Exploring Limits of Scale: Hydrothermal Relithiation for Direct Recycling

Direct recycling is a promising alternative for low-cost and more environmentally friendly disposal of lithium-ion batteries. Hydrothermal relithiation is a method of direct recycling that uses an aqueous lithium hydroxide solution to infuse lithium back into cathode black mass at high temperatures and pressures. Despite recent attention and study, the limits of scaling the hydrothermal process are not understood. Our work has built on previous advancements of optimizing hydrothermal parameters, and demonstrated that the amount of aqueous solution can be significantly limited to still recover spent cathode materials. Through a study of lithium diffusivity at various states of delithiation, it is shown that minimal excess lithium is necessary to relithiate various lithium nickel cobalt manganese oxide (NCM) cathode materials. The improved solution-to-black-mass ratio maintains high cycling performance, fully restoring to pristine electrochemical capacity, thus paving the way for at-scale rejuvenation.