Mn-Doped Fe_1–xMn_xF₃·0.33H₂O/C Cathodes for Li-Ion Batteries: First-Principles Calculations and Experimental Study

Increasing attention has been paid on iron fluoride as an alternative cathode material for Li-ion batteries (LIBs) owing to its high energy density and low cost. However, the poor electric conductivity and low diffusivity for Li-ions set great challenges for iron fluoride to be used in practical LIBs. Here, we employ first-principles calculations to probe the influence of Mn-doping on the crystal structure and electronic structure of FeF3·0.33H2O. The calculated results suggest that Mn-doping can enlarge the hexagonal cavity and reduce the band gap of FeF3·0.33H2O as well as improve its intrinsic conductivity. Furthermore, Fe1–xMnxF3·0.33H2O/C (x = 0, 0.06, 0.08, and 0.10) nanocomposites were successfully fabricated by a hydrothermal method and ball-milling. Owing to the Mn-doping effect combined with highly conductive acetylene black (AB) modification, the typical Fe0.92Mn0.08F3·0.33H2O/C composite exhibits a high discharge capacity of 180 mA h g–1 at 50 mA g–1 after 100 cycles and delivers excellent cycling stability as well as good rate capability.