High-Pressure Study of a Novel Cathode Material to 60 GPa

Lithium-rich cobalt oxyfluoride, synthesized as a disordered rock salt, is a novel cathode material for Li-ion batteries that shows high-capacity retention even after long-term cycling, despite high capacity being typically associated with ordered structures. The disordered nature is due to random occupancy of the cations in the octahedral voids and of the anions forming the cubic closed-packed array. Here high pressure is used to further characterize the material and to search for new structures. To that end, x-ray diffraction was performed up to 60 GPa, and Raman and IR spectroscopies were performed up to 50 GPa. The diffraction shows that the ambient structure persists on compression up to 60 GPa at room temperature. The x-ray data give a bulk modulus, K0, of 273(5) GPa, with a K0’ of 1.0 (0.2). A broad Raman peak near 610 cm^-1 shifts to higher wavenumber and increases in intensity under pressure, and a new peak at 660 cm^-1 emerges at 10 GPa, suggesting a change in the structure not apparent in the diffraction data. The IR measurements show that the energy absorption edge increases with pressure indicating an opening of the band gap.