Al Impurity Upcycled\nHigh-Voltage Cathodes from Spent\nLiCoO<sub>2</sub> Batteries

Al impurity is among the most likely components to enter\nthe spent\nlithium-ion battery (LIB) cathode powder due to the strong adhesion\nbetween the cathode material and the Al current collector. However,\nhigh-value metal elements tend to be lost during the deep removal\nof Al impurities to obtain high-purity metal salt products in the\nconventional hydrometallurgical process. In this work, the harmful\nAl impurity is designed as a beneficial ingredient to upcycle high-voltage\nLiCoO<sub>2</sub> by incorporating robust Al–O covalent bonds\ninto the bulk of the cathode assisted with Ti modification. Benefiting\nfrom the strong Al–O and Ti–O bonds in the bulk, the\nirreversible phase transitions of the upcycled R-LCO-AT have been\nsignificantly suppressed at high voltages, as revealed by in situ\nXRD. Moreover, a Li<sup>+</sup>-conductive Li<sub>2</sub>TiO<sub>3</sub> protective layer is constructed on the surface of R-LCO-AT by pinning\nslow-diffusion Ti on the grain boundaries, resulting in improved Li<sup>+</sup> diffusion kinetics and restrained interface side reactions.\nConsequently, the cycle stability and rate performance of R-LCO-AT\nwere significantly enhanced at a high cutoff voltage of 4.6 V, with\na discharge capacity of 189.5 mAhg<sup>–1</sup> at 1 C and\ncapacity retention of 92.9% over 100 cycles at 4.6 V. This study utilizes\nthe detrimental impurity element to upcycle high-voltage LCO cathodes\nthrough an elaborate bulk/surface structural design, offering a strategy\nfor the high-value utilization of spent LIBs.