Graphite material and preparation method thereof, negative plate, battery and electric equipment

Abstract

The invention discloses a graphite material and a preparation method thereof, a negative plate, a battery and electric equipment, the graphite material comprises a graphite core and a coating layer, the graphite core is filled with a filler, the untreated graphite material has a rich pore structure and a large specific surface area, the specific surface area of the graphite material can be reduced by filling the filler, and the specific surface area of the graphite material can be reduced by filling the filler. The high-temperature performance of the graphite material is improved; meanwhile, the surface of the graphite core is coated with the coating layer, so that the cyclic expansion effect of the graphite material can be relieved, lithium ion transmission is facilitated, the diffusion energy barrier of lithium ions at low temperature is reduced, and internal pores and an external structure of the graphite material can be optimized by filling the graphite material core and coating the graphite material. The graphite material provided by the invention has excellent low-temperature rate performance, high-temperature storage performance and cycle performance, and can be applied under high-temperature and low-temperature working conditions.

Description

Technical Field

[0001] The present invention belongs to the field of electrochemical technology, and in particular relates to a graphite material and a preparation method thereof, a negative electrode sheet, a battery and electrical equipment. Background Art

[0002] As an important component of lithium-ion batteries, graphite has the advantages of large reserves and low cost. However, its interlayer spacing is relatively high, resulting in large expansion during charging and discharging. The stress generated by the expansion during the cycle can cause the graphite sheets to detach, resulting in accelerated capacity decay. At the same time, the graphite particles are rich in pores and have large surface defects, which are prone to side reactions at high temperatures. All of these limit the use of graphite as a negative electrode material. Summary of the Invention

[0003] In order to solve at least one of the technical problems existing in the prior art, the present application provides a graphite material and a preparation method thereof, a negative electrode sheet, a battery and an electrical device.

[0004] In a first aspect, the present application provides a graphite material, which includes a graphite core and a coating layer, and the graphite core is filled with a filler.

[0005] The inventors of this application have found that the interior of the untreated graphite material has a rich pore structure and a large specific surface area. Filling the filler can reduce the specific surface area of ​​the graphite material and improve the high-temperature performance of the graphite material. At the same time, coating the surface of the graphite core with a coating layer can alleviate the cyclic expansion effect of the graphite material, facilitate lithium ion transmission, and reduce the diffusion energy barrier of lithium ions at low temperatures. By filling the core of the graphite material and coating the graphite material, the internal pores and external structure of the graphite material can be optimized. The graphite material provided by the present invention has excellent low-temperature rate performance, high-temperature storage performance and cycle performance, taking into account applications under high and low temperature conditions.

[0006] The second aspect of the present application provides a method for preparing the graphite material as described in the first aspect, comprising the following steps: mixing a graphite precursor and a filler to obtain a graphite core precursor; subjecting the graphite core precursor to a first high-temperature treatment to obtain a graphite core; and mixing the graphite core and a coating agent to a second high-temperature treatment to obtain a graphite material.

[0007] The method for preparing the graphite material provided in the present application is simple, easy to operate, has low energy consumption, and is easy to mass produce.

[0008] A third aspect of the present application provides a negative electrode sheet, comprising the graphite material described in the first aspect or the graphite material prepared by the preparation method described in the second aspect.

[0009] The fourth aspect of the present application provides a battery, comprising the negative electrode sheet described in the third aspect.

[0010] The fifth aspect of the present application provides an electrical device comprising the battery described in the fourth aspect. DETAILED DESCRIPTION

[0011] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0012] The invention provides a graphite material. The graphite material comprises a graphite core and a coating layer. The graphite core is filled with a filler.

[0013] Specifically, the interior of the untreated graphite material has a rich pore structure and a large specific surface area. Filling it with a filler can reduce the specific surface area of ​​the graphite material and improve the high-temperature performance of the graphite material. At the same time, coating the surface of the graphite core with a coating layer can alleviate the cyclic expansion effect of the graphite material, facilitate lithium ion transmission, and reduce the diffusion energy barrier of lithium ions at low temperatures. By filling the core of the graphite material and coating the graphite material, the internal pores and external structure of the graphite material can be optimized. The graphite material provided by the present invention has excellent low-temperature rate performance, high-temperature storage performance, and cycle performance, taking into account applications under both high and low temperature conditions.

