Preparation method and application of graphite-based negative electrode of fast-charging lithium battery

Abstract

The invention discloses a preparation method and application of a graphite-based negative electrode of a fast-charging lithium battery, and relates to a preparation method and application of a fast-charging composite negative electrode material of a lithium battery. The invention aims to solve the problems of low rate, poor charge-discharge performance, low first efficiency, low energy density and difficulty in meeting the requirements of some occasions on rapid energy complementation and high-power discharge of the existing fast-charge negative electrode material of the lithium ion battery. The composite negative electrode material organically combining graphite and hard carbon not only can maintain high reversible capacity and stable cycle performance of a graphite material, but also can give full play to the fast charging characteristic of hard carbon, and a lithium ion battery with high energy density and fast charging capability becomes an important direction of research on the negative electrode material of the lithium ion battery. The problems that a traditional graphite negative electrode is prone to lithium separation and fast in capacity fading under high magnification are solved, and the graphite negative electrode is suitable for the fields of electric automobiles, high-power energy storage equipment and the like with strict requirements for fast charging performance.

Description

Technical Field

[0001] The present invention relates to a preparation method and application of a fast-charging composite negative electrode material for a lithium battery. Background Art

[0002] With the global transformation of energy structures and the deepening of sustainable development concepts, fields such as electric vehicles, energy storage systems, mobile devices, and the low-altitude economy have experienced rapid development. At the same time, these applications place higher performance demands on lithium-ion batteries, particularly in terms of fast charging capability, energy density, and cycle life. While traditional graphite anode materials offer high reversible capacity and stability, their slow lithium-ion insertion and extraction kinetics limit high-rate charge and discharge performance, making it difficult to meet the demands for rapid energy replenishment and high-power discharge in certain applications.

[0003] As amorphous carbon materials, hard carbon materials have a large specific surface area and abundant lithium insertion channels, which can provide excellent rate performance and a wide lithium insertion voltage range. However, problems such as poor cycle life and low energy density of hard carbon limit its practical application as a single fast-charging negative electrode material. Summary of the Invention

[0004] The purpose of the present invention is to solve the problems of low rate, poor charge and discharge performance, low energy density, and difficulty in meeting the needs of rapid energy replenishment and high-power discharge in certain occasions of the existing fast-charging negative electrode materials of lithium-ion batteries, and to provide a preparation method and application of graphite-based negative electrodes for fast-charging lithium batteries.

[0005] The composite negative electrode material of the present invention organically combines graphite and hard carbon, which can not only maintain the high reversible capacity and stable cycle performance of the graphite material, but also give full play to the fast charging characteristics of hard carbon, realizing lithium-ion batteries with both high energy density and fast charging capability, which has become an important research direction of lithium-ion battery negative electrode materials.

[0006] Through innovative design, the present invention optimizes the ratio of graphite to hard carbon in the composite material, improves its microstructure and interface properties, optimizes the reaction kinetics, and achieves synergistic enhancement of the performance of the two materials. This material can not only significantly enhance the fast charging capability of lithium-ion batteries, but also extend battery life while maintaining high energy density, paving the way for the development of high-performance lithium batteries.

[0007] A method for preparing a graphite-based negative electrode for a fast-charging lithium battery is specifically completed by the following steps:

[0008] 1. Preparation of graphite-hard carbon composite materials:

[0009] Putting graphite and hard carbon powder into a ball mill, adding grinding balls into the ball mill, and ball milling for a period of time to obtain a graphite-hard carbon composite material;

[0010] 2. Preparation of electrodes:

[0011] Graphite-hard carbon composite material, conductive carbon black Super P and PVDF powder are mixed evenly and ground for a period of time to obtain electrode powder; N-methylpyrrolidone is added to the electrode powder and stirred for a period of time to obtain electrode slurry; the electrode slurry is evenly coated on copper foil, and then pre-baked for a period of time, and then placed in a vacuum oven for further drying to obtain a graphite-based negative electrode for a fast-charging lithium battery.

[0012] A fast-charging lithium battery graphite-based negative electrode is used in lithium batteries.

