Polymer-coated graphite negative electrode material, and preparation method therefor and use thereof

Abstract

A polymer-coated graphite negative electrode material, and a preparation method therefor and a use thereof. The preparation method comprises: polymerizing a mixed reaction system at least comprising an acrylate monomer, an initiator and a first solvent to prepare an acrylate polymer; mixing the acrylate polymer, a graphite material and a second solvent for reaction, removing the solvent, and then performing a low-temperature thermal crosslinking reaction to prepare a polymer-coated graphite negative electrode material, wherein the low-temperature thermal crosslinking reaction at least removes pendant groups of the acrylate polymer and causes self-condensation. The prepared polymer-coated graphite negative electrode material has excellent thermal stability, and batteries prepared from the polymer-coated graphite negative electrode material can work at high temperatures and also have an excellent capacity retention rate.

Description

A polymer-coated graphite anode material, its preparation method and application

[0001] This application is based on and claims priority to Chinese Patent Application No. 202410935017.X, filed on July 12, 2024, entitled "A Polymer-Coated Graphite Anode Material and Its Preparation Method and Application". Technical Field

[0002] This application specifically relates to a polymer-coated graphite anode material, its preparation method, and its application, belonging to the field of new materials and new energy technology. Background Technology

[0003] Lithium-ion batteries have entered our daily lives along with technological advancements and increasingly stringent environmental requirements. The mainstream anode material for lithium batteries is graphite-based. Due to its advantages such as small volume change rate, large specific capacity (372mAh / g), low potential, stable structure, and low cost during the lithiation process, graphite has always occupied the absolute market share of anode materials.

[0004] Among them, artificial graphite is a graphite material synthesized through a specific process. Compared with other anode materials, it exhibits many unique product characteristics and advantages. Its physical and chemical properties, such as purity, particle size distribution, and crystallinity, can be precisely controlled by adjusting the raw materials and production processes to meet the high standards required for specific industrial applications. Specifically, the layered structure of artificial graphite facilitates the rapid insertion and extraction of lithium ions, and its good conductivity helps improve the charge and discharge efficiency and power performance of the battery. Furthermore, precise manufacturing processes control its microstructure and purity, optimizing the lithium ion diffusion path and thus improving the battery's rate performance.

[0005] However, artificial graphite currently exhibits poor thermal stability in lithium-ion battery applications. When thermal runaway occurs, it often originates from the heat release caused by the thermal decomposition of the graphite surface, further exacerbating the accumulation of internal reaction heat and energy. This leads to further shrinkage of the battery separator, resulting in large-area contact between the positive and negative electrodes, short circuits, and overall thermal safety incidents affecting the battery pack. This also generates pollution and consumes significant energy. Therefore, there is an urgent need to improve the thermal stability of artificial graphite under high-temperature conditions to reduce the risk of internal short circuits and thermal runaway, thereby enhancing battery safety.

[0006] Summary of the Invention

[0007] The main objective of this application is to provide a polymer-coated graphite anode material, its preparation method, and its application, in order to overcome the shortcomings of the prior art.

[0008] To achieve the aforementioned objectives, the technical solution adopted in this application includes:

[0009] This application provides a method for preparing a polymer-coated graphite anode material, comprising:

[0010] An acrylate polymer is prepared by polymerizing a mixed reaction system containing at least an acrylate monomer, an initiator, and a first solvent.

[0011] Furthermore, the acrylate polymer, graphite material, and a second solvent are mixed and reacted, and the solvent is removed. Then, a low-temperature thermal crosslinking reaction is performed to obtain a polymer-coated graphite anode material; the low-temperature thermal crosslinking reaction at least removes the polymer side groups and causes self-condensation.

[0012] The acrylate monomers have the structure shown in formula (I):

[0013] R1 is selected from H, methyl or ethyl, R2 contains quaternary carbon atoms in its structure, and n is 20 to 2000.

[0014] This application also provides a polymer-coated graphite anode material prepared by the aforementioned method.

[0015] This application also provides a polymer-coated graphite anode material, comprising: a graphite material as a core structure and a thermally cross-linked polymer coating layer as a shell structure, wherein the graphite material is embedded within the thermally cross-linked polymer coating layer, and the thermally cross-linked polymer in the thermally cross-linked polymer coating layer has a structure as shown in formula (II):

[0016] This application also provides the use of the aforementioned polymer-coated graphite anode material in the preparation of secondary battery anodes or secondary batteries.

[0017] This application also provides a lithium-ion battery comprising the aforementioned polymer-coated graphite anode material.

[0018] Compared with the prior art, the beneficial effects of this application are as follows:

[0019] (1) This application protects the structure of artificial graphite particles in the coating layer by using a thermally cross-linked polymer coating layer, which significantly improves the thermal stability of lithium batteries based on artificial graphite.

