Mn-doped FeF 3 ·0.33H 2 O with enhanced electrochemical performance as cathode materials for lithium-ion batteries

Lithium-ion batteries with the FeF3·0.33H2O cathode material enable a high energy density and safety. However, a major challenge of FeF3·0.33H2O is its low conductivity. In this work, Fe1-2x/3MnxF3·0.33H2O (x = 0, 0.01, 0.03, 0.05, and 0.07) are prepared via the solvent thermal method. Systematic investigations have studied the effect of Mn-doping on the physical and electrochemical properties. The results indicate that Mn-doping not only does not destroy the lattice structure of FeF3·0.33H2O, but also reduces the resistance and improves the diffusion coefficient of lithium ion, which provide it with better electrochemical properties. Fe0.98Mn0.03F3·0.33H2O delivers much excellent cycling performance and rate capacity than other materials. It has a 284.2 mAh g−1 initial discharge capacity that remains at 258.9 mAh g−1 after 50 cycles at 0.1 C, giving the high capacity retention rate of 91.1%. Additionally, the initial discharge capacity of Fe0.98Mn0.03F3·0.33H2O is 245, 231, 217, and 203 mAh g−1 at 1, 2, 5, and 10 C in the voltage range of 1.5–4.5 V vs. Li+/Li, respectively.