse one mass of the first precursor in 20 times its mass of the nickel chloride solution, stir for 4 hours, separate the solid and liquid, and dry to obtain an intermediate. Place the intermediate in a furnace, heat it to 1100℃ under argon, introduce ethylamine, keep it at this temperature for 3 hours, and cool to obtain the second precursor;

[0140] (4) The second precursor is transferred to a tube furnace, heated to 1200℃ and sintered for 10h in a krypton atmosphere, cooled and sieved through a 325-mesh sieve to obtain the electrode material.

[0141] Example 4

[0142] (1) Polyaniline was heated to 500°C in a tube furnace under a krypton atmosphere, held for 2 hours, cooled, and the resulting material was crushed with a crusher with a screen mesh size of 3 mm to obtain pre-carbonized material.

[0143] (2) The pre-carbonized material is placed in a box furnace and heated to 1000°C in a nitrogen atmosphere. Water vapor is introduced, and the temperature is maintained for 3 hours. After cooling, the resulting material is pulverized to a median particle size of about 15μm to obtain the first precursor.

[0144] (3) Prepare a copper nitrate solution with a concentration of 1.5wt%, immerse the first precursor by 1 mass in a copper nitrate solution with a sulfur content of 8 masses, stir for 4 hours, separate the solid and liquid, dry to obtain an intermediate, place the intermediate in a furnace, heat to 1200℃ under argon, introduce n-propylamine, keep warm for 6 hours, cool to obtain the second precursor.

[0145] (4) The second precursor is transferred to a tube furnace and sintered at 1300°C for 0.5 h in a neon atmosphere. After cooling, it is sieved through a 325-mesh sieve to obtain the electrode material.

[0146] Example 5

[0147] (1) The walnut shells were heated to 550°C in a box furnace under a nitrogen atmosphere, kept at the temperature for 8 hours, cooled, and the resulting material was crushed with a crusher with a screen mesh size of 3 mm to obtain pre-carbonized material.

[0148] (2) The pre-carbonized material and potassium hydroxide were mixed in a mass ratio of 1:0.4 and placed in a box furnace. The mixture was heated to 600°C under nitrogen and kept at that temperature for 8 hours. After cooling, pure water was added and washed until the pH value reached 9. Solid-liquid separation was performed to obtain solid-phase pore-forming modified material. The solid-phase pore-forming modified material, hydrochloric acid (concentration of 31wt%) and water were then mixed in a mass ratio of 1:2:3, heated to 70°C, stirred for 4 hours, and solid-liquid separation was performed. The mixture was washed until the pH value reached 3.5, dried, and mechanically pulverized to a median particle size of 10μm to obtain the first precursor.

[0149] (3) Prepare a titanium chloride solution with a concentration of 5 wt%. Immerse one mass of the first precursor in ten masses of the titanium chloride solution, stir for 2 hours, separate the solid and liquid, and dry to obtain an intermediate. Place the intermediate in a furnace, heat it to 1000°C under nitrogen, introduce diethylamine, keep it at this temperature for 10 hours, and cool to obtain the second precursor.

[0150] (4) The second precursor and glucose were mixed at a mass ratio of 1:0.1, transferred to a tube furnace, heated to 1400℃ and sintered for 8 hours under a helium atmosphere, cooled, and sieved through a 325-mesh sieve to obtain the electrode material.

[0151] Example 6

[0152] (1) The starch was heated to 600°C in a box furnace under a deficient oxygen atmosphere, kept at the temperature for 4 hours, cooled, and the resulting material was crushed with a crusher with a screen mesh size of 5 mm to obtain pre-carbonized material.

[0153] (2) The pre-carbonized material and sodium hydroxide were mixed in a mass ratio of 1:1.2 and placed in a box furnace. The mixture was heated to 700°C under argon and held for 1 hour. After cooling, pure water was added and washed until the pH value reached 9. Solid-liquid separation was performed to obtain solid-phase pore-forming modified material. The solid-phase pore-forming modified material, sulfuric acid (concentration of 92.5wt%) and water were then mixed in a mass ratio of 1:0.8:3 and stirred for 6 hours. Solid-liquid separation was performed, and the mixture was washed until the pH value reached 3.5. After drying, the mixture was air-jet pulverized to a median particle size of 3μm to obtain the first precursor.

[0154] (3) Prepare a 2wt% manganese nitrate solution, immerse one mass of the first precursor in ten times the mass of the manganese nitrate solution, stir for 3 hours, separate the solid and liquid, dry to obtain an intermediate. Place the intermediate in a furnace, heat to 1100℃ under a nitrogen atmosphere, introduce ammonia, keep at the temperature for 10 hours, cool to obtain the second precursor;

[0155] (4) The second precursor was transferred to a box furnace and sintered at 1300°C for 3 hours under a nitrogen atmosphere. After cooling, it was sieved through a 325-mesh sieve to obtain the electrode material.

