Understanding solid-state batteries: The route to stability

Solid-state batteries have the promise to outperformconventional Li-ion batteries. Solid electrolytes are safer, as the solids used are generally not combustible, and especially if Li-metal anodes are enabled, higher energy densities can be obtained. However, solidstate batteries still have challenges to overcome. In this thesis the origins of the main challenges in solid-state batteries are investigated and this understanding is captured in nano- and microscopic models that can be generally applied to solid-state batteries. The relatively narrow electrochemical stability window of solid electrolytes is one of the main challenges for solid-state batteries. In Chapter 2 the redox activity and electrochemical stability of an argyrodite, NASICON and a garnet solid electrolyte are investigated. It is demonstrated that the decomposition pathway of the solid electrolytes is rather indirect via (de)lithiatedmetastable phases, instead of direct via the energetically most stable decomposition products. Because the reaction proceeds via the intermediate phases, these phases determine the electrochemical stability window, generally resulting in a larger stability window. The larger window and reaction pathway that are predicted match with electrochemical experiments and observed (de)lithiated phases in XRD and NMR experiments.