[0013] Principles and advantages of the present invention:

[0014] First, the present invention uses a mixed ball milling process of graphite and hard carbon, utilizing the mechanical shearing effect of hard carbon particles to assist in exfoliating the graphite layer, forming a composite structure of graphene and hard carbon. The introduction of hard carbon not only promotes efficient exfoliation of graphite, but also optimizes the conductive network and lithium ion diffusion path of the composite material through its disordered porous properties. The graphite-based negative electrode for fast-charging lithium batteries prepared by the present invention has high-rate charge and discharge performance and ultra-long cycle stability. After 3000 cycles under 10C high-current charge and discharge conditions, the capacity retention rate is as high as 83.3%, and after approximately 150 cycles of high-current activation, its rate performance is further significantly improved.

[0015] 2. The present invention solves the problem of easy lithium deposition and rapid capacity decay of traditional graphite negative electrodes at high rates, while avoiding the defects of high preparation cost and complex process of single graphene materials. It is suitable for fields with strict requirements on fast charging performance, such as electric vehicles and high-power energy storage equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 SEM images of the negative electrode materials prepared in Examples 1 to 3 and Comparative Examples 1 to 2, where a is Gr-bm, b is Gr75, c is Gr50, d is Gr25, and e is HC-bm;

[0017] Figure 2 The mass of graphene separated from four graphene solutions with different mass fractions;

[0018] Figure 3 Raman spectra of the negative electrode materials prepared in Example 1 and Comparative Examples 1-2;

[0019] Figure 4 XRD spectra of the negative electrode materials prepared in Example 1 and Comparative Examples 1-2;

[0020] Figure 5 SEM images of the negative electrode material prepared in Example 1 at different magnifications;

[0021] Figure 6Nitrogen adsorption isotherms of the negative electrode materials prepared in Example 1 and Comparative Examples 1-2;

[0022] Figure 7 Comparison of rate performance of lithium-ion half-cells assembled using Gr25, Gr50, G75, HC-bm, and Gr-bm, 1C=300mAg -1 ;

[0023] Figure 8 is the lithium ion diffusion coefficient of lithium ion half-cells assembled using Gr25, HC-bm, and Gr-bm, respectively;

[0024] Figure 9 Comparison of high-rate cycling performance of lithium-ion half-cells assembled using Gr25, HC-bm, and Gr-bm, 1C=300mAg -1 ;

[0025] Figure 10 This is a comparison of the rate performance of the lithium-ion half-cell assembled using Gr25 before and after high current activation;

[0026] Figure 11 A comparison of the rate performance of lithium-ion half-cells assembled using Gr25 and lithium-ion half-cells assembled using commercial graphite anodes;

[0027] Figure 12 The figure is a rate performance diagram of a lithium-ion half-cell assembled using GP25 prepared in Control Example 3;

[0028] Figure 13 Figure 4 is a rate performance diagram of a lithium-ion half-cell assembled using the GP prepared in Control Example 4;

[0029] Figure 14 This is a rate performance diagram of a lithium-ion half-cell assembled using Gr25 prepared in Example 1;

[0030] Figure 15 This is a rate performance diagram of a lithium-ion half-cell assembled using Gr25 prepared in Example 1 after cycling at a relatively high current (5C) for about 150 cycles;

[0031] Figure 16 These are rate performance graphs of a lithium-ion half-cell assembled using Gr25 prepared in Example 1, a lithium-ion half-cell assembled using Gr25 prepared in Example 1 and activated by a large current, a lithium-ion half-cell assembled using GP25 prepared in Control Example 3, and a lithium-ion half-cell assembled using GP prepared in Control Example 4 at different rates. DETAILED DESCRIPTION

[0032] Specific embodiment 1: This embodiment is a method for preparing a graphite-based negative electrode for a fast-charging lithium battery, which is specifically completed by the following steps:

[0033] 1. Preparation of graphite-hard carbon composite materials:

[0034] Putting graphite and hard carbon powder into a ball mill, adding grinding balls into the ball mill, and ball milling for a period of time to obtain a graphite-hard carbon composite material;

[0035] 2. Preparation of electrodes:

[0036] Graphite-hard carbon composite material, conductive carbon black Super P and PVDF powder are mixed evenly and ground for a period of time to obtain electrode powder; N-methylpyrrolidone is added to the electrode powder and stirred for a period of time to obtain electrode slurry; the electrode slurry is evenly coated on copper foil, and then pre-baked for a period of time, and then placed in a vacuum oven for further drying to obtain a graphite-based negative electrode for a fast-charging lithium battery.

