Re-synthesis Of LiFePO₄/C Material From Recycled Cathodes Via A Green Full-solid Route

Lithium-ion power batteries have been widely used in electric vehicles,which has promoted the development of the electric vehicle industry.At the same time,more and more lithium-ion power batteries have reached the age of retire and need to be disposed.Generally speaking,after retired from EV,the power batteries entered the echelon utilization system to extend service period.When the effective capacity is less than 20%,these power batteries will be scrapped,disassembled,and recycled the valuable materials.Unlike NCA and NCM power batteries,although LiFePO₄/C power batteries have also been widely used,there is no an effective method for recovery and regeneration.LiFePO₄/C has no valuable elements such as Ni,Co,and Mn.Thus,the benefits of recycling after being scrapped and dismantled are reduced and the difficulty is increased.If using the existing liquid phase recovery methods of the ternary power batteries,it will not only increase the recycle cost,but also cause serious secondary pollutions.At the same time,due to the lack of purification and homogenization processes,the comprehensive performances of regenerated LiFePO₄/C materials,which obtained by the existing solid-state recycling method,are poor.Therefore,in order to achieve energy-saving,environmentally friendly,safe,efficient and high-yield method to dismantle,recycle and regenerate the scrapped LiFePO₄/C cathode materials,this paper designed a new green solid-state recycling route to overcome the secondary pollution problem coming from the liquid phase.It has improved the purity,tap density and electrochemical performance of the regenerated LiFePO₄/C,and increased the added value.On this basis,the effects of P source?NH₄H2PO₄?,Li source?Li₂CO₃?as well as the regenerative heat treatment temperature and time for the regeneration of LiFePO₄/C were studied.?1?After dismantling the scrapped LiFePO₄/C power batteries by the fully enclosed automatic disassembling device,the cathode sheets were separated and heated at low temperature to peel off the cathode active material.Then,the active material was calcined at a high temperature to remove the binder?PVDF?as well as the conductive agent?Super P?impurities,and the remaining substance was completely oxidized.According to XRD pattern,during the high temperature calcined,the impurities disappeared,and the remaining substances were oxidized to Fe₂CO₃ and Li₃Fe₂?PO₄?₃.This process avoided the effect of the degree of material damage on the performance of regenerated LiFePO₄/C.On this basis,the obtained cathode material was tested by ICP.According to the ICP result,P source?NH₄H2PO₄?and C source?sucrose?were added in the cathode material,and LiFePO₄/C was regenerated with heat treatment under a reducing atmosphere?Ar/H2?.At the same time,the effects of heat treatment temperature and time on the regeneration were investigated.The XRD peaks of the regenerated products were found to be in line with LiFePO₄/C pattern,but the charge/discharge capacity in the first cycle was 135 mAh/g and 120 mAh/g,respectively,which did not meet the requirements.?2?Based on the above results,Li source?Li₂CO₃?and C source?sucrose?with different mass ratios were added in the waste LiFePO₄/C which was sintered at different temperatures and times in Ar/H2 atmosphere,in order to investigate the effect of different quality Li sources?Li₂CO₃?as well as the different regeneration temperatures and time.After testing the regenerated LiFePO₄/C,we found that the optimum sintering temperature and time was 350°C5 h+650°C for 10 h.The best Li₂CO₃ ratio was 1.4 w%.The tap density was 0.98 g/cm³.The first cycle charge/discharge test?0.2C?in CR2032 half-cells at 0.2C was 151mAh/g and 146mAh/g,respectively,and the capacity retention rate was 80%after 100 cycles.In order to research the electrochemistry property in ful-cells,we have assembled the CR2032 cells with LiFePO₄/C as cathode and Li₄Ti₅O₁₂ as anode.The first cycle charge/discharge test?0.2C?at0.2C was 151mAh/g and 146 mAh/g,respectively,and the capacity retention rate was 80%after 2000 cycles.The above results verified the guess of Li deficiency and ilustrated the feasibility of this al-solid-state regeneration route.The regenerated products could meet the requirements for commercial LiFePO₄/C cathode materials.