Research Progress on Recycling and Reuse of Cathode Materials for Waste Lithium-Ion Batteries

In recent years，China has gradually become the world's largest energy supply system and has built an energy supply pattern with coal as the mainstay，electricity as the center，and oil，natural gas and renewable energy as the overall development. Because of this，the long-term use of traditional primary resources such as coal，oil，and natural gas has created a large number of environmental problems such as the greenhouse effect，harmful gas emissions，soil and water pollution，and the waste of resources from the destruction of vegetation. As coal resources have been used in large quantities，problems such as insufficient reserves，decreasing grades and difficulties in mining and sorting have arisen，the supply of oil and gas resources is also highly uncertain with the changing political landscape of the world. In this context，vigorously developing new energy sources and promoting a green and low-carbon transition is not only the key to solving this problem but also to achieving the goal of sustainable development. The use of lithium-ion batteries，which have been commonly used in the field of energy storage，has increased dramatically with the advent of the new energy era，which has led to the environment being polluted and metal resources being in short supply. As a result，battery recycling is a key part of the green use of lithium-ion batteries. Green recycling of waste lithium-ion batteries，a high-grade non-traditional mineral resource，which is not only conducive to alleviating China's foreign dependence on some strategic metal resources，such as nickel and cobalt but also to achieve a return of resources. In this paper，the demand for lithium-ion batteries，the situation of import and storage of critical raw materials，and a series of policies about new energy vehicles and power batteries in China were summarized. Then this information was used to describe the soaring demand for lithium-ion batteries in China and the necessity of recycling waste lithium-ion batteries. Next，the research progress of traditional lithium-ion battery recycling technologies and emerging recycling processes were presented，respectively. The former was dominated by hydrometallurgy and pyrometallurgy，focusing on the destruction of the electrode material structure. The latter was more inclined to a green and low-carbon recycling process，as well as the simplification of the process. In the introduction to wet recovery，three different methods were listed：inorganic acid leaching，organic acid leaching and ammonia leaching. Inorganic acid leaching had a high leaching rate，but it produced acidic waste liquids and exhaust gases resulting in environmental pollution. Therefore，from an environmental point of view，the development towards organic acid leaching had continued in recent years. In addition to acid leaching，ammonia leaching was also a good option. This method solved the problem of equipment corrosion caused by acid leaching and enables selective leaching between elements. The progress of research on direct regeneration technology and deep eutectic solvents technology was highlighted among the new recycling technologies. The research progress of solid-phase lithium replenishment，liquid-phase and molten salt restoration methods were summarized and the advantages and disadvantages of the three different methods were compared respectively. Through comparative analysis，it could be concluded that the direct regeneration method was still the most promising new technology for the recycling of waste lithium-ion batteries. The deep eutectic solvents consisting of a hydrogen bond donor and a hydrogen bond acceptor were inexpensive and had good selectivity，but the current development still had significant limitations. Finally，the paper summarized the challenges that needed to be addressed by different recycling methods and suggests some of the problems and solutions that could lead to advances in existing technologies. For example，research in hydrometallurgy needed to shift towards the preferential extraction of elemental lithium，providing further evidence of the prevalence of deep eutectic solvents in battery recycling and the fact that direct regeneration processes could be closed loop and straightforward as a way of providing an outlook on future trends and research priorities. This paper aimed to provide a reference for an environmentally friendly and resource efficient battery. © 2023 Editorial Office of Chinese Journal of Rare Metals. All rights reserved.