[0014] According to some embodiments of the present application, the filler includes one or more of asphalt, coal tar, and heavy oil, and / or the coating layer includes one or more of asphalt, hard carbon, heavy oil, glucose, starch, and resin.

[0015] Specifically, the filler is selected from one or more of the above and can be filled into the interior of the graphite core to reduce the porosity of the graphite material, thereby reducing the specific surface area of ​​the graphite material, while improving the structural stability of the graphite material and improving its life. The coating layer is selected from one or more of the above and can be effectively coated on the surface of the graphite material, with a good coating effect, so that the graphite materials have a larger interlayer spacing, which is conducive to lithium ion transmission and reduces the diffusion energy barrier of lithium ions at low temperatures. At the same time, it reduces the direct contact between the electrolyte and the graphite material and reduces the occurrence of side reactions. In some embodiments of the present application, the resin may include epoxy resin, phenolic resin, organic resin, liquid phase resin, etc.

[0016] According to some embodiments of the present application, the covering layer includes at least two covering structures.

[0017] Specifically, the graphite material has a multi-layer coating structure, which can make the coating effect of the graphite material better and further improve the low-temperature performance of the battery.

[0018] According to some embodiments of the present application, the coating layer includes an inner coating structure close to the graphite core and an outer coating structure away from the graphite core, and the material of the inner coating structure is the same as that of the filler.

[0019] Specifically, in one embodiment of the present application, the graphite material includes a two-layer coating structure, including an inner coating structure adjacent to the graphite core and an outer coating structure distal to the graphite core. The inner coating structure is made of the same material as the filler. By using the filler to fill and coat the graphite material, the coating effect of the graphite material is enhanced, the coating uniformity of the graphite material is improved, and the occurrence of side reactions is reduced.

[0020] In another embodiment of the present application, the graphite material includes a three-layer coating structure, an inner coating structure close to the graphite core, an outer coating structure away from the graphite core, and an intermediate coating structure located between the inner coating structure and the outer coating structure. The material of the inner coating structure is a filler, and the materials of the intermediate coating structure and the outer coating structure can be coating agents, specifically resin and asphalt; more specifically, the positions of the resin and asphalt are not specifically limited, the material of the intermediate coating layer can be resin, the material of the outer coating layer can be asphalt, or the material of the intermediate coating layer can be asphalt, and the material of the outer coating layer can be resin.

[0021] According to some embodiments of the present application, the graphite material satisfies: 0.15≤BET*(I D / I G ) / OI≤0.4, wherein BET is the specific surface area of ​​the graphite material, I D / I G is the intensity ratio of the D peak and the G peak in the Raman spectrum of the graphite material, and OI is the ratio of the (004) and (110) crystal plane diffraction peak intensities of the graphite material.

[0022] Specifically, the BET of graphite materials is related to both the internal pores and external defects of the graphite materials, and the range of BET will affect the high-temperature performance of the graphite materials. D / I G It reflects the degree of defects in graphite materials and characterizes the disorder degree of the graphite material surface; OI is the ratio of the diffraction peak intensity of the (004) and (110) crystal planes of the graphite material, which characterizes the orientation of the graphite. D / I G ) / OI can characterize the electrochemical reaction activity of graphite materials and comprehensively reflect the isotropy, internal pore size and surface defect degree of graphite materials. D / I G) / OI may include but is not limited to 0.15, 0.18, 0.2, 0.25, 0.3, 0.35, 0.4, etc. Specifically, BET*(I D / I G Controlling the ) / OI ratio within the range of 0.15 to 0.4 can optimize the internal pores and external structure of the graphite material, reduce the probability of side reactions in the graphite material, and improve the high-temperature performance of the graphite material. It also alleviates the cyclic expansion effect of the graphite material, which facilitates lithium ion transport, reduces the diffusion energy barrier of lithium ions at low temperatures, and improves the low-temperature performance of the graphite material. The graphite material provided by the present invention has excellent low-temperature rate performance, high-temperature storage performance, and cycling performance, taking into account application in both high- and low-temperature conditions.

