Interface Morphogenesis with a Deformable Secondary Phase in Solid-State Lithium Batteries

The complex and uncontrolled morphological evolution of lithium metal at the interface with solid-state electrolytes limits performance of solid-state batteries, leading to inhomogeneous reactions and contact loss. Inspired by biological morphogenesis, we introduce a new interfacial self-regulation concept in which a deformable secondary phase dynamically aggregates at the interface in response to local electro-chemo-mechanical stimuli, serving to enhance contact. Stripping of a lithium electrode containing 5-20% redox-inactive sodium domains causes spontaneous sodium accumulation across the interface, with the sodium undergoing local plastic deformation as lithium is removed to attain intimate electrical contact without blocking transport channels. This process, characterized with operando X-ray tomography and electron microscopy, mitigates void formation and substantially improves battery cycling performance at the low stack pressures needed for practical applications. The counterintuitive strategy of adding inactive alkali metal to improve performance demonstrates that interfacial self-regulation is a promising pathway to efficient solid-state batteries.