Low-voltage suspension electrolysis enables redox-coupled synergistic leaching for closed-loop recycling of mixed NCM-LFP cathodes

Abstract

The rapid growth of spent lithium-ion batteries (LIBs) has created an urgent need for efficient and environmentally safe recycling technologies, particularly for mixed-cathode materials. In this study, a low-voltage suspension electrolysis enhanced-synergistic leaching process was developed to overcome the low synergy efficiency and limited throughput that restrict conventional electrochemical leaching methods for spent LIBs. Under mild conditions of 40 °C and 1.2 V, the process achieves a high throughput of 40 g L⁻¹ (25 mL g⁻¹) without evident gas-evolution side reactions, and the leaching efficiencies of Li, Ni, Co, Mn, and Fe all exceed 98% without the use of reductants. Kinetic analysis demonstrates that the leaching follows a shrinking-core model, with Li dissolution controlled by surface reactions, Ni and Co by mixed control, and Mn and Fe by chemical reactions. Mechanism studies reveal that Fe-ion-mediated electron transfer is the primary driver of redox coupling, that 1.2 V lies near the critical transition region of competing electrode processes, and that Mn undergoes unique intra-crystalline migration during NCM leaching, which accelerates particle dissipation. High-purity FePO₄, NCM precursor, and Li₂CO₃ were recovered from the leachate, and regenerated NCM and LFP exhibited good electrochemical performance. The process enables reagent recovery, avoids secondary pollution, achieves an estimated profit of $3.10 per kg black powder, and requires only 0.006 kWh kg⁻¹ black powder for DC electrolysis. The mild operating conditions, elimination of external reductants, high throughput, low direct energy input, and closed-loop regeneration demonstrate a meaningful green advance in terms of energy efficiency, reagent simplification, process intensification, and circularity. This work therefore provides an environmentally responsible and mechanistically informed route for the sustainable recycling of mixed spent LIB cathodes.