WO2024255930A1 - 一种改性天然石墨的制备方法、石墨材料及电芯 - Google Patents

一种改性天然石墨的制备方法、石墨材料及电芯 Download PDF

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WO2024255930A1
WO2024255930A1 PCT/CN2024/112609 CN2024112609W WO2024255930A1 WO 2024255930 A1 WO2024255930 A1 WO 2024255930A1 CN 2024112609 W CN2024112609 W CN 2024112609W WO 2024255930 A1 WO2024255930 A1 WO 2024255930A1
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natural graphite
graphite
preparation
treatment
heating furnace
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English (en)
French (fr)
Inventor
王斌
刘倩
利凯文
朱家乐
吴伟
张祖豪
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Eve Energy Co Ltd
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Eve Energy Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/20—Graphite
    • C01B32/21—After-treatment
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/04—Processes of manufacture in general
    • H01M4/0471—Processes of manufacture in general involving thermal treatment, e.g. firing, sintering, backing particulate active material, thermal decomposition, pyrolysis
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application relates to the technical field of graphite preparation, and in particular to a preparation method of modified natural graphite, a graphite material and a battery cell.
  • natural flake graphite Due to its material properties, natural flake graphite has more defects and impurities than artificial graphite. These impurities and defects are more likely to react with the electrolyte during high-temperature storage, consume the electrolyte, generate a large amount of by-products, and deposit on the surface of the negative electrode graphite, causing battery performance degradation.
  • natural graphite In order for natural graphite to be better used in the field of lithium batteries, it must be purified, coated, modified, and graphitized. At present, except for natural graphite that has fewer defects and impurities after graphitization, graphite treated by other treatment methods still has a large gap with artificial graphite.
  • Graphitization treatment can reduce the overall defect degree of the material, and high-temperature treatment can also burn off most of the impurities.
  • the application of natural graphite is limited and it has no competitive advantage over artificial graphite.
  • the present application provides a preparation method of modified natural graphite, a graphite material and a battery cell, which do not need to waste a lot of energy for graphitization treatment, and can effectively improve the high-temperature storage performance of natural graphite through carbonization + oxidation treatment.
  • the present application provides a method for preparing modified natural graphite, the preparation method comprising:
  • the natural graphite is subjected to carbonization treatment and oxidation treatment in sequence to obtain modified natural graphite.
  • the oxidation treatment comprises: sending natural graphite into a heating furnace for heating treatment, and simultaneously introducing reaction gas into the heating furnace for modification.
  • the present application provides a graphite material, wherein the graphite material is prepared by the preparation method described in the first aspect.
  • the present application provides a battery cell, wherein the battery cell comprises the graphite material described in the second aspect.
  • the present application provides a method for preparing modified natural graphite, a graphite material and a battery cell, which have simple processes and low costs.
  • the natural graphite is modified by carbonization + oxidation treatment, and oxygen-containing functional groups are added to the graphite surface.
  • -COOLi, -OLi or -C-OLi is formed during electrode formation, so that a structural connection is established between the lithium salt component and the boundary carbon atoms at the graphite level, greatly enhancing the high-temperature stability; at the same time, the oxidation treatment is also beneficial to remove carbon chains, carbon free atoms and other heteroatoms (defects) in the graphite, reduce the overall defects of the graphite, and help reduce the degree of side reactions during high-temperature storage, effectively improving the high-temperature storage performance of natural graphite.
  • FIG. 1 is a Raman spectrum of the modified natural graphite obtained in Example 1, Comparative Example 1 and Comparative Example 2 of the present application.
  • the present application provides a method for preparing modified natural graphite, the preparation method comprising:
  • the natural graphite is subjected to carbonization treatment and oxidation treatment in sequence to obtain modified natural graphite.
  • the oxidation treatment comprises: sending natural graphite into a heating furnace for heating treatment, and simultaneously introducing reaction gas into the heating furnace for modification.
  • the preparation method of modified natural graphite provided in the present application has a simple process and low cost.
  • oxygen-containing functional groups form -COOLi, -OLi or -C-OLi during electrode formation, so that a structural connection is established between the lithium salt component and the boundary carbon atoms at the graphite level, greatly enhancing the high-temperature stability; at the same time, the oxidation treatment is also beneficial to remove carbon chains, carbon free atoms and other heteroatoms (defects) in the graphite, reduce the overall defects of the graphite, and help reduce the degree of side reactions during high-temperature storage, effectively improving the high-temperature storage performance of natural graphite.
  • the temperature of the heat treatment is 350 ⁇ 800°C, for example, it can be 350°C, 380°C, 400°C, 430°C, 450°C, 480°C, 500°C, 550°C, 580°C, 600°C, 650°C, 680°C, 700°C, 720°C, 750°C, 780°C or 800°C, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.
  • the present application controls the heating temperature of the oxidation treatment within the above range. Too high a temperature may easily cause safety accidents and damage to operators and equipment, etc.; too low a temperature may increase the oxidation time and easily cause incomplete oxidation.
  • the heating treatment time is 1 to 5 hours, for example, it can be 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours or 5 hours, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.
  • the present application controls the heating treatment time within the above range.
  • the heating treatment time is too long, the production efficiency will be reduced; when the heating treatment time is too short, the defect of insufficient oxidation will easily occur.
  • the reaction gas includes any one of nitrogen, chlorine, oxygen, air and carbon dioxide, or a combination of at least two of them.
  • the preparation method further includes: adjusting the introduction rate of the reaction gas by adjusting the pressure in the heating furnace.
