Graphite negative electrode material and preparation method and application thereof

Abstract

The application discloses a graphite negative electrode material and a preparation method and application thereof. The graphite negative electrode material comprises artificial graphite and a coating layer uniformly coated on the surface of the artificial graphite, wherein the coating layer comprises an ion-conducting polymer and a lithium salt; the mass ratio of the artificial graphite and the ion-conducting polymer is 100:(1.8-10); and the mass ratio of the artificial graphite and the lithium salt is 100:(0.1-0.25). The graphite negative electrode material has excellent initial specific discharge capacity, initial coulombic efficiency and cycle stability.

Description

Technical Field

[0001] This invention relates to a graphite anode material, its preparation method, and its application. Background Technology

[0002] With the rapid development of electric vehicles and renewable energy storage systems, lithium-ion batteries are playing an increasingly important role in energy storage. Graphite, as a traditional anode material, is widely used due to its good conductivity and reversibility. However, during high-rate charge and discharge processes, graphite anodes often face problems of capacity decay and poor cycle stability, mainly due to the volume changes of lithium ions during charge and discharge and the formation of an unstable solid electrolyte interface (SEI).

[0003] During the charging process of traditional lithium-ion batteries, the electrolyte decomposes and forms an SEI film on the graphite surface, consuming lithium ions and leading to a decrease in initial coulombic efficiency. Furthermore, with continuous battery cycling, the expansion of the graphite negative electrode causes damage to the naturally formed SEI.

[0004] In recent years, research on constructing artificial SEI layers has gradually gained attention. Polymer-coated graphite can effectively regulate SEI formation, improve interfacial stability, and thus enhance the overall performance of the battery. Polymer coating not only provides mechanical protection for the graphite anode, reducing volume expansion during lithium-ion insertion and extraction, but also regulates ion conduction and interfacial reactions, forming a more ideal SEI layer. This design aims to enhance battery cycle life and safety, providing new insights for the development of high-performance lithium-ion batteries. Therefore, research on polymer-coated graphite anodes to construct artificial SEIs has significant theoretical and practical application value. However, the initial coulombic efficiency of polymer-coated graphite in current technologies still needs improvement. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art in which the initial discharge specific capacity, initial coulombic efficiency and cycle stability of polymer-coated graphite still need to be improved. The present invention provides a graphite anode material, its preparation method and application. The graphite anode material of the present invention has excellent initial discharge specific capacity, initial coulombic efficiency and cycle stability.

[0006] The present invention provides a graphite anode material comprising artificial graphite and a coating layer uniformly coated on the surface of the artificial graphite, wherein the coating layer comprises an ion-conducting polymer and a lithium salt; the mass ratio of the artificial graphite to the ion-conducting polymer is 100:(1.8-10); the mass ratio of the artificial graphite to the lithium salt is 100:(0.1-0.25).

[0007] In this invention, preferably, the particle size D50 of the artificial graphite is 6-8 μm, for example 7.25 μm.

[0008] In this invention, preferably, the aggregate coulombic efficiency of the artificial graphite is greater than 90%, for example 91%.

[0009] In this invention, preferably, the ion-conducting polymer is polyethylene oxide or polyurethane; the polyethylene oxide is, for example, polyethylene glycol; the polyurethane is, for example, waterborne polyurethane.

[0010] Preferably, the molecular weight of the polyethylene glycol is 18,000-22,000, for example, 20,000. In one embodiment of the invention, the polyethylene glycol is purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., with the product number P432531.

[0011] In one embodiment of the present invention, the aqueous polyurethane is purchased from Shanghai McLean Biochemical Technology Co., Ltd., with product number W909579.

[0012] In this invention, preferably, the lithium salt is selected from one or more of LiPF6, LiTFSI, LiBF4 and Li3PO4, for example, LiPF6 or LiTFSI.

[0013] In this invention, preferably, the mass ratio of the artificial graphite to the ion-conducting polymer is 100:(1.8-5), for example, 100:1.8.

[0014] In this invention, preferably, the mass ratio of the artificial graphite to the lithium salt is 100:(0.15-0.25), for example, 100:0.2.

[0015] In this invention, preferably, the mass ratio of the ion-conducting polymer to the lithium salt is (7.2-20):1, for example, 9:1.

[0016] The present invention also provides a method for preparing a graphite anode material, which includes the following steps: mixing artificial graphite with a polymer solution uniformly and drying;

[0017] The polymer solution comprises an ion-conducting polymer, a lithium salt, and a solvent; the mass ratio of the artificial graphite to the ion-conducting polymer is 100:(1.8-10); and the mass ratio of the artificial graphite to the lithium salt is 100:(0.1-0.25).

