Fast-charging negative electrode material and preparation method and application thereof

Abstract

The invention provides a fast-charging negative electrode material and a preparation method and application thereof.The preparation method comprises the following steps that a graphite material is subjected to primary ball milling, modified graphite containing graphene is obtained, and the modified graphite containing graphene comprises graphene and a graphite matrix; and carrying out secondary ball milling and carbonization on the graphene-containing modified graphite and a coating agent to obtain the fast-charging negative electrode material. According to the preparation method, modified graphite containing graphene is prepared firstly, a good conductive framework is constructed, then coating is performed, graphene in the modified graphite is inserted into a coating agent molecular chain or a pore structure, graphene serves as a bridge to connect inner core graphite with an outer coating layer, an interface potential barrier is eliminated, and the conductivity of the graphene is improved. The interface impedance of the graphite and the coating agent is reduced, the electron and ion dual-path optimization of the material is realized, and the fast charging performance of the material is greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of battery technology and relates to a fast-charging negative electrode material, its preparation method and application. Background Technology

[0002] In recent years, lithium-ion batteries have been used in a wider range of applications, such as in electric vehicles and energy storage. However, the slow charging speed of lithium-ion batteries has always hindered their further promotion. Fast charging is expected to solve the energy anxiety of new energy vehicles. Currently, the bottleneck of fast charging is mainly in the negative electrode. Since the commonly used negative electrode material for lithium-ion batteries is graphite, graphite is limited by slow lithium intercalation kinetics and low operating potential. Its capacity, stability, and safety under high-rate charge and discharge cannot meet the application requirements of fast-charging batteries. Therefore, graphite must be modified to meet the requirements of fast-charging technology.

[0003] Currently, the fast-charging performance of lithium-ion batteries is mainly improved through secondary granulation, amorphous carbon coating, and graphite surface treatment. Secondary granulation improves fast-charging performance by shortening the lithium-ion transport path and increasing the number of lithium-ion transport channels. Amorphous carbon coating enhances fast-charging performance because amorphous carbon is randomly arranged, isotropic, and has a larger interlayer spacing than graphite, which facilitates rapid lithium-ion insertion and extraction, resulting in superior fast-charging performance. Graphite surface treatment typically involves doping with elements to alter the microstructure and electronic structure of the graphite anode material, increasing electron and ion transport rates and improving its fast-charging performance.

[0004] For example, CN116454272A discloses a phosphorus-doped graphite anode material, its preparation method, anode sheet, and lithium-ion battery. This method combines surface coating with elemental doping. Phosphorus-containing compounds are mixed with organic compounds such as pitch and resin, then uniformly coated onto the graphite surface. After carbonization and sintering, the phosphorus-doped graphite anode material is obtained. This method reduces the coating amount to some extent, improving the initial efficiency of the material, but the fast-charging performance is relatively mediocre, and the specific surface area of ​​the material is too small, ranging from 0.7 to 1.5 μm². 2 / g, further proving that this material is not suitable for high-current fast charging.

[0005] For example, CN103050661A discloses a graphene composite lithium-ion battery anode material and its preparation method. Graphene sheets partially surround and separate hollow nano-anode particles, with gaps between adjacent graphene sheets. The hollow nano-anode particles consist of a carbon outer layer and a hollow metal anode material inner layer. The prepared graphene anode material has advantages such as good conductivity, large electrochemical lithium storage capacity, high energy density, and good cycle performance. However, its preparation process is relatively complex, difficult to control, and costly. Furthermore, the composite material lacks doping and coating, resulting in insufficient fast-charging performance. CN117393724A discloses a high-rate artificial graphite composite anode material, its preparation method, and its application. Transition metal salts are decomposed into metal oxide particles, which are then reacted with resin to form a modified resin. Carbon nanotubes are generated in situ under high-temperature hot pressing. However, this process generates limited carbon gas, resulting in insufficient carbon nanotubes generated by the reaction with transition metals. Moreover, the carbon gas deposition on hard carbon is uneven, limiting its improvement on the material's rate performance.

[0006] Therefore, developing a method for preparing fast-charging anode materials that is simple, controllable, low-cost, and of stable quality has become an urgent technical problem to be solved. Summary of the Invention

[0007] The purpose of this invention is to provide a fast-charging negative electrode material, its preparation method, and its application. The preparation method involves first preparing modified graphite containing graphene to construct a good conductive framework, and then coating it so that the graphene in the modified graphite is inserted into the molecular chain or porous structure of the coating agent. The graphene acts as a bridge connecting the core graphite and the outer coating layer, eliminating the interfacial barrier, reducing the interfacial impedance between graphite and the coating agent, and optimizing the electronic and ionic dual pathways of the material, thereby significantly improving the fast-charging performance of the material.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing a fast-charging negative electrode material, the method comprising the following steps:

[0010] (1) The graphite material is ball-milled once to obtain modified graphite containing graphene, wherein the modified graphite containing graphene includes graphene and graphite matrix.

