Graphite negative electrode material, preparation method thereof, lithium ion battery negative electrode plate and application of lithium ion battery negative electrode plate

Abstract

The invention relates to the technical field of lithium batteries, and discloses a graphite negative electrode material, a preparation method thereof, a lithium ion battery negative electrode plate and application thereof. The method comprises the following steps: (1) in the presence of a solvent, carrying out first mixing on graphite and a surfactant to obtain an intermediate I; the specific discharge capacity of the graphite is 340-360 mAh / g, and the specific surface area of the graphite is 0.8-2.5 m < 2 > / g; (2) carrying out second mixing on an organic aluminum compound and the intermediate I to obtain an intermediate II; and (3) sequentially carrying out drying treatment and pyrolysis treatment on the intermediate II to obtain the graphite negative electrode material, the weight ratio of the organic aluminum compound to the graphite is 1: (10-40). The graphite negative electrode material provided by the invention can effectively improve the rate capability of the lithium ion battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium batteries, in particular to a graphite-based negative electrode material, a preparation method thereof, a lithium ion battery negative electrode sheet and an application thereof. BACKGROUND

[0002] Lithium ion batteries are widely used in electric vehicles and portable devices due to their excellent energy density and cycle performance. In recent years, with the rapid development of electric vehicles and renewable energy technologies, the demand for high-power fast-charging lithium ion batteries is increasing, which puts higher requirements on the performance of lithium ion batteries.

[0003] Currently, commercial lithium ion batteries mainly use graphite as the negative electrode material. However, due to its own layered structure, the lithium ion rapid deintercalation ability of graphite material is not good at high current density, and the charge and discharge reversible capacity of graphite will be reduced to a low level, which is difficult to meet the use requirements of fast-charging application scenarios.

[0004] During the production of graphite, the kinetic performance of graphite can be improved through particle size adjustment, secondary granulation, surface coating and other means, which to some extent improves the rate performance of graphite, but still cannot meet the use requirements. Moreover, the problems of the decrease of the first cycle coulombic efficiency and the decrease of the graphite loading affect the capacity development of the positive electrode material and further limit the energy density of the battery.

[0005] CN119208598A discloses a natural graphite intercalated aluminum chloride derived negative electrode material, a preparation method thereof, a lithium ion battery negative electrode sheet and a lithium ion battery. The negative electrode material includes natural graphite and aluminum chloride between the layers of natural graphite; wherein the interlayer spacing of the negative electrode material is 1.28-1.298nm. This method can expand the interlayer spacing of natural graphite in the negative electrode material and the specific surface area of the negative electrode material by introducing aluminum chloride into the interlayer of natural graphite, thereby introducing structural defects into the negative electrode material, allowing the negative electrode material to have higher capacity, and allowing the lithium ion battery containing the negative electrode material to have improved first reversible specific capacity, first cycle coulombic efficiency, rate performance, cycle performance, capacity and capacity retention rate. However, this method only uses one-step solid-phase reaction to insert aluminum chloride into the graphite interlayer, and the stability of aluminum elements in the graphite interlayer is not enough. With the increase of the cycle number of the battery, the spatial position of aluminum elements will change, affecting the cycle stability. At the same time, the first cycle coulombic efficiency of the graphite in this method is too low, only about 60%, which is difficult to meet the application requirements.

[0006] Therefore, it is of great significance to provide a new type of graphite-based negative electrode material with excellent rate performance. SUMMARY

[0007] The present application aims to maintain the capacity retention rate of lithium batteries and improve the rate performance of lithium batteries without reducing the first cycle coulomb efficiency of lithium batteries.

[0008] To achieve the above-mentioned object, the present application provides a method for preparing a graphite-based negative electrode material, which comprises: (1) mixing graphite and a surfactant in the presence of a solvent to obtain an intermediate I; the specific discharge capacity of the graphite is 340-360 mAh / g, and the specific surface area is 0.8-2.5 m 2 / g; (2) second mixing of an organic aluminum compound with the intermediate I to obtain an intermediate II; (3) sequentially performing drying treatment and pyrolysis treatment on the intermediate II to obtain the graphite-based negative electrode material; The weight ratio of the amount of the organic aluminum compound to the amount of the graphite is 1:10-40; The organic aluminum compound is a combination of at least two of aluminum glycinate, aluminum isopropylate, aluminum citrate, aluminum diethylate, aluminum acetylacetonate, diethylaluminum chloride and aluminum acetate.

