First-principles calculations and experimental study of Al-doped Fe 1- x Al x F 3 ·0.33H 2 O/C cathodes for Li-ion batteries

As an intercalation–conversion cathode, iron fluoride cathode with ultrahigh energy density has been extensively studied. Nevertheless, the intrinsic low electric conductivity induced by the ionic nature of F-Fe restricts its electrochemical activity and results in poor electrochemical reversibility, thus preventing its practical application in Li-ion batteries. Hence, it is important to enhance the electric conductivity of FeF 3 ·0.33H 2 O for improving its electrochemical properties. Herein, first-principles calculations elucidate that the electric conductivity of FeF 3 ·0.33H 2 O can be enhanced owing to the band gap reduction by Al-doping. Then, Fe 1- x Al x F 3 ·0.33H 2 O/C ( x = 0 and 0.08) nanocomposites are prepared by a simple solvothermal approach and ball-milling route. Electrochemical tests demonstrate that Al-doping can greatly enhance the electrochemical properties of FeF 3 ·0.33H 2 O/C. Based on the synergistic effect of Al-doping and ball milling, the Fe 0.92 Al 0.08 F 3 ·0.33H 2 O/C sample delivers a high reversible capacity of 164.0 mAh g -1 at 40 mA g -1 in the region of 2.0-4.5 V after 100 cycles and good rate capability. Graphical abstract