Tuning cation ordering and Mn3+ content in non-stoichiometric LiNi0.5-Mn1.5+O4- (LNMO) for enhanced cathode stability in lithium-ion batteries

Abstract

Rapidly increasing demand for high-energy, long-cycle-life lithium-ion batteries (LIBs), particularly in electric vehicles and grid-scale applications, has highlighted the need for advanced cathode materials. High-voltage LiNi0.5Mn1.5O4 (LNMO) has attracted considerable attention owing to its elevated working potential, reduced reliance on nickel, and cobalt-free composition. In this work, a scalable co-precipitation method is employed to synthesize non-stoichiometry LNMO cathodes with varying particle size, enabling precise control over particle morphology, cation ordering and Mn3+ content. Comprehensive structural and electrochemical evaluations reveal that reducing the Ni content in LNMO elevates the Mn3+ concentration and promotes the degree if cation disorder, which facilitates a single-phase, solid-solution reaction mechanism during lithiation and de-lithiation. In such a mechanism, Li+ are inserted and extracted uniformly throughout the material without the formation of distinct phase boundaries, thereby significantly reducing kinetic barriers and polarization. Furthermore, although Mn3+ typically induces local Jahn-Teller distortions, in a highly disordered lattice these distortions are more uniformly distributed, which minimizes local stress accumulation and enhances structural stability during cycling. This uniform distribution not only supports rapid Li+ diffusion through continuous and well-connected pathways but also improves electronic conductivity by optimizing the local electronic structure. Consequently, LNMO with the highest cation disorder and Mn3+ content, exhibits superior electrochemical performance, delivering 119.6 mAh·g−1 at 2C, retaining 70.3 % of its capacity after 1000 cycles and demonstrating the best kinetics among the samples.