[0020] (2) The acrylic polymer coating of artificial graphite protected in this application is equivalent to an artificial SEI film, which plays a role in stabilizing the surface of artificial graphite particles. The thermally cross-linked polymer coating has good high temperature resistance, which is beneficial to improving the high temperature thermal stability of artificial graphite.

[0021] (3) The formation of acrylate polymers in this application is a green reaction. The acrylate monomers are used as reaction precursors and are soluble in a single solvent. The solvent used is alcohol such as ethanol, which is environmentally friendly and green. Moreover, the condensation produces cross-linked acrylate polymers, which does not cause pollution.

[0022] (4) Before thermal crosslinking, the acrylate polymer in this application forms an adhesion force with the surface of artificial graphite particles, forming a physical-induced initial coating. After heating, it generates a crosslinked acrylate polymer, which fully and uniformly coats the surface of artificial graphite.

[0023] (5) The polymer of this application is prepared by polyacrylate side chain condensation reaction. The reaction conditions are not harsh and the required temperature is low. It can be operated below 300°C, which is energy-saving and environmentally friendly. The resulting acrylate polymer has high thermal stability in the later stage. When it is heated to a high temperature, such as 300°C, the cross-linked polymer will not undergo thermal decomposition, which is beneficial to the high-temperature use of the battery. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 is an infrared spectrum of the cross-linked polyacrylate-coated artificial graphite material in Example 1 of this application;

[0026] Figure 2 is a polymer thermogravimetric analysis (DTG) curve in Example 1 of this application. Detailed Implementation

[0027] In view of the deficiencies of the prior art, the applicant, through long-term research and extensive practice, has come up with the technical solution of this application. The technical solution of this application will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0028] Specifically, as one aspect of the technical solution of this application, a method for preparing a polymer-coated graphite anode material includes:

[0029] An acrylate polymer is prepared by polymerizing a mixed reaction system containing at least an acrylate monomer, an initiator, and a first solvent.

[0030] Furthermore, the acrylate polymer, graphite material, and a second solvent are mixed and reacted, and the solvent is removed. Then, a low-temperature thermal crosslinking reaction is performed to obtain a polymer-coated graphite anode material; the low-temperature thermal crosslinking reaction at least removes the polymer side groups and causes self-condensation.

[0031] The acrylate monomers have the structure shown in formula (I):

[0032] R1 is selected from H, methyl or ethyl, R2 contains quaternary carbon atoms in its structure, and n is 20 to 2000.

[0033] In some preferred embodiments, R2 in formula (I) is selected from any one of tert-butyl, tert-pentyl, tert-hexyl, tert-octyl, 2-methyl-2-phenylpropyl, and 2-phenyl-3,3-dimethylbutyl, and is not limited thereto.

[0034] In some preferred embodiments, the acrylate monomers include any one or more combinations of tert-butyl acrylate, tert-butyl methacrylate, tert-amyl acrylate, tert-amyl methacrylate, tert-hexyl acrylate, tert-hexyl methacrylate, tert-octyl acrylate, and tert-octyl methacrylate, and are not limited thereto.

[0035] The thermally crosslinked polymer coating (acrylate polymer coating) protected in this application has a certain interaction with the electrolyte after thermal crosslinking. This interaction allows the thermally crosslinked polymer coating to protect the surface and interior of the graphite particles from easy corrosion and decomposition by the electrodes, electrolyte, and their electrochemical by-products at high temperatures. Electrochemical by-products exist in the battery, which are generally acidic products such as HF, PF5, and POF3. The thermally crosslinked polymer coating of this application protects the structure of the artificial graphite particles in the coating and significantly improves the thermal stability of lithium batteries based on artificial graphite.

[0036] The acrylate polymers in this application can be dissolved in a solvent by heating before thermal crosslinking. When the solvent is removed and the material is dried, the polymer forms an adhesion force with the surface of the artificial graphite particles under the drive of external heat, forming a physically induced initial coating. The surface of the artificial graphite is coated with a layer of polymer. Then, under dry conditions, the polymer undergoes a condensation reaction by heating, driving the polymer to efficiently generate crosslinked acrylate polymers. Due to the external heat and the exothermic effect of its own reaction, the polymer can overcome the interfacial tension between itself and the artificial graphite, and can fully and uniformly coat the surface of the artificial graphite.

[0037] In some preferred embodiments, the initiator includes, but is not limited to, azobisisobutyronitrile and / or azobisisoheptanenitrile.

[0038] In some preferred embodiments, the first solvent includes any one or more combinations of methanol, ethanol, and propanol, but is not limited thereto.

