A porous microcrystalline graphite anode material, its preparation method and application

Abstract

This invention discloses a porous microcrystalline graphite anode material, its preparation method, and its application. The preparation method includes: thoroughly contacting microcrystalline graphite with an alkaline solution and then drying it, followed by a first calcination in an inert atmosphere to obtain a first porous microcrystalline graphite with etched grain end faces; impregnating the first porous microcrystalline graphite with an alkaline solution under vacuum pressure, drying it, and then calcining it again in an inert atmosphere to obtain a second porous microcrystalline graphite with etched grain end faces and interior; repeating the aforementioned operations, with each operation using a lower concentration of alkaline solution and a higher pressure, to obtain the porous microcrystalline graphite anode material. The preparation method of this invention, by repeatedly using an alkaline solution to impregnate the microcrystalline graphite under vacuum pressure, allows the alkali to penetrate into the pore structure and etch into the particle interior at high temperatures. The resulting porous microcrystalline graphite anode material has a pore structure that facilitates rapid lithium-ion transport, significantly improving the material's charge-discharge rate performance.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery anode material technology, specifically, it relates to a porous microcrystalline graphite anode material, its preparation method and application. Background Technology

[0002] Lithium-ion batteries are widely used in power, energy storage, and consumer electronics due to their high energy density, long cycle life, and safety performance. Graphite, as the most mainstream anode material for lithium-ion batteries, has a theoretical specific capacity of up to 372 mAh / g and features abundant raw materials, low price, and mature technology. However, the rate performance of general graphite anode materials is poor, making it difficult to meet the market's fast-charging demands. Solutions to improve the fast-charging performance of graphite anode materials can be broadly categorized into raw material selection, particle size control, microstructure optimization, and surface modification. Microstructure optimization, such as pore formation, has a significant impact on performance improvement. Pore formation techniques include alkaline activation, steam activation, air activation, carbon dioxide activation, and strong oxidant activation. Among these methods, alkaline activation is widely used due to its controllable pore formation, low equipment requirements, and high safety factor. However, using alkaline activation to form pores in graphite still presents the following problems:

[0003] ① For artificial graphite, due to its good isotropy, the pores generated during the alkali activation process are evenly distributed on the surface. If further etching is performed, the reaction will still preferentially occur on the surface and cannot be etched into the interior of the particles.

[0004] ② For flake graphite, the isotropy is poor and the lamellae orientation is highly consistent. Alkali activation preferentially occurs at the end face of the graphite lamellae. During the etching process, the pore structure will extend along the lamellae direction, and the formed pore structure is prone to collapse.

[0005] ③ Current alkali activation technology can only etch within a certain range on the graphite surface, resulting in a lack of internal pore structure in the prepared porous graphite.

[0006] Therefore, selecting suitable graphite raw materials and uniformly constructing pore structures on the surface and inside of particles during the alkali activation process is the key to realizing porous microcrystalline graphite anode materials, and it is also the direction that industry researchers have been striving for for a long time. Summary of the Invention

[0007] The main objective of this invention is to provide a porous microcrystalline graphite anode material and its preparation method, so as to overcome the shortcomings of the prior art.

[0008] Another object of the present invention is to provide the application of the porous microcrystalline graphite anode material.

[0009] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:

[0010] This invention provides a method for preparing a porous microcrystalline graphite anode material, comprising:

[0011] (1) After the microcrystalline graphite is fully contacted with the alkaline solution, it is dried and then calcined in an inert atmosphere to obtain the first porous microcrystalline graphite with etched grain end faces.

[0012] (2) The first porous microcrystalline graphite obtained in step (1) is vacuum pressure impregnated with an alkaline solution, then dried, and then calcined in an inert atmosphere to obtain a second porous microcrystalline graphite with simultaneous etching on the grain end face and inside.

[0013] Repeat step (2) more than once, and each time the concentration of the alkaline solution used is reduced by 5-15% compared to the previous operation, and the pressure used in each operation is increased by 10-30% compared to the previous operation, to produce porous microcrystalline graphite anode material.

