Porous Mixed Ionic Electronic Conductor Interlayers for Solid-State Batteries

Rechargeable solid-state batteries (SSBs) have emerged as the next-generation energy storage device based on lowered fire hazard and the potential of realizing advanced battery chemistries, such as alkali metal anodes. However, ceramic solid electrolytes (SEs) generally have limited capability in relieving mechanical stress and are not chemically stable against body-centered cubic alkali metals or their alloys with minor solute elements (β-phase). Swelling-then-retreating of β-phase often causes instabilities such as SE fracture and corrosion as well as the loss of electronic/ionic contact, which leads to high charge-transfer resistance, short-circuiting, etc. These challenges have called for the cooperation from other classes of materials and novel nanocomposite architectures in relieving stress and preserving essential contacts while minimizing detrimental disruptions. In this review, we summarize recent progress in addressing these issues by incorporating other classes of materials such as mixed ion-electron conductor (MIEC) porous interlayers and ion-electron insulator (IEI) binders, in addition to SE and metals (e.g., β-phase and current collectors) that are the traditional SSB components. In particular, we focus on providing theoretical interpretations on how open nanoporous MIEC interlayers manipulate β-phase deposition and stripping behavior and thereby suppress such instabilities, referring to the fundamental thermodynamics and kinetics governing the nucleation and growth of the β-phase. The review concludes by describing avenues for the future design of porous MIEC interlayers for SSBs.