  • the pressure in the heating furnace is 3 ⁇ 8kPa, for example, it can be 3kPa, 3.5kPa, 4kPa, 4.5kPa, 5kPa, 5.5kPa, 6kPa, 6.5kPa, 7kPa, 7.5kPa or 8kPa, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.
  • the present application adjusts the pressure in the heating furnace so that the introduction rate of the reaction gas is maintained within a suitable range, thereby avoiding waste of resources due to excessively high introduction rate and preventing insufficient oxidation due to excessively low introduction rate.
  • the heating furnace includes a horizontal carbonization furnace.
  • the natural graphite is fed into a heating furnace to be heated, and after the temperature is raised to the heating treatment temperature, a reaction gas is introduced into the heating furnace to perform modification.
  • the temperature of the carbonization treatment is 1000 ⁇ 1200°C, for example, it can be 1000°C, 1020°C, 1050°C, 1080°C, 1100°C, 1120°C, 1140°C, 1150°C, 1180°C or 1200°C, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.
  • the carbonization treatment time is 3 to 10 hours, for example, it can be 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 8 hours, 9 hours, 9.5 hours or 10 hours, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.
  • the carbonization treatment is performed under a protective atmosphere.
  • the protective atmosphere in this application includes but is not limited to nitrogen.
  • the preparation method further includes: sequentially shaping, crushing and purifying the flake graphite and/or spherical graphite to obtain the natural graphite.
  • the purification treatment includes acid-base purification or hydrofluoric acid purification.
  • the particle size D50 of the natural graphite is 6-10 ⁇ m, for example, 6 ⁇ m, 6.5 ⁇ m, 7 ⁇ m, 7.5 ⁇ m, 8 ⁇ m, 8.5 ⁇ m, 9 ⁇ m, 9.5 ⁇ m or 10 ⁇ m, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.
  • the fixed carbon content of the natural graphite is 99.6-99.9%, for example, it can be 99.6%, 99.62%, 99.65%, 99.7%, 99.73%, 99.75%, 99.78%, 99.8%, 99.83%, 99.85%, 99.88% or 99.9%, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.
  • the hydrofluoric acid purification method includes: soaking treatment with a mixed acid of HCl and HF, the volume ratio of HCl to HF in the mixed acid is (0.9 ⁇ 1.3):1, the temperature of the mixed acid is 60 ⁇ 75°C, and the soaking treatment time is 12 ⁇ 24h.
  • the acid-base purification comprises: immersion treatment using an acid solution, an alkali solution and an oxidant.
  • the acid solution comprises any one of sulfuric acid, hydrochloric acid, hydrofluoric acid and phosphoric acid or a combination of at least two;
  • the alkali solution comprises any one of sodium hydroxide, potassium hydroxide and calcium hydroxide or a combination of at least two;
  • the oxidant comprises any one of hydrogen peroxide, peracetic acid, chlorine, chlorine dioxide and perchloric acid or a combination of at least two, and the immersion treatment time is 10 to 18 hours.
  • the preparation method further includes: cooling to room temperature after completing the oxidation treatment, and screening and demagnetizing the natural graphite in sequence to obtain the modified natural graphite.
  • the preparation method of modified natural graphite provided in the present application specifically comprises the following steps:
  • step S2 carbonizing the natural graphite in step S1 under a protective atmosphere, wherein the temperature of the carbonization treatment is 1000-1200° C. and the time is 3-10 hours;
  • the flake graphite and/or spherical graphite is soaked in a mixed acid of HCl and HF for 12 to 24 hours, wherein the volume ratio of HCl to HF in the mixed acid is (0.9 to 1.3):1, and the temperature of the mixed acid is 60 to 75°C.
  • the flake graphite and/or spherical graphite is impregnated for 10 to 18 hours using an acid solution, an alkaline solution and an oxidant, wherein the acid solution comprises any one of sulfuric acid, hydrochloric acid, hydrofluoric acid and phosphoric acid or a combination of at least two thereof; the alkaline solution comprises any one of sodium hydroxide, potassium hydroxide and calcium hydroxide or a combination of at least two thereof; and the oxidant comprises any one of hydrogen peroxide, peracetic acid, chlorine, chlorine dioxide and perchloric acid or a combination of at least two thereof.
  • This application modifies natural graphite by carbonization + oxidation treatment to increase the number of oxygen-containing functional groups on the graphite surface, thereby increasing the bonding force with the SEI (Solid Electrolyte Interface) membrane, and enhancing the stability of the SEI membrane during high-temperature storage.
  • the defect degree and oxygen atom content of the graphite are regulated by changing the type of gas introduced, the gas rate, the oxidation temperature and the oxidation time. Compared with traditional graphitization treatment methods, this application greatly saves preparation costs and reduces carbon emissions.
  • the present application provides a graphite material, wherein the graphite material is prepared by the preparation method described in the first aspect.
  • the total number of atoms on the surface of the graphite material is 100%, and the oxygen atom content is 2.85 ⁇ 4.53%, for example, it can be 2.85%, 2.86%, 2.90%, 2.92%, 2.95%, 2.96%, 3%, 3.22%, 3.47%, 3.50%, 3.60%, 3.70%, 3.80%, 3.83%, 4%, 4.10%, 4.12%, 4.23%, 4.30%, 4.42%, 4.5% or 4.53%, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.
  • the present application provides a battery cell, wherein the battery cell comprises the graphite material described in the second aspect.
  • the surface of the graphite material has a large number of oxygen-containing functional groups, which form -COOLi, -OLi, and -C-OLi during electrode formation, so that the lithium salt component of the SEI film on the electrode surface establishes a connection with the boundary carbon atoms on the graphite surface, increases the bonding force with the SEI film, and greatly enhances the stability of the SEI film.
