Graphite material, preparation method and application thereof

Abstract

This invention discloses a graphite material, its preparation method, and its applications. The graphite material includes a matrix and a coating layer. The matrix is ​​artificial graphite, and the coating layer is made of carbon quantum dots, a lithium replenishing agent, and a coating agent. This invention provides a soft carbon-coated graphite with a synergistic effect of compounded carbon quantum dots, lithium replenishment, and etching. The carbon quantum dots can act as conductive agents and contain abundant functional groups. After lithiation, they are compounded to achieve a lithium replenishment effect. The alkaline carbon quantum dot solution etches the graphite surface at high temperatures during the carbonization process, which can improve the disorder of the graphite surface without increasing the content of the coating agent to increase the disorder of the graphite surface. The prepared fast-charging graphite has significantly improved rate charging performance without reducing the initial coulombic efficiency.

Description

Technical Field

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

[0002] One of the biggest obstacles for electric vehicles to replace traditional gasoline vehicles is "charging anxiety." Even as the range of lithium-ion batteries gradually improves, their long charging times (1 hour for 1C slow charging and 20-30 minutes for 2-3C fast charging) still severely impact the user experience and practicality of electric vehicles. The ability to provide fast charging capabilities that approximate the refueling experience of gasoline vehicles (replenishing hundreds of kilometers of range in 5 minutes) is key to enhancing the market acceptance and competitiveness of electric vehicles.

[0003] In recent years, although CATL and BYD have released 6-8C supercharging and 10-12C flash charging technologies, 2-3C fast charging technology remains the mainstream in the market, while 4-5C fast charging technology has not been widely adopted. The biggest bottleneck in fast charging of lithium-ion batteries is the kinetic lag of graphite lithium intercalation, which easily leads to lithium plating, causing side reactions between lithium metal and electrolyte, reducing cycle life, and creating safety hazards. The graphite lithium intercalation process includes Li... + Desolvation and crossing the solid electrolyte interface (SEI), charge transfer, Li + Diffusion in graphite particles and Li + Diffusion occurs within the negative electrode. These steps are energy barrier-limited, and a lower energy barrier and a higher probability of overcoming it can improve fast charging capabilities. From a graphite perspective, by using small aggregates and secondary particle design, the Li content can be reduced simultaneously. + The diffusion barrier in graphite particles and negative electrode sheets; and the secondary particle design can improve the graphite orientation in the negative electrode sheet, thereby increasing the probability of lithium intercalation and reducing the charge transfer barrier; and the most effective way to increase the probability of lithium intercalation in graphite and reduce the charge transfer barrier is to coat graphite with soft carbon and optimize the coating layer to increase the disorder of the graphite surface. Summary of the Invention

[0004] The purpose of this invention is to provide a graphite material and a soft carbon coating method. This graphite material can simultaneously achieve high rate charging performance and high initial coulombic efficiency.

[0005] To achieve the above objectives, the following technical solution is adopted: In a first aspect, the present invention provides a graphite material (fast-charging graphite).

[0006] The graphite material provided by the present invention includes a matrix and a coating layer, wherein the matrix is ​​graphite and the coating layer is made of carbon quantum dots, lithium supplementation agent and coating agent.

[0007] In some embodiments of the present invention, the graphite is artificial graphite, the artificial graphite is secondary particles, the aggregate particle size D50 forming the secondary particles is 5-11 μm, and the particle size D50 of the secondary particles is 10-18 μm.

[0008] In some embodiments of the present invention, the coating agent is selected from at least one of asphalt, asphalt solution, and anthracene oil.

[0009] This invention provides a soft carbon-coated graphite with synergistic effects of compounded carbon quantum dots, lithium replenishment, and etching. The carbon quantum dots can act as conductive agents and contain abundant functional groups. After lithiation, they can be compounded to achieve a lithium replenishment effect. The alkaline carbon quantum dot solution etches the graphite surface at high temperature during the carbonization process, which can improve the disorder of the graphite surface without increasing the content of the coating agent to improve the disorder of the graphite surface.

[0010] Secondly, the present invention provides a method for preparing the graphite material (fast-charging graphite) described in the first aspect.

[0011] The method for preparing graphite material provided by the present invention includes the following steps: (1) Take an appropriate amount of carbon source to carry out a hydrothermal reaction to obtain a crude carbon quantum dot solution, and then microfilter the crude carbon quantum dot solution to obtain a carbon quantum dot aqueous solution; (2) Add lithium hydroxide to the carbon quantum dot aqueous solution in step (1) to obtain a carbon quantum dot lithium replenishment etching solution; (3) The carbon quantum dot lithium-added etching solution, coating agent and graphite in step (2) are mechanically fused in a certain proportion to obtain a graphite material coating precursor; (4) The fast-charging graphite coating precursor in step (3) is carbonized at high temperature, cooled, washed with water until neutral, and dried to obtain graphite material.

