Lithium extraction from spinel LiMn2O4 with simultaneous preparation of λ-MnO2 under mild conditions using sodium hypochlorite

Abstract

Lithium extraction from spinel LiMn₂O₄ is of significant importance, because it serves not only as one of the mainstream cathode materials for lithium-ion batteries (LIBs) but also as a crucial precursor for the preparation of isostructural λ-MnO₂ (delithiated LiMn₂O₄), widely used in the selective lithium extraction from brines and seawater. This study proposes a novel approach for lithium extraction from LiMn₂O₄ that preserves the structural integrity of the spinel during delithiation, by using sodium hypochlorite (NaClO) as an oxidant under comparatively mild conditions (room temperature, weakly acidic environment). At pH = 4, approximately 99.3% of lithium was selectively extracted without detectable Mn loss. Mechanistic analysis revealed that the process primarily involves Mn³⁺ oxidation to Mn⁴⁺, with a minor contribution from H⁺/Li⁺ ion exchange. The resulting λ-MnO₂ maintained its spinel morphology and exhibited good lithium uptake capacity and cyclic performance. Moreover, life cycle and techno-economic assessments demonstrate that the NaClO-based oxidative selective delithiation route offers significantly lower environmental impacts, energy consumption, and overall cost than the previously reported Na₂S₂O₈-based oxidation process. Compared with traditional acid leaching, it demonstrates advantages in terms of human toxicity and freshwater aquatic ecotoxicity, and also offers superior λ-MnO₂ yield and downstream processing owing to its higher lithium selectivity and negligible Mn loss. This work provides a simple, efficient, and sustainable strategy for λ-MnO₂ preparation and holds promise for the selective recovery of lithium from spent LiMn₂O₄ cathode materials.