[0018] In this invention, preferably, the particle size D50 of the artificial graphite is 6-8 μm, for example 7.25 μm.

[0019] In this invention, preferably, the aggregate coulombic efficiency of the artificial graphite is greater than 90%, for example 91%.

[0020] In this invention, preferably, the ion-conducting polymer is polyethylene oxide or polyurethane; the polyethylene oxide is, for example, polyethylene glycol; the polyurethane is, for example, waterborne polyurethane.

[0021] Preferably, the molecular weight of the polyethylene glycol is 18,000-22,000, for example, 20,000. In one embodiment of the invention, the polyethylene glycol is purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., with the product number P432531.

[0022] In one embodiment of the present invention, the aqueous polyurethane is purchased from Shanghai McLean Biochemical Technology Co., Ltd., with product number W909579.

[0023] In this invention, preferably, the lithium salt is selected from one or more of LiPF6, LiTFSI, LiBF4 and Li3PO4, for example, LiPF6 or LiTFSI.

[0024] In this invention, preferably, the solvent is water and / or an organic solvent, the water being, for example, deionized water, and the organic solvent being, for example, ethanol and / or acetonitrile.

[0025] In this invention, preferably, the mass ratio of the artificial graphite to the ion-conducting polymer is 100:(1.8-5), for example, 100:1.8.

[0026] In this invention, preferably, the mass ratio of the artificial graphite to the lithium salt is 100:(0.15-0.25), for example, 100:0.2.

[0027] In this invention, preferably, the mass ratio of the ion-conducting polymer to the lithium salt is (7.2-20):1, for example, 9:1.

[0028] In this invention, preferably, the ratio of the mass of the artificial graphite to the volume of the solvent is 1g:(1.2-3)mL, for example, 1g:1.8mL.

[0029] In this invention, the ion-conducting polymer and the lithium salt in the polymer solution are in a dissolved state. The polymer solution is prepared, for example, by dissolving the ion-conducting polymer and the lithium salt in the solvent and stirring to completely dissolve the ion-conducting polymer and the lithium salt.

[0030] In this invention, preferably, the mixing further includes a stirring operation; the stirring is used to uniformly disperse the artificial graphite in the polymer solution; the stirring time is a conventional time in the art.

[0031] In this invention, preferably, the drying process further includes an evaporation process, which is carried out, for example, in a water bath.

[0032] In this invention, preferably, the drying is spray drying or vacuum drying; the drying is used to remove the solvent.

[0033] Preferably, the temperature of the vacuum drying is 120-180°C, for example, 150°C.

[0034] The vacuum drying time is a conventional time in the art, for example, 8-15 hours, or for example, 10 hours.

[0035] The present invention also provides a graphite anode material, which is prepared by the graphite anode material preparation method described above.

[0036] The present invention also provides an application of the graphite anode material as described above in lithium-ion batteries.

[0037] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0038] The reagents and raw materials used in this invention are all commercially available.

[0039] The positive and progressive effects of this invention are as follows:

[0040] The graphite anode material of the present invention has excellent initial discharge specific capacity, initial coulombic efficiency and cycle stability.

[0041] The graphite anode material of this invention has a uniform coating layer on the surface of artificial graphite. This coating layer comprises an ion-conducting polymer and a lithium salt, forming a stable artificial SEI. The flexibility of the ion-conducting polymer film solves the problem of easy breakage of naturally formed SEI films, improving the ionic conductivity and electrochemical stability of the electrode material, thereby improving the overall performance of the battery. The lithium salt in the coating layer improves the lithium-ion conduction efficiency, reduces lithium metal corrosion and deposition, and effectively replenishes consumed lithium ions, further improving the initial coulombic efficiency. Furthermore, combining the ion-conducting polymer and artificial graphite to form a composite material not only improves conductivity but also enhances mechanical strength and chemical stability, thus improving the battery's cycle life. Detailed Implementation

[0042] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0043] The main raw material information involved in the embodiments and comparative examples of this invention is shown in Table 1:

[0044] Table 1

[0045]

[0046] Example 1

[0047] This embodiment provides a graphite anode material, the preparation method of which is as follows:

[0048] 1. Add 9g of polyethylene glycol and 1g of LiPF6 to 900mL of water and stir for 20min to completely dissolve them to obtain a polymer solution.

[0049] 2. Slowly add 500g of artificial graphite to the polymer solution while stirring, and continue stirring for 60 minutes until the graphite is evenly dispersed. Then evaporate the solution in a water bath to obtain a viscous slurry.

