High energy density aqueous rechargeable sodium-ion/sulfur batteries in ‘water in salt” electrolyte

Abstract

The discovery of “water in salt” electrolyte (WiSE) has resolved stability window issues of aqueous batteries. However, another aspect of forging ahead is the designing of stable high-capacity electrode materials. Herein, we have manifested a Na-ion/S battery using S@MNC-600 anode in WiSE to achieve a high-capacity of 709.13 mA h g−1 (w.r.t sulfur) with excellent cycling stability even up to 300 cycles at 0.5 C with 98.2 % of coulombic efficiency. Like organic electrolyte, polysulfide dissolution is a primary obstacle in aqueous electrolyte due to the strong polarity and high activity of water. In this study, various electrochemical, spectroscopic and visualization studies provide an evidence that polysulfide dissolution is sensitive towardoperating time, C-rates, and depth of discharges, which can be tuned by increasing salt concentration and sluggish kinetics was enhanced by using MNC-600 host. Post analysis demonstrates that high cycling stability in WiSE is due to the formation of stable SEI, consisting of Na2CO3. The full cell assembled with S@MNC-600 anode and Na0.44MnO2 cathode in WiSE delivered 110.6 Wh kg−1 energy density with remarkable stability. Further, a flexible paper-based battery demonstrates a high performance even at various deformations, making it a good contender for future energy storage applications where safety and cost are of high priority.