An improved PEG-based molecular crowding electrolyte using Zn(TFSI)2 vs. Zn(OTf)2 for aqueous Zn//V2O5 battery

Abstract

Aqueous zinc batteries (AZBs) are promising candidates for scalable and sustainable energy storage applications because of their cost and safety advantages. However, the inevitable parasitic reactions on the Zn anode, mainly attributed to water-induced side reactions, should be solved. Recently, a molecular crowding electrolyte (MCE) strategy has been proposed to mitigate these parasitic reactions, but at the cost of kinetics and thus rate. In this article, we report an improved Zn//V2O5 battery using a newly developed MCE with a crowding agent and 1 m Zn(TFSI)2 as an advanced salt (MCE–1m Zn(TFSI)2). Our MCE–1m Zn(TFSI)2 shows enhanced ionic conductivity and ion-transport properties, conferring superior rate capability to Zn//V2O5 – releasing 57 vs 0 mAh/g at 10C compared to MCE–1m Zn(OTf)2, state-of-the-art MCE. Furthermore, due to the decrease in the fraction of ‘free water’ molecules, both MCEs produce an enhanced stability window and improved reversibility of Zn plating/stripping with superior Coulombic efficiencies compared to the conventional electrolyte (1 m Zn(TFSI)2). Consequently, Zn//V2O5 in MCE–1m Zn(TFSI)2 simultaneously delivers superior cycle stability (260 (78%) vs. 0 (0%) mAh/g (capacity retention)) after 1000 and 350 cycles, respectively, and low self-discharge vs. 1 m Zn(TFSI)2. These combined results show that this advanced MCE strategy can be used to design safe, high-reversible, fast, and long-cycled AZBs for practical applications.