[0012] In some embodiments of the present invention, the carbon source in step (1) is selected from at least one of glucose, sucrose, and vitamin C.

[0013] In some embodiments of the present invention, the carbon source concentration in step (1) is 0.1~0.2 M.

[0014] In a specific embodiment of the present invention, the carbon source in step (1) is 0.1 M sucrose, 0.15 M glucose or 0.2 M vitamin C.

[0015] In some embodiments of the present invention, the temperature of the hydrothermal reaction in step (1) is 160~200℃ and the time is 4~8 h.

[0016] In a specific embodiment of the present invention, the temperature of the hydrothermal reaction in step (1) is 160°C, 180°C or 200°C; the time of the hydrothermal reaction is 4 h, 6 h or 8 h.

[0017] In some embodiments of the present invention, the pore size of the filter membrane used in step (1) is 0.1~0.5μm.

[0018] In some embodiments of the present invention, the lithium supplement in step (2) is lithium hydroxide, and the concentration of the lithium hydroxide is 0.2~0.3 M.

[0019] In some embodiments of the present invention, the graphite in step (3) is artificial graphite, the artificial graphite is secondary particles, the aggregate particle size D50 forming the secondary particles is 5 to 11 μm, and the particle size D50 of the secondary particles is 10 to 18 μm.

[0020] In some embodiments of the present invention, the coating agent in step (3) is selected from at least one of asphalt, asphalt solution, and anthracene oil.

[0021] In a specific embodiment of the present invention, the asphalt is asphalt with a softening point of 200.

[0022] In a specific embodiment of the present invention, the asphalt solution is a wash oil solution of asphalt with a softening point of 200 (the mass fraction of asphalt is 25%).

[0023] In some embodiments of the present invention, the mass ratio of carbon quantum dot lithium-added etching solution, coating agent and graphite in step (3) is (0.5~1):(2~4):100, the mechanical fusion rotation speed is 600~800 rpm and the mechanical fusion time is 6~10 min.

[0024] In a specific embodiment of the present invention, the mass ratio of carbon quantum dot lithium-added etching solution, coating agent and graphite in step (3) is 0.8:2:100, 1:3:100 or 0.5:4:100.

[0025] In some embodiments of the present invention, the carbonization temperature in step (4) is 700~800℃ and the carbonization time is 8~12 h.

[0026] In a specific embodiment of the present invention, the carbonization temperature in step (4) is 700°C, 750°C or 800°C; and the carbonization time is 8 h, 10 h or 12 h.

[0027] Thirdly, the present invention provides a negative electrode material.

[0028] The negative electrode material provided by the present invention includes the graphite material described in the first aspect of the present invention.

[0029] Fourthly, the present invention provides a lithium-ion battery.

[0030] The lithium-ion battery includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the negative electrode is made of the aforementioned negative electrode material.

[0031] The present invention also provides an electrical device that uses the above-mentioned lithium-ion battery.

[0032] Compared with the prior art, the present invention has the following beneficial effects: the fast-charging graphite prepared by the present invention has a significantly improved rate charging performance from 3C to 6C, without reducing the first coulombic efficiency. Detailed Implementation

[0033] The present invention will now be described in further detail with reference to specific embodiments. The given embodiments are merely illustrative of the invention and not intended to limit its scope. The embodiments provided below can serve as a guide for further improvements by those skilled in the art and do not constitute a limitation on the invention in any way.

[0034] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0035] Example 1 A crude carbon quantum dot solution was obtained by hydrothermal reaction at 180°C for 6 h using 0.15 M glucose as the carbon source. This crude solution was then microfiltered (0.22 μm) to obtain an aqueous carbon quantum dot solution. 0.2 M lithium hydroxide was added to the aqueous solution to obtain a lithium-added etching solution for carbon quantum dots. The lithium-added etching solution, 200 softening point pitch, and graphite with a D50 of 13 µm (aggregate D50 of 8.5 µm) were mechanically fused at 800 rpm for 6 min in a mass ratio of 0.8:2:100 to obtain a fast-charging graphite-coated precursor. This precursor was then carbonized at 800°C for 8 h, cooled, washed with water until neutral, and dried to obtain fast-charging graphite.

