The inherent advantages of MEMS (micro-electromechanical system) technology, including small size and cost-effective fabrication, make it ideal for numerous applications in a wide range of industries ranging from defense, automotive, medical, to consumer industries. For applications that require self-powered MEMS electronics, an integrated energy storage device is required. Due to their small size, excellent cycle life and high-power density, miniature supercapacitors are an excellent choice for such an integrated energy storage device. The development of electrode materials and electrode fabrication processes for supercapacitors are thus critical for the practical applications of MEMS technology in electronics.

In this presentation, Faraday Technology Inc. and Duke University will discuss a novel 3D graphenated carbon nanotube (g-CNT) network with pseudocapacitive coatings as the electrode materials for fabricating high energy density MEMS supercapacitors. The g-CNT has a high surface area three-dimensional framework of the CNTs coupled with the high edge density of graphene (Figure 1 A), which represents a potential maximum in both charge density and surface area, and thus provide the enhanced capacitance.

An innovative electrophoretic deposition (EPD) manufacturing process, based on the use of pulsed electric fields, has been developed for controlled, reproducible, and scalable deposition of g-CNTs on interdigitated electrodes (Figure 1 B). In addition, pseudocapacitive coatings (such as MnO₂) have been electrodeposited on the g-CNT coated electrode to further increasing supercapacitor energy density. Figure 1 C shows no redox peaks, which is important for using this structure as a supercapacitor application. The square shape of the cyclic voltammogram shows that ions experience free flow through the 3-D g-CNT structure. The Charge/Discharge curves (Figure 1 D) indicate the areal energy density of g-CNT/MnO₂ coated electrodes (either 50 or 100 cyclic voltametric deposition cycles) are 45 and 93 times higher than g-CNT coated electrodes, respectively.

In summary, a scalable manufacturing process for fabricating g-CNT network with pseudocapacitive coatings as electrodes has been demonstrated and shown great potential in producing high energy density MEMS supercapacitors for energy harvesting applications.

Acknowledgements: The financial support of DOD DMEA STTR program through grant No. HQ0727-21-P-0029 is acknowledged and National Institutes of Health under award number 1R21EY031271 is acknowledged. The information, data, or work presented herein was funded in part by National Aeronautics and Space Administration under Grant No. 80NSSC19K1027, the views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.