Modified graphite and preparation method thereof, negative plate and secondary battery

Abstract

The invention provides modified graphite and a preparation method thereof, a negative plate and a secondary battery. The preparation method of the modified graphite comprises the following steps: providing a liquid coating agent, atomizing the liquid coating agent, providing graphite, and dispersing the graphite. And mixing the dispersed graphite with the atomized liquid coating agent, so that the liquid coating agent is sprayed on the graphite to obtain a modified material, and carrying out carbonization treatment on the modified material. According to the application, the liquid coating agent is atomized, the graphite is dispersed, and then the dispersed graphite and the atomized liquid coating agent are mixed, so that the liquid coating agent is sprayed on the graphite, the contact area and the coating uniformity can be increased, and the coating effect is improved.

Description

Technical Field

[0001] This application belongs to the technical field of material preparation, and specifically relates to modified graphite and its preparation method, negative electrode sheets, and secondary batteries. Background Art

[0002] Graphite is currently the mainstream negative electrode material in the production of lithium-ion batteries. In the industry, soft carbon or hard carbon is usually coated on the surface of graphite to reduce the impedance in the battery to achieve fast charging. However, the current coating effect of graphite is poor. Summary of the Invention

[0003] In view of this, in the first aspect of this application, a preparation method of modified graphite is provided. The preparation method includes:

[0004] Providing a liquid coating agent and atomizing the liquid coating agent;

[0005] Providing graphite and dispersing the graphite;

[0006] Mixing the dispersed graphite with the atomized liquid coating agent so that the liquid coating agent is sprayed onto the graphite to obtain a modified material;

[0007] Performing carbonization treatment on the modified material.

[0008] Compared with the related technology where only the liquid coating agent and graphite are simply mixed and coated, in the preparation method provided in the first aspect of this application, by atomizing the liquid coating agent and dispersing the graphite respectively, the liquid coating agent is refined at this time. Subsequently, the dispersed graphite is mixed with the atomized liquid coating agent so that the liquid coating agent is sprayed onto the graphite, which can increase the contact area and the uniformity of coating, thereby improving the coating effect. Finally, the modified material is subjected to carbonization treatment to obtain coated graphite.

[0009] Among them, the step of providing a liquid coating agent and atomizing the liquid coating agent includes:

[0010] Providing a liquid coating agent and an atomizing gas;

[0011] Partially mixing the liquid coating agent with the atomizing gas, and the atomizing gas can atomize the liquid coating agent.

[0012] Among them, before the step of partially mixing the liquid coating agent with the atomizing gas, it further includes:

[0013] Stirring the liquid coating agent to make the liquid coating agent discrete;

[0014] Accelerating a part of the atomizing gas.

[0015] Among them, after partially mixing the liquid coating agent with the atomizing gas, the following steps are further included:

[0016] Mix the remaining atomizing gas with the atomized liquid coating agent to atomize the liquid coating agent again.

[0017] Among them, providing the graphite and dispersing the graphite includes:

[0018] Provide graphite and rotate the graphite, so as to disperse the graphite by using centrifugal force, and the centrifugal force can also be used to spheroidize the graphite; moreover, the airflow formed by the atomized coating agent can also impact the graphite to disperse it.

[0019] Among them, mixing the dispersed graphite with the atomized liquid coating agent includes:

[0020] Spray the atomized liquid coating agent on the dispersed and rotating graphite to mix the dispersed graphite with the atomized liquid coating agent.

[0021] Among them, providing the liquid coating agent and atomizing the liquid coating agent includes:

[0022] Provide a liquid coating agent, and the liquid coating agent is used to be introduced through the first feed port of the mixing chamber in the coating equipment to atomize the liquid coating agent;

[0023] The providing the graphite and dispersing the graphite includes:

[0024] Provide graphite, and the graphite is used to be introduced through the second feed port of the mixing chamber in the coating equipment to disperse the graphite.

[0025] Among them, the mass ratio of the liquid coating agent to the graphite is (8 - 20):(80 - 92).

[0026] Among them, the graphite includes at least one of artificial graphite, natural graphite, and recycled graphite.

[0027] Among them, before carbonizing the modified material, the following steps are further included:

[0028] Perform heat treatment on the modified material.

[0029] The second aspect of the present application provides a modified graphite, and the modified graphite is prepared by the preparation method of the modified graphite provided in the first aspect of the present application.

[0030] For the modified graphite provided in the second aspect of the present application, by adopting the preparation method provided in the first aspect of the present application, the coating effect of the modified graphite can be improved.

[0031] Among them, the D50 of the modified graphite is 5.5 μm - 15 μm; the D100 is 28.0 μm - 52 μm; the specific surface area SSA ≤ 2.5; the compaction density (5T) is 1.8 - 2.2 / g / cm 3 ; the Raman is 0.1 - 0.3.

[0032] The third aspect of the present application provides a negative electrode sheet, and the negative electrode sheet includes the modified graphite provided in the second aspect of the present application.

[0033] The fourth aspect of the present application provides a secondary battery, and the secondary battery includes the negative electrode sheet provided in the third aspect of the present application. Description of the Drawings

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required to be used in the embodiments of the present application will be described below.

[0035] Figure 1 It is a process flow chart of the preparation method of the modified graphite in an embodiment of the present application.

[0036] Figure 2 It is a process flow chart included in S100 in an embodiment of the present application.

[0037] Figure 3 It is a process flow chart included before S120 in an embodiment of the present application.

[0038] Figure 4 It is a process flow chart included after S120 in an embodiment of the present application.

[0039] Figure 5 It is a process flow chart included in S200 in an embodiment of the present application.

[0040] Figure 6 It is a process flow chart included in S300 in an embodiment of the present application.

[0041] Figure 7 It is a process flow chart included in S100 and S200 in an embodiment of the present application.

[0042] Figure 8 It is a process flow chart included in S200 in another embodiment of the present application.

[0043] Figure 9 It is a scanning electron microscope image of the aggregate in an embodiment of the present application.

[0044] Figure 10 It is a scanning electron microscope image of the graphite in an embodiment of the present application.

[0045] Figure 11This is the process flow chart included after S400 in an embodiment of the present application. Detailed implementation manners

[0046] The following are the preferred implementation manners of the present application. It should be noted that for those of ordinary skill in the art in this technical field, without departing from the principle of the present application, several improvements and retouches can still be made, and these improvements and retouches are also regarded as the protection scope of the present application.

