Composite coated graphite material and preparation method thereof

Abstract

The invention relates to the technical field of preparation of battery negative electrode materials, and discloses a composite coated graphite material and a preparation method thereof.The composite coated graphite material comprises a graphite inner core, a ZIF inner layer coating the graphite inner core and a conductive polymer outer layer coating the ZIF inner layer; and Zn and / or Co are / is doped in the ZIF inner layer. Through the collaborative design of the inner layer ion transmission channel and the outer layer electron conduction network, the ionic conductivity and the electron conductivity of the material can be improved at the same time, the specific surface area is increased, the problems of slow ion diffusion, weak electron conduction and volume expansion during fast charging of the graphite inner core are effectively solved, and the capacity retention rate of 0.1 C cycle 500 times is comprehensively and synergistically improved.

Description

Technical Field

[0001] This application relates to the field of battery anode material technology, specifically to a composite coated graphite material and its preparation method. Background Technology

[0002] Traditional graphite anodes suffer from problems such as slow ion diffusion rate, high interfacial impedance, and capacity decay due to volume expansion during cycling in high-rate (e.g., 30C) fast charging scenarios. To overcome the technical bottlenecks of traditional graphite anodes, various modification strategies have been developed, such as surface coating.

[0003] Existing surface coating improvements often employ carbon coating, highly conductive polymer coating, or metal ZIF coating. Among these, carbon coating offers limited conductivity improvement. When metal ZIF is a single metal, the ion transport channel is limited, making it difficult to simultaneously meet the requirements of high conductivity and rapid ion transport. Zn / Co bimetallic ZIF, due to the synergistic effect of the two metal ions, possesses a richer mesoporous structure and higher ion adsorption capacity, but its conductivity remains relatively poor. Highly conductive polymers, such as PEDOT:PSS, can improve electron conduction, but their bonding with the graphite interface is weak, making them prone to detachment. Summary of the Invention

[0004] This application provides a composite coated graphite material to solve the problem that existing coating methods cannot meet the electron transport requirements of fast charging, thereby making the prepared fast-charging power battery have better cycle performance.

[0005] In a first aspect, this application provides a composite-coated graphite material, comprising a graphite core, a ZIF inner layer coated on the graphite core, and a conductive polymer outer layer coated on the ZIF inner layer; wherein the ZIF inner layer is doped with Zn and / or Co.

[0006] In one optional embodiment, the graphite core has a Dv50 between 5 and 16 μm and a tap density between 1.0 and 1.3 g / cm³. 3 between.

[0007] In one alternative embodiment, the ZIF inner layer is doped with Zn²⁺. + and Co² + Zn² + With Co² + The molar ratio is (1-4):1.

[0008] In one alternative embodiment, the mass ratio between the ZIF inner layer and the conductive polymer outer layer is (0.5-5):1.

[0009] In one optional implementation, the thickness of the ZIF inner layer is 5-20 nm; and / or, the thickness of the conductive polymer outer layer is 10-30 nm; and / or, the total mass of the ZIF inner layer and the conductive polymer outer layer on the graphite inner core is 3-8 wt%.

[0010] In an alternative embodiment, the raw material of the conductive polymer outer layer comprises polymer A and diluent B, the polymer A comprises PEDOT (poly 3,4-ethylenedioxythiophene), and the diluent B comprises PSS (polystyrene sulfonate) or PEG (polyethylene glycol); or, the raw material of the conductive polymer outer layer comprises pyrrole monomer and polymerization initiator, the polymerization initiator is ammonium persulfate, and PPy (poly pyrrole) is formed on the ZIF inner layer by ammonium persulfate.

[0011] In an alternative embodiment, the mass ratio of the polymer A and the diluent B is 1: (2-4).

[0012] In a second aspect, the application further provides a preparation method of the composite coated graphite material, comprising: obtaining the graphite inner core; ZIF inner layer coating: dispersing the graphite inner core in a solvent, adding Zn source and / or Co source, adding ligand after dispersion, collecting solid after reaction, and obtaining Zn / CoZIF coated graphite product after washing and drying; conductive polymer outer layer coating: dispersing the Zn / CoZIF coated graphite product and conductive polymer solution uniformly, and then reacting to obtain the composite coated graphite material after drying.

[0013] In an alternative embodiment, the process of obtaining the graphite inner core is: crushing coke to have Dv50 between 5-16 μm, and graphitizing at 2700-3100 ℃ to obtain the graphite inner core; and / or, in the step of ZIF inner layer coating, the solvent is methanol solution, the dispersion mode is ultrasonic dispersion, the reaction temperature is 25-35 ℃, the reaction time is 2-8 h, and the drying mode is vacuum drying; and / or, in the step of conductive polymer outer layer coating, the solid content of the conductive polymer solution is 1-3%, the reaction is carried out under a protective atmosphere, the reaction temperature is 50-60 ℃, the reaction time is 2-5 h, and the drying mode is spray drying.

[0014] In an alternative embodiment, in the step of ZIF inner layer coating, the ultrasonic dispersion time is 5-60 min, and the washing solvent is methanol; The inlet temperature of the spray drying is 120-150 ℃, and the outlet temperature of the spray drying is 50-80 ℃.

[0015] The technical solution of this application has the following advantages: 1. The composite-coated graphite material provided in this application includes a graphite core, a ZIF inner layer coated on the graphite core, and a conductive polymer outer layer coated on the ZIF inner layer; the ZIF inner layer is doped with Zn and / or Co. This application effectively improves the specific surface area through the synergistic design of "inner layer ion transport channels + outer layer electron conduction network," and can simultaneously improve the ionic conductivity and electronic conductivity of the material, effectively solving the problems of slow ion diffusion, weak electronic conduction, and volume expansion during fast charging of the graphite core, and comprehensively and synergistically improving the capacity retention rate after 500 cycles at 0.1C.

[0016] 2. The composite coated graphite material provided in this application uses Zn²⁺ doped in the inner layer of ZIF. + and Co² + The inner layer of ZIF is a Zn / Co bimetallic ZIF. The synergistic effect of the two metal ions results in a richer mesoporous structure and higher ion transport capacity. It works synergistically with the conductive polymer outer layer to further improve electron conduction, meet the requirements of fast charging electron transport, and significantly improve the specific capacity, first efficiency, and capacity retention rate of the prepared negative electrode at a high rate of 30C after 500 cycles at 0.1C.

[0017] 3. The composite-coated graphite material provided in this application can produce a negative electrode with an initial discharge specific capacity of over 325 mAh / g at a high rate of 30C, an initial efficiency of over 90%, and a capacity retention rate of over 85% after 500 cycles, making it suitable for fast-charging power battery applications. Detailed Implementation

[0018] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the embodiments of this application. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion. In the description of the embodiments of the present application, the technical terms "first", "second" and the like are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise explicitly and specifically limited.

[0020] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearance of the phrase in various places in the specification does not necessarily all refer to the same embodiment, nor is it necessarily independent or alternative embodiments to each other. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. The "range" disclosed in the present application is defined in the form of lower limit and upper limit, a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a particular range. The range defined in this way can include or not include the end value, and can be arbitrarily combined, i.e. any lower limit can be combined with any upper limit to form a range. For example, if the ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that the ranges of 60-110 and 80-120 are also anticipated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4 and 5 are listed, the following ranges are all anticipated: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise stated, the numerical range "a-b" represents a shorthand notation for any real combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed herein, and "0-5" is only a shorthand notation for these numerical combinations. In addition, when a parameter is expressed as ≥2 integers, it is equivalent to disclose that the parameter is, for example, integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0021] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which means that there are three cases of A alone, A and B together, and B alone. In addition, the character " / " in this paper generally means that the front and rear associated objects are in an "or" relationship.

[0022] In the description of the embodiments of the present application, the term "multiple" means more than two (including two), and similarly, "multiple groups" means more than two groups (including two groups), and "multiple pieces" means more than two pieces (including two pieces). In the description of the embodiments of the present application, unless otherwise explicitly specified and limited, the technical terms "mounting", "connection", "connecting", "fixing" and the like should be understood in a broad sense, for example, can be fixed connection, can also be detachable connection, or integral; can be mechanical connection, can also be electrical connection; can be direct connection, can also be indirect connection through an intermediate medium, can be internal communication of two elements or interaction relationship between two elements. For those skilled in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0023] To solve the problems in the related art, according to a first aspect of the present application, a composite coated graphite material is provided, comprising a graphite inner core, a ZIF inner layer coated on the graphite inner core, and a conductive polymer outer layer coated on the ZIF inner layer; the ZIF inner layer is doped with Zn and / or Co.

