Oxygen character in the density of states as an indicator of the stability of Li-ion battery cathode materials
Abstract Oxygen gas evolution from lithium battery cathode materials during charging to high voltages is a known mechanism leading to cathode instability and ultimately Li-ion batteries fires. We present the simple thesis that the tendency toward oxygen destabilization in metal-oxide materials used as Li-ion battery cathodes can be correlated to the amount of oxygen-derived weight in the partial density of states (PDOS) near the Fermi level (E F ), which is easily calculable with density functional theory (DFT). If the oxygen PDOS dominates the total DOS at E F at any point during delithiation (charging), electrons are withdrawn from the O rather than the M states, and the O 2 − ions are oxidized to peroxide (O 2 2 − ), and then often to O 2 gas. A demonstration of the utility of this perspective is given using DFT to calculate the PDOS for compounds with a broad range of structures, transition metals and degrees of lithiation: LiFePO 4 , Li 2 CuO 2 , LiCoO 2 , LiNiO 2 , and Li 2 RuO 3 . The resulting computational spectra correlate well to the experimental stability in the modeled compounds. We conclude that the oxygen stability of cathode materials derives from their fundamental electronic structure as function of changing voltage (and lithiation).