Coated graphite material, and preparation method and application thereof

Abstract

The application provides a coated graphite material and a preparation method and application thereof, and relates to the technical field of lithium ion battery negative electrode materials. Specifically, the preparation method of the coated graphite material comprises the following steps: preparing carbon source gas through a cracking reaction of a carbon source solid; and mixing the carbon source gas with a graphite matrix to obtain a gas phase coated graphite material through a coating reaction. The preparation method of the application belongs to a novel gas phase coating process, and can effectively solve the transportation and safety problems caused by high-pressure raw material gas in the current gas phase coating process. When the coated graphite material of the application is used as a lithium ion battery negative electrode, the rate capability and high-temperature performance can be considered, and the application has a good application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion battery negative electrode materials, in particular to a coated graphite material and a preparation method and application thereof. BACKGROUND

[0002] In recent years, with the rise in oil prices, the new energy vehicle industry is in a period of vigorous development. Lithium ion batteries are the core components of new energy vehicles, and graphite negative electrodes are the key raw materials of lithium ion batteries. In order to improve the rate performance of graphite negative electrodes, a highly disordered carbon layer needs to be coated on the surface of the graphite negative electrode. Common coating methods include, but are not limited to, solid-phase coating, liquid-phase coating, and gas-phase coating.

[0003] Among them, the coated graphite negative electrode obtained by solid-phase coating and liquid-phase coating is unevenly coated, and the coating layer is relatively thick. Although the rate can be improved, the residual carbon content is relatively high, and in addition to carbon and hydrogen elements, the solid coating agent and the liquid coating agent also contain other heteroatoms such as oxygen atoms. After carbonization, they exist in the form of hydroxyl or carboxyl groups on the surface, which will consume a large amount of electrolyte during the charging, discharging, and storage processes of lithium ion batteries, and have a large negative impact on the first efficiency and high-temperature storage performance of lithium ion batteries. Correspondingly, the carbon source for gas-phase coating only contains carbon and hydrogen elements, and does not contain other heteroatoms. Compared with solid-phase coating and liquid-phase coating, the carbon layer obtained is more uniform, and has low reactivity with electrolyte, so that a coated graphite negative electrode with both rate and high-temperature performance can be obtained. However, gas-phase coating requires flammable and explosive olefins, alkynes, and other materials loaded in high-pressure containers for transportation, which has transportation and safety problems.

[0004] Therefore, the present application is proposed. SUMMARY

[0005] The first object of the present application is to provide a preparation method of a coated graphite material. The preparation method of the present application belongs to a gas-phase coating process, and is used to solve the transportation and safety problems of high-pressure raw material gas in the current gas-phase coating process.

[0006] The second object of the present application is to provide a coated graphite material that can balance rate performance and high-temperature performance when used as a battery negative electrode.

[0007] The third object of the present application is to provide a lithium ion battery negative electrode.

[0008] The fourth object of the present application is to provide a lithium ion battery.

[0009] The fifth object of the present application is to provide a preparation device for gas-phase coated graphite, which is used to simply and conveniently implement the preparation method of the coated graphite material.

[0010] In order to achieve the above object of the present application, the following technical solutions are adopted:

[0011] A preparation method of the coated graphite material comprises the following steps:

[0012] A carbon source gas is prepared by cracking reaction of a carbon source solid;

[0013] The carbon source gas is mixed with a graphite matrix, and the coated graphite material is obtained through coating reaction.

[0014] A graphite material is prepared by the preparation method of the coated graphite material as described above.

[0015] A lithium ion battery negative electrode comprises the coated graphite material as described above.

[0016] A lithium ion battery comprises the coated graphite material as described above, or comprises the lithium ion battery negative electrode as described above.

[0017] A preparation device of gas phase coated graphite is used to perform the preparation method of the coated graphite material as described above.

[0018] The device comprises a gas generating assembly, a coating generating assembly and a carrier gas source, and the gas generating assembly and the coating generating assembly are provided with independent reaction chambers, the reaction chamber of the gas generating assembly is connected with the reaction chamber of the coating generating assembly through a gas pipeline, and the carrier gas source is communicated with the reaction chamber of the gas generating assembly.