[0011] (2) The modified graphite containing graphene and the coating agent described in step (1) are subjected to secondary ball milling and carbonization to obtain the fast-charging negative electrode material.

[0012] This invention first generates graphene in situ from graphite material through ball milling, resulting in modified graphite comprising graphene and a graphite matrix. The graphene in the modified graphite constructs a well-developed conductive framework, interspersed within the graphite matrix to form a three-dimensional electronic network. Simultaneously, the graphene is embedded between graphite layers, and the wrinkled edges of the graphene expand the interlayer spacing, providing channels for lithium-ion diffusion, shortening the lithium-ion diffusion path, and improving the lithium-ion diffusion coefficient and fast-charging performance. Furthermore, the graphene sheets are uniformly dispersed between graphite particles, effectively buffering the volume expansion during charging and discharging. The in-situ generated graphene... Maintaining a continuous lattice structure with the graphite matrix, the interface is tightly bonded, and the electron transport channels are more unobstructed (interface resistance is reduced by more than 60%). Compared with purchased graphene, which requires bonding to the graphite matrix with an adhesive, it is easy to introduce interface defects and increase interface impedance. In addition, the present invention can precisely control the number and size of graphene layers, while the number of layers in purchased graphene is uneven. The appropriate number and size of graphene layers can significantly improve the ion diffusion rate, and the in-situ generated graphene has fewer defects and excellent conductivity (conductivity > 3000 S / m), which is beneficial for fast charging electron transport.

[0013] This invention involves a secondary ball milling process using modified graphite containing graphene and a coating agent. This process inserts the graphene into the molecular chains or porous structure of the coating agent. Simultaneously, the active carbon atoms at the graphene edges combine with free radicals in the coating agent to form C-C covalent bonds, and the oxygen-containing functional groups combine with free radicals in the coating agent to form CO-C covalent bonds. This eliminates the interfacial barrier between graphite and the coating agent, reducing their interfacial impedance. Furthermore, the secondary ball milling introduces defects into the surfaces of both graphene and the coating agent, enhancing reactive sites. Therefore, the graphene in the modified graphite of this invention acts as a bridge connecting the core graphite and the outer coating layer, achieving optimization of both electronic and ionic pathways and significantly improving the material's fast-charging performance.

[0014] Preferably, in the modified graphite containing graphene described in step (1), the mass percentage of graphene is 5wt% to 10wt%, for example, it can be 5wt%, 6wt%, 7wt%, 8wt%, 9wt% or 10wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0015] In step (1) of this invention, the ball milling process only generates graphene in situ from a portion of the graphite material. If too much graphene is generated in the modified graphite during the ball milling process, it will affect the capacity of the fast-charging negative electrode material. If too little graphene is generated in the modified graphite during the ball milling process, it will affect the conductivity of the fast-charging negative electrode material, and thus affect the fast-charging capability of the fast-charging negative electrode material.

[0016] Preferably, in the modified graphite containing graphene described in step (1), the number of graphene layers is ≤5, for example, it can be 5 layers, 4 layers, 3 layers, 2 layers or 1 layer, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0017] Preferably, in the modified graphite containing graphene described in step (1), the thickness of the single layer of graphene is ≤3nm, for example, it can be 3nm, 2.5nm, 2nm, 1.5nm or 1nm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0018] This invention can also control the number and thickness of graphene layers generated through a single ball milling process. The appropriate number and thickness of graphene layers are beneficial to further improve the ion diffusion rate and enhance the fast charging effect.

[0019] Preferably, the electronic conductivity of the graphene-modified graphite in step (1) is 1 to 3 times that of the graphite material, for example, it can be 1, 1.5, 2, 2.5 or 3 times, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0020] Preferably, the rotation speed of the ball mill in step (1) is 300 rpm to 500 rpm, for example, it can be 300 rpm, 350 rpm, 400 rpm, 450 rpm or 500 rpm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0021] Preferably, the ball milling time in step (1) is 0.5h to 4h, for example, it can be 0.5h, 1h, 2h, 3h or 4h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0022] Preferably, the size of the grinding balls in the first ball milling in step (1) is 1μm to 10μm, for example, it can be 1μm, 3μm, 5μm, 7μm, 9μm or 10μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0023] Preferably, the ball milling in step (1) is carried out in a protective gas, which includes any one or a combination of at least two of nitrogen, argon, carbon dioxide or air.

