4Â V Aqueous hybrid supercapacitors based on dual electrolyte technologies

Aqueous hybrid supercapacitors have the advantage of utilizing high pseudo-capacitive electrodes, but suffer from low cell voltage due to the narrow voltage window of water decomposition. This disadvantage can be overcome by combining aqueous electrochemical capacitor technologies with a water-stable anode that is protected with a solid electrolyte. In this short review, we summarize recent advances in hybrid supercapacitors with a rated voltage of ∼4 V using an aqueous catholyte and pseudo-capacitive cathode combined with a protected Li or Li-pre-doped carbon anode. Record high specific energy of >700 Wh (kg-cathode)−1 were obtained with a pseudo-capacitive positive electrode and a protected Li-pre-doped carbon anode. The newly developed hybrid supercapacitor outperforms present Li-ion capacitor technology and even has the potential to compete with rechargeable batteries.