Negative electrode composite, method for producing the same, and use thereof

Abstract

The application discloses a negative electrode composite material and a preparation method and application thereof. The negative electrode composite material comprises a hard carbon material and a soft carbon material, the hard carbon material is dispersed in the soft carbon material in a particle state, the soft carbon material and / or the surface of the hard carbon material is doped with sulfur elements, and the ratio of the area occupied by the soft carbon material to the area occupied by the hard carbon material in a transmission electron microscope image is (10-25):(75-90).

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to a negative electrode composite material, its preparation method, and its application. Background Technology

[0002] Due to the significant fluctuations in lithium battery prices, sodium-ion batteries, with their price advantage and role in stabilizing lithium battery prices, have emerged. Positioned in the energy storage field, sodium-ion batteries serve as a price stabilizer for lithium-ion batteries and an effective supplement for specific scenarios. Among these, hard carbon is the most advantageous anode material for the industrialization of sodium-ion batteries. Hard carbon possesses a graphite-like microcrystalline structure characterized by short-range order and long-range disorder. The disordered stacking of these graphite-like microcrystals creates a complex pore distribution. This complex structure hinders the directional movement of electrons, resulting in poor conductivity and rate performance of hard carbon materials. Furthermore, the high production cost of hard carbon further complicates the industrialization of sodium-ion batteries. Therefore, improving the conductivity and rate performance of sodium-ion battery anode materials and reducing their production costs are key challenges for the industrialization of sodium-ion batteries. Summary of the Invention

[0003] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, the object of this invention is to provide a negative electrode composite material, its preparation method, and its application. The negative electrode composite material of this invention, while possessing high reversible capacity and high initial coulombic efficiency, also exhibits high conductivity and rate performance.

[0004] In one aspect of the invention, a negative electrode composite material is provided. According to an embodiment of the invention, the negative electrode composite material comprises: a hard carbon material and a soft carbon material, wherein the hard carbon material is dispersed in the soft carbon material in a particulate state, and sulfur is doped in the soft carbon material and / or on the surface of the hard carbon material, wherein in a transmission electron microscope image, the ratio of the area occupied by the soft carbon material to the area occupied by the hard carbon material is (10-25):(75-90).

[0005] The negative electrode composite material according to embodiments of the present invention includes a hard carbon material and a soft carbon material. The hard carbon material is dispersed in the soft carbon material in a particulate state. Sulfur is doped into the soft carbon material and / or on the surface of the hard carbon material. The soft carbon material exhibits better conductivity than the hard carbon material. Coating the hard carbon material with soft carbon material can significantly improve the conductivity of the hard carbon material, repair surface defects, and reduce its specific surface area, thereby improving the first coulombic efficiency of the negative electrode composite material. Simultaneously, sulfur doping modifies the structure of the carbon material, promoting electron transfer and enhancing its conductivity. Sulfur doping also increases the interlayer spacing of the soft carbon material, improving its reversible sodium storage capacity. Furthermore, the negative electrode composite material of the present invention also possesses superior rate performance. Therefore, the negative electrode composite material of the present invention, while exhibiting high reversible capacity and high first coulombic efficiency, also possesses high conductivity and rate performance.

[0006] In addition, the negative electrode composite material according to the above embodiments of the present invention may also have the following additional technical features:

[0007] In some embodiments of the present invention, the total mass of the negative electrode composite material is 100%, and the sulfur content is 0.5%-2.0%.

[0008] In some embodiments of the present invention, the conductivity of the negative electrode composite material at 25 MPa is 60 S / cm-150 S / cm; and / or, in a half-cell using sodium metal as the counter electrode, the reversible specific capacity of the negative electrode composite material is >300 mAh / g; and / or, in a half-cell using sodium metal as the counter electrode, the initial coulombic efficiency of the negative electrode composite material is >85%; and / or, in the discharge curve of a half-cell using sodium metal as the counter electrode, the capacity of the ramp segment greater than 0.1 V is greater than 160 mAh / g, accounting for more than 45% of the total discharge capacity; and the 0.1C discharge capacity is greater than 310 mAh / g, accounting for more than 90% of the total discharge capacity.

[0009] In some embodiments of the present invention, the particle size D50 of the hard carbon material is ≤1.5μm and D90 is ≤3μm; and / or, the particle size D50 of the negative electrode composite material is 4μm-10μm.

[0010] In a second aspect, the present invention provides a method for preparing the negative electrode composite material of the above embodiments. According to an embodiment of the present invention, the method includes:

[0011] (1) The hard carbon material precursor is heated to a first temperature under a protective atmosphere and carbonized to obtain hard carbon material.

[0012] (2) The hard carbon material, soft carbon material precursor, solvent, surfactant and sulfiding agent are mixed and sulfur doped to obtain a first mixed slurry;

[0013] (3) The first mixed slurry is dried to obtain a mixed powder;

[0014] (4) The mixed powder is heated to a second temperature under a protective atmosphere and stirred to obtain a composite precursor;

[0015] (5) The composite precursor is crushed to obtain composite precursor particles;

[0016] (6) The composite precursor particles are heated to a third temperature in order to pre-oxidize the composite precursor particles;

[0017] (7) The pre-oxidized composite precursor particles are heated to a fourth temperature under a protective atmosphere to carry out a pyrolysis reaction, and then the pyrolyzed composite precursor particles are heated to a fifth temperature under a protective atmosphere to carry out a carbonization reaction in order to obtain the negative electrode composite material.

[0018] The fifth temperature is lower than the first temperature.

[0019] The method for preparing the negative electrode composite material according to embodiments of the present invention first carbonizes the hard carbon material precursor at a high temperature to ensure that the hard carbon material has a high sodium storage capacity, then does it with sulfur, and finally carbonizes the soft carbon material precursor at a relatively low temperature. This solves the problem that sulfur is difficult to retain during the high carbonization stage. Therefore, the negative electrode composite material prepared by this method has high reversible capacity and high initial coulombic efficiency, as well as high conductivity and rate performance.

[0020] In addition, the method according to the above embodiments of the present invention may also have the following additional technical features:

[0021] In some embodiments of the present invention, the hard carbon material precursor includes pulverized tailings of hard carbon material, and the soft carbon material precursor includes high-sulfur asphalt, wherein the sulfur content in the high-sulfur asphalt is 2%-4%.