[0009] According to a preferred embodiment, the organic aluminum compound is a combination of aluminum glycinate and aluminum citrate with a content weight ratio of 1:0.2-2.

[0010] According to a specific embodiment, the weight ratio of the amount of the surfactant to the amount of the graphite is 1:30-50.

[0011] According to a specific embodiment, the surfactant is at least one selected from ethylphenyl polyethylene glycol, sodium dodecylbenzenesulfonate, polyvinylpyrrolidone, sodium laureth sulfate and fatty acid glyceride.

[0012] In some embodiments, the conditions of the second mixing include a temperature of 50-80℃ and a time of 20-40 min.

[0013] In some embodiments, the drying treatment is rotary evaporation at a temperature of 70-90℃.

[0014] In some embodiments, the conditions of the pyrolysis treatment include a temperature of 700-900℃ and a time of 8-12 h under a protective atmosphere.

[0015] The second aspect of the present application provides a graphite-based negative electrode material prepared by the method of the aforementioned first aspect.

[0016] The third aspect of the present application provides a lithium ion battery negative electrode sheet, which comprises the graphite-based negative electrode material of the aforementioned second aspect.

[0017] The fourth aspect of the present invention provides the application of the lithium-ion battery negative electrode sheet described in the third aspect above in a lithium-ion battery.

[0018] This invention utilizes the dispersing effect of surfactants to uniformly and stably disperse graphite in a solvent; the functional groups on the graphite surface can interact and tightly bind with organoaluminum compounds, and the doping of aluminum elements into the graphite structure can significantly increase the interlayer spacing of graphite and introduce some defects on the graphite surface, promoting the lithium ion insertion / extraction rate and greatly increasing the diffusion rate of lithium ions inside the negative electrode material, thereby reducing the internal impedance of the battery and improving the kinetic performance of the material.

[0019] Furthermore, due to the stable combination of aluminum and graphite, this doped structure can remain stable during battery cycling, greatly improving the rate performance of the battery as a negative electrode material.

[0020] The preparation method provided in this invention is relatively simple and is conducive to mass production. Detailed Implementation

[0021] The endpoints and any values ​​of the ranges 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 endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0022] As previously described, a first aspect of the present invention provides a method for preparing a graphite-based anode material, the method comprising: (1) In the presence of a solvent, graphite and a surfactant are first mixed to obtain intermediate I; the graphite has a discharge specific capacity of 340-360 mAh / g and a specific surface area of ​​0.8-2.5 m². 2 / g; (2) The organoaluminum compound is mixed with intermediate I in a second mixture to obtain intermediate II; (3) The intermediate II is subjected to drying and pyrolysis treatment in sequence to obtain the graphite-based negative electrode material; The weight ratio of the organoaluminum compound to the graphite is 1:10-40; The organoaluminum compound is a combination of at least two of aluminum glycinate, aluminum isopropoxide, aluminum citrate, aluminum diethylethoxide, aluminum acetylacetone, aluminum diethyl chloride, and aluminum acetate.

[0023] According to a preferred embodiment, the organic aluminum compound is a combination of aluminum glycinate and aluminum citrate with a weight ratio of 1:0.2-2. The inventors of the present application have found that in this preferred case, the graphite-based negative electrode material provided by the present application can effectively improve the rate performance of the battery.

[0024] According to a specific embodiment, the weight ratio of the surfactant to the graphite is 1:30-50.

[0025] According to a specific embodiment, the surfactant is at least one selected from ethyl phenyl polyethylene glycol, sodium dodecyl benzene sulfonate, polyvinyl pyrrolidone, sodium laureth sulfate, and glycerol fatty acid ester.

[0026] According to a specific embodiment, the solvent is deionized water.

[0027] In the present application, the amount of the solvent is not particularly limited as long as the graphite can be completely dispersed, and those skilled in the art can select the amount of the solvent according to the conventional amount of the solvent in the art. For example, the weight ratio of the solvent to the graphite is 5-15:1.

[0028] In some embodiments, the conditions of the first mixing include a temperature of 25-50°C and a time of 10-30 min.

[0029] In some embodiments, the conditions of the second mixing include a temperature of 50-80°C and a time of 20-40 min.

[0030] In some embodiments, the drying treatment is rotary evaporation at a temperature of 70-90°C.

