Aqueous Supercapacitors with Low Cost and High Voltage Enabled by Co-Solute Crowding Effect of Electrolyte

Developing high-voltage and environmentally friendly aqueous electrolytes have become a significant trend in supercapacitors (SCs). However, achieving this goal usually requires the use of "water-in-salt" (WIS) electrolytes, inevitably increasing manufacturing costs and sometimes posing problems such as environmental pollution. Here, we developed a water/organic solvent hybrid electrolyte (8 m NaClO4-20% H2O-30% ACN-50% PEG-200) with low cost and high-voltage capacity using the water-miscible polymer polyethylene glycol (PEG) as a crowding agent to suppress water activity, and acetonitrile (ACN) as a co-solvent to improve the ion transport properties. The synergistic advantages of the two co-solvents allow SCs using this electrolyte to have a high operative voltage window of up to 2.6 V, currently the highest operating voltage for aqueous carbon-based SCs, excellent capacity retention (over 11000 cycles) and high energy densities (31.2 Wh kg(-1)). This work provides a promising method for developing green and inexpensive high-voltage window aqueous electrolytes.