[0022] In some embodiments of the present invention, step (2) includes: (2-1) mixing the hard carbon material, the soft carbon material precursor, the solvent and the surfactant, stirring to obtain a second mixed slurry; (2-2) mixing the second mixed slurry with the vulcanizing agent and performing sulfur doping for 6-12 hours to obtain the first mixed slurry.

[0023] In some embodiments of the present invention, in step (2), the mass ratio of the hard carbon material to the soft carbon material precursor is (50-80):(20-50); and / or, the mass of the vulcanizing agent is 5%-20% of the mass of the soft carbon material precursor; and / or, the mass of the surfactant is 1%-2% of the mass of the solvent; and / or, the vulcanizing agent includes at least one of ammonium sulfate, sodium sulfate, potassium sulfate, ammonium persulfate, sodium persulfate, sodium benzenesulfonate, and ammonium benzenesulfonate; and / or, the surfactant includes a quaternary ammonium salt surfactant, which includes at least one of dodecylbenzenesulfonate, hexadecyltrimethylammonium bromide, and octadecyltrimethylammonium chloride.

[0024] In some embodiments of the present invention, in step (1), the first temperature is 1200℃-1400℃ and the carbonization time is 2h-6h; and / or, in step (4), the second temperature is 300℃-400℃ and the stirring time is 30min-60min.

[0025] In some embodiments of the present invention, in step (5), the particle size D50 of the composite precursor particles is 4μm-10μm.

[0026] In some embodiments of the present invention, in step (6), the third temperature is 250°C-350°C, and the pre-oxidation time is 3h-9h.

[0027] In some embodiments of the present invention, in step (7), the fourth temperature is 450℃-600℃ and the pyrolysis reaction time is 1h-3h; and / or, the fifth temperature is 950℃-1200℃ and the carbonization time is 2h-6h.

[0028] In a third aspect, the present invention provides a negative electrode sheet. According to embodiments of the present invention, the negative electrode sheet comprises the negative electrode composite material described in the above embodiments or the negative electrode composite material prepared by the method described in the above embodiments.

[0029] In a fourth aspect, the present invention provides a battery. According to an embodiment of the invention, the battery has the negative electrode of the above embodiments. This improves the rate performance of the battery, as well as its reversible capacity and initial coulombic efficiency.

[0030] In a fifth aspect, the present invention provides an electrical device. According to an embodiment of the invention, the electrical device has the battery described above. Thus, the electrical device possesses all the advantages of a sodium-ion battery, which will not be elaborated further here.

[0031] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0032] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0033] Figure 1 This is a schematic flowchart of a method for preparing a negative electrode composite material according to an embodiment of the present invention. Detailed Implementation

[0034] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0035] In one aspect of the invention, a negative electrode composite material is provided. According to an embodiment of the invention, the negative electrode composite material comprises: a hard carbon material and a soft carbon material, wherein the hard carbon material is dispersed in the soft carbon material in a particulate state, and sulfur is doped in the soft carbon material and / or on the surface of the hard carbon material; under a transmission electron microscope, the ratio of the area occupied by the soft carbon material to the area occupied by the hard carbon material in the composite material is (10-25):(75-90).

[0036] Therefore, the negative electrode composite material of the present invention has high electrical conductivity and rate performance, in addition to having high reversible capacity and high initial coulombic efficiency.

[0037] The principle by which the negative electrode composite material proposed in this invention can achieve the above-mentioned beneficial effects will be explained in detail below:

[0038] In related technologies, hard carbon materials exhibit poor conductivity and rate performance. To address these issues, this invention provides a negative electrode composite material comprising hard carbon material and soft carbon material. The hard carbon material is dispersed in the soft carbon material in a particulate state. Sulfur is doped into the soft carbon material and / or on the surface of the hard carbon material. The soft carbon material exhibits superior conductivity compared to the hard carbon material. Coating the hard carbon material with soft carbon material significantly improves the conductivity of the hard carbon material, repairs surface defects, and reduces its specific surface area, thereby increasing the initial coulombic efficiency of the negative electrode composite material. Simultaneously, sulfur doping modifies the structure of the carbon material, promoting electron transfer and enhancing its conductivity. Furthermore, sulfur doping increases the interlayer spacing of the soft carbon material, improving its reversible sodium storage capacity. Additionally, the negative electrode composite material of this invention also possesses excellent rate performance. Therefore, the negative electrode composite material of this invention, while exhibiting high reversible capacity and high initial coulombic efficiency, also possesses high conductivity and rate performance.

[0039] In the aforementioned negative electrode composite material, the hard carbon material primarily provides sodium storage capacity, while the soft carbon material mainly repairs surface defects in the hard carbon material, reduces the specific surface area of ​​the negative electrode composite material, and improves the initial coulombic efficiency. Simultaneously, the soft carbon material's inherent conductivity and sulfur doping enhance the overall conductivity of the negative electrode composite material. In this invention, in transmission electron microscopy images, the ratio of the area occupied by the soft carbon material to the area occupied by the hard carbon material in the composite material is (10-25):(75-90).

[0040] The inventors discovered that if the area ratio of soft carbon material is too low, it will prevent the soft carbon material from fully coating the hard carbon material, making it difficult to eliminate surface defects in the hard carbon material and reduce the specific surface area of ​​the anode composite material. Furthermore, sulfur doping is mainly concentrated in the soft carbon material, reducing the doping effect and ultimately affecting the conductivity of the anode composite material, while also resulting in only a slight improvement in the rate performance. Conversely, if the area ratio of soft carbon material is too high, it will lead to a lower reversible capacity of the anode composite material. It should be noted that while the initial coulombic efficiency of soft carbon material itself is low, its low specific surface area and small area ratio in the composite material have a relatively small impact on the initial coulombic efficiency of the anode composite material. Simultaneously, sulfur doping increases the interlayer spacing of the soft carbon material, improving its reversible sodium storage capacity. Therefore, only by limiting the ratio of the area occupied by soft carbon material to that occupied by hard carbon material to the range of (10-25):(75-90) can the anode composite material be ensured to have high reversible capacity, high initial coulombic efficiency, and also high conductivity and rate performance.