[0014] In some implementations, the process conditions for vacuum pressure impregnation in step (2) include: a vacuum degree of 0.00001 Pa to 100 Pa and a pressure of 1 MPa to 50 MPa.

[0015] The present invention also provides a porous microcrystalline graphite anode material prepared by the aforementioned preparation method. The porous microcrystalline graphite anode material includes an aggregate formed by the stacking of small flake-structured grains. The porous structure is uniformly distributed on the surface and inside of the porous microcrystalline graphite anode material. The porous structure is mainly distributed along the edge of the grains and is located between the grains. The average size of the small flake-structured grains is less than 1 μm, and the true density is 2~2.29 g / cc.

[0016] Furthermore, the porous microcrystalline graphite anode material has a porosity of 5%~60% and a specific surface area of ​​1~20 m². 2 / g.

[0017] This invention also provides the application of the aforementioned porous microcrystalline graphite anode material in the preparation of lithium-ion batteries.

[0018] Accordingly, embodiments of the present invention also provide a lithium-ion battery comprising the aforementioned porous microcrystalline graphite anode material.

[0019] Compared with the prior art, the beneficial effects of the present invention include:

[0020] 1) The preparation method provided by the present invention selects microcrystalline graphite with short-range order and long-range disorder as the raw material of porous graphite anode. Its particles are formed by the accumulation of grains with a grain size of less than 1μm. During the alkaline activation process, the etching effect occurs preferentially on the end face of the graphite sheet. During the activation process, the etchant will etch along the end face of different grains into the particle, which can ensure the structural stability of the particle while creating pores inward.

[0021] 2) The preparation method provided by this invention repeatedly uses an alkaline solution to vacuum pressure impregnate microcrystalline graphite, allowing the alkali to penetrate into the pore structure. At high temperatures, it further etches into the particles, further promoting the formation of the pore structure. Simultaneously, washing away the alkali from the surface of the microcrystalline graphite effectively reduces the risk of surface structure collapse due to further etching.

[0022] 3) The porous microcrystalline graphite anode material prepared by this invention has a pore structure that facilitates the rapid transport of lithium ions, significantly improves the charge-discharge rate performance of the material, and ensures that the cycle life of the material is not reduced. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a morphology diagram of the porous microcrystalline graphite obtained in step (1) of Embodiment 1 of the present invention;

[0025] Figure 2 This is a morphology diagram of the porous microcrystalline graphite anode material obtained in step (3) of Embodiment 1 of the present invention;

[0026] Figure 3 This is a morphology diagram of the porous microcrystalline graphite anode material obtained in Comparative Example 2;

[0027] Figure 4 This is a morphology diagram of the porous microcrystalline graphite anode material obtained in Comparative Example 3. Detailed Implementation

[0028] In view of the problems existing in the prior art, after long-term research and a large number of experiments, the inventor of this case proposed the following technical solution, which mainly provides a method to generate a porous structure on the surface and inside of microcrystalline graphite particles by vacuum pressure impregnation with concentration difference alkali activation. The aim is to improve the fast charging performance of microcrystalline graphite anode materials while ensuring that the cycle life of the materials is not reduced.

[0029] The following will provide a further explanation of the technical solution, its implementation process, and its principles.

[0030] As one aspect of the technical solution of this invention, a method for preparing a porous microcrystalline graphite anode material includes:

[0031] (1) After the microcrystalline graphite is fully contacted with the alkaline solution, it is dried and then calcined in an inert atmosphere to obtain the first porous microcrystalline graphite with etched grain end faces.

[0032] (2) The first porous microcrystalline graphite obtained in step (1) is vacuum pressure impregnated with an alkaline solution, then dried, and then calcined in an inert atmosphere to obtain a second porous microcrystalline graphite with simultaneous etching on the grain end face and inside.

[0033] Repeat step (2) more than once, and each time the concentration of the alkaline solution used is reduced by 5-15% compared to the previous operation, and the pressure used in each operation is increased by 10-30% compared to the previous operation, to produce porous microcrystalline graphite anode material.

