Structural evolution of layered oxide cathodes for spent Li-ion batteries: Degradation mechanism and repair strategy

Sustainable development has long been recognized as one of the most critical issues in today's energy and environment-conscious society. It has never been more urgent to recycle and reuse the end-of-life cathode materials. Here, this work systematically investigates the structure-critical degradation mechanism of polycrystalline LiNixCoyMn1-x-yO2 (NCM), combining experimental characterization and DFT simulations. Targeting the key degradation factors, a synergistic repair strategy based on deep mechanochemical activation and heat treatment was successfully proposed to direct regenerate the degraded NCM material. Studies indicate the induction and promotion of synergistic repair technique on the reconstruction of particle morphology, the recovery of the chemical composition and crystal structure, and the favorable transformation of the impurities phase in the failed materials. In particular, the synergistic repair process induces a gradient distribution of LiF and further enables partial fluorine doping into the NCM surface, forming abundant oxygen vacancies and increasing the content of highly reactive Ni2+. Benefiting from the comprehensive treatment for the multi-scale and multi-form degradation behaviors, the repaired material exhibits a capacity of 176.8 mA h g(-1) at 0.1 C, which is comparable to the corresponding commercial material (172.8 mA h g(-1)). The satisfactory capacity of the recovered cathode proves that it is an effective direct renovating strategy.