A method for comprehensively recycling, repairing, and regenerating the cathode material of waste batteries in an integrated manner throughout the entire chain

Abstract

The present disclosure provides a method for comprehensively recycling and repairing and regenerating the cathode material of waste batteries in an integrated manner. The repair and regeneration method includes the following steps: (1) After discharging the waste batteries, pyrolysis separation is carried out to obtain cathode material powder; (2) Lithium supplementation and calcination treatment are carried out on the cathode material powder, and the waste gas is subjected to condensation recovery, acid gas removal and organic gas collection treatment; (3) The collected organic gas is mixed with silicon tetrafluoride to obtain a mixed gas, and the mixed gas is used to carry out plasma coating treatment on the powder obtained by lithium supplementation and calcination to obtain silicon carbide-coated cathode material. The obtained waste gas is recovered by using SiO2, and the obtained silicon tetrafluoride gas is recycled after drying treatment. The present disclosure not only utilizes the organic gas generated by the decomposition of the electrolyte, but also restores the performance of the lithium iron phosphate cathode material, and only silicon dioxide needs to be consumed while fixing the tail gas during the whole reaction process, with low cost.

Description

Technical Field

[0001] The present disclosure belongs to the technical field of resource recovery, for example, a method for comprehensively recycling and repairing and regenerating the cathode material of waste batteries in an integrated whole-chain manner. Background Art

[0002] With the rapid development of the new energy vehicle industry, lithium iron phosphate batteries have stood out among lithium-ion power batteries due to their advantages such as good thermal stability, high safety performance, and excellent cycle stability. However, the service life of power batteries is limited, and the retirement volume of lithium iron phosphate power batteries increases year by year. If they cannot be effectively utilized, it will cause waste of resources and environmental pollution. "Integrated whole-chain recycling" as the main means of circular economy can effectively solve the above problems.

[0003] The valuable components of lithium iron phosphate batteries mainly exist in the cathode material. Therefore, the integrated whole-chain recycling of lithium iron phosphate batteries mainly involves recycling and reusing the waste lithium iron phosphate cathode material. The commonly used recycling methods for lithium iron phosphate cathode materials are pyrometallurgical recycling and hydrometallurgical recycling. Both of these methods separate and extract valuable metals from waste cathode materials, with high energy consumption and the need to consume a large amount of acid and alkali reagents, resulting in a high overall recycling cost. Since the price of lithium iron phosphate is relatively low compared to ternary cathode materials and the content of valuable metals is low, the economic efficiency of recycling using traditional methods is not high.

[0004] CN114006070A discloses a method for high-temperature pyrolysis and pneumatic stripping and separation of waste lithium batteries. The waste gas generated by pyrolysis is treated through processes such as high-temperature incineration, rapid cooling, water washing, and alkali washing, and then discharged up to standard. This method not only consumes energy but also causes a large amount of carbon dioxide emissions, which is not conducive to the realization of the dual-carbon goal.

[0005] CN115312903A discloses a method for regenerating high-rate lithium iron phosphate from waste lithium iron phosphate. The waste lithium iron phosphate powder and ferrous disulfide are mixed into a slurry with water according to a molar ratio and stirred evenly. An acid solution is added to the slurry according to the molar ratio of the waste lithium iron phosphate powder to hydrogen ions, and water is added to adjust the slurry according to the solid-liquid ratio and stirred. The mixed slurry is transferred to an autoclave, sealed, and an oxidizing gas is introduced. After heating and stirring for reaction, it is kept warm. The filtrate after the reaction is filtered, phosphorus source and lithium source are added to the filtrate, and a dispersant is added, then it is heated and kept warm. The slurry after being kept warm and cooled is filtered and washed, and a spray material is obtained by spraying. The spray material is sintered under a protective atmosphere to obtain a carbon-coated lithium iron phosphate cathode material. The regeneration method can replenish lithium for the waste cathode material, restore the morphology, composition and electrochemical performance of the material, and realize the regeneration of the cathode material. The whole regeneration process has less reagent consumption, a short process and low environmental pollution. However, the performance of the regenerated cathode material is not very ideal. This is because, although the waste cathode material is replenished with lithium, the cathode material has poor conductivity, and there are defects in the outer carbon coating layer during the cycling process. It is difficult to completely restore or improve the conductivity of the cathode material only by replenishing lithium. Therefore, the electrochemical performance of the regenerated cathode material is not ideal.

