Battery-grade graphite, preparation method, application and lithium ion battery

Abstract

The application belongs to the technical field of battery materials, and particularly relates to a battery-grade graphite, a preparation method, application and a lithium ion battery. The preparation method of the battery-grade graphite comprises the following steps: mixing biomass, a boron-based additive and water, and obtaining boron-doped biomass powder through drying; pyrolyzing and carbonizing the boron-doped biomass powder to obtain boron-doped pyrolysis carbon; performing flash Joule heat pyrolysis on the boron-doped pyrolysis carbon to obtain graphitized carbon; and performing acid washing, drying, ball milling and sieving on the graphitized carbon in sequence to obtain the battery-grade graphite. The low-value biomass waste such as lignin is successfully converted into high-performance battery-grade graphite negative electrode material through the simple and efficient process route of "boron-doped carbonization-flash Joule heat pyrolysis-acid washing-ball milling". Not only is the efficient recovery and value-added utilization of waste carbon sources achieved, but also the raw material cost is low, the overall process is simple, and the method has significant industrial application potential and economic benefits.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, specifically relating to a battery-grade graphite, its preparation method, its application, and lithium-ion batteries. Background Technology

[0002] Lithium-ion batteries, as highly efficient energy storage and conversion devices, are widely used in consumer electronics, electric vehicles, and large-scale energy storage power stations. The performance of the anode material in a lithium-ion battery directly determines the battery's overall energy density, power density, and lifespan. Currently, commercially available lithium-ion batteries commonly use graphite-based materials as the anode, primarily due to their abundant sources, high theoretical specific capacity (approximately 372 mAh / g), stable charge-discharge platform, excellent cycle performance, and mature manufacturing processes. Existing methods for preparing graphite anode materials mainly include high-temperature carbonization, chemical vapor deposition, sol-gel methods, and hydrothermal methods. However, existing manufacturing processes generally suffer from high energy consumption, complex processes, high costs, and insufficient material performance.

[0003] Lignin is the second most abundant natural polymer in the world, mainly derived from a large amount of byproducts in the papermaking industry and biomass refining processes. Currently, most lignin is directly incinerated or used for low-value purposes, resulting in resource waste and environmental pressure. Chemically, lignin molecules contain numerous aromatic ring structures composed of phenylpropane units, theoretically making them an ideal precursor for preparing graphite-based carbon materials. Currently, the mainstream method for synthesizing graphite materials using biomass (such as lignin) as a precursor relies on traditional high-temperature heat treatment, but this method generally suffers from high energy consumption and long cycle times. Furthermore, carbon materials prepared directly from lignin precursors via high-temperature pyrolysis typically exhibit a highly disordered amorphous structure with low graphitization and poor crystallinity. This results in significantly lower electronic conductivity than ideal graphite, leading to poor rate performance, low reversible capacity, and insufficient cycle stability when used as a negative electrode material in lithium-ion batteries, severely limiting its application in practical batteries. Summary of the Invention

[0004] The purpose of this invention is to provide a battery-grade graphite, its preparation method, its application, and a lithium-ion battery, thereby overcoming the shortcomings of the prior art. By performing a series of operations such as carbonization, flash Joule pyrolysis, acid washing, and ball milling on boron-doped lignin, the carbon source in the lignin is recovered and converted into battery-grade graphite, realizing the high-value utilization of low-value lignin. Moreover, the overall process is simple, the raw material cost is low, and it has good application prospects.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] In a first aspect, the present invention provides a method for preparing battery-grade graphite, comprising the following steps:

[0007] Boron-doped biomass powder is prepared by mixing biomass, boron-based additives, and water and then drying the mixture.

[0008] Boron-doped biomass powder was pyrolyzed and carbonized to obtain boron-doped pyrolytic carbon.

[0009] Graphitized carbon was prepared by flash Joule heating of boron-doped pyrolytic carbon.

[0010] Graphitized carbon is subjected to acid washing, drying, ball milling and sieving in sequence to obtain battery-grade graphite;

[0011] The voltage range of flash Joule pyrolysis is 150-170 V, the peak temperature is 3000-4000 ℃, the energizing time is 0.5-3 s, and the vacuum degree is 1-5 Pa.

[0012] The biomass used in this invention, such as lignin, contains a large number of oxygen-containing functional groups such as phenolic hydroxyl groups and ether bonds in its molecular structure. These functional groups can interact strongly with boron-based additives such as boric acid in aqueous solutions through hydrogen bonds or coordination bonds. This interaction allows boron to be highly uniformly dispersed among the lignin molecular chains during the solution mixing stage. The introduction of boron into the boron-doped pyrolytic carbon itself can catalyze the graphitization process of carbon, lowering the energy barrier for graphitization. At the same time, the pyrolytic carbon has a certain degree of conductivity, sufficient to initiate the Joule heating pyrolysis process. The instantaneous ultra-high temperature of Joule heating not only transforms disordered carbon into a highly ordered graphite structure instantly, but more importantly, it fixes the uniformly distributed boron atoms in the precursor into the newly formed graphite lattice, mainly forming stable boron-doped graphite. In addition, boron doping can enhance the conductivity of the matrix, optimize the conductive network, and conversely enhance the Joule heating efficiency.

[0013] In some other embodiments, the mass ratio of biomass to boron-based additives is 20:(1-5);

[0014] The biomass is one or more of lignin, cellulose, starch, glucose, or corn stalks; preferably lignin.

[0015] Boron-based additives are one or more of boric acid, elemental boron, boron carbide, and borates;

[0016] The drying temperature is 40-100 ℃, and the drying time is 12-48 h.

[0017] Specifically, the mixing mass ratio of biomass to boron-based additives is 20:1, 20:2, 20:3, 20:4 or 20:5;

[0018] The drying temperature is 40, 60, 80 or 100 ℃, and the drying time is 12, 24 or 48 h.

[0019] To further improve the subsequent pyrolysis and carbonization effect, the dried mixture is also subjected to ball milling and sieving. The ball milling speed is 300-600 rpm, the ball milling time is 1-5 h, and the sieving particle size range is 100-400 mesh.

[0020] In some other embodiments, the pyrolysis atmosphere for pyrolysis carbonization is one or more of nitrogen, argon, helium, and carbon dioxide.