[0024] The present application realizes the synergistic design of "inner ion transmission channel + outer electronic conduction network" through the cooperation of the ZIF inner layer and the conductive polymer outer layer, effectively improves the specific surface area, and can simultaneously improve the ion conductivity and electronic conductivity of the material, effectively solves the problems of slow ion diffusion, weak electronic conduction and volume expansion of the graphite inner core during fast charging, and comprehensively and synergistically improves the capacity retention rate of 0.1C cycle for 500 times.

[0025] In an optional embodiment, the Dv50 of the graphite inner core is between 5-16 μm, and the tap density is between 1.0-1.3 g / cm 3 For example, the Dv50 of the graphite inner core can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm or within a range formed by any of the above values, and the tap density can be 1.0 g / cm 3 , 1.1 g / cm 3 , 1.2 g / cm 3 , 1.3 g / cm 3 or within a range formed by any of the above values.

[0026] The Dv50 of the graphite inner core of the present application is too low, the specific surface area is too large, the irreversible capacity loss during the formation of the SEI film increases, the first charge and discharge efficiency decreases; small particles are easy to agglomerate, causing blockage of the ion / electron transmission channel, serious capacity decay at 30C, and obvious volume expansion during the cycle; the Dv50 of the graphite inner core is too high, the Li +The diffusion path is too long to meet the 30C rate requirement; large particle graphite is prone to sedimentation during electrode coating, resulting in poor thickness uniformity of the negative electrode sheet, large fluctuation of the battery internal resistance, and poor consistency of the electrochemical performance; the tap density of the graphite inner core is too low, the amount of active material that can be accommodated per unit volume is reduced, the electrode resistance is increased, the polarization during charging and discharging is significantly increased, the 30C initial discharge specific capacity is reduced, the initial efficiency is reduced, and the cycle retention rate is reduced; the tap density of the graphite inner core is too high, the coating is prone to agglomeration and clumping, the electrode sheet is prone to cracking during cutting, the electrolyte is difficult to soak during the crimping test, and the rate performance and cycle life are shortened.

[0027] wherein Dv50 refers to the particle size corresponding to the cumulative volume distribution percentage of 50%, that is, the volume content of particles less than or equal to this particle size accounts for 50% of the total particle volume. The test methods of Dv50 and tap density are both referred to GB / T 24533-2019.

[0028] Since the composite coated graphite material is compared with the graphite inner core, only a nanoscale thick coating layer is coated on the surface of the graphite inner core, therefore, the Dv50 of the graphite inner core is between 5-16 μm, the tap density is between 1.0-1.3 g / cm 3 , the Dv50 of the composite coated graphite material prepared by using the graphite inner core is slightly larger than that of the graphite inner core, but is also basically between 5-16 μm, and the tap density of the composite coated graphite material is also between 1.0-1.3 g / cm 3 .

[0029] In an alternative embodiment, Zn² + and Co² + are doped in the ZIF inner layer, and the molar ratio of Zn² + to Co² + is (1-4):1. For example, the molar ratio of Zn² + to Co² + may be 1:1, 2:1, 3:1, 4:1 or within a range consisting of any of the above values.

[0030] If the molar ratio of Zn² + to Co² + is too high, the Co 2+ content is insufficient, the synergistic effect of the bimetallic is weakened, the mesoporous structure is single, and the ion adsorption capacity is reduced; the crystal structure is biased towards single metal Zn-ZIF, the volume expansion inhibition effect is weakened, the 30C discharge specific capacity is reduced, and the fast charging performance is attenuated; if the molar ratio of Zn² + to Co² + is too low, the Zn 2+ content is insufficient, the pore size of the ZIF mesopore is small, and the Li +The transmission channel is narrow, the diffusion rate is reduced, the coordination stability of metal ions is reduced, the ZIF film layer is easy to dissolve in the cycle process, and the coating fails; the bimetallic synergistic adsorption of Li + The advantage is lost, and the cycle capacity at 30C is attenuated.

[0031] Zn² + and Co² + The molar ratio is measured by ICP-MS instrument, and the detection method is as follows: 20-50mg of sample is weighed into a digestion tank, 5mL of mixed acid of nitric acid and 2mL of perchloric acid is added. After sealing the digestion tank, it is placed in a microwave digestion instrument, and the temperature rising program (2℃ / min to 180℃, holding for 30min) is set until the sample is completely dissolved into a clear solution, and cooled to room temperature. The Zn and Co standard stock solution is diluted with 1% nitric acid solution, and 5 concentration gradient mixed standard series solutions (such as 0.1, 1, 5, 10, 50mg / L) are prepared. At the same time, 1% nitric acid solution is prepared as a blank solution for baseline interference deduction. First, the blank solution is sucked in, and the instrument records the blank signal and is zeroed; then the Zn-Co mixed standard solution is sucked in from low concentration to high concentration, and the instrument automatically records the emission signal intensity or ion signal intensity corresponding to different concentrations. The software will generate a calibration curve, and the linear correlation coefficient R²≥0.999 needs to be ensured. The pretreated sample solution is introduced into the sample system, and the sample solution is detected, and the instrument automatically compares the calibration curve to calculate the concentration of Zn² + and Co² + .

[0032] In an alternative embodiment, the mass ratio between the ZIF inner layer and the conductive polymer outer layer is (0.5-5):1. For example, the mass ratio between the ZIF inner layer and the conductive polymer outer layer can be 0.5:1, 1:1, 2:1, 3:1, 4:1, 5:1 or within a range consisting of any of the above values.

[0033] If the mass ratio between the ZIF inner layer and the conductive polymer outer layer is too high, the conductivity of the composite coating layer is insufficient (electrical conductivity <5S / cm), and the electronic transmission is blocked; if the mass ratio between the ZIF inner layer and the conductive polymer outer layer is too low, a dense film layer is easily formed on the surface of the graphite, blocking the Li + channel, the specific capacity of the first discharge is reduced; and excessive flexibility leads to insufficient structural support, and the cycle capacity retention rate is reduced.

[0034] The detection method of the mass ratio between the ZIF inner layer and the conductive polymer outer layer is as follows: the Zn² + and Co² +The detection method of the molar ratio tests the mass concentration of the inner layer Zn / Co of the ZIF, and the mass of the ZIF in unit mass of the sample m1 is calculated. 5 mg of the dried sample is taken, and the mass fraction (wS, unit %) of the S element is tested by the elemental analyzer (CHNS mode); and the N and S contents in the conductive polymer standard sample are measured, and the N and S are taken as the characteristic elements of the added polymer, so that the mass of the conductive polymer in unit mass of the sample m2 is calculated. The mass ratio between the inner layer of the ZIF and the outer layer of the conductive polymer is obtained through m1:m2.

[0035] In an alternative embodiment, the thickness of the inner layer of the ZIF is 5-20 nm; and / or, the thickness of the outer layer of the conductive polymer is 10-30 nm; and / or, the total mass of the inner layer of the ZIF and the outer layer of the conductive polymer is 3-8 wt% on the total coating amount on the graphite inner core.

[0036] For example: the thickness of the inner layer of the ZIF can be 5 nm, 7 nm, 10 nm, 12 nm, 15 nm, 17 nm, 20 nm or within the range consisting of any of the above values; the thickness of the outer layer of the conductive polymer can be 10 nm, 12 nm, 15 nm, 17 nm, 20 nm, 22 nm, 25 nm, 28 nm, 30 nm or within the range consisting of any of the above values; and the total mass of the inner layer of the ZIF and the outer layer of the conductive polymer can be 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt% or within the range consisting of any of the above values on the total coating amount on the graphite inner core.

