CN113437278A - Graphite negative electrode material and preparation method and application thereof - Google Patents

Graphite negative electrode material and preparation method and application thereof Download PDF

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CN113437278A
CN113437278A CN202110876464.9A CN202110876464A CN113437278A CN 113437278 A CN113437278 A CN 113437278A CN 202110876464 A CN202110876464 A CN 202110876464A CN 113437278 A CN113437278 A CN 113437278A
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graphite
epoxy resin
curing agent
negative electrode
mass ratio
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李春
姜武
刘东任
李辉
刘芳
冯苏宁
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Jiangxi Zichen Technology Co ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
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Abstract

The invention provides a graphite cathode material and a preparation method and application thereof. The graphite cathode material is a graphite cathode material coated by a carbon layer, and the carbon layer is a hard carbon coating layer; the graphite negative electrode material is burnt at 600-1000 ℃, and has 2 heat release peaks which are respectively positioned in the range of 800-900 ℃ and 900-1000 ℃. The preparation method comprises the following steps: (1) mixing epoxy resin and a curing agent to obtain a mixed solution, and compounding the mixed solution and graphite by using mechanical force to obtain a composite material; (2) and carbonizing the composite material to obtain the graphite cathode material. According to the invention, the epoxy resin is wetted and coated on the surface of the graphite under the action of mechanical force, and reacts with the curing agent to directly obtain thermosetting resin on the surface of the graphite, and the graphite cathode material uniformly coated with hard carbon is obtained after carbonization, so that the specific surface area of the graphite cathode material can be effectively reduced, the charging rate is improved, and rapid charging is realized.

Description

Graphite negative electrode material and preparation method and application thereof
Technical Field
The invention belongs to the technical field of lithium ion batteries, and relates to a graphite cathode material, and a preparation method and application thereof.
Background
In recent years, in order to deal with the great change of the automobile industry, the market of electric vehicles has been developed rapidly, but mileage anxiety still puzzles drivers, and particularly, the charging time is too long, so that the scarce charging pile is more attractive, and therefore, a lithium ion battery with a higher charging rate is developed, the charging time is shortened, and the market demand can be met.
The key point for improving the charging rate of the lithium battery is the innovation of raw materials, graphite becomes a mainstream negative electrode material in the current market due to good chemical stability and electrical property, but Li is embedded in the lithium+The graphite sheets cannot be embedded from the basal plane and must move to the end face to be embedded with graphite, so that the charging speed of the graphite cathode material is limited. To solve this problem, the current common solution is to coat a layer of soft carbon on the surface of graphite particles, and the soft carbon microcrystals have larger interlayer spacing to make Li+Can be quickly embedded into the graphite sheet and move to the end face of the graphite sheet layer so as to improve the charging rate, can be simply understood as that the soft carbon plays the role of a funnel in the charging process, and quickly integrates Li+Graphite sheets are embedded.
Although the soft carbon layer can improve the charge rate of the graphite anode material to a certain extent, the hard carbon layer still cannot meet the market demand, and therefore the hard carbon layer with larger interlayer spacing is widely concerned. The greater interlayer spacing of the hard carbon means that less cladding can be used to improve the rate capability of the material, so the negative impact on the material in compaction and capacity is less than the impact of the soft carbon cladding.
CN103647055A discloses an epoxy resin modified graphite cathode material and a preparation method thereof, wherein the epoxy resin modified by organic silicon and natural graphite are subjected to grinding, high-temperature curing, carbonization and crushing to obtain the epoxy resin modified graphite cathode material, and epoxy resin carbon coated on the surface of the graphite can prevent co-intercalation of large-volume solvent molecules. Compared with uncoated graphite, the reversible capacity, the cycle performance and the low-temperature rate performance of the graphite cathode coated by pyrolytic carbon are greatly improved, but in the existing pyrolytic carbon coating process, the phenomena of particle bonding and uneven coating are easily generated by high-temperature pyrolysis or high-temperature curing. The improvement of the performance of the graphite material by different coating processes reaches a bottleneck, the performance requirements of the current lithium ion battery industry on the graphite cathode are difficult to meet (the first reversible capacity is higher than 360mAh/g, and the first coulombic efficiency is higher than 92%), and meanwhile, the problems of poor batch stability, high production cost and the like exist.
