Synergistic Etching-Complexation Surface Reconstruction Induced by Dual Organic Acids toward High-Performance Lithium-Rich Manganese-Based Cathodes

The practical application of lithium-rich manganese-based cathode materials (LRMs) is hampered by persistent voltage fade, sluggish rate capability, and structural instability at high voltages. Herein, a dual organic acid etching-complexation strategy is proposed to simultaneously enhance the capacity, rate performance, and structural robustness of LRMs. The optimized sample delivers a high initial capacity of 287.8 mAh g^-1 at 0.1 C and 236.9 mAh g^-1 at 3 C, together with an initial Coulombic efficiency (ICE) of 91.5% and a low voltage decay of 2.81 mV per cycle. Oxalic acid treatment induces Mn³⁺-rich surface sites and H⁺/Li⁺ exchange, generating lithium and oxygen vacancies, while citric acid forms transition metal (TM)-O-C═O complexes that suppress Li⁺/Ni²⁺ mixing and promote the formation of TM vacancies and a spinel/layered heterostructure upon calcination. The synergistic introduction of cation-anion dual vacancies decreases lattice distortion, stabilizes lattice oxygen redox above 4.5 V as evidenced by in situ differential electrochemical mass spectrometry (DEMS), and accelerates Li⁺ diffusion. Experimental results combined with theoretical calculations reveal increased vacancy formation and binding energies, accounting for the improved structural stability and Li⁺ transport. This dual-acid strategy offers an effective and eco-friendly route to overcoming the intrinsic limitations of LRMs.