Graphite composite material and preparation method and application thereof

Abstract

The invention relates to the technical field of lithium ion batteries, and discloses a graphite composite material as well as a preparation method and application thereof. The method comprises the following steps: (1) in the presence of an organic solvent, performing ultrasonic treatment on fluorinated graphene to obtain fluorinated graphene dispersion liquid; the sheet diameter of the fluorinated graphene is 4 to 10 [mu] m; and (2) contacting and mixing the fluorinated graphene dispersion liquid and graphite to obtain the graphite composite material, wherein in the step (2), the weight ratio of the fluorinated graphene to the graphite is (1-3): 100. According to the method for preparing the graphite composite material provided by the invention, the interface stability of a graphite negative electrode is enhanced, and the high conductivity of the material is reserved, so that the graphite composite material has relatively high cycling stability and rate capability.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a graphite composite material and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries are widely used in portable electronic devices, electric vehicles, and energy storage systems due to their high energy density, long cycle life, and low self-discharge rate. Graphite anode materials are the most common anode materials in commercial lithium-ion batteries, offering advantages such as excellent electrochemical stability, good conductivity, and low cost. However, in practical applications, graphite materials cannot meet the requirements of lithium-ion batteries for longer cycle life and fast charging, limiting further improvements in battery performance.

[0003] First, the graphite negative electrode undergoes volume expansion and contraction during the charge and discharge process. Long-term cycling may lead to the destruction of the material structure and pulverization of the electrode, which in turn affects the cycle life of the battery. Secondly, the reaction between the surface of the graphite negative electrode and the electrolyte forms a solid electrolyte interface film (SEI), but the stability and uniformity of this film are insufficient, which may lead to the growth of lithium dendrites and increase safety risks. In addition, the insertion and extraction process of lithium ions in graphite is limited by the diffusion rate, resulting in poor kinetic performance of the graphite negative electrode, which in turn affects the rapid charge and discharge capability of the battery. Under low temperature and high rate conditions, this limitation manifests itself as a rapid decay of battery capacity and a significant reduction in power performance. Therefore, the development of graphite negative electrode materials with higher stability and better electrochemical properties is one of the key directions for improving the performance of lithium-ion batteries.

[0004] To address the above problems, researchers have proposed a variety of graphite surface modification technologies, including surface coating (such as carbon, metal oxides and polymers), doping (such as nitrogen, boron, fluorine) and structural design (such as micro-nanostructure regulation). These technologies aim to improve the structural stability, interface stability and ion / electron transport properties of graphite. For example, surface coating technology can form a protective layer on the surface of graphite particles, effectively inhibiting the decomposition reaction of the electrolyte and reducing the growth of the solid electrolyte interface film (SEI), thereby enhancing the cycle life and interface stability; fluorine doping technology utilizes the high electronegativity and chemical stability of fluorine atoms to improve the electrochemical properties of the graphite negative electrode and inhibit side reactions. Fluorine atoms can form more stable fluorides with lithium salts in the electrolyte, thereby enhancing the stability of the SEI film. CN117855441A discloses a fluorine-doped graphite anode material and a preparation method thereof. The method comprises: mixing a fluorine-source organic compound and an amine organic compound in a stoichiometric ratio of 1-3:1, adding an organic solvent, and stirring to form a uniform suspension; heating the suspension in a heating chamber at a power of 700-1000W to produce a mixed material; and sintering the mixed material in an inert gas environment to obtain a fluorine-doped graphite anode material. However, conventional single coating and doping technologies are costly and complex, limiting their feasibility for large-scale industrial application and failing to simultaneously and effectively improve the rate performance and cycle life of graphite anode materials.

[0005] Therefore, how to provide a comprehensive modification method that improves the cycle stability and rate performance of graphite negative electrode while having a simple process flow and low cost has become an urgent problem to be solved. Summary of the Invention

[0006] The purpose of the present invention is to overcome the defects of the prior art graphite negative electrode in terms of low cycle stability and rate performance.

