Ammonium enables reversible aqueous Zn battery chemistries by tailoring the interphase

Abstract

<h2>Summary</h2> Aqueous rechargeable Zn metal batteries (RZMBs) are promising candidates for coupling with intermittent renewable energy sources to realize a carbon-neutral energy transition. However, irreversible issues of Zn metal anodes and a poor understanding of the interphasial chemistry severely limit the viability of RZMBs. Here, we demonstrate that the addition of an asymmetric alkylammonium cation, trimethylethyl ammonium-bis(trifluoromethylsulfonyl)imide (Me₃EtN-TFSI), as a supporting salt into a traditional aqueous electrolyte results in improved Zn anode reversibility. Performance improvements are attributed to the formation of interphasial chemistries including ZnF₂, ZnCO₃, and fluoro-polymeric species, especially when combined with CO_2. By tailoring the Zn interphase, this electrolyte exhibited excellent stability in Na₂V₆O₁₆ · 1.63H₂O (HNVO)/Zn full cells, with a high specific capacity sustained (>100 mAh g⁻¹) over 1,000 cycles at 300 mA g⁻¹. A combination of experiments and modeling showed the importance of tuning interphases to further improve Zn reversibility and RZMBs.