[0156] Example 7

[0157] The difference between Example 7 and Example 6 is as follows:

[0158] Step (4) is as follows: the second precursor and asphalt are mixed in a mass ratio of 1:0.02, the mixture is transferred to a box furnace, heated to 1300°C and sintered for 3 hours under a nitrogen atmosphere, cooled, and sieved through a 325-mesh sieve to obtain the electrode material; the rest is the same as in Example 6.

[0159] Example 8

[0160] The difference between Example 8 and Example 6 is as follows:

[0161] Step (3) is as follows: Prepare a 2wt% manganese nitrate solution, immerse one mass of the first precursor in ten times its mass of the manganese nitrate solution, stir for 3 hours, separate the solid and liquid, dry, and obtain an intermediate. Place the intermediate in a furnace, heat it to 1100°C under a nitrogen atmosphere, introduce methylamine, keep it at this temperature for 10 hours, cool, and obtain the second precursor; the rest is the same as in Example 6.

[0162] Example 9

[0163] The difference between Example 9 and Example 2 is as follows:

[0164] Step (1) is as follows: Phenolic resin and starch are mixed evenly in a mass ratio of 1:1 to obtain a mixed carbon source. The mixture is heated to 650°C in a box furnace under a helium atmosphere, held for 0.5 hours, cooled, and the resulting material is crushed with a crusher with a screen mesh size of 3 mm to obtain a pre-carbonized material; the rest is the same as in Example 2.

[0165] Example 10

[0166] The difference between Example 10 and Example 2 is as follows:

[0167] Step (3) is as follows: Prepare a 5 wt% ferric sulfate solution, immerse one mass of the first precursor in 20 times its mass of the ferric sulfate solution, stir for 3 hours, separate the solid and liquid, dry, and obtain an intermediate. Place the obtained intermediate in a furnace, heat it to 1400°C under a neon atmosphere, introduce methylamine, keep it at this temperature for 10 hours, cool, and obtain the second precursor; the rest is the same as in Example 2.

[0168] Example 11

[0169] The difference between Example 11 and Example 1 is as follows:

[0170] Step (2) is as follows: The pre-carbonized material and sodium hydroxide are mixed in a mass ratio of 1:0.2 and placed in a box furnace. The mixture is heated to 700°C under a nitrogen atmosphere and kept at that temperature for 1 hour. After cooling, pure water is added and the mixture is washed until the pH reaches 9. Solid-liquid separation is performed to obtain a solid-phase pore-forming modified material. The solid-phase pore-forming modified material, hydrochloric acid (concentration of 31 wt%), hydrofluoric acid (concentration of 55 wt%) and water are then mixed in a mass ratio of 1:1:0.1:5. The mixture is heated to 80°C and stirred for 12 hours. Solid-liquid separation is performed. The mixture is washed until the pH reaches 3.5, dried, and ball-milled to a median particle size of 7 μm to obtain the first precursor. The rest is the same as in Example 1.

[0171] Example 12

[0172] The difference between Example 12 and Example 1 is as follows:

[0173] Step (2) is as follows: The pre-carbonized material and sodium hydroxide are mixed in a mass ratio of 1:4 and placed in a box furnace. The mixture is heated to 700°C under a nitrogen atmosphere and kept at that temperature for 1 hour. After cooling, pure water is added and the mixture is washed until the pH reaches 9. Solid-liquid separation is performed to obtain a solid-phase pore-forming modified material. The solid-phase pore-forming modified material, hydrochloric acid (concentration of 31 wt%), hydrofluoric acid (concentration of 55 wt%) and water are then mixed in a mass ratio of 1:1:0.1:5. The mixture is heated to 80°C and stirred for 12 hours. Solid-liquid separation is performed. The mixture is washed until the pH reaches 3.5, dried, and ball-milled to a median particle size of 7 μm to obtain the first precursor. The rest is the same as in Example 1.

[0174] Example 13

[0175] The difference between Example 13 and Example 1 is as follows:

[0176] Step (2) is as follows: the pre-carbonized material and sodium hydroxide are mixed in a mass ratio of 1:1.5 and placed in a box furnace. The mixture is heated to 700°C under nitrogen and kept at that temperature for 1 hour. After cooling, pure water is added to wash the mixture until the pH reaches 9. The solid and liquid are separated, dried, and ball-milled to a median particle size of 7 μm to obtain the first precursor. The rest is the same as in Example 1.