[0050] 3. Place the slurry in a vacuum oven and dry it at a constant temperature of 150°C for 10 hours to remove moisture and obtain a graphite anode material coated with polymer and lithium salt.

[0051] Example 2

[0052] This embodiment provides a graphite anode material, the preparation method of which is as follows:

[0053] 1. Add 9g of waterborne polyurethane and 1g of LiPF6 to 900mL of water and stir for 20min to completely dissolve them to obtain a polymer solution.

[0054] 2. Slowly add 500g of artificial graphite to the polymer solution while stirring, and continue stirring for 60 minutes until the graphite is evenly dispersed. Then evaporate the solution in a water bath to obtain a viscous slurry.

[0055] 3. Place the slurry in a vacuum oven and dry it at a constant temperature of 150°C for 10 hours to remove moisture and obtain a graphite anode material coated with polymer and lithium salt.

[0056] Example 3

[0057] This embodiment provides a graphite anode material, the preparation method of which is as follows:

[0058] 1. Add 9g of polyethylene glycol and 1g of LiTFSI to 900mL of water and stir for 20min to completely dissolve them to obtain a polymer solution.

[0059] 2. Slowly add 500g of artificial graphite to the polymer solution while stirring, and continue stirring for 60 minutes until the graphite is evenly dispersed. Then evaporate the solution in a water bath to obtain a viscous slurry.

[0060] 3. Place the slurry in a vacuum oven and dry it at a constant temperature of 150°C for 10 hours to remove moisture and obtain a graphite anode material coated with polymer and lithium salt.

[0061] Comparative Example 1

[0062] This comparative example provides a graphite anode material, the preparation method of which is as follows:

[0063] 1. Add 9g of polyethylene glycol and 1g of LiPF6 to 900mL of water and stir for 20min to completely dissolve them to obtain a polymer solution.

[0064] 2. Add 500g of natural graphite slowly to the polymer solution while stirring, and continue stirring for 60 minutes until the graphite is evenly dispersed. Then evaporate the solution in a water bath to obtain a viscous slurry.

[0065] 3. Place the slurry in a vacuum oven and dry it at a constant temperature of 150°C for 10 hours to remove moisture and obtain a graphite anode material coated with polymer and lithium salt.

[0066] Comparative Example 2

[0067] This comparative example provides a graphite anode material, the preparation method of which is as follows:

[0068] 1. Add 9g of polyethylene glycol to 900mL of water and stir for 20 minutes until completely dissolved. To the polymer solution.

[0069] 2. Slowly add 500g of artificial graphite to the polymer solution while stirring, and continue stirring for 60 minutes until the graphite is evenly dispersed. Then evaporate the solution in a water bath to obtain a viscous slurry.

[0070] 3. Place the slurry in a vacuum oven and dry it at a constant temperature of 150°C for 10 hours to remove moisture and obtain a graphite anode material coated with polymer and lithium salt.

[0071] Comparative Example 3

[0072] This comparative example provides a graphite anode material, the preparation method of which is as follows:

[0073] 1. Add 1g of LiPF6 to 900mL of water and stir for 20min to completely dissolve it, thus obtaining a polymer solution.

[0074] 2. Slowly add 500g of artificial graphite to the polymer solution while stirring, and continue stirring for 60 minutes until the graphite is evenly dispersed. Then evaporate the solution in a water bath to obtain a viscous slurry.

[0075] 3. Place the slurry in a vacuum oven and dry it at a constant temperature of 150°C for 10 hours to remove moisture and obtain a graphite anode material coated with polymer and lithium salt.

[0076] Comparative Example 4

[0077] This comparative example provides a graphite anode material, the preparation method of which is as follows:

[0078] 1. Slowly add 500g of artificial graphite to 900mL of deionized water while stirring, and continue stirring for 60min until the graphite is evenly dispersed. Evaporate the solution in a water bath to obtain a viscous slurry.

[0079] 2. The slurry was placed in a vacuum oven and dried at a constant temperature of 150°C for 10 hours to obtain a graphite anode material coated with polymer and lithium salt.

[0080] Comparative Example 5

[0081] This embodiment provides a graphite anode material, the preparation method of which is as follows:

[0082] 1. Add 7.5g of polyethylene glycol and 1g of LiPF6 to 900mL of water and stir for 20min to completely dissolve them to obtain a polymer solution.

[0083] 2. Slowly add 500g of artificial graphite to the polymer solution while stirring, and continue stirring for 60 minutes until the graphite is evenly dispersed. Then evaporate the solution in a water bath to obtain a viscous slurry.