[0023] BET specific surface area test: refer to the test method of specific surface area specified in the national standard GB / T 24533-2019;

[0024] I D / I G Raman test: Raman test is used to characterize the disorder degree of graphite materials. D 1350 cm in Raman spectroscopy -1 The peak intensity at the position, I G 1580cm -1 Peak intensity at the position, peak intensity ratio I D / I G It reflects the degree of lattice defects.

[0025] OI value test: Test the OI value of the graphite material to characterize its orientation through X-ray diffraction test; calculate according to the following formula OI = I(004) / I(110), where I(004) is the intensity of the diffraction peak of the (004) crystal plane of the graphite material, and I(110) is the intensity of the diffraction peak of the (110) crystal plane of the graphite material.

[0026] According to some embodiments of the present application, BET is 1.5m 2 / g~5.0m 2 / g; and / or, I D / I G is 0.1-0.5; and / or, OI is 2-5.

[0027] Specifically, the specific surface area of ​​the graphite material is 1.5m 2 / g~5.0m 2 / g, due to the rich pore structure inside the graphite material, the untreated graphite material has a relatively large specific surface area. Reducing the specific surface area of ​​the graphite material is beneficial to improving its high temperature performance. BET can be but not limited to 1.5m 2 / g, 2.0m 2 / g, 2.5m2 / g, 3.0m 2 / g, 3.5m 2 / g, 4.0m 2 / g, 4.5m 2 / g, 5.0m 2 / g, etc.; I of graphite material D / I G 0.1~0.5, I D / I G The larger the graphite is, the more defects it has on the surface, which can provide more lithium insertion sites and channels for Li+, which is beneficial to accelerate the diffusion rate of lithium ions. D / I G The smaller the graphite material, the better the cycle stability. D / I G It can be but not limited to 0.1, 0.2, 0.3, 0.4, 0.5, etc.; the OI value of the graphite material is 2 to 5. The smaller the OI value, the better the isotropy of the graphite material, the easier Li+ is to be transmitted, and the better the low-temperature power performance of the battery. The OI can be but not limited to 2, 2.5, 3, 3.5, 4, 4.5, 5, etc. By adjusting the BET and I D / I G When OI is within the above range, the isotropy of the graphite material is better, the cycle stability is better, and the lithium ion diffusion is faster, which further improves the high-temperature and low-temperature performance of the graphite material.

[0028] According to some embodiments of the present application, the electrochemical active area of ​​the graphite material is 1.5m 2 / g~3.0m 2 / g. Specifically, the electrochemical active area of ​​the graphite material can be, but is not limited to, 1.5m 2 / g, 1.8m 2 / g, 2.0m 2 / g, 2.5m 2 / g, 3.0m 2 / g. The electrochemically active area of ​​graphite material refers to the area of ​​the graphite material surface that participates in the electrochemical reaction. If the electrochemically active area of ​​graphite material is within this range, the activity and efficiency of the chemical reaction of the graphite material in the electrode can be improved, thereby increasing the electrochemical reaction speed of the battery.

[0029] The electrochemical active area test method is as follows: assemble button-type lithium half-cells, perform AC impedance testing in a 298K constant temperature box, test frequency range 200kHz ~ 10mHz, excitation voltage 5mV, and fit the Nyquist curve using the formula The electrochemical active areas of different types of graphite materials can be obtained.

[0030] In a second aspect, the present application provides a method for preparing the graphite material described above, comprising the following steps:

[0031] S1: mixing a graphite precursor and a filler to obtain a graphite core precursor;

[0032] According to some embodiments of the present application, the graphite precursor includes one or more of artificial graphite and natural graphite, and the natural graphite includes flake graphite, microcrystalline graphite, etc. The graphite precursor can be pretreated, for example, the natural graphite material can be crushed, pickled, dried, spheroidized, etc., to obtain a graphite precursor with less impurities and regular shape, which is conducive to filling and coating it.

[0033] According to some embodiments of the present application, a graphite precursor and a filler are mixed and placed in a cold isostatic pressing apparatus for high-pressure treatment, so that the filler is filled into the graphite material, reducing the internal porosity of the graphite material, thereby reducing the specific surface area of ​​the graphite material and improving the high-temperature performance of the graphite material. Other methods can also be used in the present invention to fill the filler into the graphite core, and are not specifically limited here.

