Regeneration Of Spent Graphite Anode From Retired Lithium Batteries And Its Application In Energy Storage Field

The electric vehicle market is booming,and the demand for lithium-ion batteries is growing rapidly,which means there will be a lot of retired lithium-ion batteries in the future.However,there are few researches on spent graphite anode regeneration and the related regeneration technology is not mature.Therefore,the development of high efficiency,low cost,mass-modified spent graphite anode material technology is of great significance to realize value-added utilization of waste resources and reduce battery costs.This paper focuses on the development of spent graphite modified regeneration technology to carry out basic research,and verified the feasibility of regenerated spent graphite anode used in lithium/sodium ion battery anode material.In addition,the advantages of applying carbon materials with enlarged carbon layer spacing to sodiumion batteries are also explored.The main research contents are as follows:(1)Regenerated graphite(N-RG)with nitrogen doping and increased layer spacing was prepared by gas exfoliation with urea from spent graphite anode(SG).When N-RG is used as the anode electrode material of lithium ion battery,it owns high capacity,excellent rate performance and fast-charging performance.The capacity of N-RG can be maintained at 465.8 m Ah g-1 after 200 cycles at 0.1 A g-1.In this study,the gas exfoliation method was used to exfoliate SG and nitrogen doping,which increased the lithium storage site of the material and solved the problem of low capacity.(2)In order to solve the problem of poor cycle performance of SG,SG was modified and regenerated by ball milling mixed with urea to obtain ball milling modified nitrogendoped spent graphite(BMNG).The influence of urea content and ball milling time on material properties was explored.The results showed that the particle size and thickness of SG decreased,and nitrogen in urea was successfully doped into SG during ball milling.The capacity of BMNG is significantly increased,and thanks to the reduction of the particle size and thickness of BMNG,showing excellent cycling performance.After 2000 cycles at 1 C,the capacity retention rate of BMNG-2 can reach 84.6%,which is better than that of commercial graphite anode(CG).In this study,SG was modified by ball milling,which solved the problem of poor cycling performance in the process of SG regeneration.(3)It can be seen from the above work that the reduction of graphite thickness can effectively improve the capacity and cycle performance of the SG,so the supercritical CO2 exfoliation method is adopted to modify spent graphite.Under the conditions of 10 MPa and 50 ℃,AG was intercalated and exfoliated by supercritical CO2 fluid,and fewer layers of regenerated graphite(FLRG)were obtained.The lithium electric performance results show that the capacity of the material is increased from 285 m Ah g-1(AG)to 353 m Ah g-1(FLRG).Importantly,the significantly broadened voltage plateau means increased effective capacity,which is beneficial for practical applications.In addition,the modification technology can realize pollution-free regeneration of spent graphite anode.(4)In order to explore the application of modified SG in the anode electrode material of sodium ion batteries,Mo S2-GICs was prepared by intercalation-vulcanization method.The results show that the larger gap of the graphite intercalation compound(GICs)can alleviate the volume expansion effect of the electrode material during the charging and discharging process.And the large graphite layer spacing and excellent electrical conductivity significantly improve the fast-charging performance of Mo S2-GICs.(5)In order to verify the effect of nitrogen doping and carbon layer spacing on material capacity and fast-charging performance,edge-nitrogen enriched porous carbon nanosheets(ENPCNs)was prepared.It was found that the carbon layer spacing of ENPCNs was positively correlated with the content of pyrrolic N.At the same time,the results show that the high edge nitrogen doping and the increase of carbon layer spacing improve the Na+ storage performance and fast-charging performance of ENPCNs-800.