[0037] If the thickness of the inner layer of the ZIF is too high, the Li + The diffusion resistance increases, the 30C discharge capacity decreases, the internal stress of the film layer accumulates, cracks during the cycle process, and the interface impedance sharply increases with the number of cycles; if the thickness of the inner layer of the ZIF is too low, the film layer is incomplete, and cannot effectively inhibit the interlayer peeling of the graphite layer, the volume expansion rate is more than 10%, and the ion adsorption capacity is insufficient, Li + The concentration gradient decreases, and the fast charging rate decreases. If the thickness of the outer layer of the conductive polymer is too high, the electronic conduction network is continuous, but the Li + The channel is excessively covered, the 30C fast charging capacity decreases, the adhesion of the film layer decreases, and the film layer is easy to fall off during the cycle process. If the total mass of the inner layer of the ZIF and the outer layer of the conductive polymer is too high on the total coating amount on the graphite inner core, the coating layer is too thick, and the Li + The diffusion path is lengthened, the 30C fast charging capacity decreases, the coating layer is easy to aggregate and crack, and the cycle capacity retention rate decreases; if the total mass of the inner layer of the ZIF and the outer layer of the conductive polymer is too low on the total coating amount on the graphite inner core, the coating layer is discontinuous, cannot form a complete ion transmission channel and electronic network, the interface impedance increases, the rate decreases, and the volume expansion inhibition is insufficient, and the cycle expansion rate increases.

[0038] The thickness of the ZIF inner layer and the conductive polymer outer layer is detected by placing the sample in ethanol and ultrasonically dispersing for 20 minutes, dropping a small amount of the suspension on a micro-grid copper mesh, and then placing it in a TEM to directly measure the thickness values of different regions after the ethanol is evaporated and dried. The average value is obtained by multiple measurements to reduce errors. The total coating amount of the total mass of the ZIF inner layer and the conductive polymer outer layer on the graphite inner core is detected by weighing 5 mg of the standard sample of the ZIF inner layer and the conductive polymer outer layer, respectively, drying them at 110°C under vacuum, and then performing a thermogravimetric test under N2 atmosphere, with a temperature rise of 5°C / min to 1000°C, and recording the final thermal weight loss rate. The sample to be tested is dried and tested by thermogravimetry under the same conditions to obtain its thermal weight loss rate, and the total coating rate is calculated.

[0039] In an alternative embodiment, the raw material of the conductive polymer outer layer includes polymer A and diluent B, the polymer A includes PEDOT (poly 3,4-ethylenedioxythiophene), and the diluent B includes PSS (polystyrene sulfonate) or PEG (polyethylene glycol); or, the raw material of the conductive polymer outer layer includes a pyrrole monomer and a polymerization initiator, and the polymerization initiator is ammonium persulfate, and PPy (poly pyrrole) is formed on the ZIF inner layer by ammonium persulfate. The mass ratio of the polymer A and the diluent B is 1:(2-4). For example, the mass ratio of the polymer A and the diluent B can be 1:2, 1:3, 1:4, or within a range consisting of any of the above values.

[0040] If the mass ratio of the polymer A and the diluent B is too high, the polymer dispersibility decreases, the coating layer uniformity is poor, the film layer flexibility is weakened, the volume change during the cycle cannot be buffered, and the coating layer is easy to fall off; the surface charge density is reduced, the interaction force with the ZIF layer is weakened, and the interlayer bonding force is insufficient. If the mass ratio of the polymer A and the diluent B is too low, the polymer content is insufficient, the electronic conduction network is discontinuous, and the electrical conductivity is low; the excess diluent is an insulating component, which increases the interface impedance, blocks the electron transport at high magnification, and greatly attenuates the capacity; the film layer has too strong hydrophilicity, the side reaction with the electrolyte is intensified, and the cycle life is shortened.

[0041] In a second aspect, the application also provides a preparation method of a composite coated graphite material, which includes obtaining a graphite inner core; ZIF inner layer coating: dispersing the graphite inner core in a solvent, adding a Zn source and / or a Co source, adding a ligand after dispersion, collecting the solid after reaction, and obtaining a Zn / CoZIF coated graphite product after washing and drying; conductive polymer outer layer coating: uniformly dispersing the Zn / CoZIF coated graphite product and a conductive polymer solution, and then reacting to obtain a composite coated graphite material after drying.

[0042] In an alternative embodiment, the graphite inner core is obtained by crushing the coke to a Dv50 of 5-16 pm and graphitizing at a temperature of 2700-3100 °C; for example, the Dv50 of the crushed coke can be 5 pm, 6 pm, 7 pm, 8 pm, 9 pm, 10 pm, 11 pm, 12 pm, 13 pm, 14 pm, 15 pm, 16 pm or within a range defined by any of the foregoing values, and the graphitization temperature can be 2700 °C, 2800 °C, 2900 °C, 3000 °C, 3100 °C or within a range defined by any of the foregoing values.

[0043] If the graphitization temperature is too high, the production cost increases substantially, resulting in a reduced performance-to-price ratio of the product, and the crystal grains grow excessively, increasing the structural brittleness; specifically, the graphite layers grow abnormally at an ultra-high temperature, forming coarse columnar crystal grains, the binding force between the crystal grains decreases, the product becomes more brittle, and the product is prone to breakage during subsequent processing (such as spheroidization and compression molding), the consistency of the particle morphology decreases, the stability of the tap density is affected, and the fast-charging performance deteriorates. If the graphitization temperature is too low, the crystal grains of the raw material do not transform sufficiently, and the impurities are not completely removed because the temperature is lower than the critical energy required for graphitization, and the performance of the product does not meet the standards.

[0044] Further, the coke in the present application is one of needle coke, petroleum coke, calcined petroleum coke and pitch coke, and the graphitization equipment includes but is not limited to an Acheson graphitization furnace, a series-connected graphitization furnace, a vertical graphitization furnace, a medium-frequency furnace, a continuous graphitization furnace, an electric arc smelting furnace and the like. The process of crushing the coke to a Dv50 of 5-16 pm includes crushing the raw material coke to ≤3 mm, grinding the coke to a particle size Dv50 of 4-15 pm, and then controlling the particle size Dv50 of the shaped coke to be 5-16 pm.

[0045] In an alternative embodiment, in the step of coating the ZIF inner layer, the solvent is a methanol solution, the dispersion method is ultrasonic dispersion, the ultrasonic dispersion time is 5-60 min, the reaction temperature is 25-35 °C, the reaction time is 2-8 h, the washing solvent is methanol, and the drying method is vacuum drying; for example, the reaction temperature can be 25 °C, 26 °C, 27 °C, 28 °C, 29 °C, 30 °C, 31 °C, 32 °C, 33 °C, 34 °C, 35 °C or within a range defined by any of the foregoing values, the reaction time can be 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h or within a range defined by any of the foregoing values, and the ultrasonic dispersion time can be 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min or within a range defined by any of the foregoing values.

[0046] The temperature of the reaction is too high, the ZIF crystal grows too fast, the mesoporous structure collapses, Li + The fast transmission channel is blocked, at the same time, the metal ion coordination is uneven, forming impurities, reducing the ion adsorption capacity, and the fast charging capacity decays; the temperature of the reaction is too low, the ZIF coating is not complete and discontinuous, the volume expansion cannot be inhibited, and the crystal structure is not complete, the mesoporous distribution is uneven, Li + The transmission channel is disorderly, the fast charging performance decreases, and the reaction period is prolonged, reducing the production efficiency. The reaction time is too long, the coating layer is too thick, the ion transmission distance increases, and the 30C capacity decreases, at the same time, stress accumulation is prone to occur in the film layer, and cracking occurs in subsequent cycles; the reaction time is too short, the coating layer is thin, the mesoporous structure is not complete, the volume expansion inhibition effect is poor, and at the same time, the coordination of Zn / Co and the ligand is not sufficient.

[0047] In an alternative embodiment, the Zn source and the Co source are both water-soluble inorganic salt substances, for example: Zn(NO3)2·6H2O, Co(NO3)2·6H2O, and the ligand can be an imidazole carbon source, for example: 2-methyl imidazole or imidazole; in the reaction system after adding the ligand, the total concentration of the Zn source and the Co source is 0.1-0.3 mol / L, and the molar ratio of the ligand to the metal ion is 4:1-6:1. For example: the total concentration of the Zn source and the Co source in the reaction system can be 0.1 mol / L, 0.2 mol / L, 0.3 mol / L or within a range consisting of any of the above values, and the molar ratio of the ligand to the metal ion can be 4:1, 5:1, 6:1 or within a range consisting of any of the above values.