  • This embodiment provides a method for preparing modified natural graphite, which specifically comprises the following steps:
  • the flake graphite is shaped, crushed and purified in turn to obtain natural graphite with a particle size D50 of 8 ⁇ m, wherein the purification treatment adopts acid and alkali purification;
  • step (1) carbonizing the natural graphite in step (1) under a protective atmosphere at a temperature of 1100° C. for 6 h;
  • the natural graphite is cooled to room temperature, and the natural graphite is screened and demagnetized in turn to obtain modified natural graphite.
  • This embodiment provides a method for preparing modified natural graphite, which specifically comprises the following steps:
  • the flake graphite is shaped, crushed and purified in turn to obtain natural graphite with a particle size D50 of 6 ⁇ m, wherein the purification process is performed using hydrofluoric acid;
  • step (1) carbonizing the natural graphite in step (1) under a protective atmosphere at a temperature of 1150° C. for 4 h;
  • the natural graphite is cooled to room temperature, and the natural graphite is screened and demagnetized in turn to obtain modified natural graphite.
  • This embodiment provides a method for preparing modified natural graphite, which specifically comprises the following steps:
  • the flake graphite is shaped, crushed and purified in sequence to obtain natural graphite with a particle size D50 of 10 ⁇ m, wherein the purification process is performed using hydrofluoric acid;
  • step (1) carbonizing the natural graphite in step (1) under a protective atmosphere at a temperature of 1200° C. for 8 h;
  • the natural graphite is cooled to room temperature, and the natural graphite is screened and demagnetized in turn to obtain modified natural graphite.
  • This embodiment provides a method for preparing modified natural graphite, which specifically comprises the following steps:
  • the spherical graphite is shaped, crushed and purified in sequence to obtain natural graphite with a particle size D50 of 7 ⁇ m, wherein the purification process is performed using hydrofluoric acid;
  • step (1) carbonizing the natural graphite in step (1) under a protective atmosphere at a temperature of 1050° C. for 10 h;
  • the natural graphite is cooled to room temperature, and the natural graphite is screened and demagnetized in turn to obtain modified natural graphite.
  • This embodiment provides a method for preparing modified natural graphite, which specifically comprises the following steps:
  • the mixed raw materials of flake graphite and spherical graphite are shaped, crushed and purified in sequence to obtain natural graphite with a particle size D50 of 9 ⁇ m, wherein the purification process is performed using hydrofluoric acid;
  • step (1) carbonizing the natural graphite in step (1) under a protective atmosphere at a temperature of 1200° C. for 3 h;
  • the natural graphite is cooled to room temperature, and the natural graphite is screened and demagnetized in turn to obtain modified natural graphite.
  • This embodiment provides a method for preparing modified natural graphite, which specifically comprises the following steps:
  • the flake graphite is subjected to shaping, crushing and purification treatment in sequence to obtain natural graphite with a particle size D50 of 8 ⁇ m, wherein the purification treatment adopts hydrofluoric acid purification;
  • step (1) carbonizing the natural graphite in step (1) under a protective atmosphere at a temperature of 1150° C. for 5 h;
  • the natural graphite is cooled to room temperature, and the natural graphite is screened and demagnetized in turn to obtain modified natural graphite.
  • This embodiment provides a method for preparing modified natural graphite, which differs from Embodiment 1 in that the reaction gas used in step (3) is oxygen, and the remaining operating steps and process parameters are the same as those in Embodiment 1.
  • This embodiment provides a method for preparing modified natural graphite.
  • the difference from the embodiment 1 is that the reaction gas used in step (3) is CO 2 , and the remaining operation steps and process parameters are the same as those in the embodiment 1.
  • This embodiment provides a method for preparing modified natural graphite, which differs from Embodiment 1 in that: in step (3), the heating furnace is heated to 300° C. for modification, and the remaining operating steps and process parameters are the same as those in Embodiment 1.
  • This embodiment provides a method for preparing modified natural graphite, which differs from Embodiment 1 in that: in step (3), the heating furnace is heated to 850° C. for modification, and the remaining operating steps and process parameters are the same as those in Embodiment 1.
  • This embodiment provides a method for preparing modified natural graphite, which differs from Embodiment 1 in that the pressure in the heating furnace in step (3) is 2 kPa, and the remaining operating steps and process parameters are the same as those in Embodiment 1.
  • This embodiment provides a method for preparing modified natural graphite, which differs from Embodiment 1 in that the pressure in the heating furnace in step (3) is 9 kPa, and the remaining operating steps and process parameters are the same as those in Embodiment 1.
  • This embodiment provides a method for preparing modified natural graphite, which differs from Embodiment 1 in that the heating treatment in step (3) is for 0.5 h, and the remaining operating steps and process parameters are the same as those in Embodiment 1.
  • This embodiment provides a method for preparing modified natural graphite, which differs from Embodiment 1 in that the heating treatment in step (3) is for 5.5 h, and the remaining operating steps and process parameters are the same as those in Embodiment 1.
  • This comparative example provides a method for preparing modified natural graphite, which specifically comprises the following steps:
  • the flake graphite is shaped, crushed and purified in turn to obtain natural graphite with a particle size D50 of 8 ⁇ m, wherein the purification treatment adopts acid and alkali purification;
  • step (1) carbonizing the natural graphite in step (1) under a protective atmosphere at a temperature of 1100° C. for 6 h;
  • This comparative example provides a method for preparing modified natural graphite, which specifically comprises the following steps:
  • the flake graphite is shaped, crushed and purified in turn to obtain natural graphite with a particle size D50 of 8 ⁇ m, wherein the purification treatment adopts acid and alkali purification;
  • step (1) graphitizing the natural graphite in step (1) under a protective atmosphere at a temperature of 2800° C. for 36 hours;
  • the present application tests the surface oxygen atom content (measured by X-ray photoelectron spectroscopy test method XPS) and defect degree (measured by Raman spectroscopy test method) of the modified natural graphite obtained in Examples 1 to 14 and Comparative Examples 1 and 2, and the results are shown in Table 1 and Figure 1.
