High Power Na3V2(PO4)(3)@C/AC Bi-material Cathodes for Hybrid Battery-Capacitor Energy Storage Devices

We have reported the synthesis and electrochemical characteristics of carbon-coated sodium vanadium phosphate/activated carbon (NVP@C/AC) bi-material electrodes. We have reported that bi-material type NVP@C/AC cathodes offer superior rate performance as compared to either NVP@C or AC electrodes. Through a detailed impedance spectroscopy analyses, we demonstrated that the synergic effect observed in the bi-material electrodes correlates well with the lowering of their charge transfer resistances (R-CT) and the increase of Li(+)diffusion coefficient (DLi+) with the increase of activated carbon content from 0 to 0.60 weight fraction. Through a detailed cyclic voltammogram analyses we have delineated the faradaic and capacitive contribution towards the overall capacities of the bi-material electrodes at various rate conditions. For both these bi-materials, irrespective of the AC content and rate, capacitive contribution dominates the overall capacity. NVP@C/AC40 yields discharge capacities of 67 and 40 mAh g(-1)with capacity retention of more than 93% and 67% after 500 cycles measured at 50 and 1000 mA g(-1), respectively. These bi-materials are demonstrated to be excellent material candidates for high power density lithium titanium oxide (LTO)//NVP@C/AC hybrid battery-capacitor (bat-cap) energy storage devices.