[0047] Graphite, the anode material of lithium batteries, has advantages such as high initial efficiency, low expansion, and low potential, and is currently the mainstream anode material in the industrial production of lithium-ion batteries. With the continuous development of the new energy market towards high power and fast charging, the impedance of the anode material has become the main bottleneck faced in the design of the high-power fast-charging performance of the battery cell. To break through the mileage anxiety of energy density and the safety hazards brought by high-power fast charging, and achieve the design goals of impedance reduction and fast charging. At present, the new energy field mainly focuses on means such as the selection of coke raw material types, the control of coke crushing particle size, and the surface amorphous carbon coating modification. The resistance of the anode material of the battery includes three parts: the first part is the electrochemical conversion reaction resistance that occurs at the interface of the anode material particles for lithium ions; the second part is the diffusion resistance of lithium ions inside the anode material structure; the third part is the ohmic resistance of the anode material itself. At present, the industry mainly reduces the electrochemical conversion reaction resistance by coating soft carbon or hard carbon on the material surface.

[0048] Currently, the coating of graphite is only simply mixing the liquid coating agent with the graphite material to achieve coating, but such coating effect is poor, seriously affecting the electrochemical performance of the material. Therefore, it is of great significance to develop a preparation method with simple production process, good mixing coating effect, and excellent capacity and rate performance of the prepared electrode material.

[0049] In view of this, to solve the above problems, the present application provides a preparation method of modified graphite. Please refer to Figure 1 , Figure 1 This is the process flow chart of the preparation method of modified graphite in an embodiment of the present application. The preparation method includes S100, S200, S300, and S400. Among them, the detailed introductions of S100, S200, S300, and S400 are as follows.

[0050] S100, provide a liquid coating agent and atomize the liquid coating agent.

[0051] Graphite is a crystalline carbon. In the production process of batteries, using graphite material as the anode material can make the battery have advantages such as high initial efficiency, low expansion, and low potential, and is currently a commonly used anode material in the industrial production of lithium-ion batteries.

[0052] The liquid coating agent is a coating agent used to coat graphite, thereby improving various properties of graphite. Optionally, the liquid coating agent includes, but is not limited to, by-products of ethylene pyrolysis tar stripping. In other words, it can be one or a mixture of heterocyclic aromatic hydrocarbons, ketones, hydrocarbons, THF or NMP dissolved asphalt, and heavy oil.

[0053] The state of the liquid coating agent is a liquid substance in the form of large particles and large droplets. In this embodiment, the liquid coating agent can be atomized. In other words, the liquid coating agent in the form of large droplets is dispersed into a fog-like coating agent of fine-sized particles, forming a coated agent of fine particles after atomization. In this way, the coated agent after atomization can be evenly sprayed on the graphite, so that the graphite is mixed with the refined coating agent, effectively increasing the contact area and the uniformity of coating, thereby improving the coating effect and production capacity.

[0054] S200, Provide graphite and disperse the graphite.

[0055] The graphite includes at least one of artificial graphite, natural graphite, and recycled graphite. Among them, artificial graphite is a kind of graphite-like substance prepared artificially. Regarding the specific preparation method of artificial graphite, this application will be introduced in detail later. The traditionally prepared artificial graphite is a large-sized coarse material in which multiple artificial graphites are agglomerated together. In the related art, the above artificial graphite and the liquid coating agent are simply mixed, resulting in only the surface of the large pieces of artificial graphite being coated, but a small part of the artificial graphite cannot be coated, greatly reducing the coating effect of the artificial graphite.

[0056] In addition, natural graphite is graphite naturally formed in nature, generally occurring in ores such as graphite schist, graphite gneiss, graphite-containing schist, and metamorphic shale. Recycled graphite is obtained from the waste residues, waste liquids, waste gases generated during the production of natural graphite and artificial graphite, and the recycling of retired waste batteries.

[0057] S300, Mix the dispersed graphite with the atomized liquid coating agent so that the liquid coating agent is sprayed on the graphite to obtain a modified material.

[0058] Subsequently, the dispersed graphite is mixed with the atomized liquid coating agent so that the liquid coating agent is evenly sprayed on the graphite, which can increase the contact area and the uniformity of coating, thereby improving the coating effect.

[0059] S400, Carbonize the modified material.

[0060] The modified material obtained after mixing the liquid coating agent and the graphite also needs to be carbonized, and finally coated graphite that can be used as a negative electrode material can be obtained.

[0061] In summary, the preparation method provided by this embodiment can effectively improve the contact area and coating uniformity by dispersing and refining graphite and the liquid coating agent, thereby improving the coating effect and enabling the preparation of modified graphite materials with excellent capacity and rate performance of the electrode material.

[0062] Please refer to Figure 2 , Figure 2 which is the process flow chart included in S100 in an embodiment of this application. In this embodiment, S100 provides a liquid coating agent, and atomizing the liquid coating agent includes S110 and S120. The detailed introductions of S110 and S120 are as follows.

[0063] S110 provides a liquid coating agent and an atomizing gas.

[0064] S120 mixes part of the liquid coating agent with the atomizing gas, and the atomizing gas can atomize the liquid coating agent.

[0065] In this embodiment, the liquid coating agent and the atomizing gas can be mixed with each other. In other words, in this embodiment, not only the liquid coating agent and graphite are introduced, but also the atomizing gas is introduced together with the liquid coating agent. Optionally, the atomizing gas includes, but is not limited to, nitrogen, helium, etc. Subsequently, the atomizing gas can atomize the liquid coating agent to form an atomized air flow, so as to be mixed and coated with the dispersed graphite, effectively reducing the atomization difficulty. In addition, in this embodiment, part of the liquid coating agent and the atomizing gas can be mixed, and part of the atomizing gas is used to initially atomize the liquid coating agent, and the remaining atomizing gas can be used for secondary atomization later.

[0066] Optionally, a heated liquid coating agent can be provided to further reduce the atomization difficulty.

[0067] Optionally, a heated atomizing gas can be provided. On the one hand, it is convenient for the liquid coating agent to be atomized, and on the other hand, it can effectively remove the solvent and the volatile components of the coating agent, facilitating further granulation and carbonization, and reducing the production cost. And the introduction of the hot air flow can also reduce the kinematic viscosity of the coating agent. After the modified material is put into the rotary kiln for calcination again, it can further increase the mixing uniformity and also remove the volatile components of the coating agent, ensuring the compaction of the negative electrode material and improving the fast charging performance of the negative electrode material.

[0068] Please refer to Figure 3 , Figure 3 which is the process flow chart included in this application before S120 in an embodiment. In this embodiment, before S120 mixes part of the liquid coating agent with the atomizing gas, it further includes S111 and S112. The detailed introductions of S111 and S112 are as follows.

[0069] S111, stir the liquid coating agent to disperse the liquid coating agent.

[0070] S112, accelerate a part of the atomizing gas.

[0071] Before mixing the liquid coating agent with a part of the atomizing gas, the liquid coating agent can be stirred first by using a structure such as a spiral stirring blade, so that the liquid coating agent is preliminarily dispersed by rotary breaking and then undergoes dispersion acceleration, which can reduce the atomization difficulty when cooperating with the atomizing gas subsequently.