[0037] The hard carbon powder described in step 1 of this embodiment is purchased from Foshan Pers Carbon Material Technology Co., Ltd. and its model is Kuraray Hard Carbon Type 1.

[0038] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that the mass fraction of graphite in the graphite-hard carbon composite material described in step 1 is 25% to 75%. The other steps are the same as those in specific embodiment 1.

[0039] Specific embodiment 3: This embodiment differs from specific embodiments 1 or 2 in that the grinding balls described in step 1 are made of zirconium oxide and have a diameter of 2 mm, 5 mm, or a mixture of the two. The other steps are the same as those of specific embodiments 1 or 2.

[0040] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that the ball milling speed in step 1 is 500-700 rpm, the ball milling time is 20-40 minutes, and the ball-to-material ratio in the ball milling process in step 1 is (5-15):1. The other steps are the same as specific embodiments 1 to 3.

[0041] Specific embodiment 5: This embodiment differs from Specific embodiments 1 to 4 in that the mass ratio of the graphite-hard carbon composite material, conductive carbon black Super P, PVDF powder, and N-methylpyrrolidone described in step 2 is (0.3g-0.5g):(0.03g-0.08g):(0.03g-0.08g):(1.5g-2.5g). The other steps are the same as Specific embodiments 1 to 4.

[0042] Specific embodiment 6: This embodiment differs from specific embodiments 1 to 5 in that the grinding time in step 2 is 10 to 20 minutes; the stirring speed in step 2 is 200 to 800 rpm, and the stirring time is 4 to 8 hours. The other steps are the same as specific embodiments 1 to 5.

[0043] Specific embodiment seven: The difference between this embodiment and specific embodiments one to six is that in step two, the electrode slurry is evenly coated on the copper foil with a coating thickness of 50μm to 200μm, and then pre-baked at 60℃ to 100℃ for 1h to 5h, and then placed in a vacuum oven at 80℃ to 150℃ and continued to dry for 10 to 20h to obtain the electrode.

[0044] The other steps are the same as those in Specific Embodiments 1 to 6.

[0045] Specific embodiment eight: This embodiment is an application of a graphite-based negative electrode for a fast-charging lithium battery in a lithium battery.

[0046] Specific embodiment 9: This embodiment differs from specific embodiments 1 to 8 in that the assembly of a lithium battery using a fast-charging lithium battery graphite-based negative electrode is completed in the following steps:

[0047] A fast-charging lithium battery graphite-based negative electrode is cut into 12mm diameter pieces using a punching machine to obtain the negative electrode piece. In a glove box under an argon atmosphere, the negative electrode battery housing, spring, gasket, lithium sheet, PP separator, negative electrode piece, and positive battery housing are stacked in this order. The diameters of the lithium sheet and negative electrode piece are 12mm, and the diameter of the separator is 19mm. 50μL of electrolyte is dripped onto each side of the separator. After sealing with a button cell sealing machine, a lithium-ion half-cell is obtained. The electrolyte is a mixture of ethylene carbonate, dimethyl carbonate, and diethyl carbonate in a volume ratio of 1:1:1, with the solvent being LiPF6 at a concentration of 1 mol / L. The other steps are the same as those in Specific Embodiments 1 to 8.

[0048] Specific embodiment 10: The difference between this embodiment and specific embodiments 1 to 9 is that the lithium ion half-cell is activated by 1C to 10C current for 50 to 200 cycles, and the 1C current density is 300mAg -1 , a lithium-ion half-cell with excellent rate performance is obtained. The other steps are the same as those in the first to ninth embodiments.