[0024] This invention controls the generation of graphene with a content of 5wt%-10wt%, ≤5 layers, and a single layer thickness of ≤3nm by controlling the conditions of a single ball milling. Increasing the rotation speed of the ball milling can increase the graphene content, while decreasing the number of graphene layers and reducing the ball milling time will decrease the graphene content.

[0025] Preferably, during the ball milling in step (1), an additive is also added, which includes any one or a combination of at least two of polyethylene glycol, sodium dodecyl sulfonate, sodium dodecylbenzene sulfonate, hexadecyltrimethylammonium bromide, polyvinylpyrrolidone, choline chloride, or ammonium carbonate.

[0026] In step (1), an additive was added during the ball milling process of this invention. The additive's role is to promote the balance between graphite exfoliation and defect suppression. Since ball milling requires sufficient energy to exfoliate graphite, excessive energy can easily damage the SP2 lattice structure of graphene, causing defects. If no additive is added during ball milling, almost all the ball milling energy will be used to create defects, making it impossible to efficiently and controllably prepare graphene with application value.

[0027] Preferably, the graphite material in step (1) includes natural graphite and / or artificial graphite.

[0028] Preferably, the mass ratio of the graphite material in step (1) to the additive added during the first ball milling is 1:(0.001~10), for example, it can be 1:0.001, 1:0.01, 1:0.1, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9 or 1:10, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0029] Preferably, the content of graphene generated in the secondary ball milling stage in step (2) is less than 1 wt% (almost 0), for example, it can be 1 wt%, 0.5 wt% or 0 wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0030] In this invention, after a small amount of graphene is generated during the first ball milling, the second ball milling needs to inhibit the further exfoliation of graphite into graphene. The purpose of the second ball milling is to use mechanical force to cleverly weave different components together to form a three-dimensional network two-phase continuous structure with graphene running through it. If too much graphene is generated during the second ball milling, it will destroy the pre-designed optimized structure. The newly generated graphene has certain defects, which will randomly fill the system and block ion channels instead of building orderly and efficient electron channels. At the same time, the newly generated graphene has a large specific surface area and contains a large number of defects, which leads to a decrease in the initial efficiency of the negative electrode material and a decrease in the initial capacity and energy density of the battery.

[0031] This invention can suppress the further exfoliation of graphite into graphene by controlling the conditions of secondary ball milling, such as controlling the rotation speed, time, ball size and ratio, ball-to-material mass ratio and container filling rate, and the temperature of the grinding media and atmosphere.

[0032] Preferably, the rotation speed of the secondary ball mill in step (2) is 60 rpm to 200 rpm, for example, it can be 60 rpm, 100 rpm, 150 rpm or 200 rpm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0033] Preferably, the secondary ball milling time in step (2) is 6h to 10h, for example, it can be 6h, 6.5h, 7h, 7.5h, 8h, 9h or 10h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0034] Preferably, the temperature of the secondary ball milling in step (2) does not exceed 30°C, for example, it can be 29°C, 25°C or 20°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0035] Preferably, the size of the grinding balls in the secondary ball milling in step (2) is 15μm to 100μm, for example, it can be 15μm, 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm or 100μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0036] Preferably, the grinding ball material used in the first ball milling in step (1) and the grinding ball material used in the second ball milling in step (2) are each independently any one or a combination of at least two of the following: agate balls, corundum balls, zirconia balls, ceramic balls, or stainless steel balls.

[0037] Preferably, the secondary ball milling in step (2) is carried out in a protective gas, which includes any one or a combination of at least two of nitrogen, argon, carbon dioxide or air.

[0038] Preferably, the mass ratio of the modified graphite containing graphene to the coating agent in step (1) is 1:(0.02~0.1), for example, it can be 1:0.02, 1:0.03, 1:0.04, 1:0.05, 1:0.06, 1:0.07, 1:0.08, 1:0.09 or 1:0.1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0039] Preferably, the coating agent in step (2) includes asphalt and / or resin materials, wherein the resin materials include phenolic resin and / or furan resin.

[0040] Preferably, the carbonization in step (2) includes heating to a first temperature at a first heating rate and holding at that temperature, and then heating to a second temperature at a second heating rate and holding at that temperature.