[0006] In addition to the cathode material, the electrolyte is also one of the main components of waste lithium-ion batteries. During the pyrolysis process of battery fragments, a large amount of organic gases are decomposed from the electrolyte. Currently, the organic gases are generally treated by direct combustion. Summary of the Invention

[0007] The following is an overview of the subject matter described in detail in this document. This overview is not intended to limit the scope of protection of the claims.

[0008] The purpose of the present disclosure is to provide a method for comprehensively recycling and repairing and regenerating the cathode material of waste batteries in an integrated manner. The present disclosure not only utilizes the organic gases decomposed from the electrolyte, but also restores the performance of the lithium iron phosphate cathode material. Moreover, the whole reaction process only needs to consume silicon dioxide while fixing the tail gas, with less reagent consumption and low cost.

[0009] To achieve this disclosure purpose, the present disclosure adopts the following technical solutions:

[0010] In a first aspect, an embodiment of the present disclosure provides a method for comprehensively recycling and repairing and regenerating the cathode material of waste batteries in an integrated manner. The repair and regeneration method includes the following steps:

[0011] (1) After discharging the waste battery, it is pyrolyzed and sorted to obtain cathode material powder;

[0012] (2) Perform lithium supplementation and calcination treatment on the cathode material powder;

[0013] (3) Mix the organic gas and silicon tetrafluoride to obtain a mixed gas, and use the mixed gas to perform plasma coating treatment on the powder obtained by lithium supplementation calcination to obtain a silicon carbide-coated cathode material. The exhausted gas obtained is recycled using SiO 2 and the silicon tetrafluoride gas obtained after drying treatment is recycled.

[0014] After the waste battery in the embodiment of the present disclosure is discharged, pretreated battery fragments are obtained after disassembly and crushing treatment, and the battery fragments are pyrolyzed to obtain waste cathode material powder and exhausted gas.

[0015] In the repair and regeneration method of the embodiment of the present disclosure, the carbon capture stream can fix carbon in the coating layer of the regenerated lithium iron phosphate, without carbon dioxide emissions, which is beneficial to reducing carbon emissions. The fluorine circulation stream can realize the recycling of HF, and does not require further collection and treatment of harmful gases, which is beneficial to reducing environmental pollution. The regenerated silicon carbide-coated lithium iron phosphate can repair the damage of the carbon coating layer of the waste lithium iron phosphate, and the material has excellent electrochemical performance. The entire reaction process only needs to consume silicon dioxide while fixing the tail gas, and the cost is low.

[0016] The exhausted gas in the embodiment of the present disclosure is recycled using SiO 2 The reaction equation for the recycling is: SiO 2 + 4HF = SiF 4 + 2H 2 O.

[0017] In one embodiment, the waste battery in step (1) includes any one or at least two combinations of waste lithium iron phosphate batteries, waste lithium cobalt oxide batteries or waste ternary batteries.

[0018] In one embodiment, the temperature of the pyrolysis treatment in step (1) is 400 - 600 °C, for example: 400 °C, 450 °C, 500 °C, 550 °C or 600 °C, etc.

[0019] In one embodiment, the time of the pyrolysis treatment is 3 - 8 h, for example: 3 h, 4 h, 5 h, 6 h, 7 h or 8 h, etc.

[0020] In one embodiment, the lithium supplementation calcination treatment in step (2) includes testing the lithium deficiency amount of the cathode material powder by inductively coupled plasma mass spectrometry (ICP testing), determining the lithium source addition amount, mixing the cathode material powder and the lithium source, and performing calcination after ball milling.

[0021] In one embodiment, when the cathode material powder is lithium iron phosphate, a reducing agent is added.

[0022] In one embodiment, the reducing agent includes any one or at least two combinations of sucrose, glucose, cellulose or elemental carbon.