[0049] The following examples are used to verify the beneficial effects of the present invention:

[0050] Example 1: A method for preparing a graphite-based negative electrode for a fast-charging lithium battery is specifically completed by the following steps:

[0051] 1. Preparation of graphite-hard carbon composite materials:

[0052] Graphite and hard carbon powders were placed in a ball mill, grinding balls were added to the ball mill, and the mixture was ball milled at a speed of 600 rpm for 30 minutes to obtain a graphite-hard carbon composite material;

[0053] The mass fraction of graphite in the graphite-hard carbon composite material described in step 1 is 25%;

[0054] The hard carbon powder described in step 1 was purchased from Foshan Pers Carbon Material Technology Co., Ltd., and the model is Kuraray hard carbon type 1;

[0055] The grinding balls described in step 1 are made of zirconium oxide; the diameters of the grinding balls are 2 mm and 5 mm; the mass ratio of the grinding balls with a diameter of 2 mm to the grinding balls with a diameter of 5 mm is 1:1;

[0056] The ball-to-material ratio in the ball milling process described in step 1 is 10:1;

[0057] 2. Preparation of electrodes:

[0058] 0.4 g of graphite-hard carbon composite material, 0.05 g of conductive carbon black Super P and 0.05 g of PVDF powder were mixed evenly and ground for 10 min to obtain electrode powder; 2 g of N-methylpyrrolidone was added to the electrode powder and stirred at a speed of 500 rpm for 5 h to obtain electrode slurry; the electrode slurry was evenly coated on copper foil with a coating thickness of 100 μm, and then pre-baked at 80 ° C for 2 h, and then placed in a vacuum oven at 120 ° C for further drying for 12 h to obtain a graphite-based negative electrode for fast-charging lithium batteries (denoted as Gr25).

[0059] Example 2: This example differs from Example 1 in that the mass fraction of graphite in the graphite-hard carbon composite material described in step 1 is 50%; and the graphite-based negative electrode for a fast-charging lithium battery obtained in step 2 is designated Gr50. All other steps and parameters are the same as in Example 1.

[0060] Example 3: This example differs from Example 1 in that the mass fraction of graphite in the graphite-hard carbon composite material described in step 1 is 75%; and the graphite-based negative electrode for the fast-charging lithium battery obtained in step 2 is designated Gr75. All other steps and parameters are the same as in Example 1.

[0061] Comparative Example 1: This example differs from Example 1 in that the mass fraction of graphite in the graphite-hard carbon composite material described in Step 1 is 0%; and in Step 2, a hard carbon negative electrode material, designated HC-bm, is obtained. All other steps and parameters are the same as in Example 1.

[0062] Comparative Example 2: This example differs from Example 1 in that the mass fraction of graphite in the graphite-hard carbon composite material described in Step 1 is 100%; and in Step 2, a graphite negative electrode material, designated Gr-bm, is obtained. All other steps and parameters are the same as in Example 1.

[0063] Figure 1 SEM images of the negative electrode materials prepared in Examples 1 to 3 and Comparative Examples 1 to 2, where a is Gr-bm, b is Gr75, c is Gr50, d is Gr25, and e is HC-bm;

[0064] from Figure 1 It can be seen that the pure graphite after ball milling almost all presents a large layered graphite structure ( Figure 1 a), while the pure hard carbon after ball milling showed a sharp block structure and crushed hard carbon particles ( Figure 1 e), with the increase of hard carbon content in the mixed material ( Figure 1 b-1d), it can be clearly seen that the size of the graphite particles gradually decreases from large particles above 5μm (Gr-bm) to small particles of about 3.5μm and above (Gr75) and about 2.5μm (Gr50); and when the hard carbon content increases to 75% (Gr25), the graphite is exfoliated into a few-layer graphene of about 1μm, indicating that hard carbon plays an important role in the exfoliation of graphene during the ball milling process of the mixed material.