[0041] Preferably, the first temperature is 500℃~900℃, for example, it can be 500℃, 600℃, 700℃, 800℃ or 900℃, and the time for holding the first temperature is 1h~10h, for example, it can be 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h or 10h, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0042] Preferably, the second temperature is 1000℃~1200℃, for example, it can be 1000℃, 1050℃, 1100℃, 1150℃ or 1200℃, and the holding time at the second temperature is 3h~5h, for example, it can be 3h, 3.5h, 4h, 4.5h or 5h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0043] Preferably, the first heating rate is 1℃ / min to 8℃ / min, for example, it can be 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min or 8℃ / min, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0044] Preferably, the second heating rate is 8℃ / min to 10℃ / min, for example, it can be 8℃ / min, 8.5℃ / min, 9℃ / min, 9.5℃ / min or 10℃ / min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0045] Preferably, after carbonization in step (2), the material is further crushed, shaped, and sieved.

[0046] Preferably, the particle size D50 of the fast-charging negative electrode material in step (2) is 8μm~14μm, for example, it can be 8μm, 9μm, 10μm, 11μm, 12μm, 13μm or 14μm, and the particle size distribution range is 1.0μm~38.2μm (meaning the minimum particle size is above 1.0μm, for example, it can be 1.0μm, 2.0μm, 3.0μm, 4.0μm, 5.0μm, 6.0μm, 7.0μm or 8.0μm, and the maximum particle size is below 38.2μm, for example, it can be 38.2μm, 37μm, 36μm, 35μm, 34μm, 33μm, 32μm, 31μm or 30μm), and the specific surface area is 0.8m². 2 / g~3.0m 2 / g, for example, could be 0.8m 2 / g、1m 2 / g, 1.5m 2 / g、2m 2 / g, 2.5m 2 / g or 3m 2 / g, tap density is 0.8g / cm³ 3 ~1.5g / cm 3 For example, it could be 0.8 g / cm³ 3 1g / cm 3 1.2g / cm 3 1.4g / cm 3 Or 1.5g / cm 3 The compacted density is 1.5 g / cm³. 3 ~1.75g / cm 3 For example, it could be 1.5g / cm³ 3 1.55g / cm 3 1.6g / cm 3 1.65g / cm 3 1.7g / cm 3 Or 1.75g / cm 3 However, this does not limit the listed values; other unlisted values ​​within the range are also applicable.

[0047] Preferably, the fast-charging negative electrode material includes a graphite matrix and a hard carbon coating layer on the surface of the graphite matrix, and graphene is further included between the graphite matrix and the hard carbon coating layer, wherein the graphene links the graphite matrix and the hard carbon coating layer to form a three-dimensional network structure.

[0048] The fast-charging negative electrode material of this invention is a two-phase continuous structure with a three-dimensional network reinforcement composed of graphene linking a graphite matrix and a coating agent.

[0049] In a second aspect, the present invention provides a fast-charging negative electrode material, which is prepared by the preparation method described in the first aspect.

[0050] Thirdly, the present invention provides a battery comprising the fast-charging negative electrode material as described in the second aspect.

[0051] Compared with the prior art, the present invention has the following beneficial effects:

[0052] (1) The preparation method of the present invention has low energy consumption and no wastewater or waste gas emissions, and the preparation method has high feasibility of continuous production and can be scaled up and industrialized.

[0053] (2) The graphene generated in situ during the ball milling process described in this invention maintains a continuous lattice structure with the graphite matrix, with tight interfacial bonding and smoother electron transport channels (interfacial resistance reduced by more than 60%). In contrast, purchased graphene requires bonding with an adhesive, which can easily introduce interfacial defects and increase interfacial impedance. Furthermore, the mechanical ball milling process can precisely control the number and size of the generated graphene layers, while purchased graphene has an uneven number of layers. Appropriate number and size of layers can significantly improve the ion diffusion rate. At the same time, the graphene generated by the ball milling method has fewer defects and excellent conductivity (conductivity > 3000 S / m), which is beneficial for fast-charging electron transport.

[0054] (3) Improved fast charging performance and optimized ion diffusion path: In-situ graphene is embedded between graphite layers, which expands the interlayer spacing, shortens the lithium ion diffusion path, and improves the diffusion coefficient; buffering volume expansion: Graphene sheets are uniformly dispersed between graphite particles, which effectively buffers the volume expansion during charging and discharging, which is superior to purchased graphene composite materials.

