Morphology Control of Spinel LiNi_0.5Mn_1.5O₄ for Tuned Microstructure and Electrochemistry

High-voltage spinel LiNi_0.5Mn_1.5O₄ (LNMO) is a promising cathode for next-generation lithium-ion batteries, yet its application is limited by structural instability and poor high-temperature/high-rate performance. Here, spherical secondary polycrystalline aggregate (LNMO-PC), micron-sized primary particle (single-crystal morphology) (LNMO-SC-L), and submicron primary particle (single-crystal morphology) (LNMO-SC-S) LNMO were synthesized. Their structures, morphologies, and surface properties were characterized and electrochemical performance evaluated at room (25 °C)/high (55 °C) temperature and high rates. LNMO-SC-S exhibited the highest crystallinity, lowest Mn³⁺ content, and minimal charge-transfer resistance. It showed superior cycling stability (93.3% retention at 1 C over 500 cycles), excellent rate capability (~20 mAh g^-1 at 20 C), and enhanced high-temperature performance. The submicron primary particles suppress grain-boundary degradation and Mn³⁺ disproportionation, shortens Li⁺ paths, and improves reaction kinetics.