Carbon nanotubes based on-chip supercapacitors with improved areal energy density

Supercapacitors or electrochemical capacitors, as a kind of energy storage devices, have been intensively studied for decades as its combination of high energy density and high power density with long cycle life. The integration of on-chip supercapacitors with Si-compatible processes will further expand their application in electronic systems. Among them, porous carbon materials are quite promising, because the porous carbon owns high surface area with optimised porosity, high electrical conductivity and good electrochemical stability. It was previously reported by our group that high surface area Si-grass withcarbon nanotubes (CNTs) deposition via atmospheric pressure chemical vapor deposition (APCVD) could exhibit high areal energy density for supercapacitor application. In this paper, further improvement in areal energy density is achieved by solution-based catalyst loading into the CNTs network and subsequent CNTs growth via APCVD method in the tube furnace. The mass loading of carbon active materials are enhanced as compact integration of two dense CNT layers to achieve the high areal capacitance 159 mF/cm2 at 5 mV/s with 62 mF/cm2 increasing from one CNT layer, and the main electricity storage mechanism is still electrochemical double layer (ECDL) with the rectangle structure showed in the cyclic voltammetry (CV) curves, which shows these supercapacitors remain the high power properties. These findings demonstrated that CNT based supercapacitors are still competitive in areal energy density with improved mass loading.