[0048] The total concentration of the Zn source and the Co source is too high, the Zn / Co-ZIF crystallization rate is too fast, forming large particle agglomerates, the coating layer is dense without mesopores, Li + The 30C capacity decreases; the total concentration of the Zn source and the Co source is too low, the ZIF growth rate is slow, the coating amount is insufficient and discontinuous, and cannot play a role in ion transmission and volume inhibition, and the cycle retention rate decreases. The molar ratio of the ligand to the metal ion is too high, and the excess ligand causes the ZIF crystal grains to grow excessively, the film layer thickness exceeds 25 nm, Li + The diffusion path is lengthened, the 30C fast charging performance decreases, the ligand residue increases the interface impedance, and the initial efficiency decreases; the molar ratio of the ligand to the metal ion is too low, and the insufficient ligand causes the ZIF crystal to be incomplete, the film layer is porous and the structure is loose, cannot inhibit the volume expansion, and the cycle expansion rate is high, at the same time, the ion adsorption capacity is insufficient, and the fast charging rate decreases.

[0049] In an alternative embodiment, in the step of coating the conductive polymer outer layer, the solid content of the conductive polymer solution is 1-3%, the reaction is carried out under a protective atmosphere, the reaction temperature is 50-60°C, the reaction time is 2-5h, and the drying method is spray drying. The inlet temperature of the spray drying is 120-150°C, the outlet temperature of the spray drying is 50-80°C, the feed rate of the spray drying is 5-10mL / min, and the atomization pressure is 0.2-0.4MPa.

[0050] For example, the reaction temperature can be 50°C, 51°C, 52°C, 53°C, 54°C, 55°C, 56°C, 57°C, 58°C, 59°C, 60°C, or within a range formed by any of the above values, the reaction time can be 2h, 3h, 4h, 5h, or within a range formed by any of the above values, the inlet temperature of the spray drying can be 120°C, 125°C, 130°C, 135°C, 140°C, 145°C, 150°C, or within a range formed by any of the above values, the outlet temperature of the spray drying can be 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, or within a range formed by any of the above values, the feed rate of the spray drying can be 5mL / min, 6mL / min, 7mL / min, 8mL / min, 9mL / min, 10mL / min, or within a range formed by any of the above values, and the atomization pressure can be 0.2MPa, 0.3MPa, 0.4MPa, or within a range formed by any of the above values.

[0051] If the reaction temperature is too high, the organic coating layer is prone to phase separation, the diluent is prone to precipitation, and the conductivity of the coating layer decreases. High temperature causes the degradation of the organic coating molecular chain, and the flexibility and buffering performance of the coating layer decrease, which cannot alleviate the volume expansion of graphite, and the coating layer is prone to peeling during the cycling process. If the reaction temperature is too low, the bonding force between the organic coating layer and ZIF decreases, and a discontinuous coating layer is prone to be formed, which leads to the rupture of the electronic transmission network, the increase of the interface impedance, the significant decrease of the 30C fast-charging capacity and the cycling stability, and the decrease of the reaction rate. If the reaction time is too long, the over-reaction leads to the over-thickness of the organic coating layer, the increase of the ion transmission path length, the decrease of the Li + diffusion rate, and the deterioration of the fast-charging performance. Meanwhile, the coating layer is prone to agglomeration and cracking, and cannot effectively inhibit the volume expansion during the cycling process, resulting in a low capacity retention rate. If the reaction time is too short, the organic coating layer cannot be fully adsorbed on the surface of the ZIF-coated graphite, the coating layer is thin and has poor uniformity, and the electronic transmission is blocked during fast-charging. +The transmission channel is blocked; the temperature of the spray drying is too low, and the moisture content is high, which can easily lead to poor stability of the subsequent slurry, easy peeling of the coating layer, and weakening of the interfacial adhesion between the conductive polymer coating layer and the ZIF layer. In the cycle process, the coating layer peels off, and the volume expansion inhibition fails. If the feeding rate of the spray drying is too high, the particles are not fully dried, and agglomeration is serious; if the feeding rate is too low, the cost increases, and the coating layer is prone to be too thick. If the atomization pressure is too high, the particles are broken, and the coating layer is damaged; if the atomization pressure is too low, the uniformity of the coating layer is poor, which affects the electron transport.

[0052] The application will be further described in detail below in conjunction with specific examples, which cannot be understood as limiting the scope of the application claimed.

[0053] Example 1 A composite coated graphite material comprises: S1: Jinzhou petroleum coke is crushed to a diameter of less than 1 mm using a roller mill, and is dried at 110°C for 4 hours using a rotary kiln. The dried coke powder is ground to Dv50=9.5μm using a mechanical grinder, and then is shaped to Dv50=10.0μm using a shaper. Finally, the shaped material is calcined at high temperature in a tunnel kiln, with a temperature rising rate of 5°C / min to 500°C, and a temperature rising rate of 4°C / min to 1000°C. The material is kept at 1000°C for 600 minutes, and then is cooled to room temperature at a rate of 900 minutes. The raw material A is obtained.

[0054] S2: The raw material A is graphitized at 3000°C in a medium-frequency furnace, with a temperature rising rate of 10°C / min to 1000°C, a temperature rising rate of 5°C / min to 2500°C, and a temperature rising rate of 2°C / min to 3000°C. The material is kept at 3000°C for 100 minutes to obtain the graphitized product B.

[0055] S3: 10g of the graphitized product B is dispersed in 100mL of methanol, and 0.01mol of Zn(NO3)2·6H2O and 0.01mol of Co(NO3)2·6H2O (Zn:Co=1:1) are added. After ultrasonic treatment for 30 minutes, 0.08mol of 2-methyl imidazole methanol solution is added dropwise, and the mixture is stirred at 25°C for 4 hours (coating amount 2%). The solid is collected, washed with methanol for 3 times after centrifugation, and vacuum dried at 80°C for 8 hours to obtain the Zn / CoZIF coated artificial graphite C.

[0056] S4: The coated artificial graphite C is dispersed in 50mL of deionized water, and 10mL of PEDOT / PSS aqueous solution (solid content 2%, PEDOT:PSS=1:3) is added. The mixture is stirred at 50°C for 2 hours under nitrogen protection, and is spray dried (inlet temperature 130°C, outlet temperature 70°C, feeding rate 8mL / min) to obtain the composite coated artificial graphite D with Zn / CoZIF:PEDOT / PSS=1:1.

[0057] Example 2 A composite coated graphite material, comprising: S1: Jinzhou petroleum coke was crushed to a diameter of less than 1 mm using a roller mill, dried at 110°C for 4 hours using a rotary kiln, and then ground to Dv50 = 9.5 μm using a mechanical mill. The ground coke was then shaped to Dv50 = 10.0 μm using a shaper, and finally calcined at high temperature in a tunnel kiln, with a temperature increase of 5°C / min to 500°C, and 4°C / min to 1000°C, and then held at 1000°C for 600 min. The temperature was then decreased to room temperature over 900 min, and the material was discharged, to obtain raw material A.

[0058] S2: The raw material A was graphitized at 3000°C in a medium-frequency furnace, with a temperature increase of 10°C / min to 1000°C, 5°C / min to 2500°C, and 2°C / min to 3000°C, and then held at 3000°C for 100 min to obtain graphitized product B.

[0059] S3: 10 g of the graphitized product B was dispersed in 100 mL of methanol, and 0.015 mol of Zn(NO3)2·6H2O and 0.005 mol of Co(NO3)2·6H2O (Zn:Co = 3:1) were added. After ultrasonic treatment for 30 min, 0.12 mol of 2-methylimidazole in methanol was added dropwise, and stirred at 25°C for 6 h (coating amount 3%). After centrifugation, the product was washed with methanol 3 times, and then dried at 80°C under vacuum for 8 h to obtain Zn / CoZIF coated artificial graphite C.

[0060] S4: The coated artificial graphite C was dispersed in 50 mL of deionized water, and 5 mL of PEDOT / PSS aqueous solution (solid content 2%, PEDOT:PSS = 1:3) was added. The mixture was stirred at 50°C for 2 h under nitrogen protection, and then spray dried (inlet temperature 130°C, outlet temperature 70°C, and feeding rate 8 mL / min) to obtain composite coated artificial graphite D with Zn / CoZIF:PEDOT / PSS = 3:1.