[0039] In some preferred embodiments, the mass ratio of the initiator to the acrylate monomer is 0.05-5:100.

[0040] In some preferred embodiments, the polymerization reaction is carried out at a temperature of 60-80°C.

[0041] In some preferred embodiments, the polymerization reaction takes 1-12 hours.

[0042] In some preferred embodiments, the preparation method further includes removing the solvent from the obtained polymer emulsion after the polymerization reaction is completed.

[0043] In some preferred embodiments, the preparation method specifically includes:

[0044] The acrylate polymer, graphite material, and a second solvent are mixed and heated to react. The solvent is then removed and the mixture is dried to obtain the precursor material.

[0045] Furthermore, the precursor material is subjected to a low-temperature thermal crosslinking reaction at 200-300°C in a protective atmosphere to obtain a polymer-coated graphite anode material.

[0046] Furthermore, the graphite material includes, but is not limited to, artificial graphite materials.

[0047] Furthermore, the second solvent includes any one or more combinations of methanol, ethanol, and propanol, but is not limited thereto.

[0048] Furthermore, the reaction time of the low-temperature thermal crosslinking reaction is 2-24 hours.

[0049] The coating method described in this application involves dissolving the reactants in a solvent, followed by drying to form a uniformly dispersed reaction precursor on the surface of artificial graphite, and then performing low-temperature crosslinking. Compared to in-situ reactions that directly dissolve the reactants and mix them with artificial graphite for crosslinking, the problem with in-situ reactions is that the reactant precursor, after forming the crosslinked polymer, is most likely to be dispersed in the solvent rather than loaded or adsorbed on the surface of the artificial graphite particles. The polymer generated by free radical polymerization has poor solubility in the solvent, which can lead to polymer phase precipitation and aggregation, or even precipitation and separation, forming fine particles that are not conducive to sufficient coating with artificial graphite. Moreover, in-situ reactions leave residual unreacted monomers, making the system more complex. When the solvent is removed, i.e., during drying, the residues will adhere to the surface of the artificial graphite, causing contamination. Due to the limitation of the solvent's boiling point, the reaction temperature needs to be lower than the solvent's boiling point. Compared to in-situ reactions, non-in-situ reactions involve fully heating and dissolving the purified polymer in a good solvent. During drying, driven by heat, the polymer dynamically interacts with the surface of artificial graphite particles, forming an adhesion force and an initial physical coating. Then, in the dry state, the polymer on the surface of the artificial graphite undergoes a condensation reaction upon heating. Due to the external heat source and the exothermic effect of the reaction itself, the polymer can react well on the surface of the artificial graphite, without precipitation or separation as in the solvent state. The reaction temperature range is wider and not limited by the boiling point of the solvent, resulting in greater process adjustability.

[0050] Using the coating material and method described in this application, experiments showed that it can improve the thermal stability of artificial graphite. The possible reason is that the generated acrylate polymer coating layer is stable in the electrolyte. Under high-temperature heating, it can protect the graphite particles from being easily affected by the electrolyte, the positive and negative electrode active particles, and their high-temperature electrochemical by-reaction products, which are generally acidic products such as HF, PF5, and POF3, causing swelling, corrosion, or even decomposition. This protects the structure of the artificial graphite particles within the coating layer. Inside the battery, the polymer coating layer needs to be in long-term contact with and wetted by the electrolyte, especially at high temperatures. If swelling easily occurs, the polymer coating layer will swell and detach. During charging and discharging, the volume expansion caused by the lithium insertion / extraction of artificial graphite particles further exacerbates this, making the polymer coating layer more prone to falling off and desorbing. This prevents it from effectively coating the artificial graphite particles and providing the necessary protection.

[0051] In some more specific embodiments, the preparation method of the polymer-coated graphite anode material in this application includes the following steps:

[0052] Step (1) Polymer preparation method: Mix acrylate monomer, initiator and solvent to carry out polymerization reaction to obtain polymer emulsion. Remove solvent from the emulsion to obtain film-forming polymer.

[0053] Preferably, the monomer comprises any one or more combinations of acrylates.

[0054] Preferably, the initiator includes azobisisobutyronitrile, azobisisoheptanenitrile, etc.

[0055] Preferably, the monomer is 100% by mass, and the initiator is 0.05-5% by mass.

[0056] Preferably, the solvent includes methanol, ethanol, propanol, etc.

[0057] Preferably, the reaction temperature is 60-80°C.

[0058] Preferably, the reaction time is 1-12 hours.

