Electrochemical properties of chromium oxyfluoride CrO2−xFx with 0 ≤ x ≤ 0.3

Abstract

To overcome the limitations of graphite as a negative electrode material for lithium-ion batteries (LIBs), transition metal oxyfluorides are under active development. In this study, chromium oxyfluorides CrO_2−xF_x with 0 ≤ x ≤ 0.3 were synthesized under a high-pressure/high-temperature (HP/HT) environment, and their electrochemical properties were examined in a nonaqueous lithium cell. The HP/HT-treated CrO₂ maintained a rutile structure and exhibited a rechargeable capacity (Q_recha) of over 400 mA h g⁻¹ at 298 K. The replacement of O²⁻ ions with F⁻ ions in CrO₂ was confirmed by linear changes in the tetragonal lattice parameters, weaker ferromagnetic interactions between Cr⁴⁺ ions, and elemental mappings of F⁻ ions. The Q_recha values of the x > 0 samples at 298 K decreased to 150–300 mA h g⁻¹ because of low electric conductivity in CrO_2−xF_x. However, the Q_recha values at 318 K increased to 600–700 mA h g⁻¹, and the cycle performance over 30 cycles was better than that of the HP/HT-treated CrO₂ sample with no F⁻ substitution. Hence, CrO_2−xF_x was found to be a promising negative electrode material for LIBs, although its cycle stability should be further improved.