A negative electrode material, a preparation method thereof, a negative electrode sheet, a battery, and an electric device

Abstract

The embodiment of the application provides a kind of negative electrode material, negative electrode sheet, battery and electric device, negative electrode material includes hard carbon particle and first grafting group, the first grafting group is grafted on the surface of the hard carbon particle by covalent bond, the structure of the first grafting group is as shown in formula 1, formula 1, wherein, Ar is phenyl or substituted phenyl, R1, R2 each is independently selected from C1-C4 alkyl, n=2-6, * indicates binding site.The application is modified by grafting aryl quaternary ammonium-sulfonic acid inner salt group on the surface of hard carbon particle, the surface of hard carbon particle is modified, the surface electronic structure and surface chemical property of hard carbon particle are controlled, the defect site and active functional group on the surface of hard carbon are reduced, the adsorption and deintercalation kinetics process of sodium ion on the surface of hard carbon is optimized, the interface compatibility of hard carbon and electrolyte, binder is improved, and the overall improvement of electrochemical performance is realized.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a negative electrode material and its preparation method, a negative electrode sheet, a battery, and an electrical device. Background Technology

[0002] Lithium-ion batteries have been widely developed and applied due to their high energy density and long cycle life. However, the scarcity of lithium resources in the Earth's crust remains the biggest obstacle to their large-scale application. In recent years, sodium-ion batteries have attracted widespread attention due to their low cost and electrochemical performance similar to that of lithium-ion batteries.

[0003] Sodium-ion battery anodes include carbon-based materials, conversion materials, alloy materials, and organic materials, all of which exhibit relatively excellent cycle performance and rate performance. Among them, hard carbon anode materials have achieved commercial application due to their wide availability and superior performance. However, most sodium-ion batteries using hard carbon materials have low coulombic efficiency, and this low coulombic efficiency affects the battery's energy density.

[0004] Therefore, there is an urgent need to provide a negative electrode material that can improve the coulombic efficiency and energy density of batteries. Summary of the Invention

[0005] This application provides an anode material and its preparation method, an anode sheet, a battery, and an electrical device, aiming to improve the coulombic efficiency and energy density of sodium-ion batteries.

[0006] In a first aspect, this application provides a negative electrode material comprising hard carbon particles and a first grafting group, wherein the first grafting group is covalently grafted onto the surface of the hard carbon particles, and the structure of the first grafting group is shown in Formula 1. Formula 1, wherein Ar is a phenyl or substituted phenyl, R1 and R2 are each independently selected from C1-C4 alkyl groups, n=2-6, and * indicates the bonding site.

[0007] In this application, an aryl quaternary ammonium-sulfonic acid inner salt group of formula 1 is covalently grafted onto the surface of hard carbon particles to modify the surface of the hard carbon particles. By utilizing the synergistic effect of the quaternary ammonium cation and sulfonic acid anion in the inner salt structure, the surface electronic structure and surface chemical properties of the hard carbon particles are regulated, the defect sites and active functional groups on the hard carbon surface are reduced, and the side reactions during the battery charging and discharging process are suppressed. At the same time, the adsorption and deintercalation kinetics of sodium ions on the hard carbon surface are optimized, the interfacial compatibility between hard carbon and electrolyte and binder is improved, and the overall electrochemical performance is comprehensively improved.

[0008] Optionally, the content of the first grafting group in each gram of the hard carbon particles is 0.01-0.6 mmol. By limiting the amount of the first grafting group on the surface of the hard carbon particles, it is ensured that the grafting group can fully exert its synergistic modification effect, while avoiding the adverse effects of too much or too little grafting on the performance of the hard carbon anode, thus achieving a balance between the modification effect and the sodium ion transport performance.

[0009] Optionally, the negative electrode material further includes a second grafting group, which comprises substituted or unsubstituted sodium arylsulfonate, wherein the aryl group in the second grafting group is covalently grafted onto the surface of the hard carbon particles. Adding a second grafting group based on the first grafting group further optimizes the surface properties of the hard carbon particles, synergistically enhances the electrochemical performance, ion transport performance, and interfacial stability of the negative electrode material with the first grafting group, and simultaneously enhances the hydrophilicity of the negative electrode material, further improving its compatibility with binders and electrolytes.

[0010] Optionally, the content of the second grafting group in each gram of the hard carbon particles is 0.05-0.3 mmol. By limiting the grafting amount of the second grafting group, it is ensured that the second grafting group can form a synergistic effect with the first grafting group, which can fully exert its ion transport and interface optimization functions, while avoiding the adverse effects of improper grafting amount on the negative electrode performance, thus achieving the best synergistic effect of the two grafting groups.

[0011] Optionally, the molar ratio of the first grafting group to the second grafting group is 1:20-20:1. By limiting the molar ratio of the first grafting group to the second grafting group, the synergistic ratio of the two grafting groups is controlled, avoiding an excess or deficiency of one grafting group, which would lead to a decrease in the overall modification effect, and achieving a balanced optimization of various electrochemical properties of the anode material.

[0012] Optionally, the sulfur content in the negative electrode material is 0.1%-1.2% by mass. By limiting the sulfur content in the negative electrode material, the surface electronic structure and ion transport performance of the negative electrode material are further optimized, while ensuring that sulfur does not adversely affect battery performance, thus helping to improve coulombic efficiency and energy density.

[0013] Secondly, this application provides a method for preparing a negative electrode material, comprising the following steps: Hard carbon particles are added to a solvent and dispersed to obtain the first dispersion; The compound shown in Formula 2 was subjected to a diazotization reaction to obtain a first diazotized solution; the structure of the compound shown in Formula 2 is shown below: Formula 2, wherein Ar is a phenyl or substituted phenyl, R1 and R2 are each independently selected from C1-C4 alkyl groups, and n=2-6; The first diazotization solution is added to the first dispersion to carry out the first grafting reaction, thereby obtaining a negative electrode material grafted with the first grafting group.

[0014] The first grafting group is covalently grafted to the surface of hard carbon particles through a diazotization reaction, ensuring that the grafting group is firmly grafted and evenly distributed. At the same time, the preparation process is mild and low-cost, making it suitable for large-scale industrial production.

[0015] Optionally, after the first grafting reaction, the following steps are included: Hard carbon particles grafted with the first grafting group are added to a solvent and dispersed to obtain a second dispersion. A second diazotization solution is obtained by diazotizing aminobenzenesulfonic acid or aminobenzenesulfonate. The second diazotization solution is added to the second dispersion to carry out the second grafting reaction, thereby obtaining a negative electrode material containing the first grafting group and the second grafting group.

[0016] By performing stepwise grafting of the two grafting groups, it is ensured that the two grafting groups can be uniformly and firmly grafted onto the surface of hard carbon particles, giving full play to their synergistic effect. At the same time, the stepwise grafting method makes it easier to control the grafting amount and molar ratio of the two grafting groups, thereby improving the controllability of the preparation process.

