Mass Transport in "Water-in-Polymer Salt" Electrolytes

"Water-in-polymer salt" electrolytes (WiPSEs)basedon potassium polyacrylate (PAAK) belong to a new family of "water-in-salt"electrolytes that is envisioned as a potential solution for large-scalesupercapacitors to balance the electric grid at short time scales.The WiPSEs display a broad electrochemical stability window up to3 V, yet they are nonflammable and provide high ionic conductivity(100 mS/cm) as required in high-power devices. However, the transportof matter in PAAK-based WiPSEs has not been studied. In this work,we have extensively characterized PAAK by spectroscopic methods suchas Raman spectroscopy and NMR diffusometry to determine the stateof water and elucidate the mechanism of ionic transport as well asits interplay with water and polymer chain dynamics, which revealsthat a significant proportion of the transport in WiPSEs is attributedto hydrated cations. The results are further supported by moleculardynamics (MD) simulations. Finally, the potential of WiPSEs basedon PAAK is demonstrated in an activated carbon-based supercapacitoroperating up to 2 V with reasonable self-discharge. This proof ofconcept shows promise for low-cost and large-scale supercapacitors.