Interfaces and Interphases of All Solid State Battery

Abstract

All-solid-state batteries (ASSBs) have attracted enormous attention as one of the future critical technologies for safe and high energy batteries. With the emergence of several highly conductive solid electrolytes (SEs) in recent years, the bottleneck is no longer Li ion diffusion within the SEs. Rather, most ASSBs still suffer from low Coulombic efficiency, poor power performance, and short cycling life, due to the high resistance from the interfaces in ASSBs. Due to the varied chemical/physical/mechanical properties of different solid components in ASSBs as well as the nature of solid-solid contact, many kinds of interfaces are present in ASSBs: these involve loose physical contact, grain boundaries, chemical and electrochemical reactions, to name a few. All of these contribute to increasing resistance at the interface. Here, we will present the distinctive features of the typical interfaces and interphases in ASSBs and summarize the recent work on identifying, probing, understanding and engineering them. We will highlight the complicated but important nature of interphases, namely the composition, distribution, electronic, and ionic properties of the CEI on the cathode side and SEI on the anode; understanding these properties are the key to achieving a stable interface. In addition, conformal coatings to prevent side reactions and their selection criteria are reviewed. We emphasize the significant role of the mechanical properties of the interface as well as the mechanical property of all components, especially when the soft Li metal anode is used under constant stacking pressure. Finally, we provide full-scale (energy, spatial, and temporal) characterization methods to explore, diagnose and understand the dynamic buried interfaces and interphases.