Hard carbon negative electrode slurry, sodium-ion battery cell and preparation method thereof

Abstract

The application belongs to the technical field of secondary batteries. More particularly, it relates to a hard carbon negative electrode slurry, a sodium ion battery cell and a preparation method thereof. The negative electrode slurry comprises the following raw materials in parts by weight: 90-95 parts of hard carbon, 5-7 parts of a composite conductive agent, 6-8 parts of a binder and water; the solid content of the hard carbon negative electrode slurry is 45-48%; wherein the composite conductive agent comprises a spherical graphene oxide core and an amorphous carbon coating layer coated on the surface of the spherical graphene oxide core; the sphericity of the spherical graphene oxide core is 0.8-0.9; the binder comprises sodium polyacrylate and butadiene styrene rubber. The composite conductive agent further comprises a silicon-containing transition layer between the spherical graphene oxide core and the amorphous carbon coating layer, and the silicon-containing transition layer is obtained by carbonization of a silane coupling agent under an oxygen-free condition.

Description

Technical Field

[0001] This invention belongs to the field of secondary battery technology. More specifically, it relates to a hard carbon negative electrode slurry, a sodium-ion battery cell, and a method for preparing the same. Background Technology

[0002] In the industrial production of sodium-ion batteries, the preparation of the negative electrode slurry is the first critical step in cell manufacturing. The negative electrode slurry is typically prepared using hard carbon as the active material, conductive agent, binder, and solvent (usually water or an organic solvent) through a specific stirring process. The quality of the slurry, especially its stability, directly determines the uniformity of subsequent coating processes, the consistency of electrode quality, and ultimately affects the electrochemical performance and production yield of the battery cell.

[0003] However, those skilled in the art have found in practice that anode slurries using hard carbon as the active material generally suffer from poor storage stability. Specifically, this manifests in the following aspects: Density and sedimentation issues of hard carbon materials: Hard carbon materials have a low density, and their porous structure makes them prone to floating or agglomerating in slurry. During slurry settling or storage, due to density differences, hard carbon particles easily separate from conductive agents and binders, leading to sedimentation or stratification of the slurry. This necessitates frequent and lengthy re-stirring of the slurry before coating, increasing energy consumption and production time. More seriously, it makes it difficult to ensure the uniformity of the slurry state after each stirring, resulting in fluctuations in electrode areal density between and within batches, affecting the consistency of cell performance.

[0004] Slurry viscosity instability: The complex surface functional groups and physical structure of hard carbon materials result in poor compatibility with water-based or oil-based solvents, easily leading to problems such as binder migration and changes in solvation degree during slurry storage. This, in turn, causes significant changes in slurry viscosity over time (usually an increase in viscosity, or even gelation). This viscosity instability poses a significant challenge to the coating process, making it impossible to guarantee a uniform coating under fixed coating parameters (such as coating speed and gap), and easily resulting in defects such as streaks, lumps, or exposed foil. Summary of the Invention

[0005] The technical problem this invention aims to solve is the storage stability issue commonly found in existing hard carbon anode slurries used in sodium-ion batteries. Based on this challenge, this invention provides a hard carbon anode slurry, a sodium-ion battery cell, and a method for preparing the same.

[0006] The purpose of this invention is to provide a hard carbon anode slurry.

[0007] Another object of the present invention is to provide a method for preparing hard carbon anode slurry.

[0008] Another object of the present invention is to provide a sodium-ion battery cell.

[0009] The above-mentioned objective of this invention is achieved through the following technical solution: A hard carbon anode slurry comprises the following raw materials in parts by weight: 90-95 parts hard carbon, 5-7 parts composite conductive agent, 6-8 parts binder and water; The solid content of the hard carbon anode slurry is 45-48%; The composite conductive agent includes a spherical graphene oxide core and an amorphous carbon coating layer covering the surface of the spherical graphene oxide core. The sphericity of the spherical graphene oxide core is 0.8-0.9; The adhesive includes sodium polyacrylate and styrene-butadiene rubber.

[0010] The technical effects of the above technical solution are as follows: Carbon black conductive agents commonly used in existing technologies have extremely high specific surface areas and abundant surface defects, exhibiting strong "predatory" adsorption of water-based binder molecules (such as sodium polyacrylate). This disordered competition leads to incomplete surface coating of hard carbon particles, making them prone to agglomeration; at the same time, the concentration of free binder in the slurry changes dynamically, causing the slurry viscosity to become unstable over time, easily resulting in sedimentation and stratification.

