From Micro to Nano: Boosting γ-MnO2 Cathode Performance through Particle Size Engineering.

Fast-charging lithium-ion batteries require cathodes that sustain rapid Li+ transport while maintaining structural and interfacial stability. Here, we investigate particle-size effects in γ-MnO2 by comparing micron-sized (4.4 ± 0.8 μm) and nanosized (62 ± 21 nm) particles under identical conditions. Nanosized γ-MnO2 delivers 160.1 mAh g-1 at C/10 and retains ∼66% capacity at 5C while exhibiting lower charge-transfer and diffusion-related impedance. Cyclic voltammetry and Dunn's analysis reveal a 68.9% capacitive contribution at 2 mV s-1, indicating a shift toward faster surface-controlled charge storage enabled by increased surface area and shorter Li+ diffusion pathways. GITT measurements show deeper lithiation (x ≈ 0.65 vs 0.48 in LixMnO2) and a more homogeneous solid-solution-like intercalation regime in nanosized particles, avoiding bulk phase-transition kinetic bottlenecks. The nanosized cathode retains 70% capacity with ∼99.5% Coulombic efficiency after 400 cycles at 3C, demonstrating particle-size engineering as an effective strategy for high-rate, long-life advanced battery energy storage.