Direct upcycling of degraded NCM via low-temperature surface engineering for high performance lithium-ion batteries

Abstract

Upcycling degraded low-Ni cathode materials into Ni-rich alternatives offers significant economic and environmental benefits for lithium-ion battery production. However, the stability and safety of the upcycled materials remain challenging due to their aggressive composition. This study reports an innovative two-step upcycling method that integrates a coating process with a low-temperature annealing process, thereby successfully upcycling degraded NCM622 with a LiAlO₂ coating layer. Through comprehensive characterization, the recovery of crystal structure and uniform LiAlO₂ coating on the particle surface are confirmed by XRD and XPS results. As a result of structural recovery and surface engineering, upcycled NCM622 demonstrates an initial capacity comparable to that of NCM811 at 195.3 mA h g⁻¹ at 1 C rate, with 86.8% capacity retention after 100 cycles at a cut-off voltage of 4.6 V. Moreover, it exhibits excellent rate capability, delivering 141.9 mA h g⁻¹ at 5 C. Beyond enhancing electrochemical performance, this method significantly improves the thermal stability of degraded NCM622, with the upcycled material showing less than 0.1% weight loss at 400 °C. The findings highlight the potential of upcycled cathode materials with the LiAlO₂ coating to meet the high-performance and sustainability requirements of modern lithium-ion batteries, contributing to the circular economy of lithium-ion batteries in the future.