[0061] Example 3 A composite coated graphite material, comprising: S1: Jinzhou petroleum coke was crushed to a diameter of less than 1 mm using a roller mill, dried at 110°C for 4 hours using a rotary kiln, and then ground to Dv50 = 9.5 μm using a mechanical mill. The ground coke was then shaped to Dv50 = 10.0 μm using a shaper, and finally calcined at high temperature in a tunnel kiln, with a temperature increase of 5°C / min to 500°C, and 4°C / min to 1000°C, and then held at 1000°C for 600 min. The temperature was then decreased to room temperature over 900 min, and the material was discharged, to obtain raw material A.

[0062] S2: Graphitize raw material A in a medium frequency furnace at 3000°C, increase to 1000°C at 10°C / min, increase to 2500°C at 5°C / min, increase to 3000°C at 2°C / min, keep at 3000°C for 100 min to obtain graphitized product B.

[0063] S3: Take 10 g of graphitized product B and disperse it in 100 mL of methanol, add 0.01 mol of Zn(NO3)2·6H2O and 0.01 mol of Co(NO3)2·6H2O (Zn:Co = 1:1), ultrasonic for 30 min, then add 0.10 mol of 2-methylimidazole methanol solution dropwise, stir at 25°C for 6 h (coating amount 3%), wash with methanol for 3 times after centrifugation, vacuum dry at 80°C for 8 h to obtain Zn / CoZIF coated artificial graphite C.

[0064] S4: Disperse coated artificial graphite C in 50 mL of deionized water, add 7.5 mL of PEDOT / PSS aqueous solution (solid content 2%, PEDOT:PSS = 1:2), stir at 50°C for 2 h under nitrogen protection, spray dry (inlet 130°C, outlet 70°C, feeding rate 8 mL / min) to obtain composite coated artificial graphite D with Zn / CoZIF:PEDOT / PSS = 2:1.

[0065] Example 4 A composite coated graphite material, comprising: S1: Break the Jinzhou petroleum coke into a diameter of less than 1 mm using a roller mill, dry the broken coke powder in a rotary kiln at 110°C for 4 hours, grind the dried coke powder to Dv50 = 15.5 μm using a mechanical mill, then shape to Dv50 = 16.0 μm using a shaper, and finally calcine at high temperature through a tunnel kiln, increase to 500°C at 5°C / min, increase to 1000°C at 4°C / min, keep at 1000°C for 600 min, then decrease to room temperature over 900 min to discharge, to obtain raw material A.

[0066] S2: Graphitize raw material A in a medium frequency furnace at 3000°C, increase to 1000°C at 10°C / min, increase to 2500°C at 5°C / min, increase to 3000°C at 2°C / min, keep at 3000°C for 100 min to obtain graphitized product B.

[0067] S3: Take 10 g of graphitized product B and disperse it in 100 mL of methanol, add 0.01 mol of Zn(NO3)2·6H2O and 0.01 mol of Co(NO3)2·6H2O (Zn:Co = 1:1), ultrasonic for 30 min, then add 0.10 mol of 2-methylimidazole methanol solution dropwise, stir at 25°C for 6 h (coating amount 3%), wash with methanol for 3 times after centrifugation, vacuum dry at 80°C for 8 h to obtain Zn / CoZIF coated artificial graphite C.

[0068] S4: Disperse the coated artificial graphite C in 50 mL of deionized water, add 7.5 mL of PEDOT / PSS aqueous solution (solid content 2%, PEDOT:PSS = 1:4), stir at 50°C under nitrogen protection for 2h, spray dry (inlet 130°C, outlet 70°C, feeding rate 8 mL / min), to obtain the composite coated artificial graphite D of Zn / CoZIF:PEDOT / PSS = 2:1.

[0069] Example 5 A composite coated graphite material, comprising: S1: Break the Jinzhou petroleum coke into a diameter of less than 1 mm using a roller mill, dry the coke powder at 110°C for 4 hours using a rotary kiln, then grind the dried coke powder to Dv50 = 9.5 μm using a mechanical mill, then shape to Dv50 = 10.0 μm using a shaper, and finally calcine at high temperature through a tunnel kiln, increasing to 500°C at 5°C / min, increasing to 1000°C at 4°C / min, maintaining at 1000°C for 600 min, then decreasing to room temperature over 900 min to discharge, to obtain raw material A.

[0070] S2: Graphitize raw material A at 3100°C in a medium-frequency furnace, increasing to 1000°C at 10°C / min, increasing to 2500°C at 5°C / min, increasing to 3100°C at 2°C / min, maintaining at 3100°C for 100 min to obtain graphitized product B.

[0071] S3: Disperse 10 g of the graphitized product B in 100 mL of methanol, add 0.01 mol of Zn(NO3)2·6H2O and 0.01 mol of Co(NO3)2·6H2O (Zn:Co = 1:1), ultrasonic for 60 min, then add 0.08 mol of 2-methylimidazole methanol solution dropwise, stir at 35°C for 2h (coating amount 2%), collect the solid, wash with methanol 3 times after centrifugation, and vacuum dry at 80°C for 8h to obtain Zn / CoZIF coated artificial graphite C.

[0072] S4: Disperse the coated artificial graphite C in 50 mL of deionized water, add 10 mL of PEDOT / PSS aqueous solution (solid content 2%, PEDOT:PSS = 1:3), stir at 60°C under nitrogen protection for 2h, spray dry (inlet 150°C, outlet 80°C, feeding rate 10 mL / min, atomization pressure 0.4 MPa) to obtain the composite coated artificial graphite D of Zn / CoZIF:PEDOT / PSS = 1:1.

[0073] Example 6 A composite coated graphite material, comprising: S1: Jinzhou petroleum coke was crushed to a diameter of less than 1 mm using a roller mill, dried at 110°C for 4 hours using a rotary kiln, and then ground to Dv50 = 9.5 μm using a mechanical mill. Subsequently, the ground coke was shaped to Dv50 = 10.0 μm using a shaper, and finally calcined at high temperature in a tunnel kiln, with a temperature increase of 5°C / min to 500°C and 4°C / min to 1000°C, and then maintained at 1000°C for 600 min. The temperature was then decreased to room temperature over 900 min, and the material was discharged, to obtain raw material A.

[0074] S2: The raw material A was graphitized at 2700°C in a medium-frequency furnace, with a temperature increase of 10°C / min to 1000°C, 5°C / min to 2500°C, and 2°C / min to 2700°C, and then maintained at 2700°C for 100 min, to obtain graphitized product B.

[0075] S3: 10 g of the graphitized product B was dispersed in 100 mL of methanol, and 0.01 mol of Zn(NO3)2·6H2O and 0.01 mol of Co(NO3)2·6H2O (Zn:Co = 1:1) were added. After ultrasonic treatment for 5 min, 0.08 mol of 2-methylimidazole in methanol was added dropwise, and stirring was performed at 25°C for 8 h (coating amount 2%). The solid was collected, washed with methanol three times after centrifugation, and dried at 80°C under vacuum for 8 h, to obtain Zn / CoZIF-coated artificial graphite C.

[0076] S4: The coated artificial graphite C was dispersed in 50 mL of deionized water, and 10 mL of a PEDOT / PSS aqueous solution (solid content 2%, PEDOT:PSS = 1:3) was added. Stirring was performed at 50°C for 5 h under nitrogen protection, and spray drying was performed (inlet temperature 120°C, outlet temperature 50°C, feeding rate 5 mL / min, atomization pressure 0.2 MPa), to obtain composite-coated artificial graphite D with Zn / CoZIF:PEDOT / PSS = 1:1.

[0077] Example 7 A composite-coated graphite material, comprising: S1: Jinzhou petroleum coke was crushed to a diameter of less than 1 mm using a roller mill, dried at 110°C for 4 hours using a rotary kiln, and then ground to Dv50 = 9.5 μm using a mechanical mill. Subsequently, the ground coke was shaped to Dv50 = 10.0 μm using a shaper, and finally calcined at high temperature in a tunnel kiln, with a temperature increase of 5°C / min to 500°C and 4°C / min to 1000°C, and then maintained at 1000°C for 600 min. The temperature was then decreased to room temperature over 900 min, and the material was discharged, to obtain raw material A.

[0078] S2: The raw material A was graphitized at 3000°C in a medium-frequency furnace, with a temperature increase of 10°C / min to 1000°C, 5°C / min to 2500°C, and 2°C / min to 3000°C, and then maintained at 3000°C for 100 min, to obtain graphitized product B.