[0007] In order to achieve the above object, the first aspect of the present invention provides a method for preparing a graphite composite material, the method comprising:

[0008] (1) ultrasonically treating fluorinated graphene in the presence of an organic solvent to obtain a fluorinated graphene dispersion; the fluorinated graphene having a sheet diameter of 4-10 μm;

[0009] (2) contacting and mixing the fluorinated graphene dispersion and graphite to obtain the graphite composite material;

[0010] Wherein, in step (2), the weight ratio of the fluorinated graphene to the graphite is 1-3:100.

[0011] Preferably, in step (1), in the fluorinated graphene, the molar ratio of fluorine to carbon is 0.53-0.60:1.

[0012] Preferably, the ultrasonic treatment conditions include: power of 150-200W, and time of 60-90min.

[0013] Preferably, the weight ratio of the fluorinated graphene to the graphite is 1-3:100.

[0014] Preferably, in step (2), the specific surface area of the graphite is 2-2.5m 2 / g.

[0015] Preferably, the graphite is needle coke artificial graphite and / or natural graphite.

[0016] Preferably, in step (1), the concentration of fluorinated graphene in the fluorinated graphene dispersion is 5-10 mmol / L.

[0017] Preferably, in step (1), the organic solvent is selected from at least one of N-methylpyrrolidone, N,N-dimethylformamide, tetrahydrofuran and isopropyl alcohol.

[0018] Preferably, in step (2), the contact mixing conditions include: temperature of 20-30° C., stirring rate of 750-1000 rpm, and time of 2-5 h.

[0019] Preferably, in step (2), the method further comprises: sequentially performing solid-liquid separation and drying on the mixed liquid obtained by the contact mixing to obtain the graphite composite material.

[0020] The second aspect of the present invention provides a graphite composite material prepared by the method described in the first aspect.

[0021] Preferably, the specific surface area of the graphite composite material is 4-8m 2 / g, tap density is 1-5g / cm 3 .

[0022] Preferably, the graphite composite material includes graphite and a fluorinated graphene coating layer coated on the surface of the graphite, and the thickness of the fluorinated graphene coating layer is 3-8 nm.

[0023] The third aspect of the present invention provides use of the graphite composite material described in the second aspect in a lithium ion battery.

[0024] Through the above technical solution, the present invention has at least the following advantages over the prior art:

[0025] The method for preparing a graphite composite material provided by the present invention comprises the following steps: ultrasonically exfoliating fluorinated graphene of a specific sheet diameter to obtain a fluorinated graphene dispersion, and contacting and mixing the dispersion with graphite in a specific ratio to obtain a graphite composite material. The composite material, when applied to a lithium-ion battery, can promote the formation of a LiF-rich SEI film on the graphite surface, thereby improving the stability of the SEI film, enhancing the interface stability of the graphite negative electrode, and retaining the high conductivity of the material, thereby having high cycle stability and rate performance.

[0026] In addition, the method for preparing the graphite composite material provided by the present invention has a simple process flow, low cost, and is easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a SEM image of the original graphite of the present invention;

[0028] Figure 2 is a SEM image of the graphite composite material in Example 1 of the present invention;

[0029] Figure 3 is a TEM image of the graphite composite material in Example 1 of the present invention;

[0030] Figure 4 1 is an XPS graph of the original graphite of the present invention and the graphite composite material obtained in Example 1;

[0031] Figure 5 This is a comparison chart of the cycle performance of the lithium-ion batteries obtained in Application Example 1 of the present invention and Comparative Application Example 3. DETAILED DESCRIPTION

[0032] The endpoints of the ranges and any values disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0033] As mentioned above, the first aspect of the present invention provides a method for preparing a graphite composite material, the method comprising:

[0034] (1) ultrasonically treating fluorinated graphene in the presence of an organic solvent to obtain a fluorinated graphene dispersion; the fluorinated graphene having a sheet diameter of 4-10 μm;

[0035] (2) contacting and mixing the fluorinated graphene dispersion and graphite to obtain the graphite composite material;

[0036] Wherein, in step (2), the weight ratio of the fluorinated graphene to the graphite is 1-3:100.

