Understanding and Controlling Structural Defects and Disordering in LiNi_0.5Mn_1.5O₄ Cathodes for Direct Recycling

Despite significant progress in recycling spent lithium-ion batteries (LIBs), nondestructive, direct recycling methods still face untenable discrepancies in multiple cathode chemistries, which primarily originate from a variety of structure stabilities during the recycling process. Through systematic investigation of the microstructure evolution during the relithiation treatment, we observed the inevitably induced defects and Li/Mn disordering in the LiNi_0.5Mn_1.5O₄ cathode, contributing to the sluggish Li⁺ transport and irreversible capacity loss. Employing a defect engineering approach to achieve twin boundaries and preferred grain orientation, we show the regenerated cathodes demonstrate a substantial enhancement of Li⁺ diffusion and cycling stability, retaining 97.4% capacity after 100 cycles and 87.96% after 200 cycles at C/3. This work not only elaborates on a systematic investigation of defect inducement and structural restoration mechanism but also provides an effective approach to directly recycle high-voltage spinel-type cathodes, contributing to the sustainability of next-generation LIBs.