[0021] The pyrolysis carbonization temperature is 700-1000 ℃, the heating rate is 5-20 ℃ / min, the holding time is 0.5-3 h, and the gas flow rate is 50-200 mL / min.

[0022] Specifically, the pyrolysis carbonization temperature is 700, 800, 900, or 1000 °C, the heating rate is 5, 10, 15, or 20 °C / min, the holding time is 0.5, 1, 2, or 3 h, and the gas flow rate is 50, 100, 150, or 200 mL / min. When the pyrolysis temperature and holding time are below the above ranges, or the heating rate is above the above ranges, the volatile matter is not fully released, the electrical conductivity of the pyrolyzed carbon is poor, and the pore structure is underdeveloped. Conversely, the pores of the carbon matrix may collapse, increasing energy consumption.

[0023] Specifically, the voltage range for flash Joule pyrolysis is 150, 160, or 170 V, the peak temperature is 3000, 3200, 3400, 3600, 3800, or 4000 °C, the energizing time is 0.5, 1, 2, or 3 s, and the vacuum level is 1, 2, or 5 Pa. When the voltage, peak temperature, or energizing time exceeds the upper limit, electrode ablation and a broken reaction circuit will occur; conversely, the pyrolysis of carbon will be incomplete, resulting in a lower degree of graphitization of the carbon matrix. The vacuum environment can suppress oxidation reactions and promote carbothermic reduction reactions.

[0024] In some other embodiments, the acid solution used for pickling is one of hydrochloric acid, sulfuric acid, and nitric acid, and the concentration range of the acid solution is 1-3 mol / L; the solid-liquid ratio during pickling is 1:(5-10), and the pickling time is 2-8 h.

[0025] The drying temperature is 80-100℃, and the drying time is 12-24 hours.

[0026] The ball mill speed is 400-600 rpm, and the ball milling time is 1-6 h.

[0027] The particle size range for sieving is 400-600 mesh.

[0028] Specifically, the concentration of the acid solution ranges from 1, 2, or 3 mol / L; the solid-liquid ratio during pickling is 1:5, 1:6, 1:7, 1:8, 1:9, or 1:10; the pickling time is 2, 4, 6, or 8 hours; the drying temperature is 80, 90, or 100°C; the drying time is 12, 15, 18, 20, or 24 hours; the ball milling speed is 400, 500, or 600 rpm; the ball milling time is 1, 2, 4, or 6 hours; and the sieve particle size range is 400, 500, or 600 mesh. At excessively low ball milling speeds and short ball milling times, the particle size cannot meet the electrode coating requirements; while excessively high ball milling speeds and long ball milling times result in overly fine particles, increasing slurry viscosity, reducing coating efficiency, and increasing energy consumption.

[0029] Secondly, the present invention provides battery-grade graphite prepared by the method described in the first aspect.

[0030] In some other embodiments, the specific surface area of ​​battery-grade graphite is 5.80-8.30 m². 2 The graphitization degree is 88.70-92.08%, the coefficient of variation is 0.015-0.05%, the electrical conductivity is 146.43-206.22 S / cm, and the powder compaction density is 1.17-2.37 g / cm³. 3 The resulting graphite is battery-grade and meets the performance standards of commercial graphite.

[0031] In some other embodiments, the battery-grade graphite is boron-doped graphite with a boron doping amount of 0.41%-0.83%.

[0032] Thirdly, the present invention provides the application of the battery-grade graphite described in the second aspect in the negative electrode of a lithium-ion battery.

[0033] Fourthly, this invention provides a lithium-ion battery that uses the battery-grade graphite described in the second aspect as the negative electrode. Using the prepared graphite as the negative electrode of the lithium battery results in high initial charge-discharge coulombic efficiency, high discharge specific capacity, and high cycle stability.

[0034] The beneficial effects of this invention are:

[0035] (1) This invention successfully transforms low-value biomass waste, such as lignin, into high-performance battery-grade graphite anode materials through a simple and efficient process route of "boron-doped carbonization-flash Joule pyrolysis-acid washing-ball milling". This process not only achieves efficient recycling and value-added utilization of waste carbon sources, but also has low raw material costs, simple overall process, and significant potential for industrial application and economic benefits.

[0036] (2) The addition of boron optimizes the current conduction path, ensuring the uniformity of the thermal field distribution during Joule heating and effectively avoiding local overheating and energy concentration. The prepared graphite carbon material has a low coefficient of variation and exhibits excellent homogeneity. By performing simple post-processing (ball milling, sieving) on ​​the solid product, battery-grade graphite with highly uniform composition and structure can be obtained, resulting in good product consistency.

[0037] (3) This invention proposes for the first time a dual-function mechanism of boron in a flash Joule heating system: on the one hand, it enhances the instantaneous current density of the system, increases the peak temperature of Joule heating, and promotes the depth of graphitization reaction, thereby strengthening the Joule heating effect from a physical perspective; on the other hand, by forming a BC3 structure, it guides the directional rearrangement of carbon atoms, significantly reduces the activation energy of the reaction, and catalyzes the graphitization process from a chemical perspective, achieving synergistic promotion of chemical catalysis and physical electrothermal coupling, ultimately resulting in a graphitization degree of g≥90% for the carbon product. This synergistic effect of physical heating and chemical catalysis is the core of achieving rapid and efficient graphitization.

[0038] (4) The lignin-based graphite material prepared by the present invention has achieved the standard of commercial graphite products in terms of key electrochemical performance (such as capacity, coulombic efficiency, cycle stability, etc.) as a negative electrode of lithium-ion batteries, providing a highly competitive new material solution for the energy storage field. Attached Figure Description

[0039] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0040] Figure 1 This is a flowchart of the method for rapidly preparing battery-grade graphite from lignin in Example 1 of the present invention;

[0041] Figure 2 This is a temperature curve distribution diagram of the flash Joule thermal pyrolysis process of Embodiments 1, 4, and 5 of the present invention and Comparative Examples 1-3 and Comparative Example 5;

[0042] Figure 3 The images show the transmission electron microscope (TEM) morphology of graphite prepared in Example 1 and Comparative Example 1 of this invention, where a is the TEM morphology of Example 1 and b is the TEM morphology of Comparative Example 1.

[0043] Figure 4 The high-resolution XPS C1s spectra of graphite prepared in Example 1 of this invention before and after flash evaporation;

[0044] Figure 5 The XRD patterns of graphite prepared in Examples 1-6 of this invention are shown.