[0041] It should be noted that the ratio of the area occupied by soft carbon material to that occupied by hard carbon material in a transmission electron microscope image of a composite material is not equivalent to the volume ratio (or mass ratio) of soft carbon material to hard carbon material, but there is a strong correlation between their area ratio and volume ratio (or mass ratio). Therefore, this invention uses their area ratio to characterize their content in the composite material.

[0042] According to some specific embodiments of the present invention, based on the total mass of the negative electrode composite material being 100%, the sulfur content can be 0.5%-2.0%, for example, but not limited to 0.5%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, etc. By limiting the sulfur content within the above range, it is possible to ensure that the structure of the carbon material is modified by sulfur doping, thereby enhancing the conductivity of the carbon material. It is also possible to ensure that sulfur doping can increase the interlayer spacing of the soft carbon material and improve the reversible sodium storage capacity of the soft carbon material.

[0043] In some embodiments of the present invention, through the combined effect of sulfur doping and soft carbon material coating of hard carbon material, the powder conductivity of the negative electrode composite material at 25 MPa can be increased to 60 S / cm-150 S / cm, while the powder conductivity of most existing hard carbon materials at 25 MPa is generally between 15 S / cm-45 S / cm. It can be seen that the negative electrode composite material of the present invention has a high conductivity.

[0044] In some other embodiments of the present invention, in a half-cell with sodium metal as the counter electrode, the reversible specific capacity of the negative electrode composite material is >295300, and the initial coulombic efficiency of the negative electrode composite material is >85%. It can be seen that the negative electrode composite material of the present invention has high reversible capacity and high initial coulombic efficiency.

[0045] In some embodiments of the present invention, in the discharge curve of a half-cell using metallic sodium as the counter electrode, the capacity of the ramp segment greater than 0.1V is greater than 160 mAh / g (preferably greater than 190 mAh / g), accounting for more than 45% of the total discharge capacity; and the 0.1C discharge capacity is greater than 310 mAh / g, accounting for more than 90% of the total discharge capacity. This demonstrates that the negative electrode composite material of the present invention exhibits superior rate performance. Furthermore, in a full cell, the capacity retention rate at a 4C charge-discharge rate can reach 60%-75%, further proving that the negative electrode composite material of the present invention possesses superior rate performance.

[0046] In some embodiments of the present invention, the particle size D50 of the hard carbon material is ≤1.5 μm and D90 is ≤3 μm; and / or, the particle size D50 of the negative electrode composite material is 4 μm-10 μm. This further ensures that the negative electrode composite material of the present invention possesses high processing performance in the homogenization process, while also exhibiting high conductivity and rate performance, in addition to high reversible capacity and high initial coulombic efficiency.

[0047] In a second aspect, the present invention provides a method for preparing the negative electrode composite material of the above embodiments. According to embodiments of the present invention, refer to the appendix... Figure 1 The method includes:

[0048] S100: Carbonization treatment of hard carbon material precursors

[0049] In this step, the hard carbon material precursor is heated to a first temperature under a protective atmosphere and carbonized to obtain the hard carbon material.

[0050] As a specific example, the hard carbon material precursor can be first placed in a graphite crucible and then in a box-type atmosphere furnace. Under the protection of a nitrogen atmosphere, it is heated to 1200℃-1400℃ at a heating rate of 1-3℃ / min and carbonized at this temperature for 2-6 hours. This process allows the precursor to undergo pyrolysis, removing volatiles, surface functional groups, and impurity elements. Simultaneously, the carbon skeleton undergoes aromatic ring condensation and rearrangement due to pyrolysis. The high temperature closes the open pores of the hard carbon material precursor, repairing its surface defects. After cooling, the hard carbon material is obtained. The carbonization temperature of the hard carbon material precursor is relatively high to ensure that the open pores are fully closed, and that surface functional groups and impurity elements are fully removed, thus repairing surface defects. Excessive temperature leads to a reduction in the interlayer spacing of the hard carbon, which is detrimental to sodium ion conduction and reduces the rate performance of the anode material. Conversely, insufficient pore closure and an excessive number of impurity functional groups can result in a potential decrease in capacity and initial coulombic efficiency.

[0051] According to some specific embodiments of the present invention, the aforementioned hard carbon material precursor can be made from the pulverized waste generated during the production process of hard carbon materials. In the negative electrode material of sodium-ion batteries, to ensure the processing performance of the negative electrode slurry and the rate performance of the final cell, the particle size D50 of the negative electrode material is generally controlled within the range of 4μm-10μm. Therefore, the precursor generally needs to be pulverized. Air jet milling or mechanical milling is mainly used, but both methods generate 15%-30% pulverized waste. The particle size of the pulverized waste is D50≤1.5μm, D90≤3μm, and the specific surface area is 10m². 2 / g-50m 2 These pulverized waste materials, due to their excessively small particle size and large specific surface area, are difficult to disperse and have excessively high slurry viscosity, severely affecting the processing of the negative electrode slurry. Furthermore, after carbonization, these waste materials, when used in half-cells with metallic sodium as the counter electrode, exhibit a reversible capacity of 280mAh / g-300mAh / g, but their initial coulombic efficiency is only 65%-80%. Therefore, they cannot be directly used as negative electrode materials for sodium-ion batteries and are mostly treated as powder waste. This invention recycles and reuses the pulverized waste materials of hard carbon materials as precursors for hard carbon materials, improving the utilization rate of hard carbon precursor materials and significantly reducing the production cost of sodium-ion batteries.

[0052] In the embodiments of the present invention, the specific type of the above-mentioned pulverized tailings is not particularly limited, and may include at least one of biomass, coal, asphalt and polymer. As some specific examples, biomass can be selected, such as fruit shells, wood flour, bamboo flour, starch, etc. As further specific examples, polymers can be selected, such as phenolic resin, furfural resin, etc. As yet another specific example, coke after low-temperature (<700°C) pyrolysis of polymers can be selected.

[0053] S200: A mixture of hard carbon material, soft carbon material precursor, solvent, surfactant, and sulfurizing agent is used for sulfur doping.

