Preparation method of porous expanded-layer natural spherical graphite

Abstract

The invention discloses a preparation method of porous expanded-layer natural spherical graphite, and relates to a preparation method of a lithium ion battery negative electrode material, in particular to the preparation method of the porous expanded-layer natural spherical graphite. The invention aims to solve the technical problems of poor rapid charging performance and poor rate capability of natural graphite at present. Alkali and natural spherical graphite are fully mixed in the wet treatment process, solid particles of the alkali are attached to the surface of the natural spherical graphite after suction filtration, the alkali particles react with the graphite through high-temperature treatment, micropores are generated at reaction sites, and the graphite is subjected to high-temperature treatment. In addition, reduced alkali metal generated in the reaction process can be embedded between graphite layers to achieve the layer expansion effect and is converted into corresponding salt and oxide to be separated from the layers after the reaction, the layer expansion effect is irreversible, transmission channels and deintercalation sites of Li < + > are increased through layer expansion, the resistance of Li < + > deintercalation and intercalation between the graphite layers is reduced, and the performance of the lithium ion battery is improved. Therefore, the quick charging capability and the rate capability of the natural spherical graphite are improved.

Description

Technical Field

[0001] The invention relates to a method for preparing a lithium ion battery negative electrode material, in particular to a method for preparing porous expanded-layer natural spherical graphite. Background Art

[0002] Energy is an essential material foundation for human survival and the progress of social civilization. With the rapid development of the global economy and industrialization, human demand for energy has increased significantly, and energy supplies have become more diverse. However, overexploitation and continuous consumption of non-renewable fossil fuels such as oil, coal, and natural gas have led to a year-on-year decline in reserves, posing a risk of depletion. Furthermore, excessive fossil fuel use emits large amounts of greenhouse gases, harmful smoke, and airborne particulates, which are degrading the environment. To address the impending depletion of fossil fuels and the environmental problems associated with their use, people are seeking green and renewable energy alternatives, such as solar and wind power. However, these energy sources are intermittent and regional, and typically exist in the form of electricity, requiring advanced and stable energy storage systems to ensure a stable output. Among the various energy storage batteries, lithium-ion batteries have attracted considerable attention and research.

[0003] Lithium-ion batteries (LIBs) are relatively convenient energy storage devices that convert chemical energy into electrical energy for human use. Since Sony Corporation of Japan officially commercialized lithium-ion batteries (LIBs) in 1990, they have attracted widespread attention from researchers both domestically and internationally. Due to their advantages, such as low delithiation potential, high operating voltage, abundant resources, environmental friendliness, high specific energy, and lack of memory effect, LIBs have gained widespread application in electronic devices such as mobile phones, laptops, and digital cameras. The transition of high-energy-density lithium-ion batteries from electronic devices to electric vehicles and energy storage technology is inevitable. Electric vehicles powered by LIBs are rapidly developing, with production and sales continuing to grow rapidly. Despite this growth, the prolonged charging time of electric vehicles compared to gasoline vehicles limits their further adoption. This, in turn, places higher demands on the charging speed of LIB systems, requiring batteries with superior rate performance. Therefore, while maintaining the safety, environmental protection, low cost and long cycle life of LIBs, improving their fast charging performance and power characteristics is of great significance to promoting the development of industries such as electric vehicles, consumer electronic devices, and energy storage technologies. Among them, the performance of lithium-ion battery electrode materials has a significant impact on all aspects of lithium-ion battery performance.

[0004] In terms of negative electrode materials for lithium-ion batteries, carbon materials occupy a dominant position in the market due to their low cost and wide distribution of resources. Graphite, hard carbon and soft carbon are all carbon negative electrode materials. Graphite is the most commonly used negative electrode material in LIBs, with advantages such as high energy density, low voltage, good conductivity, abundant resources and low price. Graphite materials include artificial graphite and natural graphite, and will remain the first choice for LIBs negative electrode materials for a long time to come. Graphite materials have high crystallinity, a lamellar structure, a low lithium insertion potential, and good cycle stability and safety. However, traditional LIBs using graphite negative electrode materials are affected by slow lithium diffusion kinetics and lithium metal plating. Under fast charging conditions, these limitations hinder the growing demand for fast charging and discharging applications.

