A method for preparing high-power graphite composite material

Abstract

The present invention relates to the technical field of lithium-ion battery material preparation, and proposes a preparation method of a high-power graphite composite material, comprising the following steps: S1, adding a nitrogen source to a graphene conductive liquid and dispersing it uniformly, then adding an organic iron source compound, a metal coupling agent, and a rare earth compound and dispersing them uniformly to obtain a mixed solution; S2, reacting the mixed solution at a temperature of 100-200°C for 1-6h, and drying to obtain a porous iron oxide / graphene coated material; S3, adding a binder and an organic solvent to the porous iron oxide / graphene coated material, and dispersing them uniformly to obtain a coated mixed solution; S4, adding graphite to the coated mixed solution and mixing them uniformly for drying, and then carbonizing to obtain a graphite composite material. Through the above technical scheme, the problems of low energy density, large expansion, poor power performance, and poor cycle performance of graphite composite materials in related technologies are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion battery material preparation, and in particular to a method for preparing a high-power graphite composite material. Background Art

[0002] As the requirements for energy density and power performance of lithium-ion batteries increase, the negative electrode materials currently used in the market are mainly artificial graphite, whose actual specific capacity is about 360mAh / g, which is close to the theoretical capacity of 372mAh / g, and the fast charging performance is ≤4C, which cannot meet the needs of the next generation of high energy density and high power negative electrodes. Graphite materials are mainly composed of core graphite and its coating layer amorphous carbon, and the energy density of amorphous carbon is low (300mAh / g, 1.0g / cm 3 ) results in a low energy density for the entire composite material. One measure to increase the energy density and power performance of the material is to coat its surface to improve the power performance of the material. Currently, iron oxide, as a negative electrode with high specific capacity and good power performance, has defects such as large expansion and poor cycle performance. Therefore, how to solve these defects while taking advantage of the high specific capacity and good power performance of iron oxide, thereby improving the overall performance of graphite materials, is a technical challenge. Summary of the Invention

[0003] The present invention provides a method for preparing a high-power graphite composite material, which solves the problems of low energy density, large expansion, poor power performance and poor cycle performance of graphite composite materials in related technologies.

[0004] The technical solutions of the present invention are as follows:

[0005] A method for preparing a high-power graphite composite material comprises the following steps:

[0006] S1. Add a nitrogen source to the graphene conductive liquid and disperse it evenly, then add an organic iron source compound, a metal coupling agent, and a rare earth compound and disperse them evenly to obtain a mixed solution;

[0007] S2, reacting the mixed solution at a temperature of 100-200° C. for 1-6 hours, and then drying to obtain a porous iron oxide / graphene coated material;

[0008] S3, adding a binder and an organic solvent to the porous iron oxide / graphene coating material, and dispersing them evenly to obtain a coating mixture;

[0009] S4. Add graphite to the coating mixture, mix evenly, dry, and then carbonize to obtain a graphite composite material.

[0010] As a further technical solution, the solvent of the graphene conductive liquid in step S1 is N-methylpyrrolidone with a concentration of 1-5 wt%.

[0011] As a further technical solution, in step S1, the nitrogen source includes one or more of pyrrole, thiophene, aniline, urea, and melamine; and the metal coupling agent includes one or more of titanate coupling agents and aluminate coupling agents.

[0012] As a further technical solution, the organic iron source compound in step S1 includes one or more of ammonium ferric citrate, acetylferrocene, ferric ammonium oxalate, and ammonium ferric ethylenediaminetetraacetate.

[0013] As a further technical solution, the rare earth compound in step S1 is lanthanum hydroxide.

[0014] As a further technical solution, in step S1, the mass ratio of graphene, nitrogen source, organic iron source compound, metal coupling agent, and rare earth compound is 1-5:1-5:100:1-5:1-5.

[0015] As a further technical solution, in step S3, the binder includes one of petroleum asphalt and coal tar; and the organic solvent includes one of carbon tetrachloride, cyclohexane, xylene, and N-methylpyrrolidone.

[0016] As a further technical solution, the mass ratio of the porous iron oxide / graphene coating material, the binder, the organic solvent, and the graphite is 5-20:1-10:500-1500:100.

[0017] As a further technical solution, the drying in step S2 is freeze-drying, freezing at -40°C for 24-48 hours.