[0023] In one embodiment, the addition amount of the reducing agent is 1-5% of the mass of the cathode material powder, for example: 1%, 2%, 3%, 4% or 5%, etc. Preferably, it is 2-3%.

[0024] In one embodiment, the lithium source includes any one or a combination of at least two of lithium hydroxide, lithium carbonate, lithium nitrate, lithium oxalate, lithium acetate, lithium dihydrogen phosphate or lithium hydrogen phosphate.

[0025] In one embodiment, the ball milling time is 0.5-2 h, for example: 0.5 h, 0.8 h, 1 h, 1.5 h or 2 h, etc.

[0026] In one embodiment, the calcination temperature is 650-800 °C, for example: 650 °C, 680 °C, 700 °C, 750 °C or 800 °C, etc.

[0027] In one embodiment, the calcination time is 1-5 h, for example: 1 h, 2 h, 3 h, 4 h or 5 h, etc.

[0028] In one embodiment, the calcination atmosphere is nitrogen and / or argon.

[0029] In one embodiment, the organic gas in step (3) is obtained by condensing and recovering the waste gas pyrolyzed in step (1), removing acidic gases, and then collecting it.

[0030] In one embodiment, the organic gas includes C 2 H 4 , CH 4 or C 2 H 6 or any combination of at least two of them.

[0031] In one embodiment, the volume ratio of the organic gas to silicon tetrafluoride in step (3) is 1:(1-5), for example: 1:1, 1:2, 1:3, 1:4 or 1:5, etc.

[0032] In one embodiment, the flow rate of the mixed gas in step (3) is 50-100 mL / min, for example: 50 mL / min, 60 mL / min, 70 mL / min, 80 mL / min, 90 mL / min or 100 mL / min, etc.

[0033] In one embodiment, the electron energy of the plasma coating treatment is 20-30 eV, for example: 20 eV, 22 eV, 25 eV, 38 eV or 30 eV, etc.

[0034] In one embodiment, the temperature of the plasma coating treatment is 350 - 500 °C, for example: 350 °C, 380 °C, 400 °C, 450 °C, 500 °C, etc.

[0035] In one embodiment, the waste gas obtained from the plasma coating treatment is recycled using SiO 2 After recovery, the obtained silicon tetrafluoride gas is dried and recycled.

[0036] In one embodiment, based on the mass of the silicon carbide-coated cathode material being 100%, the mass fraction of the silicon carbide coating layer is 0.1 - 2%, for example: 0.1%, 0.5%, 0.8%, 1%, 1.5%, 2%, etc.

[0037] As an alternative embodiment of the present disclosure, the repair and regeneration method includes the following steps:

[0038] (1) After discharging the waste battery, pyrolysis treatment is carried out to obtain waste gas and cathode material powder;

[0039] (2) The lithium deficiency amount of the cathode material powder is measured by ICP to determine the lithium source addition amount. The cathode material powder, lithium source, and reducing agent are mixed and calcined at 650 - 800 °C for 1 - 5 h. The addition amount of the reducing agent is 1 - 5% of the mass of the cathode material powder. The waste gas is subjected to condensation recovery, acid gas removal, and organic gas collection treatment;

[0040] (3) The organic gas collected in step (2) and silicon tetrafluoride are mixed at a volume ratio of 1:(1 - 5) to obtain a mixed gas. The mixed gas is introduced into the plasma reactor at a flow rate of 50 - 100 mL / min. Under the conditions of an electron energy of 20 - 30 eV and adjusting the temperature of the constant temperature zone to 350 - 500 °C, the powder obtained by lithium supplementation and calcination is subjected to plasma coating treatment to obtain a silicon carbide-coated cathode material. The obtained waste gas is recycled using SiO 2 After recovery, the obtained silicon tetrafluoride gas is dried and recycled.