[0019] Compared with the prior art, the present application has the following beneficial effects:

[0020] (1) The present application uses solid material as coating carbon source, and does not need to use high-pressure container during transportation and use, so that the safety is better.

[0021] (2) The conventional gas phase coating generally uses one or several specific gas carbon sources, such as ethylene and acetylene, and the carbon layer structure formed on the graphite matrix after coating is relatively regular. In the present application, the carbon source gas with complex composition is produced by thermal cracking, which contains C1-C6 hydrocarbon radical and has strong reactivity, and the branched chain formed on the surface of the graphite matrix is more when chemical deposition is formed, and the degree of disorder is higher, so that higher rate performance is obtained when the battery negative electrode is prepared.

[0022] (3) The stability and oxidation resistance of the coated carbon layer formed by the present invention are lower than those of conventional gas-phase coated graphite, but higher than those of coated materials obtained by conventional solid-phase or liquid-phase coating. Therefore, the kinetic properties of the coated material obtained by the present invention are better than those of conventional gas-phase coated graphite; it is more stable than solid-phase or liquid-phase coated graphite, has lower reactivity with electrolyte, and better storage performance. Attached Figure Description

[0023] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0024] Figure 1 A schematic diagram of an apparatus used in an embodiment is provided. Detailed Implementation

[0025] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially. The terms "a", "b", "c", "d", etc. are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0026] The first aspect of the present invention is to provide a method for preparing a coated graphite material.

[0027] The preparation method of the coated graphite material includes the following steps: (1) obtaining carbon source gas by cracking carbon source solid; (2) mixing the carbon source gas with graphite matrix and obtaining coated graphite material by coating reaction.

[0028] Current processes for vapor-phase coated graphite typically utilize vapor deposition technology to uniformly deposit coating materials onto the graphite surface, forming a capping layer that improves various aspects of graphite's chemical, physical, and thermal properties. This invention differs from conventional vapor-phase coating by employing a special solid carbon source that is converted into a gaseous carbon source, combined with specific reaction conditions to achieve the coating reaction, thereby obtaining a vapor-phase coated graphite material. This effectively avoids the hazards of flammable and explosive gaseous carbon sources found in conventional vapor-phase coating methods, while simultaneously producing carbon-graphite materials suitable for battery anode materials that balance rate capability and high-temperature performance.

[0029] In a preferred embodiment, the carbon source solid comprises a polyolefin polymer, and the number average molecular weight of the polyolefin polymer is ≥10000.

[0030] In a more preferred embodiment, the carbon source solid includes at least one of polyethylene, polypropylene, or polystyrene.

[0031] In this invention, by selecting a specific carbon source solid, pyrolysis at high temperatures is achieved to obtain hydrocarbon gaseous compounds (i.e., carbon source gas). Appropriate selection of the type of carbon source solid can effectively reduce the difficulty of the pyrolysis reaction, thereby obtaining the carbon source gas more efficiently. The carbon source gas includes C1-C6 hydrocarbons, that is, small-molecule hydrocarbons with 1 to 6 carbon atoms.

[0032] In a preferred embodiment, the ratio of the carbon source solid to the graphite substrate by weight is 20:100 to 100:100.

[0033] In a preferred embodiment, the conditions for the pyrolysis reaction include a temperature of 650℃ to 1000℃; in an optional embodiment, the temperature of the pyrolysis reaction includes, but is not limited to, any one or any two of the following: 650, 700, 750, 800, 850, 900, 950, and 1000 (℃).

[0034] In a preferred embodiment, the pyrolysis reaction and / or the coating reaction are carried out in a protective gas environment.

[0035] In a preferred embodiment, the carbon source gas is carried by a carrier gas and mixed with the graphite matrix; the carrier gas can be an inert gas, including but not limited to nitrogen, helium, neon, argon, etc.

[0036] In a preferred embodiment, the volumetric particle size Dv50 of the graphite matrix is ​​6 μm to 22 μm; wherein, the volumetric particle size Dv50 refers to the particle size corresponding to 50% of the cumulative graphite particles.

