EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Solid-state batteries are intensively studied because they promise safer electrochemical storage with larger volumetric and gravimetric energy densities. One of the main scientific challenges in the cycling performance is the limited electrolyte stability, which leads to parasitic reactions that may lead to volumetric changes, contact loss, less conductive interphases and irreversible capacity loss. The electrochemical stability is usually evaluated by the formation energy of decomposition products using the grand potential phase diagram. However, this predicts a very limited electrochemical stability, inconsistent with experimental observations. We demonstrate a novel method calculating the intrinsic electrochemical window of solid electrolytes and apply this method on different classes of solid electrolytes. We show that the electrochemical window determined by (de)inserting Li in the solid electrolyte structure, often predicts the actual electrochemical window. Additionally, we find information about the structural stability and decomposition routes of solid electrolytes. We support our calculation with a full evaluation of an argyrodite solid electrolyte using ex-situ X-Ray Diffraction (XRD) and 6Li and 31P Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) and provide an accurate measurement of the electrochemical stability of a NASICON and garnet solid electrolyte. Since the main scientific challenge is to improve the interfaces of solid electrolytes and solid-state batteries. Redox activity and decomposition of solid electrolytes are key aspects to take into account. The provided mechanistic insights provide guidelines for interface design of solid electrolytes.