[0011] The technical solution of this invention employs a composite conductive agent design of "spherical graphene oxide core - amorphous carbon shell". First, the spherical graphene oxide core (sphericity 0.8-0.9) provides a relatively smooth and regular physical surface, significantly reducing physical entanglement and adsorption sites for long-chain polymer binders. Second, and most importantly, the outer amorphous carbon coating layer acts as a "shield" and "passivator": it effectively covers a large number of active functional groups such as carboxyl groups (-COOH) and hydroxyl groups (-OH) on the graphene oxide surface, transforming these highly reactive sites into a more chemically inert and uniform carbon layer surface.

[0012] Through this dual surface engineering, the composite conductive agent of this invention transforms from a "binder-hungry" strong adsorbent into a "binder-friendly" weak adsorbent. This allows the binder molecules (sodium polyacrylate and styrene-butadiene rubber) in the slurry to be adsorbed more preferentially, more fully, and more stably onto the surface of hard carbon particles, achieving a harmonious and stable coexistence where each component of the slurry fulfills its specific function. The result is that after static storage, the slurry exhibits no visible stratification, extremely low viscosity change rate, and excellent long-term stability.

[0013] The spherical core and coating of the composite conductive agent, in synergy with the binder system, help to form a weak but stable three-dimensional network structure when the slurry is left to stand. This structure endows the slurry with good thixotropic properties, that is, it exhibits a high-viscosity gel state when left to stand to resist sedimentation, while rapidly recovering to a low-viscosity flow state when subjected to shear force (stirring).

[0014] Therefore, even after prolonged settling, the slurry of this invention does not require high-intensity, long-term re-stirring; it can be completely restored to its initial homogeneous state in a short time with only low-speed stirring, without the formation of irreversible hard sediment. This greatly simplifies production operations and ensures the consistency and yield of electrode manufacturing.

[0015] The spherical graphene oxide units of this invention possess both good dispersibility and rolling properties, avoiding the stacking problems of sheet materials. The outer amorphous carbon coating layer acts as an excellent "welding layer," enabling multiple composite conductive agent particles to form a tighter and more stable conductive connection when they come into contact, significantly reducing the contact resistance between particles.

[0016] Furthermore, the D50 of the spherical graphene oxide core is 3-5 μm; and the thickness of the amorphous carbon coating layer is 20-40 nm.

[0017] Furthermore, the composite conductive agent also includes a silicon-containing transition layer located between the spherical graphene oxide core and the amorphous carbon coating layer, wherein the silicon-containing transition layer is obtained by carbonization of a silane coupling agent under oxygen-free conditions.

[0018] The beneficial effects of the above technical solution are as follows: The interaction between the amorphous carbon layer and the graphene oxide (GO) core is primarily physical adsorption and relatively weak van der Waals forces. During long-term cyclic shearing of the slurry or electrode rolling, there is a risk of the coating layer peeling off. Once peeled off, it degenerates into a simple physical mixture, losing the original design intent of the core-shell structure.

[0019] One end of the silane coupling agent reacts with the functional groups on the surface of graphene oxide to form strong covalent bonds; the other end is embedded or tightly bonded to the subsequently deposited amorphous carbon layer, further enhancing the integrity and durability of the core-shell structure. This allows the composite conductive agent to maintain structural stability during slurry processing and electrode manufacturing, ensuring its long-term functionality. Furthermore, this transition layer provides a second line of defense, more thoroughly "passivating" the surface of graphene oxide and minimizing unnecessary interactions with the binder. This maximizes the binder-friendliness of the composite conductive agent, further consolidating the stability of the slurry.

[0020] Furthermore, the D50 of the hard carbon is 13-17 μm.

[0021] Furthermore, the adhesive is a compound of sodium polyacrylate and styrene-butadiene rubber in a mass ratio of 1-1.5:4.

