Interactions are important: Linking multi-physics mechanisms to the performance and degradation of solid-state batteries

The behaviour of solid-state batteries to many application-relevant operating conditions is intrinsically multiphysical and multiscale, involving the electrochemical performance and chemical stability coupled with the thermal and mechanical properties of multiple components. This review presents a holistic approach to discussing the multiscale physical-electro-chemical interactions and degradation mechanisms in solid-state batteries. While the propagation of lithium filaments depends strongly on the critical current densities, we show that effective prevention of excessive Li plating and stripping requires a combined understanding of solid-state electrochemistry, microstructure, mechanics, operating conditions, and their interactions. A review of how multiphysical interactions affect the optimum design of thin-film, three-dimensional and composite solid-state cell architectures is also included. Although the use of lithium metal as negative electrodes could improve the energy densities of solid-state batteries, we show that its high homologous temperature could cause cell failure during manufacturing. By comparing published model predictions with experimental observations, we present a critical analysis of the strengths and limitations of state-of-the-art models and characterisation techniques in solid-state battery research. This comprehensive mechanistic analysis provides an insight into the interplay among the multiple complex multiphysical mechanisms, shedding light on the process of cell design for next-generation solid-state batteries.