[0037] In a preferred embodiment, the graphite matrix includes, but is not limited to, natural graphite or artificial graphite, as long as it is a graphite material without a surface coating.

[0038] In a preferred embodiment, the conditions for the coating reaction include: a temperature of 700℃~1500℃ and a time of ≥4h.

[0039] As an optional implementation, the temperature of the coating reaction includes, but is not limited to, any one or any two of the following: 700, 750, 800, 850, 900, 950, 1000, 1050, 1100, 1150, 1200, 1250, 1300, 1350, 1400, 1450, and 1500 (°C).

[0040] In a more preferred embodiment, the coating reaction temperature is 1200°C;

[0041] As an optional implementation, the coating reaction time includes, but is not limited to, any one or any two of the following: 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10 (h).

[0042] A second aspect of the present invention is to provide a coated graphite material.

[0043] The coated graphite material is prepared based on the preparation method of the coated graphite material described in the first aspect of the present invention.

[0044] The coated graphite material comprises: a graphite substrate and a thin amorphous carbon layer loaded on the surface of the graphite substrate (for example, in a typical but non-limiting case, the thickness of the amorphous carbon layer can be about 10 nm); the amorphous carbon layer increases the surface disorder of the coated graphite material, thereby further enabling the coated graphite material to have higher rate performance in lithium battery anodes.

[0045] In a preferred embodiment, the average ID / IG value of the coated graphite material is 0.1 to 0.5, as determined by Raman surface scanning. In contrast, the average ID / IG value of conventional uncoated ordinary graphite substrates is generally less than 0.1. The graphite material of the present invention has good surface disorder.

[0046] In a preferred embodiment, the surface of the coated graphite material is scanned using SEM-EDS technology. The scanned elements are carbon and oxygen, with an oxygen atom ratio of 0.5% to 2.0%. The coated graphite material of this invention does not introduce new oxygen atoms onto the graphite substrate surface compared to the graphite matrix. The low surface oxygen atom ratio of the coated graphite material results in lithium-ion batteries with better rate performance, smaller DCR growth after high-temperature storage, and higher initial efficiency and capacity recovery rate.

[0047] The following are analyses of the sources of oxygen atoms: First, although conventional artificial graphite substrates undergo high-temperature treatment at approximately 2800℃ to 3000℃ during the production process, and most of the non-carbon elements evaporate, a very small amount of oxygen may still exist between the graphite structures; Second, during the cooling stage of graphitization production and during the transportation and storage of graphite, the graphite surface will undergo an oxidation reaction with oxygen in the air, introducing a small amount of oxygen.

[0048] Traditional solid-phase or liquid-phase coatings use carbon sources containing heteroatoms such as oxygen atoms. During pyrolysis, oxygen dehydrates, creating tiny voids on the coating surface, or remains in the coating as hydroxyl or carboxyl groups after carbonization. This high reactivity with the electrolyte negatively impacts the initial efficiency and high-temperature performance of the anode material and lithium-ion batteries. In contrast, the carbon source used in this invention contains only hydrocarbons and is oxygen-free. Therefore, it does not introduce new oxygen atoms onto the graphite substrate surface after coating and may even undergo a reduction reaction on the graphite substrate surface, reducing the oxygen content on the graphite surface.

[0049] In a preferred embodiment, the volumetric particle size growth rate of the coated graphite material is ≤5% compared to the graphite substrate; it is understood that the volumetric particle size can be measured by any one of Dv10, Dv50, Dv90, and Dv100.

[0050] In a preferred embodiment, the specific surface area of ​​the coated graphite material is reduced by ≥16% compared to the graphite substrate; the specific surface area can be obtained by BET method.

[0051] By using the growth rate of the volumetric particle size and the reduction rate of the specific surface area mentioned above, it is possible to estimate the changes in the shape (or volume) of the graphite material relative to the graphite substrate before and after vapor phase coating.

[0052] In a preferred embodiment, the coated graphite material is subjected to a thermogravimetric test in an air atmosphere at a heating rate of 10°C / min, and the weight loss rate of the coated graphite material is 1% to 1.5% when the temperature is raised to 620°C.