[0022] A method for preparing a hard carbon anode slurry, the specific preparation steps of which include: Preparation of composite conductive agents: After coating the precursor onto the surface of spherical graphene oxide, carbonization is carried out under an inert atmosphere to form an amorphous carbon coating layer on the surface of spherical graphene oxide. Raw material preparation: Weigh each component according to the raw material composition; Slurry preparation: First, mix sodium polyacrylate and water to disperse them evenly to obtain a glue solution; Add a composite conductive agent to the adhesive solution, disperse it evenly, then add hard carbon, stir and disperse it evenly, then slowly add styrene-butadiene rubber latex, stir at low speed to degas, and discharge the material to obtain hard carbon negative electrode slurry.

[0023] Furthermore, the slurry preparation also includes: Divide the hard carbon into two equal parts; Add a composite conductive agent to the adhesive solution and disperse it evenly. First, add one part of hard carbon and disperse it at high speed for 30-45 minutes at a stirring speed of 1000-1200 r / min. Then, add another part of hard carbon and disperse it at low speed for 30-45 minutes at a stirring speed of 400-500 r / min. Then, slowly add styrene-butadiene rubber latex, stir at low speed to degas, and discharge the material to obtain the hard carbon negative electrode slurry.

[0024] Furthermore, the slurry preparation also includes: Divide the hard carbon into two equal parts; Add a composite conductive agent to the adhesive solution and disperse it evenly. First, add one part of hard carbon and disperse it at high speed (1000-1200 r / min) for 30-45 min. Then, add another part of hard carbon and disperse it at low speed (400-500 r / min) for 30-45 min. Next, add styrene-butadiene rubber latex at a rate of 10-15 g / min. After the addition is complete, stir at low speed (200-250 r / min) for 30-40 min to degas the material. The resulting material is hard carbon negative electrode slurry.

[0025] Furthermore, the preparation of the composite conductive agent also includes: Prepare graphene oxide and a sucrose solution with a mass fraction of 8-10% at a mass ratio of 1:0.55-0.65. First, graphene oxide and silane coupling agent KH-560 are mixed and poured into an ethanol solution with a mass fraction of 60-80%. The pH is adjusted to 7.6-8.0, and the reaction is carried out by sonication for 3-5 hours. Then, the mixture is filtered, washed, and dried to obtain pretreated graphene oxide. The amount of silane coupling agent KH-560 used is 10-12% of the mass of graphene oxide; After the pretreated graphene oxide and sucrose solution are evenly dispersed, they are dried and evaporated to remove moisture, so that sucrose is deposited on the surface of the pretreated graphene oxide. Then, the mixture is first pyrolyzed at a low temperature of 180-200℃ for 60-80 minutes, and then the temperature is further increased to 600-700℃ for high-temperature carbonization for 2-3 hours. After cooling, the material is discharged to obtain the composite conductive agent.

[0026] A sodium-ion battery cell is obtained by coating the aforementioned hard carbon negative electrode paste. Detailed Implementation

[0027] The present invention will be further illustrated below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in this technical field.

[0028] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0029] Example 1 Preparation of composite conductive agents: Graphene oxide and 8% sucrose solution were prepared at a mass ratio of 1:0.55. The graphene oxide is selected as spherical graphene oxide with a sphericity of 0.8; and the D50 of the spherical graphene oxide is 3 μm. First, graphene oxide and silane coupling agent KH-560 were mixed and poured into a 60% ethanol solution. The pH was adjusted to 7.6. After ultrasonic reaction at an ultrasonic frequency of 80 kHz and a temperature of 45 ℃ for 3 hours, the mixture was filtered, washed and dried to obtain pretreated graphene oxide. The amount of silane coupling agent KH-560 used is 10% of the mass of graphene oxide; the amount of ethanol solution used is 20 times the mass of graphene oxide. After mixing the pretreated graphene oxide and sucrose solution, the mixture was stirred and dispersed at 800 r / min for 20 min. Then, it was dried and evaporated in an oven at 90℃ to remove moisture, so that the sucrose was deposited on the surface of the pretreated graphene oxide. Then, under argon protection, it was first pyrolyzed at 180℃ for 60 min, and then the temperature was increased to 600℃ for high-temperature carbonization for 2 h. After cooling, the material was discharged to obtain the composite conductive agent. By controlling the above preparation process, an amorphous carbon coating layer with a thickness of 22 nm is formed on the surface of spherical graphene oxide. The thickness of the coating layer includes a silicon-containing transition layer located between the spherical graphene oxide and the amorphous carbon. Raw material preparation: By weight, take 90 parts hard carbon, 5 parts composite conductive agent, and 6 parts binder; The adhesive is a mixture of sodium polyacrylate and styrene-butadiene rubber in a mass ratio of 1:4. Specifically, the styrene-butadiene rubber uses a styrene-butadiene rubber latex with a solid content of 45%; the above mass ratio is calculated from the content of the effective components in sodium polyacrylate and the styrene-butadiene rubber latex. The hard carbon has a D50 of 13 μm; Slurry preparation: First, mix sodium polyacrylate and water to disperse them evenly to obtain a glue solution; Divide the hard carbon into two equal parts; Add a composite conductive agent to the adhesive solution and disperse it evenly. First, add one part of hard carbon and stir at high speed for 30 minutes at a stirring speed of 1000 r / min. Then, add another part of hard carbon and stir at low speed for 30 minutes at a stirring speed of 400 r / min. Then, add styrene-butadiene rubber latex at a rate of 10 g / min. After the addition is complete, stir at low speed for 30 minutes at a stirring speed of 200 r / min to degas the material. The hard carbon negative electrode slurry is then discharged. By adjusting the amount of water used, the solid content in the resulting hard carbon anode slurry is made to be 45%.

