CN114864935A - Method for preparing high-rate lithium battery negative electrode material from natural graphite spherical tailings - Google Patents

Abstract

The invention discloses a preparation method of a high-performance natural spherical graphite tailings-based lithium battery negative electrode material, which belongs to the field of secondary resource utilization. The method uses small-sized flake spherical tailings as raw materials, and uses graphite surface functional groups to graft high-molecular polymers to prepare high-performance lithium battery anode materials. The method is as follows: first, the natural spherical graphite tailings are oxidized, washed and dried After treatment, it is placed in an organic solution for ultrasonic treatment, a catalyst is added to activate functional groups and then a high molecular polymer is added. After a period of reaction, centrifugation, washing, suction filtration and drying are performed to obtain a high-performance lithium ion battery negative electrode material. The invention uses natural graphite ball tailings as raw materials, obtains high-performance lithium battery negative electrode materials through grafting polymers, realizes high-value utilization of spherical tailings, and the research process is green and environmentally friendly, without high-temperature links, and low cost.

Description

A method for preparing high-rate lithium battery negative electrode material from natural graphite spherical tailings

technical field

The invention belongs to the technical field of lithium ion batteries, and discloses a method for preparing a high-performance lithium ion battery negative electrode material from natural graphite spherical tails.

Background technique

With the continuous deepening of the application of lithium-ion batteries in portable devices, electric vehicles and rail transit, the market demand for new lithium-ion batteries with high energy density, high power density, high safety and long life is more urgent. Graphite-based anode materials have long been dominant in anode materials due to their low and stable charge-discharge platform, relatively high theoretical specific capacity, and good structural stability. Graphite anode materials include artificial graphite and natural graphite. Compared with artificial graphite, natural graphite has relatively high crystallinity and rich resources. At the same time, there is no high-energy consumption process such as high-temperature graphitization in the preparation process, which has significant advantages in cost. .

However, some performance properties of natural graphite are still unsatisfactory, such as rate capability and cycling stability. Natural graphite has high anisotropy. The atoms between the graphite sheets are bonded by van der Waals force, and there is translation. During the processing, smearing and extrusion of electrodes, most of them are stacked parallel to the current collector. The end face of the C-axis of the graphite crystal is inserted. When the orientation of the graphite is parallel to the current collector, the migration distance of lithium ions becomes longer and the diffusion rate becomes slower, which is the main reason for the poor rate capability of the graphite negative electrode. In order to solve the above problems, methods such as etching, expansion, and compounding with carbon nanotubes are usually used to improve the diffusion rate of lithium ions in graphite crystals. Such methods shorten the migration path of lithium ions and improve the rate performance. Besides, the rate performance and cycling stability of the graphite anode are also affected by the SEI film. The ideal SEI film should be uniform in morphology and composition, but the SEI film formed on the surface of graphite is often not of high quality, not uniform and dense, and is easy to break, causing solvated molecules to enter between the graphite layers, resulting in layer exfoliation, resulting in the cycle stability of the graphite negative electrode. worse. Moreover, the thicker SEI film will also increase the interface impedance, hinder the rapid diffusion of Li+, and affect the rate performance of the negative electrode material. Therefore, to form a uniform and stable SEI, it is crucial to accelerate the rate of Li+ crossing the SEI film.

Natural graphite spherical tailings are solid wastes produced during the spheroidization of natural flake graphite, and its essence is still high-purity natural flake graphite with high electrical conductivity, which is a potential negative electrode material for lithium batteries. Replacing spherical graphite with spherical tailings further reduces the cost of anode materials. However, the size of the spherical tailings is too small (D50≈6μm), which is prone to agglomeration, and does not change the anisotropy of graphite in essence. Most of the methods currently used are secondary granulation. Graphite-based composite anodes were prepared by introducing coking coal into graphite tailings. The colloid produced by the pyrolysis of coking coal and the spherical tailings are cross-linked to realize the granulation of the graphite spherical tailings, which changes the form of the flake-like accumulation of the graphite spherical tailings, reduces the anisotropy of the negative electrode material, and improves the Li+ concentration. Transmission rate. However, this type of method requires a pyrolysis temperature of 700°C-1000°C, which greatly increases energy consumption and production costs, and imposes a certain burden on the environment. Therefore, it is necessary to develop low-energy-consumption, low-cost natural graphite anode materials.