[0079] S3: Take 10 g of graphitized product B and disperse it in 100 mL of methanol, add 0.01 mol of Zn(NO3)2·6H2O and 0.01 mol of Co(NO3)2·6H2O (Zn:Co = 1:1), ultrasonic for 30 min, then add 0.08 mol of imidazole methanol solution dropwise, stir at 25°C for 4 h (coating amount 2%), collect the solid, wash with methanol for 3 times after centrifugation, vacuum dry at 80°C for 8 h, to obtain Zn / CoZIF coated artificial graphite C.

[0080] S4: Disperse the coated artificial graphite C in 50 mL of deionized water, add 10 mL of PEDOT / PSS aqueous solution (solid content 2%, PEDOT:PSS = 1:3), stir at 50°C for 2 h under nitrogen protection, spray dry (inlet 130°C, outlet 70°C, feeding rate 8 mL / min), to obtain the composite coated artificial graphite D with Zn / CoZIF:PEDOT / PSS = 1:1.

[0081] Example 8 A composite coated graphite material, comprising: S1: Crush the Jinzhou petroleum coke to a diameter of less than 1 mm using a roller mill, dry the crushed coke powder in a rotary kiln at 110°C for 4 hours, then grind the dried coke powder to Dv50 = 9.5 μm using a mechanical mill, then shape to Dv50 = 10.0 μm using a shaper, and finally calcine at high temperature through a tunnel kiln, with a temperature rising rate of 5°C / min to 500°C, 4°C / min to 1000°C, and keeping at 1000°C for 600 min, then cooling to room temperature at a rate of 900 min, to obtain raw material A.

[0082] S2: Graphitize the raw material A in a medium frequency furnace at 3000°C, with a temperature rising rate of 10°C / min to 1000°C, 5°C / min to 2500°C, and 2°C / min to 3000°C, and keeping at 3000°C for 100 min, to obtain graphitized product B.

[0083] S3: Take 10 g of graphitized product B and disperse it in 100 mL of methanol, add 0.01 mol of Zn(NO3)2·6H2O, ultrasonic for 30 min, then add 0.08 mol of 2-methyl imidazole methanol solution dropwise, stir at 25°C for 4 h (coating amount 2%), collect the solid, wash with methanol for 3 times after centrifugation, vacuum dry at 80°C for 8 h, to obtain Zn-ZIF coated artificial graphite C.

[0084] S4: Disperse the coated artificial graphite C in 50 mL deionized water, add 10 mL PEDOT / PSS aqueous solution (solid content 2%, PEDOT:PSS = 1:3), stir at 50°C under nitrogen protection for 2h, spray dry (inlet 130°C, outlet 70°C, feeding rate 8 mL / min), to obtain the composite coated artificial graphite D of ZnZIF:PEDOT / PSS = 1:1.

[0085] Example 9 A composite coated graphite material, comprising: S1: Break the Jinzhou petroleum coke into a diameter of less than 1 mm using a roller mill, dry the coke powder at 110°C for 4 hours using a rotary kiln, grind the dried coke powder to Dv50 = 9.5 μm using a mechanical mill, then shape to Dv50 = 10.0 μm using a shaper, and finally calcine at high temperature through a tunnel kiln, rising to 500°C at 5°C / min, rising to 1000°C at 4°C / min, maintaining at 1000°C for 600 min, then dropping to room temperature over 900 min to discharge, to obtain raw material A.

[0086] S2: Graphitize the raw material A at 3000°C in a medium-frequency furnace, rising to 1000°C at 10°C / min, rising to 2500°C at 5°C / min, rising to 3000°C at 2°C / min, maintaining at 3000°C for 100 min to obtain graphitized product B.

[0087] S3: Disperse 10 g of the graphitized product B in 100 mL of methanol, add 0.01 mol of Co(NO3)2·6H2O, ultrasonic for 30 min, then drop 0.08 mol of 2-methylimidazole methanol solution, stir at 25°C for 4h (coating amount 2%), collect the solid, wash with methanol for 3 times after centrifugation, and vacuum dry at 80°C for 8h to obtain Co-ZIF coated artificial graphite C.

[0088] S4: Disperse the coated artificial graphite C in 50 mL deionized water, add 10 mL PEDOT / PSS aqueous solution (solid content 2%, PEDOT:PSS = 1:3), stir at 50°C under nitrogen protection for 2h, spray dry (inlet 130°C, outlet 70°C, feeding rate 8 mL / min), to obtain the composite coated artificial graphite D of ZnZIF:PEDOT / PSS = 1:1.

[0089] Example 10 A composite coated graphite material, comprising: S1: Jinzhou petroleum coke was crushed to a diameter of less than 1 mm using a roller mill, dried at 110°C for 4 hours using a rotary kiln, and then ground to Dv50 = 9.5 μm using a mechanical mill. Subsequently, the ground product was shaped to Dv50 = 10.0 μm using a shaper, and finally calcined at high temperature in a tunnel kiln, with a temperature increase of 5°C / min to 500°C and 4°C / min to 1000°C, and then maintained at 1000°C for 600 min. The product was then cooled to room temperature over 900 min and discharged to obtain raw material A.

[0090] S2: The raw material A was graphitized at 3000°C in a medium-frequency furnace, with a temperature increase of 10°C / min to 1000°C, 5°C / min to 2500°C, and 2°C / min to 3000°C, and then maintained at 3000°C for 100 min to obtain graphitized product B.

[0091] S3: 10 g of the graphitized product B was dispersed in 100 mL of methanol, and 0.01 mol of Zn(NO3)2·6H2O and 0.01 mol of Co(NO3)2·6H2O (Zn:Co = 1:1) were added. After ultrasonic treatment for 30 min, 0.08 mol of 2-methylimidazole in methanol was added dropwise, and stirring was performed at 25°C for 4 h (coating amount 2%). The solid was collected, washed with methanol three times after centrifugation, and dried at 80°C under vacuum for 8 h to obtain Zn / CoZIF-coated artificial graphite C.

[0092] S4: The coated artificial graphite C was dispersed in 50 mL of deionized water, and 10 mL of a PEDOT / PEG (polyethylene glycol) aqueous solution (solid content 2%, PEDOT:PEG = 1:3) was added. Stirring was performed at 50°C for 2 h under nitrogen protection, and spray drying was performed (inlet temperature 130°C, outlet temperature 70°C, and feeding rate 8 mL / min) to obtain composite-coated artificial graphite D with Zn / CoZIF:PEDOT / PEG = 1:1.

[0093] Example 11 A composite-coated graphite material, comprising: S1: Jinzhou petroleum coke was crushed to a diameter of less than 1 mm using a roller mill, dried at 110°C for 4 hours using a rotary kiln, and then ground to Dv50 = 9.5 μm using a mechanical mill. Subsequently, the ground product was shaped to Dv50 = 10.0 μm using a shaper, and finally calcined at high temperature in a tunnel kiln, with a temperature increase of 5°C / min to 500°C and 4°C / min to 1000°C, and then maintained at 1000°C for 600 min. The product was then cooled to room temperature over 900 min and discharged to obtain raw material A.

[0094] S2: The raw material A was graphitized at 3000°C in a medium-frequency furnace, with a temperature increase of 10°C / min to 1000°C, 5°C / min to 2500°C, and 2°C / min to 3000°C, and then maintained at 3000°C for 100 min to obtain graphitized product B.

[0095] S3: Take 10 g of graphitized product B and disperse it in 100 mL of methanol, add 0.01 mol of Zn(NO3)2·6H2O and 0.01 mol of Co(NO3)2·6H2O (Zn:Co = 1:1), ultrasonic for 30 min, then add 0.08 mol of 2-methylimidazole methanol solution dropwise, stir at 25°C for 4 h (coating amount 2%), collect the solid, wash with methanol for 3 times after centrifugation, and vacuum dry at 80°C for 8 h to obtain Zn / CoZIF coated artificial graphite C.

[0096] S4: Disperse the coated artificial graphite C in 50 mL of deionized water, add 0.02 mol of pyrrole monomer and 0.01 mol of ammonium persulfate, and polymerize to generate polypyrrole (PPy) under stirring at 50°C for 2 h under nitrogen protection, and spray dry (inlet 130°C, outlet 70°C, feeding rate 8 mL / min) to obtain the composite coated artificial graphite D with Zn / CoZIF:PPy = 1:1.

