Preparation method of high-rate wide-temperature-range regenerated graphite negative electrode material

Abstract

The invention discloses a preparation method of a high-rate wide-temperature-range regenerated graphite negative electrode material, and belongs to the technical field of lithium ion battery recovery. The invention provides a preparation method of a high-magnification wide-temperature-range regenerated graphite negative electrode material, which combines a multi-section high-temperature synergistic treatment means and a lithium-rich catalytic surface modification technology, realizes impurity removal of a waste graphite negative electrode under the condition of lower energy consumption, and realizes effective repair of a graphite crystal structure. According to the method, through the synergistic effect of ultrahigh-temperature gasification and the reactive atmosphere, trace metal impurities which are most difficult to remove and fluorine-containing compounds with thermal stability are almost thoroughly removed, and the purity of the regenerated graphite is improved to be close to the level of a primary material (the purity gt is 99.9%); and a lithium-rich catalytic surface modification technology is adopted, so that the graphite surface can be stabilized, and the rate capability and low-temperature performance of the material are improved. The graphitization degree (gt; 95%) of the material is remarkably improved through the in-situ defect repairing effect driven by ultrahigh temperature, and the highly-ordered layered crystal structure and the excellent conductive network of the material are recovered.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of lithium ion battery recycling, in particular to a preparation method of high-rate wide-temperature-range regenerated graphite negative electrode material. BACKGROUND

[0002] With the wide application of lithium ion batteries in the fields of consumer electronics, electric vehicles and energy storage power stations, the amount of scrap batteries also increases explosively. The positive electrode material (such as lithium cobaltate, lithium iron phosphate and ternary material) of the lithium battery has high recycling value and is highly concerned, while the graphite negative electrode which accounts for a large proportion of the weight of the battery is often ignored and is usually buried or incinerated as waste, causing resource waste and environmental pollution.

[0003] During the long-term charging and discharging process of the graphite negative electrode, problems such as structural degradation, continuous thickening of the surface SEI film and deposition of lithium dendrites and metal impurities occur, which leads to the decline of the electrochemical performance of the graphite negative electrode. At present, the recycling of the graphite negative electrode mainly adopts a wet process, that is, an acid or alkali reagent is used to extract key metal elements in the waste battery, and the separated graphite waste is usually directly stacked or incinerated, causing serious resource waste.

[0004] The low-temperature repair technology of the graphite negative electrode has the advantages of simple operation and low energy consumption, but the repair effect is mainly limited to the surface of the graphite and cannot handle the crystal structure defects in the graphite. To fundamentally repair the damage to the graphite layer structure caused by the repeated embedding and extraction of lithium ions and realize the performance recovery and high-value utilization of the negative electrode material, it is necessary to rearrange the crystal structure of the graphite through high-temperature treatment, so as to improve the graphitization degree and structural stability. High-temperature graphitization rearranges the graphite crystal structure through high-temperature thermal activation, repairs defects such as interlayer peeling and lattice distortion, and thus improves the electrochemical performance and mechanical strength. In addition, the structural damage degree of waste graphite materials from different sources is quite different, and a simple repair process cannot realize uniform regeneration of the graphite structure. Therefore, the high-temperature repair method needs to be changed from traditional single roasting to multi-stage cooperative treatment, so as to effectively reduce the energy consumption, and then supplemented by a regenerated graphite surface interface means, so as to finally realize the preparation of the high-rate wide-temperature-range regenerated graphite negative electrode material. SUMMARY

[0005] In order to solve the above problems, the application provides a preparation method of high-rate wide-temperature-range regenerated graphite negative electrode material.

[0006] The application is realized by the following technical scheme: The preparation method of the high-rate wide-temperature-range regenerated graphite negative electrode material comprises the following steps: Step 1: the disassembled negative plate is immersed in deionized water, and the waste lithium battery graphite negative powder is obtained by ultrasonic, water washing and drying, wherein the ultrasonic time is 5-30 min; the mass ratio of the negative plate to water is 1:1-2; the water washing times are 2-4 times; and the drying conditions are 80-100 degrees Celsius and 12 hours; Step 2: the waste lithium battery graphite negative powder is placed in a mixed atmosphere for staged calcination; the mixed atmosphere includes an inert atmosphere and a specific reaction gas, the inert atmosphere is nitrogen or argon, and the specific reaction gas is chlorine or hydrogen; the staged calcination includes low-temperature calcination treatment, medium-temperature calcination treatment and high-temperature calcination treatment, the low-temperature calcination treatment process is that the low-temperature temperature is 800-1500 DEG C, and the holding time is 1-5 h, the medium-temperature calcination treatment process is that the medium-temperature temperature is 2000-2500 DEG C, and the holding time is 1-10 h, and the high-temperature temperature is 2800-3000 DEG C, and the holding time is 5-20 h; Step 3: the product obtained in step 2 is uniformly mixed with a coating agent and a catalyst, and is calcined under a nitrogen atmosphere, the mass ratio of the coating agent to the graphite negative powder is 1:5-1:50, the mass ratio of the catalyst to the negative powder is 1:100-1:10; the calcination temperature is 400-900 DEG C, and the holding time is 2-20 h.