[0041] Compared with the prior art, the present disclosure has the following beneficial effects:

[0042] (1) In the repair and regeneration method of the present disclosure, the carbon capture stream can fix carbon in the coating layer of the regenerated lithium iron phosphate, without carbon dioxide emissions, which is beneficial to reducing carbon emissions. The fluorine circulation stream can realize the recycling of HF, and does not require further collection and treatment of harmful gases, which is beneficial to reducing environmental pollution. The regenerated silicon carbide-coated lithium iron phosphate can repair the damage of the carbon coating layer of the waste lithium iron phosphate, and the coated surface is smoother, and the electrochemical performance of the material is excellent. The entire reaction process only consumes silicon dioxide while fixing the tail gas, and the cost is low.

[0043] (2) The lithium iron phosphate obtained by regenerating the method described in the present disclosure can be used to prepare a battery with a 0.1C specific capacity of more than 152.79 mAh / g, a Coulomb efficiency of more than 96.41%, a 1C specific capacity of more than 138.09 mAh / g, and a tap density of up to 2.511 g / cm 3 or more.

[0044] Other aspects will be apparent after reading and understanding the accompanying drawings and the detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The accompanying drawings are used to provide a further understanding of the technical solutions herein, and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the technical solutions herein and do not constitute a limitation to the technical solutions herein.

[0046] Figure 1 is a process flow schematic diagram of the repair and regeneration method described in Embodiment 1 of the present disclosure.

[0047] Figure 2 is an XRD pattern of the silicon carbide-coated cathode material prepared in Embodiment 1 of the present disclosure. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0048] The technical solutions of the present disclosure will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present disclosure and should not be regarded as a specific limitation to the present disclosure.

[0049] Embodiment 1

[0050] This embodiment provides a method for repairing and regenerating a battery cathode material, and the repair and regeneration method includes the following steps:

[0051] (1) The retired power battery is discharged, disassembled and crushed, and the obtained battery fragments are pyrolyzed at 600 °C for 4 h. The pyrolyzed waste gas is processed in step (2), and the waste lithium iron phosphate cathode powder is collected;

[0052] (2) Determine the Fe / Li ratio of the waste lithium iron phosphate by ICP test. A lithium source and a reducing agent are mixed into the waste lithium iron phosphate cathode material and ball-milled in a ball mill for 1 h to make Fe / Li = 1:1.05. The lithium source is lithium hydroxide, and the reducing agent is sucrose. The addition amount of the reducing agent is 3% of the mass of the waste lithium iron phosphate powder. The uniformly mixed waste lithium iron phosphate powder is calcined at 750 °C for 3 h in a nitrogen atmosphere. The electrolyte waste gas is sequentially subjected to condensation recovery, acid gas removal and organic gas collection (the main components are C 2 H 4 , CH 4 , C 2 H 6 etc.);

[0053] (3) At normal pressure, mix the organic gas and silicon fluoride gas, control the gas flow rate at 60 mL / min, and the volume ratio of the organic gas to silicon fluoride is 1:2. Evenly spread the powder obtained by lithium supplementation and calcination on a porcelain boat, place the porcelain boat in the constant temperature zone of the reactor, and then introduce the mixed gas into the plasma reactor. Set the electron energy generated by the plasma reactor at 25 eV, adjust the temperature of the constant temperature zone to 400 °C, react for 2 h to obtain lithium iron phosphate coated with silicon carbide (the mass fraction of silicon carbide is 1%), and the XRD pattern of the lithium iron phosphate coated with silicon carbide is as shown in Figure 2 shown. Collect the waste gas and recycle it using SiO 2 . The reaction equation is as follows: SiO 2 + 4HF = SiF 4 + 2H 2 O. The obtained silicon tetrafluoride gas is dried and then reused.

[0054] Example 2

[0055] This example provides a method for repairing and regenerating a battery cathode material. The repair and regeneration method includes the following steps:

[0056] (1) Discharge, disassemble and crush the retired power battery. The obtained battery fragments are pyrolyzed at 620 °C for 4 h. The waste gas after pyrolysis is processed in step (2), and the waste lithium iron phosphate cathode powder is collected;