[0053] In a preferred embodiment, the coated graphite material is subjected to a thermogravimetric test in an air atmosphere at a heating rate of 10°C / min, and the weight loss rate of the coated graphite material is 5% to 10% when the temperature is raised to 670°C.

[0054] The carbon source generated by this invention under thermal decomposition has a complex composition, containing hydrocarbon free radicals with 1-6 carbon atoms. This high reactivity leads to numerous branched chains and a high degree of disorder during chemical deposition on the graphite surface. Therefore, the resulting carbon layer exhibits lower stability and oxidation resistance compared to conventional gaseous hydrocarbon-based coating materials, but higher stability than conventional solid or liquid-phase coating materials. Consequently, the coated graphite material obtained by this invention exhibits better kinetic properties than conventional gaseous-phase coated graphite, greater stability compared to conventional solid-phase coatings, lower reactivity with electrolytes, and better storage performance.

[0055] A third aspect of the present invention is to provide a lithium-ion battery negative electrode.

[0056] The lithium-ion battery anode includes the coated graphite material as described above. In some embodiments, the lithium-ion battery anode can be made solely from the graphite material, or it can contain functional raw materials such as exogenous conductive agents and binders. In some embodiments, in addition to the graphite material, the lithium-ion battery anode also includes other anode active materials, which are mixed in any form, such as doping or coating, to obtain a composite lithium-ion battery anode. This invention does not impose any limitations on this. It is understood that as long as the lithium-ion battery anode contains the graphite material, it can be considered an embodiment of this invention.

[0057] A fourth aspect of the present invention is to provide a lithium-ion battery.

[0058] The lithium-ion battery described herein includes the coated graphite material as described above, or the lithium-ion battery negative electrode as described above. It is understood that the lithium-ion battery should also include a positive electrode and an electrolyte, as well as optional components or structural elements such as a separator or encapsulation material. This invention does not impose any restrictions on the selection of functional components or structural elements other than the negative electrode. When a normally functioning lithium-ion secondary battery can be obtained, this embodiment can be considered an embodiment of the fourth aspect of this invention.

[0059] A fifth aspect of the present invention is to provide an apparatus for preparing vapor-phase coated graphite.

[0060] The method for preparing coated graphite material as described above is carried out using the aforementioned gas-phase coated graphite preparation apparatus; the apparatus includes a gas generating component and a coating generating component, both of which have reaction chambers, and the reaction chambers of the gas generating component and the coating generating component are connected via gas pipelines; the apparatus also includes a carrier gas source, which is only connected to the reaction chamber of the gas generating component and provides carrier gas to the gas generating component.

[0061] It should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "connection," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0062] In a preferred embodiment, the device further includes an exhaust gas treatment component; the exhaust gas treatment component is connected to the reaction chamber of the coating generation component and is used to treat the exhaust gas generated in the coating generation component.

[0063] In a preferred embodiment, the gas flow direction in the device is: the carrier gas source, the gas generating component, and the coating generating component; in a more preferred embodiment, the gas flow direction in the device is: the carrier gas source, the gas generating component, the coating generating component, and the exhaust gas treatment component.

[0064] In a preferred embodiment, the gas generating assembly and the coating generating assembly include, but are not limited to, a tubular furnace or a rotary kiln.

[0065] In a preferred embodiment, the operation method of the device includes the following steps:

[0066] Step 1: Provide a carbon source solid to the gas generating component and provide a graphite substrate to the coating generating component;

[0067] Step 2: Turn on the carrier gas source to allow the carrier gas to circulate within the device;

[0068] Step 3: Operate and control the temperature of the gas generating component and the coating generating component; the carbon source in the gas generating component undergoes a cracking reaction to produce hydrocarbon gas, which is transported to the coating generating component via a carrier gas to undergo a coating reaction; maintain the temperature until the reaction is complete;

[0069] Step 4: Once the temperature has dropped to room temperature, remove the coated graphite material.

