The Treatment And Recycling Of Waste Lithium Iron Phosphate Material

Against the background of global environmental issues,the new energy vehicle industry is developing rapidly.A large number of lithium-ion batteries are used in the power system of electric vehicles,some of which are lithium iron phosphate batteries.Power lithium-ion batteries on electric vehicles face retirement issues after a period of use,which will generate a large number of spent batteries waiting to be treated.The treatment and recycling of spent lithium-ion batteries are of great significance for environmental protection and the sustainable use of global lithium resources.In most of the cases,the positive electrode material is the most valuable part of the spent lithium ion battery.The waste material of positive electrode in the battery production process also has recycling value.In this study,a kind of waste lithium iron phosphate material was used as the starting material,and an electrolytic-leaching-chemical-precipitation process in a phosphoric acid system was proposed.This thesis first analyzes the reaction mechanism of the electrolytic leaching process by cyclic voltammetry test,constant voltage electrolysis experiment and leaching experiment,and optimizes the process parameters.Then use the multi-physics model to verify the hypothesized reaction mechanism,and further study the influencing factors of the electrolytic leaching process.Finally,the principle of recovering valuable metals by chemical precipitation is analyzed,and the overall process of this study is compared with the traditional process.During the electrolytic leaching process,the main reactions of lithium iron phosphate occurring on the anode include the spontaneous dissolution and the electrochemical oxidation.Based on experimental analysis and principle assumptions,the combined process of direct leaching and electrolysis was optimized.Under the conditions of phosphoric acid concentration of 0.6 mol dm^-3 and electrolytic voltage of 2.5 V,after direct leaching for 60min and electrolysis for 30 min,the lithium ion leaching rate was 95.6%and the iron ion leaching rate was 91.3%.The multi-physics model that was constructed based on the Avrami-like equation of direct leaching and the electrochemical oxidation principal can well simulate the experimental process.Increasing the thickness of the porous anode can increase the average space-time yield of the electrolytic leaching process,but the metal leaching rate will decrease accordingly.The form of the current collector affects the electrode potential distribution during the electrolysis process,thereby affecting the final leaching rate and space-time yield of electrolytic leaching.Stepwise precipitation of iron and lithium can be achieved by controlling the ion concentration during chemical precipitation.Iron（III）phosphate dihydrate and lithium phosphate are the best recycling targets.Under the overall electrolytic leaching-chemical precipitation process,the recovery rate of iron is about 90%,and the recovery rate of lithium is about 88%.Compared with the typical acid leaching-chemical precipitation process,the process proposed in this study consumes less extra materials and produces fewer by-productsThis thesis proposes a new electrolytic-leaching-chemical-precipitation method based on phosphoric acid system to recycle valuable metals from waste lithium iron phosphate material.The process parameters are optimized and the reaction principle of the process is analyzed.This study provides new ideas for the treatment and recycling of waste lithium iron phosphate material,and provides a theoretical basis for the industrialization of the process.