[0072] Moreover, in this embodiment, a part of the atomizing gas can also be accelerated. For example, the atomizing gas can pass through components such as a reducing pipe, so that the accelerating air passage in the reducing pipe gradually narrows. Thus, when the intake air volume of the atomizing gas remains unchanged, as the diameter of the flow channel gradually becomes smaller, the flow velocity of the atomizing gas gradually increases, increasing the gas-phase kinetic energy and fully enhancing the subsequent impact atomization effect. In this way, when the accelerated atomizing gas meets the liquid coating agent after dispersion acceleration, the accelerated gas will impact the liquid coating agent, and the kinetic energy of the high-speed air flow is used to break the liquid phase, thereby atomizing the liquid coating agent into fine particle coating agents by impact, enabling the two phases to be fully mixed and initially forming a good atomized flow.

[0073] Please refer to Figure 4 , Figure 4 which is the process flow chart included after S120 in an embodiment of the present application. In this embodiment, after mixing the liquid coating agent with a part of the atomizing gas in S120, S121 is further included. Among them, the detailed introduction of S121 is as follows.

[0074] S121, mix the remaining atomizing gas with the atomized liquid coating agent to atomize the liquid coating agent again.

[0075] As can be seen from the above content, after providing the atomizing gas, the atomizing gas can be divided into two parts. A part of the atomizing gas is accelerated and then impacts with the liquid coating agent to achieve the effect of initially atomizing the coating agent. At this time, the average volume of the ejected small oil droplets is relatively small. The remaining atomizing gas can also be used to impact the coating agent after initial atomization, so that the atomized liquid droplet group of the liquid is squeezed and deformed and further atomized, thereby expanding the spraying area and reducing the droplet size, increasing the uniformity of coating and the disorder degree of the material in the cavity, reducing the agglomeration between materials, and further improving the atomization effect.

[0076] Please refer to Figure 5 , Figure 5 which is the process flow chart included in S200 in an embodiment of the present application. In this embodiment, S200 provides graphite, and dispersing the graphite includes S210. Among them, the detailed introduction of S210 is as follows.

[0077] S210, provide graphite, rotate the graphite so as to disperse the graphite by using centrifugal force, and the centrifugal force can also be used to spheroidize the graphite; moreover, the airflow formed by the atomized coating agent can also impact the graphite to disperse it.

[0078] In order to enable the graphite to be well dispersed, this embodiment provides a variety of specific embodiments. In one embodiment, when providing graphite, components such as a toothed multi-impeller rotor can be used to place the graphite in a space of a rotating airflow. The graphite will rotate under the action of the airflow in this space. When the graphite rotates, due to the action of centrifugal force, the agglomerated graphite can be dispersed and spheroidized.

[0079] Moreover, since the graphite must be in a sealed space when rotating, the graphite agglomerated together under the action of centrifugal force can also form fine particles under the impact of the bin wall of the sealed space, reducing the agglomeration of the material.

[0080] In addition, as can be seen from the above content, the accelerated atomizing gas impacts the liquid coating agent to atomize the coating agent and form an atomized airflow with a certain impact force. This airflow can also disperse the agglomerated artificial stone when it is ejected.

[0081] Optionally, the graphite can be in hot air when rotating, enabling good solvent evaporation.

[0082] Optionally, a blower can be used to blow the graphite and a suction fan can be used to negatively guide the graphite to tumble and thus enter the rotating space. Under the action of the airflow, it tumbles continuously to prevent agglomeration, making the graphite always in a relatively uniform state of fine particles, which is also convenient for the coating agent to coat on the graphite. Further optionally, the temperature of the airflow used to blow the graphite is 90°C - 110°C, which can remove the moisture in the graphite, prevent agglomeration between graphite particles, improve the coating effect of the coating agent, and prevent the coating agent from being diluted by water. It can also reduce the weight of the modified graphite particles, making the modified graphite easier to be blown up by the airflow for coating. For example, the airflow temperature can be 90°C, 95°C, 100°C, 105°C, 110°C.

[0083] The frequency of the suction fan is 26Hz - 50Hz. When the frequency of the suction fan is 26Hz - 50Hz, the particle size of the graphite is better at this time. When the fan frequency is too low, that is, lower than 26Hz, the negative pressure suction is insufficient and the graphite agglomerates and cannot enter the bin due to gravity. When the fan frequency is too high, that is, higher than 50Hz, the graphite is quickly pulled into the bin, which is not conducive to the coating of the liquid coating agent. For example, the fan frequency can be 26Hz, 30Hz, 35Hz, 40Hz, 45Hz, 50Hz.

[0084] Please refer toFigure 6 , Figure 6 is a process flow diagram included in S300 in an embodiment of the present application. In this embodiment, S300 mixing the dispersed graphite with the atomized liquid coating agent includes S310. The detailed introduction of S310 is as follows.

[0085] S310, spraying the atomized liquid coating agent onto the dispersed and rotating graphite, so as to mix the dispersed graphite with the atomized liquid coating agent.

[0086] After the graphite is dispersed and the coating agent is atomized, in this embodiment, the two are not simply mixed, but the atomized liquid coating agent is sprayed onto the dispersed and rotating graphite. In other words, the spraying direction of the atomized liquid coating agent is fixed, but the dispersed graphite is always in a rotating state. Therefore, the atomized coating agent can be evenly sprayed on the dispersed graphite, further improving the coating effect.

[0087] Optionally, when the dispersed graphite is mixed with the atomized liquid coating agent, it can move in the direction opposite to gravity under the negative pressure created by the induced draft fan and the driving of the rotating eddy current, that is, move along the vertically upward direction, and finally be input into the bin. Compared with the traditional mixing method of depositing at the bottom of the bin and moving along the direction of gravity, it can make the modified graphite move upward under the action of the eddy current and negative pressure in the mixing bin, so that the modified graphite collides with each other and is not easy to agglomerate, thus making the mixing more uniform.

[0088] Please refer to Figure 7 , Figure 7 is a process flow diagram included in S100 and S200 in an embodiment of the present application. In this embodiment, S100 provides a liquid coating agent and atomizes the liquid coating agent, including S130. The detailed introduction of S130 is as follows.

[0089] S130, providing a liquid coating agent, which is used to be introduced into the first feed port of the mixing bin of the coating equipment to atomize the liquid coating agent.

[0090] S200 provides graphite and disperses the graphite, including S220. The detailed introduction of S220 is as follows.

[0091] S220, providing graphite, which is used to be introduced into the second feed port of the mixing bin of the coating equipment to disperse the graphite.