[0034] According to some embodiments of the present application, the filler includes one or more of asphalt, coal tar, and heavy oil. The filler is selected from the above materials and can fill and coat the interior and surface of the graphite. In some embodiments of the present application, while the filler is used to fill the graphite precursor, it can also form a coating layer on the surface of the graphite precursor, further improving the pore structure of the natural graphite. According to some preferred embodiments of the present application, the filler is a liquid filler, such as liquid heavy oil.

[0035] According to some further specific embodiments of the present application, the mass ratio of the graphite precursor and the filler is 100:(10~40), and the mass ratio of the graphite precursor and the filler may include but is not limited to 100:10, 100:12, 100:15, 100:20, 100:25, 100:30, and 100:40. The mass ratio of the graphite precursor and the filler within this range can have a good filling and modification effect.

[0036] S2: subjecting the graphite core precursor to a first high-temperature treatment to obtain a graphite core;

[0037] According to some embodiments of the present application, the obtained graphite core precursor is subjected to a first high-temperature treatment to obtain a graphite core. The first high-temperature treatment includes high-temperature sintering. The obtained graphite core precursor filled with a filler is subjected to high-temperature sintering while being protected by a protective atmosphere to obtain a graphite core. The high-temperature sintering gives the graphite core a densified structure. During the sintering process, as the temperature increases, volatile components in the filler gradually escape, forming a more ordered carbon structure within the graphite material, so that the pores within the graphite material are evenly filled.

[0038] According to some embodiments of the present application, the temperature of the first high temperature treatment is 900°C to 1500°C, and the time of the first high temperature treatment is 2h to 6h. The temperature and time of the first high temperature treatment are within the above range, which can better carbonize the graphite core precursor to form a more stable graphite core. At the same time, the pores inside the graphite precursor are filled, the defects are further reduced, and the structure is more orderly. In some embodiments of the present application, the temperature of the first high temperature treatment can be, but is not limited to, 900°C, 1000°C, 1100°C, 1200°C, 1300°C, 1400°C, 1500°C, etc.; the time of the first high temperature treatment can be, but is not limited to, 2h, 3h, 4h, 5h, 6h, etc.

[0039] According to some other embodiments of the present application, the graphite kernel precursor is subjected to a first high temperature treatment to obtain a graphite kernel, and the graphite kernel is further ground (specifically ball milling) by a grinding device to be shaped to eliminate the change in its morphology caused by the aforementioned cold isostatic pressing, and a spherical graphite kernel is obtained from irregular particles. Specifically, the speed of ball milling is 100rpm~800rpm; the time of ball milling is 2h~8h, and the speed and time of ball milling are within the above range, and can change its morphology without damaging the graphite material, so that it becomes a spherical graphite particle, which is conducive to the subsequent coating of graphite. In some embodiments of the present application, the speed of ball milling can be, but is not limited to, 100rpm, 200rpm, 300rpm, 400rpm, 500rpm, 600rpm, 700rpm, 800rpm, etc.; the time of ball milling can be, but is not limited to, 2h, 3h, 4h, 5h, 6h, 7h, 8h, etc.

[0040] S3: Mixing the graphite core and the coating agent and performing a second high-temperature treatment to obtain a graphite material.

[0041] According to some embodiments of the present invention, the coating agent includes one or more of asphalt, hard carbon, heavy oil, glucose, starch and resin. The coating agent is selected from one or more of the above materials and can effectively coat the graphite core material to improve the structural stability of the graphite material; in some embodiments of the present application, the coating agent can be coated on the graphite material with the filler coating layer to form a multi-layer coating layer. The multi-layer coating can improve the coating uniformity of the graphite surface, and the structure of the coating layer is more stable and not easy to crack or fall off due to expansion during the circulation process.

[0042] According to some embodiments of the present invention, the mass ratio of the graphite core and the coating agent is 100:(3~40), and the mass ratio of the graphite core and the coating agent can be but is not limited to 100:3, 100:5, 100:10, 100:15, 100:20, 100:25, 100:30, and 100:40; the mass ratio of the graphite core and the coating agent within the above range can have a better coating effect, repair graphite surface defects, and improve the degree of disorder of the graphite surface.

