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 hybrid 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 (tZn2+) 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.

Solvent control of water O-H bonds for highly reversible zinc ion batteries

Aqueous Zn-ion batteries have attracted increasing research interest; however, the development of these batteries has been hindered by several challenges, including dendrite growth, Zn corrosion, cathode material degradation, limited temperature adaptability and electrochemical stability window, which are associated with water activity and the solvation structure of electrolytes. Here we report that water activity is suppressed by increasing the electron density of the water protons through interactions with highly polar dimethylacetamide and trimethyl phosphate molecules. Meanwhile, the Zn corrosion in the hybrid electrolyte is mitigated, and the electrochemical stability window and the operating temperature of the electrolyte are extended. The dimethylacetamide alters the surface energy of Zn, guiding the (002) plane dominated deposition of Zn. Molecular dynamics simulation evidences Zn²⁺ ions are solvated with fewer water molecules, resulting in lower lattice strain in the NaV₃O₈·1.5H₂O cathode during the insertion of hydrated Zn²⁺ ions, boosting the lifespan of Zn|| NaV₃O₈·1.5H₂O cell to 3000 cycles.