[0017] Optionally, the following steps are also included: The negative electrode material that has undergone the first or second grafting reaction is sequentially pretreated and dried with the electrolyte. The pretreatment includes steam contact or immersion of the negative electrode material with the electrolyte.

[0018] By subjecting the negative electrode material or a negative electrode sheet containing such material to steam contact or immersion pretreatment with the electrolyte, the sodium salts, solvents, and optional additives in the electrolyte can pre-wet and impregnate the surface and pore structure of the negative electrode material, improving the interfacial contact between the negative electrode material and the electrolyte. This pretreatment process facilitates the formation of a more uniform and stable interfacial film during the subsequent first charge and discharge process, reducing local side reactions and interfacial impedance growth, thereby reducing the initial irreversible capacity loss and improving the battery's initial coulombic efficiency and cycle stability.

[0019] Optionally, the following steps are also included: The negative electrode material that has undergone the second grafting reaction is added to a sodium-modification solution for sodium modification, wherein the sodium-modification solution includes at least one of sodium carbonate solution and sodium hydroxide solution.

[0020] By subjecting the double-grafted anode material to sodium treatment, sodium ions are added, optimizing the sodium intercalation capability of the anode material. At the same time, the surface chemical properties of the anode material are further adjusted to improve its compatibility with the electrolyte and ionic conductivity, thereby further improving the coulombic efficiency and energy density of the battery.

[0021] Thirdly, this application provides a negative electrode sheet, including a negative electrode current collector and a negative electrode active material layer, wherein the negative electrode active material layer includes the negative electrode material as described in any of the preceding claims, or includes the negative electrode material prepared by the preparation method described in any of the preceding claims.

[0022] The first and second grafting groups in the negative electrode material work synergistically to achieve high coulombic efficiency, high energy density, good cycle stability, and rate performance. Therefore, the negative electrode can provide the battery with high reversible capacity, reduce charge loss during charging and discharging, and improve the overall electrochemical performance of the battery. At the same time, the grafting groups in the negative electrode material can optimize interface performance, reduce interface impedance, and further improve the conductivity and ion transport performance of the negative electrode.

[0023] Fourthly, this application provides a battery including the negative electrode sheet as described above. Using the negative electrode sheet of this invention, the first grafted group in the negative electrode material can effectively suppress side reactions, reduce irreversible capacity loss, lower the side reactions during the first charge and discharge cycle, and improve the battery's initial coulombic efficiency, energy density, and cycle performance.

[0024] Fifthly, this application provides an electrical device including the battery described above. By using the battery described above, which has a high initial coulombic efficiency and energy density, the battery life of the electrical device is improved. Detailed Implementation

[0025] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0026] One embodiment of this application provides a negative electrode material, comprising hard carbon particles and a first grafting group, wherein the first grafting group is covalently grafted onto the surface of the hard carbon particles, and the structure of the first grafting group is shown in Formula 1. Formula 1, wherein Ar is a phenyl or substituted phenyl, R1 and R2 are each independently selected from C1-C4 alkyl groups, n=2-6, and * indicates the bonding site.

[0027] In this embodiment, aryl quaternary ammonium-sulfonic acid inner salt groups are covalently grafted onto the surface of hard carbon particles to modify the surface of the hard carbon particles. By utilizing the synergistic effect of quaternary ammonium cations and sulfonic acid anions in the inner salt structure, the surface electronic structure and surface chemical properties of the hard carbon particles are regulated, reducing defect sites and active functional groups on the hard carbon surface, suppressing side reactions during battery charging and discharging, and optimizing the adsorption and deintercalation kinetics of sodium ions on the hard carbon surface. This improves the interfacial stability, surface wettability, and ion transport conditions of the hard carbon anode, thereby helping to improve the first-cycle coulombic efficiency, cycle stability, rate performance, and impedance characteristics of sodium-ion batteries.

[0028] Specifically, the Ar (phenyl or substituted phenyl) group in the first grafting group possesses a conjugated π-electron system, which optimizes the electron cloud distribution on the hard carbon surface, reduces the adsorption energy of sodium ions, promotes rapid insertion and extraction of sodium ions, and reduces charge loss, thereby significantly improving the coulombic efficiency of the battery, especially the initial coulombic efficiency. The sulfonate group has strong ionic conductivity, which accelerates the adsorption, migration, and insertion / extraction of sodium ions on the hard carbon surface. Simultaneously, the quaternary ammonium cation forms a weak interaction with sodium ions, assisting sodium ions in rapidly crossing the interface layer. Furthermore, the hydrophilic-hydrophobic balance of the inner salt group can prevent excessive electrolyte adsorption or poor interfacial contact, effectively reducing the battery interface impedance, improving rate performance, and ensuring the battery's energy density.

[0029] The aryl quaternary ammonium-sulfonic acid inner salt group has an amphoteric structure. On the one hand, it can further adjust the polarity and interfacial compatibility of the hard carbon surface. On the other hand, it is beneficial to optimize the contact state between the hard carbon surface and the electrolyte and promote the stabilization of the ion transport environment at the interface.

[0030] Meanwhile, the first grafting group can regulate the charge distribution on the hard carbon surface, reduce particle agglomeration, improve the dispersion of hard carbon, facilitate the formation of a uniform conductive network, and ensure the structural stability of the negative electrode material. Furthermore, the first grafting group is stably bonded to the hard carbon surface via covalent bonds, making it less prone to detachment during battery charging and discharging compared to physical adsorption modification. Simultaneously, the chemically stable internal salt structure protects the hard carbon surface, reduces SEI film rupture and reconstruction, and extends battery cycle life.

[0031] Furthermore, substituted phenyl groups include, but are not limited to, methylphenyl, ethylphenyl, propylphenyl, butylphenyl, hydroxyphenyl, and methoxyphenyl. The sources of hard carbon particles include, but are not limited to, hard carbon materials obtained through carbonization from biomass carbon sources, pitch carbon sources, resin carbon sources, coal-based carbon sources, etc. The source, particle size distribution, and morphology of hard carbon particles are not limited.

[0032] In some embodiments, the content of the first grafted group in each gram of hard carbon particles is 0.01-0.6 mmol. By limiting the amount of the first grafted group on the surface of the hard carbon particles, the active sites on the hard carbon surface can be fully covered, effectively suppressing side reactions and improving coulombic efficiency. Simultaneously, the ionic conductivity of the internal salt structure can be optimized for sodium ion transport without hindering sodium ion transport and insertion, ensuring the high capacity advantage of the hard carbon material itself. This achieves a synergistic improvement in coulombic efficiency, energy density, and rate performance. At the same time, it avoids the adverse effects of excessive or insufficient grafting on the performance of the hard carbon anode, achieving a balance between the modification effect and sodium ion transport performance.