CN103647055A discloses a negative electrode material of epoxy resin modified graphite and a preparation method thereof, wherein the material of epoxy resin modified natural graphite is obtained by grinding, high-temperature curing, carbonizing and crushing the epoxy resin modified by organic silicon and natural graphite, although co-embedding of large-volume solvent molecules can be prevented, high-temperature pyrolysis is easy to agglomerate, the coating effect can be damaged by crushing, the phenomena of uneven coating on the graphite surface and damage of a coating layer are caused, and finally, a good coating effect cannot be realized.
Therefore, how to effectively reduce the specific surface area of the graphite negative electrode material, improve the charging rate and realize rapid charging is a technical problem which needs to be solved urgently.
Disclosure of Invention
The invention aims to provide a graphite negative electrode material and a preparation method and application thereof. According to the invention, the epoxy resin is wetted and coated on the surface of the graphite under the action of mechanical force, and reacts with the curing agent to directly obtain thermosetting resin on the surface of the graphite, and the graphite cathode material uniformly coated with hard carbon is obtained after carbonization, so that the specific surface area of the graphite cathode material can be effectively reduced, the charging rate is improved, and rapid charging is realized.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a graphite anode material, wherein the graphite anode material is a graphite anode material coated by a carbon layer, and the carbon layer is a hard carbon coating layer; the graphite negative electrode material is burnt at 600-1000 ℃, and has 2 heat release peaks which are respectively positioned in the range of 800-900 ℃ and 900-1000 ℃.
In the cathode of the conventional carbon-coated graphite material, only one exothermic peak exists when the carbon-coated graphite material is combusted at 600-1000 ℃, but the hard carbon layer and the graphite core of the graphite cathode material provided by the invention have chemical bonds which can be oxidized and release heat at higher temperature, so that at least one exothermic peak combining graphite and hard carbon exists, which shows that the hard carbon coating layer and graphite are firmly combined, the firm hard carbon coating layer is not easy to peel off in the cyclic expansion process, and the material is more stable and has a positive effect on the battery cycle.
Preferably, the specific surface area of the graphite negative electrode material is 0.5-8 m2In g, e.g. 0.5m2/g、1m2/g、2m2/g、5m2/g、7m2/g、7m2G or 8m2G, etc., preferably 0.5 to 3.5m2/g。
Preferably, the graphite negative electrode material has an accumulated value of micropore and mesopore volumes of 0.001-0.01 cm within a pore diameter range of 1-35 nm3In g, e.g. 0.001cm3/g、0.005cm3/g、0.008cm3In g or 0.01cm3The concentration is preferably 0.0020 to 0.0035cm3/g。
Preferably, the graphite negative electrode material has an average particle size of 4 to 30 μm, for example, 4 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, or 30 μm, and preferably 5 to 20 μm.
In a second aspect, the present invention provides a method for preparing the graphite anode material according to the first aspect, the method comprising the steps of:
(1) mixing epoxy resin and a curing agent to obtain a mixed solution, and compounding the mixed solution and graphite by using mechanical force to obtain a composite material;
(2) and (3) carbonizing the composite material obtained in the step (1) to obtain the graphite cathode material.
The epoxy resin provided by the invention is liquid at room temperature.
The invention uses the mechanical force to make the epoxy resinThe graphite negative electrode material particle is not easy to slip and deform and orient when preparing a negative electrode of a pole piece, so that the pole piece can keep better isotropy; and because of Li+Can only be inserted from the end face of graphite, the surface of the graphite is coated with hard carbon with low crystallinity to provide more lithium insertion points, and the orientation degree of the pole piece is low due to the coating of the hard carbon, namely Li+The embedding is convenient, so that the anode material prepared by the preparation method provided by the invention can effectively reduce the specific surface area of the material, improve the charging rate and realize rapid charging.