[0045] Figure 6 The graphite prepared in Example 1 and Comparative Example 1 of this invention is I D / I G and I 2D / I G Value distribution chart;

[0046] Figure 7 The electrical conductivity curves of the graphite prepared in Examples 1-6 and Comparative Examples 1-8 of this invention are shown.

[0047] Figure 8 The first charge-discharge curves of the lithium-ion batteries prepared in Examples 1-5 of this invention at 0.1C are shown.

[0048] Figure 9 The graphs show the rate performance test results of the lithium-ion batteries prepared in Examples 1-5 and Comparative Examples 1-6 of this invention.

[0049] Figure 10 The graph shows the performance test results of the lithium-ion batteries prepared in Examples 1-5 and Comparative Examples 1-6 of this invention after 200 cycles at 0.5C. Detailed Implementation

[0050] Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be construed as limiting the scope of the invention. Specific conditions not specified in the embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Components whose manufacturers are not specified are all commercially available conventional products.

[0051] Currently, carbon materials prepared directly from biomass such as lignin (which has low impurity content and requires no pretreatment) suffer from insufficient graphitization and poor conductivity, limiting their application in lithium-ion battery anodes. While traditional high-temperature methods can yield highly crystalline materials, their energy consumption and cost are unacceptable. For example, lignin is calcined at 1400°C for 4 hours in a rotary furnace, followed by calcination at 2700°C for 12 hours in a graphitization furnace to obtain graphite anode materials for lithium-ion batteries. This method produces lithium-ion battery graphite anode materials with a high degree of graphitization (90%), but the preparation process is energy-intensive and inefficient. Similarly, using boron-based catalysts to dope carbon paper, the boron-doped impregnated and cured paper is carbonized at 1400°C under a nitrogen atmosphere (1.5 h), and then graphitized at 2100°C under an argon atmosphere (1.5 h) to prepare graphitized carbon paper. The graphitized carbon paper prepared by this method meets the requirements for graphitization degree (g=89.5%), but the preparation process is energy-intensive and inefficient. Moreover, the graphitization degree is only 29.7% under low boron content, which makes it unsuitable for high-end applications.

[0052] While some emerging rapid processing methods (such as catalytic graphitization and flash Joule heating) have shown potential in energy saving, they still have significant shortcomings in terms of the overall high graphitization degree, structural uniformity, and performance reliability of the resulting materials. For example, hydrothermal reaction of Ganoderma lucidum mycelium residue yields mycelium residue hydrated carbon, which is then mixed with cobalt-iron metal salts and subjected to flash Joule heating to obtain cobalt-iron doped mycelium residue graphene. This method can promote the ordering of carbon atoms and the formation of graphite layer structures to a certain extent, but the catalytic effect mainly occurs in local areas, forming graphite layers only around the metal particles, making it difficult to obtain biomass carbon materials with homogeneous structure, high graphitization degree, and excellent purity. Similarly, mixing various heteroatom donor compounds with flash graphene and then using flash Joule heating technology with a voltage range of 80-100V and an energizing time of 6.5s can prepare heteroatom doped graphene. This method is simple, but the resulting graphene has a large interlayer spacing and a low degree of graphitization.

[0053] The existing technologies mentioned above struggle to efficiently, efficiently, and controllably prepare battery-grade graphite using lignin as a carbon source, failing to meet the demands for high-value utilization of lignin and the development of green energy. The solution of this invention achieves a balance between low-temperature efficiency, low energy consumption, and the production of carbon materials with uniform structure and high graphitization. Specific embodiments are described below:

[0054] Example 1

[0055] A battery-grade graphite and its preparation method, the specific process diagram is as follows: Figure 1 As shown, it includes the following steps:

[0056] S1. Weigh a certain amount of lignin powder and mix it with boric acid. Add deionized water to completely dissolve it. After stirring in a magnetic stirrer, dry, grind, and sieve to obtain boron-doped lignin powder. Specifically, mix lignin and boric acid in a ratio of 20:4 (mass ratio), stir in a magnetic stirrer for 1 hour, dry at 60°C for 48 hours, ball mill at 300 rpm for 1 hour, and sieve to 200 mesh.

[0057] S2. Boron-doped lignin powder is placed in a heating furnace for pyrolysis and carbonization to obtain boron-doped pyrolytic carbon. Specifically, a tubular heating furnace is selected, the pyrolysis temperature is 900℃, the heating rate is 5℃ / min, the holding time is 1h, and the nitrogen flow rate is 100mL / min.

[0058] S3. The boron-doped pyrolytic carbon is subjected to flash Joule heating to obtain highly graphitized carbon. Specifically, the Joule heating voltage is 160V, the peak temperature is 3600℃, the energizing time is 1 second, and the vacuum degree is 2Pa.

[0059] S4. The graphite carbon product is subjected to acid washing, filtration, washing, drying, ball milling, and sieving to obtain lithium-ion battery anode material. Specifically, the concentration of hydrochloric acid solution is 1 mol / L; the solid-liquid ratio during acid washing is 1:10, and stirring is carried out at room temperature for 2 h; the drying temperature is 80 ℃, the drying time is 24 h, the ball milling speed is 500 rpm, the ball milling time is 5 h, and the material is sieved to 500 mesh.

[0060] Example 2

[0061] A battery-grade graphite and its preparation method, specifically including the following steps:

[0062] S1. Weigh a certain amount of lignin powder and mix it with boric acid. Add deionized water to completely dissolve it. After stirring in a magnetic stirrer, dry, grind, and sieve to obtain boron-doped lignin powder. Specifically, mix lignin and boric acid in a ratio of 20:4 (mass ratio), stir in a magnetic stirrer for 1 hour, dry at 60°C for 48 hours, ball mill at 300 rpm for 1 hour, and sieve to 200 mesh.

[0063] S2. The above boron-doped lignin powder is placed in a heating furnace for pyrolysis and carbonization to obtain boron-doped pyrolytic carbon. Specifically, a tubular heating furnace is selected, the pyrolysis temperature is 900℃, the heating rate is 5℃ / min, the holding time is 1h, and the nitrogen flow rate is 100mL / min.

[0064] S3. The boron-doped pyrolytic carbon is subjected to flash Joule heating to obtain highly graphitized carbon. Specifically, the Joule heating voltage is 150V, the peak temperature is 3446℃, the energizing time is 1 second, and the vacuum degree is 2Pa.