[0033] When the amount of the first grafting group is too low, there are too few first grafting groups covering the active functional groups and defect sites on the surface of hard carbon particles. This weakens the ability to suppress side reactions on the surface of hard carbon, reduces ionic conductivity, and makes the improvement in coulombic efficiency and energy density insignificant.

[0034] When the amount of the first grafting group is too high, too many aryl quaternary ammonium-sulfonic acid inner salt groups will form a dense covering layer on the surface of hard carbon particles, which will easily increase the transport resistance of sodium ions and lead to an increase in the surface impedance of the negative electrode material.

[0035] Specifically, the content of the first grafting group in each gram of the hard carbon particles includes, but is not limited to, 0.01 mmol, 0.05 mmol, 0.1 mmol, 0.15 mmol, 0.2 mmol, 0.25 mmol, 0.3 mmol, 0.35 mmol, 0.4 mmol, 0.45 mmol, 0.5 mmol, 0.55 mmol, or 0.6 mmol.

[0036] The content of the first grafting group in the negative electrode material can be determined by one or more of the following methods: elemental analysis, X-ray photoelectron spectroscopy, ion chromatography, or inductively coupled plasma atomic emission spectroscopy.

[0037] In some embodiments, the negative electrode material further includes a second grafting group, which comprises substituted or unsubstituted sodium arylsulfonate, wherein the aryl group in the second grafting group is covalently grafted onto the surface of the hard carbon particles. Adding a second grafting group based on the first grafting group further optimizes the surface properties of the hard carbon particles, synergistically enhances the electrochemical performance, ion transport performance, and interfacial stability of the negative electrode material with the first grafting group, and simultaneously enhances the hydrophilicity of the negative electrode material, further improving its compatibility with binders and electrolytes.

[0038] The sodium aryl sulfonate group imparts certain ionic and electrolyte-loving properties to the hard carbon surface, which is beneficial for improving the wettability of the hard carbon surface and facilitating the migration and distribution of sodium ions on the negative electrode surface. Simultaneously, the second grafting group is fixed to the hard carbon surface through aryl-carbon covalent bonds, which can be used to construct a more stable surface chemical layer, thereby helping to reduce surface side reactions and improve the negative electrode interface state. When the second grafting group is used in conjunction with the first grafting group, it can further enrich the ionic chemical composition of the hard carbon surface.

[0039] Sodium ions in the sodium sulfonate group can provide an additional sodium ion source, and the sodium sulfonate group has strong ionic conductivity. It forms a synergistic effect with the inner salt structure of the first graft group, which can further accelerate the adsorption, migration and deintercalation of sodium ions on the hard carbon surface, reduce interfacial impedance, improve the rate performance of the battery, and at the same time reduce charge loss during sodium ion transport, further improving energy density.

[0040] Specifically, substituted or unsubstituted sodium aryl sulfonates include, but are not limited to, sodium benzenesulfonate, sodium p-toluenesulfonate, sodium p-ethylbenzenesulfonate, and sodium p-hydroxybenzenesulfonate.

[0041] In some embodiments, the content of the second grafting group in each gram of the hard carbon particles is 0.05-0.3 mmol. By limiting the grafting amount of the second grafting group, it is ensured that the second grafting group can form a synergistic effect with the first grafting group, which can fully exert its ion transport and interface optimization functions, while avoiding the adverse effects of improper grafting amount on the negative electrode performance, thus achieving the best synergistic effect of the two grafting groups.

[0042] It should be noted that the content of the second grafting group in each gram of the hard carbon particles refers to hard carbon particles that have been grafted with the first grafting group, or hard carbon particles that have not been grafted with the first grafting group. If the hard carbon particles are grafted with the second grafting group first and then with the first grafting group, then the hard carbon particles in "content of the first grafting group in each gram of the hard carbon particles" refer to hard carbon particles grafted with the second grafting group.

[0043] Specifically, the grafting content of the second grafting group can form an optimal synergistic effect with the first grafting group. The hydrophilicity and ionic conductivity of the second grafting group can optimize the interfacial performance and accelerate sodium ion transport, while the first grafting group can suppress side reactions and optimize ion transport. The synergistic effect of the two can achieve a comprehensive improvement in coulombic efficiency, energy density, rate performance and cycle stability.

[0044] Specifically, the content of the second grafting group in each gram of hard carbon particles includes, but is not limited to, 0.05 mmol, 0.1 mmol, 0.15 mmol, 0.2 mmol, 0.25 mmol, and 0.3 mmol.

[0045] In some embodiments, the molar ratio of the first grafting group to the second grafting group is 1:20-20:1. By limiting the molar ratio of the first grafting group to the second grafting group, the synergistic ratio of the two grafting groups is controlled, avoiding an excess or deficiency of one grafting group, which would lead to a decrease in the overall modification effect, and achieving a balanced optimization of various electrochemical properties of the anode material.

[0046] When the proportion of the second grafting group is too high, the surface chemical composition of hard carbon particles tends to be regulated by a single anionic group, making it difficult to fully reflect the auxiliary regulatory effect of the aryl quaternary ammonium-sulfonic acid inner salt group on the surface polarity and interfacial compatibility of hard carbon particles. When the proportion of the aryl quaternary ammonium-sulfonic acid inner salt group is too high, the proportion of zwitterionic structures on the surface of hard carbon particles increases, and the density of organic groups on the surface of hard carbon particles is too high, which easily affects the ion migration and electron transport rate.

[0047] Therefore, controlling the molar ratio of the two within the range of 1:20-20:1 is beneficial to taking into account the synergistic regulatory effect of different types of ionic functional groups on the chemical environment of the hard carbon particle surface, making the chemical composition of the hard carbon particle surface more balanced, and is conducive to the unification of the interface stability and processing adaptability of the anode material.

[0048] Specifically, the molar ratio of the first grafting group to the second grafting group includes, but is not limited to, 1:20, 1:17, 1:15, 1:13, 1:10, 1:7, 1:5, 1:3, 1:1, 3:1, 5:1, 7:1, 10:1, 13:1, 15:1, 17:1 or 20:1.

[0049] In some embodiments, the sulfur content in the negative electrode material is 0.1%-1.2% by mass. The sulfur in the negative electrode material originates from the first grafting group and the second grafting group. The sulfur content accurately reflects the effective grafting amount of the grafting group. By limiting the sulfur content in the negative electrode material, the surface electronic structure and ion transport performance of the negative electrode material are further optimized, while ensuring that sulfur does not adversely affect battery performance, thus helping to improve coulombic efficiency and energy density.

[0050] Specifically, the mass content of sulfur in the negative electrode material includes, but is not limited to, 0.1%, 0.3%, 0.5%, 0.7%, 0.9%, 1.1%, or 1.2%.