[0043] According to some embodiments of the present invention, the coating agent includes two or more coating agents, such as phenolic resin and asphalt. The use of two or more coating agents can form a multi-layer coating layer, thereby improving the coating effect on the graphite core, thereby facilitating the improvement of the low-temperature rate performance of the battery. In some embodiments of the present invention, when phenolic resin and asphalt are used as the coating agents, the mass ratio of the graphite core, phenolic resin, and asphalt can be, but is not limited to, 100:10:2.5, 100:10:5, 100:30:2.5, or 100:30:3.

[0044] According to some embodiments of the present invention, the second high temperature treatment includes high temperature sintering, the temperature of the second high temperature treatment is 900℃~1500℃, and the time of the second high temperature treatment is 2h~6h. The purpose of the second high temperature treatment is to form a coating layer on the graphite core material, alleviate the cyclic expansion effect of the graphite material, facilitate lithium ion transmission, reduce the diffusion energy barrier of lithium ions at low temperatures, and improve the low temperature performance of the graphite material. In some embodiments of the present application, the temperature of the second high temperature treatment can be, but is not limited to, 900℃, 1000℃, 1100℃, 1200℃, 1300℃, 1400℃, 1500℃, etc.; the time of the second high temperature treatment can be, but is not limited to, 2h, 3h, 4h, 5h, 6h, etc.

[0045] Compared with the prior art, the preparation method of the graphite material provided in the present application is simple, easy to operate, has low energy consumption, and is easy to mass produce.

[0046] In a third aspect, the present application provides a negative electrode sheet comprising the graphite material described in the first aspect, or a graphite material prepared by the method for preparing a graphite material described in the second aspect. The resulting negative electrode sheet has excellent isotropy, high energy density, high initial charge and discharge efficiency, and good compatibility with the electrolyte.

[0047] According to some embodiments of the present application, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer arranged on the negative electrode current collector, the negative electrode active material layer includes a negative electrode active material, wherein the negative electrode current collector can be a metal foil or a composite current collector (the metal material can be arranged on a polymer substrate to form a composite current collector), for example, the negative electrode current collector can be copper foil.

[0048] According to some embodiments of the present application, the negative electrode active material includes the graphite material described in the first aspect, or the graphite material prepared by the preparation method of the graphite material described in the second aspect, and may also include at least one of the following materials: soft carbon, hard carbon, silicon-based material, tin-based material and lithium titanate, etc.

[0049] According to some embodiments of the present application, the negative electrode active material layer may further optionally include a conductive agent, which may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers.

[0050] According to some embodiments of the present application, the negative electrode active material layer may optionally further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0051] According to some embodiments of the present application, the negative electrode sheet can be prepared by the following method: the above-mentioned components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, and the binder are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0052] In a fourth aspect, the present application provides a battery comprising the negative electrode sheet described above, which has excellent cycle performance and rate performance while also having a high energy density.

[0053] For example, a battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. The separator is located between the positive and negative electrodes. During the battery's charge and discharge processes, active ions are inserted and removed from the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator is located between the positive and negative electrodes, primarily to prevent short circuits between the positive and negative electrodes while allowing ions to pass through.

[0054] According to an embodiment of the present application, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active material. The positive electrode current collector can be a metal foil or a composite current collector (a metal material can be disposed on a polymer substrate to form a composite current collector), for example, aluminum foil.

[0055] In the embodiments of the present application, the specific type of the positive electrode active material is not particularly limited. As some specific embodiments, the positive electrode active material includes at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, lithium nickel oxide, lithium cobalt phosphate, lithium manganese phosphate, lithium nickel phosphate, lithium manganese oxide, binary materials, and ternary materials.

[0056] According to some embodiments of the present application, the positive electrode active material layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, or a fluorine-containing acrylate resin.

[0057] According to some embodiments of the present application, the positive electrode active material layer may further optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers.

[0058] According to some embodiments of the present application, a positive electrode sheet can be prepared by the following method: the above-mentioned components for preparing a positive electrode sheet, such as a positive electrode active material, a positive electrode lithium supplement material, a conductive agent, a binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on a positive electrode current collector, and after drying, cold pressing and other processes, a positive electrode sheet can be obtained.

