Natural product driven redox-recovery of lithium cobalt oxide cathodes under mild conditions

Abstract

Closed-loop recycling of lithium cobalt oxide (LCO) cathodes with low cost and high reward via a hydrometallurgical approach based on natural products, remains a challenge. Additionally, traditional hydrometallurgical methods require harsh conditions, generate secondary pollutants, and rely on hazardous reducing agents. Herein, a sustainable closed-loop process is proposed for efficient and selective metal recovery under mild conditions; utilizing the natural amino acid cysteine (Cys), which features multifunctional groups (–SH, –COOH, –NH₂) to act as a leaching agent, and using the natural oxalic acid as a selective recovery reagent of Co. The approach avoids the use of additional reducing agents and harsh conditions. Leaching efficiencies of 94.85% for cobalt (Co) and 99.38% for lithium (Li) were achieved using Cys to realize leaching at 73 °C for 1.5 hours. The results significantly outperform conventional organic acids and deep eutectic solvents (DES). Mechanistic studies revealed that the synergistic redox activity of –SH and coordination capabilities of –COOH/–NH₂ enable rapid reduction of Co³⁺ to Co²⁺ and subsequent complexation, as confirmed by XPS, FTIR, and DFT calculations. The regenerated LCO cathode material exhibited superior electrochemical performance, with a capacity retention of 76.52% after 100 cycles at 1C, comparable to that of commercial counterparts. An economic analysis demonstrated a net profit of 58.26 $ per kg of processed LCO, highlighting the scalability and cost-effectiveness of this green approach. This work contributes to the advancement of bio-based solvents for sustainable battery recycling, in alignment with the principles of a circular economy.