[0065] S4. The graphite carbon product is subjected to acid washing, filtration, washing, drying, ball milling, and sieving to obtain lithium-ion battery anode material. Specifically, the concentration of hydrochloric acid solution is 1 mol / L; the solid-liquid ratio during acid washing is 1:10, and stirring is carried out at room temperature for 2 h; the drying temperature is 80 ℃, the drying time is 24 h, the ball milling speed is 500 rpm, the ball milling time is 5 h, and the material is sieved to 500 mesh.

[0066] Example 3

[0067] A battery-grade graphite and its preparation method, specifically including the following steps:

[0068] S1. Weigh a certain amount of lignin powder and mix it with boric acid. Add deionized water to completely dissolve it. After stirring in a magnetic stirrer, dry, grind, and sieve to obtain boron-doped lignin powder. Specifically, mix lignin and boric acid in a ratio of 20:4 (mass ratio), stir in a magnetic stirrer for 1 hour, dry at 60°C for 48 hours, ball mill at 300 rpm for 1 hour, and sieve to 200 mesh.

[0069] S2. The above boron-doped lignin powder is placed in a heating furnace for pyrolysis and carbonization to obtain boron-doped pyrolytic carbon. Specifically, a tubular heating furnace is selected, the pyrolysis temperature is 900℃, the heating rate is 5℃ / min, the holding time is 1h, and the nitrogen flow rate is 100mL / min.

[0070] S3. The boron-doped pyrolytic carbon is subjected to flash Joule heating to obtain highly graphitized carbon. Specifically, the Joule heating voltage is 170V, the peak temperature is 3568℃, the energizing time is 1 second, and the vacuum degree is 2Pa.

[0071] S4. The graphite carbon product is subjected to acid washing, filtration, washing, drying, ball milling, and sieving to obtain lithium-ion battery anode material. Specifically, the concentration of hydrochloric acid solution is 1 mol / L; the solid-liquid ratio during acid washing is 1:10, and stirring is carried out at room temperature for 2 h; the drying temperature is 80 ℃, the drying time is 24 h, the ball milling speed is 500 rpm, the ball milling time is 5 h, and the material is sieved to 500 mesh.

[0072] Example 4

[0073] A battery-grade graphite and its preparation method, specifically including the following steps:

[0074] S1. Weigh a certain amount of lignin powder and mix it with boric acid. Add deionized water to completely dissolve it. After stirring in a magnetic stirrer, dry, grind, and sieve to obtain boron-doped lignin powder. Specifically, mix lignin and boric acid in a ratio of 20:1 (mass ratio), stir in a magnetic stirrer for 1 hour, dry at 60℃ for 48 hours, ball mill at 300 rpm for 1 hour, and sieve to 200 mesh.

[0075] S2. The above boron-doped lignin powder is placed in a heating furnace for pyrolysis and carbonization to obtain boron-doped pyrolytic carbon. Specifically, a tubular heating furnace is selected, the pyrolysis temperature is 900℃, the heating rate is 5℃ / min, the holding time is 1h, and the nitrogen flow rate is 100mL / min.

[0076] S3. The boron-doped pyrolytic carbon is subjected to flash Joule heating to obtain highly graphitized carbon. Specifically, the Joule heating voltage is 160V, the peak temperature is 3600℃, the energizing time is 1 second, and the vacuum degree is 2Pa.

[0077] S4. The graphite carbon product is subjected to acid washing, filtration, washing, drying, ball milling, and sieving to obtain lithium-ion battery anode material. Specifically, the concentration of hydrochloric acid solution is 1 mol / L; the solid-liquid ratio during acid washing is 1:10, and stirring is carried out at room temperature for 2 h; the drying temperature is 80 ℃, the drying time is 24 h, the ball milling speed is 500 rpm, the ball milling time is 5 h, and the material is sieved to 500 mesh.

[0078] Example 5

[0079] A battery-grade graphite and its preparation method, specifically including the following steps:

[0080] S1. Weigh a certain amount of lignin powder and mix it with boric acid. Add deionized water to completely dissolve it. After stirring in a magnetic stirrer, dry, grind, and sieve to obtain boron-doped lignin powder. Specifically, mix lignin and boric acid in a ratio of 20:2 (mass ratio), stir in a magnetic stirrer for 1 hour, dry at 60℃ for 48 hours, ball mill at 300 rpm for 1 hour, and sieve to 200 mesh.

[0081] S2. The above boron-doped lignin powder is placed in a heating furnace for pyrolysis and carbonization to obtain boron-doped pyrolytic carbon. Specifically, a tubular heating furnace is selected, the pyrolysis temperature is 900℃, the heating rate is 5℃ / min, the holding time is 1h, and the nitrogen flow rate is 100mL / min.

[0082] S3. The boron-doped pyrolytic carbon is subjected to flash Joule heating to obtain highly graphitized carbon. Specifically, the Joule heating voltage is 160V, the peak temperature is 3600℃, the energizing time is 1 second, and the vacuum degree is 2Pa.

[0083] S4. The graphite carbon product is subjected to acid washing, filtration, washing, drying, ball milling, and sieving to obtain lithium-ion battery anode material. Specifically, the concentration of hydrochloric acid solution is 1 mol / L; the solid-liquid ratio during acid washing is 1:10, and stirring is carried out at room temperature for 2 h; the drying temperature is 80 ℃, the drying time is 24 h, the ball milling speed is 500 rpm, the ball milling time is 5 h, and the material is sieved to 500 mesh.

[0084] Example 6

[0085] A battery-grade graphite and its preparation method, differing from Example 1 in that lignin is replaced in equal amounts with cellulose, starch, glucose, and corn stalks, respectively, specifically including the following steps (taking corn stalks as an example):

[0086] S1. Weigh a certain amount of corn stalk powder and mix it with boric acid. Add deionized water to completely dissolve the powder. After stirring in a magnetic stirrer, dry, grind, and sieve to obtain boron-doped stalk powder. Specifically, mix the stalk powder and boric acid powder in a ratio of 20:4 (mass ratio), stir in a magnetic stirrer for 1 hour, dry at 60℃ for 48 hours, ball mill at 300 rpm for 1 hour, and sieve to 200 mesh.