[0054] According to some specific embodiments of the present invention, step S200 may include:

[0055] S210: Mix hard carbon material, soft carbon material precursor, solvent and surfactant, stir to obtain a second mixed slurry;

[0056] In this step, a solvent (e.g., pure water) can be added to the reactor first, along with a surfactant to enhance the dispersion performance of the hard carbon material in the solution. The mixture is then mechanically stirred until the surfactant is completely dissolved. The hard carbon material and the soft carbon material precursor are then poured into the reactor according to the specified ratio, and the mixture is stirred until both the hard carbon material and the soft carbon material precursor are completely dispersed in the solution.

[0057] According to some specific embodiments of the present invention, the mass ratio of hard carbon material to soft carbon material precursor can be (50-80):(20-50). By limiting the mass ratio of hard carbon material to soft carbon material precursor within the above range, it can be ensured that the soft carbon material precursor fully coats the hard carbon material, effectively eliminates the surface defects of the hard carbon material, and effectively reduces the specific surface area of ​​the negative electrode composite material. At the same time, it can avoid the problem of low reversible capacity of the negative electrode composite material caused by excessive soft carbon material precursor content.

[0058] According to some specific embodiments of the present invention, the above-mentioned soft carbon material precursor can be high-sulfur asphalt, which has a sulfur content of 2%-4%, a softening point of 120℃-180℃, and a price of 3500 RMB / t-4000 RMB / t. Currently, high-sulfur asphalt is only used in road construction and has not been found to be used in the negative electrode material of sodium-ion batteries. Compared with low-sulfur petroleum asphalt (sulfur content <1%, price 4500 RMB / t-5000 RMB / t) used as a graphite precursor, high-sulfur asphalt is cheaper. Therefore, using inexpensive high-sulfur asphalt as a soft carbon material precursor significantly reduces the production cost of sodium-ion batteries. When high-sulfur asphalt is used as a soft carbon material precursor, it is first crushed to a powder with a particle size D50 of 2μm-6μm through mechanical crushing and air jet milling.

[0059] According to some specific embodiments of the present invention, the mass of the surfactant can be 1%-2% of the mass of the solvent, and the mass of the solvent can be 3-6 times the mass of the hard carbon material.

[0060] The specific type of surfactant is not particularly limited, but quaternary ammonium salt surfactants are preferred. Quaternary ammonium salt surfactants include at least one of ammonium dodecylbenzenesulfonate, hexadecyltrimethylammonium bromide, and octadecyltrimethylammonium chloride. These types of quaternary ammonium salt surfactants can decompose nearly completely during the subsequent pyrolysis process, avoiding an increase in the impurity ash content of the final negative electrode material.

[0061] S220: The second mixed slurry is mixed with a vulcanizing agent and subjected to sulfur doping for 6-12 hours to obtain the first mixed slurry. Sulfur doping mainly occurs on the surface of soft carbon material layers and hard carbon material layers. For example, in high-sulfur asphalt, asphalt molecules are transformed into larger molecules through sulfur doping.

[0062] According to some specific embodiments of the present invention, the mass of the vulcanizing agent can be 5%-20% of the mass of the soft carbon material precursor. By limiting the amount of vulcanizing agent within the above range, the conductivity of the negative electrode composite material can be effectively improved.

[0063] In the embodiments of the present invention, the specific type of vulcanizing agent is not particularly limited, and those skilled in the art can select according to actual needs. As some specific examples, the vulcanizing agent may include, but is not limited to, at least one of ammonium sulfate, sodium sulfate, potassium sulfate, ammonium persulfate, sodium persulfate, sodium benzenesulfonate, and ammonium benzenesulfonate.

[0064] S300: Drying the first mixed slurry

[0065] In this step, the first mixed slurry after sulfur doping is poured into a plastic container and dried in an oven at 100℃-120℃ for 12h-18h. After cooling, it is depolymerized and sieved to obtain a mixed powder.

[0066] S400: Under a protective atmosphere, heat the mixed powder to a second temperature and stir.

[0067] In this step, the mixed powder can be placed in an electric heating reactor and stirred and heated to a second temperature in a protective atmosphere (such as a nitrogen atmosphere) so that the vulcanized modified high sulfur asphalt softens and coats and fills the stacked gaps of the crushed tailings of hard carbon material. After heating and stirring, the composite precursor can be obtained after cooling.

[0068] According to some specific embodiments of the present invention, the second temperature can be 300℃-400℃ and the stirring time can be 30min-60min, thereby enabling the softened high-sulfur asphalt to fully coat and fill the stacked gaps of the crushed tailings of hard carbon materials.

[0069] S500: Crushes the composite precursor

[0070] In this step, the composite precursor can be pulverized by mechanical pulverization or air jet pulverization to obtain composite precursor particles.

[0071] According to some specific embodiments of the present invention, the particle size D50 of the composite precursor particles can be 4μm-10μm. The particle size of the composite precursor particles is almost the same as the particle size of the prepared negative electrode composite material. The limitation of the particle size of the composite precursor particles here further ensures that the negative electrode composite material of the present invention has high conductivity and rate performance, while having high reversible capacity and high initial coulombic efficiency.

[0072] In addition, the pulverized tailings generated during the pulverization process can be recycled to step S100 for reuse.

[0073] S600: Heating the composite precursor particles to the third temperature

[0074] In this step, the composite precursor particles are heated to a third temperature to pre-oxidize them, during which the soft carbon material precursor undergoes an oxygen-bridge cross-linking reaction. Taking high-sulfur asphalt as an example, the oxygen-bridge cross-linking of asphalt molecules increases their softening point temperature, making it higher than the pyrolysis temperature in subsequent steps. This suppresses the formation of the intermediate liquid phase in the asphalt components during pyrolysis, preventing particle aggregation. Simultaneously, the oxygen-bridge cross-linking of asphalt molecules inhibits graphitization and increases the interlayer spacing of the soft carbon.

[0075] According to some specific embodiments of the present invention, the third temperature can be 250℃-350℃, and the pre-oxidation time can be 3h-9h. By limiting the third temperature and the pre-oxidation time to the above range, it is possible to prevent the softening of the asphalt components and the adhesion of powder particles caused by subsequent heating, and at the same time, it is possible to further effectively suppress the formation of the intermediate liquid phase of the asphalt components during the subsequent pyrolysis process, and further suppress the tendency of graphitization, increase the interlayer spacing of soft carbon, and at the same time, effectively avoid the problem of asphalt oxidation and decomposition caused by excessively high third temperature.