[0018] As a further technical solution, the carbonization in step S4 is to heat the material to 700-1200° C. at a heating rate of 1-10° C. / min under an inert atmosphere and keep the temperature for 1-6 hours.

[0019] The working principle and beneficial effects of the present invention are:

[0020] 1. The present invention prepares a porous iron oxide / graphene coated material by a hydrothermal method from an organic iron-based compound, a metal coupling agent, lanthanum hydroxide, and graphene. On the one hand, the impedance of the coating material is reduced by relying on graphene, and on the other hand, a network structure is formed by the coupling agent to constrain the expansion of the iron-based material. At the same time, the porous iron oxide / graphene coated material is carbonized after mixing with a binder and an organic solvent to convert it into amorphous carbon, which plays a synergistic role with the iron-based oxide. On the one hand, the electronic conductivity of the amorphous carbon is improved, so that the porous iron-based material has high energy density and high electronic conductivity. On the other hand, its porous structure improves the material's liquid absorption and retention capacity, the lithium ion insertion and extraction rate during the charge and discharge process, and its cycle performance. The resulting graphite composite material not only has a higher specific capacity and power performance, but also solves the defects of large iron oxide expansion and poor cycle performance, thereby improving the comprehensive performance of the graphite material.

[0021] 2. In the present invention, doping with lanthanum hydroxide provides an alkaline environment for the hydrothermal reaction to improve the reaction process. On the other hand, doping with lanthanum after the lanthanum hydroxide reaction improves the electronic conductivity of the iron compound. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] Figure 1 This is the SEM image of the graphite composite material prepared in Example 1. DETAILED DESCRIPTION

[0024] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0025] Example 1

[0026] A method for preparing a high-power graphite composite material comprises the following steps:

[0027] S1. Weigh 100 g of 3 wt% graphene conductive liquid and add the graphene to disperse uniformly, then add 100 g of ammonium ferric citrate, 3 g of isopropyl titanate tristearate, and 3 g of lanthanum hydroxide and disperse uniformly by ultrasonication to obtain a mixed solution;

[0028] S2. The mixed solution was transferred to a high-pressure reactor, reacted at a temperature of 150° C. for 3 h, and then freeze-dried at -40° C. for 24 h to obtain a porous iron oxide / graphene coated material;

[0029] S3, weighing 10g of porous iron oxide / graphene coating material, 5g of petroleum asphalt and 800g of carbon tetrachloride and dispersing them evenly to obtain a coating mixture;

[0030] S4. Add 100 g of artificial graphite to the coating mixture, mix well, spray dry, heat to 900° C. at a heating rate of 5° C. / min under an argon inert atmosphere, and keep warm for 3 h. Then, crush and classify to obtain a graphite composite material.

[0031] Example 2

[0032] A method for preparing a high-power graphite composite material comprises the following steps:

[0033] S1. Weigh 100 g of 1 wt% graphene conductive liquid and add 1 g of aniline to disperse evenly, then add 100 g of acetylferrocene, 1 g of diisostearylethyl titanate, and 1 g of lanthanum hydroxide and disperse evenly by ultrasonication to obtain a mixed solution;

[0034] S2. The mixed solution was transferred to a high-pressure reactor, reacted at 100° C. for 6 h, and then freeze-dried at -40° C. for 24 h to obtain a porous iron oxide / graphene coated material;

[0035] S3, weighing 5g of porous iron oxide / graphene coating material, 1g of coal tar pitch and 500g of cyclohexane and dispersing them evenly to obtain a coating mixture;

[0036] S4. Add 100 g of artificial graphite to the coating mixture, mix well, spray dry, and then heat to 700° C. at a heating rate of 1° C. / min under an argon inert atmosphere and keep warm for 6 h. Crush and classify to obtain a graphite composite material.

[0037] Example 3

[0038] A method for preparing a high-power graphite composite material comprises the following steps:

[0039] S1: Weigh 100g of 5wt% graphene conductive liquid and add 5g of melamine to disperse evenly, then add 100g of ammonium ferric oxalate, 5g of isopropyl titanate tristearate, and 5g of lanthanum hydroxide and disperse evenly by ultrasonication to obtain a mixed solution.