[0031] In the present application, the time of the drying treatment is not particularly limited as long as the solvent is completely volatilized to dryness.

[0032] In some embodiments, the conditions of the pyrolysis treatment include a temperature of 700-900°C and a time of 8-12 h under a protective atmosphere.

[0033] In some embodiments, the protective atmosphere is at least one selected from nitrogen, argon, and helium.

[0034] In some embodiments, the conditions of the pyrolysis treatment further include a heating rate of 3-8°C / min.

[0035] In some embodiments, after the pyrolysis treatment, the graphite-based negative electrode material is obtained by cooling to room temperature at a rate of 1-3°C / min.

[0036] As described above, the second aspect of the present application provides a graphite-based negative electrode material prepared by the method of the aforementioned first aspect.

[0037] As described above, the third aspect of the present application provides a lithium-ion battery negative electrode sheet comprising the graphite-based negative electrode material of the aforementioned second aspect.

[0038] As described above, the fourth aspect of the present application provides the use of the lithium-ion battery negative electrode sheet of the aforementioned third aspect in a lithium-ion battery.

[0039] The present application will be described in detail below through examples. In the following examples, the various raw materials used are all commercially available unless otherwise specified.

[0040] Some of the raw materials used in the following examples and their sources are as follows: Graphite-I: having a discharge specific capacity of 350.8 mAh / g and a specific surface area of 1.27 m 2 / g, with a brand of GHT-360M, purchased from Shenzhen Intrinsic Equation Graphene Technology Co., Ltd.; Graphite-II: having a discharge specific capacity of 372.4 mAh / g and a specific surface area of 4.12 m 2 / g, with a brand of GGO-400, purchased from Shenzhen Intrinsic Equation Graphene Technology Co., Ltd.; Ethylphenyl polyethylene glycol (NP-40): CAS 68412-54-4, with a brand of I854506, purchased from Shanghai Macklin Biochemical Technology Co., Ltd.; Fatty acid glyceride: with a brand of D984241, purchased from Shanghai Macklin Biochemical Technology Co., Ltd.; Aluminum glycinate: with a brand of A822689, purchased from Shanghai Macklin Biochemical Technology Co., Ltd.; Aluminum citrate: with a brand of A723274, purchased from Shanghai Macklin Biochemical Technology Co., Ltd.; Sodium dodecylbenzenesulfonate: with a brand of S817806, purchased from Shanghai Macklin Biochemical Technology Co., Ltd.; In the present application, the room temperature is 25±2℃.

[0041] Example 1 (1) Take 20 g of graphite-I and 0.5 g of polyvinylpyrrolidone, disperse them in 200 mL of deionized water, and ultrasonically stir at 25℃ for 20 min to obtain intermediate I; (2) Add 0.6 g of aluminum glycinate and 0.4 g of aluminum citrate to the above intermediate I, ultrasonically stir at 60℃ for 30 min, and then continue to stir at the same temperature for 12 h to obtain a stable precursor mixture (i.e. intermediate II); (3) The precursor mixture is subjected to rotary evaporation at 80°C to remove the solvent to obtain a pre-product; the pre-product is placed in a tube furnace, argon gas is introduced as an inert gas, the heating rate is controlled at 5°C / min, heated to 800°C and kept for 10 hours, and then cooled to room temperature at a rate of 2°C / min to obtain the graphite-based negative electrode material.

[0042] Example 2 (1) 20 g of graphite-I and 0.4 g of fatty acid glyceride are dispersed in 200 mL of deionized water, ultrasonically stirred at 25°C for 20 min to obtain an intermediate I; (2) 0.3 g of aluminum glycinate and 0.2 g of aluminum citrate are added to the intermediate I, ultrasonically stirred at 60°C for 30 min, and then continuously stirred at the same temperature for 12 h to obtain a stable precursor mixture (i.e., intermediate II); (3) The precursor mixture is subjected to rotary evaporation at 70°C to remove the solvent to obtain a pre-product; the pre-product is placed in a tube furnace, nitrogen gas is introduced as an inert gas, the heating rate is controlled at 5°C / min, heated to 900°C and kept for 8 hours, and then cooled to room temperature at a rate of 2°C / min to obtain the graphite-based negative electrode material.