[0065] In order to quantify the content of graphene peeled off by ball milling at different ratios, four portions of 0.5g graphene were weighed and dissolved in four portions of anhydrous ethanol to prepare graphene solutions with mass fractions of 25%, 50%, 75% and 100%, respectively, namely Gr25, Gr50, Gr75 and Grbm. First, ultrasonic dispersion was performed for 30 minutes, and centrifuged at a speed of 10000rpm for 10 minutes. The supernatant liquid contained unseparated graphene. The supernatant liquid after centrifugation of the five samples was centrifuged for a second time at the same speed for 1 hour. After removing the supernatant liquid from the second centrifugation, the precipitate was dried and extracted, and the quality of the five precipitates was tested separately. Although the graphite content in Gr25 is the lowest, it has the relatively highest graphene content, such as Figure 2 shown.

[0066] Figure 2 The mass of graphene separated from four graphene solutions with different mass fractions;

[0067] Figure 2 This shows that by rationally designing the ball milling ratio of graphite and hard carbon, the exfoliation efficiency of graphene can be greatly improved.

[0068] Figure 3 Raman spectra of the negative electrode materials prepared in Example 1 and Comparative Examples 1-2;

[0069] from Figure 3 It can be seen that: located at 1352cm -1 (D belt) and 1580cm -1 The peaks of (G band) belong to sp 3 Type disorder and sp 2 HC-bm exhibits a strong D peak, indicating the presence of numerous defects, consistent with the characteristics of hard carbon. Furthermore, the peak intensity ratio between the D and G bands of Gr25 is greater than that of Gr-bm, indicating the introduction of more defects and electrochemically active centers on the material surface. The increased G' peak intensity of Gr25 compared to Gr-bm indicates the presence of few-layer graphene in Gr25, demonstrating successful graphene exfoliation.

[0070] Figure 4 XRD spectra of the negative electrode materials prepared in Example 1 and Comparative Examples 1-2;

[0071] from Figure 4 The results show that Gr25 matches the characteristic peaks of Gr, retaining the basic crystalline characteristics of graphite. The broadening of the 002 peak indicates that Gr25 has a higher degree of disorder than Gr-bm. In addition, the decrease in the intensity of the 002 peak indicates that Gr25 may have a smaller grain size. Combined with the Raman spectroscopy G' peak, which is consistent with the characteristics of few-layer graphene, further confirms the presence of graphene.

[0072] Figure 5 SEM images of the negative electrode material prepared in Example 1 at different magnifications;

[0073] from Figure 5 In a, it can be seen that there are a lot of few-layer graphene in the sample. Figure 5 b shows that graphene is closely distributed around the blocky hard carbon, which can increase the surface roughness, increase the surface area of the sample, and provide space for lithium ions; the uniform distribution of graphite on the hard carbon can also promote uniform lithium insertion during fast charging. Figure 5 As can be clearly seen in Figure c), Gr has a uniform flaky crystalline structure, while HC exhibits a unique amorphous structure. Gr25, on the other hand, exhibits a dense intercalation of graphite within hard carbon. This unique structure of hard carbon and exfoliated few-layer graphene effectively enhances lithium-ion mass transfer, thereby improving surface lithiophilicity, reducing the occurrence of dead lithium, and improving fast-charging performance.

[0074] Figure 6 Nitrogen adsorption isotherms of the negative electrode materials prepared in Example 1 and Comparative Examples 1-2;

[0075] from Figure 6 It can be seen that Gr25 has the largest specific surface area of 22.9551m due to its special structure. 2 g -1HC-bm and Gr-bm showed blocky structures with small surface areas of 19.8289m 2 g -1 and 10.5598m 2 g -1 The presence of graphene in Gr25 determines its large specific surface area, which illustrates the superiority of the Gr25 structural design.

