Probing Solid-Solid Interfacial Reactions in All-Solid-State Batteries

We have developed a hierarchy of DFT-based approaches to understand and design electrode/buffer/SE interfaces in all-solid-state batteries. Even with relatively efficient thermodynamics approximations, we reveal that S-O exchange reactions between oxides (O2-) and thiophosphates (PS4 3-) resulting in the formation of phosphates (PO4 3-) are responsible for large reaction driving force between the common NaMO2 (M = Co, Ni, Fe, Mn) cathodes and Na3PS4 SE. Such reactions, with their associated large volume changes, can be mitigated by careful selection of the cathode/SE combination, or the use of buffer layers with good stability between both materials. We have also identified several promising binary oxides with similar or better chemical compatibility with most electrodes and SEs than the commonly-used Al2O3. Despite the success of thermodynamics-based approximations, we further demonstrate that explicit modelling of the electrode/SE interface via ab initio molecular dynamics (AIMD) simulations sometimes yield different and more realistic predictions of interfacial reaction products. For example, AIMD predicts that formation of SO4 2– are kinetically favored over the formation of PO4 3– at the NaCoO2/Na3PS4 interface model, in contrast to the predictions of the thermodynamic models. These observations have been validated experimentally. We have also extended such studies to the LiNi0.85Co0.1Al0.05O2/Li6PS5Cl interface, with and without buffer layers, and the predicted interfacial reactions are in good agreement with experimental characterizations.