Investigating the mechanism of niobium doping for mitigating voltage decay in LiMn0.6Fe0.4PO4

Olivine-type LiMn x Fe 1- x PO 4 (LMFP) is a promising cathode material that combine the safety and structural stability of LiFePO 4 with a higher operating voltage and energy density. However, it suffers from severe voltage decay during electrochemical cycling and poor rate capability. Here, we present a crystal-field regulation strategy via niobium doping to simultaneously enhance the reaction kinetics and structural stability of LiMn 0.6 Fe 0.4 PO 4 . The strong Nb‑O bond widens Li + diffusion channels, promoting a continuous solid-solution reaction pathway and stabilizing the host lattice framework. The robust framework ensures highly reversible Fe and Mn redox reactions and mitigates the inherent instability of Mn species. As a result, the Nb-doped LiMn 0.6 Fe 0.4 PO 4 cathode exhibits superior rate retention at high C-rates and outstanding cycling stability under high-temperature conditions, retaining 96.9% of its initial capacity after 500 cycles at 45 °C. This work demonstrates that high-valent doping-induced bulk lattice engineering, distinct from conventional interfacial approaches, is an effective strategy to unlock the high-performance potential of LMFP cathodes.