[0087] S2. Boron-doped straw powder is placed in a heating furnace for pyrolysis and carbonization to obtain boron-doped pyrolytic carbon. Specifically, a tubular heating furnace is selected, with a pyrolysis temperature of 900℃, a heating rate of 5℃ / min, a holding time of 1h, and a nitrogen flow rate of 100mL / min.

[0088] S3. The boron-doped pyrolytic carbon is subjected to flash Joule heating to obtain highly graphitized carbon. Specifically, the Joule heating voltage is 160V, the peak temperature is 3600℃, the energizing time is 1 second, and the vacuum degree is 2Pa.

[0089] S4. The graphite carbon product is subjected to acid washing, filtration, washing, drying, ball milling, and sieving to obtain lithium-ion battery anode material. Specifically, the concentration of hydrochloric acid solution is 1 mol / L; the solid-liquid ratio during acid washing is 1:10, and stirring is carried out at room temperature for 2 h; the drying temperature is 80 ℃, the drying time is 24 h, the ball milling speed is 500 rpm, the ball milling time is 5 h, and the material is sieved to 500 mesh.

[0090] Comparative Example 1

[0091] A battery-grade graphite and its preparation method are disclosed. Unlike Example 1, boron is not added in step S1 of this comparative example. Specifically, the method includes the following steps:

[0092] S1. Weigh a certain amount of lignin powder, without boron adulteration, dry, grind, and sieve to obtain pure lignin powder. Specifically, the drying temperature is 60℃, the drying time is 48 h; the ball milling speed is 300 rpm, the ball milling time is 1 h, and the powder is sieved to 200 mesh.

[0093] S2. The above-mentioned pure lignin powder is placed in a heating furnace for pyrolysis and carbonization to obtain lignin pyrolysis char. Specifically, a tubular heating furnace is selected, the pyrolysis temperature is 900℃, the heating rate is 5℃ / min, the holding time is 1h, and the nitrogen flow rate is 100mL / min.

[0094] S3. The pyrolytic lignin carbon is subjected to flash Joule heating to obtain graphitized carbon. Specifically, the Joule heating voltage is 160V, the peak temperature is 3275℃, the energizing time is 1 second, and the vacuum degree is 2Pa.

[0095] S4. The graphite carbon product is subjected to acid washing, filtration, washing, drying, ball milling, and sieving to obtain lithium-ion battery anode material. Specifically, the concentration of hydrochloric acid solution is 1 mol / L; the solid-liquid ratio during acid washing is 1:10, and stirring is carried out at room temperature for 2 h; the drying temperature is 80℃, the drying time is 24 h, the ball milling speed is 500 rpm, the ball milling time is 5 h, and the material is sieved to 500 mesh.

[0096] Comparative Example 2

[0097] A battery-grade graphite and its preparation method are disclosed. Unlike Example 1, the boron doping method in this comparative example involves pre-carbonization followed by loading. Specifically, the method includes the following steps:

[0098] S1. Weigh a certain amount of lignin powder, without boron adulteration, dry, grind, and sieve to obtain pure lignin powder. Specifically, the drying temperature is 60℃, the drying time is 48 h; the ball milling speed is 300 rpm, the ball milling time is 1 h, and the powder is sieved to 200 mesh.

[0099] S2. The above-mentioned pure lignin powder is placed in a heating furnace for pyrolysis and carbonization to obtain lignin pyrolysis char. Specifically, a tubular heating furnace is selected, the pyrolysis temperature is 900℃, the heating rate is 5℃ / min, the holding time is 1h, and the nitrogen flow rate is 100mL / min.

[0100] S3. Mix lignin pyrolysis char with boric acid, add deionized water to completely dissolve it; stir in a magnetic stirrer, then dry to obtain boron-doped pyrolysis char. Specifically, mix lignin pyrolysis char and boric acid in a ratio of 20:4 (mass ratio).

[0101] S4. The boron-doped pyrolytic carbon is subjected to flash Joule heating to obtain graphitized carbon. Specifically, the Joule heating voltage is 160V, the peak temperature is 3600℃, the energizing time is 1 second, and the vacuum degree is 2Pa.

[0102] S5. The graphite carbon product is subjected to acid washing, filtration, washing, drying, ball milling, and sieving to obtain lithium-ion battery anode material. Specifically, the concentration of hydrochloric acid solution is 1 mol / L; the solid-liquid ratio during acid washing is 1:10, and stirring is carried out at room temperature for 2 h; the drying temperature is 80℃, the drying time is 24 h, the ball milling speed is 500 rpm, the ball milling time is 5 h, and the material is sieved to 500 mesh.

[0103] Comparative Example 3

[0104] A battery-grade graphite and its preparation method, differing from Example 1 in that boron is removed after in-situ doping in this comparative example. Specifically, it includes the following steps:

[0105] S1. Weigh a certain amount of lignin powder and mix it with boric acid. Add deionized water to completely dissolve it. After stirring in a magnetic stirrer, dry, grind, and sieve to obtain boron-doped lignin powder. Specifically, mix lignin and boric acid in a ratio of 20:4 (mass ratio), stir in a magnetic stirrer for 1 hour, dry at 60°C for 48 hours, ball mill at 300 rpm for 1 hour, and sieve to 200 mesh.

[0106] S2. The above boron-doped lignin powder is placed in a heating furnace for pyrolysis and carbonization to obtain boron-doped pyrolytic carbon. Specifically, a tubular heating furnace is selected, the pyrolysis temperature is 900℃, the heating rate is 5℃ / min, the holding time is 1h, and the nitrogen flow rate is 100mL / min.

[0107] S3. The boron-doped pyrolytic carbon is subjected to acid washing (deboronization), filtration, washing, and drying. Specifically, the concentration of the hydrochloric acid solution is 1 mol / L; the solid-liquid ratio during acid washing is 1:10, and stirring is carried out at room temperature for 2 hours; the drying temperature is 80℃, and the drying time is 24 hours.

[0108] S4. The deboronized lignin pyrolysis carbon is subjected to flash Joule heating to obtain graphitized carbon. Specifically, the Joule heating voltage is 160V, the peak temperature is 3378℃, the energizing time is 1 second, and the vacuum degree is 2Pa.

[0109] S5. The graphite carbon product is ball-milled and sieved to obtain the lithium-ion battery anode material. Specifically, the ball milling speed is 500 rpm, the ball milling time is 5 h, and the material is sieved to 500 mesh.