[0051] One embodiment of this application provides a method for preparing a negative electrode material, including the following steps: Hard carbon particles are added to a solvent and dispersed to obtain the first dispersion; The compound shown in Formula 2 was subjected to a diazotization reaction to obtain a first diazotized solution; the structure of the compound shown in Formula 2 is shown below: Formula 2, wherein Ar is a phenyl or substituted phenyl, R1 and R2 are each independently selected from C1-C4 alkyl groups, and n=2-6; The first diazotization solution is added to the first dispersion to carry out the first grafting reaction, thereby obtaining a negative electrode material grafted with the first grafting group.

[0052] The first grafting group is covalently grafted to the surface of hard carbon particles through a diazotization reaction, ensuring that the grafting group is firmly grafted and evenly distributed. At the same time, the preparation process is mild and low-cost, making it suitable for large-scale industrial production.

[0053] Furthermore, the solvent is a mixture of water and organic solvent, with a volume ratio of organic solvent to water of 10:90-70:30, a liquid-to-solid ratio of 5-50 L / kg for the first dispersion, a dispersion temperature of 0-25℃, a dispersion time of 10-60 min, and a stirring speed of 200-800 rpm; the organic solvent includes, but is not limited to, ethanol, isopropanol, and acetone.

[0054] Further, the compound shown in Formula 2 is subjected to a diazotization reaction, including the following steps: The compound shown in Formula 2 is added to water and dissolved by stirring at 0-5°C. The pH of the system is adjusted to 0.5-3.0 using an acidic solution. The acidic solution includes, but is not limited to, hydrochloric acid, sulfuric acid, methanesulfonic acid, or phosphoric acid. The concentration of hydrochloric acid is 0.5-6.0 mol / L, and the concentration of sulfuric acid is 0.5-3.0 mol / L.

[0055] Prepare a nitrite solution with a concentration of 0.05-2.0 mol / L. Add the nitrite solution dropwise to the solution of compound 2 at 0-5℃ for 5-60 min. After the addition is complete, continue the reaction for another 5-60 min to obtain the first diazotization solution.

[0056] The molar ratio of nitrite to compound of formula 2 is 1-1.2:1. Nitrite includes, but is not limited to, sodium nitrite, potassium nitrite, or lithium nitrite.

[0057] Furthermore, the addition time of the first diazotization solution is 5-120 min, the reaction temperature of the first grafting reaction is 0-25℃, the reaction time is 0.5-12 h, the pH of the grafting reaction system is 0.5-4.0, and the stirring speed is 200-1000 rpm. Specifically, the solution after the first grafting reaction is subjected to solid-liquid separation, the filter cake is collected, and the filter cake is washed. The number of washings is 3-10 times, and the liquid-to-solid ratio of each washing is 5-50 L / kg.

[0058] In some embodiments, after the first grafting reaction, the following steps are included: Hard carbon particles grafted with the first grafting group are added to a solvent and dispersed to obtain a second dispersion. A second diazotization solution is obtained by diazotizing aminobenzenesulfonic acid or aminobenzenesulfonate. The second diazotization solution is added to the second dispersion to carry out the second grafting reaction, thereby obtaining a negative electrode material containing the first grafting group and the second grafting group.

[0059] By performing stepwise grafting of the two grafting groups, it is ensured that the two grafting groups can be uniformly and firmly grafted onto the surface of hard carbon particles, giving full play to their synergistic effect. At the same time, the stepwise grafting method makes it easier to control the grafting amount and molar ratio of the two grafting groups, thereby improving the controllability of the preparation process.

[0060] Specifically, the reaction raw materials for the second diazotization solution are aminobenzenesulfonic acid / aminobenzenesulfonate and nitrite. The molar ratio of aminobenzenesulfonic acid / aminobenzenesulfonate and nitrite is 1-1.2:1.

[0061] The solution following the second grafting reaction can be subjected to solid-liquid separation, and the filter cake can be collected, washed, and dried. The washing process is repeated 3–10 times, with a liquid-to-solid ratio of 5–50 L / kg per wash. Drying conditions are 60–140 °C, a vacuum of 10–1000 Pa, and a drying time of 4–24 h.

[0062] It should be noted that the reaction order of the first and second grafting groups is not limited. Hard carbon particles can be grafted with the second grafting group first, and then with the first grafting group.

[0063] Furthermore, a terminator can be added to the reaction system before the first diazotization solution is added to the first dispersion, or after the first grafting reaction, or before the second diazotization solution is added to the second dispersion, or after the second grafting reaction, to consume the nitrite ions involved in the reaction system and reduce the risk of subsequent side reactions. The terminator includes, but is not limited to, aminosulfonic acid or urea. The amount of terminator added is 0.9-1.2 times the molar amount of nitrite.

[0064] In some embodiments, the following steps are also included: The negative electrode material, after undergoing the first or second grafting reaction, is sequentially pretreated and dried with an electrolyte. The pretreatment includes steam contact or immersion of the negative electrode material in the electrolyte. Specifically, the methods of contacting the negative electrode material or electrode sheet with the electrolyte during pretreatment also include rapid liquid-phase immersion, spray wetting, and drop-addition wetting. Rapid liquid-phase immersion typically refers to the material or electrode sheet being removed immediately after contact with the pretreated electrolyte within seconds to minutes, followed by liquid absorption, draining, or vacuum drying. Steam contact typically refers to the material or electrode sheet being placed in a closed environment containing volatile components of the pretreated electrolyte without direct immersion in the liquid.

[0065] Specifically, the pretreatment temperature is 20-60 ℃, and the pretreatment time is 2-24 h. The sodium salt concentration of the pretreatment electrolyte is 0.3–2.0 mol / L; After pretreatment, vacuum drying is carried out under the following conditions: 30-80℃, vacuum degree 10-1000 Pa, and time 0.5-8h.

[0066] By subjecting the negative electrode material or a negative electrode sheet containing such material to steam contact or immersion pretreatment with the electrolyte, the sodium salts, solvents, and optional additives in the electrolyte can pre-wet and impregnate the surface and pore structure of the negative electrode material, improving the interfacial contact between the negative electrode material and the electrolyte. This pretreatment process facilitates the formation of a more uniform and stable interfacial film during the subsequent first charge and discharge process, reducing local side reactions and interfacial impedance growth, thereby reducing the initial irreversible capacity loss and improving the battery's initial coulombic efficiency and cycle stability.

[0067] The electrolyte comprises a sodium salt, a solvent, and additives. The sodium salt includes, but is not limited to, at least one of NaPF6, NaFSI, and NaClO4. The concentration of the sodium salt is 0.3-2.0 mol / L.

