Symmetry breaking-induced quasi octahedral sites for direct regeneration of spent lithium-ion battery cathodes

Recycling spent lithium-ion batteries is essential for alleviating resource shortages and environmental pollution, with cathode material recovery being especially significant due to its high content of valuable elements. Relithiation is crucial for the direct regeneration of spent cathodes, and defective structures (Li vacancies, spinel/rock salt) in layered cathodes can only be completely repaired in an environment with adequate Li. However, cathode materials recycled by relithiation suffer the formation of dense spinel/rock salt structure, induced by the migration of transition metals (TMs) to the Li layer and resulting in the creation of TMO₆ octahedron, which hinders Li⁺ transport between adjacent LiO₄ tetrahedra, and further greatly impedes the relithiation of the spent cathodes. Here, we regulated lattice stress at the defect structures to break the lattice symmetry of the unfavorable TMO₆ octahedron and consequently form a quasi LiO₆ octahedral sites with a low Li⁺ transport energy barrier. This approach ensures a Li-sufficient environment, facilitating the effective relithiation and structural repair of spent cathodes. The combination of theoretical calculations and experimental approaches proves the advantage of symmetry breaking over the traditional relithiation process in repairing the structure of spent cathodes. The proposed repair strategy paves the way for the exploration of more efficient repair methods for spent cathode materials. (Figure presented.)