[0055] (4) The present invention uses graphite and coating agent as raw materials. The modified graphite containing graphene is first prepared by mechanical ball milling to construct a good conductive framework. After adding the coating agent, the graphene is inserted into the molecular chain or pore structure of the coating agent through ball milling reaction. At the same time, the active carbon atoms at the edge of the graphene combine with the free radicals in the coating agent to form C-C covalent bonds, and the oxygen-containing functional groups combine with the free radicals in the coating agent to form COC covalent bonds, which eliminates the interface barrier and reduces the interface impedance between graphite and coating agent. Furthermore, the ball milling reaction can introduce defects on the surface of graphene and coating agent to enhance the reactive sites. Therefore, the graphene in the modified graphite of the present invention acts as a bridge to connect the core graphite and the outer coating layer, realizing the optimization of the electronic and ionic dual paths of the material and greatly improving the fast charging performance of the material. Detailed Implementation

[0056] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0057] Example 1

[0058] This embodiment provides a method for preparing a fast-charging negative electrode material, the method comprising the following steps:

[0059] (1) 300g of artificial graphite and 10g of polyethylene glycol were placed in a planetary ball mill (the mass ratio of artificial graphite to polyethylene glycol was 1:0.033), and 5μm corundum balls were placed in the mill. The ball-to-material ratio was 15:1. Argon gas was introduced, and the mill was run at 320rpm for 1h. After the reaction was completed, modified graphite containing graphene was obtained.

[0060] Among them, the modified graphite containing graphene includes graphene and graphite matrix, with the mass ratio of graphene being 3.5wt%, the number of graphene layers being 4, and the thickness of a single graphene layer being 2nm.

[0061] (2) Place 20g of asphalt, the graphene-modified graphite described in step (1), and 15μm corundum balls into a planetary ball mill. The mass ratio of the graphene-modified graphite to the asphalt is 1:0.067, and the ball-to-material ratio is 3:1. Nitrogen gas is introduced, and the mixture is ball-milled at 70 rpm for 6 hours while maintaining a temperature of 25℃. After the reaction is complete, a mixture is obtained, and the newly generated graphene content in the mixture is 0.1wt%.

[0062] The mixture was heated to 600°C under nitrogen at a heating rate of 5°C / min and held for 3 hours. Then it was heated to 1200°C at a heating rate of 8°C / min and held for 4 hours. After cooling, crushing, shaping and sieving, the fast-charging negative electrode material was obtained.

[0063] Example 2

[0064] This embodiment provides a method for preparing a fast-charging negative electrode material, the method comprising the following steps:

[0065] (1) 300g of artificial graphite and 8g of hexadecyltrimethylammonium bromide were placed in a planetary ball mill (the mass ratio of artificial graphite to hexadecyltrimethylammonium bromide was 1:0.027), and 7μm zirconium oxide balls were placed in the mill. The ball-to-material ratio was 15:1. Argon gas was introduced, and the mill was run at 320rpm for 1h. After the reaction was completed, modified graphite containing graphene was obtained.

[0066] Among them, the modified graphite containing graphene includes graphene and graphite matrix, with graphene accounting for 6wt% by mass, the number of graphene layers being 4, and the thickness of a single graphene layer being 2nm.

[0067] (2) 20g of phenolic resin, the graphene-modified graphite described in step (1), and 15μm zirconium oxide balls were placed in a planetary ball mill. The mass ratio of the graphene-modified graphite to the pitch was 1:0.067, and the ball-to-material ratio was 2:1. Nitrogen gas was introduced, and the mixture was ball-milled at 70 rpm for 7 hours while maintaining a temperature of 30℃. After the reaction was completed, a mixture was obtained, and the newly generated graphene content in the mixture was 0.2wt%.

[0068] The mixture was heated to 600°C under nitrogen at a heating rate of 5°C / min and held for 3 hours. Then it was heated to 1200°C at a heating rate of 8°C / min and held for 4 hours. After cooling, crushing, shaping and sieving, the fast-charging negative electrode material was obtained.

[0069] Example 3

[0070] This embodiment provides a method for preparing a fast-charging negative electrode material, the method comprising the following steps:

[0071] (1) 300g of artificial graphite and 10g of polyethylene glycol were placed in a planetary ball mill (the mass ratio of artificial graphite to polyethylene glycol was 1:0.033), and 3μm corundum balls were placed in the mill. The ball-to-material ratio was 15:1. Argon gas was introduced, and the mill was run at 450rpm for 0.8h. After the reaction was completed, modified graphite containing graphene was obtained.

[0072] Among them, the modified graphite containing graphene includes graphene and graphite matrix, with the mass ratio of graphene being 8wt%, the number of graphene layers being 2, and the thickness of a single graphene layer being 1.5nm.

[0073] (2) The asphalt, the graphene-modified graphite described in step (1), and 50μm corundum balls were placed in a planetary ball mill, wherein the mass ratio of the graphene-modified graphite to the asphalt was 1:0.04, the ball-to-material ratio was 3:1, nitrogen gas was introduced, and the mixture was ball-milled at 85 rpm for 9 hours while the temperature was controlled at 25℃. After the reaction was completed, a mixture was obtained, and the content of newly generated graphene in the mixture was 0.2wt%.