[0092] In this embodiment, the liquid coating agent and graphite can be introduced into the mixing chamber of the coating equipment through different feeding ports respectively. For example, the liquid coating agent is evenly fed into the first feeding port of the mixing chamber of the coating equipment, and graphite is evenly fed into the second feeding port of the mixing chamber of the coating equipment. This facilitates the subsequent atomization and dispersion of graphite and the liquid coating agent respectively, and improves the modification uniformity.

[0093] Please refer to Figures 8 - 10 , Figure 8 , which is the process flow chart included in S200 in another embodiment of the present application. Figure 9 , which is the scanning electron micrograph of the aggregate in one embodiment of the present application. Figure 10 , which is the scanning electron micrograph of graphite in one embodiment of the present application. In this embodiment, S200 for providing graphite includes S230 and S240. The detailed descriptions of S230 and S240 are as follows.

[0094] S230 provides coke materials and pitch, and mixes the crushed coke materials and the pitch to obtain primary granulated materials.

[0095] The coke materials can be oil-based coke or coal-based coke, both of which are commonly used materials for making artificial graphite for battery anodes. By using the above materials, battery anode materials with good electrical conductivity, good heat shock resistance and high strength can be obtained. Crushing can decompose large-diameter particles into small-diameter particles. Modification means storing the coke materials and pitch in the same container and stirring them, so that they are evenly distributed to obtain modified materials. Optionally, the coke materials are crushed to D50 = 5.5μm - 10.5μm, D100 ≤ 28.0μm - 52μm, that is, the particle size corresponding to the cumulative particle size distribution percentage of the coke materials reaching 50% is 5.5μm - 10.5μm, and the particle size corresponding to the cumulative particle size distribution percentage of the coke materials reaching 100% is not greater than 28.0μm - 52μm. Specifically, at least half of the coke material particles have a diameter between 5.5μm and 10.5μm, and all the coke material particles have a diameter less than or equal to 28.0μm - 52μm, so as to obtain coke particles with a particle size within a suitable range, which is convenient for subsequent mixing operations with other materials and improves the uniformity after mixing. For example, half of the coke material particles can have a diameter of 5.5μm, 6μm, 7μm, 8μm, and all the coke material particles have a diameter less than 28.0μm, 30μm, 32μm, 34μm, 36μm, 38μm, 40μm.

[0096] Furthermore, the crushed coke materials can be deeply shaped or spheroidized and classified to obtain aggregates with relatively round particle morphologies, such as Figure 9As shown in the figure, the aggregate particle size is controlled such that D50 = 6.0 μm - 11.0 μm and D100 ≤ 28.0 μm - 52 μm. That is, the particle size corresponding to when the cumulative particle size distribution percentage of the aggregate reaches 50% is 6.0 - 11.0 μm, and the particle size corresponding to when the cumulative particle size distribution percentage of the aggregate reaches 100% is not greater than 28.0 - 52 μm. Specifically, at least half of the aggregate particles have a diameter between 6.0 - 11.0 μm, and all of the aggregate particles have a diameter less than or equal to between 28.0 - 52 μm, thereby obtaining coke-like aggregates with a particle size within a suitable range, facilitating subsequent mixing operations with other materials and improving the uniformity after mixing. For example, at least half of the aggregate particle sizes can be 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm. All of the aggregate particles have a diameter less than or equal to 29 μm, 33 μm, 37 μm, 41 μm, 45 μm, 49 μm, 52 μm.

[0097] Optionally, the crushing method can be one of a jet mill, a mechanical mill, and a roller press mill, and the shaping equipment can be one or a combination of a shaping machine and a spheroidizing machine.

[0098] In the anode material, asphalt, as an important additive, plays an irreplaceable role. It can not only act as a binder to improve the mechanical strength and durability of the anode material, but also act as a conductive agent to improve the charge and discharge performance and efficiency of the battery. Optionally, the asphalt can be low-temperature asphalt, medium-temperature asphalt, and high-temperature asphalt, thereby being able to improve the electrical properties of the anode material.

[0099] The coke-like material for crushing and shaping is a powdered material for making pellets. By mixing the powdered material for making pellets with asphalt, a primary pelletized material is obtained. Optionally, the mass ratio of the powdered material for making pellets to asphalt during mixing is (88 - 100):(0 - 12). It can be understood that when the mass ratio of the powdered material for making pellets to asphalt is the largest, it is 100:0, that is, asphalt can be not added, and only the coke-like material is used for subsequent graphitization treatment to produce the anode material with the required special properties. The smallest mass ratio of the powdered material for making pellets to asphalt is 88:12. The mixing time is 50 min. When the mixing time is too short, the mixing is uneven, which will affect the performance of the modified graphite. When the mixing time is too long, the production efficiency will be affected. For example, the mass ratio of the powdered material for making pellets to asphalt during mixing is 88:12, 90:10, 92:8, 94:6, 96:4, 98:2, 100:0.

[0100] Optionally, after mixing the powdered material for making pellets with asphalt, heat treatment is carried out under the protection of a nitrogen atmosphere. The temperature of the heat treatment is 300°C - 700°C, and the time of the heat treatment is 5 h - 7 h. For example, the temperature of the heat treatment is 300°C, 400°C, 500°C, 600°C, 700°C, and the time of the heat treatment is 5 h, 5.5 h, 6 h, 6.5 h, 7 h.

[0101] Further optionally, the equipment used for heat treatment can be conventional heat treatment equipment in the art, such as a roller furnace, a horizontal kettle or a vertical kettle, preferably a vertical kettle.

[0102] S240, subject the primary granulated material to graphitization treatment to obtain artificial graphite.

[0103] After obtaining the first granulated material by mixing crushed and shaped coke materials with pitch, it is necessary to subject the primary granulated material or the primary powdered material to graphitization treatment, so as to improve the electrical conductivity, thermal conductivity, thermal shock resistance, chemical stability, lubricity and abrasion resistance of the material, and obtain artificial graphite, as Figure 10 shown. Optionally, in this embodiment, the primary granulated material is subjected to graphitization treatment under the conditions of 2500°C - 3000°C. If the graphitization temperature is too low, the graphitization effect will be affected, resulting in poor related properties of the artificial graphite. If the graphitization temperature is too high, it will cause waste of heat and increase production costs. For example, the ambient temperature for graphitization treatment can be 2500°C, 2850°C, 3000°C.

[0104] In this embodiment, the mass ratio of the coating agent to the graphite during mixing is (8 - 20):(80 - 92). When the coating agent and the graphite are mixed, they will be mixed in a certain proportion, so that the coating agent and the graphite can be evenly mixed, avoiding excessive residual carbon during the production process and causing waste of raw materials. The mass ratio of the coating agent to the graphite during mixing is (8 - 20):(80 - 92) to achieve a designed residual carbon of 1% - 2.5%. In other words, the maximum mass ratio of the coating agent to the graphite during mixing is 20:80, and the minimum is 8:92, which can achieve a lower designed residual carbon. When the proportion of the coating agent is small, it will lead to uneven coating, and finally the fast charging performance of the battery is poor. When the proportion of the coating agent is high, the coating carbon layer is thicker, resulting in a significant decrease in the specific capacity, that is, the capacitance of a certain mass of the battery becomes lower. For example, the mass ratio of the coating agent to the graphite during mixing can be 8:92, 10:90, 12:88, 14:86, 16:84, 18:82, 20:80.