SUMMARY OF THE INVENTION

In order to solve the problem of poor rate performance of natural graphite spherical tailings, the present invention provides a method for modifying natural graphite spherical tailings, which utilizes the grafting of graphite surface functional groups and high molecular polymers to prepare high-performance lithium battery negative electrode materials, which are graphite solid wastes. Processing provides a new path, the specific steps are as follows:

Step 1: Weigh a certain quality of purified natural graphite spherical tailings, add a certain amount of oxidant, and stir at room temperature for 2-8 hours for oxidation treatment;

Step 2: The graphite in step 1 is washed with deionized water for several times, then suction filtered, and the oxidized graphite is dried to obtain product 1.

Step 3: ultrasonically disperse the product 1 in an organic solution for 30-60 min, add catalyst, stir at room temperature for 30-60 min, add high molecular polymer, and stir at room temperature for 6-12 h. Product 2 is obtained.

Step 4: After washing the product 2 with a large amount of organic solvent, centrifugation, suction filtration, drying at high temperature to remove the organic solvent, and obtaining the final product.

Further, in the step 1, the particle size D50 of the spherical tailings is 100 nm to 20 μm, and the fixed carbon content after purification is greater than 99%. In the step 1, the oxidant can be a combination of one or more of the following reagents: hydrogen peroxide, concentrated nitric acid, concentrated sulfuric acid, concentrated hydrochloric acid, potassium permanganate, potassium hydroxide, and sodium hydroxide. The solid-liquid ratio of graphite to oxidant is 1:50 to 1:100.

Further, the organic solvent in the step 3 can be a combination of one or more of the following reagents: N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), ethanol, Diethyl ether, ethyl acetate, acetonitrile. The solid-liquid ratio of graphite to organic solution is 1:50～1:100. In the step 3, the catalyst can be a combination of one or more of the following reagents: N-hydroxysuccinimide (NHS), 1-ethyl-(3-dimethylaminopropyl) carbodiimide ( EDC), HATU, dicyclohexylcarbodiimide (DCC), N,N'-diisopropylcarbodiimide (DIC), 1-hydroxybenzotriazole (HOBt), the mass ratio of graphite to catalyst is 1:1 to 1:6. The high molecular polymer in the step 3 can be the following reagents: mPEG-NH2, PEA. The mass ratio of graphite and high molecular polymer is 1:2～1:10.

Further, in the step 4, the high temperature drying temperature is 100°C to 150°C.

The invention aims to combine the characteristics of natural graphite spherical tailings to carry out certain surface modification. First, the natural graphite spherical tailings are oxidized, and an amide bond is formed by amidation reaction between the carboxyl groups on the surface of the graphite and the terminal amino groups of the polymer. The chemical bond force is connected, which improves the bonding between the polymer and the graphite interface. During the cycling process, the polymer contains a large number of C-O-C bonds, and the lone pair electrons of O coordinate with Li+, which accelerates the rate of Li+ crossing the SEI film, and relieves the anisotropy of the graphite anode material to a certain extent, thereby improving the anode. The rate capability of the material. At the same time, a large number of C-O-C bonds on the surface of spherical tailings are beneficial to improve the compatibility of graphite and electrolyte, and play a stable role in the formation of SEI film, which improves the cycle stability of negative electrode materials.

The method of the invention has simple operation, short modification period, all required modifiers are conventional cheap reagents, and has strong operability, and is an effective means for realizing efficient utilization of natural graphite spherical tailings. It can improve the shortcomings of carbon-based materials such as poor rate capability while reducing costs, and has a very broad application prospect.

Description of drawings

Fig. 1 is a process flow diagram of the present invention.

Fig. 2 is the blue electric test cycle stability diagram of natural graphite spherical tailings before and after modification in specific embodiment 1 of the present invention.

Fig. 3 is the blue electric test magnification diagram of natural graphite spherical tailings before and after modification in the specific embodiment of the present invention 1.

Detailed ways

The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited to the following embodiments. The experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials can be obtained from commercial sources unless otherwise specified.

Example 1

The purified natural graphite spherical tailings were placed in a beaker, a certain amount of 30% H2O2 solution was added, and the solid-liquid ratio of graphite to H2O2 solution was 1:50 to form a suspension, which was stirred at room temperature for 4 hours, and the reacted suspension was The turbid liquid was washed with a large amount of deionized water, filtered with suction and dried to obtain product 1. A certain amount of product 1 was mixed with organic solvent DMF, the solid-liquid ratio of graphite and DMF was 1:00, the catalyst NHS and EDC were added after ultrasonic dispersion for 30 minutes, the mass ratio of graphite and catalyst was 1:3, stirred at room temperature for 30 minutes, and then added The PEA solution with a molecular weight of 2000, the solid-liquid ratio of graphite to PEA is 1:6, and stirred at room temperature for 6 hours. The reacted product was washed with a large amount of DMF, centrifuged, filtered with suction and dried to obtain the final product.

