Operando Evolution of a Hybrid Metallic Alloy Interphase for Reversible Aqueous Zinc Batteries

Aqueous Zn‐ion batteries (AZIBs) are widely acknowledged as viable future energy storage solutions, particularly for low‐cost stationary applications. However, the interfacial instability of zinc anodes represents a major challenge to the commercial potential of Zn‐ion systems, promoting an array of side reactions including spontaneous corrosion, hydrogen evolution, and dendrite growth that destabilize cell performance, lower Coulombic efficiency (CE) and ultimately lead to early cell failure. While other commercially relevant battery systems benefit from a spontaneously forming solid electrolyte interphase (SEI), no such layer forms in AZIBs. Herein, we have designed and engineered an operando evolved metallic alloy interphase for AZIBs. This interfacial layer is initially deposited in the form of a thin film of Ag and In, but develops in situ to become an intimate mix of an AgxZny alloy and metallic indium. Importantly, this dual‐heterometallic layer acts to synergistically regulate the migration of zinc ions through the alloy interphase and enables the dense, planar deposition Zn, simultaneously overcoming all major drivers of Zn anode degradation. Symmetric and full cells containing this modified metallic zinc anode exhibit stable electrochemical performance, offering high‐capacity retention. Hence, this scalable approach represents a viable route towards the commercial utilization of this energy storage system.