[0105] In this embodiment, when the dispersed graphite is mixed with the atomized liquid coating agent, the atomization temperature of the liquid coating agent is 30°C - 150°C. When the atomization temperature is low, that is, when the atomization temperature is lower than 30°C, or when the atomization temperature is high, that is, when the atomization temperature is higher than 150°C, the kinematic viscosity of the coating agent will become higher and the fluidity of the coating agent will become worse, so that the coating agent is not easily evenly distributed on the surface of the graphite and the coating effect becomes worse. For example, the atomization temperature can be 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C.

[0106] Optionally, the rotational speed of the rotor device is 20 Hz - 50 Hz. When the rotational speed of the rotor device is less than 20 Hz, the effect of the air flow is too weak, and the graphite is prone to agglomeration. When the rotational speed of the rotor device is greater than 50 Hz, the movement trajectory of the graphite particles is too complex, resulting in smaller collision particles between the graphite and poorer mixing uniformity with the coating agent. For example, the rotational speed of the rotor device can be 20 Hz, 25 Hz, 30 Hz, 35 Hz, 40 Hz, 45 Hz, 50 Hz.

[0107] In this embodiment, before the modified material is carbonized, a heat treatment step is also included, where the working temperature of the heat treatment is 300 °C - 700 °C, and the time is 6 h to obtain a semi-finished product. When the material is flammable and explosive, it is necessary to pass inert gases such as nitrogen and helium in the reaction vessel to prevent the presence of oxygen in the environment during the heat treatment and cause an explosion. Optionally, the heat treatment can be carried out in a converter. Optionally, the equipment used for the heat treatment can be conventional heat treatment equipment in the art, such as a roller furnace, a horizontal kettle or a vertical kettle, preferably a vertical kettle.

[0108] And under the protection of a nitrogen atmosphere, the carbonization treatment is carried out at a constant temperature of 1000 °C - 1300 °C for 4 h - 8 h. If the carbonization time is too short, the material cannot be fully converted into carbide. If the carbonization time is too long, the material structure will be loose and over-burned. For example, the temperature during the carbonization treatment can be 1000 °C, 1050 °C, 1100 °C, 1150 °C, 1200 °C, 1250 °C, 1300 °C, and the constant temperature duration can be 4 h, 4.5 h, 5 h, 5.5 h, 6 h, 6.5 h, 7 h, 7.5 h, 8 h. Optionally, the equipment for the carbonization treatment can be conventional equipment in the art, such as a roller hearth kiln, a pusher kiln or a tunnel kiln.

[0109] Please refer to Figure 11 , Figure 11 , which is the process flow chart included after S400 in an embodiment of the present application. In this embodiment, after the modified material is sequentially subjected to heat treatment and carbonization treatment in S400, S500 is further included. Among them, the detailed introduction of S500 is as follows.

[0110] S500, the carbonized modified material is sequentially depolymerized, mixed and screened to obtain modified graphite.

[0111] After the heat treatment and carbonization of the modified material, a carbonized material of the modified material is obtained. Subsequently, the carbonized material needs to be depolymerized, mixed, and screened to reduce the particle size and ensure that the particle diameters are within a certain range, thereby obtaining the finished product. Specifically, the carbonized material is slightly depolymerized by a hydrocyclone mill or a rod mill, then mixed in a ribbon mixer for 40 min - 60 min, and then screened in an ultrasonic vibrating screen with a screening mesh size of 200 - 350 meshes to obtain the finished modified graphite.

[0112] Optionally, the mixing time can be 40 min, 45 min, 50 min, 55 min, or 60 min. The screening mesh size can be 200 meshes, 250 meshes, 300 meshes, 310 meshes, 320 meshes, 325 meshes, 330 meshes, 340 meshes, or 350 meshes.

[0113] In addition to the above-provided preparation method of modified graphite, this embodiment also provides a modified graphite. The preparation method of the modified graphite and the modified graphite provided in this embodiment can both achieve the technical effects of this embodiment. The two can be used together, and of course, they can also be used separately. This embodiment has no special restrictions on this. For example, as an embodiment, the preparation method of the above-mentioned modified graphite can be used to prepare the following modified graphite.

[0114] The modified graphite provided in this embodiment is used as the anode material of a lithium battery. From the above content, it can be seen that by using the above preparation method for preparation, the graphite and the liquid coating agent can be fully mixed during the preparation process, improving the coating effect. It can also output the mixture while mixing the graphite and the liquid coating agent, realizing continuous and non-stop production and improving the production capacity.

[0115] In this embodiment, the D50 of the modified graphite is 5.5 μm - 15 μm; D100 is 28.0 μm - 52 μm; the specific surface area SSA ≤ 2.5; the tap density (5T) is 1.8 - 2.2 / g / cm 3 ; the Raman is 0.1 - 0.3. The modified graphite prepared by the above preparation method can improve the discharge capacity, initial efficiency and rate performance, and fast charging performance of the modified graphite anode material.

[0116] This application also provides five specific examples and a comparative example. The specific differences are as follows:

[0117] Example 1:

[0118] Step 1: Provide coke materials for crushing, crushing to D50 = 8.0 ± 1.0 μm, D100 ≤ 28 μm. Later, use a shaping machine for deep shaping or spheroidization classification to obtain aggregates with relatively round particle morphology. The aggregate particle size is controlled to be D00 ≥ 2.0 μm, D50 = 8.7 ± 0.5 μm, and D100 ≤ 28 μm.

[0119] Step 2: The crushed coke material and asphalt are fully mixed in a VC mixer with a mass ratio of 93:7 and a mixing time of 50 minutes. The mixture is heat-treated in a vertical kettle under nitrogen atmosphere at a temperature of 700°C for 6 hours to obtain a primary granulated material.

[0120] Step 3: graphitizing the primary granulated material or the primary powdered material at 3000° C. to obtain graphite.

[0121] Step 4: Mix the liquid coating agent and graphite in a mass ratio of 15:85 (designed residual carbon 1.5%), use hot air flow to make the graphite in motion, and then spray the atomized liquid coating agent on the moving graphite for coating. The atomization temperature of the liquid coating agent is 100°C, the rotation speed is 25Hz, the induced draft fan frequency is 35Hz, and the liquid coating agent is a by-product of ethylene cracking tar stripping to obtain a modified material.