[0074] The mixture was heated to 700°C under nitrogen at a heating rate of 3°C / min and held for 7 hours. Then it was heated to 1100°C at a heating rate of 9°C / min and held for 4 hours. After cooling, crushing, shaping and sieving, the fast-charging negative electrode material was obtained.

[0075] Example 4

[0076] This embodiment provides a method for preparing a fast-charging negative electrode material, the method comprising the following steps:

[0077] (1) 300g of artificial graphite and 30g of polyethylene glycol were placed in a planetary ball mill (the mass ratio of artificial graphite to polyethylene glycol was 1:0.01), and 1μm corundum balls were placed in the mill. The ball-to-material ratio was 15:1. Argon gas was introduced, and the mill was run at 500rpm for 0.5h. After the reaction was completed, modified graphite containing graphene was obtained.

[0078] Among them, the modified graphite containing graphene includes graphene and graphite matrix, with the mass ratio of graphene being 10wt%, the number of graphene layers being 2, and the thickness of a single graphene layer being 1nm.

[0079] (2) The asphalt, the graphene-containing modified graphite described in step (1), and 100μm corundum balls were placed in a planetary ball mill, wherein the mass ratio of the graphene-containing modified graphite to the asphalt was 1:0.1, the ball-to-material ratio was 3:1, nitrogen gas was introduced, and the mixture was ball-milled at 60 rpm for 10 h, while the temperature was controlled at 30℃. After the reaction was completed, a mixture was obtained, and the content of newly generated graphene in the mixture was 0.3wt%.

[0080] The mixture was heated to 900°C under nitrogen at a heating rate of 8°C / min and held for 1 hour. Then it was heated to 1200°C at a heating rate of 10°C / min and held for 3 hours. After cooling, crushing, shaping and sieving, the fast-charging negative electrode material was obtained.

[0081] Example 5

[0082] This embodiment provides a method for preparing a fast-charging negative electrode material, the method comprising the following steps:

[0083] (1) 300g of artificial graphite and 50g of polyethylene glycol were placed in a planetary ball mill (the mass ratio of artificial graphite to polyethylene glycol was 1:0.167), and 10μm corundum balls were added. The ball-to-material ratio was 15:1. Argon gas was introduced, and the mill was run at 300rpm for 4h. After the reaction was completed, modified graphite containing graphene was obtained.

[0084] Among them, the modified graphite containing graphene includes graphene and graphite matrix, with graphene accounting for 5wt% by mass, 5 layers of graphene, and a thickness of 3nm for a single layer of graphene.

[0085] (2) The asphalt, the graphene-containing modified graphite described in step (1), and 15μm corundum balls were placed in a planetary ball mill, wherein the mass ratio of the graphene-containing modified graphite to the asphalt was 1:0.02, the ball-to-material ratio was 3:1, nitrogen gas was introduced, and the mixture was ball-milled at 200 rpm for 6 hours while the temperature was controlled at 20℃. After the reaction was completed, a mixture was obtained, and the content of newly generated graphene in the mixture was 0.5wt%.

[0086] The mixture was heated to 500°C at a heating rate of 1°C / min under nitrogen atmosphere and held for 10 hours. Then, it was heated to 1000°C at a heating rate of 8°C / min and held for 5 hours. After cooling, crushing, shaping and sieving, the fast-charging negative electrode material was obtained.

[0087] Example 6

[0088] This embodiment provides a method for preparing a fast-charging negative electrode material. Except for step (1) where the rotation speed is 200 rpm, the mass percentage of graphene in the modified graphite containing graphene is 3 wt%, and the number and thickness of graphene layers are adapted to change, the preparation method is the same as in Example 1.

[0089] Example 7

[0090] This embodiment provides a method for preparing a fast-charging negative electrode material. Except for step (1) where the rotation speed is 550 rpm, the mass percentage of graphene in the modified graphite containing graphene is 15 wt%, and the number and thickness of graphene layers are adapted to change, the preparation method is the same as in Example 1.

[0091] Example 8

[0092] This embodiment provides a method for preparing a fast-charging negative electrode material. Except for step (2), where the rotation speed is 250 rpm and the content of newly generated graphene in the mixture is 2 wt%, the preparation method is the same as in Example 1.

[0093] Example 9

[0094] This embodiment provides a method for preparing a fast-charging negative electrode material. Except for step (2), where the rotation speed is 40 rpm to make the content of newly generated graphene in the mixture 0.5 wt%, the preparation method is the same as in Example 1.

[0095] Comparative Example 1

[0096] This comparative example provides a method for preparing a negative electrode material. The preparation method is the same as in Example 1 except that step (1) is omitted and the artificial graphite in step (1) is directly replaced with the same mass of the modified graphite containing graphene in step (2).