[0076] Assembling a lithium-ion half-cell is done by following these steps:

[0077] The fast-charging lithium battery graphite-based negative electrode (Gr25) prepared in Example 1 was cut into pole pieces with a diameter of 12 mm using a punching machine to obtain a negative pole piece; in a glove box under an argon atmosphere, the negative electrode battery shell, spring sheet, gasket, lithium sheet, PP diaphragm, negative pole piece, and positive battery shell were stacked in this order; wherein the diameter of the lithium sheet and the negative pole piece was 12 mm, the diameter of the diaphragm was 19 mm, 50 μL of electrolyte was dripped on both sides of the diaphragm, and after sealing with a button battery sealing machine, a lithium ion half-cell was obtained; the electrolyte was a solvent in which ethylene carbonate, dimethyl carbonate, and diethyl carbonate were mixed in a volume ratio of 1:1:1, the solvent was LiPF6, and the concentration of LiPF6 was 1 mol / L;

[0078] According to the above method, Gr50, G75, HC-bm, and Gr-bm were cut into pole pieces with a diameter of 12 mm, and then assembled into lithium-ion half-cells;

[0079] Test the rate performance of lithium-ion half-cells assembled with five different materials, see Figure 7 As shown;

[0080] Figure 7 Comparison of rate performance of lithium-ion half-cells assembled using Gr25, Gr50, G75, HC-bm, and Gr-bm, 1C=300mAg -1 ;

[0081] from Figure 7 It can be seen that at 0.2C, Gr-bm has a much higher specific capacity than HC-bm, indicating that graphite has a higher energy density; while at 10C, HC-bm has a much higher specific capacity than Gr-bm, indicating that hard carbon has a better rate performance. After the two materials were mixed and ball-milled, Gr25 showed a higher energy density (0.2C 292.7mAh g -1 , slightly lower than Gr bm324.4mAh g -1 , much higher than HC bm: 197.2mAh g -1 ) and excellent rate performance (10C123.3mAh g -1, even better than HC bm: 107.5mAh g -1 , much higher than Gr bm: 25mAh g -1 ), and compared to the other two materials with different ratios, Gr50 and Gr75, it has a significant advantage in capacity at high currents. This demonstrates its excellent overall performance. By rationally designing the composite ratio of graphite and hard carbon, the respective advantages of graphite and hard carbon can be fully utilized, achieving a good synergistic effect between graphite and hard carbon.

[0082] The lithium ion diffusion coefficients of three half-cells were tested by GITT. Figure 8 As shown;

[0083] Figure 8 is the lithium ion diffusion coefficient of lithium ion half-cells assembled using Gr25, HC-bm, and Gr-bm, respectively;

[0084] from Figure 8 It can be seen that Gr25 has the main lithium storage potential of graphite (platform area: about 0.01~0.2V vs.Li / Li + ) has a lithium ion diffusion coefficient significantly better than Gr-bm, and in the main lithium storage potential of hard carbon (slope region: >0.05V vs.Li / Li + ) at most potentials. The advantage of Gr25 in lithium ion diffusion coefficient at various potentials contributes to its good rate performance.

[0085] The cycling performance of lithium-ion half-cells assembled with Gr-bm, Gr25, and HC-bm was tested at a high current of 10C. Figure 9 As shown;

[0086] Figure 9 Comparison of high-rate cycling performance of lithium-ion half-cells assembled using Gr25, HC-bm, and Gr-bm, 1C=300mAg -1 ;

[0087] from Figure 9 It can be seen that the Gr-bm has poor rate performance, with the capacity dropping to 43.5% of its maximum capacity around 1500 cycles. The HC-bm, which has better rate performance, also drops to 80% of its maximum capacity around 1440 cycles. However, the Gr25 exhibits excellent high-rate cycling performance. After 3000 cycles at 10C, the remaining capacity is still 83.3% of its maximum capacity, demonstrating the excellent high-current cycling performance of the Gr25.

[0088] After about 150 cycles of high current (5C) for lithium-ion half-cells assembled with Gr25, the rate performance was further improved, such as Figure 10 shown.

[0089] Figure 10 This is a comparison of the rate performance of the lithium-ion half-cell assembled using Gr25 before and after high current activation;

[0090] Figure 10 The rate performance of lithium-ion half-cells assembled using Gr25 at different rates;

[0091] from Figure 10 It can be seen that after high current cycling, the 10C capacity is 123mAh g -1 Increased to 164mAh g -1 , increased by 41mAh g -1 ; 5C capacity has increased most significantly, from 140mAh g -1 Increased to 228mAh g -1 , increased by 88mAh g -1 This indicates that high current activation can significantly improve the rate performance of Gr25.

