Aqueous Electrochemical Energy Storage with a Mediator‐Ion Solid Electrolyte

This study presents a battery concept with a “mediator-ion” solid electrolyte for the development of next-generation electrochemical energy storage technologies. The active anode and cathode materials in a single cell can be in the solid, liquid, or gaseous form, which are separated by a sodium-ion solid-electrolyte separator. The uniqueness of this mediator-ion strategy is that the redox reactions at the anode and the cathode are sustained by a shuttling of a mediator sodium ion between the anolyte and the catholyte through the solid-state electrolyte. Use of the solid-electrolyte separator circumvents the chemical-crossover problem between the anode and the cathode, overcomes the dendrite-problem when employing metal-anodes, and offers the possibility of using different liquid electrolytes at the anode and the cathode in a single cell. The battery concept is demonstrated with two low-cost metal anodes (zinc and iron), two liquid cathodes (bromine and potassium ferricyanide), and one gaseous cathode (air/O2) with a sodium-ion solid electrolyte. This novel battery strategy with a mediator-ion solid electrolyte is applicable to a wide range of electrochemical energy storage systems with a variety of cathodes, anodes, and mediator-ion solid electrolytes.