[0034] Specifically, the slower the gradient concentration decreases, the greater the pressure required to force the alkaline solution into the deeper parts of the particle pore structure. This allows for more effective formation of the pore structure during subsequent heat treatment, resulting in deeper pores and higher porosity.

[0035] In some specific implementations, step (1) includes: mixing microcrystalline graphite and alkaline solution evenly, drying the obtained mixture, introducing inert gas, heating to a selected temperature at a heating rate of 1~20 ℃ / min for a first calcination, and obtaining a first porous microcrystalline graphite with etched grain end faces.

[0036] In some specific implementations, the pores in the first porous microcrystalline graphite have a size of 10 nm to 1 μm and a depth of 500 nm to 3 μm.

[0037] In some specific implementations, the microcrystalline graphite used in step (1) includes microcrystalline graphite powder. This invention selects short-range ordered and long-range disordered microcrystalline graphite as the raw material for porous graphite anodes. Its particles are composed of grains with a grain size of less than 1 μm. During the alkali activation process, the etching effect preferentially occurs at the end face of the microcrystalline graphite sheets. During the activation process, the alkali acts as an etchant and etches into the particles along the end faces of different grains, creating pores inward while ensuring the structural stability of the particles.

[0038] Furthermore, the particle size D of the microcrystalline graphite 50 The range is from 1μm to 100μm.

[0039] In some specific implementations, in step (1), the concentration of the alkaline solution is 16wt%~45wt%.

[0040] In some specific implementations, in step (1), the alkali contained in the alkaline solution may include at least one of potassium hydroxide, sodium hydroxide, etc., but is not limited to this.

[0041] In some specific implementations, in step (1), the mass ratio of the microcrystalline graphite to the alkaline solution is 1~100:100, that is, the mass content of the microcrystalline graphite in the alkaline solution is 1~100wt%.

[0042] In some specific implementations, in step (1), the temperature of the first calcination is 600°C to 1000°C, and the time of the first calcination is 6h to 20h.

[0043] In some specific implementations, step (2) includes: placing the first porous microcrystalline graphite obtained in step (1) into a reaction vessel, evacuating it and letting it stand, then adding an alkaline solution, stirring it evenly, and applying pressure to perform the vacuum pressure impregnation; the standing time is 5 min to 10 min.

[0044] Furthermore, step (2) also includes: after completing vacuum pressure impregnation, drying, cleaning to remove alkali, and drying again, followed by a second calcination at a heating rate of 1~20 ℃ / min. Cleaning away the alkali from the powder surface in this step effectively reduces further etching of the particle surface, which could lead to surface structure collapse.

[0045] In some specific implementations, the process conditions for vacuum pressure impregnation in step (2) include: vacuum degree of 0.00001 Pa to 100 Pa and pressure of 1 MPa to 50 MPa.

[0046] In some specific implementations, in step (2), the temperature of the second calcination is 600°C to 1000°C, the time of the second calcination is 6h to 20h, and the second calcination is carried out in an atmosphere in which an inert gas is formed.

[0047] Furthermore, in steps (1) and (2), the inert gas may include at least one of nitrogen, argon, etc., but is not limited to this.

[0048] In some specific implementations, the concentration of the alkaline solution used in each repeated step (2) of vacuum pressure impregnation is reduced by 5-15% compared to the concentration of the alkaline solution used in the previous operation, while the pressure used in each operation is increased by 10-30% compared to the pressure used in the previous operation. This invention uses repeated vacuum pressure impregnation of porous microcrystalline graphite with alkaline solution, allowing the alkali to penetrate into the pore structure and further etch into the particle interior at high temperatures, thereby further promoting the formation of the pore structure.

[0049] Furthermore, the preparation method specifically includes: repeating the vacuum pressure impregnation and second calcination of step (2) multiple times until the porosity of the obtained porous microcrystalline graphite anode material is 5~60%.