[0097] Example 12 A composite coated graphite material, comprising: S1: Crush the Jinzhou petroleum coke to a diameter of less than 1 mm using a roller mill, dry the crushed coke powder in a rotary kiln at 110°C for 4 hours, grind the dried coke powder to Dv50 = 9.5 μm using a mechanical mill, then shape to Dv50 = 10.0 μm using a shaper, and finally calcine at high temperature in a tunnel kiln, with a temperature rising rate of 5°C / min to 500°C, 4°C / min to 1000°C, and holding at 1000°C for 600 min, and then cooling to room temperature at a rate of 900 min to obtain raw material A.

[0098] S2: Graphitize the raw material A in a medium frequency furnace at 3000°C, with a temperature rising rate of 10°C / min to 1000°C, 5°C / min to 2500°C, and 2°C / min to 3000°C, and holding at 3000°C for 100 min to obtain graphitized product B.

[0099] S3: Take 10 g of graphitized product B and disperse it in 100 mL of methanol, add 0.017 mol of Zn(NO3)2·6H2O and 0.017 mol of Co(NO3)2·6H2O (Zn:Co = 1:1), ultrasonic for 30 min, then add 0.13 mol of 2-methylimidazole methanol solution dropwise, stir at 25°C for 4 h (coating amount 3.3%), collect the solid, wash with methanol for 3 times after centrifugation, and vacuum dry at 80°C for 8 h to obtain Zn / CoZIF coated artificial graphite C.

[0100] S4: Disperse the coated artificial graphite C in 50 mL deionized water, add 2 mL PEDOT / PSS aqueous solution (solid content 2%, PEDOT:PSS = 1:3), stir at 50°C under nitrogen protection for 2h, spray dry (inlet 130°C, outlet 70°C, feeding rate 8 mL / min), to obtain composite coated artificial graphite D of Zn / CoZIF:PEDOT / PSS = 5:1.

[0101] Example 13 A composite coated graphite material comprises: S1: Break the Jinzhou petroleum coke into a diameter of less than 1 mm using a roller mill, dry the dried coke powder in a rotary kiln at 110°C for 4 hours, then grind the dried coke powder to Dv50 = 9.5 μm using a mechanical mill, then shape to Dv50 = 10.0 μm using a shaper, and finally calcine at high temperature through a tunnel kiln, with a temperature rise of 5°C / min to 500°C, a temperature rise of 4°C / min to 1000°C, a temperature holding of 1000°C for 600 min, and a temperature drop of 900 min to room temperature to obtain raw material A.

[0102] S2: Graphitize the raw material A in a medium frequency furnace at 3000°C, with a temperature rise of 10°C / min to 1000°C, a temperature rise of 5°C / min to 2500°C, a temperature rise of 2°C / min to 3000°C, and a temperature holding of 3000°C for 100 min to obtain graphitized product B.

[0103] S3: Disperse 10 g of the graphitized product B in 100 mL of methanol, add 0.007 mol of Zn(NO3)2·6H2O and 0.007 mol of Co(NO3)2·6H2O (Zn:Co = 1:1), ultrasonic for 30 min, then add 0.05 mol of 2-methylimidazole methanol solution dropwise, stir at 25°C for 4h (coating amount 1.3%), collect the solid, wash with methanol for 3 times after centrifugation, and vacuum dry at 80°C for 8h to obtain Zn / CoZIF coated artificial graphite C.

[0104] S4: Disperse the coated artificial graphite C in 50 mL deionized water, add 20 mL PEDOT / PSS aqueous solution (solid content 2%, PEDOT:PSS = 1:3), stir at 50°C under nitrogen protection for 2h, spray dry (inlet 130°C, outlet 70°C, feeding rate 8 mL / min) to obtain composite coated artificial graphite D of Zn / CoZIF:PEDOT / PSS = 0.5:1.

[0105] Comparative Example 1 A composite coated graphite material comprises: S1: Jinzhou petroleum coke was crushed to less than 1 mm in diameter using a roller mill, dried at 110°C for 4 hours using a rotary kiln, and then ground to Dv50 = 9.5 μm using a mechanical mill. The ground coke was then shaped to Dv50 = 10.0 μm using a shaper, and finally calcined at high temperature in a tunnel kiln, with a temperature increase of 5°C / min to 500°C, 4°C / min to 1000°C, and holding at 1000°C for 600 min. The temperature was then decreased to room temperature over 900 min, and the material was discharged to obtain raw material A.

[0106] S2: The raw material A was graphitized at 3000°C in a medium-frequency furnace, with a temperature increase of 10°C / min to 1000°C, 5°C / min to 2500°C, and 2°C / min to 3000°C, and holding at 3000°C for 100 min to obtain graphitized product B.

[0107] Comparative Example 2 A composite coated graphite material, comprising: S1: Jinzhou petroleum coke was crushed to less than 1 mm in diameter using a roller mill, dried at 110°C for 4 hours using a rotary kiln, and then ground to Dv50 = 9.5 μm using a mechanical mill. The ground coke was then shaped to Dv50 = 10.0 μm using a shaper, and finally calcined at high temperature in a tunnel kiln, with a temperature increase of 5°C / min to 500°C, 4°C / min to 1000°C, and holding at 1000°C for 600 min. The temperature was then decreased to room temperature over 900 min, and the material was discharged to obtain raw material A.

[0108] S2: The raw material A was graphitized at 3000°C in a medium-frequency furnace, with a temperature increase of 10°C / min to 1000°C, 5°C / min to 2500°C, and 2°C / min to 3000°C, and holding at 3000°C for 100 min to obtain graphitized product B.

[0109] S3: 10 g of the graphitized product B was dispersed in 100 mL of methanol, and 0.01 mol of Zn(NO3)2·6H2O and 0.01 mol of Co(NO3)2·6H2O (Zn:Co = 1:1) were added. After ultrasonic treatment for 30 min, 0.08 mol of 2-methylimidazole in methanol was added dropwise, and stirring was performed at 25°C for 4 h (coating amount 2%). The solid was collected, washed with methanol 3 times after centrifugation, and dried at 80°C under vacuum for 8 h to obtain Zn / CoZIF coated artificial graphite C.

[0110] Comparative Example 3 A composite coated graphite material, comprising: S1: Jinzhou petroleum coke was crushed to a diameter of less than 1 mm using a roller mill, dried at 110°C for 4 hours using a rotary kiln, and then ground to Dv50 = 9.5 μm using a mechanical mill. The ground coke was then shaped to Dv50 = 10.0 μm using a shaper, and finally calcined at high temperature in a tunnel kiln, with a temperature increase of 5°C / min to 500°C, and 4°C / min to 1000°C, and then held at 1000°C for 600 min. The temperature was then decreased to room temperature over 900 min, and the material was discharged, to obtain raw material A.

[0111] S2: The raw material A was graphitized at 3000°C in a medium-frequency furnace, with a temperature increase of 10°C / min to 1000°C, 5°C / min to 2500°C, and 2°C / min to 3000°C, and then held at 3000°C for 100 min, to obtain graphitized product B.

[0112] S3: 10 g of the graphitized product B was dispersed in 50 mL of deionized water, 10 mL of a PEDOT / PSS aqueous solution (solid content 2%, PEDOT:PSS = 1:3) was added, and the mixture was stirred at 50°C under nitrogen protection for 2 h. The mixture was spray dried (inlet temperature 130°C, outlet temperature 70°C, and feed rate 8 mL / min), to obtain PEDOT / PSS-coated graphitized product C.

[0113] Comparative Example 4 A composite coated graphite material, comprising: S1: Jinzhou petroleum coke was crushed to a diameter of less than 1 mm using a roller mill, dried at 110°C for 4 hours using a rotary kiln, and then ground to Dv50 = 9.5 μm using a mechanical mill. The ground coke was then shaped to Dv50 = 10.0 μm using a shaper, and finally calcined at high temperature in a tunnel kiln, with a temperature increase of 5°C / min to 500°C, and 4°C / min to 1000°C, and then held at 1000°C for 600 min. The temperature was then decreased to room temperature over 900 min, and the material was discharged, to obtain raw material A.