[0036] Example 2 A crude carbon quantum dot solution was obtained by hydrothermal reaction at 200°C for 4 h using 0.1 M sucrose as the carbon source. This crude solution was then microfiltered (0.22 μm) to obtain an aqueous carbon quantum dot solution. 0.2 M lithium hydroxide was added to the aqueous solution to obtain a lithium-added etching solution for carbon quantum dots. The lithium-added etching solution, a wash oil solution of 200 softening point asphalt (25% by mass), and graphite with a D50 of 13 µm (aggregate D50 of 8.5 µm) were mechanically fused at 700 rpm for 8 min in a mass ratio of 1:3:100 to obtain a fast-charging graphite-coated precursor. The fast-charging graphite-coated precursor was then carbonized at 700°C for 12 h, cooled, washed with water until neutral, and dried to obtain fast-charging graphite.

[0037] Example 3 A crude carbon quantum dot solution was obtained by hydrothermal reaction at 160°C for 8 h using 0.2 M vitamin C as the carbon source. This crude solution was then microfiltered (0.22 μm) to obtain an aqueous carbon quantum dot solution. 0.3 M lithium hydroxide was added to the aqueous solution to obtain a lithium-added etching solution for carbon quantum dots. The lithium-added etching solution, anthracene oil, and graphite with a D50 of 13 µm (aggregate D50 of 8.5 µm) were mechanically fused at 600 rpm for 10 min in a mass ratio of 0.5:4:100 to obtain a fast-charging graphite-coated precursor. The fast-charging graphite-coated precursor was then carbonized at 750°C for 10 h, cooled, washed with water until neutral, and dried to obtain fast-charging graphite.

[0038] Comparative Example 1 200 softening point bitumen and graphite with a D50 of 13 µm (aggregate D50 of 8.5 µm) were mechanically fused at 800 rpm for 6 min at a mass ratio of 2:100 to obtain a fast-charging graphite-coated precursor. The fast-charging graphite-coated precursor was then subjected to high-temperature carbonization at 800 degrees Celsius for 8 h to obtain fast-charging graphite.

[0039] Comparative Example 2 A wash oil solution of 200 softening point asphalt (asphalt mass fraction 25%) and graphite with a D50 of 13 µm (aggregate D50 of 8.5 µm) were mechanically fused at 700 rpm for 8 min at a mass ratio of 3:100 to obtain a fast-charging graphite-coated precursor. The fast-charging graphite-coated precursor was then subjected to high-temperature carbonization at 700 degrees Celsius for 12 h to obtain fast-charging graphite.

[0040] Comparative Example 3 Anthracene oil and graphite with a D50 of 13 µm (aggregate D50 of 8.5 µm) were mechanically fused at a mass ratio of 4:100 at 600 rpm for 10 min to obtain a fast-charging graphite-coated precursor. The fast-charging graphite-coated precursor was then subjected to high-temperature carbonization at 750 degrees Celsius for 10 h to obtain fast-charging graphite.

[0041] Comparative Example 4 200 softening point asphalt and graphite with a D50 of 13 µm (aggregate D50 of 8.5 µm) were mechanically fused at 800 rpm for 6 min at a mass ratio of 3:100 to obtain a fast-charging graphite-coated precursor. The fast-charging graphite-coated precursor was then subjected to high-temperature carbonization at 800 degrees Celsius for 8 h to obtain fast-charging graphite.

[0042] The graphite from Examples 1-3 and Comparative Examples 1-4 was used to prepare negative electrode sheets (material composition and mass ratio: graphite 96.5%, conductive agent Super P 0.5%, dispersant CMC 1.2%, binder SBR 1.8%, coating single-sided surface density 81.5 g / m²). 2 The compacted density is 1.6 g / cm³. 3 ), and lithium iron phosphate cathode sheet (material composition and mass ratio: LiFePO4 96.8%, conductive agent Super P and graphene conductive paste 1.2%, binder PVDF 2%, coating single-sided areal density of 170 g / m²). 2 The compacted density is 2.40 g / cm³. 3 The cells are made by stacking PP separators and aluminum-plastic film, then encapsulated with aluminum-plastic film and injected with electrolyte to form a soft-pack battery.

[0043] The batteries of Examples 1-3 and Comparative Examples 1-4 were subjected to capacity tests at 25°C, and the initial coulombic efficiency (ICE) of the batteries was calculated. The results are shown in Table 1. Charge tests at 0.5C, 1C, 2C, 3C, 4C, 5C, and 6C rates were conducted at 25°C, and the constant current charge ratio of the batteries was calculated. The results are shown in Table 1.

