A divalent quaternary alkyl ammonium salt as the electrolyte for high-energy electric double-layer capacitors

▸ Divalent salt based on tetramethyl piperazine as the electrolyte. ▸ Divalent cations enlarge capacities of electric double-layer capacitors (EDLCs). ▸ Heavy solvation of divalent cations has negative effects. ▸ The electrolyte solutions have low ionic conductivity. ▸ EDLCs using the divalent salt show poor cycle performance.