Li+ transportation kinetics of FeF3 · 0.33H2O/C nanocomposite synthesized by one-step solid state method

A new cathode material for lithium ion battery FeF3 · 0.33H2O/C was synthesized successfully by a simple one-step chemico-mechanical method. It showed a noticeable initial discharge capacity of 233.9 mAh g−1 and corresponding charge capacity of 186.4 mAh g−1. A reversible capacity of ca.157.4 mAh g−1 at 20 mA g−1 can be obtained after 50 charge/discharge cycles. To elucidate the lithium ion transportation in the cathode material, the methods of electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT) were applied to obtain the lithium diffusion coefficients of the material. Within the voltage level of 2.05–3.18 V, the method of EIS showed that \( {D}_{{\mathrm{Li}}^{+}} \) varied in the range of 1.2 × 10−13 ~ 3.6 × 10−14 cm2 s−1 with a maximum of 1.2 × 10−13 cm2 s−1 at 2.5 V. The method of GITT gave a result of 8.1 × 10−14 ~ 1.2 × 10−15 cm2 s−1. The way and the range of the variation for lithium ion diffusion coefficients measured by the GITT method show close similarity with those obtained by the EIS method. Besides, they both reached their maximum at a voltage level of 2.5 V.