Evolution of Ni and Co during the direct regeneration of spent ternary cathodes

In light of environmental protection and resource reutilization, efficiently recycling lithium-ion batteries has become a key issue. In the spent ternary cathode (SNCM523), the oxidation states, symmetry, spin states, and coordination structures of Ni and Co elements undergo significant changes. Specifically, the reduction of Ni³⁺ (d7) and Co³⁺ (d6) oxidation states lead to an increase in unpaired electrons in the eg orbitals, which enhances the super-exchange interaction between Ni²⁺-O-Ni³⁺ and Ni²⁺-O-Co²⁺, thereby exacerbating the Li⁺/Ni²⁺ cation mixing. Traditional XAS provides limited information on transition metal compounds' symmetry, spin, and covalency. In this study, we employ L3-edge RIXS to investigate the evolution of Ni and Co elements during the regeneration of SNCM523, thereby contributing to the rational design of more efficient recycling strategies for SNCM523.