[0005] At present, the methods to solve the poor fast charging performance and rate performance of graphite negative electrode mainly include surface modification, coating and doping with modified elements. The literature (Guo Dechao, Zeng Xierong, Deng Fei, et al. Preparation and electrochemical properties of micro-expanded graphite lithium ion battery negative electrode materials [J]. New Carbon Materials, 2015, 30 (5): 419-424.) uses potassium permanganate and concentrated sulfuric acid to oxidize and intercalate graphite to obtain micro-expanded layered graphite. The larger interlayer spacing (0.336nm) of micro-expanded layered graphite is more conducive to Li + The diffusion of boron-oxygen functional groups on the graphite surface was effectively improved, and the capacity retention rate of graphite at 2C rate was better than that of the original state (96.9%, graphite 94.5%). The literature (YEO JS, PARK TH, SEO MH, et al. Enhancement of the rate capability of graphite via the introduction of boron-oxygen functional groups [J]. International Journal of Electrochemical Science, 2013, 8 (1): 1308-1315.) used boric acid ball milled graphite and introduced B-O functional groups on the graphite surface after heat treatment at 1000 ° C, which effectively reduced the Li +The migration barrier and charge transfer resistance of the anode are reduced, and the specific capacity of the anode is still as high as 330 mAh / g at a 5C rate, showing excellent fast charging performance. The literature (HAN YJ, KIM J, YEO JS, et al. Coating of graphite anode with coal tar pitch as an effective precursor for enhancing the rate performance in lithium batteries: Effects of composition and softening points of coal tar pitch [J]. Carbon, 2015, 94: 432-438.) forms a uniform carbon coating on the graphite surface through high-temperature pyrolysis of pitch, reducing the charge transfer resistance between the graphite anode material and the electrolyte, thereby improving the rate performance of the graphite. The specific capacity of the material reaches 298 mAh / g at a 5C rate, an increase of 192% compared to the control group. However, the above solution still has problems such as complex process, cumbersome technology, and high raw material costs.

[0006] Therefore, by adopting a more efficient modification method of strong alkali treatment, the purpose of pore formation and layer expansion of natural spherical graphite is achieved to minimize Li + The diffusion resistance in graphite lays a good foundation for the practical application of graphite negative electrodes for fast charging of lithium-ion batteries, and has a very important research significance for further improving the fast charging performance of lithium-ion batteries. Summary of the Invention

[0007] The present invention aims to solve the technical problems of poor rapid charging performance and poor rate performance of current natural graphite, and provides a method for preparing porous expanded-layer natural spherical graphite.

[0008] The preparation method of the porous expanded layer natural spherical graphite of the present invention is carried out according to the following steps:

[0009] 1. Wet treatment: dissolve strong alkali in deionized water, then add natural spherical graphite to the strong alkali solution and stir thoroughly;

[0010] The mass ratio of the strong alkali to the natural spherical graphite is 2:(0.8-1.2);

[0011] 2. Pour the mixed solution after step 1 into a Buchner funnel for suction filtration, and then dry the filter cake in a vacuum drying oven;

[0012] 3. Pre-calcine the dried product in step 2 under a protective atmosphere, then heat it to 800°C to 850°C and keep it at that temperature for 1h to 1.5h, cool it naturally to room temperature and then take out the product;

[0013] The pre-firing temperature is 200°C to 220°C;

[0014] Fourth, the product obtained in step 3 is added with water and filtered to remove soluble impurities, and then dried in a drying oven, and fully ground to obtain porous expanded layer natural spherical graphite.

[0015] The present invention uses a wet alkali treatment method to mix alkali and natural spherical graphite, filter it, vacuum dry it, and then place it in a protective atmosphere for high-temperature treatment. The obtained product is then filtered, and after filtering out soluble impurities, it is dried and ground to obtain porous expanded natural spherical graphite. During the wet treatment process, the alkali and natural spherical graphite are fully mixed, and after filtration, the solid particles of the alkali are attached to the surface of the natural spherical graphite. The high-temperature treatment causes the alkali particles to react with the graphite, generating micropores at the reaction sites, and the reduced alkali metal generated during the reaction process is also embedded in the graphite interlayer to achieve a certain expansion effect, and after the reaction, it is converted into corresponding salts and oxides and removed from the interlayer. The expansion effect is irreversible, and the expansion increases Li + transmission channels and deintercalation sites, reducing the Li + The resistance of natural spherical graphite to escape and embedding in the graphite layers is reduced, thereby increasing the fast charging ability and rate performance of natural spherical graphite to a certain extent. In terms of cycle performance, after the different alkali-modified materials prepared by the present invention are used as the positive electrode and assembled into a half-cell with a lithium sheet as the negative electrode, at a high current density of 1C, the initial charge capacity of LiOH-21800, NaOH-21800 and KOH-21800 are 282.9mAh / g, 255.7mAh / g and 360.7mAh / g, respectively. After 500 cycles, the capacity retention rates are as high as 103.3%, 97.8% and 73.9%, respectively. In terms of rate performance, at a high current of 5C, the charge capacity of LiOH-21800, NaOH-21800 and KOH-21800 can reach 211.8mAh / g, 91.1mAh / g and 57.3mAh / g, respectively. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 XRD patterns of porous expanded-layer natural spherical graphite prepared for experiments 1 to 3 and untreated natural spherical graphite;