[0007] Preferably, the volume ratio of the specific reaction gas in step 2 to the mixed atmosphere is 0.1%-5%.

[0008] Preferably, the coating agent in step 3 is one or more of starch, sucrose, glucose and citric acid.

[0009] Preferably, the catalyst in step 3 is a lithium salt, including one or more of lithium carbonate, lithium chloride, lithium sulfate, lithium nitrate and lithium fluoride.

[0010] Compared with the prior art, the present application has the following beneficial effects: The present application provides a preparation method of a high-rate wide-temperature-range regenerated graphite negative material, which combines multi-stage high-temperature cooperative treatment means and lithium-rich catalytic surface modification technology, and can realize the removal of impurities from waste graphite negative electrodes and the effective repair of graphite crystal structures under lower energy consumption conditions.

[0011] The present application adopts high-temperature gas heating repair, realizes the nearly complete removal of trace metal impurities and heat-stable fluorine-containing compounds which are most difficult to remove through the synergistic effect of ultrahigh-temperature gasification and reactive atmosphere, and improves the purity of the regenerated graphite to a level close to that of the original material (such as >99.9%); at the same time, the lithium-rich catalytic surface modification technology can stabilize the graphite surface and improve the rate performance and low-temperature performance of the material. At the same time, the in-situ defect repair effect driven by ultrahigh temperature significantly improves the graphitization degree of the material (which can be >95%), restores the highly ordered layered crystal structure and excellent conductive network. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 XRD pattern of the sample obtained in Example 1 of the present application; Figure 2 SEM image of the sample obtained in Example 1 of the present application; Figure 3 Cycle performance graph of the sample obtained in Example 2 of the present application; Figure 4 SEM image of the sample obtained in Example 2 of the present application. DETAILED DESCRIPTION

[0013] The present application is further described below with reference to the accompanying drawings: A preparation method of a high-rate wide-temperature-range regenerated graphite negative electrode material, comprising the following steps: Step 1: The disassembled negative electrode sheet is immersed in deionized water, and waste lithium battery graphite negative electrode powder is obtained through ultrasonic, water washing and drying, wherein the ultrasonic time is 5-30 min; the mass ratio of the negative electrode sheet to water is 1:1-2; the water washing times are 2-4 times; and the drying conditions are 80-100 degrees Celsius for 12 hours.

[0014] Step 2: The waste lithium battery graphite negative electrode powder is placed in a mixed atmosphere for stage calcination; the mixed atmosphere includes an inert atmosphere and a specific reaction gas, the inert atmosphere is nitrogen or argon, and the specific reaction gas is chlorine or hydrogen; the stage calcination includes low-temperature calcination treatment, medium-temperature calcination treatment and high-temperature calcination treatment, the low-temperature calcination treatment process is: a low-temperature temperature of 800-1500°C and a holding time of 1-5h, and the purpose is to remove part of metal impurities, such as lithium, which has a boiling point of 1342°C and is removed in the low-temperature calcination section; the medium-temperature calcination treatment process is: a medium-temperature temperature of 2000-2500°C and a holding time of 1-10h, and the purpose is to reduce oxides and remove part of impurities; a high-temperature temperature of 2800-3000°C and a holding time of 5-20h, and the purpose of the high-temperature calcination stage is to repair the graphite lattice.

[0015] Step 3: The above product is uniformly mixed with a coating agent and a catalyst, and calcined under a nitrogen atmosphere. The coating agent is one or more of starch, sucrose, glucose, citric acid; the catalyst is lithium salt, including one or more of lithium carbonate, lithium chloride, lithium sulfate, lithium nitrate, lithium fluoride; the mass ratio of the coating agent to the negative electrode powder is 1:50-1:5; the mass ratio of the catalyst to the negative electrode powder is 1:100-1:10; and the calcination condition is 400-900°C for 2-20h. The purpose of this step is to form a uniform thin layer of carbon on the surface of the regenerated graphite particles, to improve the cycle stability and rate performance of the material. At the same time, the addition of lithium salt can supplement lithium source, effectively improving the first circle coulomb efficiency. Example 1

[0016] Step one: the disassembled negative electrode sheet was immersed in deionized water, and ultrasonic was applied for 10 minutes at 120W power. The peeled black powder was collected by suction filtration and washed with water for 3 times. The recovered waste graphite negative electrode powder was dried at 80℃ for 12 hours.

[0017] Step two: the above waste graphite powder was put into a graphitization furnace and heated to 800℃ for 2h, 2200℃ for 2h and 2800℃ for 6h in hydrogen-argon mixed gas (hydrogen volume ratio is 1%).

[0018] Step three: the product of step two was uniformly mixed with sucrose and lithium carbonate at a mass ratio of 90:8:2, and calcined at 800℃ for 4h in a nitrogen atmosphere to obtain the final product.