[0068] Solvents include, but are not limited to, at least one of EC (ethylene carbonate) / DEC (diethyl carbonate), PC (propylene carbonate), DME (dimethyl ethanol), and DEGDME (diethylene glycol dimethyl ether).

[0069] Additives include, but are not limited to, film-forming additives, and the mass content of additives in the electrolyte is 0%-5%.

[0070] It should be noted that the negative electrode sheet containing the negative electrode material can also be pretreated with an electrolyte.

[0071] In some embodiments, the following steps are also included: The negative electrode material undergoing the second grafting reaction is added to a sodium-modification solution for sodium modification. The sodium-modification solution comprises at least one of sodium carbonate solution and sodium hydroxide solution. The concentration of the sodium carbonate solution is 0.05-1.0 mol / L, and the concentration of the sodium hydroxide solution is 0.01-1.0 mol / L. The target pH for sodium modification is 7.0-10.5, the sodium modification temperature is 15-60℃, and the sodium modification time is 0.2-6 h.

[0072] After sodium treatment, the negative electrode material is washed and dried under the following conditions: 60-140℃, vacuum degree 10-1000Pa, and time 4-24h.

[0073] By subjecting the double-grafted anode material to sodium treatment, sodium ions are added, optimizing the sodium intercalation capability of the anode material. At the same time, the surface chemical properties of the anode material are further adjusted to improve its compatibility with the electrolyte and ionic conductivity, thereby further improving the coulombic efficiency and energy density of the battery.

[0074] It should be noted that the sodium treatment is performed after the hard carbon particles are grafted with a second graft group.

[0075] One embodiment of this application provides a negative electrode sheet, including a negative electrode current collector and a negative electrode active material layer, wherein the negative electrode active material layer includes the negative electrode material as described in any of the preceding claims, or includes the negative electrode material prepared by the preparation method described in any of the preceding claims.

[0076] The first and second grafting groups in the negative electrode material work synergistically to achieve high coulombic efficiency, high energy density, good cycle stability, and rate performance. Therefore, the negative electrode can provide the battery with high reversible capacity, reduce charge loss during charging and discharging, and improve the overall electrochemical performance of the battery. At the same time, the grafting groups in the negative electrode material can optimize interface performance, reduce interface impedance, and further improve the conductivity and ion transport performance of the negative electrode.

[0077] Furthermore, the negative electrode current collector includes copper foil with a thickness of 6-20 μm.

[0078] The negative electrode active material layer also includes a binder and a conductive agent. The binder includes, but is not limited to, PVDF or CMC / SBR. The mass content of the binder in the negative electrode active material layer is 2wt%-12wt%.

[0079] The conductive agent includes, but is not limited to, at least one of conductive carbon black, acetylene black, Super P, carbon nanotubes, and graphene conductive paste. The mass content of the conductive agent in the negative electrode active material layer is 1wt%-10wt%.

[0080] One embodiment of this application provides an electrical device including the battery described above. By using the battery described above, which has a high initial coulombic efficiency and energy density, the range of the electrical device is improved. Exemplary examples include, but are not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, aircraft, and robots.

[0081] The present application will be further illustrated by the following examples.

[0082] Example 1 This embodiment is used to illustrate the negative electrode material, its preparation method, negative electrode sheet, and battery disclosed in this application.

[0083] 1. Preparation of negative electrode materials Preparation of S10 hard carbon dispersion Weigh 20.0 g of hard carbon particles and add 400 mL of ethanol / water mixed solvent (ethanol / water volume ratio 30:70) to make the liquid-solid ratio 20 L / kg. Stir at 500 rpm for 30 min at 15 °C; then disperse by ultrasonication at 200 W for 10 min to obtain a hard carbon dispersion.

[0084] Preparation of S20 diazotization solution Weigh 6.0 mmol of p-aminobenzenesulfonic acid and add it to 120 mL of deionized water. Dissolve the solution by stirring at 0–5 °C. Adjust the pH of the system to 1.5 using hydrochloric acid solution (1.0 mol / L). Separately prepare 6.6 mL of sodium nitrite solution (1.0 mol / L) (sodium nitrite to aromatic amine precursor A molar ratio of 1.1:1). Add the sodium nitrite solution dropwise to the acidic p-aminobenzenesulfonic acid solution at 0–5 °C over a period of 20 min. After the addition is complete, continue stirring for another 20 min to obtain the diazotized solution.

[0085] S30, covalent grafting reaction The diazotization solution in S20 was added to the hard carbon dispersion over 60 minutes at 0-10°C, maintaining the pH of the system at 1.5–3.0 during the addition. After the addition was complete, the reaction was continued for 3.0 hours at 10°C with stirring at 700 rpm to obtain the grafted product slurry.

[0086] S40, Solid-Liquid Separation and Washing The grafted product slurry was filtered, and the filter cake was collected. It was washed five times with deionized water, using 500 mL of water each time (liquid-to-solid ratio approximately 25 L / kg each time); then washed twice with 200 mL of ethanol each time. The resulting washed filter cake was obtained.

[0087] S50, sodium treatment / neutralization and drying The washed filter cake was redispersed in 300 mL of deionized water and stirred at 40 °C. Sodium carbonate solution (0.20 mol / L) was added to adjust the pH to 9.0, and the reaction was maintained at 40 °C for 2.0 h. After the reaction was complete, the mixture was filtered, and the filter cake was washed five times with 400 mL of deionized water each time. The washed filter cake was dried in a vacuum drying oven at 110 °C and 200 Pa for 12 h to obtain the grafted hard carbon anode material, denoted as material A.

[0088] S60, secondary dispersion Weigh 20.0 g of material A and add 400 mL of ethanol / water mixed solvent (ethanol / water volume ratio 30:70) to make the liquid-solid ratio 20 L / kg. Stir at 500 rpm for 30 min at 15 °C; then disperse by ultrasonication at 200 W for 10 min to obtain a secondary dispersion.

[0089] S70, Preparation of Secondary Diazotization Solution Weigh out compound NH2-Ar-N of formula 2. + (CH3)2-CH2-CH2-SO3 - 2.0 mmol. Compound of Formula 2 was added to 80 mL of deionized water and dissolved by stirring at 0–5 °C. The pH of the system was adjusted to 1.5 using hydrochloric acid solution (1.0 mol / L). Separately, 2.2 mL of sodium nitrite solution (1.0 mol / L) was prepared (molar ratio of sodium nitrite to compound of Formula 2 1.1:1). The sodium nitrite solution was added dropwise to the acidic solution of compound of Formula 2 at 0–5 °C over a period of 15 min. After the addition was complete, the reaction was stirred for another 20 min to obtain a secondary diazotized solution.