Compared with the conventional resin coating, if the powdery resin is mixed with graphite, and then the resin is automatically leveled and coated on the surface of graphite particles by utilizing the melt fluidity of the resin in the carbonization and temperature rise processes, the coating uniformity is poor. Or the liquid resin is mixed with the graphite and wetted, and the resin still has fluidity in the carbonization and temperature rise process, so that the coating uniformity is also reduced. In the process of carbon coating of graphite, the epoxy resin containing the curing agent is forcibly wetted on the surface of graphite particles by the action of mechanical force and is cured to form the thermosetting resin, the thermosetting resin has no fluidity in the carbonization and temperature rise process, and the resin is directly pyrolyzed into hard carbon at high temperature in a mechanically uniform and mixed coating state before being maintained, so that the coating is more uniform and complete.
After graphite is subjected to carbon coating by adopting a conventional technical means, only one exothermic peak, namely graphite oxidation exothermic peak, exists in the negative electrode of the graphite material when the graphite material is combusted at 600-1000 ℃, and the graphite negative electrode material prepared by the preparation method provided by the invention forms a hard carbon coating layer with higher disorder degree than the graphite on the surface of graphite particles, so that besides the graphite oxidation exothermic peak, a chemical bond exists between a hard carbon layer and a graphite core, the chemical bond can be oxidized and emit heat at a higher temperature, and at least one exothermic peak combining graphite and hard carbon exists, which shows that the hard carbon coating layer and the graphite are firmly combined, and the firm hard carbon coating layer is not easy to peel off in the cyclic expansion process, so that the material is more stable and has a positive effect on battery cycle.
Preferably, the epoxy resin of step (1) is mixed with a solvent before being mixed with the curing agent of step (1).
In the present invention, a solvent may be added in order to further improve the fluidity of the epoxy resin.
Preferably, the solvent comprises water.
Preferably, the mass ratio of the epoxy resin to the water in the step (1) is 100 (0-100), such as 0, 100:1, 50:1, 25:1, 10:1, 5:1 or 1:1.
In the present invention, the endpoint value of 0 in the mass ratio of the epoxy resin to water in the step (1) means that no solvent may be added, or the epoxy resin may be in a liquid state.
Preferably, the mass ratio of the epoxy resin in the step (1) to the curing agent in the step (1) is 100 (5-200), such as 20:1, 10:1, 5:1, 4:1, 1:1.2, 1:1.5, 1:1.8 or 1: 2.
In the invention, the mixing mass ratio is adjusted according to the difference of the curing speeds of different types of epoxy resins and curing agents after mixing, so that the curing time meets the production rhythm, and the phenomenon that the curing agglomeration is caused when the curing time is too short and the curing agglomeration is not mixed with graphite is avoided, or the coating is not uniform because the resin flows in the carbonization process because the curing time is too long is avoided.
Preferably, the epoxy resin in step (1) comprises any one of or a combination of at least two of bisphenol a type epoxy resin, bisphenol F type epoxy resin, glycerin epoxy resin, amine based epoxy resin, glycidyl ester type epoxy resin, resorcinol diglycidyl ether or trimesotriglycidyl.
Preferably, the curing agent in the step (1) comprises any one or a combination of at least two of an amine curing agent, an anhydride curing agent or an imidazole curing agent.
Preferably, the mechanical force of step (1) comprises any one or a combination of at least two of a shear force, a squeezing force or a friction force.
Preferably, the graphite of step (1) comprises artificial graphite and/or natural graphite.
Preferably, the graphite has a median particle diameter of 4 to 30 μm, for example 4 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm or 30 μm, preferably 5 to 20 μm.
In the present invention, the smaller the median particle diameter of graphite is, in general, the smaller Li+The shorter the migration path inside the graphite particles, the better the quick charging performance, but the lower the energy density of the material, so the preferred median diameter is 5 to 20 μm.
Preferably, the mass ratio of the graphite in the step (1) to the mixed solution in the step (1) is 100 (3-50), for example, 100:3, 20:1, 10:1, 5:1, 4:1 or 2: 1.
In the invention, the coating is easy to be uneven and incomplete when the proportion of the mixed solution is too small, and hardening or too much volatile (water and gas decomposed by resin) is easy to occur when the proportion of the mixed solution is too large, and the carbonization and temperature rise need to consume more heat, so that the production cost is increased.
