Ligand-Substitution Chemistry Enabling Wide-Voltage Aqueous Hybrid Electrolyte for Ultrafast-Charging Batteries

Abstract

The further development of sodium-zinc hybrid batteries (SZBs) is seriously impeded by the narrow electrochemical stability window (ESW) of aqueous electrolytes. Exploring appropriate electrolytes with both wide ESW and high ionic conductivity is of great importance to achieve high-performance SZBs yet remain challenging. Here, a rationally designed Na⁺/Zn²⁺ hybrid electrolyte is developed via a ligand-substitution strategy, which effectively extends the ESW up to 2.9 V and combines with high ionic conductivity of 19.6 mS cm⁻¹. The ligand exchange process reconfigures the cation solvation structure and optimizes the carrier mobility environment. Furthermore, Na⁺/Zn²⁺ hybrid cells are assembled by pairing Zn anode with two different kinds of sodium superionic conductor (NASICON) type cathodes, achieving a promising rate performance and long cycle life (3 A g⁻¹ over 1000 cycles). Meanwhile, the high electrochemical reactivity of water molecules promotes the formation of the high-quality NaF/ZnF<inf>2</inf>-rich cathode electrolyte interphases, inhibiting the uncontrolled decomposition of the electrolyte on the cathode interface. This work provides guidance for designing aqueous hybrid electrolytes with wide ESW and high carrier mobility.