High-energy-density on-chip Li-ion capacitors

This paper presents an on-chip Li-ion capacitor featured by higher energy density than that of supercapacitor under the same level of charge/discharge rate by building the hybrid cell containing a supercapacitor electrode and a Li-ion battery electrode, to take advantage of power of supercapacitor and capacity of Li-ion battery. Activated carbon (AC), a supercapacitor material, is used as the positive electrode, while graphite, an anode material of Li-ion battery, is used as negative electrode, and the electrolyte used in Li-ion battery serves as electrolyte in the device. The on-chip prototype with 100-μm-thick interdigital electrodes is fabricated and shows a capacity of 175μAh/cm² with an energy density of about 1550mJ/cm² under a charge/discharge current of 0.5mA/cm² and a cell voltage of 3.4V, which is higher than that of a symmetric AC-based supercapacitor with the same dimensions.