Oxygen hole formation controls stability in LiNiO2 cathodes
Annalena R. Genreith‐Schriever, Hrishit Banerjee, Ashok S. Menon, Euan N. Bassey, Louis F. J. Piper, Clare P. Grey, Andrew J. Morris
Abstract
Ni-rich lithium-ion cathode materials achieve both high voltages and capacities but are prone to structural instabilities and oxygen loss. The origin of the instability lies in the pronounced oxidation of O during delithiation: for LiNiO 2 , NiO 2 , and the rock salt NiO, density functional theory and dynamical mean-field theory calculations based on maximally localized Wannier functions yield a Ni charge state of ca . +2, with O varying between −2 (NiO), −1.5 (LiNiO 2 ), and −1 (NiO 2 ). Calculated X-ray spectroscopy Ni K and O K -edge spectra agree well with experimental spectra. Using ab initio molecular dynamics simulations, we observe loss of oxygen from the (012) surface of delithiated LiNiO 2 , two surface O ⋅− radicals combining to form a peroxide ion, and the peroxide ion being oxidized to form O 2 , leaving behind two O vacancies and two O 2− ions. Preferential release of 1 O 2 is dictated via the singlet ground state of the peroxide ion and spin conservation.