It is of great economic, environmental and social benefit to discover harmless treatment and resource utilization options for spent lithium-ion batteries (LIBs), which contain a large proportion of valuable metal elements (e.g., Li, Ni, Co, Mn, Cu, and Al) and poisonous chemicals (e.g., lithium hexafluorophosphate and polyvinylidene fluoride). The present work summarized the leading technologies and hot issues in the disposal of spent LIBs from new energy vehicles. Moreover, development of the trend of innovative technologies for the recycling of spent LIBs is recommended.

The chromium elution behavior of stainless steel (SS) slag depends highly on the chromium distribution, and the molten modification process proved to effectively improve the chromium enrichment in stable phases. However, the phase transformation and variation of chromium stability during the subsequent cooling process is still poorly understood. In this work, the phase composition and chromium distribution of SS slag from different quenching temperatures were experimentally studied, and the stability of chromium-bearing phases was evaluated using standard leaching tests. The results indicated that dicalcium silicate and spinel phases had formed in the molten slag at 1600 °C, while the dicalcium silicate disappeared and the phases of merwinite and melilite precipitated when the temperature decreased from 1600 to 1300 °C (at a rate of 5 °C/min). During this cooling process, the chromium migrated from other phases into the spinel, significantly suppressing the chromium elution. The leaching results also demonstrated that the potential chromium-bearing phases of glass, dicalcium silicate and merwinite are unstable and are presumably the main source of chromium release. The treated SS slag meets the requirements for the utilization of chromium-bearing slag in the cement and brick industries.