The natural graphite spherical tailings-based electrode material prepared in Example 1 was directly used as a negative electrode material for a lithium ion battery, with a metal lithium sheet as the counter electrode, Celgard2325 as a separator, 1mol/L LiPF6 (solvent is a volume ratio of 1:1) ethylene carbonate and dimethyl carbonate mixture) as the electrolyte, CR2032 button battery shell, assembled into a button battery in an argon-protected glove box. Charge and discharge test, the charge and discharge current density in the test procedure is 0.1A/g, 0.2A/g, 0.5A/g, 1.0A/g, 2.0A/g, 5.0A/g, 2.0A/g, 1.0A/g g, 0.5A/g, 0.2A/g, 0.1A/g, the number of charge-discharge cycles under the same current density is 10 cycles, and the voltage charge-discharge range is 0.01-3V. The charge-discharge rate cycle performance of the battery is shown in Figure 2. When the current density is 0.1A/g, the specific capacity of the modified spherical tail-based negative electrode is 418.1 mA h/g, and when the current density is 1.0A/g, the modified spherical tail When the specific capacity of the negative electrode is 321.9mAh/g and the current density is 5.0A/g, the specific capacity of the modified ball-tail negative electrode is 61mA h/g, and the negative electrode can still maintain the low-current charge-discharge performance well after high-current discharge. In the charge-discharge test, the charge-discharge current density in the test procedure was 0.2A/g, and the number of charge-discharge cycles under the same current density was 200 cycles. The modified negative electrode material showed high cycle stability.

Example 2

Put a certain mass of natural graphite spherical tailings after purification, sulfuric acid (concentration of 98.8wt.%) with a mass fraction of 5% of the graphite tailings and 30% H2O2 in a beaker to form a mixture, and use deionized water according to the solid-liquid ratio of 1. : 150 to a constant volume, after forming a suspension, stir at room temperature for 4 hours, rinse the reacted suspension with a large amount of deionized water, suction filtration and dry to obtain product 1. A certain amount of product 1 is mixed with organic solvent ethanol, the solid-liquid ratio of graphite and ethanol is 1:100, the catalyst HOBt is added after ultrasonic dispersion for 30min, the mass ratio of graphite and catalyst is 1:3, stirred at room temperature for 30min, and then added with a molecular weight of 2000 mPEG-NH2 solution, the solid-liquid ratio of graphite and mPEG-NH2 is 1:6, and stirred at room temperature for 6h. The reacted product was washed with a large amount of ethanol, centrifuged, suction filtered and dried to obtain the final product.

The final material was assembled into a half-button battery for charge-discharge performance test. The charge-discharge rate cycle performance of the battery is shown in Figure 3. When the current density is 0.1A/g, the specific capacity of the modified ball-tail negative electrode is 409.7mA h/g, When the current density is 1.0A/g, the specific capacity of the modified balltail negative electrode is 278.5mAh/g, when the current density is 5.0A/g, the specific capacity of the modified balltail negative electrode is 61.3mA h/g, and after high current discharge , the negative electrode can still better maintain the low current charge and discharge performance. In the charge-discharge test, the charge-discharge current density in the test procedure was 0.2A/g, and the number of charge-discharge cycles under the same current density was 200 cycles. The modified negative electrode material showed high cycle stability.

Example 3

Put a certain mass of natural graphite spherical tailings after purification and potassium permanganate solid powder with a mass fraction of 20% of the graphite tailings in a beaker to form a mixture, and use deionized water to make a solid-liquid ratio of 1:50 to form a suspension. The solution was stirred at room temperature for 8 h, the reacted suspension was washed with a large amount of deionized water, suction filtered and dried to obtain product 1. A certain amount of product 1 was mixed with organic solvent acetonitrile, the solid-liquid ratio of graphite and acetonitrile was 1:150, the catalyst DCC was added after ultrasonic dispersion for 30min, the mass ratio of graphite and catalyst was 1:2, stirred at room temperature for 30min, and then polyethylene was added. The solid-liquid ratio of imine, graphite and polyethyleneimine was 1:4, and the mixture was stirred at room temperature for 12 h. The reacted product was washed with a large amount of acetonitrile, centrifuged, suction filtered and dried to obtain the final product. The final material was assembled into a half-button battery for charge-discharge performance testing. When the current density was 0.1A/g, the specific capacity of the modified ball-tail negative electrode was 478.8mA h/g, and when the current density was 1.0A/g, the modified ball-tail negative electrode had a specific capacity of 478.8mA h/g. When the specific capacity of the tail negative electrode is 345.6mAh/g and the current density is 5.0A/g, the specific capacity of the modified ball-tail negative electrode is 72.2mA h/g, and after high current discharge, the negative electrode can still maintain the low current charge and discharge performance. . In the charge-discharge test, the charge-discharge current density in the test procedure was 0.2A/g, and the number of charge-discharge cycles under the same current density was 200 cycles. The modified negative electrode material showed high cycle stability.

