| With the rapid development of the global economy,more and more lithium-ion batteries are widely used in portable electronic products and new energy vehicles,and large-scale applications of lithium-ion batteries will lead to a large number of scrap batteries.Discarding spent lithium-ion batteries will not only seriously pollute the environment,but also cause waste of resources such as lithium,transition metals,copper,and aluminum.However,compared to the scale of scrap,the recovery of lithium-ion batteries has fallen far short of expectations.Therefore,the harmless treatment of waste lithium-ion batteries and resource reuse is of great significance.The recycling of spent lithium-ion battery can not only protect the environment but also save resources.The ternary cathode material LiNi0.5Co0.2Mn0.3O2 has been widely used in power batteries due to its higher energy density and discharge specific capacity.This thesis mainly focused on the safe recycling and reuse of positive electrode materials of spent lithium-ion LiNi0.5Co0.2Mn0.3O2 batteries.From the safe decomposition and recycling technology of single battery to the modification and reuse of waste positive electrode materials,the optimal modification conditions were determined.(1)First,the physical discharge method of immersing the waste lithium battery in copper powder was used to achieve safe discharge.Then,the stainless steel case,the tab,the positive electrode sheet,the negative electrode sheet and the separator were disassembled and separated in a sealed glove box.These components were immersed in DMF to remove the electrolyte.The positive electrode sheet was immersed in a 1 mol·L-1 KOH solution to remove the electrolyte LiPF6 and aluminum foil,and the obtained spent positive electrode material was centrifuged,dried,sieved and annealed at 600? for 6 h to remove the binder PVDF and conductive carbon black,to achieve the recovery of pure spent LiNi0.5Co0.2Mn0.3O2(SNCM).The negative electrode sheet was immersed in 0.01 mol·L-1 KOH solution to remove the binder SBR and electrolyte LiPF6 and the anode material was centrifuged,dried,and sieved the negative electrode material to obtain waste graphite materials(SG),and the copper foil was recoverd.(2)Using 0.38LiOH-0.62LiNO3 as the molten salt system,the recovered used ternary cathode material SNCM was mixed with the molten salt system,and the molten salt method was used to assist gradient calcination to regenerate the cathode material LiNi0.5Co0.2Mn0.3O2.According to the molten salt ratios of Li:(Ni+Co+Mn)=0.8,1.1 and 4,the effects of different molten salt ratios on the properties of recycled NCM materials were explored.The layered structure in regenerated materials was restored,and the particles were single crystal particles.The MS1.1 sample with a molten salt ratio of 1.1 had a specific discharge capacity of 152.5 mAh·g-1 in the first cycle at 0.2 C,and the capacity retention rate after 100 cycles was 86.3%.The MS 1.1(MS=Molten-salt)sample had higher specific discharge capacities than MS0.8 and MS4 at different rates,the best cycle stability,the highest Li+transfer rate,and the best electrochemical performance.(3)Based on the optimal molten salt ratio,the effects of calcination temperatures of 850?,930? and 990? on the electrochemical performance of recycled materials were further compared.The initial specific discharge capacity of the MS 1.1-1 sample calcined at 930? was 158.9 mAh.g-1 at 0.2 C,and the capacity retention rate was 87%after 100 cycles.The discharge specific capacity at different rates was better than MS1.1,the particles of MS 1.1-2 calcined at 990? were large,uneven in size and abnormal in discharge capacity.Electrochemical tests showed that the MS 1.1-1 sample had better cycle stability and higher Li+ transfer rate. |
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