[0050] As one more specific implementation, the preparation method of the porous microcrystalline graphite anode material may include the following steps:

[0051] (1) After the microcrystalline graphite is fully contacted with the alkaline solution, it is dried and then calcined in an inert atmosphere to obtain the first porous microcrystalline graphite with etched grain end faces.

[0052] The specific preparation method of the first porous microcrystalline graphite is as follows: microcrystalline graphite powder and alkaline solution are mixed evenly, then dried, placed in an atmosphere furnace, inert gas is introduced, and the temperature is raised to a certain temperature for a first calcination for a certain time to obtain the first porous microcrystalline graphite with etched grain end faces.

[0053] In step (1) of this invention, the end faces of the microcrystalline graphite particles are etched, forming irregular openings. The size of the formed openings is between 10 nm and 1 μm, and the depth is between 500 nm and 3 μm.

[0054] In step (1) of the present invention, the temperature of the first calcination is 600°C to 1000°C, and the time of the first calcination is 6h to 20h.

[0055] In step (1) of the present invention, the reaction mechanism for preparing the first porous microcrystalline graphite is as follows:

[0056] Reaction 1: Alkaline solution reacts with microcrystalline graphite at high temperature to perform etching: 4MOH + C → M2CO3 + M2O + 2H2↑, where M is K or Na;

[0057] Reaction 2: Potassium carbonate decomposes at high temperature: M2CO3 → M2O + CO2↑;

[0058] Reaction 3: Carbon dioxide reacts with microcrystalline graphite at high temperature to perform etching: CO2 + C → 2CO↑.

[0059] (2) Vacuum pressure impregnation of the first porous microcrystalline graphite powder etched on the grain end face using alkaline solution. Specifically, the container containing the first porous microcrystalline graphite powder is evacuated to 0.00001 Pa~100 Pa and left to stand for 5~10 min. Then, 1~45% alkaline solution is added and stirred evenly. After being pressurized to 1 MPa~50 MPa, it is taken out. After drying, the residual alkaline substances on the surface are washed away with deionized water. After drying again, it is placed in an atmosphere furnace, nitrogen is introduced, and the temperature is raised to 600~1000℃ for a second calcination for 6~20 hours. Then, the second porous microcrystalline graphite with further etching and simultaneous etching on the grain end face and inside is obtained.

[0060] In both steps (1) and (2) of this invention, etching is performed between the grains to create holes. However, compared to the first porous microcrystalline graphite obtained in step (1), the second porous microcrystalline graphite obtained in step (2) has a larger pore size on its outer surface and more pore structures inside the particles that penetrate deeper into the particle core.

[0061] (3) Based on the particle size and the required porosity (5~60%) of the porous microcrystalline graphite, repeat step S2 a certain number of times, each time reducing the concentration of the alkaline solution by 5~15% and increasing the pressure by 10~30% to obtain the porous microcrystalline graphite anode material.

[0062] The final pores produced by the preparation method of the present invention are etched along the grain boundaries inside the particles, and thus are uniformly distributed inside the microcrystalline graphite particles; the size and depth of the pores are related to the etching concentration and the number of etching cycles.

[0063] As another aspect of the technical solution of the present invention, it also relates to a porous microcrystalline graphite anode material prepared by the aforementioned method. The porous microcrystalline graphite anode material includes an aggregate formed by the mutual stacking of grains with small flake structures. The porous structure is uniformly distributed on the surface and inside of the porous microcrystalline graphite anode material. The porous structure is mainly distributed along the edge of the grains and is located between the grains. The average size of the grains with small flake structures is less than 1 μm, and the true density is 2~2.29 g / cc.

[0064] Furthermore, the porous microcrystalline graphite anode material has a porosity of 5%~60% and a specific surface area of ​​1~20 m². 2 / g. The porous microcrystalline graphite anode material prepared by the method of the present invention has a pore structure that facilitates the rapid transport of lithium ions, significantly improving the charge-discharge rate performance of the material.