[0037] In the present invention, fluorinated graphene (FG) is a new two-dimensional material, in which fluorine atoms are uniformly distributed on the surface of graphene.

[0038] Preferably, the ultrasonic treatment conditions include: a power of 150-200 W and a duration of 60-90 minutes. The inventors of the present invention have found that, under this preferred condition, the method provided by the present invention can facilitate the exfoliation and dispersion of the fluorinated graphene, avoid destroying the integrity of the fluorinated graphene, and promote the formation of a uniform fluorinated graphene coating on the surface of the graphite substrate, thereby obtaining a graphite composite material with higher cycle stability and rate performance.

[0039] It should be noted that the above time is 60-90 minutes, for example, it can be any time among 60 minutes, 70 minutes, 80 minutes, or 90 minutes.

[0040] Preferably, in step (1), in the fluorinated graphene, the fluorine-carbon molar ratio is 0.53-0.60: 1. In this preferred embodiment, the method provided by the present invention can obtain a graphite composite material with higher cycle stability and rate performance.

[0041] Further preferably, the specific surface area of the fluorinated graphene is 4-8m 2 / g.

[0042] Preferably, in step (2), the specific surface area of the graphite is 2-2.5m 2 / g;

[0043] According to a preferred embodiment, the graphite is needle coke artificial graphite and / or natural graphite.

[0044] Preferably, in step (1), the concentration of fluorinated graphene in the fluorinated graphene dispersion is 5-10 mmol / L.

[0045] Preferably, in step (1), the organic solvent is selected from at least one of N-methylpyrrolidone, N,N-dimethylformamide, tetrahydrofuran, and isopropyl alcohol, and preferably at least one of N-methylpyrrolidone, tetrahydrofuran, and isopropyl alcohol. In this preferred embodiment, the method provided by the present invention can facilitate ultrasonic exfoliation and dispersion of fluorinated graphene, so that a uniform fluorinated graphene coating is formed on the graphite surface.

[0046] Preferably, in step (2), the contact mixing conditions include: temperature of 20-30° C., stirring rate of 750-1000 rpm, and time of 2-5 h.

[0047] It should be noted that the above time is 2-5 hours, for example, it can be any time among 2 hours, 3 hours, 4 hours, or 5 hours.

[0048] Preferably, in step (2), the method further comprises: sequentially performing solid-liquid separation and drying on the mixed liquid obtained by the contact mixing to obtain the graphite composite material.

[0049] The present invention has no particular limitation on the solid-liquid separation and drying methods, and those skilled in the art may adopt known technical means in the art. For example, the solid-liquid separation method may be centrifugal separation or filtration separation, and the drying method may be freeze-drying.

[0050] The method of the present invention further includes post-processing operations such as washing. For example, the material obtained from the solid-liquid separation is washed with deionized water and then dried to obtain the graphite composite material. The present invention will not be described in detail herein, and those skilled in the art should not be construed as limiting the present invention.

[0051] As mentioned above, the second aspect of the present invention provides a graphite composite material prepared by the method described in the first aspect.

[0052] Preferably, the specific surface area of the graphite composite material is 4-8m 2 / g, tap density is 1-5g / cm 3 .

[0053] Preferably, the graphite composite material comprises graphite and a fluorinated graphene coating layer coated on the surface of the graphite, and the thickness of the fluorinated graphene coating layer is 3-8 nm, preferably 3-6 nm.

[0054] Preferably, the F content in the graphite composite material is 7-14 wt%, preferably 8-14 wt%.

[0055] As mentioned above, the third aspect of the present invention provides the use of the graphite composite material described in the second aspect in a lithium ion battery.