[0090] S80, secondary covalent grafting reaction The secondary diazotization solution in S70 was added to the secondary dispersion over 60 minutes at 0-10°C, maintaining the pH of the system at 1.5-3.0 during the addition. After the addition was complete, the reaction was continued for 3.0 hours at 700 rpm under 10°C to obtain the secondary covalent grafting product slurry.

[0091] S90, solid-liquid separation, washing and drying The slurry of the product from the secondary covalent grafting reaction was filtered, and the filter cake was washed five times with deionized water (500 mL each time), and then washed twice with ethanol (200 mL each time). The washed filter cake was dried in a vacuum drying oven at 110 °C and 200 Pa for 12 h to obtain the grafted hard carbon anode material.

[0092] 2. Preparation of negative electrode sheet S10. The negative electrode material, conductive agent Super P (conductive carbon black), and binder PVDF are uniformly mixed at a mass ratio of 90:5:5, using NMP as the solvent. After stirring evenly to obtain a slurry, it is coated onto a copper foil current collector with a wet film thickness of 150 μm. It is pre-dried at 60℃ for 30 min, and then placed in a vacuum drying oven at 120℃ and 100 Pa for 12 h to obtain a dried electrode sheet. The dried electrode sheet is rolled at 50℃ with a linear pressure of 150 N / mm; it is then punched into sheets to obtain electrode sheet A.

[0093] S20. Prepare the pretreatment electrolyte: the sodium salt is NaPF6, with a concentration of 1.0 mol / L; the solvent system is EC / DEC (volume ratio 1:1).

[0094] S30. Place electrode A in a sealed container and add 5 mL of pretreatment electrolyte to the bottom of the container, so that electrode A and the pretreatment electrolyte are in a vapor contact environment. Place the sealed container in an environment of 40°C for 12 hours to complete the pretreatment.

[0095] S40. Take out electrode A and dry it in a vacuum drying oven at 50°C and 500Pa for 2 hours to obtain the pretreated negative electrode.

[0096] 3. Preparation of positive electrode sheet The positive electrode active material Na3V3(PO4)3 (NVP), conductive agent Super-P, and binder PVDF are mixed in a mass ratio of 94:3:3. The mixture is thoroughly stirred in NMP solvent to form a uniform positive electrode slurry. This slurry is coated onto at least one side of the positive electrode current collector aluminum foil, and after drying, rolling, and die-cutting, a satisfactory positive electrode sheet is obtained.

[0097] 4. Preparation of electrolyte Sodium salt NaPF6 was dissolved in organic solvent EC / DEC (volume ratio 1:1) to obtain an electrolyte at a concentration of 1M.

[0098] 5. Battery manufacturing The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. Then, one end of each of the positive electrode, separator, and negative electrode is wound around the separator to form a core. The wound core is then placed in a pre-formed aluminum-plastic film bag. The electrolyte prepared above is injected into the baked and dried cell. After vacuum sealing, settling, and formation processes, a 1Ah battery is obtained.

[0099] Example 2 Example 2 illustrates the negative electrode material and its preparation method, negative electrode sheet, and battery disclosed in this application, including most of the operation steps in Example 1 above, except that: the preparation of the negative electrode material; Preparation of S10 hard carbon dispersion Weigh 20.0 g of hard carbon particles and add 400 mL of ethanol / water mixed solvent (ethanol / water volume ratio 30:70) to make the liquid-solid ratio 20 L / kg. Stir at 500 rpm for 30 min at 15 °C; then disperse by ultrasonication at 200 W for 10 min to obtain a hard carbon dispersion.

[0100] Preparation of S20 diazotization solution Weigh out compound NH2-Ar-N of formula 2. + (CH3)2-CH2-CH2-SO3 - 2.0 mmol. Compound of Formula 2 was added to 80 mL of deionized water and dissolved by stirring at 0–5 °C. The pH of the system was adjusted to 1.5 using hydrochloric acid solution (1.0 mol / L). Separately, 2.2 mL of sodium nitrite solution (1.0 mol / L) was prepared (molar ratio of sodium nitrite to compound of Formula 2 1.1:1). The sodium nitrite solution was added dropwise to the acidic solution of compound of Formula 2 at 0–5 °C over a period of 15 min. After the addition was complete, the reaction was stirred for another 20 min to obtain the diazotized solution.

[0101] S30, covalent grafting reaction The diazotization solution in S20 was added to the dispersion over 60 minutes at 0-10°C, maintaining the pH of the system at 1.5-3.0 during the addition. After the addition was complete, the reaction was continued for 3.0 hours at 700 rpm with stirring at 10°C to obtain a slurry of the covalent grafting product.

[0102] S40, Solid-liquid separation, washing and drying The covalent grafting reaction product slurry was filtered, and the filter cake was washed five times with deionized water (500 mL each time), and then washed twice with ethanol (200 mL each time). The washed filter cake was dried in a vacuum drying oven at 110 °C and 200 Pa for 12 h to obtain the grafted hard carbon anode material.

[0103] Example 3 Example 3 illustrates the negative electrode material and its preparation method, negative electrode sheet, and battery disclosed in this application. It includes most of the operational steps in Example 1 above, except that: Compound NH2-Ar-N of Formula 2... + (CH3)2-CH2-CH2-SO3 - The amount added was 0.2 mmol.

[0104] Example 4 Example 4 illustrates the negative electrode material and its preparation method, negative electrode sheet, and battery disclosed in this application. It includes most of the operational steps in Example 1 above, except that: Compound NH2-Ar-N of Formula 2+ (CH3)2-CH2-CH2-SO3 - The amount added was 12 mmol.

[0105] Example 5 Example 5 is used to illustrate the negative electrode material and its preparation method, negative electrode sheet and battery disclosed in this application. It includes most of the operation steps in Example 1 above, except that: the amount of p-aminobenzenesulfonic acid added in S20 is 1 mmol, that is, the content of the second grafting group in each gram of hard carbon particles is 0.05 mmol.

[0106] Example 6 Example 6 is used to illustrate the negative electrode material and its preparation method, negative electrode sheet and battery disclosed in this application. It includes most of the operation steps in Example 1 above, except that: the amount of p-aminobenzenesulfonic acid added in S20 is 4 mmol, that is, the content of the second grafting group in each gram of hard carbon particles is 0.2 mmol.

[0107] Example 7 Example 7 is used to illustrate the negative electrode material and its preparation method, negative electrode sheet and battery disclosed in this application. It includes most of the operation steps in Example 1 above, except that: the amount of p-aminobenzenesulfonic acid added in S20 is 8 mmol, that is, the content of the second grafting group in each gram of hard carbon particles is 0.4 mmol.

[0108] Example 8 Example 8 illustrates the negative electrode material and its preparation method, negative electrode sheet, and battery disclosed in this application. It includes most of the operational steps in Example 1 above, except that: the amount of p-aminobenzenesulfonic acid added in S20 is 4 mmol, and the compound of formula 2, NH2-Ar-N, is added in S7. + (CH3)2-CH2-CH2-SO3 - The amount added was 0.2 mmol.