[0017] Figure 2 These are SEM images of natural spherical graphite without any treatment in step 1 of experiment 1 at different magnifications;

[0018] Figure 3SEM images of LiOH-21800 prepared in Experiment 1 at different magnifications;

[0019] Figure 4 SEM images of NaOH-21800 prepared in Experiment 2 at different magnifications;

[0020] Figure 5 SEM images of KOH-21800 prepared in Experiment 3 at different magnifications;

[0021] Figure 6 The rate performance diagram of the battery assembled for test 4 and the comparative test;

[0022] Figure 7 The first cycle charge and discharge curves of the assembled battery in test 4 and the comparative test at 0.1C;

[0023] Figure 8 Comparison of the performance curves of the assembled batteries in Test 4 and the comparative test after 100 cycles at 0.2C;

[0024] Figure 9 This is a comparison chart of the performance curves of the assembled batteries in test four and the comparative test after 500 cycles at 1C. DETAILED DESCRIPTION

[0025] Specific embodiment 1: This embodiment is a method for preparing porous expanded layer natural spherical graphite, which is specifically carried out according to the following steps:

[0026] 1. Wet treatment: dissolve strong alkali in deionized water, then add natural spherical graphite to the strong alkali solution and stir thoroughly;

[0027] The mass ratio of the strong alkali to the natural spherical graphite is 2:(0.8-1.2);

[0028] 2. Pour the mixed solution after step 1 into a Buchner funnel for suction filtration, and then dry the filter cake in a vacuum drying oven;

[0029] 3. Pre-calcine the dried product in step 2 under a protective atmosphere, then heat it to 800°C to 850°C and keep it at that temperature for 1h to 1.5h, cool it naturally to room temperature and then take out the product;

[0030] The pre-firing temperature is 200°C to 220°C;

[0031] Fourth, the product obtained in step 3 is added with water and filtered to remove soluble impurities, and then dried in a drying oven, and fully ground to obtain porous expanded layer natural spherical graphite.

[0032] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that the strong base in step 1 is lithium hydroxide, sodium hydroxide or potassium hydroxide. Other steps are the same as those in specific embodiment 1.

[0033] Specific embodiment 3: This embodiment differs from specific embodiment 1 or 2 in that the mass ratio of the strong base to the natural spherical graphite in step 1 is 2:1. Other aspects are the same as specific embodiment 1 or 2.

[0034] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that the stirring in step 1 is magnetic stirring for 1 hour. Other aspects are the same as specific embodiments 1 to 3.

[0035] Specific embodiment 5: This embodiment differs from specific embodiment 4 in that the drying temperature in step 2 is 100° C. The rest is the same as specific embodiment 4.

[0036] Specific embodiment 6: This embodiment differs from specific embodiment 5 in that the drying time in step 2 is 12 hours. Other aspects are the same as specific embodiment 5.

[0037] Specific embodiment 7: This embodiment differs from specific embodiment 6 in that the protective atmosphere in step 3 is a mixture of H2 and Ar, wherein H2 accounts for 5% by volume and the rest is Ar. Other aspects are the same as specific embodiment 6.

[0038] Specific embodiment eight: This embodiment differs from specific embodiment seven in that the pre-burning time in step three is 30 minutes. Other aspects are the same as specific embodiment seven.

[0039] Specific embodiment 9: This embodiment differs from specific embodiment 8 in that the heating rate for heating to 800°C-850°C after pre-sintering in step 3 is 10°C / min. Other aspects are the same as specific embodiment 8.

[0040] Specific embodiment 10: This embodiment differs from specific embodiment 9 in that the drying temperature in step 4 is 100° C. The rest is the same as specific embodiment 9.