[0122] Step 5: heat-treat the modified material in a vertical kettle under the protection of a nitrogen atmosphere at a temperature of 600° C. for 4 hours to obtain a semi-finished product.

[0123] Step 6: Under the protection of nitrogen atmosphere, heat in a roller kiln for carbonization treatment, and the carbonization treatment is kept at a constant temperature of 1150°C for 4 hours.

[0124] Step 7: The carbonized material obtained in step 6 is slightly deagglomerated by a cyclone mill, and then mixed in a ribbon mixer for 50 minutes, and then sieved in an ultrasonic vibration sieve with a sieve mesh of 325 to obtain a finished modified graphite.

[0125] Embodiment 2:

[0126] Step 1: Provide coke materials for crushing, crushing to D50 = 8.0 ± 1.0 μm, D100 ≤ 28 μm. Later, use a shaping machine for deep shaping or spheroidization classification to obtain aggregates with relatively round particle morphology. The aggregate particle size is controlled to be D00 ≥ 2.0 μm, D50 = 8.7 ± 0.5 μm, and D100 ≤ 28 μm.

[0127] Step 2: The crushed coke material and asphalt are fully mixed in a VC mixer with a mass ratio of 95:5 and a mixing time of 50 minutes. The mixture is heat-treated in a vertical kettle under nitrogen atmosphere at a temperature of 700°C for 6 hours to obtain a primary granulated material.

[0128] Step 3: graphitizing the primary granulated material or the primary powdered material at 3000° C. to obtain graphite.

[0129] Step 4: Mix the liquid coating agent and graphite in a mass ratio of 8:92 (designed residual carbon 0.8%), use hot air flow to make the graphite in motion, and then spray the atomized liquid coating agent on the moving graphite for coating. The atomization temperature of the liquid coating agent is 150°C, the rotation speed is 50Hz, the induced draft fan frequency is 50Hz, and the liquid coating agent is a by-product of ethylene cracking tar stripping to obtain a modified material.

[0130] Step 5: heat-treat the modified material in a horizontal kettle under the protection of a nitrogen atmosphere at a temperature of 600° C. for 4 hours to obtain a semi-finished product.

[0131] Step 6: Under the protection of nitrogen atmosphere, heat in a roller kiln for carbonization treatment, and the carbonization treatment is kept at a constant temperature of 1150°C for 5 hours.

[0132] Step 7: Grind and slightly deagglomerate the carbonized material rod obtained in step 6, mix it in a ribbon mixer for 50 minutes, and then sieve it in an ultrasonic vibration screen with a sieve size of 325 to obtain finished modified graphite.

[0133] Embodiment 3:

[0134] Step 1: Provide coke materials for crushing, crushing to D50 = 8.0 ± 1.0 μm, D100 ≤ 28 μm. Later, use a shaping machine for deep shaping or spheroidization classification to obtain aggregates with relatively round particle morphology. The aggregate particle size is controlled to be D00 ≥ 2.0 μm, D50 = 8.7 ± 0.5 μm, and D100 ≤ 28 μm.

[0135] Step 2: The crushed coke material and asphalt are fully mixed in a VC mixer with a mass ratio of 90:10 and a mixing time of 50 minutes. The mixture is heat-treated in a vertical kettle under nitrogen atmosphere at a temperature of 700°C for 6 hours to obtain a primary granulated material.

[0136] Step 3: graphitizing the primary granulated material or the primary powdered material at 3000° C. to obtain graphite.

[0137] Step 4: Mix the liquid coating agent and graphite in a mass ratio of 10:90 (designed residual carbon 1%), use hot air flow to make the graphite in motion, and then spray the atomized liquid coating agent on the moving graphite for coating. The atomization temperature of the liquid coating agent is 120°C, the rotation speed is 30Hz, the induced draft fan frequency is 38Hz, and the liquid coating agent is a by-product of ethylene cracking tar stripping to obtain a modified material.

[0138] Step 5: heat-treat the modified material in a vertical kettle under the protection of a nitrogen atmosphere at a temperature of 550° C. for 6 hours to obtain a semi-finished product.

[0139] Step 6: Under the protection of nitrogen atmosphere, heat in a tunnel kiln for carbonization treatment, and the carbonization treatment is kept at a constant temperature of 1150°C for 4.5 hours.

[0140] Step 7: The carbonized material obtained in step 6 is slightly deagglomerated by a cyclone mill, and then mixed in a ribbon mixer for 50 minutes, and then sieved in an ultrasonic vibration sieve with a sieve mesh of 325 to obtain a finished modified graphite.

[0141] Embodiment 4:

[0142] Step 1: Provide coke materials for crushing, crushing to D50 = 8.0 ± 1.0 μm, D100 ≤ 28 μm. Later, use a shaping machine for deep shaping or spheroidization classification to obtain aggregates with relatively round particle morphology. The aggregate particle size is controlled to be D00 ≥ 2.0 μm, D50 = 8.7 ± 0.5 μm, and D100 ≤ 28 μm.

[0143] Step 2: The crushed coke material and asphalt are fully mixed in a VC mixer with a mass ratio of 92:8 and a mixing time of 50 minutes. The mixture is heat-treated in a vertical kettle under nitrogen atmosphere at a temperature of 700°C for 6 hours to obtain a primary granulated material.

[0144] Step 3: graphitizing the primary granulated material or the primary powdered material at 3000° C. to obtain graphite.

[0145] Step 4: Mix the liquid coating agent and graphite in a mass ratio of 12.5:87.5 (designed residual carbon 1.25%), use hot air flow to make the graphite in motion, and then spray the atomized liquid coating agent on the moving graphite for coating. The atomization temperature of the liquid coating agent is 100°C, the rotation speed is 35Hz, the induced draft fan frequency is 42Hz, and the liquid coating agent is a by-product of ethylene cracking tar stripping to obtain a modified material.

[0146] Step 5: heat-treat the modified material in a vertical kettle under the protection of a nitrogen atmosphere at a temperature of 500° C. for 8 hours to obtain a semi-finished product.

[0147] Step 6: Under the protection of nitrogen atmosphere, heat in a tunnel kiln for carbonization treatment, and the carbonization treatment is kept at a constant temperature of 1150°C for 6 hours.

[0148] Step 7: The carbonized material obtained in step 6 is slightly deagglomerated by a cyclone mill, and then mixed in a ribbon mixer for 50 minutes, and then sieved in an ultrasonic vibration sieve with a sieve mesh of 325 to obtain a finished modified graphite.

[0149] Embodiment 5:

[0150] Step 1: Provide coke materials for crushing, crushing to D50 = 8.0 ± 1.0 μm, D100 ≤ 28 μm. Later, use a shaping machine for deep shaping or spheroidization classification to obtain aggregates with relatively round particle morphology. The aggregate particle size is controlled to be D00 ≥ 2.0 μm, D50 = 8.7 ± 0.5 μm, and D100 ≤ 28 μm.