[0065] Furthermore, the porous microcrystalline graphite anode material has a size of 1~100 μm and a graphitization degree of 80~99%.

[0066] Furthermore, the average adsorption pore size of the porous microcrystalline graphite anode material is 10~50 nm, and the average desorption pore size is 2~10 nm.

[0067] As another aspect of the technical solution of the present invention, it also relates to the application of the porous microcrystalline graphite anode material in the preparation of lithium-ion batteries.

[0068] Furthermore, another aspect of the present invention provides a lithium-ion battery comprising the aforementioned porous microcrystalline graphite anode material.

[0069] In summary, this invention selects short-range ordered and long-range disordered microcrystalline graphite as the raw material for porous graphite anodes. During alkaline activation, the etching effect occurs preferentially on the end face of the graphite sheets. During activation, the etchant will etch the particles into the interior along the end faces of different grains, creating pores inward while ensuring the structural stability of the particles.

[0070] To make the objectives, technical solutions, and applications of this invention clearer, the technical solutions of this invention will be further described in detail below with reference to several preferred embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention. The implementation conditions used in the following embodiments can be further adjusted according to actual needs; implementation conditions not specified are generally conditions in conventional experiments.

[0071] Example 1

[0072] (1) Mix a 30wt% potassium hydroxide solution with D 50 Microcrystalline graphite with a diameter of 17µm was mixed uniformly at a mass ratio of 1:0.5, dried, and then calcined in a nitrogen-atmosphere furnace by introducing nitrogen gas. The temperature was then increased to 950℃ at a heating rate of 5℃ / min for the first calcination, held at a constant temperature for 7 hours, and then allowed to cool naturally. The morphology of the obtained porous microcrystalline graphite is shown in the figure below. Figure 1 As shown.

[0073] (2) Place the microcrystalline graphite with etched end faces of the grains obtained in step (1) into a vacuum pressure impregnation device. First, the vacuum degree is evacuated to 0.00001 Pa, then a potassium hydroxide solution with a concentration of 35 wt% is injected, and the pressure is increased to 10 MPa. After drying, the potassium hydroxide solution on the powder surface is washed off with deionized water. Nitrogen gas is introduced into a nitrogen atmosphere furnace, and then the temperature is raised to 900℃ at a heating rate of 10 ℃ / min for a second calcination. The temperature is kept constant for 10 hours, and then the temperature is naturally cooled to obtain porous microcrystalline graphite with etched end faces and interiors.

[0074] (3) Repeat step (2) twice, each time reducing the potassium hydroxide concentration by 5 wt% and increasing the pressure by 10%, to finally obtain a porous microcrystalline graphite anode material. The morphology of the porous microcrystalline graphite anode material finally obtained in this embodiment is shown in the figure below. Figure 2 As shown, it comprises aggregates formed by the stacking of small-scaled grains, and the porous microcrystalline graphite anode material has a uniformly distributed porous structure on its surface and interior. The porous structure is mainly distributed along the edges of the grains and is located between the grains. The average size of the small-scaled grains is less than 1 μm. The porosity of the porous microcrystalline graphite anode material is 30%, and its specific surface area is 18 m². 2 / g, with a size of 25-35 nm, and a 2C charge capacity retention rate of 40%.

[0075] Example 2

[0076] (1) Mix a 20wt% potassium hydroxide solution with D 50 Microcrystalline graphite with a diameter of 25µm was mixed uniformly at a mass ratio of 1:0.3, dried, and then nitrogen was introduced into a nitrogen atmosphere furnace. The temperature was then raised to 850℃ at a heating rate of 8℃ / min for the first calcination, and kept at a constant temperature for 10 hours, followed by natural cooling.

[0077] (2) Place the microcrystalline graphite with etched end faces of the grains obtained in step (1) into a vacuum pressure impregnation device. First, the vacuum degree is evacuated to 0.0001 Pa, then a potassium hydroxide solution with a concentration of 25 wt% is injected, and the pressure is increased to 15 MPa. After drying, the potassium hydroxide solution on the powder surface is washed off with deionized water. Nitrogen gas is introduced into a nitrogen atmosphere furnace, and then the temperature is raised to 800℃ at a heating rate of 8 ℃ / min for a second calcination. The temperature is kept constant for 20 hours, and then the temperature is naturally cooled to obtain porous microcrystalline graphite with etched end faces and interiors.

