Cr-Doped Fe_1-CrF₃·0.33H₂O Nanomaterials as Cathode Materials for Sodium-Ion Batteries

Due to the high theoretical specific capacity and low cost, FeF₃·0.33H₂O has become one of the potential choices of cathode materials for sodium-ion batteries. However, the poor intrinsic conductivity limits its practical applications. Herein, the atomic substitution is used to improve its intrinsic conductivity. The first-principles calculation results show that Cr³⁺ doping can reduce the band gap of FeF₃·0.33H₂O to improve its intrinsic conductivity. The discharge specific capacity of Fe_0.95Cr_0.05F₃·0.33H₂O with a narrowest band gap is 194.02 mA h/g at 0.1 C within the range of 1.4-4.0 V, which is higher than that of FeF₃·0.33H₂O (136.47 mA h/g). Using the electrochemical impedance spectroscopy and galvanostatic intermittent titration technique tests, it is found that R_ct of Fe_0.95Cr_0.05F₃·0.33H₂O is reduced and D_Na is almost unchanged, as compared to FeF₃·0.33H₂O.