[0056] Preferably, the application method includes:

[0057] (1) coating a slurry containing the graphite composite material, a conductive additive and a binder on a surface of a copper foil, and then drying the slurry to obtain an electrode;

[0058] (2) Assembling the electrode, metal lithium sheet, diaphragm and electrolyte to obtain a lithium-ion battery.

[0059] Preferably, the conductive additive is conductive carbon black (Super P).

[0060] Preferably, the binder is carboxymethyl cellulose (CMC) and / or styrene-butadiene rubber, more preferably a combination of carboxymethyl cellulose and styrene-butadiene rubber.

[0061] The present invention has no particular limitation on the amount and ratio of the graphite composite material, the conductive additive, and the binder. Those skilled in the art can add and use them according to conventional methods in the field, and these persons skilled in the art should not interpret this as a limitation on the present invention.

[0062] Preferably, the electrolyte is a mixed solution of LiPF6, dimethyl carbonate (DMC), ethylene carbonate (EC), and ethyl methyl carbonate (EMC).

[0063] The present invention has no special requirements for the assembly process of the lithium-ion battery, and the assembly can be performed using methods known in the art. The present invention will not describe them one by one here, and those skilled in the art should not understand this as a limitation of the present invention.

[0064] The present invention will be described in detail below by way of examples. In the following examples, the reagents and instruments used are all commercially available.

[0065] Fluorinated graphene: purchased from MacLean, with a fluorine-carbon molar ratio of 0.53-0.60:1 and a sheet diameter of 4-10 μm.

[0066] Graphite: Needle coke artificial graphite, purchased from Hunan Rongli New Material Technology Co., Ltd., with a specific surface area of 1.9-2.3m 2 / g.

[0067] In the following examples, the test methods involved are as follows:

[0068] (1) Thickness of the fluorinated graphene coating layer: measured using a Talos F200x transmission electron microscope (FEI, USA).

[0069] (2) F content: measured by Thermo Fisher Scientific's Nexsa G2 instrument.

[0070] (3) SEM (scanning electron microscope) image: obtained by scanning electron microscope test using Japan Hitachi S-4800.

[0071] (4) TEM (Transmission Electron Microscope) image: obtained by testing using a transmission electron microscope Talos F200x from FEI, USA.

[0072] (5) XPS (X-ray photoelectron spectroscopy) diagram: obtained by X-ray photoelectron spectroscopy test using Nexsa G2.

[0073] Example 1

[0074] (1) Add 5 mg of fluorinated graphene to 50 mL of organic solvent and ultrasonicate to obtain a fluorinated graphene dispersion;

[0075] (2) contacting and mixing the graphite with the fluorinated graphene dispersion obtained in step (1) (the concentration of the fluorinated graphene is 8 mmol / L), and stirring to obtain a mixed solution;

[0076] (3) The mixed solution obtained in step (2) is filtered and washed with deionized water, and then freeze-dried to obtain a graphite composite material, and its performance parameters and indicators are tested.

[0077] The raw materials and their ratios, reaction conditions and product parameters of this example are shown in Table 1.

[0078] Example 2 and Example 3 were prepared using the same preparation method as Example 1, except that the raw materials and their ratios, and the reaction conditions were different, resulting in products with different performance and index parameters, as shown in Table 1.

[0079] Table 1

[0080]

[0081]

[0082] Example 4

[0083] The method was similar to that of Example 1, except that the organic solvent in this example was N,N-dimethylformamide;

[0084] The rest of the graphite composite material S4 was obtained by the test. The thickness of the fluorinated graphene coating layer in the composite material was 5 nm and the specific surface area was 6.17 m 2 / g, and the tap density is 1.06g / cm 3 , the F content is 10wt%.

[0085] Example 5

[0086] The method was similar to that of Example 1, except that the ultrasonic treatment conditions in this example were: power 100 W, time 40 min;

[0087] The rest of the graphite composite material S5 was obtained by the test, and the specific surface area of the composite material was 6.08m 2 / g, and the tap density is 1.11g / cm 3 The thickness of the fluorinated graphene coating layer is 7 nm and the F content is 12 wt%.

