Salting-in electrolyte enables reversible heavy p-block electrochemistry in water

Heavy p-block elements (HPEs; Sn, Pb, Sb, Bi, Se and Te)1,2, with flexible electronic structures and rich multielectron redox chemistry, hold promise for electrochemically driven technologies in functional coatings, electronics, and energy conversion and storage3–15. However, their aqueous electrochemistry remains challenging because direct exposure of HPE cations to water readily triggers parasitic reactions, including hydrolysis, corrosion, precipitation, gas evolution, and passivation16–21. Here we challenge the prevailing assumption in electrolyte design that dissolving HPE cations necessitates hydration, and propose a counterintuitive principle of “dissolved but not hydrated” to unlock aqueous HPE electrochemistry. We implement this concept through a dual-salt salting-in electrolyte strategy, distilled into a two-parameter design principle. The auxiliary cation should be strongly hydrated yet weakly ion-pairing to suppress water activity, while the auxiliary anion should preferentially coordinate HPE cations to expel water from their solvation shells. First-principles descriptor screening, corroborated by spectroscopic analyses, interrogates a curated library of hundreds of cation–anion combinations and identifies Ca2+–Cl– as the uniquely optimal auxiliary-ion pair that most effectively suppresses water activity and drives anion coordination to HPE cations, thereby forming water-shielded chlorocomplexes that stabilize HPE cations in water. This electrolyte design enables reversible plating and stripping across the HPE family (Sn, Pb, Sb, Bi, Se and Te), yielding uniform electrodeposits and rendering HPEs viable multielectron electrodes in aqueous batteries. The proposed HPE-based aqueous batteries enabled by this salting-in electrolyte exhibit stable rechargeability with high capacity retention. By rendering an intrinsically unstable class of elements redox-active in water, this work overcomes long-standing barriers to heavy p-block electrochemistry and establishes a general framework for multielectron aqueous electrochemical systems.