[0041] The present invention is verified by the following test:

[0042] Experiment 1: This experiment is a method for preparing porous expanded layer natural spherical graphite, which is specifically carried out according to the following steps:

[0043] 1. Wet treatment: Dissolve 6 g of strong alkali in 40 mL of deionized water, then add 3 g of natural spherical graphite to the strong alkali solution, and then stir and mix on a magnetic stirrer for 1 hour;

[0044] The strong base is lithium hydroxide;

[0045] 2. Pour the mixed solution after step 1 into a Buchner funnel for suction filtration, and then dry the filter cake in a vacuum drying oven for 12 hours at a drying temperature of 100°C;

[0046] 3. Pre-calculate the dried product in step 2 under a protective atmosphere for 30 minutes, then heat it to 800°C at a heating rate of 10°C / min and keep it at that temperature for 1 hour. Then cool it naturally to room temperature and take out the product;

[0047] The protective atmosphere is a mixture of H2 and Ar, wherein H2 accounts for 5% by volume and the rest is Ar gas;

[0048] The pre-firing temperature is 200°C;

[0049] 4. The product obtained in step 3 was added with water and filtered to remove soluble impurities, and then dried in a drying oven at a temperature of 100° C., and then fully ground to obtain porous expanded layer natural spherical graphite, which was recorded as LiOH-21800.

[0050] Experiment 2: This experiment differs from Experiment 1 in that the strong base in step 1 is sodium hydroxide, and the resulting porous expanded-layer natural spherical graphite is designated as NaOH-21800. Other conditions are the same as Experiment 1.

[0051] Experiment 3: This experiment differs from Experiment 1 in that the strong base in step 1 is potassium hydroxide, and the resulting porous expanded-layer natural spherical graphite is designated as KOH-21800. Other conditions are the same as Experiment 1.

[0052] Experiment 4: The porous expanded layer natural spherical graphite obtained in experiments 1, 2 and 3 after treatment with three different strong alkalis was mixed with a conductive agent and a binder to form a positive electrode, which was assembled with a lithium sheet (negative electrode) into a CR2032 button half-cell and tested.

[0053] Comparative test: The difference between this test and test 4 is that untreated natural spherical graphite is mixed with a conductive agent and a binder to form a positive electrode. The rest is the same as test 4, recorded as NG sample battery and tested.

[0054] Figure 1The XRD patterns of the porous expanded layer natural spherical graphite prepared in experiments 1 to 3 and the untreated natural spherical graphite are shown. All diffraction peaks in the spectrum show the lamellar structure unique to graphite, and no diffraction peaks of any other impurities are observed. The peaks are sharp and clear, the diffraction peak intensity is high, and the crystallinity is good. The porous expanded layer natural spherical graphite prepared in experiments 1 to 3 are all pure phases. The strong alkali treatment did not change the layered crystal structure of the original material, but the graphite characteristic peak (002) was left-biased to varying degrees, which indicates that the interlayer spacing has expanded to varying degrees. As the ionic radius of the alkali metal cation increases, the degree of interlayer expansion increases. This shows that the strong alkali treatment can produce an expansion effect on the natural spherical graphite, and the increase in interlayer spacing can reduce Li + Diffusion resistance between graphite layers.

[0055] Table 1 is Figure 1 From the graphite interlayer spacing data of the samples in , it can be seen that the interlayer spacing of natural spherical graphite increases to varying degrees after alkali treatment, and with the increase of the radius of alkali metal ions, the interlayer spacing also gradually increases.

[0056] Table 1

[0057] 2θ(°)(002) d(nm) NG 26.3877 0.3375 LiOH-21800 26.1652 0.3403 NaOH-21800 26.1247 0.3408 KOH-21800 26.1045 0.3410

[0058] Figure 2 These are SEM images of natural spherical graphite without any treatment in step 1 of experiment 1 at different magnifications, with Figures a, b, and c being magnified 2000 times, 5000 times, and 10000 times, respectively. Figure 3 These are the SEM images of LiOH-21800 prepared in experiment 1 at different magnifications. Figures a, b, and c are magnified 2000 times, 5000 times, and 10000 times, respectively. Figure 4 These are the SEM images of NaOH-21800 prepared in Experiment 2 at different magnifications. Figures a, b, and c are magnified 2000x, 5000x, and 10000x, respectively. Figure 5 The SEM images of KOH-21800 prepared in Experiment 3 at different magnifications are shown in Figures a, b, and c at 2000, 5000, and 10000 times, respectively. It can be seen from the figures that micropores appear on the surface of natural spherical graphite after different alkali treatments, and the surface roughness of graphite particles increases. The appearance of micropores on the surface of the material can increase Li + The embedded channels and more electrochemical reaction sites in the graphite basal plane increase the activity of the electrochemical reaction and reduce the Li + Resistance to diffusion.

