Using high accuracy many-body methods (QMC and sCI) to describe ground state and excited state properties of strongly correlated battery cathodes

Since the commercialization of the first Lithium Ion Batteries (LIB) with LiCoO$_2$ as the active material in the cathodes, its electrochemical performance has been extensively studied both experimentally and theoretically. Increasing the capacity of LIB with high voltage leads to oxygen loss and surface reconstruction resulting in a rapid capacity fade and impedance growth. Using surface coating treatment stabilizes the surface and minimizes reactions with electrolytes but requires a good understanding of the electronic structure and properties of LiCoO$_2$. In the past decades, many studies using Density Functional Theory (DFT) corrected for strong correlation with an ad-hoc Hubbard U energy were published reproducing many important properties of the material. While DFT+U can reproduce a known property (band gap or lattice parameter), the value of U needs to be updated for each new property making the approach non-predictive. In this talk we use a combination of Diffusion Monte Carlo (DMC) and select Configuration Interaction (sCI) for solids to describe the orbitals of LiCoO$_2$, leading to a better description of the band gaps of strongly correlated transition metal oxide materials and open the path to more reliable and trial-wavefunction invariant DMC calculations.