  • the positive electrode of the battery cell uses a nickel-cobalt-manganese ternary positive electrode material
  • the negative electrode is made of the above-mentioned modified natural graphite
  • the separator is an alumina ceramic separator.
  • the positive electrode sheet, separator and negative electrode sheet are placed in order from top to bottom, assembled by winding, and then injected with electrolyte, packaged and aged to obtain a battery cell.
  • Example 7 Compared with Example 1 which uses a mixed gas as a reaction gas, the oxygen atom content on the surface of the modified natural graphite in Examples 7 and 8 is reduced. This is mainly because Examples 7 and 8 only use a single reaction gas to modify the natural graphite, which weakens the oxidation effect and reduces the generation of oxygen-containing functional groups.
  • Example 10 Compared with Example 1, since the oxidation temperature in Example 9 is too low, the oxidation is incomplete, which reduces the surface oxygen atom content, thereby causing the capacity retention rate of the battery cell to decrease; in addition, the oxygen atom content on the surface of the modified natural graphite in Example 10 is slightly different from that in Example 1, but the production cost increases due to the increase in the oxidation temperature.
  • Example 1 It is not difficult to see from Example 1, Example 11 and Example 12 that when the pressure in the heating furnace is too high or too low, it will affect the oxidation effect, resulting in a decrease in the oxygen atom content on the graphite surface, thereby causing the capacity retention rate of the battery cell at high temperature to be reduced.
  • Example 13 has a too short heating treatment time, resulting in only partial oxidation of the natural graphite, reducing the oxygen atom content on the surface of the material, resulting in reduced high-temperature performance of the battery cell; and Example 14 has a too long heating time, which increases the production cost.
  • Example 1 It can be seen from Example 1 and Comparative Example 1 that the oxygen atom content on the surface of the modified natural graphite in Example 1 is higher, the surface defect degree is lower, and the capacity retention rate and capacity recovery rate of the battery cell are increased. This is mainly because Example 1 oxidizes the carbonized natural graphite to increase the number of oxygen-containing functional groups on the graphite surface. During the battery cell formation stage, a connection can be formed between the graphite and the lithium salt, thereby improving the stability of the battery cell at high temperature and effectively reducing the surface defect degree of the graphite.