[0043] Example 3 (1) 20 g of graphite-I and 0.6 g of sodium dodecyl benzene sulfonate are dispersed in 200 mL of deionized water, ultrasonically stirred at 25°C for 20 min to obtain an intermediate I; (2) 1.5 g of aluminum glycinate and 0.5 g of aluminum citrate are added to the intermediate I, ultrasonically stirred at 60°C for 30 min, and then continuously stirred at the same temperature for 12 h to obtain a stable precursor mixture (i.e., intermediate II); (3) The precursor mixture is subjected to rotary evaporation at 90°C to remove the solvent to obtain a pre-product; the pre-product is placed in a tube furnace, argon gas is introduced as an inert gas, the heating rate is controlled at 5°C / min, heated to 700°C and kept for 12 hours, and then cooled to room temperature at a rate of 2°C / min to obtain the graphite-based negative electrode material.

[0044] Example 4 This example is carried out by using a method similar to that of Example 1, except that in step (2), the total amount of the organoaluminum compound is kept unchanged, and the organoaluminum compound is adjusted to a combination of 0.25 g of aluminum glycinate and 0.75 g of aluminum citrate, and the rest of the operations are the same as in Example 1 to obtain the graphite-based negative electrode material.

[0045] Example 5 This example was carried out by using the similar method of Example 1, except that in step (2), the total amount of the organoaluminum compound was kept unchanged, and the organoaluminum compound was adjusted to a combination of 0.6 g aluminum isopropoxide and 0.4 g aluminum acetylacetonate, and the rest of the operations were the same as in Example 1, to prepare a graphite-based negative electrode material.

[0046] Comparative Example 1 This comparative example was carried out by using the similar method of Example 1, except that in step (1), no surfactant polyvinylpyrrolidone was added, and the rest of the operations were the same as in Example 1, to prepare a graphite-based negative electrode material.

[0047] Comparative Example 2 This comparative example was carried out by using the similar method of Example 1, except that in step (2), 1 g of aluminum glycinate was used to replace the combination of 0.6 g aluminum glycinate and 0.4 g aluminum citrate in Example 1, and the rest of the operations were the same as in Example 1, to prepare a graphite-based negative electrode material.

[0048] Comparative Example 3 This comparative example was carried out by using the similar method of Example 1, except that in step (2), 1 g of aluminum chloride was used to replace the combination of 0.6 g aluminum glycinate and 0.4 g aluminum citrate in Example 1, and the rest of the operations were the same as in Example 1, to prepare a graphite-based negative electrode material.

[0049] Comparative Example 4 This comparative example was carried out by using the similar method of Example 1, except that in step (2), the amount of the organoaluminum compound was adjusted to 1.5 g aluminum glycinate and 1 g aluminum citrate, and the rest of the operations were the same as in Example 1, to prepare a graphite-based negative electrode material.

[0050] Comparative Example 5 This comparative example was carried out by using the similar method of Example 1, except that in step (1), equal weight of graphite-II was used to replace graphite-I in Example 1, and the rest of the operations were the same as in Example 1, to prepare a graphite-based negative electrode material.

[0051] Test Example (1) This test example was used to test the physicochemical properties of the graphite-based negative electrode materials prepared in the above examples and comparative examples, specifically: Diffusion coefficient: determined by using the constant current intermittent titration method (GITT), with the unit of 10 -6 cm 2 / s; Resistivity: tested by using a four-probe tester, with the unit of Ω·cm; Interlayer spacing: tested by using an X-ray diffractometer, with the unit of nm.

[0052] The specific test results are shown in Table 1.

[0053] Table 1

[0054] As can be seen from the results in Table 1, the graphite-based negative electrode material provided by the application has a significantly higher diffusion coefficient and a lower resistivity, and the interlayer spacing of the graphite is also improved to a certain extent, indicating that the doping of aluminum elements can increase the interlayer spacing of the graphite and improve the diffusion rate of lithium ions inside the negative electrode material.

[0055] (2) In this test example, the graphite-based negative electrode materials prepared in the above examples and comparative examples were prepared into negative electrode sheets, assembled into button cells, and subjected to electrochemical performance tests, specifically: Preparation of negative electrode slurry: the graphite-based negative electrode material, conductive carbon black, and negative electrode binder were uniformly dispersed in deionized water in a mass ratio of 96:1:3 by stirring to obtain a lithium ion battery negative electrode slurry with a viscosity of 5000 mPa.s and a solid content of 40-50%.