[0097] Comparative Example 2

[0098] This comparative example provides a method for preparing a negative electrode material. The preparation method is the same as in Example 1 except that step (1) is omitted, and the artificial graphite in step (1) is directly replaced with the same mass of artificial graphite as the modified graphite containing graphene. At the same time, 6.5 wt% of purchased graphene is added to artificial graphite for step (2).

[0099] Comparative Example 3

[0100] This comparative example provides a method for preparing a negative electrode material. Except for step (1), where the ball milling conditions are: ball-to-material ratio of 150:1, argon gas is introduced and ball milling is performed at 1200 rpm for 10 hours to generate graphene from all the graphite, and the obtained graphene, artificial graphite and pitch are then subjected to step (2), the rest of the preparation method is the same as in Example 1. Among them, the graphene is 6.5 wt% of the total mass of graphene and artificial graphite, and the mass ratio of the total mass of graphene and artificial graphite to pitch is 1:0.067.

[0101] The particle size D50, particle size distribution, specific surface area, tap density, and compaction density of the negative electrode materials obtained in the above embodiments and comparative examples are shown in Table 1. The particle size D50 and particle size distribution were tested using laser particle size analysis, where the sample is irradiated with a laser, and the particle size and distribution are measured using the principle of light scattering. The specific surface area was tested using nitrogen adsorption, where the specific surface area is calculated by measuring the nitrogen adsorption isotherm based on the adsorption law of gases on solid surfaces. The tap density was measured using a mechanical vibration device, where the sample in a steel cylinder is vibrated in a tap density tester, and the volume after vibration is calculated from the depth of descent. The weight of the sample is then divided by the volume after vibration. The compaction density was measured using a two-probe mode to measure the density change of the sample during pressurization.

[0102] The negative electrode materials obtained in the above embodiments and comparative examples were used to prepare lithium-ion batteries. The preparation process of lithium-ion batteries included coin cell and full cell testing: The negative electrode materials, sodium carboxymethyl cellulose, conductive agent and binder obtained in the above embodiments and comparative examples were dispersed in deionized water at a mass ratio of 96:1.2:1.5:1.3 and stirred for 3 hours to obtain an electrode slurry. The slurry was coated on copper foil, rolled, and dried to obtain a coin electrode sheet. The coin electrode sheet was assembled with a lithium sheet to form a coin cell battery for testing. The test conditions were: charge / discharge voltage range of 0.01~2V, charge / discharge rate of 0.1C, and the initial discharge capacity and initial efficiency were tested. The coin electrode sheets obtained above were assembled with a ternary positive electrode to form a small soft-pack battery for testing. The test conditions were: charge / discharge voltage range of 2.8~4.25V, test temperature of 25±2℃, charging at 2C and 4C respectively, and discharging at 1C. The constant current ratio of charging at different rates was tested. The test results are shown in Table 1.

[0103] Table 1

[0104]

[0105] As can be seen from Table 1:

[0106] (1) As can be seen from Example 1 and Comparative Example 1, when the ball milling in step (1) is not performed, graphene is not generated in the graphite. If the graphite is directly coated, the effects of graphene in expanding the interlayer spacing of graphite, improving conductivity, and reducing the interfacial impedance between graphite and coating agent cannot be achieved. The fast-charging performance of the resulting material will be significantly reduced. As can be seen from Example 1 and Comparative Example 2, even if graphene is added, since the graphene of the present invention is in-situ generated graphene, compared with purchased graphene, the in-situ generated graphene maintains a continuous lattice structure with the graphite matrix, the interface is tightly bonded, the electron transport channel is smoother, and no interface defects are introduced. Moreover, the number of graphene layers and the size can be controlled. Therefore, the fast-charging performance of the material obtained in Comparative Example 2 is also not as good as that of the present invention. Invention; As can be seen from Example 1 and Comparative Example 3, after completely converting graphite into graphene in Comparative Example 3, the graphene, graphite, and coating agent were ball-milled and carbonized. Compared with the present invention, the resulting material has low initial efficiency, low capacity, low tap density, low compaction density, and poor fast-charging performance. Because graphite is completely converted into graphene, its specific surface area will increase sharply, and it will undergo a violent and irreversible reaction with the electrolyte. Furthermore, since graphene is a two-dimensional sheet material with a large number of pores inside, the tap density and compaction density will decrease. A large amount of graphene will seriously stack and agglomerate, which will easily block the lithium-ion diffusion channels, slow down the ion transport kinetics, and thus affect the fast-charging performance, which runs counter to the original intention of using the high conductivity of graphene to improve the fast-charging performance.