[0030] Example 2 Preparation of composite conductive agents: Graphene oxide and a 9% sucrose solution were prepared at a mass ratio of 1:0.6. The graphene oxide is selected from spherical graphene oxide with a sphericity of 0.85; and the D50 of the spherical graphene oxide is 4 μm. First, graphene oxide and silane coupling agent KH-560 were mixed and poured into a 70% ethanol solution. The pH was adjusted to 7.8. After ultrasonic reaction at a frequency of 90 kHz and a temperature of 50 ℃ for 4 hours, the mixture was filtered, washed and dried to obtain pretreated graphene oxide. The amount of silane coupling agent KH-560 used is 11% of the mass of graphene oxide; the amount of ethanol solution used is 22 times the mass of graphene oxide. After mixing pretreated graphene oxide and sucrose solution, the mixture was stirred and dispersed at 860 r / min for 26 min. Then, it was dried and evaporated in an oven at 90℃ to remove moisture, allowing sucrose to coat and deposit on the surface of the pretreated graphene oxide. Subsequently, under argon protection, the mixture was first pyrolyzed at 190℃ for 70 min, and then heated to 650℃ for high-temperature carbonization for 2.3 h. After cooling, the mixture was discharged to obtain the composite conductive agent. By controlling the above preparation process, an amorphous carbon coating layer with a thickness of 29 nm is formed on the surface of spherical graphene oxide. The thickness of the coating layer includes a silicon-containing transition layer located between the spherical graphene oxide and the amorphous carbon. Raw material preparation: By weight, take 92 parts hard carbon, 6 parts composite conductive agent, and 7 parts binder; The adhesive is a compound of sodium polyacrylate and styrene-butadiene rubber in a mass ratio of 1.3:4. Specifically, the styrene-butadiene rubber uses a styrene-butadiene rubber latex with a solid content of 45%; the above mass ratio is calculated from the content of the effective components in sodium polyacrylate and the styrene-butadiene rubber latex. The hard carbon has a D50 of 15 μm; Slurry preparation: First, mix sodium polyacrylate and water to disperse them evenly to obtain a glue solution; Divide the hard carbon into two equal parts; Add a composite conductive agent to the adhesive solution and disperse it evenly. First, add one part of hard carbon and disperse it at high speed for 35 minutes at a stirring speed of 1100 r / min. Then, add another part of hard carbon and disperse it at low speed for 35 minutes at a stirring speed of 450 r / min. Then, add styrene-butadiene rubber latex at a rate of 12 g / min. After the addition is complete, stir at low speed for 35 minutes at a stirring speed of 220 r / min to degas the material. The hard carbon negative electrode slurry is then discharged. By adjusting the amount of water used, the solid content in the resulting hard carbon anode slurry was made to be 46%.