[0084] 3. Place the slurry in a vacuum oven and dry it at a constant temperature of 150°C for 10 hours to remove moisture and obtain a graphite anode material coated with polymer and lithium salt.

[0085] Comparative Example 6

[0086] This embodiment provides a graphite anode material, the preparation method of which is as follows:

[0087] 1. Add 9g of polyethylene glycol and 1.5g of LiPF6 to 900mL of water and stir for 20min to completely dissolve them to obtain a polymer solution.

[0088] 2. Slowly add 500g of artificial graphite to the polymer solution while stirring, and continue stirring for 60 minutes until the graphite is evenly dispersed. Then evaporate the solution in a water bath to obtain a viscous slurry.

[0089] 3. Place the slurry in a vacuum oven and dry it at a constant temperature of 150°C for 10 hours to remove moisture and obtain a graphite anode material coated with polymer and lithium salt.

[0090] Effect Example

[0091] The particle size and electrochemical performance of the graphite anode materials obtained in the examples and comparative examples were tested respectively.

[0092] 1. Test methods for particle sizes Dmin, D50, and Dmax

[0093] The particle size range and distribution of the material were tested using a Malvern MS3000 laser particle size analyzer.

[0094] 2. Test methods for electrochemical performance

[0095] The graphite anode materials prepared in each embodiment and comparative example were coated onto copper foil, and then vacuum dried and rolled to prepare anode sheets. Using commercially available lithium cobalt oxide electrolyte, a polypropylene microporous membrane as the separator, and a lithium metal sheet as the positive electrode, coin cells were assembled in an argon-filled inert gas glove box system. Charge-discharge tests were conducted on the coin cells using a battery testing system. Under normal temperature conditions, constant current charge-discharge was applied at 0.1C, with the charge-discharge voltage limited to 0.005-1.5V. Cycle stability was assessed by comparing the percentage of the initial specific capacity after 10 charge-discharge cycles under the same test conditions. A lower value indicates a faster capacity decrease and poorer cycle stability. The charge-discharge tests of the coin cells were performed using the LAND battery testing system from Wuhan Landian Electronics Co., Ltd.

[0096] The graphite anode materials prepared in the various embodiments and comparative examples were coated onto copper foil, and then vacuum dried and rolled to prepare anode sheets. Commercially available lithium cobalt oxide was used as the electrolyte, a polypropylene microporous membrane as the separator, and a lithium metal sheet as the positive electrode. The coin cells were assembled in an argon-filled inert gas glove box system. Charge-discharge tests of the coin cells were conducted at room temperature using a battery testing system with a constant current of 0.1C and a charge-discharge voltage limited to 0.005–1.5V. The initial discharge specific capacity and initial coulombic efficiency were obtained during the first cycle. Cycle stability was determined by comparing the percentage of the initial specific capacity after 10 charge-discharge cycles under the same test conditions; a lower value indicates a faster capacity decrease and poorer cycle stability. The charge-discharge tests of the coin cells were performed using the LAND battery testing system from Wuhan Landian Electronics Co., Ltd.

[0097] The electrochemical performance parameters of the graphite anode materials obtained in Examples 1-3 and Comparative Examples 1-6 are shown in Table 2 below:

[0098] Table 2

[0099]

[0100] As shown in Table 2, the initial discharge specific capacity, initial coulombic efficiency, and 10-cycle capacity retention of the graphite anode materials of Examples 1-3 of the present invention are all superior to those of Comparative Examples 1-6.

Claims

1. A graphite anode material, characterized in that, It includes artificial graphite and a coating layer uniformly coated on the surface of the artificial graphite, the coating layer comprising an ion-conducting polymer and a lithium salt; the mass ratio of the artificial graphite to the ion-conducting polymer is 100:(1.8-10); the mass ratio of the artificial graphite to the lithium salt is 100:(0.1-0.25). The ion-conducting polymer is polyethylene glycol or waterborne polyurethane; the lithium salt is LiPF6 or LiTFSI.

2. The graphite anode material as described in claim 1, characterized in that, It satisfies one or more of the following conditions: (1) The particle size D50 of the artificial graphite is 6-8 μm; (2) The aggregate coulombic efficiency of the artificial graphite is greater than 90%; (3) The molecular weight of the polyethylene glycol is 18,000-22,000; (4) The waterborne polyurethane was purchased from Shanghai McLean Biochemical Technology Co., Ltd., and its product number is W909579.