[0109] Example 9 Example 9 illustrates the negative electrode material and its preparation method, negative electrode sheet, and battery disclosed in this application. It includes most of the operational steps in Example 1 above, except that: the amount of p-aminobenzenesulfonic acid added in S20 is 1 mmol, and the compound of formula 2, NH2-Ar-N, is added in S7. + (CH3)2-CH2-CH2-SO3 - The amount added was 20 mmol.

[0110] Example 10 Example 10 illustrates the negative electrode material and its preparation method, negative electrode sheet, and battery disclosed in this application. It includes most of the operational steps in Example 1 above, except that: the amount of p-aminobenzenesulfonic acid added in S20 is 0.5 mmol, and in S70, compound NH2-Ar-N of formula 2... + (CH3)2-CH2-CH2-SO3 - The amount added was 15 mmol.

[0111] Example 11 Example 11 illustrates the negative electrode material and its preparation method, negative electrode sheet, and battery disclosed in this application, including most of the operational steps in Example 1 above, except that: in S70, compound of formula 2 is NH2-C6H4-N + (CH3)2-CH2CH2CH2-SO3 - Ar is phenyl, R1 and R2 are both methyl, n=3; the graft compound in S20 is p-aminobenzenesulfonic acid.

[0112] Example 12 Example 12 is used to illustrate the negative electrode material and its preparation method, negative electrode sheet, and battery disclosed in this application. It includes most of the operation steps in Example 1 above, except that: in S70, compound of formula 2 is 4-amino-3-methyl-N-ethyl-N-methyl-N-(2-sulfoethyl)phenylammonium inner salt, that is, Ar is 3-methyl-substituted phenyl, R1 is methyl, R2 is ethyl, and n=2; the diazotizing raw material in S20 is amino-substituted sodium p-toluenesulfonate, which forms a second graft group of sodium p-toluenesulfonate type after diazotization and grafting.

[0113] Example 13 Example 13 illustrates the negative electrode material and its preparation method, negative electrode sheet, and battery disclosed in this application. It includes most of the operation steps in Example 1 above, except that S20-S40 are not included in the preparation process of the negative electrode sheet.

[0114] Comparative Example 1 Comparative Example 1 is used to illustrate the negative electrode material and its preparation method, negative electrode sheet and battery disclosed in this application. It includes most of the operation steps in Example 1, except that S60-S90 are not included in the preparation process of the negative electrode material.

[0115] Comparative Example 2 Comparative Example 2 is used to illustrate the negative electrode material and its preparation method, negative electrode sheet and battery disclosed in this application. It includes most of the operation steps in Example 1, except that the negative electrode material is hard carbon particles without the first grafting group and the second grafting group.

[0116] Performance testing I. The following performance tests were performed on the negative electrode materials and batteries prepared in the above embodiments and comparative examples: 1. Testing of element content and grafting amount in anode materials The negative electrode material was dried in a vacuum drying oven at 110℃ and 200Pa for 12 hours, and then transferred to a sealed container for storage. The following tests were performed: (1) Elemental analysis (CHNS), the test items are S and N content (wt%).

[0117] Sample weight: 1-5 mg; Number of replicates: n=2-5.

[0118] (2) Inductively coupled plasma optical emission spectroscopy (ICP-OES) is used for the determination of Na content.

[0119] Digestion system: nitric acid / hydrogen peroxide (volume ratio 1:0-10:1); digestion temperature: 120℃; digestion time: 4h.

[0120] (3) X-ray photoelectron spectroscopy (XPS) is used to confirm the existence of functional groups.

[0121] Vacuum degree: ≤10 -7 mbar; energy step: 0.05–1.0 eV; data processing: C 1s correction, fitting S 2p and N1s peaks.

[0122] The "grafting amount" is expressed as functional group equivalent (mmol / g, dry basis) and can be calculated based on elemental content.

[0123] 2. First-cycle discharge capacity: At 25°C, charge and discharge cycles are performed using a constant current and constant voltage charge and discharge instrument (such as a Battery Testing System) at a set current density, including the following test steps: a. Charge to the set cutoff voltage of 4.3V at the set current density (0.1C).

[0124] b. Discharge at the same current density (0.1C) until the set discharge cutoff voltage of 2.8V is reached.

[0125] c. Record the specific capacity of the first discharge, in mAh / g.

[0126] 3. First charge capacity: The battery was tested for the first time at 25℃ using a constant current and constant voltage charge / discharge tester. The battery was charged at a constant current rate of 0.1C to 4.3V, and then charged at a constant voltage rate to the cutoff current of 0.05C. The first charge capacity of the battery during this process was recorded in mAh / g.

[0127] 4. First-cycle coulombic efficiency: At 25℃, using a constant current constant voltage charge-discharge instrument, the amount of electricity passing through the battery during the first charge-discharge process is measured, including the following test steps: a. Charge to the set voltage and record the total charge (Q_charge).

[0128] b. Discharge to the set cutoff voltage and record the total amount of charge discharged (Q_discharge).

[0129] c. Calculate the Coulomb efficiency for the first cycle: Coulomb efficiency = (Q_discharge / Q_charge) × 100%.

[0130] 5. Coulombic efficiency after 300 cycles: At 25°C, the battery was subjected to cyclic charge-discharge tests at a 0.5C rate within a voltage range of 2.8-4.3 V. The charge capacity and discharge capacity after 300 cycles were recorded, and the coulombic efficiency after 300 cycles was calculated using the following formula: Coulomb efficiency on the 300th cycle = (Discharge capacity on the 300th cycle / Charge capacity on the 300th cycle) × 100%.

[0131] 6. Capacity retention test: At 25℃, under the same current density and voltage window, the negative electrode material is subjected to 300 charge-discharge cycles, including the following test steps: a. Perform 300 charge-discharge cycles on the battery and record the discharge capacity periodically for each cycle; b. Calculate the capacity retention rate after 300 cycles: Capacity retention rate = (300th week discharge capacity / first discharge capacity) × 100%.

[0132] 7. Battery Impedance Test: At 25℃, the battery was adjusted to 50% SOC and allowed to stand for 2 hours before AC impedance testing was performed using an electrochemical workstation. The test frequency range was 100 kHz to 0.01 Hz, and the AC disturbance voltage was 5 mV. The solution resistance Rs, interfacial film impedance Rsei, and charge transfer impedance Rct were obtained by fitting the Nyquist plot and equivalent circuit.

[0133] Among them, Rs is used to characterize the ohmic internal resistance of the electrolyte and the battery, Rsei is used to characterize the interface film impedance of the negative electrode surface, and Rct is used to characterize the charge transfer impedance of the electrode / electrolyte interface.