[0059] According to other embodiments of the present application, the type of isolation membrane is not particularly limited, and any known porous structure isolation membrane with good chemical and mechanical stability can be selected. As an example, the material of the isolation membrane may include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, or polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0060] According to some other embodiments of the present application, the type of electrolyte is not specifically limited and can be selected according to needs. According to some specific embodiments of the present application, the electrolyte is an electrolyte solution, and the electrolyte solution includes a lithium salt and a solvent.

[0061] According to some specific embodiments of the present application, the lithium salt may include lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium phosphate (LiBOB), and lithium difluorophosphate (LiPO2F2).

[0062] According to some specific embodiments of the present application, the solvent may include at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, ethylene glycol dimethyl ether, methyl ethyl sulfone or diethyl sulfone.

[0063] In some embodiments of the present application, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0064] In a fifth aspect, the present application provides an electrical device. According to an embodiment of the present application, the electrical device includes the above-mentioned battery. The features and advantages described above for the battery also apply to the electrical device and will not be repeated here.

[0065] Specifically, the electrical equipment may include, but is not limited to, electric vehicles, battery vehicles, mobile phones, tablet computers, laptop computers, electric toys, ships, spacecraft, etc. Electric toys may include fixed or mobile electric toys, such as game consoles, electric vehicle toys, electric ship toys, and electric airplane toys, etc. Spacecraft may include airplanes, rockets, space shuttles, and spacecraft, etc.

[0066] The examples described below are exemplary and are intended only to explain the present invention and are not to be construed as limiting the present invention. Where specific techniques or conditions are not specified in the examples, the methods or conditions described in the literature within the art or in the product specifications were used. Where the manufacturer of the reagents or instruments is not specified, all are commercially available conventional products.

[0067] The present invention is further described in detail below by way of examples.

[0068] Example 1

[0069] This embodiment is used to illustrate the graphite material and its preparation method, negative electrode sheet, and battery disclosed in the present invention, and includes the following steps:

[0070] (1) Preparation of graphite materials:

[0071] The flake graphite is crushed, pickled, dried and spheroidized to obtain a graphite precursor, the graphite precursor and filler heavy oil are evenly mixed in a mass ratio of 100:15, and processed using a cold isostatic pressing device at 100 MPa to obtain a graphite core precursor, which is sintered at 1200°C for 6 hours while introducing N2 protection to obtain a graphite core; the graphite core is shaped by a ball mill at a speed of 200 r / min and a ball milling time of 3 hours to eliminate the changes in its morphology caused by cold isostatic pressing, and a spherical graphite core is obtained from irregular particles; the graphite core and coating agent 1 phenolic resin and coating agent 2 asphalt are mixed in a ratio of 100:10:2.5, sintered at 1200°C for 4 hours while introducing N2 protection, and demagnetized by screening to obtain a graphite material.

[0072] (2) Preparation of negative electrode sheet:

[0073] The graphite material, conductive carbon black, carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) prepared above were mixed and homogenized in NMP at a mass ratio of 96.5:1:1.5:1, and then coated on a copper current collector, dried, roll-pressed, and die-cut to obtain a negative electrode sheet.

[0074] (3) Preparation of positive electrode sheet:

[0075] Lithium iron phosphate, carbon nanotubes, and polyvinylidene fluoride (PVDF) were mixed and homogenized in NMP at a mass ratio of 100:3:2, and then coated on an aluminum current collector, dried, rolled, and die-cut to obtain a positive electrode sheet.

[0076] (4) Preparation of batteries:

[0077] The positive electrode sheet, separator, negative electrode sheet and electrolyte prepared above were assembled to prepare a full battery; a solution of LiPF6+EC:DEC:DMC (volume ratio of 1:1:1) plus an appropriate amount of additives was used as the electrolyte, and a polypropylene film was used as the separator.

[0078] Examples 2-14

[0079] Examples 2-14 are basically the same as Example 1, except that the preparation of graphite materials is different. Specific parameters are shown in Table 1.