[0110] Comparative Example 4

[0111] A battery-grade graphite and its preparation method are disclosed. Unlike Example 1, the boron addition amount (excess) in this comparative example is not within the set range. Specifically, the method includes the following steps:

[0112] S1. Weigh a certain amount of lignin powder and mix it with boric acid. Add deionized water to completely dissolve it. After stirring in a magnetic stirrer, dry, grind, and sieve to obtain boron-doped lignin powder. Specifically, mix lignin and boric acid in a ratio of 20:6 (mass ratio), stir in a magnetic stirrer for 1 hour, dry at 60°C for 48 hours, ball mill at 300 rpm for 1 hour, and sieve to 200 mesh.

[0113] S2. The above boron-doped lignin powder is placed in a heating furnace for pyrolysis and carbonization to obtain boron-doped pyrolytic carbon. Specifically, a tubular heating furnace is selected, the pyrolysis temperature is 900℃, the heating rate is 5℃ / min, the holding time is 1h, and the nitrogen flow rate is 100mL / min.

[0114] S3. Boron-doped pyrolytic carbon is subjected to flash Joule heating to obtain graphitized carbon. Specifically, the Joule heating voltage is 160V, the peak temperature is 3600℃, the energizing time is 1 second, and the vacuum degree is 2Pa.

[0115] S4. The graphite carbon product is subjected to acid washing, filtration, washing, drying, ball milling, and sieving to obtain lithium-ion battery anode material. Specifically, the concentration of hydrochloric acid solution is 1 mol / L; the solid-liquid ratio during acid washing is 1:10, and stirring is carried out at room temperature for 2 h; the drying temperature is 80 ℃, the drying time is 24 h, the ball milling speed is 500 rpm, the ball milling time is 5 h, and the material is sieved to 500 mesh.

[0116] Comparative Example 5

[0117] A battery-grade graphite and its preparation method differ from Example 1 in that the Joule pyrolysis voltage (too low) in this comparative example is not within the set range. Specifically, it includes the following steps:

[0118] S1. Weigh out lignin powder and mix with boric acid, add deionized water to completely dissolve it; stir in a magnetic stirrer, then dry, grind, and sieve to obtain boron-doped lignin powder. Specifically, mix lignin and boric acid in a ratio of 20:4 (mass ratio), stir in a magnetic stirrer for 1 hour, dry at 60℃ for 48 hours; ball mill at 300 rpm for 1 hour, and sieve to 200 mesh.

[0119] S2. The above boron-doped lignin powder is placed in a heating furnace for pyrolysis and carbonization to obtain boron-doped pyrolytic carbon. Specifically, a tubular heating furnace is selected, the pyrolysis temperature is 900℃, the heating rate is 5℃ / min, the holding time is 1h, and the nitrogen flow rate is 100mL / min.

[0120] S3. Boron-doped pyrolytic carbon is subjected to flash Joule heating to obtain graphitized carbon. Specifically, the Joule heating voltage is 130V, the peak temperature is 3282℃, the energizing time is 1 second, and the vacuum degree is 2Pa.

[0121] S4. The graphite carbon product is subjected to acid washing, filtration, washing, drying, ball milling, and sieving to obtain lithium-ion battery anode material. Specifically, the concentration of hydrochloric acid solution is 1 mol / L; the solid-liquid ratio during acid washing is 1:10, and stirring is carried out at room temperature for 2 h; the drying temperature is 80 ℃, the drying time is 24 h, the ball milling speed is 500 rpm, the ball milling time is 5 h, and the material is sieved to 500 mesh.

[0122] Comparative Example 6

[0123] A battery-grade graphite and its preparation method differ from Example 1 in that the Joule pyrolysis voltage (too high) in this comparative example is not within the set range. Specifically, it includes the following steps:

[0124] S1. Weigh a certain amount of lignin powder and mix it with boric acid. Add deionized water to completely dissolve it. After stirring in a magnetic stirrer, dry, grind, and sieve to obtain boron-doped lignin powder. Specifically, mix lignin and boric acid in a ratio of 20:4 (mass ratio), stir in a magnetic stirrer for 1 hour, dry at 60°C for 48 hours, ball mill at 300 rpm for 1 hour, and sieve to 200 mesh.

[0125] S2. The above boron-doped lignin powder is placed in a heating furnace for pyrolysis and carbonization to obtain boron-doped pyrolytic carbon. Specifically, a tubular heating furnace is selected, the pyrolysis temperature is 900℃, the heating rate is 5℃ / min, the holding time is 1h, and the nitrogen flow rate is 100mL / min.

[0126] S3. Boron-doped pyrolytic carbon is subjected to flash Joule heating to obtain graphitized carbon. Specifically, the Joule heating voltage is 180V, the peak temperature is 3147℃, the energizing time is 1 second, and the vacuum degree is 2Pa.

[0127] S4. The graphite carbon product is subjected to acid washing, filtration, washing, drying, ball milling, and sieving to obtain lithium-ion battery anode material. Specifically, the concentration of hydrochloric acid solution is 1 mol / L; the solid-liquid ratio during acid washing is 1:10, and stirring is carried out at room temperature for 2 h; the drying temperature is 80 ℃, the drying time is 24 h, the ball milling speed is 500 rpm, the ball milling time is 5 h, and the material is sieved to 500 mesh.

[0128] Comparative Example 7

[0129] A battery-grade graphite and its preparation method, differing from Example 1 in that lignin is replaced with bamboo powder in equal amounts in this comparative example, specifically including the following steps:

[0130] S1. Weigh a certain amount of bamboo powder and mix it with boric acid. Add deionized water to completely dissolve the mixture. After stirring in a magnetic stirrer, dry, grind, and sieve to obtain boron-doped bamboo powder. Specifically, mix bamboo powder and boric acid in a ratio of 20:4 (mass ratio), stir in a magnetic stirrer for 1 hour, dry at 60℃ for 48 hours, ball mill at 300 rpm for 1 hour, and sieve to 200 mesh.

[0131] S2. Boron-doped bamboo powder is placed in a heating furnace for pyrolysis and carbonization to obtain boron-doped pyrolytic carbon. Specifically, a tubular heating furnace is selected, with a pyrolysis temperature of 900℃, a heating rate of 5℃ / min, a holding time of 1h, and a nitrogen flow rate of 100mL / min.