[0078] (3) Continue etching twice as per step (2), each time reducing the potassium hydroxide concentration by 8 wt% and increasing the pressure by 15%, to finally obtain a porous microcrystalline graphite anode material with a porosity of 20% and a specific surface area of ​​15 m². 2 / g, with a size of 10-20nm, and a 2C charging capacity retention rate of 23%.

[0079] Example 3

[0080] (1) Mix a 40wt% potassium hydroxide solution with D 50Microcrystalline graphite with a diameter of 35µm was mixed uniformly at a mass ratio of 1:0.2, dried, and then argon gas was introduced into an argon atmosphere furnace. The temperature was then raised to 750℃ at a heating rate of 6℃ / min for the first calcination, and kept at a constant temperature for 15 hours, followed by natural cooling.

[0081] (2) Place the microcrystalline graphite with etched end faces of the grains obtained in step (1) into a vacuum pressure impregnation device. First, the vacuum degree is evacuated to 0.1 Pa, then a potassium hydroxide solution with a concentration of 40 wt% is injected, and the pressure is increased to 25 MPa. After drying, the potassium hydroxide solution on the powder surface is washed off with deionized water. Argon gas is introduced into an atmosphere furnace with an argon atmosphere, and then the temperature is raised to 700℃ at a heating rate of 6 ℃ / min for a second calcination. The temperature is kept constant for 12 hours, and then the temperature is naturally cooled to obtain porous microcrystalline graphite with etched end faces and interiors.

[0082] (3) Continue etching three times according to step (2), each time reducing the potassium hydroxide concentration by 10 wt% and increasing the pressure by 18%, finally obtaining a porous microcrystalline graphite anode material with a porosity of 35% and a specific surface area of ​​20 m². 2 / g, with a size of 40-50 nm, and a 2C charge capacity retention rate of 48%.

[0083] Example 4

[0084] (1) Mix a 45wt% potassium hydroxide solution with D 50 Microcrystalline graphite with a diameter of 50µm was mixed uniformly at a mass ratio of 1:1, dried, and then argon gas was introduced into an argon atmosphere furnace. The temperature was then raised to 1000℃ at a heating rate of 20℃ / min for the first calcination, and kept at a constant temperature for 6 hours, followed by natural cooling.

[0085] (2) Place the microcrystalline graphite with etched end faces of the grains obtained in step (1) into a vacuum pressure impregnation device. First, the vacuum degree is evacuated to 10 Pa, then a potassium hydroxide solution with a concentration of 40 wt% is injected, and the pressure is increased to 1 MPa. After drying, the potassium hydroxide solution on the powder surface is washed off with deionized water. Argon gas is introduced into an atmosphere furnace with an argon atmosphere, and then the temperature is raised to 1000℃ at a heating rate of 20 ℃ / min for a second calcination. The temperature is kept constant for 6 hours, and then the temperature is naturally cooled to obtain porous microcrystalline graphite with etched end faces and interiors.

[0086] (3) Continue etching twice as per step (2), each time reducing the potassium hydroxide concentration by 15 wt% and increasing the pressure by 20%, to finally obtain a porous microcrystalline graphite anode material with a porosity of 15% and a specific surface area of ​​10 m². 2 / g, with a size of 30-40 nm, and a 2C charge capacity retention rate of 18%.

[0087] Example 5

[0088] (1) Mix a 16wt% sodium hydroxide solution with D 50 Microcrystalline graphite with a diameter of 10µm was mixed uniformly at a mass ratio of 1:0.01, dried, and then nitrogen was introduced into a nitrogen atmosphere furnace. The temperature was then raised to 600℃ at a heating rate of 1℃ / min for the first calcination, and kept at a constant temperature for 20 hours, followed by natural cooling.