[0040] S2. The mixed solution was transferred to a high-pressure reactor, reacted at a temperature of 200° C. for 1 h, and then freeze-dried at -40° C. for 24 h to obtain a porous iron oxide / graphene coated material;

[0041] S3, weighing 20g of porous iron oxide / graphene coating material, 10g of petroleum asphalt and 1500g of N-methylpyrrolidone and dispersing them evenly to obtain a coating mixture;

[0042] S4. Add 100 g of artificial graphite to the coating mixture, mix well, spray dry, and then heat to 1200° C. at a heating rate of 10° C. / min under an inert atmosphere and keep warm for 1 hour. Crush and classify to obtain a graphite composite material.

[0043] Example 4

[0044] Compared with Example 3, Example 4 replaces ferric ammonium oxalate with an equal amount of ferric ammonium ethylenediaminetetraacetate, and the rest is the same as Example 3.

[0045] Example 5

[0046] Compared with Example 3, in step S1 of Example 5, 100 g of 5 wt% graphene conductive liquid was weighed and 5 g of melamine, 100 g of ammonium ferric oxalate, 5 g of isopropyl tristearate titanate, and 5 g of lanthanum hydroxide were added and ultrasonically dispersed uniformly to obtain a mixed solution. The rest was the same as in Example 3.

[0047] Comparative Example 1

[0048] 100 g of 5 wt% graphene conductive liquid, 5 g of petroleum asphalt and 100 g of artificial graphite were added to a ball mill and mixed evenly. The mixture was then transferred to a tube furnace and heated to 900 ° C under an argon atmosphere and kept warm for 3 h. The mixture was then cooled to room temperature under an argon atmosphere and crushed to obtain a graphite composite material.

[0049] Comparative Example 2

[0050] 10g of ammonium ferric citrate, 5g of petroleum asphalt and 800g of carbon tetrachloride were weighed and dispersed evenly to obtain a coating mixture. Then 100g of artificial graphite was added, mixed evenly, spray-dried, and then heated to 900℃ at a heating rate of 5℃ / min under an argon inert atmosphere and kept warm for 3h. The graphite composite material was crushed and classified.

[0051] Comparative Example 3

[0052] Compared with Example 3, Comparative Example 3 does not add a nitrogen source, and the rest is the same as Example 3.

[0053] Comparative Example 4

[0054] Compared with Example 3, Comparative Example 4 replaces ferric ammonium oxalate with an equal amount of ferric chloride, and the rest is the same as Example 3.

[0055] Comparative Example 5

[0056] Compared with Example 3, the addition amount of lanthanum hydroxide in Comparative Example 5 was changed to 7 g, and the others were the same as in Example 3.

[0057] Experimental Example 1

[0058] (1) SEM test

[0059] The graphite composite negative electrode material prepared in Example 1 was subjected to SEM testing, and the results were as follows: Figure 1 As shown. Figure 1 It can be seen that the particle size is between 10-15μm, the particle size distribution is reasonable, and there is a slight granulation structure.

[0060] (2) Physical and chemical properties test

[0061] The conductivity, tap density, specific surface area, and particle size of the graphite composite negative electrode materials in Examples 1-5 and Comparative Examples 1-5 were tested according to the test methods in the standard GB / T-24533-2019, "Graphite Anode Materials for Lithium-ion Batteries." The test results are shown in Table 1.

[0062] Table 1 Physical and chemical properties test results

[0063]

[0064] Comparative Example 1 is not coated with iron oxide. As can be seen from Table 1, the conductivity, tap density and specific surface area of ​​the graphite composite negative electrode material prepared in Example 1-4 are all higher than those in Comparative Example 1. The reason may be that the surface of the embodiment material is coated with porous iron oxide with high electronic conductivity, which reduces the impedance and increases the specific surface area. At the same time, iron oxide has a high tap density, thereby increasing the tap density of the composite material. Comparative Example 2 changes the preparation method of the graphite composite material, and the physical and chemical properties of the prepared graphite composite negative electrode material are all lower than those of Examples 1-4. Example 5 adds a nitrogen source to a graphene conductive liquid together with an organic iron source compound, a metal coupling agent and a rare earth compound and mixes them evenly. Comparative Example 3 does not add a nitrogen source. Comparative Example 5 increases the amount of lanthanum hydroxide added. The conductivity, tap density and specific surface area of ​​the graphite composite material prepared are all lower than those of Examples 1-4. Comparative Example 4 replaces ferric ammonium oxalate with an equal amount of ferric chloride. It is impossible to form a porous structure and the poor uniformity leads to a decrease in conductivity and specific surface area.