[0070] like Figure 1 The diagram shows the apparatus used in the following embodiments. The apparatus includes a nitrogen source (carrier gas), a gas passage, a first tubular furnace (which can be regarded as a coating gas carbon source generating device), a gas passage, a second tubular furnace (which can be regarded as a coating generating device), a gas passage, and a tail gas treatment; a solid carbon source and a graphite matrix are respectively provided in the first tubular furnace and the second tubular furnace.

[0071] Example 1

[0072] 1) The first tube furnace and the second tube furnace are respectively equipped with 2000g of polyethylene (number average molecular weight distribution of 1000-1200) and 2000g of artificial graphite (graphite type G1, manufacturer: Jiangxi Zichen New Material Technology Co., Ltd.), and the median particle size of artificial graphite is 20μm.

[0073] 2) The second tube furnace heats up to 1200℃ at a rate of 2℃ / min. After the temperature reaches the preset temperature, the first tube furnace heats up to 800℃ at a rate of 2℃ / min.

[0074] 3) After the first tubular furnace reaches the preset temperature, wait for 4 hours;

[0075] 4) Turn off the heating program and wait for the tube furnace to cool down to room temperature before obtaining the coated graphite material of this embodiment in the second tube furnace.

[0076] Example 2

[0077] It is basically the same as Example 1, except that the first tube furnace is heated to 650°C.

[0078] Example 3

[0079] It is basically the same as Example 1, except that the second tube furnace is heated to 700°C.

[0080] Example 4

[0081] It is basically the same as Example 1, except that the first tube furnace is heated to 1000°C.

[0082] Example 5

[0083] It is basically the same as Example 1, except that the second tube furnace is heated to 1500°C.

[0084] Example 6

[0085] It is basically the same as Example 1, except that polyethylene is replaced with polypropylene.

[0086] Comparative Example 1

[0087] It is basically the same as Example 1, except that the first tube furnace is heated to 600°C.

[0088] Comparative Example 2

[0089] It is basically the same as Example 1, except that the second tube furnace is heated to 600°C.

[0090] Comparative Example 3

[0091] It is basically the same as Example 1, except that: after the first tube furnace is heated to the preset temperature, it waits for 3 hours.

[0092] Comparative Example 4

[0093] 1) Add artificial graphite (with the same specifications as the artificial graphite in Example 1) and asphalt (coking value 50%) to a mixer at a weight ratio of 100:2 and mix them evenly to obtain a mixture of graphite and asphalt.

[0094] 2) Place the mixture into a graphite crucible, then place the graphite crucible into a box-type carbonization furnace, set the heating program of the box-type carbonization furnace to heat to 1200℃ at 2℃ / min, hold for 4 hours, and cool to room temperature to obtain the solid-phase coated graphite anode material of this comparative example.

[0095] Comparative Example 5

[0096] 1) Add artificial graphite (with the same specifications as the artificial graphite in Example 1) and asphalt solution (solvent is N-methylpyrrolidone, asphalt mass fraction is 33%, asphalt coking value is 50%) into a mixer at a weight ratio of 100:6, and mix the two evenly to obtain a mixture of graphite and asphalt solution.

[0097] 2) Place the mixture into a graphite crucible, then place the graphite crucible into a box-type carbonization furnace, set the heating program of the box-type carbonization furnace to heat to 1200℃ at 2℃ / min, hold for 4 hours, and cool to room temperature to obtain the liquid-phase coated graphite anode material of this comparative example.

[0098] Comparative Example 6

[0099] 1) Place the uncoated graphite substrate into a tube furnace and introduce acetylene as the coating gas and nitrogen as the carrier gas.

[0100] 2) Set the heating program for the tube furnace to a heating rate of 2℃ / min, heat to 1200℃, and start the heating program.

[0101] 3) After the reaction at 1200℃ for 4 hours, the heating program was turned off and the material was cooled to room temperature to obtain the conventional vapor-phase coated graphite anode material of this comparative example.

[0102] Comparative Example 7: Artificial Graphite

[0103] The artificial graphite in this comparative example has the same specifications as the artificial graphite in Example 1. Specific surface area is 1.20 m² / g, specific capacity is 355.0 mAh / g, and initial coulombic efficiency is 94.1%.

