Synergy of organoiodide additives and co-solvent enabling high-performance wide-temperature Zn metal batteries

Abstract

Although Zn metal batteries (ZMBs) are promising next-generation energy storage systems due to their high safety and low cost, serious parasitic reactions and a narrow operating-temperature range derived from aqueous electrolytes hinder their development. Herein, an optimized tetrahydrofuran (THF)/H₂O (volume ratio: 50 : 50) hybrid electrolyte with a triethyl sulfonium iodide (TSI) additive (T50 + TSI) is developed for ZMBs. Incorporation of THF reconfigures the hydrogen-bonding network between water molecules, reducing the freezing point of T50 + TSI. Additionally, the synergy of organoiodide and THF optimizes the solvated Zn²⁺ structure and facilitates the desolvation kinetics, realizing uniform Zn deposition, lowering Zn plating/stripping overpotentials and inhibiting H₂ evolution/Zn corrosion. Consequently, T50 + TSI-based Zn//Zn cells achieve a low polarization voltage of 92 mV at 2 mA cm⁻² over 7100 hours at room temperature, normally operate even at −50 °C, and stably cycle over 6400 hours at −30 °C. As a result, the Zn//NVO (NaV₃O₈·1.5H₂O) batteries with T50 + TSI display stable voltage curves for 1500 cycles at 1 A g⁻¹. With an ultra-high loading of 15.3 mg cm⁻², the NVO cathode in T50 + TSI still exhibits a large capacity (264.0 mAh g⁻¹) at 0.1 A g⁻¹. Surprisingly, the T50 + TSI-based Zn//NVO batteries present long-term stability over 1480 cycles even at an extreme temperature of −30 °C.