[0019] Figure 1 is the X-ray diffraction (XRD) pattern of the sample obtained in Example 1. According to the Franklin formula G=(0.3440-d002) / (0.3440-0.3354)×100%, it can be calculated that the in-situ defect repair effect driven by ultra-high temperature significantly improves the graphitization degree of the material, and the graphitization degree of the sample reaches >95%. Example 2

[0020] Step one: the disassembled negative electrode sheet was immersed in deionized water, and ultrasonic was applied for 10 minutes at 120W power. The peeled black powder was collected by suction filtration and washed with water for 3 times. The recovered waste graphite negative electrode powder was dried at 80℃ for 12 hours.

[0021] Step two: the above waste graphite powder was put into a graphitization furnace and heated to 1000℃ for 3h, 2000℃ for 2h and 2800℃ for 10h in hydrogen-argon mixed gas (hydrogen volume ratio is 1%).

[0022] Step three: the product of step two was uniformly mixed with sucrose and lithium carbonate at a mass ratio of 92:7:1, and calcined at 800℃ for 4h in a nitrogen atmosphere to obtain the final product.

[0023] High-efficiency removal of metal impurities, residual fluorine-containing compounds, etc. is achieved. At the same time, high temperature gives carbon atoms extremely high migration ability, which promotes the dynamic in-situ repair of various lattice defects in the graphite crystal and at the boundary due to fragmentation, lithium intercalation / deintercalation or impurity erosion under high temperature thermal activation, and realizes lattice rearrangement and structure ordering.

[0024] Figure 3is a graph of the electrical performance test of the sample of Example 2 as a negative material of lithium ion battery, from which it can be seen that the sample material exhibits excellent cycle stability within 200 cycles: the initial specific discharge capacity is about 400 mAh / g, the specific capacity fluctuates very little in subsequent cycles, and is maintained at about 300 mAh / g as a whole, and the capacity attenuation rate is very low, indicating that the material obtained in Example 2 has stable structure and excellent electrochemical performance.

[0025] Figure 2 is a scanning electron microscope graph of the sample of Example 1, Figure 4 is a scanning electron microscope graph of the sample of Example 2, from which it can be seen that the graphite has an irregular flaky structure and restores a highly ordered layered crystal structure.

[0026] From the test data of the sample obtained in the example, it can be concluded that the present application provides a preparation method of a high-rate wide-temperature-range regenerated graphite negative material, which uses high-temperature gas heating repair, realizes nearly complete removal of trace metal impurities and thermally stable fluorine-containing compounds that are most difficult to remove through synergistic effect of ultrahigh-temperature gasification and reactive atmosphere, and improves the purity of the regenerated graphite to a level close to that of the primary material (such as >99.9%); at the same time, the lithium-rich catalytic surface modification technology used can stabilize the graphite surface and improve the rate performance and low-temperature performance of the material. At the same time, the in-situ defect repair effect driven by ultrahigh temperature significantly improves the graphitization degree of the material (which can be >95%) and restores its highly ordered layered crystal structure and excellent conductive network.

[0027] In conclusion, the above is only a preferred embodiment of the present application, and is not intended to limit the scope of the present application, and any equivalent changes and modifications made in the shape, structure, features and spirit of the present application within the scope of the claims of the present application shall be included in the scope of the claims of the present application.

Claims

1. A method for preparing a high-rate, wide-temperature-range regenerated graphite anode material, characterized in that: Includes the following steps: Step 1: Immerse the disassembled negative electrode sheet in deionized water, and obtain waste lithium battery graphite negative electrode powder through ultrasonication, water washing, and drying. The ultrasonication time is 5-30 minutes; the mass ratio of negative electrode sheet to water is 1:1-2; the number of water washing times is 2-4; the drying conditions are 80-100 degrees Celsius for 12 hours. Step 2: Place the waste lithium battery graphite anode powder in a mixed atmosphere for staged calcination; the mixed atmosphere includes an inert atmosphere and a specific reactive gas, the inert atmosphere being nitrogen or argon, and the specific reactive gas being chlorine or hydrogen; the staged calcination includes low-temperature calcination, medium-temperature calcination, and high-temperature calcination. The low-temperature calcination process is: low temperature 800-1500℃, holding time 1-5h; the medium-temperature calcination process is: medium temperature 2000-2500℃, holding time 1-10h; and the high-temperature calcination process is: high temperature 2800-3000℃, holding time 5-20h. Step 3: Mix the product obtained in Step 2 with the coating agent and catalyst evenly, and calcine it under a nitrogen atmosphere. The mass ratio of the coating agent to the graphite anode powder is 1:5-1:50, and the mass ratio of the catalyst to the anode powder is 1:100-1:

10. The calcination temperature is 400-900℃, and the holding time is 2-20h.

2. The method for preparing a high-rate, wide-temperature-range regenerated graphite anode material according to claim 1, characterized in that: In step 2, the volume ratio of the specific reactive gas added is 0.1%-5% of the mixed atmosphere.

3. The method for preparing a high-rate, wide-temperature-range regenerated graphite anode material according to claim 1, characterized in that: The coating agent in step 3 is one or more of starch, sucrose, glucose, and citric acid.

4. The method for preparing a high-rate, wide-temperature-range regenerated graphite anode material according to claim 1, characterized in that: The catalyst in step 3 is a lithium salt, including one or more of lithium carbonate, lithium chloride, lithium sulfate, lithium nitrate, and lithium fluoride.

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