[0080] Comparative Example 1

[0081] (1) Preparation of graphite materials:

[0082] The flake graphite is crushed, pickled, dried and spheroidized to obtain a graphite precursor. The graphite precursor and filler heavy oil are evenly mixed in a ratio of 100:25, and processed using a cold isostatic pressing device at 100 MPa to obtain a graphite core precursor. The graphite core precursor is sintered at a high temperature of 1200°C for 6 hours while introducing N2 protection to obtain a second precursor; the second precursor is shaped by a ball milling device with a rotation speed of 200 r / min and a ball milling time of 3 hours to eliminate the changes in its morphology caused by cold isostatic pressing, and a spherical graphite material is obtained from irregular particles.

[0083] Comparative Example 2

[0084] (1) Preparation of graphite materials:

[0085] The flake graphite is crushed, pickled, dried and spheroidized to obtain a graphite precursor. The graphite precursor and the coating agent 1 phenolic resin and the coating agent 2 asphalt are mixed in a ratio of 100:10:2.5, sintered at a high temperature of 1200°C for 4 hours, and N2 protection is introduced at the same time. After screening and demagnetization, the graphite material is obtained.

[0086] Comparative Example 3

[0087] (1) Preparation of graphite materials:

[0088] The flake graphite is crushed, pickled, dried and spheroidized to obtain a graphite precursor. The graphite precursor and filler heavy oil are evenly mixed at a ratio of 100:15, and processed using a cold isostatic pressing device at 100 MPa to obtain a graphite core precursor. The graphite core precursor is sintered at a high temperature of 1200°C for 6 hours while introducing N2 protection to obtain a second precursor; the second precursor is shaped by a ball milling device with a rotation speed of 200 r / min and a ball milling time of 3 hours to eliminate the changes in its morphology caused by cold isostatic pressing, and a spherical graphite material is obtained from irregular particles.

[0089] Comparative Example 4

[0090] (1) Preparation of graphite materials:

[0091] The flake graphite is crushed, pickled, dried and spheroidized to obtain a graphite precursor. The graphite precursor and the coating agent 1 phenolic resin and the coating agent 2 asphalt are mixed in a ratio of 100:10:1.5, sintered at 1200°C for 4 hours while introducing N2 protection, and demagnetized by screening to obtain a graphite material.

[0092] Test method:

[0093] -10℃ 2C / 0.2C rate discharge capacity ratio test:

[0094] At room temperature, the battery was charged to 3.8V with 1C constant current and constant voltage CCCV; the battery was placed at -10℃ for 6 hours, discharged to 1.9V at 0.2C, and the discharge capacity was recorded. The battery was taken out and placed at 25℃ for 6 hours, and then charged to 3.8V with 1C constant current and constant voltage CCCV; the battery was placed at -10℃ for another 6 hours, discharged to 1.9V at 2C, and the discharge capacity was recorded. The 2C / 0.2C rate discharge capacity ratio at -10℃ was calculated.

[0095] -10℃ charging DCIR test:

[0096] The battery was placed at -10°C for 6 hours, and the voltage E1 before discharge began was recorded. The battery was charged at a constant current of 1C for 10 seconds with an upper limit voltage of 3.8V. The voltage E2 at this time was recorded, and the charging DCIR at -10°C was calculated using the formula (E2-E1) / 1C.

[0097] 45℃ cycle capacity retention rate:

[0098] The battery was placed in a 45°C environmental chamber for 4 h, charged to 3.8 V at 1C constant current and constant voltage, cut off at 0.05C, placed for 30 min, and then discharged to 2.0 V at 1C constant current, and the 1C discharge capacity was recorded; placed for 30 min, the cycle was terminated after 300 cycles, and the discharge capacity after 300 cycles was recorded. The 45°C cycle capacity retention rate was obtained as (discharge capacity after 300 cycles / 1C discharge capacity)×100%.

[0099] Capacity recovery rate after 2 months storage at 60℃:

[0100] The battery was charged to 3.8V at 1C constant current and constant voltage CCCV with a cutoff current of 0.05C, and then discharged to 2V at 1C constant current after standing for 30 minutes to obtain the initial 1C discharge capacity of the battery; the battery was stored in a high temperature box at 60°C for 2 months, then stood at room temperature for 4 hours, and then discharged to 2V at 1C constant current, stood for 30 minutes, and charged to 3.8V at 1C constant current and constant voltage CCCV with a cutoff current of 0.05C, and then stood for 30 minutes to discharge to 2V at 1C constant current to obtain the recovery capacity of the battery. The capacity recovery rate after storage at 60°C for 2 months was obtained by dividing the recovery capacity by the initial 1C discharge capacity (before storage).