  • Example 1 adopts a modification method of carbonization + oxidation treatment. Compared with the high-temperature graphitization method adopted in Comparative Example 2, it can increase the oxygen atom content on the graphite surface and reduce the surface defects.
  • the heating treatment temperature is much lower than the graphitization temperature, which greatly reduces the production cost.
  • the present application can obtain natural graphite with excellent high-temperature storage performance through carbonization + oxidation treatment without using a high-energy graphitization process, and optimize the high-temperature storage performance of natural graphite by adjusting parameters such as the air flow rate, gas type, temperature, and time.

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Abstract

本申请提供了一种改性天然石墨的制备方法、石墨材料及电芯，所述的制备方法包括：对天然石墨依次进行碳化处理与氧化处理，得到改性天然石墨；所述氧化处理包括：将天然石墨送入加热炉内进行加热处理，同时向加热炉内通入反应气体进行改性。本申请通过碳化+氧化处理即可有效地提升天然石墨高温存储性能。

Description

一种改性天然石墨的制备方法、石墨材料及电芯
本申请要求在2023年12月13日提交中国专利局、申请号为2023117200502的中国专利申请的优先权，以上申请的全部内容通过引用结合在本申请中。
技术领域
本申请涉及石墨制备技术领域，具体涉及一种改性天然石墨的制备方法、石墨材料及电芯。
 背景技术
由于锂离子电池的快速发展，天然石墨作为一种价格低廉的原料被大量使用，但是天然石墨中存在的大量杂质和缺陷限制了其在锂离子电池负极的应用。为满足不同应用场景的要求，锂电池的高温存储性能显得愈加重要，而且考虑到产品开发的时效性，一般使用高温加速衰减来模拟电池长期使用寿命，因此提升锂电池的高温存储性能至关重要。
天然鳞片石墨因其材料特性相比人造石墨存在更多的缺陷和杂质，这些杂质和缺陷在高温存储过程中较易与电解液发生副反应，消耗电解液，且生成大量副产物，并沉积在负极石墨表面，造成电池性能衰减。为了天然石墨能够更好地应用在锂电池领域，必须对天然石墨进行提纯、包覆、改性、石墨化等工序。目前，除了经过石墨化处理的天然石墨具有较少的缺陷和杂质，采用其余处理方式处理后的石墨仍与人造石墨存在较大的差距。
 技术问题
石墨化处理能减少材料整体的缺陷度，高温处理也能烧掉绝大部分杂质，但由于石墨化具有相对较长的处理周期及高昂的成本，使得天然石墨的应用受到限制，相对于人造石墨并无竞争优势。
本申请提供一种改性天然石墨的制备方法、石墨材料及电芯，无需浪费大量能源进行石墨化处理，通过碳化+氧化处理即可有效地提升天然石墨高温存储性能。
 技术解决方案
第一方面，本申请提供了一种改性天然石墨的制备方法，所述的制备方法包括：
对天然石墨依次进行碳化处理与氧化处理，得到改性天然石墨。
所述氧化处理包括：将天然石墨送入加热炉内进行加热处理，同时向加热炉内通入反应气体进行改性。
第二方面，本申请提供了一种石墨材料，所述的石墨材料采用第一方面所述的制备方法制得。
第三方面，本申请提供了一种电芯，所述的电芯包括第二方面所述的石墨材料。
 有益效果
与相关技术相比，本申请的有益效果为：
本申请提供的一种改性天然石墨的制备方法、石墨材料及电芯，工艺简单，成本较低，采用碳化+氧化处理的方式对天然石墨进行改性，增加了石墨表面含氧官能团，在电极化成时形成-COOLi、-OLi或-C-OLi，使得锂盐成分与石墨层面的边界碳原子之间建立结构上的联系，大大增强了高温稳定性；同时，氧化处理还有利于去除石墨中的碳链、碳自由和其他杂原子（缺陷），减少石墨整体缺陷，并有助于降低高温存储过程中副反应的程度，有效地提升天然石墨高温存储性能。
在阅读并理解了附图和详细描述后，可以明白其他方面。
 附图说明
图1为本申请中实施例1、对比例1与对比例2制得的改性天然石墨的拉曼光谱图。
 本发明的实施方式
第一方面，本申请提供了一种改性天然石墨的制备方法，所述的制备方法包括：
对天然石墨依次进行碳化处理与氧化处理，得到改性天然石墨。
所述氧化处理包括：将天然石墨送入加热炉内进行加热处理，同时向加热炉内通入反应气体进行改性。
本申请提供的改性天然石墨的制备方法工艺简单，成本较低，采用碳化+氧化处理的方式对天然石墨进行改性，增加了石墨表面含氧官能团（-COOH、-OH、-C=O等），这些含氧官能团在电极化成时形成-COOLi、-OLi或-C-OLi，使得锂盐成分与石墨层面的边界碳原子之间建立结构上的联系，大大增强高温稳定性；同时，氧化处理还有利于去除石墨中的碳链、碳自由和其他杂原子（缺陷），减少石墨整体缺陷，并有助于降低高温存储过程中副反应的程度，有效地提升天然石墨的高温存储性能。