[0076] S700: Under a protective atmosphere, the pre-oxidized composite precursor particles are heated to a fourth temperature for pyrolysis, and then under a protective atmosphere, the pyrolyzed composite precursor particles are heated to a fifth temperature for carbonization.

[0077] In this step, the pre-oxidized composite precursor particles are loaded into a graphite crucible and placed in a box-type atmosphere furnace. Under a protective atmosphere (e.g., nitrogen atmosphere), the temperature is increased to a fourth temperature at a certain heating rate (e.g., 1℃ / min-5℃ / min) to carry out a pyrolysis reaction, forming a carbon skeleton and initially removing surface functional groups and surface defects from the soft carbon component. Then, the temperature is increased to a fifth temperature at a certain heating rate (e.g., 1℃ / min-5℃ / min) to carry out a carbonization reaction, further removing surface functional groups and surface defects from the soft carbon component. After cooling, the negative electrode composite material is obtained.

[0078] According to some specific embodiments of the present invention, the fourth temperature can be 450℃-600℃, and the pyrolysis reaction time can be 1h-3h.

[0079] According to some specific embodiments of the present invention, the fifth temperature is 950℃-1200℃, and the carbonization time is 2h-6h. The inventors found that if the fifth temperature is too low, there will be more surface functional groups and surface defects in the soft carbon component, resulting in a lower reversible capacity and a lower first-stage efficiency of the final composite anode material. If the fifth temperature is too high, the interlayer spacing of the soft carbon component will decrease, the intercalation sodium storage capacity will decrease, and the sodium ion diffusion rate will also be reduced. At the same time, as the fifth temperature increases, the sulfur content decreases. If the fifth temperature is too high, the sulfur doping in the composite anode material will be too low, and the characteristic of sulfur doping to improve conductivity cannot be effectively utilized.

[0080] To ensure uniform doping and improve interlayer spacing, sulfur is typically doped before carbonization in related technologies. However, the doped sulfur is difficult to retain during the subsequent high-temperature carbonization stage. Therefore, the effective sulfur doping content in these technologies is generally low, resulting in limited improvement in conductivity. It should be noted that the carbonization temperature of hard carbon precursors is higher than that of soft carbon precursors. Based on this, this invention first carbonizes the hard carbon precursor at a higher temperature to ensure a higher sodium storage capacity in the hard carbon material. Then, sulfur is doped, and finally, the soft carbon precursor is carbonized at a relatively lower temperature. This solves the problem of sulfur retention during the higher carbonization stage.

[0081] The method for preparing the negative electrode composite material according to embodiments of the present invention has at least one of the following advantages:

[0082] 1. The negative electrode composite material prepared by this method has high reversible capacity and high initial coulombic efficiency, as well as high conductivity and rate performance.

[0083] 2. This method first carbonizes the hard carbon material precursor at a high temperature to ensure that the hard carbon material has a high sodium storage capacity, then does sulfur, and finally carbonizes the soft carbon material precursor at a relatively low temperature, thus solving the problem that sulfur is difficult to retain at a high carbonization stage.

[0084] 3. High-sulfur asphalt has the self-doping effect of sulfur element. It is modified by chemical cross-linking with sulfurizing agent and modified by oxidative cross-linking with inexpensive air, which increases the softening point of asphalt, inhibits the tendency of liquid phase rearrangement of asphalt during pyrolysis, and prevents particle agglomeration during heating.

[0085] 4. Due to its excessively small particle size and large specific surface area, the initial coulombic efficiency of the hard carbon precursor pulverization tailings is only 65%-80%. This method uses inexpensive high-sulfur pitch to coat the pulverization tailings, repairing the surface defects of the hard carbon material, reducing the specific surface area of ​​the anode composite material, and improving the initial coulombic efficiency of the anode composite material. Simultaneously, the conductivity of the anode composite material is improved by the conductivity of the high-sulfur pitch itself and sulfur doping. Therefore, this invention not only reduces the production cost of sodium-ion batteries but also enables the obtained anode composite material to possess high reversible capacity and high initial coulombic efficiency, as well as high conductivity and rate performance.

[0086] 5. The method of the present invention first carbonizes the hard carbon material precursor at a high temperature to ensure that the hard carbon material has a high sodium storage capacity, then does sulfur element, and finally carbonizes the soft carbon material precursor at a relatively low temperature, thereby solving the problem that sulfur element is difficult to retain at a high carbonization stage.

[0087] In a third aspect, the present invention provides a negative electrode sheet. According to embodiments of the present invention, the negative electrode sheet comprises the negative electrode composite material of the above embodiments or the negative electrode composite material prepared by the method of the above embodiments. Specifically, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer being disposed on at least one surface of the negative electrode current collector, the negative electrode active material layer comprising a negative electrode active material, a negative electrode binder, and a conductive agent, the negative electrode active material comprising the negative electrode composite material as described above.

[0088] In embodiments of the present invention, the specific type of the negative electrode current collector is not particularly limited. For example, metal foil, porous metal plate, or composite current collector can be used. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.). As another example, the negative electrode is a negative electrode of a sodium-ion battery, and the negative electrode current collector can be copper foil or aluminum foil.

[0089] In embodiments of the present invention, the specific type of the negative electrode binder is not particularly limited. For example, the negative electrode binder may be selected from at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon.

[0090] In some exemplary embodiments, the negative electrode active material layer may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0091] In embodiments of the present invention, the negative electrode sheet can be prepared according to conventional methods in the art. For example, the above-mentioned negative electrode composite material and optional other negative electrode active materials, optional conductive agents, binders and optional thickeners are dispersed in a solvent, which can be N-methylpyrrolidone (NMP) or deionized water, to form a uniform negative electrode slurry. The negative electrode slurry is coated on a negative electrode current collector, and the negative electrode sheet is obtained through processes such as drying and cold pressing.

[0092] In a fourth aspect, the present invention provides a battery. According to an embodiment of the invention, the battery has the negative electrode of the above embodiments. This improves the rate performance of the battery, as well as its reversible capacity and initial coulombic efficiency.