[0132] S3. Boron-doped pyrolytic carbon is subjected to flash Joule heating to obtain graphitized carbon. Specifically, the Joule heating voltage is 160V, the peak temperature is 3600℃, the energizing time is 1 second, and the vacuum degree is 2Pa.

[0133] S4. The graphite carbon product is subjected to acid washing, filtration, washing, drying, ball milling, and sieving to obtain lithium-ion battery anode material. Specifically, the concentration of hydrochloric acid solution is 1 mol / L; the solid-liquid ratio during acid washing is 1:10, and stirring is carried out at room temperature for 2 h; the drying temperature is 80 ℃, the drying time is 24 h, the ball milling speed is 500 rpm, the ball milling time is 5 h, and the material is sieved to 500 mesh.

[0134] Comparative Example 8

[0135] A battery-grade graphite and its preparation method, differing from Example 1 in that the comparative example uses indirect heating with carbon paper in the flash Joule thermal pyrolysis process, specifically including the following steps:

[0136] S1. Weigh a certain amount of lignin powder and mix it with boric acid. Add deionized water to completely dissolve it. After stirring in a magnetic stirrer, dry, grind, and sieve to obtain boron-doped lignin powder. Specifically, mix lignin and boric acid in a ratio of 20:4 (mass ratio), stir in a magnetic stirrer for 1 hour, dry at 60°C for 48 hours, ball mill at 300 rpm for 1 hour, and sieve to 200 mesh.

[0137] S2. Boron-doped lignin powder is placed in a heating furnace for pyrolysis and carbonization to obtain boron-doped pyrolytic carbon. Specifically, a tubular heating furnace is selected, the pyrolysis temperature is 900℃, the heating rate is 5℃ / min, the holding time is 1h, and the nitrogen flow rate is 100mL / min.

[0138] S3. The boron-doped pyrolytic carbon is subjected to flash Joule heating (indirect heating) to obtain graphitized carbon. Specifically, the Joule heating voltage is 160V, the peak temperature is 3479℃, the energizing time is 1 second, and the vacuum degree is 2Pa.

[0139] S4. The graphite carbon product is subjected to acid washing, filtration, washing, drying, ball milling, and sieving to obtain lithium-ion battery anode material. Specifically, the concentration of hydrochloric acid solution is 1 mol / L; the solid-liquid ratio during acid washing is 1:10, and stirring is carried out at room temperature for 2 h; the drying temperature is 80 ℃, the drying time is 24 h, the ball milling speed is 500 rpm, the ball milling time is 5 h, and the material is sieved to 500 mesh.

[0140] The performance of samples prepared in the comparative examples and comparative examples was tested, and the specific results are as follows:

[0141] Figure 2 This is a temperature curve distribution diagram of the flash Joule heating pyrolysis process in Embodiments 1, 4, and 5 of the present invention, and Comparative Examples 1-3 and Comparative Example 5. Figure 2 It can be seen that the peak temperature of Examples 1, 4, 5 and Comparative Example 2 all reached 3600℃, which is much higher than that of Comparative Example 1, Comparative Example 3 and Comparative Example 5. This is because the introduction of boron enhances the instantaneous current density of the system, which is beneficial to the ordering of the carbon network.

[0142] Figure 3 The images show the transmission electron microscope (TEM) morphology of graphite prepared in Example 1 and Comparative Example 1 of this invention, where a is the TEM morphology of Example 1 and b is the TEM morphology of Comparative Example 1. Figure 3 It can be seen that in Example 1, the graphene layers exhibit oriented and ordered AB stacking, forming large-scale graphite crystal domains with interlayer spacing close to that of standard graphite. In contrast, Comparative Example 1 shows a disordered, interwoven few-layer graphene structure with a larger interlayer spacing. This indicates that boron doping enhances the graphitization driving force during the carbonization process.

[0143] Figure 4 These are the high-resolution XPS C1s spectra of graphite prepared in Example 1 of this invention before and after flash evaporation. Figure 4 It can be seen that after flash evaporation, the C=C peak is significantly enhanced and the CC peak is weakened, indicating that the sp2 hybridization ratio in the carbon skeleton increases and the graphite sheet structure grows and diffuses. The intensity of the OC=O and CO / BO peaks decreases, indicating that the instantaneous high temperature of flash evaporation leads to dehydroxylation and decarboxylation reactions. The formation of BC bonds indicates that boron atoms are successfully incorporated into the carbon network, which changes the charge distribution, lowers the energy barrier for structural rearrangement, and promotes graphitization.

[0144] Figure 5 The images show the XRD patterns of the graphite prepared in Examples 1-6. Figure 5 It was found that all samples exhibited diffraction peaks around 26.5°, corresponding to the 002 crystal plane of graphitic carbon. With increasing boron content (Examples 1, 4, and 5), the diffraction peak intensity increased and became sharper. At the same boron content (Examples 1, 2, and 3), with increasing voltage, the diffraction peak intensity first increased and then decreased, reaching a maximum at 160V, with a graphitization degree as high as 92.82%.

[0145] Figure 6 The image shows the ID / IG and I2D / IG value distributions of the graphite prepared in Example 1 and Comparative Example 1. Figure 6 It can be seen that the ID / IG and I2D / IG point distributions in Example 1 are more concentrated, indicating that the overall boron doping defect density is reduced and the distribution is more uniform. This is because the high temperature increases the current density, accelerates the growth of graphite structure, and successfully induces structural homogenization.

[0146] Figure 7 The graphs show the electrical conductivity of the graphite prepared in Examples 1-6 and Comparative Examples 1-8. Figure 7 It can be seen that the conductivity of Examples 1-6 is significantly higher than that of Comparative Examples 1-8. Under the same operating conditions, with the increase of boron addition (Examples 1, 4, and 5), the conductivity of boron-doped graphite carbon significantly increases, reaching a maximum value in Example 1 (206.22 S / cm). Further addition of boron actually decreases the conductivity (Comparative Example 4). This indicates that the appropriate introduction of boron optimizes electron migration through the π-π interactions between the ordered stacked graphene layers, thus improving conductivity; while excessive boron addition leads to lattice distortion and defect scattering of charge carriers, resulting in a decrease in conductivity.