[0059] Step (2) Polymer coating process for artificial graphite: The polymer, artificial graphite material, and solvent obtained in step (1) are thoroughly mixed and heated and stirred for 2-6 hours at a temperature of 40-60°C. The solvent is then removed, and the dried product is placed in a furnace and reacted at 200-300°C for 2-24 hours under an inert atmosphere to obtain polymer-coated artificial graphite material. Heating in the furnace allows the polymer side groups to be removed and self-condensed, resulting in a cross-linking reaction on the surface of the artificial graphite and the formation of a strong polymer coating layer. This allows the artificial graphite to be embedded inside the polymer, forming a core, while the polymer wraps around the outside, forming a shell, thus forming a coating structure.

[0060] Preferably, the solvent includes methanol, ethanol, propanol, etc.

[0061] Preferably, the reaction temperature is 200-300℃.

[0062] Preferably, the reaction is carried out in an inert atmosphere for 2-24 hours. The furnace can be a tubular furnace, a box furnace, a rotary furnace, or other heating equipment. The inert gas can be nitrogen, argon, or other gases.

[0063] Another aspect of the embodiments of this application provides a polymer-coated graphite anode material prepared by the aforementioned preparation method.

[0064] Another aspect of this application provides a polymer-coated graphite anode material, comprising: a graphite material as a core structure, and a thermally cross-linked polymer coating layer as a shell structure, wherein the graphite material is embedded within the thermally cross-linked polymer coating layer, and the thermally cross-linked polymer in the thermally cross-linked polymer coating layer has a structure as shown in formula (II):

[0065] In some preferred embodiments, the content of the thermally crosslinked polymer coating layer in the polymer-coated graphite anode material is 1-5 wt%.

[0066] In some preferred embodiments, the thickness of the thermally crosslinked polymer coating layer is 2-200 nm.

[0067] In some preferred embodiments, the specific surface area of ​​the polymer-coated graphite anode material is 1.2-1.9 m². 2 / g.

[0068] In some preferred embodiments, the particle size D50 of the polymer-coated graphite anode material is 12-14 μm.

[0069] In some preferred embodiments, the compaction density of the polymer-coated graphite anode material is 1.7-1.85 g / cm³. 3 .

[0070] The polymer-coated graphite anode material in this application, through infrared characterization, was found to have a high spectral density at 2560 cm⁻¹. -1 The peak corresponds to the stretching vibration of COC in the polymer, at 1680 cm⁻¹. -1 The peaks correspond to the stretching vibration of the C=O bond in the carbonyl group. The ratio of the peak intensities of the infrared peaks, i.e. the ratio of the absorption rates, is between 0.15 and 0.4.

[0071] In this application, the polymer-coated artificial graphite interacts with the electrolyte. Its color (Ch) can be measured by immersing it in the electrolyte (1M LiPF6 in dimethyl carbonate DMC) at room temperature (25°C) for 4 days. Through repeated experiments, it was found that Ch is between 400-600 Hazen.

[0072] The polymer coating in this application can wet the surface of artificial graphite, fill defects and pits, and exhibit a low specific surface area characteristic, with a specific surface area S of 1.2-1.9 μm. 2 / g, the particle size (D50) of coated artificial graphite is generally between 12-14 μm, and the compacted density (d) is between 1.7-1.85 g / cm³. 3 .

[0073] The polymer corresponding to the thermally crosslinked polymer coating layer reported in this application is a crosslinked polyacrylate. Before thermal crosslinking, the main chain contains one or more acrylate monomers, and the specific structure is as follows:

[0074] Wherein, R1 is H or methyl, and R2 is tert-butyl, tert-amyl, tert-hexyl, or tert-octyl. The acrylate monomers include any one or more combinations of tert-butyl acrylate, tert-butyl methacrylate, tert-amyl acrylate, tert-amyl methacrylate, tert-hexyl acrylate, tert-octyl acrylate, and tert-octyl methacrylate. R2 contains a quaternary carbon atom and can undergo thermal condensation at a temperature of 200-300°C, producing thermal crosslinking of the acrylate and forming a thermally stable network polymer.

[0075] In this application, polymer coating is used to improve the thermal stability of artificial graphite. The polymer coating is generated by the condensation reaction of polymer side chains on the surface of artificial graphite to form an acrylate polymer, which is then cross-linked to form a polymer network that is uniformly coated on the surface of artificial graphite particles.