[0177] Example 14

[0178] The difference between Example 14 and Example 1 is as follows:

[0179] Step (3) is as follows: Prepare a cobalt nitrate solution with a concentration of 2.5 wt%. Immerse one mass of the first precursor in ten masses of the cobalt nitrate solution, stir for 12 h, separate the solid and liquid, dry to obtain an intermediate, place the intermediate in a furnace, heat to 700 °C under a nitrogen atmosphere, introduce ammonia, keep at this temperature for 5 h, cool to obtain the second precursor; the rest is the same as in Example 1.

[0180] Example 15

[0181] The difference between Example 15 and Example 1 is as follows:

[0182] Step (3) is as follows: Prepare a cobalt nitrate solution with a concentration of 2.5 wt%. Immerse one mass of the first precursor in ten masses of the cobalt nitrate solution, stir for 12 h, separate the solid and liquid, dry to obtain an intermediate, place the intermediate in a furnace, heat to 1500 °C under a nitrogen atmosphere, introduce ammonia, keep at the temperature for 5 h, cool to obtain the second precursor; the rest is the same as in Example 1.

[0183] Example 16

[0184] The difference between Example 16 and Example 1 is as follows:

[0185] Step (4) is as follows: the second precursor and asphalt are mixed at a mass ratio of 1:0.02, the mixture is transferred to a tube furnace, heated to 1100°C and sintered for 3 hours under a nitrogen atmosphere, cooled, and sieved through a 325-mesh sieve to obtain the electrode material; the rest is the same as in Example 1.

[0186] Example 17

[0187] The difference between Example 17 and Example 1 is as follows:

[0188] Step (4) is as follows: the second precursor and asphalt are mixed at a mass ratio of 1:0.02, the mixture is transferred to a tube furnace, heated to 1600℃ and sintered for 3 hours under a nitrogen atmosphere, cooled, and sieved through a 325-mesh sieve to obtain the electrode material; the rest is the same as in Example 1.

[0189] Example 18

[0190] The difference between Example 18 and Example 2 is as follows:

[0191] Step (3) is as follows: Prepare a 0.5 wt% ferric sulfate solution, immerse one mass of the first precursor in two masses of the ferric sulfate solution, stir for 3 hours, separate the solid and liquid, dry, and obtain an intermediate. Place the obtained intermediate in a furnace, heat to 1400°C under a neon atmosphere, introduce methylamine, keep at this temperature for 10 hours, cool, and obtain the second precursor; the rest is the same as in Example 1.

[0192] Example 19

[0193] The difference between Example 19 and Example 2 is as follows:

[0194] Step (3) is as follows: Prepare a 5 wt% ferric sulfate solution, immerse one mass of the first precursor in 25 times its mass of the ferric sulfate solution, stir for 3 hours, separate the solid and liquid, dry, and obtain an intermediate. Place the obtained intermediate in a furnace, heat it to 1400°C under a neon atmosphere, introduce methylamine, keep it at this temperature for 10 hours, cool, and obtain the second precursor; the rest is the same as in Example 1.

[0195] Comparative Example 1

[0196] The difference between Comparative Example 1 and Example 1 is as follows:

[0197] Step (2) is as follows: the pre-carbonized material, hydrochloric acid (concentration of 31wt%), hydrofluoric acid (concentration of 55wt%) and water are mixed in a mass ratio of 1:1:0.1:5, heated to 80°C, stirred for 12 hours, solid-liquid separation is performed, the mixture is washed until the pH value is 3.5, dried, and ball-milled to a median particle size of 7μm to obtain the first precursor; the rest is the same as in Example 1.

[0198] Comparative Example 2

[0199] The difference between Comparative Example 2 and Example 1 is as follows:

[0200] Step (3) is as follows: the first precursor is placed in a furnace, heated to 1200°C under nitrogen, ammonia is introduced, kept at the temperature for 5 hours, and then cooled to obtain the second precursor; the rest is the same as in Example 1.

[0201] Comparative Example 3

[0202] The difference between Comparative Example 3 and Example 1 is as follows:

[0203] Step (3) is as follows: Prepare a cobalt nitrate solution with a concentration of 2.5 wt%. Immerse one mass of the first precursor in ten masses of the cobalt nitrate solution, stir for 12 h, separate the solid and liquid, dry to obtain an intermediate, place the intermediate in a furnace, heat to 1200 °C under nitrogen, keep at that temperature for 5 h, cool to obtain the second precursor; the rest is the same as in Example 1.

[0204] Comparative Example 4

[0205] (1) In a tube furnace, coconut shells are heated to 500°C under nitrogen, kept at that temperature for 12 hours, cooled, and the resulting material is crushed with a crusher with a screen mesh size of 5 mm to obtain pre-carbonized material.

[0206] (2) The pre-carbonized material, hydrochloric acid (concentration of 31wt%), hydrofluoric acid (concentration of 55wt%) and water were mixed in a mass ratio of 1:1:0.1:5, heated to 80℃, stirred for 12h, separated into solid and liquid, washed until the pH value was 3.5, dried, and ball-milled to a median particle size of 7μm to obtain the first precursor.