[0093] Specifically, the aforementioned battery can be either a sodium-ion battery or a lithium-ion battery. The following explanation uses a sodium-ion battery as an example:

[0094] The sodium-ion battery includes a negative electrode, a positive electrode, and a separator as described in the above embodiments, with the separator disposed between the negative electrode and the positive electrode. The separator includes at least one of PP separator, PE separator, single-sided ceramic separator, double-sided ceramic separator, non-woven fabric separator, and glass fiber separator.

[0095] The positive electrode sheet includes a positive current collector and a positive active material layer formed on the positive current collector. The positive active material layer includes a positive active material, a positive binder, and a positive conductive agent. In embodiments of the present invention, the positive current collector can be made of a material with good conductivity and mechanical strength, preferably aluminum foil.

[0096] In the embodiments of the present invention, the specific types of positive electrode active materials are not particularly limited, and those skilled in the art can select them according to actual needs. As some specific examples, the positive electrode active materials include at least one of sodium vanadium phosphate, sodium vanadium fluorophosphate, sodium iron phosphate, sodium iron pyrophosphate, and compound sodium iron phosphate.

[0097] In the embodiments of the present invention, the specific type of positive electrode conductive agent is not particularly limited, and those skilled in the art can select according to actual needs. As some specific examples, the positive electrode conductive agent includes at least one of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0098] Similarly, the specific type of positive electrode binder is not particularly limited, and those skilled in the art can choose according to actual needs. As some specific examples, the positive electrode binder includes at least one of polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE).

[0099] The preparation method of the positive electrode sheet includes: mixing the positive electrode active material, positive electrode binder and positive electrode conductive agent evenly according to a preset ratio, adding solvent and stirring evenly to form a positive electrode slurry, then coating it onto the current collector, drying it, and finally cutting it into a specific shape of positive electrode sheet for later use according to the different battery casings.

[0100] Cell preparation: The positive and negative electrode sheets are added to the separator and wound. After winding, the positive and negative electrode tabs are welded. Then, the bare cell is encapsulated in an aluminum-plastic film. After encapsulation, the cell is vacuum baked for 10-20 hours. Then, after liquid injection, standing, high temperature and high pressure formation, degassing and encapsulation, and capacity testing, the sodium-ion battery is obtained.

[0101] In a fifth aspect, the present invention provides an electrical device. According to an embodiment of the invention, the electrical device has a sodium-ion battery as described above. Thus, the electrical device possesses all the advantages of a sodium-ion battery, which will not be elaborated further here.

[0102] Specifically, the aforementioned electrical equipment can include, but is not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Among them, electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., and spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0103] The embodiments of the present invention are described in detail below. It should be noted that the embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. In addition, unless otherwise specified, all reagents used in the following embodiments are commercially available or can be synthesized according to the methods described herein or known to others. For reaction conditions not listed, they are also readily available to those skilled in the art.

[0104] Example 1

[0105] This embodiment provides a negative electrode composite material, the preparation method of which includes:

[0106] Step 1: Take 1000g of coconut shell crushed tailings and put them into a graphite crucible. Place it in a box-type atmosphere furnace and heat it to 1300℃ under the protection of nitrogen atmosphere at a heating rate of 2℃ / min. Carbonize it at a constant temperature for 4 hours. After cooling, you will get carbonized crushed tailings - hard carbon A.

[0107] Step 2: First, add 3000g of pure water and 30g of ammonium dodecylbenzenesulfonate to the reactor. Stir mechanically at 300r / min for 10min until the ammonium dodecylbenzenesulfonate is completely dissolved. Then, add 700g of hard carbon A and 300g of high-sulfur asphalt powder to the reactor in sequence and continue stirring for 30min until the hard carbon A and high-sulfur asphalt powder are completely dispersed in the aqueous solution.

[0108] The third step is to add 45g of ammonium sulfate, heat the reactor to 80℃, stir the reaction at a rate of 300r / min for 10h, and then cool to obtain mixed slurry E;

[0109] Step 4: Pour the mixed slurry E after the reaction is complete into a plastic tray, place it in a 120℃ oven to dry for 12 hours to remove moisture, cool to room temperature, and then mechanically crush and depolymerize it into powder F that passes through a 100-mesh sieve.

[0110] Step 5: The depolymerized powder F is placed in an electric heating reactor and stirred and heated to 350°C in a nitrogen atmosphere. This softens the vulcanized modified asphalt, coats and fills the stacked gaps of the carbonized tailings. After heating and stirring for 30 minutes and cooling, the composite precursor G of the desired composite carbon material is obtained.

[0111] Step 6: The composite precursor G is pulverized into irregular particles with D50 = 6.5μm ± 0.5μm by mechanical pulverization or air jet milling.

[0112] Step 7: Take 100g of the pulverized composite precursor G, place it in a rotary kiln, and slowly heat it to 300℃ at a rate of 0.5℃ / min in an air atmosphere. The air flow rate is 250mL / min. The oxidation reaction is carried out for 6 hours. After cooling, the pre-oxidized composite precursor H is obtained.

[0113] Step 8: The pre-oxidized composite precursor H is placed in a graphite crucible and then placed in a box-type atmosphere furnace. Under a nitrogen atmosphere, the temperature is increased to 550℃ at 2℃ and held at that temperature for 2 hours for pyrolysis. Then, the temperature is increased to 1050℃ at a rate of 2℃ / min and held at that temperature for 4 hours for carbonization. After cooling, a sodium-ion battery composite carbon anode material with high sulfur doping soft carbon coating hard carbon is obtained.

[0114] Example 2

[0115] The only difference between this embodiment and Embodiment 1 is that:

[0116] Replace the coconut shell crushed tailings in Example 1 with cedar wood crushed tailings;

[0117] All other contents are the same as in Example 1.

[0118] Example 3

[0119] The only difference between this embodiment and Embodiment 1 is that:

[0120] Replace the coconut shell crushed tailings in Example 1 with bamboo crushed tailings;

[0121] All other contents are the same as in Example 1.

[0122] Example 4

[0123] The only difference between this embodiment and Embodiment 1 is that:

[0124] In the second step, 800g of hard carbon A and 200g of high sulfur asphalt powder are used;

[0125] All other contents are the same as in Example 1.

[0126] Example 5

[0127] The only difference between this embodiment and Embodiment 1 is that:

[0128] In the second step, 500g of hard carbon A and 500g of high sulfur asphalt powder are used.

