Ammonium enables reversible aqueous Zn battery chemistries by tailoring the interphase

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 CO2. 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.