[0151] Step 2: The crushed coke material and asphalt are fully mixed in a VC mixer with a mass ratio of 93:7 and a mixing time of 50 minutes. The mixture is heat-treated in a vertical kettle under nitrogen atmosphere at a temperature of 700°C for 6 hours to obtain a primary granulated material.

[0152] Step 3: graphitizing the primary granulated material or the primary powdered material at 3000° C. to obtain graphite.

[0153] Step 4: Mix the liquid coating agent and graphite in a mass ratio of 15:85 (designed residual carbon 1.5%), use hot air flow to make the graphite in motion, and then spray the atomized liquid coating agent on the moving graphite for coating. The atomization temperature of the liquid coating agent is 100°C, the rotation speed is 25Hz, the induced draft fan frequency is 35Hz, and the liquid coating agent is a by-product of ethylene cracking tar stripping to obtain a modified material.

[0154] Step 5: Under the protection of nitrogen atmosphere, heat in a roller kiln for carbonization treatment, and the carbonization treatment is kept at a constant temperature of 1150°C for 4 hours.

[0155] Step 6: The carbonized material obtained in step 5 is slightly deagglomerated by a cyclone mill, and then mixed in a ribbon mixer for 50 minutes, and then sieved in an ultrasonic vibration sieve with a sieve mesh of 325 to obtain a finished modified graphite.

[0156] Comparative Example 1:

[0157] Step 1: Provide coke materials for crushing, crushing to D50 = 8.0 ± 1.0 μm, D100 ≤ 28 μm. Later, use a shaping machine for deep shaping or spheroidization classification to obtain aggregates with relatively round particle morphology. The aggregate particle size is controlled to be D00 ≥ 2.0 μm, D50 = 8.7 ± 0.5 μm, and D100 ≤ 28 μm.

[0158] Step 2: The crushed coke-like materials and pitch are fully mixed in a VC mixer with a mass ratio of 88:12 and a mixing time of 50 min. The mixture is heat-treated in a vertical kettle under a nitrogen atmosphere. It is treated at 700 °C for 6 h to obtain the primary granulated material.

[0159] Step 3: The primary granulated material or the primary powdered material is graphitized at 3000 °C to obtain graphite.

[0160] Step 4: The liquid coating agent and graphite are kneaded according to a mass ratio of 15:85 (designed residual carbon 1.5%). The kneading time is 50 min. The liquid-phase coating agent is the by-product of the stripping of ethylene cracking tar to obtain the modified material.

[0161] Step 5: The modified material is heat-treated in a vertical kettle under a nitrogen atmosphere at a temperature of 600 °C for 4 h to obtain the semi-finished product.

[0162] Step 6: Under the protection of a nitrogen atmosphere, it is heated in a roller hearth kiln for carbonization treatment. The carbonization treatment is carried out at a constant temperature of 1150 °C for 4 h.

[0163] Step 7: The carbonized material obtained in Step 6 is slightly depolymerized by a vortex mill, then mixed in a ribbon mixer for 50 min, and then screened in an ultrasonic vibrating screen with a screening mesh size of 325 meshes to obtain the finished modified graphite.

[0164] This application continued to test the physical properties and electrical properties of Examples 1-5 and Comparative Example 1. The specific test contents and test results are as follows:

[0165] The physical properties of the modified graphite anode materials obtained in each example and comparative example were tested. The specific test methods are as follows, and the test results are shown in Table 1.

[0166] Test method for the 5T compaction density of powder: The specific surface area (SSA) of the modified graphite anode material can be tested by methods known in the art. For example, it can refer to GB / T24533-2019. Weigh 1.0 g of the sample and add it to a special compaction mold with a diameter of 13 mm. Place a metal disc on each side of the mold hole. Put the powder between the metal discs and place a metal cylinder on the top. Place the mold on a compaction density instrument (model: Sansi Zongheng UTM7305), set the pressure to 5T, the pressure application displacement rate to 10 mm / min, the pressure holding time to 30 s, and the pressure relief displacement rate to 30 mm / min. Read the thickness of the sample after pressure relief, and then calculate the volume of the compacted powder. Finally, calculate according to the density formula ρ = m / v to obtain the compaction density of the powder at 5T.

[0167] Raman test method: Select an area of 100μm×100μm on the negative electrode active material layer, and use a laser confocal Raman spectrometer (Raman, HR Evolution, HORIBA Scientific Instruments Division) to scan the particles within this area to obtain the D peak and G peak of all particles within this area. Use LabSpec software to process the data to obtain the peak intensities of the D peak and G peak of each particle, which are ID and IG respectively, to obtain a normal distribution graph, count these particles, and calculate the ratio of Dn(0.15) to Dn(1). Dn(0.15) is the number of particles with Id / Ig≤0.15 in the ascending order of confocal Raman, and Dn(1) is the total number of particles with Id / Ig ranging from 0 to 1 in the ascending order of confocal Raman. The laser wavelength of the Raman spectrometer can be in the range of 532nm to 785nm.

[0168] Specific surface area test method: The specific surface area (SSA) of the modified graphite negative electrode material can be tested by methods known in the art. For example, it can be tested by the nitrogen adsorption specific surface area analysis test method with reference to GB / T19587-2017 and calculated by the BET (Brunauer Emmett Teller) method. Among them, the nitrogen adsorption specific surface area analysis test can be carried out by a Tri-Star 3020 specific surface area and pore size analyzer of Micromeritics Company, USA.

[0169] Perform electrical property tests on the modified graphite negative electrode materials obtained in each example and comparative example. The specific test methods are as follows:

[0170] Preparation method of lithium-ion battery (button cell): The preparation method of the coin-type lithium-ion battery can be tested by methods known in the art. Mix the above-prepared modified graphite negative electrode material, conductive agent (Super P), binder (SBR), and thickener (CMC-Na) in a mass ratio of 96.2:0.8:1.8:1.2 in an appropriate amount of deionized water and stir well to form a uniform negative electrode slurry. Then coat the negative electrode slurry on the surface of the negative electrode current collector copper foil. After drying and cold pressing, a negative electrode sheet is obtained. The coating thickness of the negative electrode sheet is 200μm. Use the above negative electrode sheet, a lithium sheet as the counter electrode, a polyethylene (PE) film as the separator, and a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) with a volume ratio of 1:1:1 as the electrolyte to assemble a coin-type lithium-ion battery.

[0171] Discharge specific capacity test method: Place the button cell in the thermostat of a blue battery test cabinet (T-3002A - 5V 1mA) at 25°C. Let the cell stand for 6 hours. Discharge the button cell at 0.1C until 1.0 mV, then let it stand for 10 minutes, and discharge it at 0.01C until 1.0 mV. Record the capacity of the button cell at this time, which is denoted as the discharge specific capacity.

