High-initial-efficiency fast-charging graphite composite material and preparation method thereof

Abstract

The invention discloses a high-initial-efficiency fast-charge graphite composite material and a preparation method thereof, the composite material is of a core-shell structure, the core is graphite, and the shell is lithium sulfonate / lithium molybdate and an amorphous carbon coating layer thereof; the mass ratio of the shell is 5-15 wt% according to the mass ratio of the composite material being 100%. The preparation method comprises the following steps: adding a molybdenum compound into a solvent to prepare a solution, adding graphite oxide, an inorganic lithium salt and a carbon nanotube conductive solution, reacting for 2-12 hours at the temperature of 50-120 DEG C, filtering, carbonizing filter residues to obtain a lithium molybdate conductive agent coated graphite material, and depositing a lithium sulfonate derivative on the surface of the lithium molybdate conductive agent coated graphite material by an atomization method to obtain the lithium molybdate conductive agent coated graphite material. The electron and ion conductivity of the material can be improved, and the rate and the first efficiency of the material can be improved.

Description

Technical Field

[0001] This invention belongs to the field of secondary battery material preparation, specifically a high initial efficiency fast-charging graphite composite material, and also relates to the preparation method of the high initial efficiency fast-charging graphite composite material. Background Technology

[0002] With the increasing market demand for lithium-ion battery energy density and fast charging, the anode materials used must not only have high energy density but also improved fast charging performance. The main factors affecting graphite energy density are specific capacity, compaction density, and initial efficiency. Typically, battery energy density is improved primarily by increasing specific capacity and compaction density, while improving the initial efficiency of the anode material is less common. Currently, the main measures to improve the initial efficiency of materials include reducing material defects, decreasing fine powder content, and surface coating modification. For example, Chinese patent application number 202010633943.3 discloses a method for preparing a boron-doped lithium lanthanum zirconate-coated graphite composite material. The prepared material utilizes the boron-doped lithium lanthanum zirconate, amorphous carbon, and graphene in the coating layer to improve the electronic and ionic conductivity of the material, thus improving rate performance. However, the improvement in initial efficiency is not significant. Furthermore, the core of the material is artificial graphite, which has poor kinetics, affecting the improvement of its fast charging performance. Summary of the Invention

[0003] The purpose of this invention is to overcome the above-mentioned shortcomings and provide a high first-charge efficiency fast-charging graphite composite material that can improve the electronic and ionic conductivity of the material, improve the rate capability and its first-charge efficiency.

[0004] Another object of the present invention is to provide a method for preparing the high first-charge efficiency fast-charging graphite composite material. The present invention provides a high first-charge efficiency fast-charging graphite composite material, which has a core-shell structure, with the core being graphite and the outer shell being lithium sulfonate / lithium molybdate and its amorphous carbon coating layer; based on the composite material mass ratio of 100%, the mass ratio of the outer shell is 5-15 wt%.

[0005] The present invention discloses a method for preparing a high initial efficiency fast-charging graphite composite material, comprising the following steps: Step S1: According to the mass ratio of molybdenum compound: graphite oxide: inorganic lithium salt: carbon nanotube conductive liquid = 5-10:100:5-10:100, add molybdenum compound to deionized water to prepare a 1-10wt% solution, then add graphite oxide, inorganic lithium salt, and carbon nanotube conductive liquid, and react at a temperature of 50-120℃ for 2-12 hours. After filtration, the resulting filter residue is carbonized at 1000-1300℃ for 1-6 hours to obtain graphite material coated with lithium molybdate conductive agent. Step S2: According to the mass ratio of lithium sulfonate derivative to lithium molybdate conductive agent-coated graphite material = 1-5:100, add the lithium sulfonate derivative to an organic solvent and disperse it evenly to prepare a 1-10 wt% lithium sulfonate solution. Add the lithium molybdate conductive agent-coated graphite material to a vacuum furnace. Under a vacuum degree of 10-100 Pa and a temperature of 50-150℃, atomize the lithium sulfonate solution into a gas and deposit it for 30-300 min at an atomization rate of 1-5 ml / min to deposit the lithium sulfonate solution on the surface of the lithium molybdate conductive agent-coated graphite material. Then, vacuum dry the obtained material at a temperature of 120℃ for 24 h to obtain the final product.