[0104] Test case

[0105] The graphite materials prepared in the above embodiments and comparative examples were tested as follows. The test results are shown in Tables 1 and 2 below.

[0106] I. Particle size test: Tested according to Appendix A of GB / T 24533-2019 "Graphite Anode Materials for Lithium-ion Batteries".

[0107] II. Specific surface area test: The test shall be conducted in accordance with the provisions of GB / T 19587-2017 "Determination of specific surface area of ​​solid substances by gas adsorption BET method".

[0108] III. Capacity and Initial Efficiency Tests: Anode sheets were prepared using the graphite anode materials obtained in the above examples and comparative examples (anode material ratio: graphite:sp:CMC:SBR = 96.5:1:1.1:1.4, single-sided areal density 8.5 mg / cm³). 2 Compacted density 1.65 g / cm³ 3 Tested according to Appendix G of GB / T 24533-2019 "Graphite Anode Materials for Lithium-ion Batteries".

[0109] IV. Battery performance testing (including DCR and high-temperature storage testing): The soft-pack batteries with a capacity of 2.4Ah and an operating voltage of 3.0V to 4.35V, made from the negative electrode sheets of the above-prepared embodiments and comparative examples and combined with lithium cobalt oxide positive electrodes, were tested according to HPPC (2C, 30s); the 50% SOC discharge DCR before and after 7 days of storage at 45°C was tested to obtain the DCR growth rate after 7 days of storage at 45°C.

[0110] V. Raman surface scanning: laser wavelength 532nm, scanning range 900-1900cm-1, number of scanning points 400, exposure time 4s, equipment Renishaw inVia, to obtain the average ID / IG value.

[0111] VI. Oxygen atom content (EDS test): HV 10Kv, WD 10mm, electron beam intensity 0.8nA, scanned elements are carbon and oxygen.

[0112] VII. Thermogravimetric parameters: air atmosphere (20% volume fraction oxygen, 80% volume fraction nitrogen), air flow rate 20 min / mL, heating rate 10℃ / min, temperatures 620℃ and 670℃ respectively, heating start temperature is room temperature, heating stop temperature is 1000℃.

[0113] Table 1

[0114]

[0115]

[0116] Table 2

[0117]

[0118]

[0119] The data from the above embodiments and comparative examples show that:

[0120] (1) The coated graphite anode material prepared by the preparation method of the present invention has a higher ID / IG ratio on the surface than the uncoated graphite material (Comparative Example 6), and a lower DCR than the uncoated graphite anode material (Comparative Example 6). The DCR is comparable to that of the solid-phase coated graphite anode material (Comparative Example 4) and the liquid-phase coated graphite anode material (Comparative Example 5).

[0121] (2) The graphite anode material prepared by the preparation method of the present invention has a relatively dense oxygen-free coating layer on its surface. The oxygen atom content detected by EDS is less than that of traditional solid-phase graphite anode material (Comparative Example 4), liquid-phase graphite anode material (Comparative Example 5) and uncoated graphite anode material (Comparative Example 6). It also has fewer side reactions with the electrolyte. Therefore, the DCR growth rate after 7 days of storage at 45 degrees Celsius is smaller than that of Comparative Example 4, Comparative Example 5 and Comparative Example 6, and the first efficiency is higher than that of Comparative Example 4, Comparative Example 5 and Comparative Example 6.

[0122] (3) In the graphite materials obtained in the various embodiments of the present invention, the carbon layer formed only contains carbon and hydrogen elements. Its stability and oxidation resistance are lower than those of conventional gas phase coating materials with gaseous hydrocarbons as carbon sources, but higher than those of conventional solid or liquid phase coating materials. Specifically, the weight loss rate at 620°C in an air atmosphere is higher than that of comparative examples 1 to 3, and lower than that of comparative examples 6 and 7.

[0123] (4) Comparative Example 1 shows that when the temperature of the gas generating device is below 650°C, the solid carbon source cannot undergo a cracking reaction or the amount of gas produced by cracking is insufficient. The performance of the coated graphite anode material obtained by coating is consistent with that of the uncoated graphite anode material (Comparative Example 6), and it does not achieve the expected improvement in rate performance, first efficiency and high temperature performance.