[0059] Figure 6 This is the rate performance diagram of the battery assembled in test 4 and the comparative test. Figure 7 The first cycle charge and discharge curves of the assembled battery in test 4 and comparison test at 0.1C are shown in Table 2. Figure 6 The corresponding data show that at a high current density of 5C, the charge specific capacities of NG, LiOH-21800, NaOH-21800, and KOH-21800 are 44 mAh / g, 211.8 mAh / g, 91.1 mAh / g, and 57.3 mAh / g, respectively. At a high current density of 2C, the charge specific capacities of NG, LiOH-21800, NaOH-21800, and KOH-21800 are 137.1 mAh / g, 244.3 mAh / g, 142.5 mAh / g, and 159 mAh / g, respectively. In summary, at high current density, the rate performance of the modified materials is significantly improved compared to the original natural spherical graphite.

[0060] Table 2

[0061]

[0062] Figure 8 This is a comparison chart of the performance curves of the assembled batteries in test 4 and the comparative test after 100 cycles at 0.2C. Figure 9 The performance curve comparison of the assembled battery in test 4 and the comparative test at 1C cycle 500 cycles is shown in Table 3. Figure 9 From the data, we can see that the corresponding batteries of LiOH-21800, NaOH-21800, and KOH-21800 can reach a capacity of 282.9mAh / g, 255.7mAh / g, and 360.7mAh / g during the 1C cycle, and the capacity retention rates can reach 103.3%, 97.8%, and 73.9%, respectively. The capacity of NG at 1C is 269.9mAh / g, and the capacity retention rate is 66%. This shows that the modification of natural spherical graphite by different alkali treatments makes its performance of high current and long cycle better.

[0063] Table 3

[0064]

Claims

1. A method for preparing porous expanded layer natural spherical graphite, characterized in that The preparation method of porous expanded layer natural spherical graphite is carried out according to the following steps:

1. Wet treatment: dissolve the strong alkali in deionized water, then add natural spherical graphite to the strong alkali solution, and then stir and mix thoroughly; The mass ratio of the strong alkali to the natural spherical graphite is 2:(0.8-1.2); 2. Pour the mixed solution after step 1 into a Buchner funnel for suction filtration, and then dry the filter cake in a vacuum drying oven; 3. Pre-calculate the dried product in step 2 under a protective atmosphere, then heat it to 800°C to 850°C and keep it for 1h to 1.5h, cool it naturally to room temperature and then take out the product; The pre-burning temperature is 200°C to 220°C; Fourth, the product obtained in step 3 is added with water and filtered to remove soluble impurities, and then dried in a drying oven, and after sufficient grinding, porous expanded layer natural spherical graphite is obtained.

2. The method for preparing a porous expanded layer natural spherical graphite according to claim 1, characterized in that The strong base described in step 1 is lithium hydroxide, sodium hydroxide or potassium hydroxide.

3. The method for preparing a porous expanded layer natural spherical graphite according to claim 1, characterized in that The mass ratio of the strong alkali and the natural spherical graphite described in step 1 is 2:

1.

4. The method for preparing a porous expanded layer natural spherical graphite according to claim 1, characterized in that The stirring in step 1 is magnetic stirring for 1 h.

5. The method for preparing a porous expanded layer natural spherical graphite according to claim 1, characterized in that The drying temperature in step 2 is 100°C.

6. The method for preparing a porous expanded layer natural spherical graphite according to claim 5, characterized in that The drying time in step 2 is 12 hours.

7. The method for preparing a porous expanded layer natural spherical graphite according to claim 1, characterized in that The protective atmosphere described in step 3 is a mixed gas of H2 and Ar, wherein H2 accounts for 5% by volume and the rest is Ar gas.

8. The method for preparing a porous expanded layer natural spherical graphite according to claim 1, characterized in that The pre-burning time in step 3 is 30 minutes.

9. The method for preparing a porous expanded layer natural spherical graphite according to claim 1, characterized in that In step 3, the temperature is raised to 800°C to 850°C after pre-sintering at a heating rate of 10°C / min.

10. The method for preparing a porous expanded layer natural spherical graphite according to claim 1, characterized in that The drying temperature in step 4 is 100°C.

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