[0065] (3) Button battery test

[0066] The graphite composite negative electrode materials prepared in Examples 1-5 and the graphite composite negative electrode materials in Comparative Examples 1-5 were assembled into button batteries according to the following method:

[0067] The graphite composite negative electrode materials prepared in Examples 1-5 and Comparative Examples 1-5 served as negative electrodes and were assembled into button-type batteries with a lithium sheet, electrolyte, and separator in a glove box maintained at an argon atmosphere and a water content below 0.1 ppm. The separator was Celebard 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) in a 1:1 weight ratio.

[0068] The button cell battery performance was tested using a Blue Battery Tester under the following conditions: a 0.1C charge / discharge rate, a voltage range of 0.05-2V, and a three-cycle cycle. The test results are shown in Table 2.

[0069] Table 2 Button battery performance test results

[0070]

[0071] As can be seen from Table 2, the button batteries made with the graphite composite negative electrode materials of Examples 1-4 have significantly higher discharge capacity and efficiency than those of Comparative Examples 1-2. The experimental results show that the graphite composite material obtained by the preparation method of the present invention can enable the battery to have good discharge capacity and efficiency. The reason is that porous iron oxide is doped into the graphite to increase the specific capacity of the material, and the porous structure is used to reduce its full-charge expansion. In Example 5, a nitrogen source is added to the graphene conductive liquid together with an organic iron source compound, a metal coupling agent, and a rare earth compound and mixed evenly. In Comparative Example 3, no nitrogen source is added. In Comparative Example 4, ferric ammonium oxalate is replaced with an equal amount of ferric chloride. In Comparative Example 5, the amount of lanthanum hydroxide added is increased. The button battery performance of the obtained graphite composite material is lower than that of Examples 1-4.

[0072] (4) Soft pack battery performance test

[0073] The graphite composite negative electrode of Examples 1-5 and Comparative Examples 1-5 is used as the negative electrode active material, and the positive electrode active material ternary material (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2), electrolyte and diaphragm are assembled into a 5Ah soft-pack battery.

[0074] The diaphragm is celegard 2400, and the electrolyte is LiPF6 solution (the solvent is a mixed solution of EC and DEC with a volume ratio of 1:1, and the concentration of LiPF6 is 1.3 mol / L).

[0075] In Examples 1-5 and Comparative Examples 1-5, 5Ah soft-pack batteries and their corresponding negative electrode sheets were prepared, and the liquid absorption and retention capacity and cycle performance of the negative electrode sheets were tested. The results are shown in Table 3. The test method is as follows:

[0076] a. Liquid absorption capacity:

[0077] Using a 1mL burette, draw up VmL of electrolyte and drip one drop onto the electrode surface. The time is measured until the electrolyte is completely absorbed. The time t is recorded and the electrode absorption rate (V / t) is calculated. The test results are shown in Table 3.

[0078] b. Liquid retention rate test:

[0079] According to the electrode parameters, calculate the theoretical liquid absorption amount m1 of the electrode, and weigh the weight of the electrode m2. Then place the electrode in the electrolyte and soak it for 24 hours. Weigh the weight of the electrode as m3, calculate the liquid absorption amount of the electrode m3-m2, and calculate according to the following formula: liquid retention rate = (m3-m2)*100% / m1.

[0080] c. Cycle performance: The battery's cycle performance is tested at a charge and discharge rate of 1C / 1C, a voltage range of 2.5V-4.2V, and a temperature of 25±3°C;

[0081] d. Rate performance: Charge the battery to 100% SOC at a rate of 2C using constant current + constant voltage mode, and then calculate the constant current ratio = constant current capacity / (constant current capacity + constant voltage capacity).