[0207] (3) The first precursor and asphalt were mixed at a mass ratio of 1:0.02. The mixture was transferred to a tube furnace and sintered at 1300℃ for 3 hours under a nitrogen atmosphere. After cooling, the mixture was sieved through a 325-mesh sieve to obtain the electrode material.

[0208] Test methods

[0209] The following tests were performed on the electrode materials prepared in Examples 1 to 19 and Comparative Examples 1 to 4:

[0210] (I) Compacted density of 3T powder (g / cm³) 3 ) and particle porosity testing:

[0211] The testing method was as follows: A Shenzhen Sansi Zongheng Battery Powder Compacted Density Tester UTM7305 was used. A sample of specified mass was placed in a mold, and a pressure of 3.0T was applied. After holding the pressure for 30 seconds, the pressure was released to 20N to measure the thickness. The compacted density (unit: g / cm³) was automatically output by the instrument's software according to the formula ρ = 10 * (m / s * H). 3 ).

[0212] Particle porosity = (1 - ρ / ρ0) * 100%;

[0213] Where ρ is the 3T powder compaction density of the electrode material (g / cm3); ρ0 is the 3T powder compaction density of the reference sample (referring to unmodified coconut shell-based hard carbon with a median particle size of 6μm, sintered at 1250℃), and ρ0 is conventionally defined as 1.05 g / cm3. 3The physical meaning of particle porosity is the ratio of the pore volume of pores generated by pore-forming modification or the inherent pore volume of carbon derived from carbon source to the electrode material (carbon-based volume + pore volume). It is specified that the particle porosity of the modified reference material is 0.

[0214] (II) Powder conductivity test:

[0215] The testing method is as follows: The electrical conductivity of the powder material was tested using a Mitsubishi Chemical MCP-PD51 tester. The sample was added and tested at 20 kN to obtain the electrical conductivity data (unit: S / cm).

[0216] (III) Testing of median particle size:

[0217] The test method was as follows: A MasterSizer 3000 was used for testing. The particle refractive index was 2.42, the absorptivity was 1.0, and the dispersant was water with a refractive index of 1.33. The method was as follows: approximately 0.1 g of sample was weighed into a 100 mL beaker, water was added to a final volume of 50 mL, and the mixture was sonicated for 1 min. The sample was then added until the opacity was 8-12%, and the mixture was subjected to internal sonication.

[0218] (iv) Carbon interlayer content test:

[0219] The testing method was as follows: A Panalytical X'Pert PRO MPD instrument was used, with Kα rays (wavelength λ = 0.1541 nm) from a Cu target as the light source, and XRD data were obtained within the 2Theta range of 10°-90°. The carbon interlayer spacing was calculated (in nm) by substituting the (002) diffraction angle of the XRD into the Scherrer formula.

[0220] (v) Specific surface area test:

[0221] The test method is as follows: Nitrogen adsorption was measured at 77K using a McMeter meter (model ASAP2460) to obtain the specific surface area. The specific surface area was calculated using the BET formula (unit: m²). 2 / g).

[0222] (vi) Hard carbon test using SEM images:

[0223] The testing method is as follows: the sample is scanned using a Hitachi S4800 scanning electron microscope to obtain SEM images.

[0224] (vii) Metal nitride content test:

[0225] Sample pretreatment methods:

[0226] (A) The electrode material (HC-1) obtained in this invention is placed in a vacuum furnace, heated to 2200°C under a vacuum atmosphere, held for 4 hours, and cooled to room temperature to obtain electrode material HC-2.

[0227] (B) Prepare a 1.0M hydrochloric acid solution. Immerse one mass of the electrode material in 10 times its volume of the 1.0M hydrochloric acid solution and stir for 6 hours. Separate the solid and liquid phases. Wash with pure water until the pH is ≥4. Dry the material to obtain hard carbon HC-3. Place the dried HC-3 in a vacuum furnace and heat it to 2200℃ under a vacuum atmosphere. Hold the temperature for 4 hours. Cool it to room temperature and remove the material to obtain electrode material HC-4.

[0228] Ash content testing method: Dry the electrode material at 100℃ for 4 hours; pre-calcine the ash crucible at 900℃ for 0.5 hours, cool it to room temperature in a desiccator, weigh it, and obtain the mass of the empty crucible. Weigh approximately 2g of the dried electrode material, place it in a muffle furnace and ignite it at 900℃ to constant weight (approximately 2 hours), cool it to room temperature in a desiccator, weigh it, and calculate the ash content using the formula:

[0229] Ash content (wt%) = (mass of the fully ignited crucible - mass of the empty crucible) * 100% / sample mass.