[0129] All other contents are the same as in Example 1.

[0130] Example 6

[0131] The only difference between this embodiment and Embodiment 1 is that:

[0132] In the first step, heat to 1200℃;

[0133] All other contents are the same as in Example 1.

[0134] Example 7

[0135] The only difference between this embodiment and Embodiment 1 is that:

[0136] In the first step, heat to 1400℃;

[0137] All other contents are the same as in Example 1.

[0138] Example 8

[0139] The only difference between this embodiment and Embodiment 1 is that:

[0140] In the third step, add 15g of ammonium sulfate;

[0141] All other contents are the same as in Example 1.

[0142] Example 9

[0143] The only difference between this embodiment and Embodiment 1 is that:

[0144] In the third step, add 60g of ammonium sulfate;

[0145] All other contents are the same as in Example 1.

[0146] Example 10

[0147] The only difference between this embodiment and Embodiment 1 is that:

[0148] In step seven, the temperature is raised to 250°C, and the pre-oxidation reaction is carried out for 9 hours.

[0149] All other contents are the same as in Example 1.

[0150] Example 11

[0151] The only difference between this embodiment and Embodiment 1 is that:

[0152] In step seven, the mixture is heated to 350°C and subjected to a pre-oxidation reaction for 3 hours.

[0153] All other contents are the same as in Example 1.

[0154] Example 12

[0155] The only difference between this embodiment and Embodiment 1 is that:

[0156] In step 8, the final carbonization temperature is 950℃, and the carbonization is carried out at a constant temperature for 6 hours; all other contents are the same as in Example 1.

[0157] Example 13

[0158] The only difference between this embodiment and Embodiment 1 is that:

[0159] In step eight, the final carbonization temperature is 1200℃, and the carbonization is carried out at a constant temperature for 2 hours; all other contents are the same as in Example 1.

[0160] Example 14

[0161] The only difference between this embodiment and Embodiment 1 is that:

[0162] In the third step, add 45g of ammonium persulfate;

[0163] All other contents are the same as in Example 1.

[0164] Comparative Example 1

[0165] Dry coconut shell powder (passed through a 50-mesh sieve) was pulverized by an air jet mill to a D50 of 6.5 μm ± 0.5 μm. 100 g of the pulverized coconut shell powder was placed in a graphite crucible and then placed in a corundum tube furnace. Under a nitrogen atmosphere, the temperature was increased to 600 °C at a rate of 2 °C / min and held at that temperature for 2 h. The temperature was then increased to 1300 °C at a rate of 2 °C / min and held at that temperature for 4 h to obtain coconut shell-based hard carbon.

[0166] Comparative Example 2

[0167] Dry cedar wood powder (passed through a 50-mesh sieve) was pulverized by an air jet mill to a D50 of 6.5 μm ± 0.5 μm. 100 g of the air-jet-milled cedar wood powder was placed in a graphite crucible and then placed in a corundum tube furnace. Under a nitrogen atmosphere, the temperature was increased to 600 °C at a rate of 2 °C / min and held at that temperature for 2 h. The temperature was then increased to 1300 °C at a rate of 2 °C / min and held at that temperature for 4 h to obtain cedar wood-based hard carbon.

[0168] Comparative Example 3

[0169] Dry bamboo powder (passed through a 50-mesh sieve) was pulverized by an air jet mill to a D50 of 6.5 μm ± 0.5 μm. 100 g of the air-jet-milled bamboo powder was placed in a graphite crucible and then placed in a corundum tube furnace. Under a nitrogen atmosphere, the temperature was increased to 600 °C at a rate of 2 °C / min and held at that temperature for 2 h. The temperature was then increased to 1300 °C at a rate of 2 °C / min and held at that temperature for 4 h to obtain bamboo-based hard carbon.

[0170] The area ratio of hard carbon material to soft carbon material in the negative electrode composite materials prepared in Examples 1-14 was tested. Specifically, the negative electrode composite material was embedded with polytetrafluoroethylene. Ten slices with a thickness of 100nm-200nm were cut from different thicknesses of the negative electrode composite material. The slices were scanned using a transmission electron microscope at a 50nm scale. 100 images were randomly selected from each slice. The images were processed using image scanning-integration software, and each image was divided into 5nm*5nm units. Units with a majority of ordered carbon layers were defined as soft carbon units, while units with a majority of disordered carbon layers were defined as hard carbon units. The number of soft carbon units and hard carbon units was accumulated by integration, and the ratio of the two was considered the area ratio of the soft carbon component to the hard carbon component. The average area ratio of the soft carbon component to the hard carbon component in the 10 slices was taken as the area ratio of the hard carbon material to the soft carbon material in the negative electrode composite material. The results are shown in Table 1.

[0171] The sulfur content in the negative electrode composite materials prepared in Examples 1-14 and Comparative Examples 1-3 was tested by coulometric titration (GBT 214-2007), and the results are shown in Table 1.

[0172] The conductivity of the negative electrode composite materials prepared in Examples 1-14 and Comparative Examples 1-3 at 25 MPa was tested using the four-needle method, and the results are shown in Table 1.

[0173] The negative electrode composite materials, binder CMC, conductive agent SP, and SBR prepared in Examples 1-14 and Comparative Examples 1-3 were mixed and dispersed in water solvent. The mass ratio of the negative electrode composite material, binder CMC, conductive agent SP, and SBR was 94.40:1.50:1.50:2.60, forming a uniform negative electrode slurry. The negative electrode slurry was coated onto a copper foil current collector, and the negative electrode sheet was obtained through drying and cold pressing. Then, the negative electrode sheet was used to make a coin cell with a sodium sheet as the counter electrode. The reversible capacity, 0.1C discharge capacity, initial coulombic efficiency, and >0.1V slope discharge capacity of the negative electrode composite materials prepared in Examples 1-13 and Comparative Examples 1-3 were tested using coin cells. The results are shown in Table 1. The 4C capacity retention rate is the ratio of the reversible capacity at 4C rate to the reversible capacity at 0.1C rate.