3. The graphite anode material as described in claim 2, characterized in that, It satisfies one or more of the following conditions: (1) The particle size D50 of the artificial graphite is 7.25 μm; (2) The aggregate coulombic efficiency of the artificial graphite is 91%; (3) The molecular weight of the polyethylene glycol is 20,000.

4. The graphite anode material as described in claim 1, characterized in that, It satisfies one or more of the following conditions: (1) The mass ratio of the artificial graphite to the ion-conducting polymer is 100:(1.8-5). (2) The mass ratio of the artificial graphite to the lithium salt is 100:(0.15-0.25); (3) The mass ratio of the ion-conducting polymer to the lithium salt is (7.2-20):

1.

5. The graphite anode material as described in claim 4, characterized in that, It satisfies one or more of the following conditions: (1) The mass ratio of the artificial graphite to the ion-conducting polymer is 100:1.8; (2) The mass ratio of the artificial graphite to the lithium salt is 100:0.2; (3) The mass ratio of the ion-conducting polymer to the lithium salt is 9:

1.

6. A method for preparing a graphite anode material, characterized in that, It includes the following steps: mixing artificial graphite with a polymer solution until homogeneous and then drying; The polymer solution comprises an ion-conducting polymer, a lithium salt, and a solvent; the mass ratio of the artificial graphite to the ion-conducting polymer is 100:(1.8-10); the mass ratio of the artificial graphite to the lithium salt is 100:(0.1-0.25); the ion-conducting polymer is polyethylene glycol or waterborne polyurethane; and the lithium salt is LiPF6 or LiTFSI.

7. The method for preparing the graphite anode material as described in claim 6, characterized in that, It satisfies one or more of the following conditions: (1) The particle size D50 of the artificial graphite is 6-8 μm; (2) The aggregate coulombic efficiency of the artificial graphite is greater than 90%; (3) The solvent is water and / or an organic solvent.

8. The method for preparing the graphite anode material as described in claim 7, characterized in that, It satisfies one or more of the following conditions: (1) The particle size D50 of the artificial graphite is 7.25 μm; (2) The aggregate coulombic efficiency of the artificial graphite is 91%; (3) The water is deionized water; (4) The organic solvent is ethanol and / or acetonitrile.

9. The method for preparing the graphite anode material as described in claim 6, characterized in that, It satisfies one of the following conditions (1) and / or (2): (1) The molecular weight of the polyethylene glycol is 18,000-22,000; (2) The waterborne polyurethane was purchased from Shanghai McLean Biochemical Technology Co., Ltd., and its product number is W909579.

10. The method for preparing the graphite anode material as described in claim 9, characterized in that, The molecular weight of the polyethylene glycol is 20,000.

11. The method for preparing the graphite anode material as described in claim 6, characterized in that, It satisfies one or more of the following conditions: (1) The mass ratio of the artificial graphite to the ion-conducting polymer is 100:(1.8-5). (2) The mass ratio of the artificial graphite to the lithium salt is 100:(0.15-0.25); (3) The mass ratio of the ion-conducting polymer to the lithium salt is (7.2-20):1; (4) The ratio of the mass of the artificial graphite to the volume of the solvent is 1 g: (1.2-3) mL.

12. The method for preparing the graphite anode material as described in claim 11, characterized in that, It satisfies one or more of the following conditions: (1) The mass ratio of the artificial graphite to the ion-conducting polymer is 100:1.8; (2) The mass ratio of the artificial graphite to the lithium salt is 100:0.2; (3) The mass ratio of the ion-conducting polymer to the lithium salt is 9:1; (4) The ratio of the mass of the artificial graphite to the volume of the solvent is 1g:1.8mL.

13. The method for preparing the graphite anode material as described in claim 6, characterized in that, It satisfies one or more of the following conditions: (1) The mixing also includes a stirring operation; (2) The drying process also includes an evaporation process; (3) The drying is spray drying or vacuum drying.

14. The method for preparing the graphite anode material as described in claim 13, characterized in that, It satisfies one or more of the following conditions: (1) The evaporation process is carried out in a water bath; (2) The temperature of the vacuum drying is 120-180℃; (3) The vacuum drying time is 8-15 hours.

15. The method for preparing the graphite anode material as described in claim 14, characterized in that, The vacuum drying temperature is 150°C; And / or, the vacuum drying time is 10 hours.

16. A graphite anode material, characterized in that, It is prepared by the method for preparing graphite anode material as described in any one of claims 6-15.

17. The application of a graphite anode material as described in any one of claims 1-5 or claim 16 in a lithium-ion battery.

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