Direct recycling of degraded lithium-ion batteries of an electric vehicle using hydrothermal relithiation

This study aims to directly recycle degraded LiNi0.15Mn0.15Co0.70O2 cathode materials of spent lithium-ion batteries from an electric vehicle. By combining hydrothermal relithiation with sintering, degradation issues of lithium deficiency, microcrack, and phase transformation are resolved. When the degraded cathode material is hydrothermally relithiated at 220 °C for 2 h and then sintered at 850 °C for 4 h in air, a discharge capacity of 150.7 mAh/g at 50 mA/g in the first cycle with a capacity retention of 91.2% after 50 cycles is achieved. The hydrothermal relithiation conforms to pseudo-second-order kinetic model and Langmuir isotherm model, suggesting that the hydrothermal relithiation is mainly controlled by chemisorption and monolayer adsorption, respectively. The thermodynamic parameters reveal that the hydrothermal relithiation is endothermic and non-spontaneous in nature. This study presents a fundamental understanding of hydrothermal relithiation mechanism for degraded cathodes and provides an alternative recycling route to pyrometallurgy and hydrometallurgy.