Study On Graphene-based Microsupercapacitors

With advantages like high-power discharge and lower pollution, and so on, supercapacitor which is an emerging energy storage device is widely applied to everywhere. With the electronic product is became gradually microminiaturized and portable, the size of power source matched the product is need to be lower, and the power density must be increased for not lower the electric capacity, so that the research about the microminiaturization of supercapacitor has got more and more attentions for meeting the need of extremely high power density and small size at the same time. For supercapacitor, the structure and material of microsupercapacitor electrode is the key part for the capacitor properties. And the carbon material is one of the normal electrode materials of microsupercapacitor for its stable chemical performance and low cost. Among the carbon materials, that graphene is applied to microsupercapacitor with many advantages to other carbon materials, like outstanding electric and force properties and extremely huge specific surface area, which can make the size of device lower. Generally, graphene is smeared to the surface of current collector, but this would generate big contact resistance between graphene and current collector. So, in this thesis, we use PECVD to grow graphene layer onto nickel current collector thin film, that the contact resistance would be solved. Besides, the fabrication of graphene by PECVD is fast and lower deposition temperature, which is helpful for the application at IC and fulfilling the need of commercialized production.Among many outstanding properties of microsupercapacitor, the power density is mostly key part. The formula of specific energy density is E=(1/2)CV2,so that specific capacitance C and voltage window V is the key factor for E. And, when graphene works as electrode, the capacitor’s work principle is double electrode layer mechanism whose specific capacitance formula is C=εSU2/2d. According the formula, we use Ar plasma bombard the nickel thin film to increase the effective specific surface area of electrode S, which grow on the nickel thin film, to improve the specific capacitance C. Besides, the manganese dioxide is the representative electrode material for faradaic pseudocapacitance with huge voltage window and capacitance, but less stable. So, in the thesis, we recombine manganese dioxide and graphene as microsupercapacitor’s electrode material to increase the voltage window V and stabilize the properties of manganese dioxide. It turns out two kind electrode materials show excellent electrochemistry properties. Subsequently, we make the electrode patterned into interdigital electrode and packing them into supercapacitor device.