[0076] The innovation of this application lies in proposing a low-temperature, energy-saving coating method. Based on the dry polymerization of acrylate polymers at a lower temperature, it can efficiently condense to form cross-linked polymers, resulting in cross-linked acrylate polymers. Due to the hydrogen bonding between the acrylate polymers and defects such as hydroxyl and carbonyl groups on the surface of artificial graphite particles, they can be well dispersed on the surface of the artificial graphite particles. The condensation temperature is below 300℃, far lower than the temperature of conventional resin coating and carbonization on the surface of artificial graphite (approximately 1000-2000℃), resulting in low energy consumption. The formation of acrylate polymers is a green reaction. The acrylate monomers, as reaction precursors, are soluble in a single solvent, namely an alcohol. Furthermore, the resulting products are small molecules such as acrylate polymers and alcohols. The small molecule alcohols volatilize rapidly at 100℃ and can be fully dried at the aforementioned dry synthesis temperature, without causing pollution. Moreover, this condensation reaction is not demanding on reaction conditions, and the synthesis temperature is relatively low. The resulting cross-linked polyacrylate polymers exhibit high thermal stability in later stages. Reheating to 250°C does not cause a reaction, and even at higher temperatures, such as 300°C, the cross-linked polymers do not undergo thermal decomposition, which is beneficial for the high-temperature use of batteries. The cross-linked polyacrylates possess a network structure that can firmly coat the surface of artificial graphite. The network structure can be represented as follows:

[0077] The acrylate polymers in this application are reaction precursors, wherein the polymer side chains of the acrylates are adjustable, and the side groups can be selected from tert-butyl, tert-amyl, tert-hexyl, tert-octyl, etc.

[0078] The acrylate polymers of this application, in addition to exhibiting swelling with the electrolyte, weak reactivity, and resistance to acidic byproducts, can also form hydrogen bonds with the hydroxyl and carbonyl groups on the surface of artificial graphite particles. The acrylic structure can also form multi-site hydrogen bonds with defects on the surface of artificial graphite particles, which is beneficial for the surface dispersion and adsorption of the acrylate polymers. Because of their good adhesive properties, the acrylate polymers facilitate the bonding of artificial graphite particles, preventing them from detaching during lithium insertion / extraction, thus avoiding the failure of electron or ion contact pathways and the inability to achieve the desired electrochemical capacity.

[0079] The coating layer in this application is a polymer, requiring a small amount, generally between 1-5%, but its effective effect is significant, especially in significantly improving the thermal stability of batteries based on artificial graphite. Another aspect of this application also provides the use of the aforementioned polymer-coated graphite anode material in the preparation of secondary battery anodes or secondary batteries.

[0080] Another aspect of this application provides a lithium-ion battery comprising the aforementioned polymer-coated graphite anode material.

[0081] The technical solution of this application will be further described in detail below with reference to several preferred embodiments and accompanying drawings. This embodiment is implemented on the premise of the invention technical solution, and provides detailed implementation methods and specific operation processes. However, the protection scope of this application is not limited to the following embodiments.

[0082] Unless otherwise specified, the experimental materials used in the examples below can be purchased from conventional biochemical reagent companies.

[0083] Example 1

[0084] A polymer-coated artificial graphite material is prepared by the following method:

[0085] (1) Add 1 wt% azobisisobutyronitrile to an ethanol solution of tert-butyl acrylate and react at 80°C for 8 h, then dry to obtain the polymer.

[0086] (2) The obtained 3g polymer, 100g artificial graphite material and 500mL ethanol are thoroughly mixed and heated and stirred for 4h at a temperature of 50℃. The solvent is then removed by rotary evaporation. The obtained artificial graphite material is transferred to a tube furnace and reacted at 250℃ for 6h under a nitrogen atmosphere to obtain cross-linked polyacrylate-coated artificial graphite material.

[0087] The infrared spectrum of the cross-linked polyacrylate-coated artificial graphite material prepared in this embodiment is shown in Figure 1. It can be observed in the infrared spectrum that at 2560 cm⁻¹... -1The peak corresponds to the stretching vibration of COC in the polymer, at 1680 cm⁻¹. -1 The peak corresponds to the stretching vibration of the C=O bond in the carbonyl group.

[0088] The polymer thermogravimetric curve (DTG) in this embodiment is shown in Figure 2. As can be seen from the figure, the polymer undergoes a thermal crosslinking reaction at 250°C to generate a crosslinked polymer. Due to the condensation and removal of the side chains, a mass change occurs, forming the most obvious DTG peak.

[0089] Example 2

[0090] A polymer-coated artificial graphite material, differing from Example 1 in its polymer structure, is as follows:

[0091] (1) Add 1 wt% azobisisobutyronitrile to an ethanol solution of tert-amyl acrylate and react at 80°C for 8 h, then dry to obtain the polymer.

[0092] (2) The obtained 3g polymer, 100g artificial graphite material and 500mL ethanol are thoroughly mixed and heated and stirred for 4h at a temperature of 50℃. The solvent is then removed by rotary evaporation. The obtained artificial graphite material is transferred to a tube furnace and reacted at 250℃ for 6h under a nitrogen atmosphere to obtain cross-linked polyacrylate-coated artificial graphite material.

