Fe2+/Fe3+-Mediated synergistic electrochemical leaching of spent lithium-ion batteries under low voltage: a green chemistry approach

Abstract

To lower the costs and environmental impact of hydrometallurgy leaching while improving safety, electrochemical leaching of spent lithium-ion battery (LIB) cathodes has gained attention. This study proposes the use of an active cathode and anode in the electrochemical leaching process and introduces a low-voltage electrochemical synergistic leaching process for spent LiNi_0.5Co_0.2Mn_0.3O₂(NCM) and LiFePO₄(LFP) cathodes in sulfuric acid solution. Thermodynamic analysis demonstrates that various elements can be leached without additional redox agents through electrochemical methods. Under optimal conditions (1 V, 1 M acid, 60 °C, and 120 min), leaching efficiencies of Li, Ni, Co, Mn, and Fe are above 98%. Fe leaching was identified as diffusion-controlled, while the leaching of other elements was primarily governed by chemical reactions. The ion diffusion inside the electrode during the electrochemical leaching process was analyzed through finite element simulations. Higher voltage restricted transition metal leaching due to diffusion-limited current densities and side reactions involving gas evolution. Fe²⁺/Fe³⁺ acting as an electron mediator between the cathode and anode achieved a synergistic effect and suppressed gas evolution reactions. This method solves the challenges for gas evolution in electrochemical leaching of spent LIBs using Fe ion cycling instead of conventional reductants, reduces energy consumption and provides a greener approach for LIB recovery.