[0006] The above-mentioned method for preparing a high first-charge efficiency fast-charging graphite composite material, wherein: the molybdenum compound in step S1 is one of molybdenum trichloride, molybdenum sulfate, or molybdenum nitrate; the inorganic lithium salt is one of lithium phosphate, lithium zirconate, lithium cerium oxide, or lithium niobate; and the mass concentration of the carbon nanotube conductive liquid is 1-5 wt%.

[0007] The above-mentioned method for preparing a high first-charge efficiency fast-charging graphite composite material, wherein: in step S2, the lithium sulfonate derivative is one of lithium trifluoromethanesulfonate, lithium perfluorohexanesulfonate, lithium perfluorobutylsulfonate, or lithium 4-methylbenzenesulfonate; and the organic solvent is diethyl carbonate or dimethyl carbonate.

[0008] Compared with existing technologies, this invention has significant advantages. As can be seen from the above technical solution: this invention improves the ionic and electronic conductivity of the material and enhances rate performance by coating the graphite surface with lithium molybdate and a conductive agent; and by coating the outermost layer with a lithium sulfonate derivative, it exhibits good compatibility with the electrolyte, improving storage performance. Simultaneously, the outer lithium sulfonate compound has good solvation ability with the electrolyte, enhancing the lithium-ion transport rate. This invention leverages the excellent high-temperature performance of the core lithium molybdate and the excellent low-temperature performance of the outer lithium sulfonate, utilizing the synergistic effect between the two to improve the material's initial efficiency, rate performance, and high and low temperature performance. Attached Figure Description

[0009] Figure 1 The image shows a SEM image of the graphite composite material prepared in Example 1. Detailed Implementation

[0010] The following, in conjunction with the accompanying drawings and preferred embodiments, details the specific implementation, structure, features, and effects of the high first-charge efficiency fast-charging graphite composite material and its preparation method proposed in this invention: Example 1 A method for preparing a high-initial-efficiency fast-charging graphite composite material includes the following steps: Step S1: Add 8g of molybdenum trichloride to 500g of deionized water to prepare a solution, then add 100g of graphite oxide, 8g of lithium phosphate, 100g of 3wt% carbon nanotube conductive liquid and mix evenly. React at 80℃ for 6h, filter, and carbonize the resulting filter residue at 1100℃ for 3h to obtain graphite material coated with lithium molybdate conductive agent. Step S2: Add 3g of lithium trifluoromethanesulfonate to 60g of diethyl carbonate organic solvent and disperse evenly to prepare a 5wt% lithium sulfonate solution; add 100g of lithium molybdate conductive agent-coated graphite material to the deposition layer in a vacuum furnace, and then atomize the lithium sulfonate solution into gas at a vacuum of 50pa and a temperature of 100℃ using an atomization method, and deposit it for 150min at an atomization rate of 3ml / min to deposit the lithium sulfonate solution on the surface of the lithium molybdate conductive agent-coated graphite material. Then, vacuum dry the obtained material at a temperature of 120℃ for 24h to obtain the final product.

[0011] Example 2 A method for preparing a high-initial-efficiency fast-charging graphite composite material includes the following steps: Step S1: Add 5g of molybdenum sulfate to 500g of deionized water to prepare a solution, then add 100g of graphite oxide, 5g of lithium zirconate, 100g of 1wt% carbon nanotube conductive liquid, and react at 50℃ for 12h. Filter the solution, and carbonize the resulting filter residue at 1000℃ for 6h to obtain graphite material coated with lithium molybdate conductive agent. Step S2: Add 1g of lithium perfluorohexane sulfonate to 100g of diethyl carbonate organic solvent and disperse evenly to prepare a 1wt% lithium sulfonate solution; add 100g of lithium molybdate conductive agent-coated graphite material to a vacuum furnace, and then atomize the lithium sulfonate solution into gas at a vacuum of 10 Pa and a temperature of 50℃ using an atomization method, and deposit it for 300min at an atomization rate of 1ml / min to deposit the lithium sulfonate solution on the surface of the lithium molybdate conductive agent-coated graphite material. Then, vacuum dry the obtained material at a temperature of 120℃ for 24h to obtain the final product.