[0088] Comparative Example 1

[0089] A method similar to that of Example 1 was used, except that the amount of fluorinated graphene used in this example remained unchanged, and the weight ratio of fluorinated graphene to graphite was adjusted to 0.5:100;

[0090] The rest of the graphite composite material D1 was obtained by the test, and the specific surface area of the composite material was 2.35m 2 / g, and the tap density is 1.11g / cm 3 The thickness of the fluorinated graphene coating layer is 1.3 nm and the F content is 4.1 wt%.

[0091] Comparative Example 2

[0092] A method similar to that of Example 1 was used, except that the amount of fluorinated graphene used in this example remained unchanged, and the weight ratio of fluorinated graphene to graphite was adjusted to 5:100;

[0093] The rest of the graphite composite material D2 was obtained by being the same. The fluorinated graphene in the composite material was unevenly coated. The specific surface area of the composite material was 13.9 m 2 / g, and the tap density is 1.15g / cm 3 The thickness of the fluorinated graphene coating layer is 15 nm and the F content is 23 wt%.

[0094] Application Example 1

[0095] (1) Preparation of negative electrode sheet

[0096] The active material (graphite composite material S1), conductive additive (Super P), carboxymethyl cellulose, and styrene-butadiene rubber were thoroughly mixed in a mass ratio of 90:5:2.5:2.5, dissolved in deionized water, and magnetically stirred for 12 hours to form a slurry. The resulting slurry was cast onto copper foil using a spatula. The resulting copper foil was then dried in an 80°C forced air drying oven for 2 hours and further dried in a 120°C vacuum oven for 6 hours. Finally, the copper foil was cut into 12mm pole pieces, and the density of the electrode material on the pole piece was 1.3mg·cm -2 .

[0097] (2) Assembling lithium-ion batteries

[0098] In an inert gas-protected glove box, batteries were assembled using CR2025 battery shells, with the water and oxygen content in the glove box required to be less than 0.5 ppm, to obtain lithium-ion battery Y1. During the production process, a metallic lithium sheet was used as the counter electrode, and the electrolyte used was a mixed solution formed by dissolving 1 mol / L LiPF6 in a 1:1:1 volume ratio of dimethyl carbonate (DMC) / ethylene carbonate (EC) / ethyl methyl carbonate (EMC). A polypropylene microporous membrane (Celgard 2400) was used as the separator.

[0099] Application Examples 2 to 5

[0100] A method similar to that of Application Example 1 was used, except that the graphite composite material S1 was replaced by graphite composite material S2, graphite composite material S3, graphite composite material S4, and graphite composite material S5, respectively;

[0101] The rest are the same, and lithium ion battery Y2, lithium ion battery Y3, lithium ion battery Y4, and lithium ion battery Y5 are obtained respectively.

[0102] Comparative Application Example 1 to Comparative Application Example 2

[0103] A method similar to that of Application Example 1 was used, except that the graphite composite material S1 was replaced by the graphite composite material D1 and the graphite composite material D2 respectively;

[0104] The rest of the process was the same, and lithium-ion batteries DY1 and DY2 were obtained respectively.

[0105] Comparative Application Example 3

[0106] A method similar to that of Application Example 1 was used, except that pristine graphite was used instead of the graphite composite material S1;

[0107] The rest of the process was the same, and a lithium-ion battery DY3 was obtained.

[0108] Test Case

[0109] The lithium-ion battery obtained according to the corresponding use case was subjected to a cycle rate performance test. The test method includes: the assembled battery is left to stand at room temperature for 24 hours, and the electrochemical performance is tested using a Neware battery testing system; the 0.1C first cycle discharge specific capacity and the cycle performance at a voltage range of 0.05-2.0V and a charge and discharge rate of 0.5C (1C=360mAh / g) are tested at room temperature (25℃±2℃). The results are shown in Table 2.