[0230] The principle of the metal nitride content test in this invention:

[0231] (A) The total metal nitride content of the obtained electrode material was tested by taking advantage of the characteristic that metal nitrides sublimate in a vacuum atmosphere and at high temperature (2200℃).

[0232] (B) Metal nitrides and other impurities on the negative electrode surface are converted into soluble substances after purification with hydrochloric acid solution and removed by washing with pure water. Hydrogen ions from the 1.0M hydrochloric acid solution have difficulty entering the sealed pores; therefore, the metal nitrides within the sealed pores are retained in the hydrochloric acid-purified electrode material. Treating the hydrochloric acid-purified electrode material under vacuum and high temperature (2200℃) converts the metal nitrides within the sealed pores into gas molecules, thereby removing the metal nitrides. The sample after high-temperature treatment is then measured.

[0233] The ash content of HC-1, HC-2, HC-3, and HC-4 was tested separately as A1, A2, A3, and A4.

[0234] Total metal nitride content (wt%) = A1 - A2 * (100 - A1) / (100 - A2);

[0235] The content of metal nitrides in the closed pore (wt%) = A3-A4*(100-A3) / (100-A4).

[0236] (viii) Testing of specific capacity and initial efficiency:

[0237] The electrode material, conductive agent, and binder obtained from the examples and comparative examples were mixed in a mass ratio of 91:3:6. The mixture was adjusted to a solid content of 50% with deionized water, coated on one side of a copper foil current collector, dried at 130°C for 2 hours, and rolled to a surface density of 5.5 ± 0.5 mg / cm³. 2 The electrode was prepared by cutting the material into 14mm diameter circular pieces. GD-120 glass fiber was used as the separator, and a 16mm diameter sodium sheet was used as the counter electrode. 1M sodium hexafluorophosphate was dispersed in diethylene glycol dimethyl ether (100 vol%) to prepare the electrolyte. The electrolyte, electrode, separator, counter electrode, and CR2032 battery casing were assembled into a coin cell. The coin cell was tested at room temperature (around 25℃) using an Arbin battery testing system. The nominal specific capacity was set to 300 mAh / g. The battery was first discharged at a constant current of 0.1C to 1mV, and then discharged at a constant voltage of 1mV to a current density of 3.5*10⁻⁶. -6 A. Discharge cutoff; after standing, charge again at 0.1C with a cutoff voltage of 2V. The test results are shown in Table 2. Specific capacity (mAh / g) is the initial charge capacity divided by the weight of electrode material contained in the negative electrode sheet, and the initial efficiency is the ratio of the initial charge capacity to the initial discharge capacity.

[0238] (ix) Electrochemical performance testing of finished soft-pack batteries:

[0239] Using BTR layered oxide BNH-O3A as the positive electrode, the positive electrode material, conductive agent, and binder were mixed at a mass percentage of 96:2:2. The mixture was adjusted to a solid content of 50% with N-methylpyrrolidone, and then coated on both sides of an aluminum foil current collector. After drying and rolling, the areal density was controlled at 300 g / m². 2 The positive electrode sheet was obtained. The electrode materials, conductive agent, and binder obtained in Examples 1 to 10 and Comparative Examples 1 to 13 were mixed at a mass percentage of 91:3:6. The mixture was adjusted to a solid content of 50% with deionized water, coated on both sides onto a copper foil current collector, dried, and rolled to a surface density of 150 g / m². 2 The negative electrode sheet is obtained;

[0240] An electrolyte was prepared by dispersing 1M sodium hexafluorophosphate in an organic solvent with a volume ratio of ethylene carbonate: dimethyl carbonate: ethyl methyl carbonate = 1:1:1. The positive and negative electrodes were assembled into a 554065 soft-pack battery with an NP excess ratio of 20%, a PP separator, and the electrolyte. The test voltage range was 2V-4V.

[0241] 6C / 0.2C rate charge retention rate (%) test: At room temperature, the batteries after capacity division were subjected to constant current charge and discharge tests at 0.2C / 0.2C and 6C / 6C respectively. The 6C charging capacity was divided by the 0.2C charging capacity to obtain the 6C / 0.2C rate charge retention rate.

[0242] 1C / 1C 500-cycle retention rate (%) test: At room temperature, a 1C / 1C constant current charge-discharge cycle test was conducted. The discharge capacity of the 500th cycle was divided by the discharge capacity of the first cycle to obtain the 1C / 1C 500-cycle retention rate.