[0044] Table 1: Test performance of batteries in Examples 1-3 and Comparative Examples 1-4

[0045] Table 1 shows that the conventional soft carbon-coated graphite in Comparative Examples 1-3 can only achieve a charging rate of 3C. Comparing Comparative Examples 1 and 4, it can be seen that further improving the rate performance of graphite can be achieved by increasing the coating amount, increasing the graphite disorder, and increasing the number of lithium intercalation sites. Increasing the coating amount by 50% increases the charging rate to 4C, but the initial coulombic efficiency is significantly reduced. The soft carbon-coated graphite in the examples, with its synergistic effect of compounded carbon quantum dots, lithium replenishment, and etching, utilizes carbon quantum dots as a conductive agent and contains abundant functional groups. After lithiation, the compounding process provides lithium replenishment. The alkaline carbon quantum dot solution etches the graphite surface at high temperatures during carbonization, increasing the graphite surface disorder without requiring an increase in coating agent content. The resulting fast-charging graphite exhibits a significantly improved rate charging performance from 3C to 6C without reducing the initial coulombic efficiency.

[0046] The present invention has been described in detail above. For those skilled in the art, the invention can be practiced in a wide range of ways with equivalent parameters, concentrations, and conditions without departing from its spirit and scope, and without requiring unnecessary experiments. Although specific embodiments have been given, it should be understood that further modifications can be made to the invention. In summary, according to the principles of the invention, this application is intended to include any changes, uses, or improvements to the invention, including changes made using conventional techniques known in the art that depart from the scope disclosed herein. Some of the essential features can be applied within the scope of the following appended claims.

Claims

1. A graphite material comprising a matrix and a coating layer, wherein the matrix is ​​graphite and the coating layer is made of carbon quantum dots, a lithium supplement, and a coating agent.

2. The graphite material according to claim 1, characterized in that: The graphite is artificial graphite, the artificial graphite is secondary particles, the aggregate particle size D50 forming the secondary particles is 5-11 μm, and the particle size D50 of the secondary particles is 10-18 μm. And / or, the coating agent is selected from at least one of asphalt, asphalt solution, and anthracene oil.

3. A method for preparing the graphite material according to claim 1 or 2, comprising the following steps: (1) Take an appropriate amount of carbon source to carry out a hydrothermal reaction to obtain a crude carbon quantum dot solution, and then microfilter the crude carbon quantum dot solution to obtain a carbon quantum dot aqueous solution; (2) Add lithium replenishing agent to the carbon quantum dot aqueous solution in step (1) to obtain carbon quantum dot lithium replenishing etching solution; (3) The carbon quantum dot lithium-added etching solution, coating agent and graphite in step (2) are mechanically fused in a certain proportion to obtain a graphite material coating precursor; (4) The fast-charging graphite coating precursor in step (3) is subjected to high-temperature carbonization to obtain the graphite material.

4. The preparation method according to claim 3, characterized in that: The carbon source in step (1) is selected from at least one of glucose, sucrose, and vitamin C; And / or, the concentration of the carbon source in step (1) is 0.1~0.2 M; And / or, the temperature of the hydrothermal reaction in step (1) is 160~200℃ and the time is 4~8 h.

5. The preparation method according to claim 4, characterized in that: The lithium supplement agent in step (2) is lithium hydroxide, and the concentration of the lithium hydroxide is 0.2~0.3 M.

6. The preparation method according to claim 4, characterized in that: The graphite in step (3) is artificial graphite, which is a secondary particle. The aggregate particle size D50 forming the secondary particle is 5-11 μm, and the particle size D50 of the secondary particle is 10-18 μm. And / or, the coating agent in step (3) is selected from at least one of asphalt, asphalt solution, and anthracene oil.

7. The preparation method according to claim 4, characterized in that: The mass ratio of carbon quantum dot lithium-added etching solution, coating agent, and graphite in step (3) is (0.5~1):(2~4):100; And / or, the rotation speed of mechanical fusion in step (3) is 600~800 rpm, and the mechanical fusion time is 6~10 min.

8. The preparation method according to claim 4, characterized in that: The carbonization temperature in step (4) is 700~800℃, and the carbonization time is 8~12 h.

9. A negative electrode material, characterized in that: The negative electrode material includes the graphite material as described in claim 1 or 2, or the graphite material prepared by the method described in any one of claims 3-8.

10. A lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that: The negative electrode sheet comprises the negative electrode material as described in claim 9.

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