Preferably, the carbonization atmosphere in the step (2) is a protective atmosphere.
Preferably, the temperature rise rate of the carbonization in the step (2) is 1-5 ℃/min, such as 1 ℃/min, 2 ℃/min, 3 ℃/min, 4 ℃/min or 5 ℃/min.
The carbonization process is preferably carried out by heating in sections, for example, the carbonization process can be carried out at a slow speed and a fast speed in combination at various heating rates.
In the invention, the heating speed is adjusted slowly when the heat loss of the resin is larger or the temperature rise is near the pyrolysis temperature, so that the gas generated by the degradation of the resin is slowly released, a smaller specific surface can be obtained, if the temperature rise is too fast, a large number of air holes are generated in the coating layer, the specific surface is increased, and if the heating speed is always very slow, the production efficiency is obviously reduced.
Preferably, the carbonization temperature in step (2) is 700-1300 ℃, such as 700 ℃, 750 ℃, 800 ℃, 850 ℃, 900 ℃, 950 ℃, 1000 ℃, 1050 ℃, 1100 ℃, 1150 ℃, 1200 ℃, 1250 ℃ or 1300 ℃.
Preferably, the heat preservation time of the carbonization in the step (2) is 1-12 h, such as 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h or 12 h.
Preferably, the carbonized product obtained in the step (2) is mixed and screened.
Preferably, the mesh number of the sieving screen is 200-600 meshes, such as 200 meshes, 300 meshes, 400 meshes, 500 meshes or 600 meshes.
As a preferable technical scheme, the preparation method of the graphite negative electrode material comprises the following steps:
(1) mixing epoxy resin and water according to the mass ratio of 100 (0-100), adding a curing agent, and continuously mixing, wherein the mass ratio of the epoxy resin to the curing agent is 100 (5-200), so as to obtain a mixed solution, and compounding the mixed solution with graphite with the median particle size of 4-30 mu m by using a mechanical force, wherein the mass ratio of the graphite to the mixed solution is 100 (3-50), so as to obtain a composite material;
(2) and (2) heating the composite material obtained in the step (1) to 700-1300 ℃ at a heating rate of 1-5 ℃/min in a protective atmosphere, carbonizing, keeping the temperature for 1-12 h, cooling, mixing, and sieving by using a 200-600 mesh sieve to obtain the graphite cathode material.
In a third aspect, the present invention also provides a lithium ion battery, which includes the graphite negative electrode material according to the first aspect.
Compared with the prior art, the invention has the following beneficial effects:
according to the invention, epoxy resin is wetted and coated on the surface of graphite through the mechanical force, and reacts with a curing agent to directly obtain thermosetting resin on the surface of graphite, and the graphite cathode material uniformly coated with hard carbon is obtained after carbonization, so that the specific surface area of the graphite cathode material can be effectively reduced, the charging rate is improved, rapid charging is realized, the CC/CC + CV constant current charging ratio is obviously improved, the electrochemical performance is not reduced, the capacity is above 339.2mAh/g under the conditions of 0.6mA and 0.005V, and the first effect can reach more than 91.7%.
Drawings
Fig. 1 is a graph showing the results of thermogravimetric differential thermal analysis of the graphite anode materials provided in example 1 and comparative example 1.
Fig. 2 is a graph showing the results of thermogravimetric differential thermal analysis of the graphite anode materials provided in example 2 and comparative example 2.
Fig. 3 is a graph showing the results of thermogravimetric differential thermal analysis of the graphite anode materials provided in example 3 and comparative example 3.
Fig. 4 is a graph showing the results of thermogravimetric differential thermal analysis of the graphite anode materials provided in example 4 and comparative example 4.
Fig. 5 is a graph showing the results of thermogravimetric differential thermal analysis of graphite and hard carbon.
Detailed Description
The technical solution of the present invention is further explained by the following embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.
Example 1
The present example provides a hard carbon coated graphite anode material.
