Electrical double-layer capacitors bring numerous strengths to the energy storage landscape but have limited use due to their high unit energy cost and low specific energy. Water-in-salt electrolytes have been recently purported as an option to provide more affordable energy storage, but high viscosity and limited conductivity hinder their direct use in high-power devices such as capacitors. By using solid-state NMR and electrolyte-tuned porosity carbons, we demonstrate, at the molecular level, a drastic impact of relative pore/ion size on proper electrolyte propagation deep down the pore volume. The NMR results also provide a rationale for the radical changes in low-and high-rate electrochemical response observed using carbons with differently nanosized pores and a water-in-salt electrolyte.

We thank the financial support from MCIN/AEI/10.13039/501100011033/ and FEDER “Una manera de hacer Europa” through the project RTI2018–096199-B-I00.

Peer reviewed