[0089] (2) Place the microcrystalline graphite with etched end faces of the grains obtained in step (1) into a vacuum pressure impregnation device. First, the vacuum degree is evacuated to 100 Pa, then a sodium hydroxide solution with a concentration of 30 wt% is injected, and the pressure is increased to 50 MPa. After drying, the sodium hydroxide solution on the powder surface is washed off with deionized water. Nitrogen gas is introduced into a nitrogen atmosphere furnace, and then the temperature is raised to 600℃ at a heating rate of 1 ℃ / min for a second calcination. The temperature is kept constant for 20 hours, and then the temperature is naturally cooled to obtain porous microcrystalline graphite with etched end faces and interiors.

[0090] (3) Continue etching three times according to step (2), each time reducing the potassium hydroxide concentration by 5 wt% and increasing the pressure by 30%, finally obtaining a porous microcrystalline graphite anode material with a porosity of 45% and a specific surface area of ​​25 m². 2 / g, with a size of 20-30 nm, and a 2C charge capacity retention rate of 55%.

[0091] Compare with Example 1

[0092] This comparative example is basically the same as Example 1, except that steps (2) and (3) were not performed.

[0093] The obtained porous microcrystalline graphite anode material has a porosity of 10%. When applied to the preparation of lithium-ion batteries, the charge-discharge rate performance test results of the battery show that the 2C charge capacity retention rate is 12%.

[0094] Compare with Example 2

[0095] This comparative example is basically the same as Example 1, except that the concentration of the potassium hydroxide solution used in the vacuum pressure impregnation in step (3) is the same as that in step (2).

[0096] The morphology of the obtained porous microcrystalline graphite anode material is as follows: Figure 3As shown, the results indicate that an excessively large internal pore structure leads to unstable particle structure and easy collapse, resulting in poor rate performance. When applied to the fabrication of lithium-ion batteries, the charge / discharge rate performance test results show that the 2C charging capacity retention rate is 30%.

[0097] Compare with Example 3

[0098] This comparative example is basically the same as Example 1, except that the vacuum pressure impregnation in step (2) is too low.

[0099] The morphology of the obtained porous microcrystalline graphite anode material is as follows: Figure 4 As shown, the porosity is 15%, and it is used in the preparation of lithium-ion batteries. The charge / discharge rate performance test results of this battery show that the 2C charge capacity retention rate is 19%. The reason may be that the vacuum is too low, and the alkaline solution cannot penetrate to the deeper part of the previous etching hole for further etching, thus failing to etch into the particle interior, resulting in a low particle porosity, which is not conducive to performance improvement.

[0100] Compare with Example 4

[0101] This comparative example is basically the same as Example 1, except that the pressure used for vacuum pressure impregnation in step (2) is too low. The reason may be that the pressure is too low, so the alkaline solution cannot penetrate to the deeper part of the etched hole in the previous step, thus it cannot etch into the particle, resulting in low porosity of the particle, which is not conducive to performance improvement.

[0102] Compare with Example 5

[0103] The conventional alkali fusion method is used. However, this method can only create pores on the surface of the particles, and cannot continuously create pores inside the particles, resulting in low porosity of the powder and limited performance improvement.

[0104] The present invention can continuously generate a porous structure inside the microcrystalline graphite particles, making it easier for lithium ions to be inserted and extracted, thereby significantly improving performance.

[0105] In addition, the inventors of this case also conducted experiments with other raw materials and conditions listed in this specification, referring to Examples 1-5, and similarly obtained porous microcrystalline graphite anode materials with excellent charge-discharge rate performance.

[0106] It should be understood that the above are merely specific application examples of the present invention and do not constitute any limitation on the scope of protection of the present invention. All technical solutions formed by equivalent transformations or equivalent substitutions fall within the scope of protection of the present invention.