[0093] Example 3

[0094] A polymer-coated artificial graphite material, differing from Example 1 in its polymer structure, is as follows:

[0095] (1) Add 1 wt% azobisisobutyronitrile to an ethanol solution of tert-hexyl acrylate and react at 80°C for 8 h, then dry to obtain the polymer.

[0096] (2) The obtained 3g polymer, 100g artificial graphite material and 500mL ethanol are thoroughly mixed and heated and stirred for 4h at a temperature of 50℃. The solvent is then removed by rotary evaporation. The obtained artificial graphite material is transferred to a tube furnace and reacted at 250℃ for 6h under a nitrogen atmosphere to obtain cross-linked polyacrylate-coated artificial graphite material.

[0097] Example 4

[0098] A polymer-coated artificial graphite material, differing from Example 1 in its polymer structure, is as follows:

[0099] (1) Add 1 wt% azobisisobutyronitrile monomer to an ethanol solution of tert-butyl methacrylate and react at 80°C for 8 h, then dry to obtain the polymer.

[0100] (2) The obtained 3g polymer, 100g artificial graphite material and 500mL ethanol are thoroughly mixed and heated and stirred for 4h at a temperature of 50℃. The solvent is then removed by rotary evaporation. The obtained artificial graphite material is transferred to a tube furnace and reacted at 250℃ for 6h under a nitrogen atmosphere to obtain cross-linked polyacrylate-coated artificial graphite material.

[0101] Example 5

[0102] A polymer-coated artificial graphite material, differing from Example 1 in the initiator, is as follows:

[0103] (1) Add 1 wt% azobisisoheptanenitrile to an ethanol solution of tert-butyl acrylate and react at 80°C for 8 h, then dry to obtain the polymer.

[0104] (2) The obtained 3g polymer, 100g artificial graphite material and 500mL ethanol are thoroughly mixed and heated and stirred for 4h at a temperature of 50℃. The solvent is then removed by rotary evaporation. The obtained artificial graphite material is transferred to a tube furnace and reacted at 250℃ for 6h under a nitrogen atmosphere to obtain cross-linked polyacrylate-coated artificial graphite material.

[0105] Example 6

[0106] A polymer-coated artificial graphite material differs from Example 1 in that it has a polymer synthesis temperature, as detailed below:

[0107] (1) Add 1 wt% azobisisobutyronitrile to an ethanol solution of tert-butyl acrylate and react at 60°C for 8 h, then dry to obtain the polymer.

[0108] (2) The obtained 3g polymer, 100g artificial graphite material and 500mL ethanol are thoroughly mixed and heated and stirred for 4h at a temperature of 50℃. The solvent is then removed by rotary evaporation. The obtained artificial graphite material is transferred to a tube furnace and reacted at 250℃ for 6h under a nitrogen atmosphere to obtain cross-linked polyacrylate-coated artificial graphite material.

[0109] Example 7

[0110] A polymer-coated artificial graphite material differs from Example 1 in the polymer thermal crosslinking temperature, as detailed below:

[0111] (1) Add 1 wt% azobisisobutyronitrile to an ethanol solution of tert-butyl acrylate and react at 80°C for 8 h, then dry to obtain the polymer.

[0112] (2) The 3g polymer, 100g artificial graphite material and 500mL ethanol were thoroughly mixed and heated and stirred for 4h at 50℃. The solvent was then removed by rotary evaporation. The artificial graphite material was transferred to a tube furnace and reacted at 280℃ for 4h under a nitrogen atmosphere to obtain cross-linked polyacrylate-coated artificial graphite material.

[0113] Example 8

[0114] A polymer-coated artificial graphite material, differing from Example 1 in the polymer thermal crosslinking time, is detailed below:

[0115] (1) Add 1 wt% azobisisobutyronitrile to an ethanol solution of tert-butyl acrylate and react at 80°C for 8 h, then dry to obtain the polymer.

[0116] (2) The obtained 3g polymer, 100g artificial graphite material and 500mL ethanol are thoroughly mixed and heated and stirred for 4h at a temperature of 50℃. The solvent is then removed by rotary evaporation. The obtained artificial graphite material is transferred to a tube furnace and reacted at 250℃ for 12h under a nitrogen atmosphere to obtain cross-linked polyacrylate-coated artificial graphite material.

[0117] Example 9

[0118] A polymer-coated artificial graphite material, differing from Example 1 in the amount of polymer added, is as follows:

[0119] (1) Add 1 wt% azobisisobutyronitrile to an ethanol solution of tert-butyl acrylate and react at 80°C for 8 h, then dry to obtain the polymer.

[0120] (2) Mix 5g of polymer, 100g of artificial graphite material and 500mL of ethanol thoroughly, heat and stir for 4h at 50℃, remove the solvent by rotary evaporation, transfer the artificial graphite material to a tube furnace, react for 12h at 250℃ under nitrogen atmosphere to obtain cross-linked polyacrylate-coated artificial graphite material.