The preparation method of the graphite negative electrode material comprises the following steps:
(1) uniformly mixing tetrahydrobenzene dimethyl ester epoxy resin with a curing agent in a mass ratio of 100:70 to obtain liquid B, wherein the curing agent is a mixture of hexacyanobenzene anhydride and triethylenetetramine in a weight ratio of 1: 1;
(2) wetting the liquid B on the surface of the artificial graphite powder with the median particle size of 5 microns by the action of shearing force to obtain a resin and graphite composite material A, wherein the mass ratio of the artificial graphite powder to the liquid B is 100: 3;
(3) and (3) placing the composite material A in a carbonization furnace, heating to 700 ℃ at a heating rate of 1 ℃/min under a nitrogen atmosphere, sintering for 4h, cooling to room temperature, uniformly mixing through mixing equipment, and screening through a 600-mesh screen to obtain the hard carbon coated graphite cathode material.
Example 2
The present example provides a hard carbon coated graphite anode material.
The preparation method of the graphite negative electrode material comprises the following steps:
(1) fully and uniformly mixing water-based bisphenol A epoxy resin and water according to a mass ratio of 100:100 to obtain liquid A; adding the curing agent into the liquid A according to the mass ratio of 100:100 of the waterborne bisphenol A epoxy resin to the triethylene tetramine curing agent, and uniformly mixing to obtain liquid B;
(2) wetting the liquid B on the surface of natural graphite powder with the median particle size of 10 mu m under the action of extrusion force to obtain a resin and graphite composite material A, wherein the mass ratio of the artificial graphite powder to the liquid B is 2: 1;
(3) and (3) placing the composite material A in a carbonization furnace, heating to 850 ℃ at a heating rate of 3 ℃/min in a nitrogen atmosphere, sintering for 12h, cooling to room temperature, uniformly mixing through mixing equipment, and screening through a 500-mesh screen to obtain the hard carbon coated graphite cathode material.
Example 3
The present example provides a hard carbon coated graphite anode material.
The preparation method of the graphite negative electrode material comprises the following steps:
(1) fully and uniformly mixing o-cresol formaldehyde epoxy resin and water according to the mass ratio of 100:30 to obtain liquid A; adding the curing agent into the liquid A according to the mass ratio of 100:5 of the o-cresol formaldehyde epoxy resin to the 2-ethyl-4-methylimidazole curing agent, and uniformly mixing to obtain liquid B;
(2) wetting the liquid B on the surface of artificial graphite powder with the median particle size of 25 mu m under the action of friction force to obtain a resin-graphite composite material A, wherein the mass ratio of the artificial graphite powder to the liquid B is 100: 15;
(3) and (3) placing the composite material A in a carbonization furnace, heating to 1100 ℃ at a heating rate of 5 ℃/min under a nitrogen atmosphere, sintering for 8h, cooling to room temperature, uniformly mixing through mixing equipment, and screening through a 400-mesh screen to obtain the hard carbon coated graphite cathode material.
Example 4
The present example provides a hard carbon coated graphite anode material.
The preparation method of the graphite negative electrode material comprises the following steps:
(1) fully and uniformly mixing epoxy resin and water according to the mass ratio of 100:70 to obtain liquid A, wherein the epoxy resin is a mixture of resorcinol diglycidyl ether and tetrahydrobenzene dimethyl ester epoxy resin, and the mass ratio of each component is 1: 1; adding the curing agent into the liquid A according to the mass ratio of 100:200 of the epoxy resin to the triethylene tetramine curing agent, and uniformly mixing to obtain liquid B;
(2) wetting the liquid B on the surface of natural graphite powder with the median particle size of 18 mu m by the action of shearing force to obtain a resin and graphite composite material A, wherein the mass ratio of the artificial graphite powder to the liquid B is 100: 25;
(3) and (3) placing the composite material A in a carbonization furnace, heating to 1300 ℃ at the heating rate of 4 ℃/min under the nitrogen atmosphere, sintering for 1h, cooling to room temperature, uniformly mixing by using mixing equipment, and screening by using a 270-mesh screen to obtain the hard carbon coated graphite cathode material.
Example 5
The difference between this example and example 1 is that in step (2) of this example, the mass ratio of the artificial graphite powder to the liquid B was 100: 1.
The remaining preparation methods and parameters were in accordance with example 1.