[0057] (2) Determine the Fe / Li ratio of the waste lithium iron phosphate by ICP test. Mix a lithium source and a reducing agent into the waste lithium iron phosphate cathode material and ball mill it in a ball mill for 1 h to make Fe / Li = 1:1.02. The lithium source is lithium hydroxide, and the reducing agent is sucrose. The addition amount of the reducing agent is 3.2% of the mass of the waste lithium iron phosphate powder. Place the evenly mixed waste lithium iron phosphate powder in a nitrogen atmosphere and calcine it at 780 °C for 2.5 h. Condense and recover the electrolyte waste gas, remove the acidic gas, and collect the organic gas (mainly composed of C 2 H 4 , CH 4 , C 2 H 6 , etc.);

[0058] (3) At normal pressure, mix the organic gas and silicon fluoride gas, control the gas flow rate at 70 mL / min, and the volume ratio of the organic gas to silicon fluoride is 1:3. Evenly spread the powder obtained by lithium supplementation and calcination on a porcelain boat, place the porcelain boat in the constant temperature zone of the reactor, and then introduce the mixed gas into the plasma reactor. Set the electron energy generated by the plasma reactor at 27 eV, adjust the temperature of the constant temperature zone to 380 °C, react for 2 h to obtain lithium iron phosphate coated with silicon carbide (the mass fraction of silicon carbide is 1.1%). Collect the waste gas and recycle it using SiO2 Recycling is carried out, and the reaction equation is as follows: SiO 2 + 4HF = SiF 4 + 2H 2 O. The obtained silicon tetrafluoride gas is dried and then recycled.

[0059] Example 3

[0060] The difference between this example and Example 1 is only that the addition amount of the reducing agent is 1% of the mass of the waste lithium iron phosphate powder, and other conditions and parameters are exactly the same as those in Example 1.

[0061] Example 4

[0062] The difference between this example and Example 1 is only that the addition amount of the reducing agent is 5% of the mass of the waste lithium iron phosphate powder, and other conditions and parameters are exactly the same as those in Example 1.

[0063] Example 5

[0064] The difference between this example and Example 1 is only that the electron energy in step (3) is 15 eV, and other conditions and parameters are exactly the same as those in Example 1.

[0065] Example 6

[0066] The difference between this example and Example 1 is only that the electron energy in step (3) is 35 eV, and other conditions and parameters are exactly the same as those in Example 1.

[0067] Example 7

[0068] The difference between this example and Example 1 is only that the volume ratio of the organic gas to silicon tetrafluoride in step (3) is 2:1, and other conditions and parameters are exactly the same as those in Example 1.

[0069] Example 8

[0070] The difference between this example and Example 1 is only that the volume ratio of the organic gas to silicon tetrafluoride in step (3) is 1:10, and other conditions and parameters are exactly the same as those in Example 1.

[0071] Comparative Example 1

[0072] This comparative example provides a method for repairing and regenerating the cathode material of a battery. The repairing and regenerating method includes the following steps:

[0073] S1: Discharge, disassemble and crush the retired power battery;

[0074] S2: Pyrolyze the battery fragments after the pretreatment of S1, carry out condensation and recovery treatment on the pyrolysis exhaust gas, and collect the waste lithium iron phosphate cathode powder;

[0075] S3: Determine the Fe / Li ratio of waste lithium iron phosphate by ICP test, mix lithium source and reducing agent into waste lithium iron phosphate positive electrode material, and ball mill for 1h in a ball mill to make Fe / Li=1:1.05, the lithium source is lithium hydroxide, the reducing agent is sucrose, and the amount of reducing agent added is 10% of the mass of waste lithium iron phosphate powder. Place the mixed waste lithium iron phosphate powder in a nitrogen atmosphere and calcine at 750℃ for 3h. Obtain repaired and regenerated carbon-coated lithium iron phosphate.

[0076] Comparative Example 2

[0077] This comparative example directly uses silicon carbide solid phase coating of commercial lithium iron phosphate positive electrode material.