[0121] Comparative Example 1

[0122] The same artificial graphite material as in the examples, but without cross-linked polyacrylate.

[0123] The high-temperature cycling performance of the full cells in Example 1 and Comparative Example 1 of this application is shown in Table 1. It can be seen that, after polymer coating and thermal crosslinking, the full cells of Example 1 and Comparative Example 1 have higher capacity retention and better thermal cycling stability at high temperatures during high-temperature cycling.

[0124] Comparative Example 2

[0125] A polymer-coated artificial graphite material, differing from Example 1 in that the polymer is not cross-linked, is detailed below:

[0126] (1) Add 1 wt% azobisisobutyronitrile to an ethanol solution of tert-butyl acrylate and react at 80°C for 8 h, then dry to obtain the polymer.

[0127] (2) The prepared 3g polymer, 100g artificial graphite material and 500mL ethanol are thoroughly mixed, heated and stirred for 4h at 50℃, and then the solvent is removed by rotary evaporation to obtain uncrosslinked polyacrylate-coated artificial graphite material.

[0128] Comparative Example 3

[0129] A polymer-coated artificial graphite material differs from Example 1 in the polymer thermal crosslinking temperature, as detailed below:

[0130] (1) Add 1 wt% azobisisobutyronitrile to an ethanol solution of tert-butyl acrylate and react at 80°C for 8 h, then dry to obtain the polymer.

[0131] (2) The obtained 3g polymer, 100g artificial graphite material and 500mL ethanol are thoroughly mixed and heated and stirred for 4h at a temperature of 50℃. The solvent is then removed by rotary evaporation. The obtained artificial graphite material is transferred to a tube furnace and reacted at 150℃ for 6h under a nitrogen atmosphere to obtain polyacrylate-coated artificial graphite material.

[0132] Comparative Example 4

[0133] A polymer-coated artificial graphite material, differing from Example 1 in its polymer structure, is as follows:

[0134] (1) Add 1 wt% azobisisobutyronitrile to an ethanol solution of methyl acrylate and react at 80°C for 8 h, then dry to obtain the polymer.

[0135] (2) The obtained 3g polymer, 100g artificial graphite material and 500mL ethanol are thoroughly mixed and heated and stirred for 4h at 50℃. The solvent is then removed by rotary evaporation. The obtained artificial graphite material is transferred to a tube furnace and reacted at 250℃ for 6h under a nitrogen atmosphere to obtain polyacrylate-coated artificial graphite material.

[0136] Test method:

[0137] Particle size:

[0138] Particle size was measured using an MS3000 laser particle size analyzer. The principle is that when a laser beam passes through a dispersed particle sample, the intensity of the scattered light is measured to determine the particle size. Then, the particle size distribution is simulated based on the scattering spectrum of the material. D represents the particle size corresponding to a cumulative particle size distribution percentage of 50% for a sample.

[0139] Infrared spectrum:

[0140] A Bruker TENSOR 27 was used to measure the infrared spectrum of the material, with a spectral range of 4000 cm⁻¹. -1 ~500cm -1 .

[0141] Thermogravimetric test:

[0142] After preheating for 3 hours, 10 mg was weighed using a 1 / 20000 balance and placed in a small ceramic crucible. The parameters of the TGA5500 thermogravimetric analyzer were set, and the temperature was increased from room temperature (25℃) to 850℃ at a rate of 10℃ / min. Nitrogen gas was purged during the test at a rate of 40 mL / min. The first derivative curve of the mass loss ratio versus temperature was obtained.

[0143] Colorimetric detection:

[0144] The sample was tested using a PFXi195-1 automatic colorimeter, and the measurement results displayed by the instrument were recorded.

[0145] Methods for testing specific surface area:

[0146] By measuring the amount of gas adsorbed on the solid surface at different relative pressures under constant temperature and low temperature, the amount of monolayer adsorption of the sample is obtained, and the specific surface area of ​​the graphite material is calculated.

[0147] Compacted density test:

[0148] The test was conducted using an automatic compaction tester. The instrument was first pre-compacted and then zeroed. 1g of sample was weighed and placed in the mold. The mold was then placed on the automatic compaction device, and the compaction density of the sample at 3T was tested.

[0149] Adiabatic accelerated calorimeter test:

[0150] Using the ARC device set to ADSC mode, the temperature was increased at a rate of 0.25℃ / min starting at a constant temperature of 45℃. The thermal runaway initiation temperature T1 and thermal decomposition temperature T2 of the full-charged cell were recorded.