Comparative example 1
The present comparative example provides a graphite negative electrode material in which the graphite raw material is the artificial graphite powder having a median particle diameter of 5 μm provided in step (2) of example 1, and the preparation method is as follows:
the artificial graphite powder having a median particle diameter of 5 μm was subjected to the same shearing force treatment as in example 1, and then subjected to the same treatment step as in step (4) in example 1, to obtain the graphite negative electrode material.
Comparative example 2
This comparative example provides a graphite negative electrode material in which the graphite raw material is the natural graphite powder having a median particle diameter of 10 μm provided in step (2) of example 2, and the preparation method is as follows:
and (3) wetting and coating natural graphite powder with the median particle size of 10 microns and water according to the mass ratio of 6:1 by virtue of extrusion force, and then performing the same treatment steps as the step (4) in the example 2 to obtain the graphite negative electrode material.
Comparative example 3
This comparative example provides a graphite negative electrode material in which the graphite raw material was the artificial graphite powder having a median particle diameter of 25 μm provided in step (2) of example 3, and the preparation method was as follows:
the artificial graphite powder with the median particle size of 25 μm and water were subjected to wet coating by a frictional force action in a mass ratio of 30:1, and then the same treatment steps as in step (4) in example 3 were performed to obtain the graphite negative electrode material.
Comparative example 4
This comparative example provides a graphite negative electrode material in which the graphite raw material is the natural graphite powder having a median particle diameter of 18 μm provided in step (2) of example 4, and the preparation method is as follows:
and (3) wetting and coating the natural graphite powder with the median particle size of 18 microns and water according to the mass ratio of 52:5 by virtue of a shearing force, and then performing the same treatment steps as the step (4) in the example 4 to obtain the graphite negative electrode material.
Comparative example 5
This comparative example differs from example 1 in that in step (1) of this comparative example, no curing agent was added.
The remaining preparation methods and parameters were in accordance with example 1.
Comparative example 6
The difference between the comparative example and the example 2 is that the epoxy resin is changed into powdery bisphenol A type epoxy resin with the softening point of 135-150 ℃.
The remaining preparation methods and parameters were in accordance with example 2.
Comparative example 7
The difference between the comparative example and the example 1 is that the resin obtained in the step (2) and the graphite in the comparative example are ground and pressure-molded to obtain a mixture A; heating to 250 ℃ in a nitrogen gas separation system, and curing for 1.5h to obtain a mixture B; heating the mixture B to 700 ℃ and carbonizing for 5h to obtain a mixture C; and cooling the mixture C, and crushing to obtain the graphite cathode material modified by the epoxy resin in the comparative example, wherein the particle size of the mixture C is 6 mu m.
As can be seen from fig. 1-5, the thermogravimetric differential thermal analysis includes: in the air atmosphere, the temperature is increased from room temperature to 1000 ℃ at the temperature increase rate of 10 ℃/min, 2 exothermic peaks are burnt in the range of 600-1000 ℃, compared with a comparative example, the exothermic peak at the relatively low temperature in the embodiment is a graphite oxidation exothermic peak, and the exothermic peak at the hard carbon oxidation is usually lower than the graphite oxidation exothermic peak (as shown in figure 5), so that the exothermic peak at the relatively higher temperature in the embodiment is the energy released by the chemical bond formed by combining graphite and hard carbon in the oxidation destruction process, which shows that the hard carbon coating layer is firmly combined with the graphite, the firm hard carbon coating layer is not easy to peel off in the cyclic expansion process, and the material is more stable and has a positive effect on the battery cycle.
The graphite anode materials provided in examples 1 to 5 and comparative examples 1 to 7 were subjected to tests including:
(1) carrying out test calculation on the median particle diameters of the graphite anode materials provided in examples 1-5 and comparative examples 1-7;
(2) XRD tests are carried out on the graphite cathode materials provided in examples 1-5 and comparative examples 1-7, and diffraction intensities under different crystal directions and crystal planes are obtained.
(3) With N2The specific surface area, the pore volume and the average pore diameter of the graphite anode materials provided in examples 1 to 5 and comparative examples 1 to 7 are obtained through adsorption test
The data results of the above tests are shown in table 1.
