Recycling Of Cathode Materials For Lithium-ion Batteries Based On Reusable Deep Eutectic Solvent

The global population growth and economic development have made energy and environmental issues increasingly severe.Lithium-ion batteries have dominated the market due to their many advantages such as light weight,small size,high energy density,and low self-discharge rate.As the production of lithium-ion batteries surges but their cycle life is limited,a huge amount of waste is generated every year.It is crucial to achieve efficient recycling technology for waste lithium-ion batteries to cope with the resource and environmental crisis.Hydrometallurgical process has attracted extensive research due to its potential to reduce energy consumption and environmental threat.However,it is still challenging to realize green,efficient,and closed-loop recycling simultaneously.This thesis adopts a low-melting solvent based on choline chloride-oxalic acid（ChCl:OA）type to achieve closed-loop and efficient recovery of precious metal elements from waste batteries.Firstly,the leaching conditions are explored.The low-melting solvent has the characteristic of dissolving metal oxides.A super-fast leaching process of 10 seconds was observed at high temperature of 180℃ without visible residues.It also has good leaching efficiency under mild reaction conditions,and temperature has a more significant effect on leaching efficiency.The leaching process is divided into two stages that occur simultaneously:the breaking and recombination of metal bonds and the reduction to coordination complexes.The activation energy barrier of the process is calculated to be 113.9 kJ/mol.The apparent activation energy E_a can be used to judge the controlling step of the leaching process.The study shows that the leaching of cobalt element in ChCl:OA DES system is mainly controlled by chemical reaction rather than diffusion.Secondly,co-precipitation method was used to recover the valuable metals from the cathode materials.The coordination environment of this system can be regulated by simply adding/evaporating deionized water without introducing additional precipitants,thus achieving cobalt precipitation separation.The evolution of the leaching solvent composition was revealed by ¹³C NMR,indicating that the structure of choline chloride remained stable,while the hydrogen bonding effect of oxalic acid was weakened and some consumption occurred.However,the leaching ability of DES could be reversibly restored after evaporating water,thus realizing a closed-loop recycling process of cobalt element with reusable leaching agent.The precipitates were characterized by XRD,SEM and other methods,proving that they were cobalt oxalate dihydrate with rod-like morphology,good crystallinity and regular crystal shape.The precipitates were annealed into cobalt trioxide in a muffle furnace and characterized,proving that they had a similar but more porous rod-like structure to cobalt oxalate dihydrate.Finally,the annealed precursor was calcined at high temperature by solid-state reaction,with a lithium mole ratio of 1.05:1.The regenerated synthesized lithium cobaltate material had good crystallinity and morphology after XRD and SEM structural characterization.The electrochemical performance of the regenerated synthesized lithium cobaltate material was evaluated by button cell,including charge-discharge cycling performance,CV curve and EIS curve,rate performance,etc.,and compared with commercial lithium cobaltate material.The regenerated synthesized lithium cobaltate material showed a specific capacity of 180.7 mAh/g at the first discharge at a current density of 0.2 C and a voltage range of 3.0-4.5 V,and still maintained 84.8%of the initial capacity after 50 cycles;it also had good rate performance at current densities of 0.1 C-3 C.The results showed that the regenerated synthesized lithium cobaltate material had good reversible specific capacity,cycle stability,kinetic performance and rate performance,comparable to commercial material.This study can provide theoretical basis and experimental foundation for the recycling of waste lithium-ion batteries based on reusable leaching agent.