[0172] First efficiency test method: Place the button cell in the thermostat of a blue battery test cabinet (T-3002A - 5V 1mA) at 25°C. Let the cell stand for 6 hours. Discharge the button cell at 0.1C until 1.0 mV, then let it stand for 10 minutes, and discharge it at 0.01C until 1.0 mV. Record the discharge capacity D; charge it at 0.05C until 1.5V, and record the charging capacity of the button cell at this time, which is denoted as the specific capacity C. The first cycle efficiency (%) = C / D × 100%.

[0173] Rate performance test: Place the button cell in the thermostat of a blue battery test cabinet (T-3002A - 5V 1mA) at 25°C. Let the cell stand for 1 hour to make the lithium-ion battery reach a constant temperature. Place the button cell in the thermostat of a blue battery test cabinet (T-3002A - 5V 1mA) at 25°C. Let the cell stand for 6 hours. Discharge the button cell at 0.1C until 1.0 mV, then let it stand for 10 minutes, and discharge it at 0.01C until 1.0 mV. Record the discharge capacity D; keep it at a constant temperature. Discharge the lithium-ion battery that has reached a constant temperature at a constant current of 0.2C until the voltage reaches 3.0V, let it stand for 5 minutes, charge it at a constant current of 0.5C to a voltage of 4.45V, then charge it at a constant voltage of 4.45V until the current reaches 0.05C and then let it stand for 5 minutes. Adjust the discharge rate and conduct discharge tests at 0.2C, 0.5C, 1C, 1.5C, and 2.0C respectively to obtain the discharge capacities. Compare the capacity obtained at each rate with the capacity obtained at 0.2C, and compare the rate performance by comparing the ratio of 2C to 0.2C.

[0174] Table 1

[0175]

[0176]

[0177] From the data results of Examples 1 - 4, it can be seen that as the modification ratio increases, the compaction, specific surface area, and gram capacity gradually decrease, but its rate performance, Raman, and first efficiency increase slightly. This is because after the modification ratio increases, the defects on the surface of the graphitized product are coated and modified, the specific surface area will decrease, and the lithium required to form the SEI film decreases, resulting in an increase in the first efficiency; the carbonization of the coating agent forms an amorphous carbon layer, which will increase Raman and decrease compaction. The lithium storage sites of the carbon layer are few, and the gram capacity is low, but the more uniform carbon layer can improve the interfacial impedance between the modified graphite and the electrolyte and enhance the fast charging performance of the modified graphite.

[0178] From the data results of Example 1 and Example 5, it can be seen that when the modification ratio is fixed, direct carbonization of the mixture will lead to a decrease in capacity, rate performance and compaction. This is because the mixture has not been stirred in a converter and the volatile components have not been removed.

[0179] From the data results of Example 1 and Comparative Example 1, it can be seen that atomizing and spraying the liquid coating agent discretely on the surface of highly dispersed graphite is more uniform than intermittent kneading and mixing. It can improve the discharge capacity, initial efficiency and rate performance of the modified graphite anode material on the premise of ensuring production capacity.

[0180] The above has introduced in detail the content provided by the embodiments of the present application. The principle and implementation manner of the present application have been elaborated and explained herein. The above description is only used to help understand the method and its core idea of the present application; at the same time, for those of ordinary skill in the art, according to the idea of the present application, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present application.

Claims

1. A method for preparing modified graphite, characterized in that, The preparation method includes: Providing a liquid coating agent and atomizing the liquid coating agent; Providing graphite and dispersing the graphite; Mixing the dispersed graphite with the atomized liquid coating agent so that the liquid coating agent is sprayed onto the graphite to obtain a modified material; Performing carbonization treatment on the modified material.

2. The preparation method of the modified graphite according to claim 1, characterized in that, The step of providing a liquid coating agent and atomizing the liquid coating agent includes: Providing a liquid coating agent and an atomizing gas; Partially mixing the liquid coating agent with the atomizing gas, and the atomizing gas can atomize the liquid coating agent.

3. The preparation method of the modified graphite according to claim 2, wherein, Before the partial mixing of the liquid coating agent with the atomizing gas, it further includes: Stirring the liquid coating agent to make the liquid coating agent discrete; Accelerating a part of the atomizing gas.

4. The preparation method of the modified graphite according to claim 2, wherein, After the partial mixing of the liquid coating agent with the atomizing gas, it further includes: Mixing the remaining atomizing gas with the atomized liquid coating agent to atomize the liquid coating agent again.

5. The preparation method of the modified graphite according to claim 1, wherein, The step of providing graphite and dispersing the graphite includes: Providing graphite and rotating the graphite so as to disperse the graphite by using centrifugal force, and the centrifugal force can also be used to spheroidize the graphite; and the airflow formed by the atomized coating agent can also impact the graphite to disperse it.

6. The preparation method of the modified graphite according to claim 5, wherein, The step of mixing the dispersed graphite with the atomized liquid coating agent includes: Spraying the atomized liquid coating agent onto the dispersed and rotating graphite so that the dispersed graphite is mixed with the atomized liquid coating agent.

7. The preparation method of the modified graphite according to claim 1, characterized in that, The step of providing a liquid coating agent and atomizing the liquid coating agent includes: Providing a liquid coating agent, and the liquid coating agent is introduced through the first feed port of the mixing chamber in the coating equipment to atomize the liquid coating agent; The step of providing graphite and dispersing the graphite includes: Providing graphite, and the graphite is introduced through the second feed port of the mixing chamber in the coating equipment to disperse the graphite.

8. The preparation method of the modified graphite according to claim 1, characterized in that, The mass ratio of the liquid coating agent to the graphite is (8 - 20):(80 - 92).

9. The preparation method of the modified graphite according to claim 1, wherein, The graphite includes at least one of artificial graphite, natural graphite, and recycled graphite.

10. The preparation method of the modified graphite according to claim 1, characterized in that, Before performing carbonization treatment on the modified material, it further includes: Performing heat treatment on the modified material.

11. A modified graphite, characterized in that, The modified graphite is prepared by the preparation method of the modified graphite according to any one of claims 1 - 10.

12. The modified graphite according to claim 11, wherein, The D50 of the modified graphite is 5.5 μm - 15 μm; the D100 is 28.0 μm - 52 μm; the specific surface area SSA ≤ 2.5 m 2 / g; the compaction density (5T) is 1.8 - 2.2 / g / cm 3 ; the Raman is 0.1 - 0.

3.

13. A negative electrode sheet, characterized in that, The negative electrode sheet includes the modified graphite according to claim 11.

14. A secondary battery, characterized in that, The secondary battery includes the negative electrode sheet according to claim 13.

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