The Study Of Electrode Material Based On MEMS Microcapacitor

A supercapacitor with advantages of large capacitance, low leakage current, etc. is a newenergy storage element, which has been used in many fields widely. But as more and moremicro-nano-sized microdevices are applied, ordinary supercapacitors, due to their large size,have been unable to provide the energy for these microdevices. So by combining MEMStechnology with supercapacitors, people developed a new micro-nano-sized supercapacitor,which is called MEMS supercapacitor or MEMS microcapacitor. MEMS microcapacitor hasadvantages of large energy storage, long cycle life, volume miniaturization, etc.. It canprovide stable and reliable energy for the microdevices. As an important branch ofsupercapacitor, the performance of MEMS microcapacitor depends on its electrode materialsuch as carbon material, metal oxide and conductive polymer. Wherein the conductivepolymers, polypyrrole (PPy) has become the hotspot due to its good conductivity, simplesynthesis, good environmental stability. However, MEMS microcapacitor with PPy has twoproblems generally: small specific capacitance and poor cycling stability. To solve theseproblems, this paper prepared new functional films as the electrode materials of MEMSmicrocapacitor by compounding PPy and carbon, and tested them.Firstly, this paper made a preliminary study on the energy storage mechanism ofdouble-layer capacitance and pseudocapacitance of MEMS microcapacitor, determined thedesign of MEMS microcapacitor, chose carbon nanotube (CNT) and graphene (GR) in carbonmaterials as experimental materials, and prepared three electrode materials on the surface ofidentical3D Ni-based basic microstructures: PPy, PPy/CNT, PPy/GR. The capacitance ofMEMS microcapacitors with the three different electrode materials were simulated usingANSYS software. Their capacitance values are all above20μF. Next, prepared three MEMSmicrocapacitor samples by MEMS technology and electrochemical deposition technology,measured the quantities of the three electrode materials loading on the surface of3D basic microstructures. The results are0.056mg/cm2,0.039mg/cm2,0.034mg/cm2in turn.Finally, microstructures of the electrode materials were characterized using S4700scanning electron microscopy, electrochemical performances including cyclic voltammetry,electrochemical impedance spectroscopy, galvanostatic charge/discharge and cycling of thethree MEMS microcapacitor samples were tested using μAUTOLABⅢ electrochemicalworkstation. The microstructure characterization results indicate that, the microstructures ofPPy/CNT, PPy/GR composite electrode materials are significantly different from PPy, whichhelp to improve the capacitance of the electrode materials and increase the adhesive forcebetween electrode materials and3D basic microstructures. The results of electrochemicalperformance test are that, specific capacitances of the three MEMS microcapacitors are7.0，8.0and8.3mF/cm2at a discharge current of1mA, their capacitance values are25,28,30μF,matching the ANSYS capacitance simulation result. After cycling performance test, thespecific capacitance retentions are72.9%，85.0%and89.2%for PPy, PPy/CNT and PPy/GR,respectively. All above indicate that, PPy/CNT, PPy/GR composite electrode materials havehigher specific capacitances, capacitances, and better cycling performance than PPy. PPy/GRcomposite electrode material performs best. Therefore, PPy/carbon composite material caneffectively solve the problems of PPy material. Its preparation and application to MEMSmicrocapacitor are of great significance and practical value.