[0092] In order to verify the practical application potential of Gr25 materials, a high-loaded Gr25 electrode (~9 mg cm) with the same loading amount of active material as commercial graphite anode was prepared. -2 ), and the rate performance test was carried out, see Figure 11 As shown;

[0093] Figure 11 A comparison of the rate performance of lithium-ion half-cells assembled using Gr25 and lithium-ion half-cells assembled using commercial graphite anodes;

[0094] from Figure 11 It can be seen that at 0.2C, due to the large theoretical capacity of graphite, the specific capacity of commercial graphite electrodes is relatively high. When the current density is increased to 1C and above, Gr25 shows a higher specific capacity. This shows that the rate performance of Gr25 at high loading is better than that of current commercial graphite anodes, showing great potential application value.

[0095] In order to verify the superiority of graphite + hard carbon + graphene electrode materials, graphene + hard carbon negative electrode materials were prepared as follows:

[0096] Comparative Example 3: This example differs from Example 1 in that the graphite in step 1 is replaced with physically produced few-layer graphene purchased from Suzhou Tanfeng Graphene Technology Co., Ltd.; the mass fraction of graphene in the graphene-hard carbon composite material obtained in step 1 is 25%; and the negative electrode material obtained in step 2 is designated GP25. All other steps and parameters are the same as in Example 1.

[0097] Comparative Example 4: This example differs from Example 1 in that the graphite in step 1 is replaced with physically prepared few-layer graphene purchased from Suzhou Tanfeng Graphene Technology Co., Ltd.; the mass fraction of graphene in the graphene-hard carbon composite material obtained in step 1 is 100%; and the negative electrode material obtained in step 2 is designated GP. All other steps and parameters are the same as in Example 1.

[0098] According to the above method, GP25 and GP were cut into pole pieces with a diameter of 12 mm, and then assembled into lithium-ion half-cells.

[0099] Figure 12 The figure is a rate performance diagram of a lithium-ion half-cell assembled using GP25 prepared in Control Example 3;

[0100] Figure 13 Figure 4 is a rate performance diagram of a lithium-ion half-cell assembled using the GP prepared in Control Example 4;

[0101] Figure 14 This is a rate performance diagram of a lithium-ion half-cell assembled using Gr25 prepared in Example 1;

[0102] Figure 15 This is a rate performance diagram of a lithium-ion half-cell assembled using Gr25 prepared in Example 1 after cycling at a relatively high current (5C) for about 150 cycles;

[0103] from Figures 12 to 15 It can be seen that the rate performance of Gr25 (10C 123.3mAh g -1 ) is superior to the rate performance of GP and GP25 (10C 7.5mAh g -1 ,70mAh g -1 ), indicating that the electrode material containing graphite, hard carbon, and graphene prepared by hard carbon-assisted exfoliation of graphite has a significant improvement in rate compared to pure graphene and graphene-hard carbon mixed negative electrodes. In addition, after 150 cycles of high current (5C) activation, Gr25 showed further improved rate performance (10C 164.2mAh g -1 ).

[0104] The lithium ion half-cell assembled with Gr25 prepared in Example 1 was activated for 150 cycles at a high current of 5C, and then its rate performance at different rates was tested. Figure 16 As shown in the curve after Gr25 activation;

[0105] Figure 16The figure shows the rate performance of a lithium ion half-cell assembled using Gr25 prepared in Example 1, a lithium ion half-cell assembled using Gr25 prepared in Example 1 after high current activation, a lithium ion half-cell assembled using GP25 prepared in Control Example 3, and a lithium ion half-cell assembled using GP prepared in Control Example 4 at different rates;

[0106] from Figure 16 It can be seen that the graphene produced by the hard carbon-assisted exfoliation of graphite prepared by the present invention has better rate performance than pure graphene and a mixture of graphene and hard carbon, and the performance is improved after high current activation.