[0124] Comparative Example 2 shows that when the coating reaction temperature is below 700℃, the coating gas cannot undergo chemical deposition reaction with the graphite substrate or the chemical deposition reaction rate is low. The performance of the resulting coated graphite anode material is consistent with that of the uncoated graphite anode material (Comparative Example 6), and it does not achieve the expected improvement in rate performance, first efficiency and high temperature performance.

[0125] Comparative Example 3 shows that when the coating reaction time is less than 4 hours, the time for the coating gas to undergo chemical deposition reaction with the graphite substrate is not long enough, and the resulting coated graphite anode material does not achieve the expected improvement in rate performance, first-pass efficiency and high-temperature performance.

[0126] Comparative Example 6 is a conventional gas phase coating. Compared with the preparation process proposed in this invention, the coating gas composition is a single component, resulting in a coating layer with lower disorder, i.e., lower specific surface area and ID / IG ratio than the example, but higher DCR, and lower rate capability and impedance than the example.

[0127] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A method for preparing a coated graphite material, characterized in that, The preparation method of the coated graphite material includes the following steps: Carbon source gas is prepared by cracking solid carbon source; The carbon source gas is mixed with a graphite matrix, and the coated graphite material is obtained through a coating reaction. The carbon source solid includes polyolefin polymers, and the number average molecular weight of the polyolefin polymers is ≥10000.

2. The method for preparing the coated graphite material according to claim 1, characterized in that, The carbon source solid includes at least one of polyethylene, polypropylene, or polystyrene.

3. The method for preparing the coated graphite material according to claim 1, characterized in that, The carbon source gas includes C1 to C6 hydrocarbons.

4. The method for preparing the coated graphite material according to claim 1, characterized in that, The carbon source gas is carried by a carrier gas and mixed with the graphite matrix.

5. The method for preparing the coated graphite material according to claim 4, characterized in that, The carrier gas is an inert gas; the inert gas includes at least one of nitrogen, helium, neon or argon.

6. The method for preparing the coated graphite material according to claim 1, characterized in that, The pyrolysis reaction is carried out at a temperature of 650℃~1000℃.

7. The method for preparing the coated graphite material according to claim 1, characterized in that, The coating reaction is carried out at a temperature of 700℃ to 1500℃ for a duration of ≥4h.

8. The coated graphite material prepared by the method for preparing coated graphite material according to any one of claims 1 to 7.

9. The coated graphite material according to claim 8, characterized in that, Raman surface scanning analysis showed that the average ID / IG ratio of the coated graphite material was 0.1 to 0.

5. And / or, by amount of substance, the oxygen atom content on the surface of the coated graphite material is 0.5% to 2.0%; And / or, in an air atmosphere, when the temperature is increased to 620°C at a rate of 10°C / min, the weight loss rate of the coated graphite material is 1%~1.5%; And / or, when heated to 670°C at a rate of 10°C / min in air, the weight loss rate of the coated graphite material is 5%~10%.

10. A lithium-ion battery negative electrode, characterized in that, The lithium-ion battery negative electrode comprises the coated graphite material as described in claim 8 or 9.

11. A lithium-ion battery, characterized in that, The lithium-ion battery includes the coated graphite material as described in claim 8 or 9, or the lithium-ion battery negative electrode as described in claim 10.

12. An apparatus for preparing vapor-phase coated graphite, characterized in that, The apparatus is used to prepare the coated graphite material as described in any one of claims 1 to 7. The device includes a gas generating component, a coating generating component, and a carrier gas source. The gas generating component and the coating generating component are provided with independent reaction chambers. The reaction chambers of the gas generating component and the coating generating component are connected through gas pipelines. The carrier gas source is connected to the reaction chamber of the gas generating component.

13. The apparatus for preparing vapor-phase coated graphite according to claim 12, characterized in that, The device further includes an exhaust gas treatment component, which is connected to the reaction chamber of the coating generation component.

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