[0151] Full battery fabrication and testing:

[0152] The graphite material prepared above was dissolved in deionized water with carboxymethyl cellulose and styrene-butadiene rubber at a mass ratio of 96.5:1.5:1, with the solid content controlled at 50%. This solution was then coated onto a copper foil current collector and vacuum dried to obtain the negative electrode. Lithium cobalt oxide, polyvinylidene fluoride, and conductive carbon were dissolved in N-methylpyrrolidone at a mass ratio of 97:2:1, with the solid content controlled at 50%. This solution was then coated onto an aluminum foil current collector and vacuum dried to obtain the positive electrode. The battery pack was then assembled in a dew point chamber. After assembly and activation, the battery was charged and discharged at 45°C within a range of 3V to 4.4V. The specific conditions were: constant temperature at 45°C for 1 hour, followed by constant current charging at 4C for 9 minutes, constant current charging at 2.5C for 4.8 minutes, constant current and constant voltage charging at 1.5C to 4.4V, cutoff current at 0.05C, resting for 5 minutes, constant current discharge at 1C, cutoff voltage at 3V, and resting for 5 minutes. This cycle was repeated for 600 cycles, and the capacity retention rate R was recorded. The results are shown in Table 1.

[0153] Table 1

[0154] In addition, the inventors of this case also conducted experiments with other raw materials, process operations, and process conditions described in this specification, referring to the aforementioned embodiments, and obtained relatively ideal results in all cases.

[0155] It should be understood that the technical solution of this application is not limited to the specific implementation examples mentioned above. Any technical modifications made to the technical solution of this application without departing from the spirit and scope of protection of the claims shall fall within the scope of protection of this application.

Claims

1. A method for preparing a polymer-coated graphite anode material, characterized in that, include: An acrylate polymer is prepared by polymerizing a mixed reaction system containing at least an acrylate monomer, an initiator, and a first solvent. Furthermore, the acrylate polymer, graphite material, and a second solvent are mixed and heated to react, then the solvent is removed and dried to obtain a precursor material; then, in a protective atmosphere, the precursor material is subjected to a low-temperature thermal crosslinking reaction at 200-300°C to obtain a polymer-coated graphite anode material; the low-temperature thermal crosslinking reaction at least removes the polymer side groups and causes self-condensation. The acrylate monomers have the structure shown in formula (I): R1 is selected from H, methyl or ethyl, R2 contains quaternary carbon atoms in its structure, and n is 20 to 2000.

2. The preparation method according to claim 1, characterized in that: R2 is selected from any one of tert-butyl, tert-pentyl, tert-hexyl, tert-octyl, 2-methyl-2-phenylpropyl, and 2-phenyl-3,3-dimethylbutyl. And / or, the initiator includes azobisisobutyronitrile and / or azobisisoheptanenitrile; And / or, the first solvent includes any one or more combinations of methanol, ethanol, and propanol.

3. The preparation method according to claim 1, characterized in that: The acrylate monomers include any one or more combinations of tert-butyl acrylate, tert-butyl methacrylate, tert-amyl acrylate, tert-amyl methacrylate, tert-hexyl acrylate, tert-hexyl methacrylate, tert-octyl acrylate, and tert-octyl methacrylate.

4. The preparation method according to claim 1, characterized in that: The mass ratio of the initiator to the acrylate monomer is 0.05-5:100; And / or, the reaction temperature of the polymerization reaction is 60-80℃; and / or, the reaction time of the polymerization reaction is 1-12h.

5. The preparation method according to claim 1, characterized in that... Also includes: After the polymerization reaction is complete, the solvent in the obtained polymer emulsion is removed.

6. The preparation method according to claim 1, characterized in that: The graphite material includes artificial graphite material; And / or, the second solvent includes any one or more combinations of methanol, ethanol, and propanol; And / or, the reaction time of the low-temperature thermal crosslinking reaction is 2-24 hours.

7. The polymer-coated graphite anode material prepared by any one of claims 1-6.

8. The polymer-coated graphite anode material according to claim 7, characterized in that: The content of the thermally cross-linked polymer coating layer in the polymer-coated graphite anode material is 1-5 wt%. And / or, the thickness of the thermally crosslinked polymer coating layer is 2-200 nm; And / or, the specific surface area of ​​the polymer-coated graphite anode material is 1.2-1.9 m². 2 / g; And / or, the particle size D50 of the polymer-coated graphite anode material is 12-14 μm; And / or, the compaction density of the polymer-coated graphite anode material is 1.7-1.85 g / cm³. 3 .

9. The use of the polymer-coated graphite anode material according to claim 7 or 8 in the preparation of a secondary battery anode or a secondary battery.

10. A lithium-ion battery, characterized in that, It includes the polymer-coated graphite anode material as described in claim 7 or 8.

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