[0110] Table 2

[0111] 0.1C first cycle discharge capacity (mAh / g) Capacity retention after 100 cycles at 0.5C (%) Y1 389.4 100 Y2 380.3 100 Y3 360.8 100 Y4 357.8 94 Y5 371.4 93 DY1 359.4 90 DY2 358.4 77 DY3 358.3 93

[0112] The present invention is exemplified in Figure 1 The SEM images of the original graphite are provided in Figure 2 The SEM images of the graphite composite material in Example 1 are provided in Figure 1 、 Figure 2 and Figure 3 It can be seen that the surface morphology of the original graphite (G) is rough, while the wrinkles of fluorinated graphene can be clearly observed on the surface of the graphite composite material (G@FG).

[0113] The present invention is exemplified in Figure 3 The TEM image of the graphite composite material in Example 1 is provided in Figure 3 It can be seen that in the graphite composite material, a uniformly coated fluorinated graphene coating layer is successfully formed on the graphite surface.

[0114] The present invention is exemplified in Figure 4 The XPS graphs of the original graphite and the graphite composite material obtained in Example 1 are provided in Figure 4 It can be seen that there is no F-doping peak in the original graphite, but there is an obvious F-doping peak in the graphite composite material.

[0115] The present invention is exemplified in Figure 5 A comparison chart of the cycle performance of the lithium-ion batteries obtained in Application Example 1 and Comparative Application Example 3 is provided. Figure 5 It can be seen that the graphite composite material provided by the present invention exhibits excellent cycle stability and rate performance as a negative electrode material compared to original graphite.

[0116] From the above results, it can be seen that the method provided by the present invention can obtain a graphite composite material with high cycle stability and rate performance, which has significantly better effects than traditional graphite negative electrode materials.

[0117] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A method for preparing a graphite composite material, characterized in that: The method includes: (1) ultrasonically treating fluorinated graphene in the presence of an organic solvent to obtain a fluorinated graphene dispersion; the fluorinated graphene having a sheet diameter of 4-10 μm; (2) contacting and mixing the fluorinated graphene dispersion and graphite to obtain the graphite composite material; Wherein, in step (2), the weight ratio of the fluorinated graphene to the graphite is 1-3:

100.

2. The method according to claim 1, wherein The ultrasonic treatment conditions include: power of 150-200W, time of 60-90min.

3. The method according to claim 1, wherein In step (2), the specific surface area of the graphite is 2-2.5m 2 / g; And / or, the graphite is needle coke artificial graphite and / or natural graphite.

4. The method according to any one of claims 1 to 3, wherein: In step (1), the concentration of fluorinated graphene in the fluorinated graphene dispersion is 5-10 mmol / L.

5. The method according to any one of claims 1 to 3, wherein: In step (1), the organic solvent is selected from at least one of N-methylpyrrolidone, N,N-dimethylformamide, tetrahydrofuran and isopropyl alcohol.

6. The method according to any one of claims 1 to 3, wherein: In step (2), the contact mixing conditions include: temperature of 20-30° C., stirring rate of 750-1000 rpm, and time of 2-5 h.

7. The method according to any one of claims 1 to 3, wherein: In step (2), the method further comprises: sequentially performing solid-liquid separation and drying on the mixed liquid obtained by the contact mixing to obtain the graphite composite material.

8. A graphite composite material prepared by the method according to any one of claims 1 to 7.

9. The graphite composite material according to claim 8, wherein The specific surface area of the graphite composite material is 4-8m 2 / g, tap density is 1-5g / cm 3 ; And / or, the graphite composite material includes graphite and a fluorinated graphene coating layer coated on the surface of the graphite, and the thickness of the fluorinated graphene coating layer is 3-8 nm.

10. Use of the graphite composite material according to claim 8 or 9 in lithium ion batteries.

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