作为本申请一个可选技术方案，所述加热处理的温度为350~800℃，例如可以是350℃、380℃、400℃、430℃、450℃、480℃、500℃、550℃、580℃、600℃、650℃、680℃、700℃、720℃、750℃、780℃或800℃，但并不仅限于所列举的数值，该数值范围内其他未列举的数值同样适用。
本申请将氧化处理的加热温度控制在上述范围内，温度过高容易引起安全事故，对操作人员与设备等造成损害；温度过低使得氧化时间增加，容易造成氧化不充分。
可选地，所述加热处理的时间为1~5h，例如可以是1h、1.5h、2h、2.5h、3h、3.5h、4h、4.5h或5h，但并不仅限于所列举的数值，该数值范围内其他未列举的数值同样适用。
本申请将加热处理的时间控制在上述范围内，当加热处理时间过长，会导致生产效率降低；当加热处理时间过短，容易出现氧化不充分的缺陷。
作为本申请一个可选技术方案，所述反应气体包括氮气、氯气、氧气、空气与二氧化碳中的任一种或至少两种的组合。
作为本申请一个可选技术方案，所述的制备方法还包括：通过调节所述加热炉内的压力，调整所述反应气体的通入速率。
可选地，所述加热炉内的压力为3~8kPa，例如可以是3kPa、3.5kPa、4kPa、4.5kPa、5kPa、5.5kPa、6kPa、6.5kPa、7kPa、7.5kPa或8kPa，但并不仅限于所列举的数值，该数值范围内其他未列举的数值同样适用。
本申请通过调节加热炉内的压力，使得反应气体的通入速率保持在适合范围内，避免通入速率过高造成资源浪费，同时，防止通入速率过低导致氧化不充分。
可选地，所述加热炉包括卧式碳化炉。
可选地，将所述天然石墨送入加热炉内进行升温，在升温至所述加热处理的温度后，再向所述加热炉内通入反应气体进行改性。
作为本申请一个可选技术方案，所述的碳化处理的温度为1000~1200℃，例如可以是1000℃、1020℃、1050℃、1080℃、1100℃、1120℃、1140℃、1150℃、1180℃或1200℃，但并不仅限于所列举的数值，该数值范围内其他未列举的数值同样适用。
可选地，所述碳化处理的时间为3~10h，例如可以是3h、3.5h、4h、4.5h、5h、5.5h、6h、6.5h、7h、8h、9h、9.5h或10h，但并不仅限于所列举的数值，该数值范围内其他未列举的数值同样适用。
可选地，所述碳化处理在保护气氛下进行。
本申请中保护气氛包括但不限于氮气。
作为本申请一个可选技术方案，所述的制备方法还包括：对鳞片石墨和/或球形石墨依次进行整形粉碎与提纯处理，得到所述天然石墨。
可选地，所述提纯处理包括酸碱法提纯或氢氟酸法提纯。
可选地，所述天然石墨的粒径D 50为6~10μm，例如可以是6μm、6.5μm、7μm、7.5μm、8μm、8.5μm、9μm、9.5μm或10μm，但并不仅限于所列举的数值，该数值范围内其他未列举的数值同样适用。
可选地，所述天然石墨的固定碳含量99.6~99.9%，例如可以是99.6%、99.62%、99.65%、99.7%、99.73%、99.75%、99.78%、99.8%、99.83%、99.85%、99.88%或99.9%，但并不仅限于所列举的数值，该数值范围内其他未列举的数值同样适用。
需要说明的是，所述的氢氟酸法提纯包括：采用HCl与HF的混合酸进行浸泡处理，所述混合酸中HCl与HF的体积比为(0.9~1.3):1，所述混合酸的温度为60~75℃，所述浸泡处理的时间为12~24h。
所述的酸碱提纯包括：采用酸溶液、碱溶液与氧化剂进行浸渍处理。所述酸溶液包括硫酸、盐酸、氢氟酸与磷酸中的任一种或至少两种的组合；所述碱溶液包括氢氧化钠、氢氧化钾与氢氧化钙中的任一种或至少两种的组合；所述氧化剂包括双氧水、过氧乙酸、氯气、二氧化氯与高氯酸中的任一种或至少两种的组合，所述浸渍处理的时间为10~18h。
作为本申请一个可选技术方案，所述的制备方法还包括：结束所述氧化处理后冷却至室温，对天然石墨依次进行筛分与除磁，得到所述改性天然石墨。
示例性地，本申请提供的改性天然石墨的制备方法具体包括如下步骤：
S1对鳞片石墨和/或球形石墨依次进行整形粉碎与提纯处理，得到粒径D 50为6~10μm的天然石墨；
S2在保护气氛下对步骤S1中天然石墨进行碳化处理，碳化处理的温度为1000~1200℃，时间为3~10h；
S3将碳化后的天然石墨置于加热炉内，将加热炉升温至350~800℃，随后通入反应气体，加热处理1~5h，期间通过调节加热炉内的压力为3~8kPa，进而调整反应气体的通入速率，采用的反应气体包括氮气、氯气、氧气、空气与二氧化碳中的任一种或至少两种的组合；
S4结束所述氧化处理后冷却至室温，对天然石墨依次进行筛分与除磁，得到改性天然石墨。
其中，本申请针对于步骤S1中提纯处理提供了两种方案：
（1）采用HCl与HF的混合酸对鳞片石墨和/或球形石墨进行12~24h的浸泡处理，混合酸中HCl与HF的体积比为(0.9~1.3):1，所述混合酸的温度为60~75℃。
（2）采用酸溶液、碱溶液与氧化剂对鳞片石墨和/或球形石墨进行10~18h的浸渍处理，酸溶液包括硫酸、盐酸、氢氟酸与磷酸中的任一种或至少两种的组合；所述碱溶液包括氢氧化钠、氢氧化钾与氢氧化钙中的任一种或至少两种的组合；所述氧化剂包括双氧水、过氧乙酸、氯气、二氧化氯与高氯酸中的任一种或至少两种的组合。
本申请通过碳化+氧化处理的方法对天然石墨进行改性，增加石墨表面含氧官能团数量，从而增加与SEI（固体电解质界面膜，Solid Electrolyte Interface）膜的键合力，使得SEI膜在高温存储过程中稳定性增强。同时，通过改变通入气体的种类、气体速率、氧化温度与氧化时间来调控石墨的缺陷度和含氧原子含量。相比于传统的石墨化处理方法，本申请大大节约了制备成本，并减少了碳排放。
第二方面，本申请提供了一种石墨材料，所述的石墨材料采用第一方面所述的制备方法制得。