[0078] Performance Testing:

[0079] The lithium iron phosphate prepared in the embodiment and the comparative example, the conductive agent acetylene black, and the binder PVDF were fully stirred and mixed at a mass ratio of 90:5:5, and an appropriate amount of N-methylpyrrolidone was added. The slurry was coated on an aluminum foil sheet and dried at 120°C for 12 hours in a vacuum dryer to prepare a positive electrode sheet. A half-cell was assembled with a metal lithium sheet as the negative electrode, and the electrochemical performance was tested. The test results are shown in Table 1:

[0080] Table 1

[0081]

[0082] As can be seen from Table 1, according to Examples 1-2, the lithium iron phosphate battery regenerated by the method of the present disclosure can have a 0.1C gram capacity of more than 152.79 mAh / g, a coulombic efficiency of more than 96.41%, a 1C gram capacity of more than 138.09 mAh / g, and a compaction density of 2.511 g / cm 3 above.

[0083] By comparing Example 1 with Examples 3-4, it can be seen that in the repair and regeneration method disclosed in the present invention, the amount of the reducing agent added will affect the effect of obtaining the silicon carbide coated positive electrode material. The amount of the reducing agent added is controlled to 2-3% of the mass of the positive electrode material powder, and the effect of obtaining the silicon carbide coated positive electrode material is better. If the amount of the reducing agent added is too large, the carbon coating layer of the regenerated lithium iron phosphate will be too thick, which will reduce its capacity. If the amount of the reducing agent added is too low, the valence state of the iron element in the waste lithium iron phosphate cannot be completely reduced, and it is difficult to initially repair the defective carbon coating layer, resulting in the electrochemical performance and cycle stability of the repaired lithium iron phosphate being difficult to meet commercial needs.

[0084] Comparing Example 1 with Examples 5 - 6, it can be obtained that in the repair and regeneration method described in the present disclosure, the electron energy of the plasma coating treatment will affect the effect of the prepared silicon carbide-coated cathode material. Controlling the electron energy of the plasma coating treatment within 20 - 30 eV results in a better effect of the prepared silicon carbide-coated cathode material. If the electron energy is too high, although the reaction is promoted, the reaction proceeds rapidly, which may cause non-specific reactions, reducing the specific capacity and rate performance, and the Coulomb efficiency decreases slightly. If the electron energy is too low, the proportion of organic gas is too small, the reaction rate is slow, and the product selectivity is affected, resulting in an overall reduction in electrochemical performance, and it cannot ensure that the reaction can occur or the reaction rate is slow.

[0085] Comparing Example 1 with Examples 7 - 8, it can be obtained that in the repair and regeneration method described in the present disclosure, the volume ratio of the organic gas to silicon fluoride will affect the effect of the prepared silicon carbide-coated cathode material. Controlling the volume ratio of the organic gas to silicon fluoride between 1:1 and 1:5 results in a better effect of the prepared silicon carbide-coated cathode material. If the proportion of the organic gas is too large, although the reaction is promoted, a relatively thick carbon coating layer will be produced, reducing the specific capacity of the repair material. If the proportion of the organic gas is too small, the reaction rate is slow, and the product selectivity is affected.

[0086] Comparing Example 1 with Comparative Example 1, it can be obtained that using silicon carbide-coated recycled lithium iron phosphate can repair the defects of the surface coating layer of waste lithium iron phosphate, which is beneficial to restoring its electrochemical performance.

[0087] Comparing Example 1 with Comparative Example 2, it can be obtained that the silicon carbide-coated cathode material recovered by the repair method described in the present disclosure has an effect similar to that of the silicon carbide-coated cathode material prepared from commercial lithium iron phosphate. Moreover, the carbon capture stream can fix carbon in the coating layer of the recycled lithium iron phosphate without carbon dioxide emissions, which is beneficial to reducing carbon emissions. The fluorine circulation stream can realize the recycling of HF and does not require further collection and treatment of harmful gases, which is beneficial to reducing environmental pollution.

Claims

1. A method for comprehensively recycling, repairing and regenerating the cathode material of waste batteries in an integrated manner, wherein, the method comprises the following steps: (1) After discharging the waste batteries, pyrolysis separation is carried out to obtain cathode material powder; (2) Carry out lithium supplementation calcination treatment on the cathode material powder; (3) Mix organic gas and silicon tetrafluoride to obtain a mixed gas, and use the mixed gas to carry out plasma coating treatment on the powder obtained by lithium supplementation calcination to obtain silicon carbide-coated cathode material; The organic gas includes C 2 H 4 , CH 4 or C 2 H 6 or a combination of any one or at least two of them.