[0147] Figure 8 The graphs show the initial charge-discharge curves of the lithium-ion batteries prepared in Examples 1-5 at 0.1C. Figure 8 It can be seen that as the amount of boron added increases (Examples 1, 4 and 5), the capacity is significantly improved, and all meet the battery-grade graphite (≥300 mAh / g) standard.

[0148] Figure 9 The graphs show the rate performance test results of the lithium-ion batteries prepared in Examples 1-5 and Comparative Examples 1-6. Figure 9 It can be seen that the discharge specific capacity of Examples 1-5 is significantly higher than that of Comparative Examples 1-6. With increasing boron addition (Examples 1, 4, and 5), the discharge specific capacity increases, reaching its maximum in Example 1. This indicates that boron doping can reduce the resistivity of carbon materials, accelerate electron transport, allow more active sites to participate in lithium insertion / extraction reactions, and reduce capacity loss caused by kinetic limitations. Furthermore, moderate graphitization forms a graphite structure with certain interlayer spacing and structural defects. These structural defects and appropriate interlayer spacing provide more sites for Li+ insertion, thereby improving the specific capacity of the material.

[0149] Figure 10 The graphs show the performance of the lithium-ion batteries prepared in Examples 1-5 and Comparative Examples 1-6 after 200 cycles at 0.5C. Figure 10 It can be seen that the capacity retention rate of Examples 1-5 is almost unaffected after 200 cycles, while that of Comparative Examples 1-6 is significantly reduced. This shows that the performance of graphite carbon directly affects the battery performance.

[0150] Table 1 lists the performance standards of petroleum coke in artificial graphite under the standard GB / T 24533-2019.

[0151] Table 1 Performance Standards of Petroleum Ordinary Coke

[0152]

[0153] The performance data of Examples 1-5 and Comparative Examples 1-6 are shown in Table 2 below.

[0154] Table 2 Performance Data

[0155]

[0156] In Table 2, the heat generation efficiency = actual Joule heat generated / total energy input to the system × 100%; the coefficient of variation = standard deviation / (mean of ID / IG).

[0157] As shown in Table 2, the increased graphitization degree in this invention is the result of the synergistic effect of "boron chemical catalysis" and "peak temperature physical enhancement": Boron catalysis is the "core driving force" for the leap in graphitization degree. The peak temperatures of Comparative Example 1 (undoped, 3275℃) and Comparative Example 5 (doped, 3282℃) differ by only 7℃, but the graphitization degree increases from 29.62% to 77.52%. Boron guides carbon atom rearrangement by forming a BC3 structure, reducing the activation energy of the reaction and solving the bottleneck of "high temperature and low efficiency" in traditional non-catalyst systems. Peak temperature is an "auxiliary enhancing factor" for improving graphitization degree. The peak temperature increases from 3282℃ (Comparative Example 5) to 3600℃ (Example 1), and the calculated heat generation efficiency increases from 64.28% to 96.27%. This further reduces defects and interlayer spacing, increasing the graphitization degree from 77.52% to 92.08%, achieving a performance upgrade from "qualified" to "high-quality".

[0158] The performance data for Example 6 are shown in Table 3 below.

[0159] Table 3 Performance of Example 6

[0160]

[0161] This invention utilizes a series of processes, including carbonization of boron-doped biomass such as lignin, flash Joule heating pyrolysis, acid washing, and ball milling, to recover the carbon source from lignin and convert it into battery-grade graphite, achieving the performance standards of petroleum coke. This enables the high-value utilization of low-value lignin, and the overall process is simple with low raw material costs, showing promising application prospects.

[0162] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing battery-grade graphite, characterized in that, Includes the following steps: Boron-doped biomass powder is prepared by mixing biomass, boron-based additives, and water and then drying the mixture. Boron-doped biomass powder was pyrolyzed and carbonized to obtain boron-doped pyrolytic carbon. Graphitized carbon was prepared by flash Joule heating of boron-doped pyrolytic carbon. Graphitized carbon is subjected to acid washing, drying, ball milling and sieving in sequence to obtain battery-grade graphite; The voltage range of the flash Joule pyrolysis is 150-170 V, the peak temperature is 3400-4000 ℃, the energizing time is 0.5-3 s, and the vacuum degree is 1-5 Pa. The mass ratio of the biomass to the boron-based additive is 20:(2-5); The flash Joule pyrolysis is an indirect heating process; The biomass is one or more of lignin, cellulose, starch, glucose, or straw; The boron-based additive is one or more of boric acid, elemental boron, boron carbide, and borate.

2. The method for preparing battery-grade graphite according to claim 1, characterized in that, The drying temperature is 40-100℃, and the drying time is 12-48 h.

3. The method for preparing battery-grade graphite according to claim 1, characterized in that, The pyrolysis atmosphere for pyrolysis carbonization is one or more of nitrogen, argon, helium, and carbon dioxide; The pyrolysis carbonization temperature is 700-1000 ℃, the heating rate is 5-20 ℃ / min, the holding time is 0.5-3 h, and the gas flow rate is 50-200 mL / min.

4. The method for preparing battery-grade graphite according to claim 1, characterized in that, The acid solution used for pickling is one of hydrochloric acid, sulfuric acid, and nitric acid, and the concentration range of the acid solution is 1-3 mol / L; the solid-liquid ratio during pickling is 1:(5-10), and the pickling time is 2-8 h; The drying temperature is 80-100℃, and the drying time is 12-24 h; The ball mill rotates at 400-600 rpm and the milling time is 1-6 h. The sieving process involves a particle size range of 400-600 mesh.

5. Battery-grade graphite prepared by the method of any one of claims 1-4.

6. The battery-grade graphite according to claim 5, characterized in that, The specific surface area of ​​the battery-grade graphite is 5.80-8.30 m². 2 The graphitization degree is 88.70-92.08%, the coefficient of variation is 0.015-0.05%, the electrical conductivity is 146.43-206.22 S / cm, and the powder compaction density is 1.17-2.37 g / cm³. 3 .

7. The battery-grade graphite according to claim 5, characterized in that, The battery-grade graphite is boron-doped graphite with a boron doping content of 0.41%-0.83%.

8. The application of battery-grade graphite as described in any one of claims 5-7 in the negative electrode of a lithium-ion battery.

9. A lithium-ion battery, characterized in that, The battery-grade graphite described in any one of claims 6-7 is used as the negative electrode.

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