作为本申请一个可选技术方案，所述石墨材料表面的各原子数总计为100%，氧原子含量为2.85~4.53%，例如可以是2.85%、2.86%、2.90%、2.92%、2.95%、2.96%、3%、3.22%、3.47%、3.50%、3.60%、3.70%、3.80%、3.83%、4%、4.10%、4.12%、4.23%、4.30%、4.42%、4.5%或4.53%，但并不仅限于所列举的数值，该数值范围内其他未列举的数值同样适用。
第三方面，本申请提供了一种电芯，所述的电芯包括第二方面所述的石墨材料。
本申请中石墨材料表面具有较多的含氧官能团，在电极化成时形成-COOLi、-OLi、-C-OLi，使得电极表面的SEI膜的锂盐成分与石墨层面的边界碳原子建立联系，增加与SEI膜的键合力，大大增强了SEI膜的稳定性。
本申请所述的数值范围不仅包括上述例举的点值，还包括没有例举出的上述数值范围之间的任意的点值，限于篇幅及出于简明的考虑，本申请不再穷尽列举所述范围包括的具体点值。
下面结合附图并通过具体实施方式来进一步说明本申请的技术方案。
实施例1
本实施例提供了一种改性天然石墨的制备方法，具体包括如下步骤：
（1）对鳞片石墨依次进行整形粉碎与提纯处理，得到粒径D 50为8μm的天然石墨，其中提纯处理采用酸碱提纯；
（2）在保护气氛下对步骤（1）中天然石墨进行碳化处理，碳化处理的温度为1100℃，时间为6h；
（3）将碳化后的天然石墨置于加热炉内，将加热炉升温至680℃，随后通入反应气体，加热处理3h，期间通过调节加热炉内的压力为6kPa，采用的反应气体为氧气与空气的混合气体；
（4）结束氧化处理后冷却至室温，对天然石墨依次进行筛分与除磁，得到改性天然石墨。
实施例2
本实施例提供了一种改性天然石墨的制备方法，具体包括如下步骤：
（1）对鳞片石墨依次进行整形粉碎与提纯处理，得到粒径D 50为6μm的天然石墨，其中提纯处理采用氢氟酸提纯；
（2）在保护气氛下对步骤（1）中天然石墨进行碳化处理，碳化处理的温度为1150℃，时间为4h；
（3）将碳化后的天然石墨置于加热炉内，将加热炉升温至350℃，随后通入反应气体，加热处理4h，期间通过调节加热炉内的压力为4kPa，采用的反应气体为氧气与空气的混合气体；
（4）结束氧化处理后冷却至室温，对天然石墨依次进行筛分与除磁，得到改性天然石墨。
实施例3
本实施例提供了一种改性天然石墨的制备方法，具体包括如下步骤：
（1）对鳞片石墨依次进行整形粉碎与提纯处理，得到粒径D 50为10μm的天然石墨，其中提纯处理采用氢氟酸提纯；
（2）在保护气氛下对步骤（1）中天然石墨进行碳化处理，碳化处理的温度为1200℃，时间为8h；
（3）将碳化后的天然石墨置于加热炉内，将加热炉升温至800℃，随后通入反应气体，加热处理5h，期间通过调节加热炉内的压力为4kPa，采用的反应气体为二氧化碳与空气的混合气体；
（4）结束氧化处理后冷却至室温，对天然石墨依次进行筛分与除磁，得到改性天然石墨。
实施例4
本实施例提供了一种改性天然石墨的制备方法，具体包括如下步骤：
（1）对球形石墨依次进行整形粉碎与提纯处理，得到粒径D 50为7μm的天然石墨，其中提纯处理采用氢氟酸提纯；
（2）在保护气氛下对步骤（1）中天然石墨进行碳化处理，碳化处理的温度为1050℃，时间为10h；
（3）将碳化后的天然石墨置于加热炉内，将加热炉升温至700℃，随后通入反应气体，加热处理2h，期间通过调节加热炉内的压力为4kPa，采用的反应气体为空气；
（4）结束氧化处理后冷却至室温，对天然石墨依次进行筛分与除磁，得到改性天然石墨。
实施例5
本实施例提供了一种改性天然石墨的制备方法，具体包括如下步骤：
（1）对鳞片石墨与球形石墨的混合原料依次进行整形粉碎与提纯处理，得到粒径D 50为9μm的天然石墨，其中提纯处理采用氢氟酸提纯；
（2）在保护气氛下对步骤（1）中天然石墨进行碳化处理，碳化处理的温度为1200℃，时间为3h；
（3）将碳化后的天然石墨置于加热炉内，将加热炉升温至500℃，随后通入反应气体，加热处理2h，期间通过调节加热炉内的压力为5kPa，采用的反应气体为氧气与空气的混合气体；
（4）结束氧化处理后冷却至室温，对天然石墨依次进行筛分与除磁，得到改性天然石墨。
实施例6
本实施例提供了一种改性天然石墨的制备方法，具体包括如下步骤：
（1）对鳞片石墨依次进行整形粉碎与提纯处理，得到粒径D 50为8μm的天然石墨，其中提纯处理采用氢氟酸提纯；
（2）在保护气氛下对步骤（1）中天然石墨进行碳化处理，碳化处理的温度为1150℃，时间为5h；
（3）将碳化后的天然石墨置于加热炉内，将加热炉升温至450℃，随后通入反应气体，加热处理3h，期间通过调节加热炉内的压力为8kPa，采用的反应气体为氧气与空气的混合气体；
（4）结束氧化处理后冷却至室温，对天然石墨依次进行筛分与除磁，得到改性天然石墨。
实施例7
本实施例提供了一种改性天然石墨的制备方法，与实施例1的区别在于：步骤（3）中采用的反应气体为氧气，其余操作步骤及工艺参数与实施例1相同。
实施例8
本实施例提供了一种改性天然石墨的制备方法，与实施例1的区别在于：步骤（3）中采用的反应气体为CO 2，其余操作步骤及工艺参数与实施例1相同。
实施例9
本实施例提供了一种改性天然石墨的制备方法，与实施例1的区别在于：步骤（3）中加热炉升温至300℃进行改性，其余操作步骤及工艺参数与实施例1相同。
实施例10
本实施例提供了一种改性天然石墨的制备方法，与实施例1的区别在于：步骤（3）中加热炉升温至850℃进行改性，其余操作步骤及工艺参数与实施例1相同。
实施例11
本实施例提供了一种改性天然石墨的制备方法，与实施例1的区别在于：步骤（3）中加热炉内的压力为2kPa，其余操作步骤及工艺参数与实施例1相同。
实施例12
本实施例提供了一种改性天然石墨的制备方法，与实施例1的区别在于：步骤（3）中加热炉内的压力为9kPa，其余操作步骤及工艺参数与实施例1相同。
实施例13
本实施例提供了一种改性天然石墨的制备方法，与实施例1的区别在于：步骤（3）中加热处理为0.5h，其余操作步骤及工艺参数与实施例1相同。