[0243] The test results are shown in Tables 1 and 2 below:

[0244] Table 1

[0245]

[0246]

[0247] Table 2

[0248]

[0249]

[0250] As shown in Table 1 and Table 2, Figure 2 , Figure 3 and Figure 4 As shown, the sodium-ion batteries containing the electrode materials of Examples 1-19 have a specific capacity of 254.5 mAh / g-451.1 mAh / g, an initial efficiency of 84.4%-93.8%, a capacity retention rate of 73.1%-93.1% at 6C / 0.2C charging, and a cycle retention rate of 73.5%-97.2% at 1C / 1C@500 cycles. The sodium-ion batteries containing the electrode materials of Examples 1-10 exhibit excellent electrochemical performance, demonstrating that the electrode materials provided by this invention possess advantages such as high capacity, high initial efficiency, high rate capability, and long cycle life. This is because the electrode materials provided by this invention, through processes such as pore-forming treatment, metal salt solution impregnation, and secondary conversion (metal salt is converted into metal oxide at high temperature, and the metal oxide is then converted into metal nitride under the action of process gas), achieve the nano-sizing and uniform loading of metal nitride on the surface and pores of the carbon matrix, improving the electronic conductivity and pore volume of the carbon matrix surface and pore region, thus providing a prerequisite for improving the sodium storage activity of the electrode material. In addition, the high-temperature sintering process transforms the open pores of the carbon matrix into closed pores with sodium storage activity. This process also facilitates the fixation of metal nitrides in the closed pores, thereby improving the sodium storage activity of the pores and the sodium storage utilization rate of the carbon matrix pore volume. This enhances the sodium storage capacity, rate performance, and cycle performance of the electrode material.

[0251] Analysis of Examples 1-19 and Comparative Examples 1 and 4 shows that pore-forming treatment of pre-carbonized materials can improve the particle porosity and sodium storage sites of electrode materials, providing a structural basis for improving the sodium storage activity of electrode materials and facilitating the subsequent formation of closed pores and the fixation of metal nitrides in the closed pores. In addition, the high total content of metal nitrides in Examples 1 to 19 is also beneficial to improving the rate performance and cycle performance of electrode materials.

[0252] Analysis of Examples 1, 2, 5, 11 and 12 shows that controlling the mass ratio of pre-carbonized material to solid pore-forming agent within an appropriate range is beneficial to the formation of closed pores, ensuring that the electrode material has a suitable particle porosity, increasing the content of metal nitrides in the electrode material, and further improving the sodium storage capacity, rate performance and cycle performance of the electrode material.

[0253] Analysis of Examples 1 and 13 shows that purifying the pore-forming modified material can further improve the sodium storage capacity, rate performance, and cycle performance of the electrode material. Purification removes residual pore-forming agents or impurities from the pore-forming modified material, reducing side reactions caused by these agents and impurities during battery charging and discharging. Simultaneously, it prevents residual pore-forming agents and impurities from occupying the pore volume of the first precursor, increasing the loaded metal nitride content of the electrode material, and further ensuring that the electrode material has good sodium storage capacity, rate performance, and cycle performance.

[0254] Analysis of Examples 6 and 7 shows that uniformly mixing the coated carbon source with the second precursor followed by high-temperature sintering can increase the content of metal nitrides in the closed pores, thereby improving the sodium storage capacity, rate performance, and cycle performance of the electrode material. The coated carbon source promotes the transformation of open pores into closed pores, restricts the escape of metal nitrides from the pores, effectively fixes the metal nitrides in the pore structure, increases the sodium storage sites in the pores, and thus improves the sodium storage capacity, rate performance, and cycle performance of the electrode material.

[0255] Analysis of Examples 1-19, Comparative Example 3 and Comparative Example 4 shows that reacting the intermediate with the process gas at high temperature is beneficial to converting the metal salt into metal nitride, increasing the content of metal nitride in the electrode material, improving the electronic conductivity of the carbon matrix surface and pore region, thereby improving the sodium storage capacity, rate performance and cycle performance of the electrode material.

[0256] Analysis of Examples 1, 2, 5, 14, and 15 shows that when the intermediate reacts with the process gas at high temperature, controlling the reaction temperature within an appropriate range is beneficial to increasing the content of metal nitrides in the electrode material, thereby improving the sodium storage capacity, rate performance, and cycle performance of the electrode material. Controlling the reaction temperature within an appropriate range can increase the conversion rate of metal nitrides and reduce their sublimation, thus increasing the content of metal nitrides in the electrode material.

[0257] Analysis of Examples 6 and 8 shows that using a process gas containing carbon atoms and amino groups can increase the content of metal nitrides in the closed pores, thereby improving the sodium storage capacity, rate performance, and cycle performance of the electrode material. The process gas containing carbon atoms and amino groups can generate ammonia, which can react with metal oxides at high temperatures to form metal nitrides. Simultaneously, the carbon atoms in the process gas can act as a carbon source for carbon coating of intermediates, reducing the pore size of the intermediate openings, facilitating the formation of closed pores, inhibiting the escape of the generated metal nitrides from the pore structure, and ensuring the effectiveness of the metal nitride modification of the closed pores.