Comparative Example 1

The product 1 in Example 1 was assembled into a half-button battery for charge-discharge performance testing. When the current density was 0.1A/g, the specific capacity of the modified ball-tail negative electrode was 388.7mA h/g, and the current density was 1.0A/g. , the specific capacity of the modified ball-tail negative electrode is 100.8mAh/g, and when the current density is 5.0A/g, the specific capacity of the modified ball-tail negative electrode is 32.9mA h/g. In the charge-discharge test, the charge-discharge current density in the test procedure is 0.2A/g, and the number of charge-discharge cycles under the same current density is 200 cycles. The negative electrode material shows poor cycle stability.

In the description of this specification, reference is made to the description of the terms "one embodiment", "some embodiments", "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. It is intended that a particular feature, structure, material or characteristic described in connection with this embodiment or example is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

The above content is a further detailed description of the present invention in conjunction with specific embodiments, and it cannot be considered that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art to which the present invention pertains, some simple deductions or substitutions can be made without departing from the concept of the present invention.

Claims (4)

1. a kind of natural graphite spherical tail material prepares high performance lithium ion battery negative pole method, it is characterized in that, may further comprise the steps: Step 1: weighing a certain quality of purified natural graphite spherical tailings, adding a certain amount of oxidant, and stirring at room temperature for 2-8 hours for oxidation treatment; Step 2: The graphite in step 1 is washed with deionized water for several times, and then suction filtered, and the oxidized graphite is dried to obtain product 1. Step 3: ultrasonically disperse the product 1 in an organic solution for 30-60 min, add catalyst, stir at room temperature for 30-60 min, add high molecular polymer, and stir at room temperature for 6-12 h. Product 2 is obtained. Step 4: After washing the product 2 with a large amount of organic solvent, centrifugation, suction filtration, drying at high temperature to remove the organic solvent, and obtaining the final product. 2. a kind of natural graphite spherical tailings as claimed in claim 1 prepares high performance lithium ion battery negative electrode method, it is characterized in that, in described step 1, spherical tailings particle diameter D50 is 100nm～20μm, and the fixed carbon content after purification is greater than 99%. In the step 1, the oxidant can be a combination of one or more of the following reagents: hydrogen peroxide, concentrated nitric acid, concentrated sulfuric acid, concentrated hydrochloric acid, potassium permanganate, potassium hydroxide, and sodium hydroxide. The solid-liquid ratio of graphite to oxidant is 1:50 to 1:100. 3. a kind of natural graphite spherical tail material as claimed in claim 1 prepares high performance lithium ion battery negative electrode method, it is characterized in that, in described step 3, organic solvent can be the combination of one or more of following reagents: N,N - Dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), ethanol, ether, ethyl acetate, acetonitrile. The solid-liquid ratio of graphite to organic solution is 1:50～1:100. In the step 3, the catalyst can be a combination of one or more of the following reagents: N-hydroxysuccinimide (NHS), 1-ethyl-(3-dimethylaminopropyl) carbodiimide ( EDC), HATU, dicyclohexylcarbodiimide (DCC), N,N'-diisopropylcarbodiimide (DIC), 1-hydroxybenzotriazole (HOBt), the mass ratio of graphite to catalyst is 1:1 to 1:6. The high molecular polymer in the step 3 can be the following reagents: mPEG-NH2, PEA, polyaniline, polyethyleneimine, polyacrylamide. The mass ratio of graphite and high molecular polymer is 1:2～1:10. 4 . The method for preparing a high-performance lithium-ion battery negative electrode from natural graphite spherical tailings according to claim 1 , wherein the high-temperature drying temperature in the step 4 is 100° C.˜150° C. 5 .

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