[0174] The coin cell for the negative electrode material undergoes a process of first discharging and then charging; therefore, the reversible capacity is the same as the charging capacity. A three-stage discharge process is employed: the first stage is a constant current discharge at 0.1C, cutoff at 0.005V; the second stage is a constant current discharge at 0.05C, cutoff at 0.005V; and the third stage is a constant current discharge at 0.01C, cutoff at 0.005V. During the charging stage, the material is charged at a constant current rate of 0.1C to 2.0V.

[0175] Table 1

[0176]

[0177]

[0178] As can be seen from Table 1, compared with Comparative Examples 1-3, the negative electrode composite materials of Examples 1-14, while maintaining high reversible capacity and first coulombic efficiency, also significantly improved the conductivity, >0.1V slope discharge capacity, 0.1C discharge capacity and 4C capacity retention rate of the negative electrode composite materials through sulfur doping and soft carbon coating. That is, the conductivity and rate performance of the negative electrode composite materials of Examples 1-13 were significantly improved.

[0179] In addition, Table 1 shows that sulfur content has a strong positive correlation with the conductivity of the anode composite material. Sulfur doping can modify the structure of carbon materials and promote electron transfer, thereby enhancing the conductivity of the anode composite material. High conductivity is beneficial to improving the rate performance of the anode composite material. Sulfur content and discharge capacity in the ramp section (>0.1V) show a positive correlation. Sulfur doping can improve the sodium storage performance of the anode composite material by generating defects, pores and increasing interlayer spacing, especially improving the reversible capacity in the ramp section. High ramp section capacity is beneficial to improving the rate performance of the anode composite material.

[0180] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0181] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a negative electrode composite material, characterized in that, include: (1) The hard carbon material precursor is heated to a first temperature under a protective atmosphere and carbonized to obtain hard carbon material; (2) The hard carbon material, soft carbon material precursor, solvent, surfactant and sulfiding agent are mixed and sulfur doped to obtain a first mixed slurry; (3) The first mixed slurry is dried to obtain a mixed powder; (4) The mixed powder is heated to a second temperature under a protective atmosphere, so that the sulfurized modified soft carbon material precursor softens and coats and fills the stacked gaps of the crushed tail material of the hard carbon material. Stirring is carried out to obtain a composite precursor. (5) The composite precursor is crushed to obtain composite precursor particles; (6) The composite precursor particles are heated to a third temperature in order to pre-oxidize the composite precursor particles; (7) The pre-oxidized composite precursor particles are heated to a fourth temperature under a protective atmosphere to carry out a pyrolysis reaction, and then the pyrolyzed composite precursor particles are heated to a fifth temperature under a protective atmosphere to carry out a carbonization reaction in order to obtain the negative electrode composite material. The fifth temperature is lower than the first temperature; The negative electrode composite material includes hard carbon material and soft carbon material. The hard carbon material is dispersed in the soft carbon material in the form of particles. Sulfur element is doped in the soft carbon material and / or on the surface of the hard carbon material. In the transmission electron microscope image, the ratio of the area occupied by the soft carbon material to the area occupied by the hard carbon material is (10-25):(75-90).

2. The method according to claim 1, characterized in that, The total mass of the negative electrode composite material is 100%, and the sulfur content is 0.5%-2.0%.

3. The method according to claim 2, characterized in that, The negative electrode composite material has an electrical conductivity of 60S / cm-150S / cm at 25MPa; And / or, in a half-cell with sodium metal as the counter electrode, the reversible specific capacity of the negative electrode composite material is >300 mAh / g. And / or, in a half-cell with sodium metal as the counter electrode, the initial coulombic efficiency of the negative electrode composite material is >85%; And / or, in the discharge curve of a half-cell with sodium metal as the counter electrode, the capacity of the ramp segment greater than 0.1V is greater than 160mAh / g, accounting for more than 40% of the total discharge capacity; and the 0.1C discharge capacity is greater than 310mAh / g, accounting for more than 90% of the total discharge capacity.

4. The method according to any one of claims 1-3, characterized in that, The particle size of the hard carbon material is D50≤1.5µm and D90≤3µm; And / or, the particle size D50 of the negative electrode composite material is 4µm-10µm.

5. The method according to claim 1, characterized in that, The hard carbon material precursor includes pulverized tailings of hard carbon materials, and the soft carbon material precursor includes high-sulfur asphalt, wherein the sulfur content of the high-sulfur asphalt is 2%-4%.

6. The method according to claim 1, characterized in that, Step (2) includes: (2-1) The hard carbon material, the soft carbon material precursor, the solvent and the surfactant are mixed and stirred to obtain a second mixed slurry; (2-2) The second mixed slurry is mixed with the vulcanizing agent and sulfur doping is carried out for 6-12 hours to obtain the first mixed slurry.

7. The method according to claim 1, characterized in that, In step (2), the mass ratio of the hard carbon material to the soft carbon material precursor is (50-80):(20-50); And / or, the mass of the vulcanizing agent is 5%-20% of the mass of the soft carbon material precursor; And / or, the mass of the surfactant is 1%-2% of the mass of the solvent; And / or, the vulcanizing agent includes at least one of ammonium sulfate, sodium sulfate, potassium sulfate, ammonium persulfate, sodium persulfate, sodium benzenesulfonate, and ammonium benzenesulfonate; And / or, the surfactant includes a quaternary ammonium salt surfactant, which includes at least one of ammonium dodecylbenzenesulfonate, hexadecyltrimethylammonium bromide, and octadecyltrimethylammonium chloride.

8. The method according to claim 1, characterized in that, In step (1), the first temperature is 1200℃-1400℃, and the carbonization time is 2h-6h; And / or, in step (4), the second temperature is 300℃-400℃ and the stirring time is 30min-60min.

9. The method according to claim 1, characterized in that, In step (5), the particle size D50 of the composite precursor particles is 4µm-10µm.

10. The method according to claim 1, characterized in that, In step (6), the third temperature is 250℃-350℃, and the pre-oxidation time is 3h-9h.

11. The method according to claim 1, characterized in that, In step (7), the fourth temperature is 450℃-600℃, and the pyrolysis reaction time is 1h-3h; And / or, the fifth temperature is 950℃-1200℃, and the carbonization time is 2h-6h.

12. A negative electrode sheet, characterized in that, Includes the negative electrode composite material prepared by the method according to any one of claims 1-11.

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

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

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