[0107] (2) As can be seen from Examples 1 and 6-7, the graphene content in the modified graphite affects the performance of graphene. It is preferable that the graphene content in the modified graphite is within a suitable range, which can further improve the fast charging performance of the material. As can be seen from Examples 1 and 8, if too much graphene is generated during the secondary ball milling, it will destroy the pre-designed optimized structure. The newly generated graphene has certain defects, which will randomly fill the system and block the ion channels instead of building an ordered and efficient electron channel. At the same time, the newly generated graphene has a large specific surface area and contains a large number of defects, which leads to a decrease in the initial efficiency of the negative electrode material and a decrease in the initial capacity and energy density of the battery. As can be seen from Examples 1 and 9, although less graphene is generated during the secondary ball milling, if the rotation speed of the secondary ball milling is too low, it will affect the coating effect of the coating agent, thereby affecting the performance of the material.

[0108] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a fast-charging negative electrode material, characterized in that, The preparation method includes the following steps: (1) The graphite material is ball-milled once to obtain modified graphite containing graphene, wherein the modified graphite containing graphene includes graphene and graphite matrix. (2) The modified graphite containing graphene and the coating agent described in step (1) are subjected to secondary ball milling and carbonization to obtain the fast-charging negative electrode material.

2. The preparation method according to claim 1, characterized in that, In step (1), the modified graphene containing graphene has a mass percentage of 5 wt% to 10 wt%; And / or, in the graphene-containing modified graphite described in step (1), the number of graphene layers is ≤5. And / or, in the graphene-containing modified graphite of step (1), the thickness of the single-layer graphene is ≤3nm.

3. The preparation method according to claim 1 or 2, characterized in that, The rotation speed of the ball mill in step (1) is 300 rpm to 500 rpm; And / or, the ball milling time in step (1) is 0.5h to 4h; And / or, the size of the grinding balls in the first ball milling in step (1) is 1μm~10μm; And / or, the ball milling in step (1) is carried out in a protective gas.

4. The preparation method according to claim 1 or 2, characterized in that, In step (1), an additive was added during the ball milling process. The additive included any one or a combination of at least two of the following: polyethylene glycol, sodium dodecyl sulfonate, sodium dodecylbenzene sulfonate, hexadecyltrimethylammonium bromide, polyvinylpyrrolidone, choline chloride, or ammonium carbonate. And / or, the mass ratio of the graphite material in step (1) to the additives added during the first ball milling is 1:(0.001~10).

5. The preparation method according to claim 1 or 2, characterized in that, The rotation speed of the secondary ball mill in step (2) is 60 rpm to 200 rpm; And / or, the secondary ball milling time in step (2) is 6h~10h; And / or, the temperature of the secondary ball milling in step (2) does not exceed 30°C; And / or, the size of the grinding balls in the secondary ball milling in step (2) is 15μm~100μm; And / or, the secondary ball milling in step (2) is carried out in a protective gas.

6. The preparation method according to claim 1 or 2, characterized in that, The mass ratio of the graphene-containing modified graphite to the coating agent in step (1) is 1:(0.02~0.1); And / or, the coating agent in step (2) includes bituminous materials and / or resinous materials.

7. The preparation method according to claim 1 or 2, characterized in that, The carbonization in step (2) includes heating to a first temperature at a first heating rate and holding at that temperature, and then heating to a second temperature at a second heating rate and holding at that temperature. The first temperature is 500℃~900℃, and the holding time at the first temperature is 1h~10h; The second temperature is 1000℃~1200℃, and the holding time at the second temperature is 3h~5h; The first heating rate is 1℃ / min to 8℃ / min; The second heating rate is 8℃ / min to 10℃ / min.

8. The preparation method according to claim 1 or 2, characterized in that, After carbonization in step (2), the material was further crushed, shaped, and sieved. And / or, the particle size D50 of the fast-charging negative electrode material in step (2) is 8μm~14μm, the particle size distribution range is 1.0μm~38.2μm, and the specific surface area is 0.8m². 2 / g~3.0m 2 / g, tap density is 0.8g / cm³ 3 ~1.5g / cm 3 The compacted density is 1.5 g / cm³. 3 ~1.75g / cm 3 ; And / or, the fast-charging negative electrode material includes a graphite matrix and a hard carbon coating layer on the surface of the graphite matrix, and graphene is also included between the graphite matrix and the hard carbon coating layer, and the graphene links the graphite matrix and the hard carbon coating layer to form a three-dimensional network structure.

9. A fast-charging negative electrode material, characterized in that, The fast-charging negative electrode material is prepared by the preparation method described in any one of claims 1-8.

10. A battery, characterized in that, The battery includes the fast-charging negative electrode material as described in claim 9.

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