[0258] Analysis of Examples 1, 2, 16, and 17 shows that controlling the high-temperature sintering temperature within an appropriate range during the second precursor sintering process can further ensure the sodium storage capacity, rate performance, and cycle performance of the electrode material. Controlling the high-temperature sintering temperature within an appropriate range promotes the effective conversion of open pores into closed pores, while reducing the collapse or partial collapse of closed pores, thereby increasing the particle porosity and the volume of closed pores in the electrode material. Furthermore, controlling the high-temperature sintering temperature within an appropriate range reduces the sublimation of metal nitrides, which is beneficial for increasing the content of metal nitrides in the electrode material, thus improving the sodium storage capacity, rate performance, and cycle performance of the electrode material.

[0259] Analysis of Examples 1-19 and Comparative Example 2 shows that Examples 1-19 exhibit higher sodium storage capacity, rate performance, and cycle performance. This may be because the intermediate in Comparative Example 2 was not impregnated in a metal salt solution, thus preventing the formation of metal nitrides in the electrode material; while the electrode materials of Examples 1-19 do form metal nitrides. Metal nitrides possess high electronic conductivity, which can increase the overall electronic conductivity of the electrode material and the utilization rate of sodium storage in the central region of the closed pore, thereby improving the sodium storage capacity, rate performance, and cycle performance of the electrode material.

[0260] Analysis of Examples 2, 10, 18 and 19 shows that controlling the concentration of the metal salt solution and the mass ratio between the intermediate and the metal salt solution within a suitable range can further ensure the content of metal nitrides in the electrode material and the particle porosity of the electrode material, thereby improving the sodium storage capacity, rate performance and cycle performance of the electrode material.

[0261] The embodiments of the present invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for preparing an electrode material, characterized in that, Includes the following steps: The carbon source is pre-carbonized to obtain pre-carbonized material; The pre-carbonized material is subjected to pore-forming treatment and crushed to obtain the first precursor; The first precursor was immersed in a metal salt solution to obtain an intermediate; The intermediate is reacted with process gas at high temperature to obtain a second precursor; The second precursor is subjected to high-temperature sintering to obtain the electrode material; The electrode material includes: A carbon matrix having closed pores; the closed pores are slits and not completely closed, through which sodium ions can enter and exit the closed pores, while solid metal nitrides in the closed pores cannot overflow the closed pores through the slits. A metal nitride, wherein the metal nitride is doped into the carbon matrix; The sealed hole is filled with the metal nitride; the metal nitride includes any one or more combinations of iron nitride, cobalt nitride, nickel nitride, copper nitride, vanadium nitride, titanium nitride, manganese nitride, and zirconium nitride; The process gas is one or a combination of at least two of the following: methylamine, ethylamine, diethylamine, n-propylamine, and isopropylamine; The high-temperature sintering temperature is 1200℃-1500℃; The metal nitride in the sealed pore has a mass percentage of 0.35%-2.2% in the electrode material.

2. The preparation method according to claim 1, characterized in that, The carbon source includes any one or more combinations of plant-based carbon sources, sugar-based carbon sources, and polymer-based carbon sources; and / or The pre-carbonization treatment temperature is 450℃-650℃; and / or The pre-carbonization treatment time is 0.5h-24h; and / or The pre-carbonization treatment is carried out in an inert gas atmosphere or an oxygen-deficient atmosphere. The inert gas atmosphere includes any one or a combination of at least two of nitrogen, argon, neon, helium, xenon, or krypton atmospheres. The oxygen-deficient atmosphere is a gas atmosphere with an oxygen content of ≤1wt%.

3. The preparation method according to claim 1 or 2, characterized in that, The pulverization includes: pulverizing the product of the pore-forming treatment to a median particle size of 3μm-15μm, and / or, the pulverization treatment includes one or more combinations of air jet milling and mechanical milling; and / or The pore-forming process includes solid-phase pore-forming, which comprises the following steps: uniformly mixing the pre-carbonized material with a solid-phase pore-forming agent under an inert atmosphere and subjecting it to high-temperature treatment to obtain a solid-phase pore-forming modified material; and / or The pore-forming process includes gas-phase pore-forming, which includes the following steps: placing the pre-carbonized material in a reactor, introducing pore-forming gas, heating to a first temperature and then holding it at that temperature to obtain a gas-phase pore-forming modified material.

