Low‐Frequency Phonon Dispersion Relation Enabling Stable Cathode from Spent Lithium‐Ion Batteries

Direct recycling technology can effectively solve the environmental pollution and resource waste problems caused by spent lithium-ion batteries. However, the repaired LiNi_0.5Co_0.2Mn_0.3O₂ (NCM) black mass by direct recycling technology shows an unsatisfactory cycle life, which is attributed to the formation of spinel/rock salt phases and rotational stacking faults caused by the in-plane and out-of-plane migration of transition metal (TM) atoms during charge/discharge. Herein, local lattice stress is introduced into the regenerated cathode during repair. The resulting stress gradient leads to the localization of the phonon mode and changes the phonon dispersion relation of materials, lowers the bending and stretching vibration frequencies of the TM─O covalent bond in cathode materials, and inhibits the TM atoms migration and the formation of defect structures. Beneficial from the favorable low-frequency phonon dispersion relation, the regenerated NCM represents remarkably enhanced structural stability during cycling, and exhibits good electrochemical performance. This reconstructed phonon dispersion relation approach broadens the perspective for lattice stress field engineering to suppress the defective structure raised from TM migration and paves the way for the development of regenerated cathodes with long durability.