2. The method according to claim 1, wherein, the waste batteries in step (1) include any one or a combination of at least two of waste lithium iron phosphate batteries, waste lithium cobalt oxide batteries or waste ternary batteries.

3. The method according to claim 1, wherein, the temperature of the pyrolysis treatment in step (1) is 400-600 °C.

4. The method according to claim 3, wherein, the time of the pyrolysis treatment is 3-8 h.

5. The method according to claim 1, wherein, the method of the lithium supplementation calcination treatment in step (2) is as follows: Test the lithium deficiency amount of the cathode material powder by an inductively coupled plasma mass spectrometer to determine the lithium source addition amount; Mix the cathode material powder and the lithium source, and carry out calcination after ball milling.

6. The method according to claim 5, wherein, when the cathode material powder is lithium iron phosphate, a reducing agent is added.

7. The method according to claim 6, wherein, the reducing agent includes any one or a combination of at least two of sucrose, glucose, cellulose or elemental carbon.

8. The method according to claim 6, wherein, the addition amount of the reducing agent is 1-5% of the mass of the cathode material powder.

9. The method according to claim 6, wherein, the addition amount of the reducing agent is 2-3% of the mass of the cathode material powder.

10. The method according to claim 5, wherein, the lithium source includes any one or a combination of at least two of lithium hydroxide, lithium carbonate, lithium nitrate, lithium oxalate, lithium acetate, lithium dihydrogen phosphate or lithium hydrogen phosphate.

11. The method according to claim 5, wherein, the time of the ball milling is 0.5-2 h.

12. The method according to claim 5, wherein, the temperature of the calcination is 650-800 °C.

13. The method according to claim 5, wherein, the time of the calcination is 1-5 h.

14. The method according to claim 5, wherein, the atmosphere of the calcination is nitrogen and / or argon.

15. The method according to claim 1, wherein, the organic gas in step (3) is obtained by condensing and recovering the waste gas obtained by the pyrolysis in step (1), removing acidic gases and then collecting.

16. The method according to claim 1, wherein, the volume ratio of the organic gas to silicon tetrafluoride in step (3) is 1:(1-5).

17. The method according to claim 1, wherein, the flow rate of the mixed gas in step (3) is 50-100 mL / min.

18. The method according to claim 1, wherein, the electron energy of the plasma coating treatment in step (3) is 20-30 eV.

19. The method according to claim 1, wherein, The temperature of the plasma coating treatment is 350 to 500 °C.

20. The method according to claim 1, wherein, The waste gas obtained by the plasma coating treatment uses SiO 2 for recycling, and the obtained silicon tetrafluoride gas is recycled after drying treatment.

21. The method according to claim 1, wherein, Based on the mass of the silicon carbide-coated cathode material being 100%, the mass fraction of the silicon carbide coating is 0.1 to 2%.

22. The method according to claim 1, wherein, The method comprises the following steps: (1) After discharging the waste battery, pyrolysis treatment is carried out to obtain waste gas and cathode material powder; (2) The lithium deficiency amount of the cathode material powder is tested by ICP to determine the lithium source addition amount. The cathode material powder, lithium source and reducing agent are mixed and calcined at 650 to 800 °C for 1 to 5 h. The addition amount of the reducing agent is 1 to 5% of the mass of the cathode material powder. The waste gas is subjected to condensation recovery, acid gas removal and organic gas collection treatment; (3) Mix the organic gas collected in step (2) and silicon tetrafluoride in a volume ratio of 1:(1 - 5) to obtain a mixed gas. Then, introduce the mixed gas into a plasma reactor at a flow rate of 50 - 100 mL / min. Under the conditions that the electron energy is 20 - 30 eV and the temperature of the constant temperature zone is adjusted to 350 - 500 °C, perform plasma coating treatment on the powder obtained by lithium supplementation calcination for 1 - 5 h to obtain a silicon carbide-coated cathode material. The exhausted gas obtained is recycled by using SiO 2 for recovery. After the obtained silicon tetrafluoride gas is dried, it is recycled.

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