4. The preparation method according to claim 3, characterized in that, In the solid-phase pore-forming process, the high-temperature treatment is performed at a temperature of 600℃-800℃ for a duration of 0.5h-8h; and / or The mass ratio of the pre-carbonized material to the solid pore-forming agent is 1:(0.4-3.0); and / or The solid pore-forming agent includes at least one of sodium hydroxide, potassium hydroxide, sodium oxide, potassium oxide, sodium carbonate, potassium carbonate, potassium bicarbonate, sodium bicarbonate, calcium oxide, and zinc chloride; and / or In the solid-phase pore formation, the inert atmosphere includes any one or a combination of at least two of the following: nitrogen atmosphere, argon atmosphere, neon atmosphere, helium atmosphere, xenon atmosphere, or krypton atmosphere; and / or The solid-phase pore-forming treatment further includes purification treatment of the solid-phase pore-forming modification material. The purification treatment of the solid-phase pore-forming modification material includes: mixing the solid-phase pore-forming modification material, acid solution, and pure water at a mass ratio of 1:(0.5-2):(2-5) and stirring for 0.5h-24h; after stirring, performing solid-liquid separation; washing the purified product obtained from the solid-liquid separation to a pH of 2.5-4.5 and drying it; the acid solution includes one or a combination of at least two of hydrochloric acid, hydrofluoric acid, nitric acid, phosphoric acid, and sulfuric acid; and / or In the aforementioned vapor-phase pore formation, the first temperature is 800℃-1000℃, and the holding time is 1h-8h; and / or The pore-forming gas includes any one or a combination of at least two of the following: water vapor, carbon dioxide, chlorine, oxygen, ozone, and air; and / or The vapor phase pore formation process further includes purification treatment of the vapor phase pore formation modifier material. The purification treatment of the vapor phase pore formation modifier material includes: mixing the vapor phase pore formation modifier material, acid solution, and pure water in a ratio of 1:(0.5-2):(1.2-5) and stirring for 0.5h-24h. After stirring, solid-liquid separation is performed. The purified product obtained from the solid-liquid separation is washed until the pH is 4-8 and then dried. The acid solution includes one or a combination of at least two of hydrochloric acid, hydrofluoric acid, nitric acid, phosphoric acid, and sulfuric acid.

5. The preparation method according to claim 1 or 2, characterized in that, The step of immersing the first precursor in a metal salt solution to obtain the intermediate specifically includes: The first precursor is immersed in the metal salt solution and stirred for 3-24 hours. After solid-liquid separation and drying, the intermediate is obtained.

6. The preparation method according to claim 5, characterized in that, The concentration of the metal salt solution is 0.5wt%-5wt%, and the mass ratio of the first precursor to the metal salt solution is 1:(3-20); and / or The median particle size of the first precursor is 3 μm-15 μm; and / or The metal salt includes soluble salts of Co, Ni, Cu, V, Ti, Mn, Fe, or Zr, and the soluble salt includes one or a combination of at least two of sulfates, nitrates, and chlorides.

7. The preparation method according to claim 1 or 2, characterized in that, The step of reacting the intermediate with a process gas at high temperature to obtain the second precursor specifically includes: Under inert atmosphere conditions, the intermediate is placed in a reactor, process gas is introduced, the temperature is raised to a second temperature and then held at that temperature before cooling to obtain the second precursor.

8. The preparation method according to claim 7, characterized in that, The second temperature is 1000℃-1400℃, and the heat preservation time is 3h-10h; and / or The inert atmosphere includes any one or a combination of at least two of the following: nitrogen atmosphere, argon atmosphere, neon atmosphere, helium atmosphere, xenon atmosphere, or krypton atmosphere.

9. The preparation method according to claim 1 or 2, characterized in that, In the step of high-temperature sintering the second precursor to obtain the electrode material, the high-temperature sintering is carried out under an inert atmosphere, and / or the high-temperature sintering time is 0.5h-10h; and / or Before the second precursor is sintered at high temperature, the following steps are also included: mixing the coated carbon source with the second precursor evenly.

10. The preparation method according to claim 9, characterized in that, The mass ratio between the second precursor and the coated carbon source is 1:(0.01-0.1); and / or The coated carbon source includes any one or more combinations of asphalt, sucrose, phenolic resin, polyacrylic resin, glucose, polystyrene, polyvinyl chloride, polytetrafluoroethylene, polyvinyl alcohol, epoxy resin, urea-formaldehyde resin, and melamine resin; and / or The inert atmosphere is any one or a combination of at least two of the following: nitrogen atmosphere, argon atmosphere, neon atmosphere, helium atmosphere, xenon atmosphere, or krypton atmosphere.

11. An electrode material, characterized in that, The electrode material is prepared by the preparation method according to any one of claims 1 to 10.

12. An electrode sheet, characterized in that, Includes the electrode material as described in claim 11.

13. A sodium-ion battery, characterized in that, Includes the electrode material of claim 11 or the electrode sheet of claim 12.

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