[0134] The test results are shown in Tables 1-3.

[0135] Table 1 Table 2 Table 3 The test results of the examples and comparative examples in Tables 1-3 are compared and explained below.

[0136] As shown in Table 1, compared to the ungrafted Comparative Example 2, significant sulfur (S) content was detected in the negative electrode materials of Examples 1-13 and Comparative Example 1, indicating that the sulfonic acid-containing grafting groups were successfully introduced onto the surface of the hard carbon particles. In Examples 1-13, nitrogen (N) was further detected, proving that the first grafting group containing the quaternary ammonium structure was successfully grafted onto the surface of the hard carbon particles. The low S, N, and Na content in Comparative Example 2 indicates that the corresponding grafting groups are essentially absent from the surface of the unmodified hard carbon particles. The grafting amounts in Examples 4, 9, and 10 show that the grafting amount per gram of hard carbon particle surface is limited.

[0137] As shown in Table 2, compared to the negative electrode material in Comparative Example 2 without the first and second grafting groups, the batteries prepared in Examples 1-13 all exhibit higher first-cycle coulombic efficiency and 300-cycle capacity retention. This indicates that introducing the first and second grafting groups onto the surface of hard carbon particles can effectively improve the interfacial compatibility between the hard carbon negative electrode and the electrolyte, reduce irreversible capacity loss during the first charge-discharge process, and improve cycle stability. In Example 1, the content and ratio of the first and second grafting groups are more suitable, and the negative electrode sheet is pretreated with the electrolyte; therefore, its first-cycle coulombic efficiency, 300-cycle capacity retention, and 300-cycle coulombic efficiency are all superior to those of other examples.

[0138] As can be seen from the comparison between Example 1 and Example 2 and Comparative Example 1, grafting only the first grafting group or grafting only the second grafting group can improve the performance of hard carbon anode. However, when the first grafting group and the second grafting group coexist, they can produce a synergistic effect in terms of interface regulation, ion transport and side reaction suppression.

[0139] A comparison of Example 1 and Example 13 shows that Example 13, which did not undergo electrolyte pretreatment, had slightly lower first-cycle coulombic efficiency, capacity retention rate, and impedance performance than Example 1. This indicates that electrolyte pretreatment is beneficial for improving the wettability between the negative electrode and the electrolyte and helps to form a more stable interface film.

[0140] A comparison of Examples 1 with Examples 3, 7, 9, and 10 shows that battery performance decreases when the content of the first or second grafting group is too low or too high, or when their molar ratio deviates from the preferred range. When the grafting amount is too low, it is difficult to fully cover the defect sites and active functional groups on the surface of the hard carbon particles; when the grafting amount is too high, excessive organic grafting groups may form a thicker interface layer on the surface of the hard carbon particles, increasing sodium ion transport resistance, thereby leading to a decrease in capacity utilization, coulombic efficiency, and cycle stability.

[0141] As shown in Table 3, the Rsei and Rct values ​​of Example 1 are lower than those of Comparative Examples 1 and 2, further demonstrating that the synergistic modification by the first and second grafting groups can reduce the interfacial film impedance and charge transfer impedance of the negative electrode, and improve the transport kinetics of sodium ions on the hard carbon negative electrode surface. Comparative Example 2 has the highest Rsei and Rct values, indicating more side reactions on the surface of the unmodified hard carbon particles, resulting in poor interfacial film stability and a significant increase in interfacial impedance and charge transfer impedance.

[0142] The terms “first,” “second,” etc., in this application (if applicable) are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0143] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A negative electrode material, characterized in that, The negative electrode material comprises hard carbon particles and a first grafting group, wherein the first grafting group is covalently grafted onto the surface of the hard carbon particles, and the structure of the first grafting group is shown in Formula 1. Formula 1, wherein Ar is a phenyl or substituted phenyl, R1 and R2 are each independently selected from C1-C4 alkyl groups, n=2-6, and * indicates the bonding site.

2. The negative electrode material according to claim 1, characterized in that, The content of the first grafted group in each gram of the hard carbon particles is 0.01-0.6 mmol.

3. The negative electrode material according to claim 1 or 2, characterized in that, The negative electrode material further includes a second grafting group, which includes substituted or unsubstituted sodium arylsulfonate, wherein the aryl group in the second grafting group is covalently grafted onto the surface of the hard carbon particles.

4. The negative electrode material according to claim 3, characterized in that, The content of the second grafting group in each gram of hard carbon particles is 0.05-0.3 mmol.

5. The negative electrode material according to claim 4, characterized in that, The molar ratio of the first grafting group to the second grafting group is 1:20-20:

1.

6. The negative electrode material according to claim 1, characterized in that, The mass content of sulfur in the negative electrode material is 0.1%-1.2%.

7. The method for preparing the negative electrode material according to any one of claims 1-6, characterized in that, Includes the following steps: Hard carbon particles are added to a solvent and dispersed to obtain the first dispersion; The compound shown in Formula 2 was subjected to a diazotization reaction to obtain a first diazotized solution; the structure of the compound shown in Formula 2 is shown below: Formula 2, wherein Ar is a phenyl or substituted phenyl, R1 and R2 are each independently selected from C1-C4 alkyl groups, and n=2-6; The first diazotization solution is added to the first dispersion to carry out the first grafting reaction, thereby obtaining a negative electrode material grafted with the first grafting group.

8. The preparation method according to claim 7, characterized in that, Following the first grafting reaction, the following steps are included: Hard carbon particles grafted with the first grafting group are added to a solvent and dispersed to obtain a second dispersion. A second diazotization solution is obtained by diazotizing aminobenzenesulfonic acid or aminobenzenesulfonate. The second diazotization solution is added to the second dispersion to carry out the second grafting reaction, thereby obtaining a negative electrode material containing the first grafting group and the second grafting group.

9. The preparation method according to claim 7 or 8, characterized in that, It also includes the following steps: The negative electrode material that has undergone the first or second grafting reaction is sequentially pretreated and dried with the electrolyte. The pretreatment includes steam contact or immersion of the negative electrode material with the electrolyte.

10. The preparation method according to claim 8, characterized in that, It also includes the following steps: The negative electrode material that has undergone the second grafting reaction is added to a sodium-modification solution for sodium modification, wherein the sodium-modification solution includes at least one of sodium carbonate solution and sodium hydroxide solution.

11. A negative electrode sheet, characterized in that, It includes a negative electrode current collector and a negative electrode active material layer, wherein the negative electrode active material layer includes the negative electrode material as described in any one of claims 1-6, or includes the negative electrode material prepared by the preparation method described in any one of claims 7-10.

12. A battery, characterized in that, Includes the negative electrode as described in claim 11.

13. An electrical appliance, characterized in that, Includes the battery as described in claim 12.

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