Ultra-dilute electrolytes for simultaneous cycling and calendar aging stability in metal anodes

Abstract While numerous improvements in cycling stability have been demonstrated for next-generation battery chemistries with metallic anodes, their calendar aging (e.g., capacity loss during idle periods of rest) performance painfully lags behind and remains a critical bottleneck hindering their practical deployment. In contrast to their commercial counterparts, metallic anodes exhibit colossal capacity loss during calendar aging, with Zn losing its entire capacity within just a week. Despite several recent studies exploring the underlying reasons for calendar aging, few solutions have been proposed to mitigate this key issue. Here, we design an ultralow concentration electrolyte (0.1 M ZnSO₄) that can reduce calendar aging losses in Zn metal chemistries by more than an order of magnitude (<1.5% capacity fade after 24 hours of aging) while still maintaining excellent cycling stability (>3,300 cycles) with an average Coulombic efficiency (CE) of 99.8%. We find that solvated water molecules (rather than unsolvated water molecules) drive Zn corrosion, motivating our effort to minimize these reactive solvated water molecules through a holistic approach centered around concentration reduction, aided by isotopic solvent substitution and targeted additives. This strategy is broadly applicable to other battery chemistries and provides an approach that can uniquely address both calendar aging and cycling stability, both of which are necessary for practical applications.