A non-flammable hydrous organic electrolyte for sustainable zinc batteries

Aqueous zinc (Zn) batteries have long been considered a potentially more sustainable alternative to lithium-ion batteries because of their better environmental compatibility, enhanced safety and cost advantage. However, in the presence of an aqueous electrolyte, the Zn anode is poised to undergo dendrite failure, corrosion and hydrogen evolution, all of which resonate with each other leading to fast performance degradation. Here, in a break from the current aqueous battery path, we report a low-cost hydrous organic electrolyte involving a hydrated Zn(BF4)2 salt and an ethylene glycol solvent, which not only promotes the in situ formation of a favourable ZnF2 passivation layer to protect Zn from dendrite growth and side reactions but also embraces excellent non-flammability. Remarkably, the present Zn anode sustains a long-term cycling over 4,000 h at a current density of 0.5 mA cm−2 with a high Coulombic efficiency of 99.4% and shows an areal capacity as high as 5 mAh cm−2. Equally intriguingly, the electrolyte can run across a wide temperature range from −30 °C to 40 °C without seriously compromising performance. The Zn//V2O5 full cells with our electrolyte also perform much better in terms of capacity retention than a device with an aqueous ZnSO4 electrolyte. Our findings suggest a promising direction for developing electrolyte solutions for practical Zn batteries which combine safety, performance and sustainability. Aqueous Zn batteries offer safety, but the Zn anodes are vulnerable to dendrite failure and side reaction. Here the authors show a low-cost electrolyte that involves hydrate salt and organic solvent but proves inflammable. The Zn battery cell delivers excellent performance even at a low temperature of −30 °C.