Discovery of a high-pressure phase of rutile-like CoO2 and its potential as a cathode material

Abstract

Due to the structural failure of layered CoO₂, there has been considerable effort to improve the reversible capacity of commercial LiCoO₂ cathode materials. Using a global structural search, we have discovered a rutile-like CoO₂ phase as the ground state at 50 GPa. The material is thermally, mechanically and dynamically stable, even after removing the pressure. We show that, when lithiated, this LiCoO₂ material can serve as an improved cathode material for Li-ion batteries. Its many advantages include good structural stability against transition metal migration and oxygen loss, one-dimensional channels for Li ion diffusion with variable energy barriers (0.36–0.86 eV), enhanced ionic mobility, and good intrinsic electronic conductivity brought about by its metallic band structure. Furthermore, with a voltage platform of 3.2–3.8 V, it provides better stability against conventional carbonate solvents than conventional layered cathode materials (>4.0 V). All these features demonstrate that the non-layered CoO₂ phase synthesized at high pressure would be a promising cathode material, providing a performance beyond that of the currently used layered phase.