实施例14
本实施例提供了一种改性天然石墨的制备方法，与实施例1的区别在于：步骤（3）中加热处理为5.5h，其余操作步骤及工艺参数与实施例1相同。
对比例1
本对比例提供了一种改性天然石墨的制备方法，具体包括如下步骤：
（1）对鳞片石墨依次进行整形粉碎与提纯处理，得到粒径D 50为8μm的天然石墨，其中提纯处理采用酸碱提纯；
（2）在保护气氛下对步骤（1）中天然石墨进行碳化处理，碳化处理的温度为1100℃，时间为6h；
（3）结束碳化处理后，对天然石墨依次进行筛分与除磁，得到改性天然石墨。
对比例2
本对比例提供了一种改性天然石墨的制备方法，具体包括如下步骤：
（1）对鳞片石墨依次进行整形粉碎与提纯处理，得到粒径D 50为8μm的天然石墨，其中提纯处理采用酸碱提纯；
（2）在保护气氛下对步骤（1）中天然石墨进行石墨化处理，石墨化处理的温度为2800℃，时间为36h；
（3）结束碳化处理后，对天然石墨依次进行筛分与除磁，得到改性天然石墨。
本申请对实施例1~14，以及对比例1与2得到的改性天然石墨的表面氧原子含量（采用X射线光电子能谱测试方法XPS进行测量）及缺陷度（采用拉曼光谱测试方法进行测量）进行测试，结果如表1与图1所示。
本申请将实施例1~14，以及对比例1与2得到的改性天然石墨制成电芯，分别测试其在高温存储（85℃，25d）过程中性能的表现，结果如表1所示。
其中，电芯的正极采用镍钴锰三元正极材料，负极采用上述改性天然石墨制得，隔膜采用氧化铝陶瓷隔膜。将正极极片、隔膜与负极极片自上而下的顺序放置，通过卷绕方式装配，再注入电解液，封装陈化得到电芯。
表1
由表1的内容可以看出，实施例1~14中得到的改性天然石墨的表面氧原子含量较高，缺陷度较小，且在高温下保持较高的容量，具有较好的高温存储性能。
相比于实施例1采用混合气体作为反应气体，实施例7与实施例8中改性天然石墨表面的氧原子含量有所降低，这主要是由于实施例7与实施例8仅采用单一反应气体进行天然石墨的改性，削弱了氧化效果，降低了含氧官能团的生成。
相比于实施例1，由于实施例9中氧化温度过低，导致氧化不完全，使得表面氧原子含量降低，进而造成电芯的容量保持率下降；另外，实施例10的改性天然石墨表面的氧原子含量与实施例1差距较小，但由于氧化温度的升高，使得制作成本增加。
由实施例1、实施例11与实施例12不难看出，当加热炉内压力过高或过低均会影响氧化效果，导致石墨表面氧原子含量的降低，进而造成电芯在高温下的容量保持率有所降低。
由表1不难看出，相比于实施例1，实施例13由于加热处理时间过短，导致天然石墨仅部分氧化，降低了材料表面的氧原子含量，导致电芯高温性能降低；而实施例14加热时间过长，使得制作成本随之增加。
由实施例1与对比例1可知，实施例1的改性天然石墨表面的氧原子含量较高，表面缺陷度较低，且电芯的容量保持率与容量恢复率均有增加，这主要是由于实施例1通过对碳化后的天然石墨进行氧化处理，使得石墨表面的含氧官能团数量增加，在电芯化成阶段，石墨与锂盐之间能够形成联系，提高了电芯在高温下的稳定性，同时还有效地降低了石墨表面缺陷度。
实施例1采用碳化+氧化处理的改性方式，相比于对比例2采用的高温石墨化方式，能够增加石墨表面的氧原子含量，同时降低表面缺陷度，且加热处理温度远低于石墨化温度，使得制作成本大大降低。
本申请可在不使用高能耗石墨化工序情况下，通过碳化+氧化处理的方式得到高温存储性能优异的天然石墨，并通过调整通入气流速率、气体种类、温度、时间等参数来优化天然石墨的高温存储性能。

Claims (15)

  1. 一种改性天然石墨的制备方法，其包括：
    对天然石墨依次进行碳化处理与氧化处理，得到改性天然石墨；
    所述氧化处理包括：将天然石墨送入加热炉内进行加热处理，同时向加热炉内通入反应气体进行改性。
  2. 根据权利要求1所述的制备方法，其中，所述加热处理的温度为350~800℃。
  3. 根据权利要求1或2所述的制备方法，其中，所述加热处理的时间为1~5h。
  4. 根据权利要求1-3任一项所述的制备方法，其中，所述反应气体包括氮气、氯气、氧气、空气与二氧化碳中的任一种或至少两种的组合。
  5. 根据权利要求1-4任一项所述的制备方法，其中，所述的制备方法还包括：通过调节所述加热炉内的压力，调整所述反应气体的通入速率；
    可选地，所述加热炉内的压力为3~8kPa；
    可选地，所述加热炉包括卧式碳化炉；
    可选地，将所述天然石墨送入加热炉内进行升温，在升温至所述加热处理的温度后，再向所述加热炉内通入反应气体进行改性。
  6. 根据权利要求1-5任一项所述的制备方法，其中，所述的碳化处理的温度为1000~1200℃；
    可选地，所述碳化处理的时间为3~10h。
  7.  根据权利要求1-6任一项所述的制备方法，其中，所述碳化处理在保护气氛下进行。
  8. 根据权利要求1-7任一项所述的制备方法，其中，所述的制备方法还包括：对鳞片石墨和/或球形石墨依次进行整形粉碎与提纯处理，得到所述天然石墨。
  9. 根据权利要求8所述的制备方法，其中，所述提纯处理包括酸碱法提纯或氢氟酸法提纯。
  10. 根据权利要求8或9所述的制备方法，其中，所述天然石墨的粒径D 50为6~10μm。
  11. 根据权利要求8-10任一项所述的制备方法，其中，所述天然石墨的固定碳含量99.6~99.9%。
  12. 根据权利要求1-11任一项所述的制备方法，其中，所述的制备方法还包括：结束所述氧化处理后冷却至室温，对天然石墨依次进行筛分与除磁，得到所述改性天然石墨。
  13. 一种石墨材料，其中，所述的石墨材料采用权利要求1-12任一项所述的制备方法制得。
  14. 根据权利要求13所述的石墨材料，其中，所述石墨材料表面的各原子数总计为100%，氧原子含量为2.85~4.53%。
  15. 一种电芯，其中，所述的电芯包括权利要求13或14所述的石墨材料。
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