Enhancing Cycle Life of Rechargeable Zinc Hybrid Batteries in a Low-Cost, Nonfluorinated Dual-Cation Electrolyte

Rechargeable zinc batteries (RZBs) are highly attractive as energy storage solutions due to their low cost and sustainability. Nevertheless, the use of fluorine-free zinc electrolyte systems to create affordable, ecofriendly, and safe RZBs has been largely overlooked in the battery community. Previously, we showcased the utilization of a fluorine-free, nonaqueous electrolyte comprising zinc dicyanamide (Zn(dca)₂) in dimethyl sulfoxide (DMSO) to enable the electrochemical cycling of zinc. Herein we present a dual-cation-based electrolyte, [1.0 M Na(dca) +1.0 M Zn(dca)₂]/DMSO, in pursuit of a rechargeable zinc <i>hybrid</i> battery. Fourier-transform infrared spectroscopy and molecular dynamics simulation studies indicate that the presence of Na(dca) diminishes ion-pairing in Zn(dca)₂ through [dca]^- anion bridging between Zn²⁺ and Na⁺ ions, thereby enhancing Zn²⁺ ion transport in the electrolyte. Thus, the electrolyte exhibits high ionic conductivity and transference numbers (<i>t</i>_Zn²⁺) of 7.9 mS cm^-1 and 0.83, respectively, at 50 °C, making it particularly suitable for high-temperature battery applications. Furthermore, we demonstrate, for the first time, the cycling of a full cell with a zinc anode and triphylite sodium iron phosphate cathode (NFP) in an organic electrolyte, showcasing stable performance over 100 cycles at 0.1C rate. These encouraging findings pave the way for affordable battery technologies using, fluorine-free electrolyte.