[0031] Example 3 Preparation of composite conductive agents: Graphene oxide and a 10% sucrose solution were prepared at a mass ratio of 1:0.65. The graphene oxide is selected as spherical graphene oxide with a sphericity of 0.9; and the D50 of the spherical graphene oxide is 5 μm. First, graphene oxide and silane coupling agent KH-560 were mixed and poured into an 80% ethanol solution. The pH was adjusted to 8.0. After ultrasonic reaction at 100 kHz and 55 ℃ for 5 hours, the mixture was filtered, washed and dried to obtain pretreated graphene oxide. The amount of silane coupling agent KH-560 used is 12% of the mass of graphene oxide; the amount of ethanol solution used is 25 times the mass of graphene oxide. After mixing the pretreated graphene oxide and sucrose solution, the mixture was stirred and dispersed at 900 r / min for 30 min. Then, it was dried and evaporated in an oven at 90℃ to remove moisture, so that the sucrose was deposited on the surface of the pretreated graphene oxide. Then, under argon protection, it was first pyrolyzed at 200℃ for 80 min, and then the temperature was increased to 700℃ for high-temperature carbonization for 3 h. After cooling, the material was discharged to obtain the composite conductive agent. By controlling the above preparation process, an amorphous carbon coating layer with a thickness of 40 nm is formed on the surface of spherical graphene oxide. The thickness of the coating layer includes a silicon-containing transition layer located between the spherical graphene oxide and the amorphous carbon. Raw material preparation: By weight, take 95 parts hard carbon, 7 parts composite conductive agent, and 8 parts binder; The adhesive is a compound of sodium polyacrylate and styrene-butadiene rubber in a mass ratio of 1.5:4. Specifically, the styrene-butadiene rubber uses a styrene-butadiene rubber latex with a solid content of 45%; the above mass ratio is calculated from the content of the effective components in sodium polyacrylate and the styrene-butadiene rubber latex. The hard carbon has a D50 of 17 μm; Slurry preparation: First, mix sodium polyacrylate and water to disperse them evenly to obtain a glue solution; Divide the hard carbon into two equal parts; Add a composite conductive agent to the adhesive solution and disperse it evenly. First, add one part of hard carbon and disperse it at high speed for 45 minutes at a stirring speed of 1200 r / min. Then, add another part of hard carbon and disperse it at low speed for 45 minutes at a stirring speed of 500 r / min. Then, add styrene-butadiene rubber latex at a rate of 15 g / min. After the addition is complete, stir at low speed for 40 minutes at 250 r / min to degas the material. The resulting material is hard carbon negative electrode slurry. By adjusting the amount of water used, the solid content in the resulting hard carbon anode slurry was made to be 48%.

[0032] Example 4 The difference between this embodiment and Example 1 is that no silane coupling agent was added, while all other conditions remained unchanged.

[0033] Comparative Example 1 The difference between this comparative example and Example 1 is that the sphericity of the graphene oxide is 0.6, while the other conditions remain unchanged.

[0034] Comparative Example 2 The difference between this comparative example and Example 1 is that graphene oxide with a sphericity of 0.8 and the conductive agent SuperP are mixed at a mass ratio of 10:1 to replace the composite conductive agent in Example 1 and added to the hard carbon anode slurry system; the D50 of graphene oxide is the same as in Example 1, and the other conditions are basically the same.

[0035] The performance of the products obtained in the above embodiments and comparative examples was evaluated, and the specific evaluation methods and results are as follows: Settlement rate test: Take 50 mL of fresh slurry prepared in each example or comparative example, pour it into a transparent graduated container, and then keep it standing at 25°C. After standing for 72 hours, record the height h1 of the supernatant and the total height h of the slurry. Settlement rate = (h - h1) / h × 100%. The smaller this value, the better the stability. See Table 1 for details. Redispersibility performance test: Take 50 mL of fresh slurry prepared in each example or comparative example, and use a rotational viscometer with an SC4-14 rotor to measure its initial viscosity x. Keep the fresh slurry at 25°C for 72 h, and then use a planetary mixer to stir at 500 r / min for 5 min. Test its viscosity y again. Viscosity change rate = (xy) / x × 100%. If y > x, the calculation formula is adjusted to: Viscosity recovery rate = (xy) / x × 100%. The smaller this value, the better the stability. See Table 1 for details. Table 1: Product Performance Evaluation Results As can be seen from the test results in Table 1, the product obtained by this invention has good storage stability.

[0036] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A hard carbon anode slurry, characterized in that, The ingredients include the following parts by weight: 90-95 parts hard carbon, 5-7 parts composite conductive agent, 6-8 parts binder and water; The solid content of the hard carbon anode slurry is 45-48%; The composite conductive agent includes a spherical graphene oxide core and an amorphous carbon coating layer covering the surface of the spherical graphene oxide core. The sphericity of the spherical graphene oxide core is 0.8-0.9; The adhesive includes sodium polyacrylate and styrene-butadiene rubber.

