Advanced characterization guiding rational design of regeneration protocol for spent-LiCoO2

Exploring the structure transformation mechanism of the spent cathodes during their regeneration process is the key to optimizing the processing protocol. The spent cathode materials are in different state of health (SOH) due to their different operation history, which leads to the challenge of restoring them in one-pot. Herein, to address the effect of SOH on the direct regeneration protocol, we systematically investigated the spent LiCoO2 (LCO) cathode with low and high SOH. We find that lithium-deficiency and Al impurity are the two important factors in affecting the regeneration quality of the spent LCO. Lithium-deficiency can cause void defects and disordered lattice structure. Al impurity is brought to the LCO surface during lithium replenishment process, which further diffuses into the LCO subsurface layer during the following high temperature sintering. Based on our understanding of the regeneration process, the regeneration protocol is optimized accordingly, which can successfully restore the spent LCO with different SOH.