[0101] In summary, from the test results of Examples 1-14 and Comparative Examples 1-4, it can be seen that internal filling and external coating of the graphite material can optimize the internal pores and external structure of the graphite material, reduce the probability of side reactions of the graphite material, thereby improving the low-temperature discharge rate of the battery, reducing the low-temperature resistance of the battery, and improving the high-temperature cycle retention rate of the battery, as well as the storage capacity recovery rate; Comparing Examples 1-12 and Examples 13-14, the graphite material satisfies 0.15≤BET*(I D / I G) / OI≤0.4, which can further improve the battery's low-temperature rate performance, high-temperature storage performance and cycle performance.

[0102] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

[0103] Table 1 Parameter settings for each embodiment and comparative example

[0104]

[0105] Table 2 Test results of various embodiments and comparative examples

[0106]

Claims

1. A graphite material, characterized in that: The graphite material includes a graphite core and a coating layer, and the graphite core is filled with a filler.

2. The graphite material according to claim 1, characterized in that The filler includes one or more of asphalt, coal tar and heavy oil, and / or the coating layer includes one or more of asphalt, hard carbon, heavy oil, glucose, starch and resin.

3. The graphite material according to claim 1 or 2, characterized in that The coating layer comprises at least two coating structures.

4. The graphite material according to claim 3, characterized in that The coating layer includes an inner coating structure close to the graphite core and an outer coating structure away from the graphite core. The material of the inner coating structure is the same as that of the filler.

5. The graphite material according to any one of claims 1 to 4, characterized in that The graphite material satisfies: 0.15≤BET*(I D / I G ) / OI≤0.4, wherein BET is the specific surface area of ​​the graphite material, I D / I G is the intensity ratio of the D peak and the G peak in the Raman spectrum of the graphite material, and OI is the ratio of the (004) and (110) crystal plane diffraction peak intensities of the graphite material.

6. The graphite material according to claim 5, characterized in that The BET is 1.5m 2 / g~5.0m 2 / g; and / or, said I D / I G is 0.1-0.5; and / or, the OI is 2-5.

7. The graphite material according to claim 5 or 6, characterized in that The electrochemical active area of ​​the graphite material is 1.5m 2 / g~3.0m 2 / g.

8. A method for preparing the graphite material according to any one of claims 1 to 7, characterized in that: The method comprises the following steps: mixing a graphite precursor and the filler to obtain a graphite core precursor; subjecting the graphite core precursor to a first high-temperature treatment to obtain the graphite core; The graphite core and the coating agent are mixed and subjected to a second high-temperature treatment to obtain the graphite material.

9. The method for preparing the graphite material according to claim 8, wherein: The step of subjecting the graphite core precursor to a first high-temperature treatment to obtain the graphite core further includes subjecting the graphite core to a grinding treatment.

10. The method for preparing a graphite material according to claim 8 or 9, characterized in that: The graphite precursor includes one or more of artificial graphite and natural graphite.

11. The method for preparing a graphite material according to any one of claims 8 to 10, characterized in that: The mass ratio of the graphite precursor to the filler is 100:(10-40); and / or the mass ratio of the graphite core to the coating agent is 100:(3-40).

12. The method for preparing a graphite material according to any one of claims 8 to 11, characterized in that: The temperature of the first high temperature treatment is 900°C to 1500°C; and / or, the time of the first high temperature treatment is 2h to 6h; and / or, the temperature of the second high temperature treatment is 900°C to 1500°C; and / or, the time of the second high temperature treatment is 2h to 6h.

13. The method for preparing a graphite material according to any one of claims 9 to 12, characterized in that: The grinding process includes ball milling, the speed of the ball milling is 100 rpm to 800 rpm, and the time of the ball milling is 2 hours to 8 hours.

14. A negative electrode sheet, characterized in that: The invention comprises the graphite material according to any one of claims 1 to 7 or the graphite material prepared according to the method for preparing the graphite material according to any one of claims 8 to 13.

15. A battery, characterized in that: Including the negative electrode sheet according to claim 14.

16. An electrical device, characterized in that: Including the battery according to claim 15.

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