TABLE 1
Figure BDA0003186994850000121
Figure BDA0003186994850000131
From the data results of examples 1 to 4 and comparative examples 1 to 4, it can be seen that the graphite negative electrode material provided by the present invention, after being carbonized and sintered and coated with epoxy resin, forms a hard carbon coating layer with higher disorder degree than graphite on the surface of graphite particles, has a slightly larger median diameter, increases the peak strength ratios of I100/I002 and I101/I002 crystal orientations, and decreases the specific surface, pore volume and pore diameter due to the blocking of pores on the surface of graphite powder particles by the hard carbon coating layer.
And preparing the graphite cathode materials provided in the examples 1-5 and the comparative examples 1-7 to obtain a cathode pole piece, and further preparing the CR2430 button half-cell, wherein the counter electrode is a metal lithium piece. Firstly, carrying out capacity and first effect test on the material, wherein the test steps are as follows: constant current discharge (0.6mA, 0.005V), standing (10min), constant current discharge (0.06mA, 0.005V), standing (10min), constant current charge (0.6mA, 2.000V). Then Li is added under different multiplying power+The graphite negative electrode was inserted to obtain a (constant current, CC)/(constant current + constant voltage, CC + CV) value in which the constant voltage (5mV) partial off current was 0.01C, and the results are shown in table 2.
TABLE 2
Figure BDA0003186994850000132
Figure BDA0003186994850000141
From the data results of the embodiment 1 and the embodiment 5, when the graphite is coated, too little coating liquid can not completely coat the graphite, which is represented by a larger material ratio table, a higher OI value, a lower constant current charging ratio and an unobvious improvement of the dynamic performance of the material.
From the data results of examples 1-4 and comparative examples 1-4, it can be seen that the graphite negative electrode material provided by the present invention has significantly increased constant Current Charge (CC)/(constant current + constant voltage, CC + CV) values, and the specific surface, pore volume and pore diameter of the material are also greatly reduced, compared to the negative electrode material without epoxy resin coating.
From the data results of example 1 and comparative example 5, it is understood that the thermosetting resin was not formed on the surface of the material before carbonization without mixing the epoxy resin with the curing agent, and the fluidity of the epoxy resin was strong with the increase of the carbonization temperature, so that the coating unevenness was increased. In terms of performance, the comparative example 5 has a larger specific surface, a lower first effect, a smaller constant current charging ratio and poor dynamics.
From the data results of example 1 and comparative example 6, it is known that conventional solid (solid at room temperature) epoxy resin coating is difficult to obtain a uniform hard carbon coating layer on the graphite surface, and the coating does not decrease or increase in the specific surface area, indicating that the surface defects of the material increase and adversely affect the cycle of the battery. In addition, the electrical property test results show that the kinetic increase of the material is not obvious.
From the data results of the embodiment 1 and the comparative example 7, it can be known that the epoxy resin is subjected to pressure forming, then is cured, carbonized and finally crushed, so that the surface defects of the material are increased, the specific surface is larger, the first effect is lower, and the dynamic performance of the material is not obviously improved.
In conclusion, the liquid epoxy resin can be uniformly and effectively coated on the surface of the graphite cathode powder under the action of mechanical force, and the hard carbon-coated high-rate graphite cathode material can be obtained through carbonization, sintering and screening, so that the purposes of improving the charging rate and shortening the charging time are achieved.
The applicant declares that the above description is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be understood by those skilled in the art that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are within the scope and disclosure of the present invention.

Claims (10)

1. The graphite cathode material is characterized in that the graphite cathode material is a graphite cathode material coated by a carbon layer, and the carbon layer is a hard carbon coating layer; the graphite negative electrode material is burnt at 600-1000 ℃, and has 2 heat release peaks which are respectively positioned in the range of 800-900 ℃ and 900-1000 ℃.
2. The graphitic negative electrode material according to claim 1, characterized in that it is a graphitic negative electrode materialThe specific surface area of (A) is 0.5 to 8m2A preferred range is 0.5 to 3.5 m/g2/g；
Preferably, the graphite negative electrode material has an accumulated value of micropore and mesopore volumes of 0.001-0.01 cm within a pore diameter range of 1-35 nm3/g；
Preferably, the average particle size of the graphite negative electrode material is 4-30 μm, and preferably 5-20 μm.