[0082] Table 3 Test results of liquid absorption speed and liquid retention rate of soft pack batteries

[0083]

[0084] Table 4 Capacity retention and fast charging performance test results of soft-pack batteries after 500 cycles

[0085]

[0086]

[0087] As shown in Table 3, the graphite composite materials obtained in Examples 1-4 exhibit significantly higher liquid absorption and retention capabilities than those in Comparative Examples 1-5, demonstrating that the graphite composite materials of the present invention possess a high specific surface area and a porous structure, which enhances the material's liquid absorption capacity. As shown in Table 4, the cycling performance of the batteries in Examples 1-4 is significantly better than that in Comparative Examples 1-5. This is due to the low expansion coefficient of the graphite composite materials obtained in Examples 1-4, which reduces electrolyte consumption during cycling, reduces side reactions, and enhances cycling performance. Furthermore, the graphite composite materials obtained in Examples 1-4 possess a larger specific surface area, which enhances the material's liquid absorption and retention capabilities, thereby improving cycling performance. Furthermore, the materials in Examples 1-4 exhibit excellent electrical conductivity, which enhances the material's rate capability.

[0088] In Example 5, a nitrogen source is added to the graphene conductive liquid together with an organic iron source compound, a metal coupling agent, and a rare earth compound and mixed evenly. In Comparative Example 3, no nitrogen source is added. In Comparative Example 4, ammonium ferric oxalate is replaced with an equal amount of ferric chloride. In Comparative Example 5, the amount of lanthanum hydroxide added is increased. The comprehensive performance of the soft-pack batteries of the obtained graphite composite materials is lower than that of Examples 1-4.

[0089] It can be seen from Table 1, Table 2 and Table 3 that by not performing coating treatment in Comparative Example 1, changing the preparation method of the graphite composite material in Comparative Example 2, changing the order of adding materials in Example 5, not adding a nitrogen source in Comparative Example 3, replacing ammonium ferric oxalate with an equal amount of ferric chloride in Comparative Example 4, and increasing the amount of lanthanum hydroxide added in Comparative Example 5, the physical and chemical properties of the graphite composite material and its performance as the negative electrode of button batteries and soft-pack batteries cannot be improved.

[0090] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a high-power graphite composite material, characterized in that: The following steps are involved: S1. Add a nitrogen source to the graphene conductive liquid and disperse it evenly, then add an organic iron source compound, a metal coupling agent, and a rare earth compound and disperse them evenly to obtain a mixed solution; S2, reacting the mixed solution at a temperature of 100-200° C. for 1-6 hours, and then drying to obtain a porous iron oxide / graphene coated material; S3, adding a binder and an organic solvent to the porous iron oxide / graphene coating material, and dispersing them evenly to obtain a coating mixture; S4, adding graphite to the coating mixture, mixing evenly, drying, and carbonizing to obtain a graphite composite material; The rare earth compound in step S1 is lanthanum hydroxide; In step S1, the mass ratio of graphene, nitrogen source, organic iron source compound, metal coupling agent and rare earth compound is 1-5:1-5:100:1-5:1-5.

2. The method for preparing a high-power graphite composite material according to claim 1, characterized in that: The solvent of the graphene conductive liquid in step S1 is N-methylpyrrolidone, and the concentration is 1-5 wt %.

3. The method for preparing a high-power graphite composite material according to claim 1, characterized in that: In step S1, the nitrogen source includes one or more of pyrrole, thiophene, aniline, urea, and melamine; and the metal coupling agent includes one or more of titanate coupling agents and aluminate coupling agents.

4. The method for preparing a high-power graphite composite material according to claim 1, characterized in that: The organic iron source compound in step S1 includes one or more of ammonium ferric citrate, acetylferrocene, ferric ammonium oxalate, and ammonium ferric ethylenediaminetetraacetate.

5. The method for preparing a high-power graphite composite material according to claim 1, characterized in that: In step S3, the binder includes one of petroleum asphalt and coal asphalt; the organic solvent includes one of carbon tetrachloride, cyclohexane, xylene, and N-methylpyrrolidone.

6. The method for preparing a high-power graphite composite material according to claim 1, characterized in that: The mass ratio of the porous iron oxide / graphene coating material, the binder, the organic solvent and the graphite is 5-20:1-10:500-1500:

100.

7. The method for preparing a high-power graphite composite material according to claim 1, characterized in that: The drying in step S2 is freeze drying, freezing at -40°C for 24-48 hours.

8. The method for preparing a high-power graphite composite material according to claim 1, characterized in that: The carbonization in step S4 is to heat the material to 700-1200° C. at a heating rate of 1-10° C. / min under an inert atmosphere and keep the temperature for 1-6 hours.

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