2. The hard carbon anode slurry according to claim 1, characterized in that, The spherical graphene oxide core has a D50 of 3-5 μm; and the thickness of the amorphous carbon coating layer is 20-40 nm.

3. The hard carbon anode slurry according to claim 1, characterized in that, The composite conductive agent also includes a silicon-containing transition layer located between the spherical graphene oxide core and the amorphous carbon coating layer, wherein the silicon-containing transition layer is obtained by carbonization of a silane coupling agent under oxygen-free conditions.

4. The hard carbon negative electrode slurry according to claim 1, characterized in that, The hard carbon has a D50 of 13-17 μm.

5. The hard carbon anode slurry according to claim 1, characterized in that, The adhesive is a compound of sodium polyacrylate and styrene-butadiene rubber in a mass ratio of 1-1.5:

4.

6. A method for preparing a hard carbon anode slurry as described in any one of claims 1-5, characterized in that, The specific preparation steps include: Preparation of composite conductive agents: After coating the precursor onto the surface of spherical graphene oxide, carbonization is carried out under an inert atmosphere to form an amorphous carbon coating layer on the surface of spherical graphene oxide. Raw material preparation: Weigh each component according to the raw material composition; Slurry preparation: First, mix sodium polyacrylate and water to disperse them evenly to obtain a glue solution; Add a composite conductive agent to the adhesive solution, disperse it evenly, then add hard carbon, stir and disperse it evenly, then slowly add styrene-butadiene rubber latex, stir at low speed to degas, and discharge the material to obtain hard carbon negative electrode slurry.

7. The method for preparing a hard carbon negative electrode slurry according to claim 6, characterized in that, The slurry preparation also includes: Divide the hard carbon into two equal parts; Add a composite conductive agent to the adhesive solution and disperse it evenly. First, add one part of hard carbon and disperse it at high speed for 30-45 minutes at a stirring speed of 1000-1200 r / min. Then, add another part of hard carbon and disperse it at low speed for 30-45 minutes at a stirring speed of 400-500 r / min. Then, slowly add styrene-butadiene rubber latex, stir at low speed to degas, and discharge the material to obtain the hard carbon negative electrode slurry.

8. The method for preparing a hard carbon negative electrode slurry according to claim 7, characterized in that, The slurry preparation also includes: Divide the hard carbon into two equal parts; Add a composite conductive agent to the adhesive solution and disperse it evenly. First, add one part of hard carbon and disperse it at high speed (1000-1200 r / min) for 30-45 min. Then, add another part of hard carbon and disperse it at low speed (400-500 r / min) for 30-45 min. Next, add styrene-butadiene rubber latex at a rate of 10-15 g / min. After the addition is complete, stir at low speed (200-250 r / min) for 30-40 min to degas the material. The resulting material is hard carbon negative electrode slurry.

9. The method for preparing a hard carbon negative electrode slurry according to claim 6, characterized in that, The preparation of the composite conductive agent further includes: Prepare graphene oxide and a sucrose solution with a mass fraction of 8-10% at a mass ratio of 1:0.55-0.

65. First, graphene oxide and silane coupling agent KH-560 are mixed and poured into an ethanol solution with a mass fraction of 60-80%. The pH is adjusted to 7.6-8.0, and the reaction is carried out by sonication for 3-5 hours. Then, the mixture is filtered, washed, and dried to obtain pretreated graphene oxide. The amount of silane coupling agent KH-560 used is 10-12% of the mass of graphene oxide; After the pretreated graphene oxide and sucrose solution are evenly dispersed, they are dried and evaporated to remove moisture, so that sucrose is deposited on the surface of the pretreated graphene oxide. Then, the mixture is first pyrolyzed at a low temperature of 180-200℃ for 60-80 minutes, and then the temperature is further increased to 600-700℃ for high-temperature carbonization for 2-3 hours. After cooling, the material is discharged to obtain the composite conductive agent.

10. A sodium-ion battery cell, characterized in that, The sodium-ion battery cell is obtained by coating with the hard carbon negative electrode slurry as described in any one of claims 1-5.

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