H ⁺ /OH ⁻ Switchable Coordination Chemistry Enables Sustainable and Selective Critical Metal Recovery from Spent Li‐Ion Batteries

Sustainable end-of-life management of lithium-ion batteries (LIBs) is essential for minimizing environmental impact and enhancing supply chain resilience. Here, we present a novel H⁺/OH^- switchable reversible coordination chemistry mechanism that utilizes a cost-effective, recyclable K₄Fe(CN)₆ aqueous solution for highly efficient and selective recovery of critical metals from various spent LIB cathodes. Under H⁺-rich acidic conditions, the LiCoO₂ (LCO) cathode demonstrates a high Li leaching efficiency of 96.57%, while cobalt selectively reacts with K₄Fe(CN)₆ to precipitate as K_0.5H_1.5CoFe(CN)₆·H₂O. Subsequent OH^--rich base treatment facilitates the stepwise recovery of cobalt from K_0.5H_1.5CoFe(CN)₆·H₂O to form CoOOH, achieving a 95.18% recovery efficiency and K₄Fe(CN)₆ regeneration. In situ powder X-ray diffraction and time-dependent Raman spectroscopy reveal the dynamic crystal structural evolution and reversible coordination chemistry between Co─O bonding in LiCoO₂/CoOOH and Co─N bonding in K_0.5H_1.5CoFe(CN)₆·H₂O, driven by the H⁺/OH^- pair in the K₄Fe(CN)₆ solution. This strategy is applicable for recovering critical metals from a wide range of LIBs cathodes (e.g., NCMs, LFP), offering significant techno-economic and environmental benefits, and lays the foundation for sustainable critical metals recycling from urban minerals beyond spent LIBs.