Abstract: Spinel-type LiNi₀.₅Mn₁.₅O₄ (LNMO), owing to its high operating voltage and related advantages, is considered a promising cathode material for high–energy density lithium-ion batteries. However, under high-temperature and high-voltage conditions, LNMO tends to generate Mn³⁺, which reacts with the electrolyte and leads to capacity degradation—a problem that is particularly pronounced in nanoparticle systems. To balance electrochemical activity and structural stability, this study employs a sol–gel method to synthesize micron-sized single-crystal LNMO and systematically investigates the effects of various processing parameters—including complexing-agent ratios (4:1, 2:1), pH values (5, 6, 7), calcination temperatures (750, 850, 950℃), calcination durations (8, 12, 16 h), and dispersants—on its structure and electrochemical performance.The results indicate that the sample prepared with a complexing-agent ratio of 2:1, pH = 6, calcination at 850℃ for 12 h, and with polyethylene glycol added exhibits the best overall performance. It delivers an initial discharge capacity of 112 mAh·g⁻¹ with a Coulombic efficiency of 93.7%, and retains 95.33% of its capacity after 100 cycles at 1 C.On this basis, Nb₂O₅ coating modification was further introduced, and the effects of different coating amounts (0.5%, 1%, 2%) on electrochemical performance were evaluated. The results show that a 1% coating yields the most optimized performance, achieving an initial discharge capacity of 118 mAh·g⁻¹, a Coulombic efficiency of 93.77%, and an improved capacity retention of 96.6% after 100 cycles. These findings demonstrate that Nb₂O₅ coating effectively enhances the cycling stability of LNMO, providing a feasible pathway for developing high-performance cobalt-free cathode materials.