Unraveling the importance of water ratio in direct lithium-ion battery cathode recycling

This study investigates the impact of water ratio on the direct aqueous recycling of NMC811. Three different ratios of NMC811 to water were examined. The results demonstrate that the water ratio significantly affects the electrochemical performance of NMC811. Capacity fading is observed in all water-exposed samples, with the sample having the lowest water ratio showing less fading compared to the samples processed with higher water ratios. Both samples with higher water ratios exhibit similar performance, suggesting an equilibrium at the NMC811-water interface is established. Characterization of the cathode materials reveals variations in the amount and type of surface species. The pristine sample, not exposed to water, only shows Li₂CO₃ and NiO as surface species, while the water-exposed NMC811 samples exhibit nickel carbonates and hydroxides along with associated water. The poorer performance of samples exposed to higher water ratios is likely due to higher amounts of these species forming on the particle surface. Additionally, lithium, cobalt, and manganese carbonates, as well as lithium hydroxide with associated water, are detected and could further contribute to the poorer performance.