Green Recycling Of LiFePO₄ Cathode From Spent Power Lithium-ion Batteries And Regeneration Of FePO₄ Cathode

The emergence of new energy vehicles has greatly alleviated environmental pollution,which caused by the shortage of petroleum energy and exhaust gas.However,lithium batteries,as the power source of electric vehicles（EVs）,have reached the retired period in recent years.Therefore,the recovery and comprehensive utilization of spent power lithium batteries is an inevitable way to achieve high-value utilization of resources and alleviate environmental risk.At present,the recycling of batteries is mainly divided into pyrometallurgy and hydrometallurgy methods.Leaching is one of the main methods in hydrometallurgy,which has the advantages of comprehensive utilization and flexible application.Hence,in this thesis,an organic acid leaching method and advanced oxidation method are designed to separate and purify lithium compound and FePO₄from spent LiFePO₄cathode materials.Then,FePO₄is directly used as cathode material of LIBs and SIBs,and further improve the electrochemical performance of FePO₄through graphene compounding and vanadium oxide coating.The dissertation primarily includes the following three aspects:（1）Two green methods which are organic acid leaching and advanced oxidation method,are employed for recovering spent LiFePO₄cathodes.Lemon juice and citric acid are used as organic acid sources,respectively.With strong oxidizing Na₂S₂O₈as oxidant,FePO₄can be directly obtained by one-step leaching and separation.On the one hand,FePO₄is directly used as cathode material of lithium-ion and sodium-ion batteries.On the other hand,FePO₄is regenerated into LiFePO₄by calcining with Li-source,and then use them as cathode of LIBs and SIBs.（2）In order to improve the electronic conductivity of composite,the graphene oxide was coating on FePO₄.It can be seen that FePO₄-GO-2 exhibits the most excellent performance.When used as cathode for LIBs,it delivers a reversible specific capacity of140 m Ah g^-1after 300 cycles at 1 C.It still exhibits a reversible specific capacity of 62m Ah g^-1after 300 cycles at 1 C for SIBs.（3）The FePO₄-GO was composed with vanadium oxide in order to further improve its rechargeable capacity and cycling stability.Electrochemical performance results indicate that the FePO₄-V₂O₅sample exhibited the best electrochemical performance when the adding content of V source is 10%NH₄VO₃during the leaching reaction.The results show that the FePO₄-V₂O₅-GO delivered high reversible capacity of 145 m Ah g^-1at the current density of 1 C after 300 cycles for LIBs cathode;and the high specific capacity of 75 m Ah g^-1can be retained after 300 cycles at the current density of 1 C for cathode of SIBs.