LAUSR

Abstract This paper aims to demonstrate a novel electrochemical energy storage device, a hybrid Na-ion capacitor with organic electrolyte. Sodium manganese oxide having formula Na 0.4 MnO 2 has been chosen and synthesized as the most suitable battery-type positive electrode, while activated carbon (AC) has been utilized as the capacitor-type negative electrode. Due to the application of propylene carbonate based organic electrolyte, the maximum safe operating voltage of the device has been established as high as 2.7 V, giving rise to a specific capacitance of 17.4 F g −1 , significantly higher as compared to the analogous symmetrical EDLC measured in our laboratory based on AC electrodes in the same electrolyte.