Claims

1. A method for preparing a graphite-based negative electrode for a fast-charging lithium battery, characterized in that The preparation method is specifically completed according to the following steps:

1. Preparation of graphite-hard carbon composite materials: Putting graphite and hard carbon powder into a ball mill, adding grinding balls into the ball mill, and ball milling for a period of time to obtain a graphite-hard carbon composite material; 2. Preparation of electrodes: Graphite-hard carbon composite material, conductive carbon black Super P and PVDF powder are mixed evenly and ground for a period of time to obtain electrode powder; N-methylpyrrolidone is added to the electrode powder and stirred for a period of time to obtain electrode slurry; the electrode slurry is evenly coated on copper foil, and then pre-baked for a period of time, and then placed in a vacuum oven for further drying to obtain a graphite-based negative electrode for a fast-charging lithium battery.

2. The method for preparing a graphite-based negative electrode for a fast-charging lithium battery according to claim 1, characterized in that The mass fraction of graphite in the graphite-hard carbon composite material described in step 1 is 25% to 75%.

3. The method for preparing a graphite-based negative electrode for a fast-charging lithium battery according to claim 1, characterized in that The grinding balls in step 1 are made of zirconium oxide; the diameter of the grinding balls is 2 mm, 5 mm, or a mixture of the two diameters.

4. The method for preparing a graphite-based negative electrode for a fast-charging lithium battery according to claim 1, characterized in that The ball milling speed in step 1 is 500 rpm to 700 rpm, and the ball milling time is 20 min to 40 min; the ball-to-material ratio in the ball milling process in step 1 is (5 to 15):

1.

5. The method for preparing a graphite-based negative electrode for a fast-charging lithium battery according to claim 1, characterized in that The mass ratio of the graphite-hard carbon composite material, conductive carbon black Super P, PVDF powder and N-methylpyrrolidone described in step 2 is (0.3g~0.5g):(0.03g~0.08g):(0.03g~0.08g):(1.5g~2.5g).

6. The method for preparing a graphite-based negative electrode for a fast-charging lithium battery according to claim 1, characterized in that The grinding time in step 2 is 10 min to 20 min; the stirring speed in step 2 is 200 rpm to 800 rpm, and the stirring time is 4 h to 8 h.

7. The method for preparing a graphite-based negative electrode for a fast-charging lithium battery according to claim 1, characterized in that In step 2, the electrode slurry is evenly coated on the copper foil with a coating thickness of 50μm to 200μm, and then pre-baked at 60℃ to 100℃ for 1h to 5h, and then placed in a vacuum oven at 80℃ to 150℃ for further drying for 10 to 20h to obtain the electrode.

8. Application of a graphite-based negative electrode for a fast-charging lithium battery prepared by the preparation method according to claim 1, characterized in that A fast-charging lithium battery graphite-based negative electrode is used in lithium batteries.

9. The application of a graphite-based negative electrode for a fast-charging lithium battery according to claim 8, characterized in that The assembly of a lithium battery using a fast-charging lithium battery graphite-based negative electrode is specifically completed in the following steps: A sheet punching machine is used to cut the graphite-based negative electrode of a fast-charging lithium battery into electrodes with a diameter of 12 mm to obtain negative electrode electrodes; in a glove box under an argon atmosphere, the negative electrode battery shell, spring sheet, gasket, lithium sheet, PP diaphragm, negative electrode electrode sheet, and positive electrode battery shell are stacked in this order; wherein, the diameter of the lithium sheet and the negative electrode electrode sheet is 12 mm, the diameter of the diaphragm is 19 mm, 50 μL of electrolyte is dripped on both sides of the diaphragm, and after sealing with a button battery sealing machine, a lithium ion half-cell is obtained; the electrolyte is a mixture of ethylene carbonate, dimethyl carbonate and diethyl carbonate in a volume ratio of 1:1:1, the solvent is LiPF6, and the concentration of LiPF6 is 1 mol / L.

10. The application of a graphite-based negative electrode for a fast-charging lithium battery according to claim 9, characterized in that The lithium ion half-cell is activated by 1C to 10C current for 50 to 200 cycles, and the 1C current density is 300mA g -1 , obtaining a lithium-ion half-battery with excellent rate performance.

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