[0012] Example 3 A method for preparing a high-initial-efficiency fast-charging graphite composite material includes the following steps: Step S1: Add 10g of molybdenum nitrate to 100g of deionized water to prepare a solution, then add 100g of graphite oxide, 10g of lithium cerate, 100g of 5wt% carbon nanotube conductive liquid, and react at 120℃ for 2h. Filter the solution, and carbonize the resulting filter residue at 1300℃ for 1h to obtain graphite material coated with lithium molybdenum conductive agent. Step S2: Add 5g of lithium perfluorobutyl sulfonate to 50g of dimethyl carbonate organic solvent and disperse evenly to prepare a 10wt% lithium sulfonate solution; add 100g of lithium molybdate conductive agent-coated graphite material to a vacuum furnace, and atomize the lithium sulfonate solution into gas at a vacuum degree of 100pa and a temperature of 150℃, and deposit it for 30min at an atomization rate of 5ml / min to deposit the lithium sulfonate solution on the surface of the lithium molybdate conductive agent-coated graphite material. Then, vacuum dry the obtained material at a temperature of 120℃ for 24h to obtain the final product.

[0013] Comparative Example 1: A method for preparing a composite material includes: unlike Example 1, step S1 does not involve the addition of molybdenum trichloride and lithium phosphate, while the rest is the same as in Example 1.

[0014] Comparative Example 2: A method for preparing a composite material includes: unlike Example 1, step S2 is omitted, and graphite material coated with lithium molybdate conductive agent from step S1 is used as the negative electrode material.

[0015] Comparative Example 3: A method for preparing a composite material includes: Unlike Example 1, step S2 does not employ atomization to deposit lithium sulfonate; instead, a liquid-phase method is used to deposit lithium sulfonate on the surface of a graphite material coated with a lithium molybdate conductive agent. The preparation process is as follows: 3g of lithium trifluoromethanesulfonate is added to 60g of diethyl carbonate organic solvent and dispersed evenly to prepare a 5wt% lithium sulfonate solution. Then, 100g of lithium molybdate conductive agent is added to coat the graphite material and dispersed evenly. The mixture is then spray-dried to obtain the graphite composite material.

[0016] Experiment 1: SEM Test The graphite composite material prepared in Example 1 was subjected to SEM testing, and the results are as follows: Figure 1 As shown. By Figure 1 It can be seen that the material exhibits a secondary particle structure with a particle size between 5-10 μm, uniform particle size distribution, and smooth surface.

[0017] Experimental Example 2: Physicochemical Properties Test The specific surface area and tap density of the graphite composite anode materials in Examples 1-3 and Comparative Examples 1-3 were tested according to the test methods in standard GB / T-24533-2019 "Graphite Anode Materials for Lithium-ion Batteries". The OI value of the powder materials was tested by XRD; the diffusion coefficient was tested by GITT. The test results are shown in Table 1.

[0018] Table 1 As can be seen from Table 1, the graphite composite materials prepared in Examples 1-3 have significantly higher diffusion coefficients and electrical conductivity than those in Comparative Examples 1-3. This may be because the surface of the materials in the examples is coated with lithium molybdate and lithium sulfonate, which improves the lithium-ion diffusion coefficient and initial efficiency. At the same time, the lithium coating agent releases lithium ions during charging and discharging, which improves the diffusion coefficient of the material. Furthermore, the atomization method for depositing lithium sulfonate has the characteristics of good deposition uniformity and high density, which improves the tap density.

[0019] Test Example 3: Button Cell Test The graphite composite materials obtained in Examples 1-3 and the graphite composite anode materials in Comparative Examples 1-3 were assembled into coin cells according to the following methods: The graphite composite anode materials prepared in Examples 1-3 and Comparative Examples 1-3 were used as anodes and assembled into coin cells with lithium sheets, electrolytes, and separators in a glove box with argon and water contents both below 0.1 ppm. The separator was Celegard 2400; the electrolyte was a LiPF6 solution with a LiPF6 concentration of 1 mol / L, and the solvent was a mixed solution of ethylene carbonate (EC) and diethyl carbonate (DMC) at a weight ratio of 1:1.

[0020] The fabricated coin cells were tested using a Blue Electricity tester. The test conditions were: 0.1C charge / discharge rate, voltage range of 0.005-2V, 3 cycles followed by a stop, and then the discharge capacity at 1C was tested. Simultaneously, the specific capacity at -20℃ (0.1C) was measured, and the low-temperature capacity retention rate was calculated. The low-temperature charging DCR (-20℃, 0.05C, 50% SOC) and low-temperature rate performance (-20℃ & 0.1C / 25℃ & 0.1C) were also tested. The test results are shown in Table 2.