3. The method for preparing the graphite anode material according to claim 1 or 2, characterized by comprising the steps of:
(1) mixing epoxy resin and a curing agent to obtain a mixed solution, and compounding the mixed solution and graphite by using mechanical force to obtain a composite material;
(2) and (3) carbonizing the composite material obtained in the step (1) to obtain the graphite cathode material.
4. The method for preparing the graphite anode material according to the claim 3, wherein the epoxy resin in the step (1) is mixed with a solvent before the curing agent in the step (1) is mixed;
preferably, the solvent comprises water;
preferably, the mass ratio of the epoxy resin to the water in the step (1) is 100 (0-100).
5. The preparation method of the graphite anode material according to claim 3 or 4, wherein the mass ratio of the epoxy resin in the step (1) to the curing agent in the step (1) is 100 (5-200);
preferably, the epoxy resin in step (1) comprises any one of or a combination of at least two of bisphenol a type epoxy resin, bisphenol F type epoxy resin, glycerin epoxy resin, amine epoxy resin, glycidyl ester type epoxy resin, resorcinol diglycidyl ether or trimesoyl triglycidyl;
preferably, the curing agent in the step (1) comprises any one or a combination of at least two of an amine curing agent, an anhydride curing agent or an imidazole curing agent.
6. The method for preparing a graphite anode material according to any one of claims 3 to 5, wherein the mechanical force of step (1) comprises any one or a combination of at least two of a shearing force, a squeezing force or a friction force;
preferably, the graphite of step (1) comprises artificial graphite and/or natural graphite;
preferably, the median particle size of the graphite is 4-30 μm;
preferably, the mass ratio of the graphite in the step (1) to the mixed solution in the step (1) is 100 (3-50).
7. The preparation method of the graphite negative electrode material as claimed in any one of claims 3 to 6, wherein the atmosphere for carbonization in the step (2) is a protective atmosphere;
preferably, the temperature rise rate of the carbonization in the step (2) is 1-5 ℃/min;
preferably, the carbonization temperature in the step (2) is 700-1300 ℃;
preferably, the heat preservation time of the carbonization in the step (2) is 1-12 h.
8. The preparation method of the graphite anode material according to any one of claims 3 to 7, characterized in that the carbonized product in the step (2) is subjected to mixing and screening;
preferably, the screen mesh number used for screening is 200-600 meshes.
9. The method for preparing a graphite anode material according to any one of claims 3 to 8, characterized by comprising the steps of:
(1) mixing epoxy resin and water according to the mass ratio of 100 (0-100), adding a curing agent, and continuously mixing, wherein the mass ratio of the epoxy resin to the curing agent is 100 (5-200), so as to obtain a mixed solution, and compounding the mixed solution with graphite with the median particle size of 4-30 mu m by using a mechanical force, wherein the mass ratio of the graphite to the mixed solution is 100 (3-50), so as to obtain a composite material;
(2) and (2) heating the composite material obtained in the step (1) to 700-1300 ℃ at a heating rate of 1-5 ℃/min in a protective atmosphere, carbonizing, preserving heat for 1-12 hours, cooling, mixing, and sieving with a 200-600-mesh sieve to obtain the graphite cathode material.
10. A lithium ion battery comprising the graphite negative electrode material according to claim 1 or 2.
CN202110876464.9A 2021-07-29 2021-07-29 Graphite negative electrode material and preparation method and application thereof Pending CN113437278A (en)

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CN101209837A (en) * 2006-12-27 2008-07-02 宁波杉杉新材料科技有限公司 Modification method of graphite and modified graphite
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CN101209837A (en) * 2006-12-27 2008-07-02 宁波杉杉新材料科技有限公司 Modification method of graphite and modified graphite
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CN114094168A (en) * 2021-11-25 2022-02-25 东莞新能安科技有限公司 Electrochemical device, charging method for electrochemical device, charging device, electronic apparatus, and storage medium
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