Tailoring potential window of aqueous electrolyte via steric molecular engineering for high voltage supercapacitors

Abstract

Manufacturing economical and environmentally friendly aqueous electrolytes having a large operating potential is crucial to accomplish safe, high-energy and long-life supercapacitors. An emerging approach of superconcentrated Water-in-Salt (WIS) electrolyte significantly improves the performance through a stable, improved thermodynamic potential of water by reducing the free water molecules in the electrolyte. However, this approach raises concern about the cost and toxicity. By the way, we have achieved a similar performance by creating a hydrogen bonding network through the incorporation of additive with electrolyte, which suppresses the water electrolysis even at low salt concentration. This work demonstrates a hydrogen bond constructed electrolyte (Steric effect) using the additive to reduce water activity. In that way, it delivered an extensive operational voltage (>2.3 V) to the electrolyte at a low salt concentration (5M NaClO4). Further, the carbon-based symmetric supercapacitor cell with this electrolyte delivered a capacitance of 112 mF with good capacitance retention (71.4%) after 50,000 cycles. Further, the cell showed its excellency via a low self-discharge rate and leakage current. The performance of the coin cell-type supercapacitor is evaluated as per IEC standards and as well as the traditional method and compared with superconcentrated Water-in-Salt NaClO4. This work opens up new direction for designing high-voltage water-based electrolyte for inexpensive and very stable energy storage devices.