[0021] Table 2 As can be seen from Table 2, the coin cells made using the graphite composite materials of Examples 1-3 have significantly better discharge specific capacity, initial efficiency, and low-temperature DCR than those of Comparative Examples 1-3. This is because the surface of the graphite is coated with organic and inorganic lithium salts, which reduces the irreversible capacity of the material and improves the initial efficiency. Furthermore, under low-temperature conditions, lithium sulfonate has an excellent low-temperature diffusion coefficient, which improves the low-temperature rate capability and reduces the low-temperature charging DCR.

[0022] Test Example 4: Performance Testing of Pouch Batteries Using the graphite composite materials from Examples 1-3 and Comparative Examples 1-3 as the negative electrode active material, a 5Ah pouch cell was assembled with the positive electrode active material LFP, an electrolyte, and a separator. The separator was Celegard 2400, and the electrolyte was a LiPF6 solution (a 1:1 volume ratio mixture of EC and DEC, with a LiPF6 concentration of 1.3 mol / L). The pouch cells were tested for cycle and rate performance; the results are detailed in Table 3.

[0023] 1) Low-temperature cycle performance: The battery cycle performance was tested at a charge / discharge rate of 0.1C / 0.1C, a voltage range of 2.0V-3.65V, a cycle count of 200 cycles, and a temperature of -20±3℃. 2) Rate performance: At a temperature of 25±3℃, the battery is charged to 100% SOC using a constant current + constant voltage mode at a 2C rate. Then, the constant current ratio is calculated as constant current capacity / (constant current capacity + constant voltage capacity).

[0024] Table 3 Table 3 shows the low-temperature cycling performance and room-temperature fast-charging performance of the soft-pack batteries prepared from the obtained graphite composite materials. As can be seen from the table, the cycling performance and fast-charging performance of the batteries in the examples are significantly better than those in the comparative examples. This is because the graphite composite materials obtained in the examples have a low OI value, which reduces expansion, and the surface coating of lithium molybdate and lithium sulfonate reduces the consumption of lithium ions during charging and discharging, as well as a large specific surface area, which improves their cycling performance. At the same time, the materials in the examples have excellent diffusion coefficients, which improve the fast-charging performance and low-temperature performance of the materials.

[0025] The above are merely preferred embodiments of the present invention and do not impose any limitations on the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from any technical solution of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A high first efficiency fast charging graphite composite material, presenting a core-shell structure, the inner core being graphite, and the outer shell being lithium sulfonate / lithium molybdate and its amorphous carbon coating layer; the mass ratio of the outer shell being 5-15wt% according to 100% of the mass of the composite material. 2.A method for preparing a high first efficiency fast charging graphite composite material, comprising the following steps: Step S1: adding a molybdenum compound into deionized water to configure a 1-10wt% solution according to the mass ratio of molybdenum compound: graphite oxide: inorganic lithium salt: carbon nanotube conductive liquid = 5-10: 100: 5-10: 100, then adding graphite oxide, inorganic lithium salt, and carbon nanotube conductive liquid, and reacting at a temperature of 50-120℃ for 2-12h, filtering, carbonizing the obtained filter residue at 1000-1300℃ for 1-6h to obtain a lithium molybdate conductive agent coated graphite material; Step S2: adding a lithium sulfonate derivative into an organic solvent to disperse uniformly and configure a 1-10wt% lithium sulfonate solution, adding the lithium molybdate conductive agent coated graphite material into a vacuum furnace, atomizing the lithium sulfonate solution into a gas at a vacuum degree of 10-100pa and a temperature of 50-150℃, and depositing it on the surface of the lithium molybdate conductive agent coated graphite material according to an atomization rate of 1-5ml / min for 30-300min, and then vacuum drying the obtained material at a temperature of 120℃ for 24h.

3. The method of claim 2, wherein: The molybdenum compound in step S1 is one of molybdenum trichloride, molybdenum sulfate, and molybdenum nitrate; the inorganic lithium salt is one of lithium phosphate, lithium zirconate, lithium cerate, or lithium niobate; and the mass concentration of the carbon nanotube conductive liquid is 1-5wt%.

4. The method of claim 2, wherein: The lithium sulfonate derivative in step S2 is one of lithium triflate, lithium perfluorohexanesulfonate, lithium perfluorobutylsulfonate, or lithium 4-methylbenzenesulfonate; and the organic solvent is diethyl carbonate or dimethyl carbonate.

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