Enhanced structural stability and electrochemical performance of niobium-doped Li-rich manganese-based cathode materials

Lithium-rich Mn-based layered oxides are promising cathodes for next-generation high-energy-density lithium-ion batteries. However, their practical use is limited by rapid voltage fading and sluggish high-rate performance. Introducing high-valent dopants such as Nb 5+ is expected to induce charge compensation and strengthen the local TM–O framework, thereby mitigating high-voltage degradation. Here we introduce Nb into cobalt-free Li 1.2 Mn 0.6−x Nb x Ni 0.2 O 2 (x = 0, 0.01, 0.02, 0.03) through a coprecipitation-compatible, water-assisted wet-grinding step followed by calcination, aiming to improve precursor-level mixing and enable controllable high-valent doping. Among the compositions, LLO-0.02Nb delivers the best overall performance, retaining 80% capacity after 200 cycles at 1C (vs. 78% for pristine LLO) and providing 163 and 142 mAh·g −1 at 5C and 10C, respectively, together with a reduced voltage-decay tendency (1.87 mV per cycle). After-cycling electrode analyses (XRD/SEM) reveal better preserved layered-related features and less severe surface degradation for the Nb-doped electrode. Surface spectroscopy (XPS/EPR) further indicates that Nb incorporation regulates the near-surface oxygen environment and transition-metal valence states via charge compensation. These results suggest that a mild Nb addition, enabled by a simple wet-assisted introduction route, can simultaneously enhance voltage stability, cycling durability, and rate capability of Li-rich Mn-based cathodes.