[0056] Preparation of negative electrode sheet: the lithium ion battery negative electrode slurry obtained above was uniformly coated on a 9-micron-thick copper foil using an automatic film coating machine, and the coating surface density was 0.01 g / cm 2 Then, it was placed in a vacuum drying oven to remove the solvent and obtain a negative electrode sheet.

[0057] Preparation of button cell: the prepared negative electrode sheet was punched into a 10-mm-diameter disc using a sheet punching machine and transferred to an argon-filled glove box, and pure lithium sheet was used as the counter electrode and Celgard 2325 was used as the separator; the electrolyte was a mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) containing 1 mol / L lithium hexafluorophosphate (LiPF), and the volume ratio of EC to DEC was 1:1, and a 2032 button-type half cell was assembled.

[0058] Electrochemical performance test: the assembled button-type half cell was left to stand for 12 h, and in the test, the lithium sheet side was used as the low potential side and the graphite electrode sheet side was used as the high potential side, and the voltage range was 0.01-2.5 V, and the cycle charging and discharging test was carried out at a rate of 0.1 C for one week and then at a rate of 2 C. The capacity retention rate data was obtained after 500 cycles. The specific test results are shown in Table 2.

[0059] Table 2

[0060] As can be seen from the results of Table 2, the lithium ion battery prepared from the graphite-based negative electrode material provided by the application has a significantly higher capacity retention rate after 500 cycles at a current density of 2C, and the initial specific discharge capacity and the first-cycle coulombic efficiency are not significantly reduced, and the first-cycle coulombic efficiency is as high as 95.68%, indicating that the doping of aluminum elements can effectively improve the rate performance of the lithium ion battery, while not affecting the initial specific discharge capacity and the coulombic efficiency of the battery.

[0061] The preferred embodiments of the application are described in detail above, but the application is not limited thereto. Within the technical concept of the application, various simple modifications can be made to the technical solutions of the application, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be considered as disclosed by the application and fall within the protection scope of the application.

Claims

1. A method for producing a graphite-based negative electrode material, characterized by, The method includes: (1) mixing graphite and a surfactant in the presence of a solvent to obtain an intermediate I; the graphite has a discharge specific capacity of 340-360 mAh / g and a specific surface area of 0.8-2.5 m 2 / g (2) mixing the intermediate I and a binder to obtain a mixture; the binder has a glass transition temperature of 150-200°C and a melting point of 200-220°C (3) mixing the mixture and a solvent to obtain a slurry; the solvent has a boiling point of 100-200°C ( (2) The organoaluminum compound is mixed with intermediate I in a second mixture to obtain intermediate II; (3) The intermediate II is subjected to drying and pyrolysis treatment in sequence to obtain the graphite-based negative electrode material; The weight ratio of the organoaluminum compound to the graphite is 1:10-40; The organoaluminum compound is a combination of at least two of aluminum glycinate, aluminum isopropoxide, aluminum citrate, aluminum diethylethoxide, aluminum acetylacetone, aluminum diethyl chloride, and aluminum acetate.

2. The method of claim 1, wherein, The organoaluminum compound is a combination of aluminum glycinate and aluminum citrate in a weight ratio of 1:0.2-2.

3. The method of claim 1, wherein, The surfactant is used in a weight ratio of 1:30-50 to the graphite.

4. The method of any of claims 1-3, wherein, The surfactant is selected from at least one of ethylphenyl polyethylene glycol, sodium dodecylbenzenesulfonate, polyvinylpyrrolidone, sodium lauryl ether sulfate, and fatty acid glycerides.

5. The method of any of claims 1-3, wherein, The conditions for the second mixing include a temperature of 50-80°C and a time of 20-40 minutes.

6. The method of any of claims 1-3, wherein, The drying process is rotary evaporation at a temperature of 70-90℃.

7. The method of any of claims 1-3, wherein, The conditions for the pyrolysis treatment include: a protective atmosphere, a temperature of 700-900℃, and a time of 8-12 hours.

8. The graphite-based anode material prepared by the method according to any one of claims 1-7.

9. A negative electrode sheet for a lithium-ion battery, characterized in that, The negative electrode sheet includes the graphite-based negative electrode material as described in claim 8.

10. The application of the lithium-ion battery negative electrode sheet according to claim 9 in a lithium-ion battery.

Images