[0114] S2: The raw material A was graphitized at 3000°C in a medium-frequency furnace, with a temperature increase of 10°C / min to 1000°C, 5°C / min to 2500°C, and 2°C / min to 3000°C, and then held at 3000°C for 100 min, to obtain graphitized product B.

[0115] S3: 10 g of the graphitized product B was dispersed in 100 mL of methanol, 0.05 mol of LiOH and 0.02 mol of H3PO4 were added, and the mixture was ultrasonicated for 30 min, and then stirred at 35°C for 6 h. The pH was adjusted to 7-8, the mixture was centrifuged, and then washed with deionized water 3 times. The mixture was vacuum dried at 80°C for 8 h, to obtain Li3PO4-coated artificial graphite C (coating amount 2%).

[0116] S4: Li3PO4-coated artificial graphite C was dispersed in 50 mL deionized water, 10 mL PEDOT / PSS aqueous solution (solid content 2%, PEDOT:PSS = 1:3) was added, stirring at 50°C for 2h under nitrogen protection, spray drying (inlet 130°C, outlet 70°C, feeding rate 8 mL / min), to obtain composite-coated artificial graphite D with Li3PO4:PEDOT / PSS = 1:1.

[0117] Experimental Example 1 The volume particle size Dv50 and specific surface area of the composite-coated graphite material in each example and comparative example were obtained; wherein the volume particle size Dv50 was measured by laser method using Malvern Mastersizer 3000, and the specific surface area was measured using Micromeritics ASAP-2020 physical adsorption instrument.

[0118] 30C initial discharge specific capacity and initial efficiency (%) were measured using Shenzhen Xinwei button battery test system, and the test method was as follows: the composite-coated graphite material was used as a negative electrode material, and a negative electrode active slurry was prepared by mixing the negative electrode material with a solvent in a ratio of negative electrode material: SP:SBR:CMC = 96:1:1.5:1.5. The negative electrode active slurry was coated on a current collector to form a negative electrode sheet. A lithium metal sheet was used as a counter electrode, 20 μL of electrolyte (specific components: 15% LiPF6, 28% EC, 28% EMC, 28% DMC, 1% VC) was added, and a CR2430 button cell was assembled in a vacuum glove box. The charge and discharge steps were as follows: standing for 600 min, 0.1C discharging to 0.005V, standing for 30 min, 30C discharging to 0.005V, standing for 30 min, 20 μA to 0.005V, obtaining the initial lithium intercalation capacity of the material, standing for 120 min, charging to 2.0V at 30C, completing the first cycle, obtaining the initial lithium extraction capacity of the material, which was the 30C initial discharge specific capacity, and the ratio of the initial lithium extraction capacity to the lithium intercalation capacity was the initial efficiency (%).

[0119] The cycle performance is measured by a Shenzhen Xinwei button battery test system, and the test method is as follows: the composite coated graphite material is used as a negative electrode material, and is mixed with a solvent to prepare a negative electrode active slurry in a ratio of negative electrode material: SP: SBR: CMC = 96: 1: 1.5: 1.5, the negative electrode active slurry is coated on a current collector to prepare a negative electrode sheet, a lithium sheet is used as a counter electrode, 20 μL of electrolyte (specific components: 15% LiPF6, 28% EC, 28% EMC, 28% DMC, 1% VC) is added, and a CR2430 button cell is assembled in a vacuum glove box, and the charge and discharge steps are as follows: standing for 12 h, 0.1C discharging to 0.005V, 0.005V constant voltage discharging, and the cutoff current is 0.005C; standing for 10 min, 0.1C constant current charging to 1.5V, standing for 10 min, 0.1C constant current discharging to 0.005V, 0.005V constant voltage discharging, and the cutoff current is 0.005C; standing for 10 min, the next cycle is carried out, after 500 cycles, the capacity ratio compared with the initial capacity is calculated, and the 0.1C cycle 500 times capacity retention rate (%) is obtained.

[0120] The effect data of the above detection is shown in Table 1.

[0121] Table 1

[0122] From the above results, it can be seen that by setting the ZIF inner layer and the conductive polymer outer layer on the graphite inner core, the synergistic design of "inner ion transmission channel + outer electron conduction network" can be realized, the specific surface area can be effectively improved, and the ion conductivity and electronic conductivity of the negative electrode material can be simultaneously improved, the problems of slow ion diffusion, weak electronic conduction and volume expansion of the graphite inner core during fast charging are effectively solved, and the 0.1C cycle 500 times capacity retention rate is comprehensively improved. It can be seen from the comparison of Example 1 with Examples 8 and 9 that the synergistic effect of two metal ions in Zn / Co bimetallic ZIF has more abundant mesoporous structure and higher ion transmission capacity, and the mutual synergistic effect with the conductive polymer outer layer can further improve the electronic conduction to meet the fast charging electronic transmission demand, significantly improve the first discharge specific capacity and the initial efficiency of the prepared negative electrode at 30C high rate, and also obviously improve the 0.1C cycle 500 times capacity retention rate.

[0123] Obviously, the above examples are only examples for clearly illustrating but not limiting the embodiments. Based on the above description, other different forms of changes or variations can be made by those skilled in the art. All the embodiments do not need to be exhausted here. The obvious changes or variations derived therefrom are still within the protection scope of the application.

Claims

1. A composite coated graphite material, characterized by, The graphite inner core, the ZIF inner layer coated on the graphite inner core, and the conductive polymer outer layer coated on the ZIF inner layer; the ZIF inner layer is doped with Zn and / or Co.

2. The composite coated graphite material of claim 1, wherein, The graphite inner core has a Dv50 of between 5-16 pm and a tap density of between 1.0-1.3 g / cm 3 .

3. The composite-coated graphite material according to claim 1 or 2, characterized in that, The ZIF inner layer is doped with Zn2 + and Co2 + The molar ratio of Zn2 + and Co2 + is (1-4):

1.

4. The composite-coated graphite material of any one of claims 1-3, wherein, The mass ratio between the ZIF inner layer and the conductive polymer outer layer is (0.5-5):

1.

5. The composite-coated graphite material of any one of claims 1-4, wherein, The thickness of the ZIF inner layer is 5-20 nm; And / or, the thickness of the conductive polymer outer layer is 10-30 nm; And / or, the total mass of the ZIF inner layer and the conductive polymer outer layer on the graphite inner core is 3-8 wt%.

6. The composite-coated graphite material of any one of claims 1-5, wherein, The raw material of the conductive polymer outer layer includes polymer A and diluent B, the polymer A includes PEDOT, and the diluent B includes PSS or PEG; or, the raw material of the conductive polymer outer layer includes a pyrrole monomer and a polymerization initiator, and the polymerization initiator is ammonium persulfate.

7. The composite-coated graphite material of claim 6, wherein The mass ratio of the polymer A to the diluent B is 1:(2-4).

8. A method for producing a composite coated graphite material, characterized by, The graphite inner core is obtained; The ZIF inner layer is coated: the graphite inner core is dispersed in a solvent, a Zn source and / or a Co source are added, a ligand is added after dispersion, and the solid is collected after reaction, washed, and dried to obtain a Zn / CoZIF coated graphite product; The conductive polymer outer layer is coated: the Zn / CoZIF coated graphite product is uniformly dispersed with a conductive polymer solution, and then reacted, and the dried product is a composite coated graphite material. The graphite inner core is obtained by crushing coke to have a Dv50 of 5-16 μm and graphitizing at 2700-3100 °C; 9. The preparation method according to claim 8, characterized in that, And / or, in the step of coating the ZIF inner layer, the solvent is a methanol solution, the dispersion is ultrasonic dispersion, the reaction temperature is 25-35 °C, the reaction time is 2-8 h, and the drying method is vacuum drying; And / or, in the step of coating the conductive polymer outer layer, the solid content of the conductive polymer solution is 1-3%, the reaction is carried out in a protective atmosphere, the reaction temperature is 50-60 °C, the reaction time is 2-5 h, and the drying method is spray drying. In the step of coating the ZIF inner layer, the ultrasonic dispersion time is 5-60 min, and the washing solvent is methanol; 10. The method of claim 9, wherein, The inlet temperature of the spray drying is 120-150 °C, the outlet temperature of the spray drying is 50-80 °C, the feed rate of the spray drying is 5-10 mL / min, and the atomization pressure is 0.2-0.4 MPa. ​

Images