Spent lithium-ion batteries contain rare metals such as lithium, cobalt, nickel and manganese, which are limited and unevenly distributed. Through recovery, we can effectively reduce the dependence on the exploitation of new mineral resources and realize the sustainable utilization of resources. It can reduce the cost of raw materials for the production of new batteries, and the development of the battery recycling industry can create new job opportunities and promote economic growth. As lithium-ion batteries contain heavy metals and other harmful substances, if discarded at will, these substances may seep into the soil and water sources, causing serious environmental pollution. The energy consumption in the process of battery production and recycling will produce greenhouse gases. If not handled properly, it may cause fire or explosion due to internal short circuit, overheating and other reasons, resulting in safety accidents. Therefore, effective recycling can reduce the energy consumption needed for the production of new batteries, thereby reducing greenhouse gas emissions. In terms of policies and regulations, many countries and regions have laws and regulations on e-waste disposal, which require the recycling of decommissioned batteries. Enterprises can show their sense of social responsibility and enhance their corporate image by recycling retired batteries. This can not only promote the development of related environmental protection technology and material science, establish a perfect battery recycling system, but also help to form a complete closed-loop industry chain from battery production to recycling. In a word, the recycling of spent lithium-ion batteries not only is of great significance to environmental protection and resource conservation, but also has a far-reaching impact on promoting economic development, meeting the requirements of laws and regulations, and promoting corporate social responsibility. With the popularity of electric vehicles and other portable electronic devices, the number of retired batteries will continue to increase, and the importance of battery recycling will become more and more prominent.Recycling the valuable metal resources of spent lithium-ion batteries can generate significant economic benefit. Among various recycling technologies, hydrometallurgy reveals better application potential due to its high maturity and recovery rate. This review focus on the development of hydrometallurgy, including the methods of leaching, separation, purification and re-synthesis of spent cathode materials. The first part introduces the leaching strategies, using acid, ammonia, deep eutectic solvent, bioleaching, and electrochemical leaching, as well as the auxiliary methods for such methods. The second part summarized the purification technologies for the leaching solution and the following re-synthesis process, while the former includes the chemical precipitation method, solvent extraction method, ion exchange method, and membrane separation method and the latter contains the high temperature solid state method and sol-gel method. In the thrid part, the bottlenecks of hydrometallurgy are summarized, and possible solutions are provided for the development of hydrometallurgy regeneration technology.Summary and prospectsHydrometallurgy has high efficiency and practicability in the large-scale application of recycling the cathode materials of spent lithium-ion battery. However, it consumes a large number of chemical reagents during the leaching process, generating pollutants and arousing attention. Therefore, the key issue is to reduce the negative environmental impact caused by hydrometallurgy. The selection of green and efficient leaching technology is beneficial to reduce the production of “three wastes” pollutants in the hydrometallurgy recycle technology, in which the environment-friendly organic acid has the characteristics of both leaching agent and chelating agent, promising to partly replace the inorganic acid leaching in the future. Using the microorganisms to leaches the spent lithium-ion batteries is an environmentally friendly and cheap method, which can design a targeted leaching process by adjusting its own redox properties. However, its strict cultivation environment and inefficiency have become a major difficulty in industrialization. Compared with the traditional acid leaching technology, deep eutectic solvent technology and electrochemistry technology still do not have the advantage in cost. For different cathode materials, auxiliary leaching methods such as mechanical activation, Fe ion medium and wave assistance can be adopted to reduce the amount of leaching agent, increasing the leaching efficiency and economic benefit. The traditional chemical precipitation and solvent extraction for separating and purifying often reveal a complex process, increasing the burden on the environment. The advanced purification technologies such as ion exchange and membrane separation generate positive effects on the environment, its cost still needs to be considered. Besides, enormous efforts have been paid on recycling the single cathode materials. However, the spent cathode materials collected from the market often consisted of a mixture of different cathode materials, which trend to increase the cost of pretreatment and separation process. Therefore, recycling technology for mixed cathode materials should be studied. For recycling other components used in lithium-ion batteries, such as anode materials, separator, current collector and so on, although it generates lower economic benefits than that of cathode materials, the closed-loop recycle of all components of spent lithium-ion batteries is still important in the future, which realizes high-value and deeply utilization of the whole components of spent lithium-ion batteries.