Claims

1. A method for preparing a porous microcrystalline graphite anode material, characterized in that, include: (1) After the microcrystalline graphite is fully contacted with the alkaline solution, it is dried and then calcined in an inert atmosphere to obtain the first porous microcrystalline graphite with etched grain end faces. (2) The first porous microcrystalline graphite obtained in step (1) is vacuum pressure impregnated with an alkaline solution, then dried, and then calcined in an inert atmosphere to obtain a second porous microcrystalline graphite with simultaneous etching on the grain end face and inside. Repeat step (2) more than once, and each time the concentration of the alkaline solution used is reduced by 5-15% compared to the previous operation, and the pressure used in each operation is increased by 10-30% compared to the previous operation, to produce porous microcrystalline graphite anode material.

2. The preparation method according to claim 1, characterized in that, Step (1) includes: mixing microcrystalline graphite and alkaline solution evenly, drying the obtained mixture, introducing inert gas, heating to a selected temperature at a heating rate of 1~20 ℃ / min for the first calcination, and obtaining the first porous microcrystalline graphite with etched grain end faces. And / or, the pores in the first porous microcrystalline graphite have a size of 10 nm to 1 μm and a depth of 500 nm to 3 μm.

3. The preparation method according to claim 1 or 2, characterized in that: In step (1), the microcrystalline graphite comprises microcrystalline graphite powder, the particles of which are formed by the accumulation of grains with a grain size of less than 1 μm; and / or, the particle size D of the microcrystalline graphite 50 The range is from 1μm to 100μm; And / or, in steps (1) and (2), the concentration of the alkaline solution is 16wt%~45wt%; And / or, in steps (1) and (2), the alkali solution contains at least one of potassium hydroxide and sodium hydroxide; And / or, in step (1), the mass ratio of the microcrystalline graphite to the alkaline solution is 1~100:

100.

4. The preparation method according to claim 2, characterized in that: In step (1), the temperature of the first calcination is 600°C to 1000°C, and the time of the first calcination is 6h to 20h; and / or, the inert gas includes at least one of nitrogen and argon.

5. The preparation method according to claim 1, characterized in that, Step (2) includes: placing the first porous microcrystalline graphite obtained in step (1) into a reaction vessel, evacuating it and letting it stand, then adding an alkaline solution, stirring it evenly, and applying pressure to perform the vacuum pressure impregnation; the standing time is 5 min to 10 min. And / or, step (2) further includes: after completing vacuum pressure impregnation, drying, cleaning to remove alkali, and drying again, followed by heating at a rate of 1~20 °C / min for the second calcination.

6. The preparation method according to claim 1 or 5, characterized in that, In step (2), the process conditions for vacuum pressure impregnation include: vacuum degree of 0.00001 Pa to 100 Pa and pressure of 1 MPa to 50 MPa.

7. The preparation method according to claim 1, characterized in that, In step (2), the second calcination temperature is 600°C to 1000°C, the second calcination time is 6h to 20h, and the second calcination is carried out in an atmosphere of inert gas, wherein the inert gas includes at least one of nitrogen and argon.

8. A porous microcrystalline graphite anode material prepared by the preparation method according to any one of claims 1-7, characterized in that, The porous microcrystalline graphite anode material comprises an aggregate formed by the stacking of grains with small flake structures. The porous structure is uniformly distributed on the surface and inside of the porous microcrystalline graphite anode material. The porous structure is mainly distributed along the edge of the grains and is located between the grains. The average size of the grains with small flake structures is less than 1 μm, and the true density is 2~2.29 g / cc. The porous microcrystalline graphite anode material has a porosity of 5%~60% and a specific surface area of ​​1~20 m². 2 / g; The porous microcrystalline graphite anode material has a size of 1~100 μm and a graphitization degree of 80~99%; The average adsorption pore size of the porous microcrystalline graphite anode material is 10~50 nm, and the average desorption pore size is 2~10 nm.

9. The application of the porous microcrystalline graphite anode material according to claim 8 in the preparation of lithium-ion batteries.

10. A lithium-ion battery, characterized in that, Including the porous microcrystalline graphite anode material as described in claim 8.

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