High density capacitors: bridging the performance gap between conventional capacitors and electric double layer capacitors

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The low capacitance density of electrolytic capacitors is becoming a limiting factor on circuit board profile and circuit performance. The capacitance density of the current generation of electric double layer supercapacitors is several orders of magnitude higher, but they are limited to a charge-discharge rate of about 1 second, or a characteristic frequency of 1 hertz, and thus not suitable for those circuit applications requiring capacitors that must run in the hundreds of hertz to kilohertz range. In other words, there exists a significant performance gap, in terms of capacitance/frequency, between currently available supercapacitor and traditional circuit capacitor technologies. The proposed research addresses this performance gap through studies aimed at developing ultrafast supercapacitors with novel nanostructured electrodes and a high capacitance density that run in the hundreds of hertz to kilohertz range and are suitable for circuit applications. This research, if successful, will bring about disruptive change in capacitor design and ground-breaking applications in crucial circuit functions like decoupling, timing, filtering, and power supply and conditioning. The proposed nanostructured electrodes can additionally be utilized in battery and electrocatalyst applications. Education and outreach activities are integrated in this project for the training of undergraduate and graduate students. In addition to supported Research Experiences for Undergraduates program students, several undergraduate students will be involved in the project through their Project Lab course work, to inspire their interest in advanced studies. Attention will be paid to recruiting female and minority students, particularly first-generation college students, to secure diversity and broad participation. An outreach component on nanomaterials for energy technologies will be developed to educate students who will serve as ambassadors in subsequent outreach efforts coordinated by the T-STEM Center of Texas Tech University.The proposed research will characterize and demonstrate high-density capacitors running in the hundreds of hertz to kilohertz frequency range. This represents a disruptive advance in capacitor technology for compact and efficient ultrafast electric double layer capacitors as discrete components, for line-frequency alternating current filtering, and on-chip integrated high-density micro-capacitor needs. The proposed electrode is based on perpendicularly edge-oriented multilayer graphene grown on a cellulose nanofiber scaffold. This novel material has a shallow, straight forward, wide-open pore structure that ensures high frequency response while its large specific surface area and especially high density of fully exposed graphene edges offer the possibility of large capacitance. Edge-oriented multilayer graphene growth and cellulose fiber carbonization into carbon nanofiber are implemented in a process that requires only a few minutes' time. The ultrafast electric double layer capacitors based on this new material could allow at least two orders of volume reduction compared to low-voltage aluminum electrolytic capacitors for filtering. The resulting freestanding electrodes can also be transferred to a substrate or an integrated circuit chip for in-package or on-chip capacitor integration. This project comprises comprehensive nanomaterial and charge storage studies, device modeling, fabrication and performance testing. If successful, it will ultimately bridge the frequency/capacitance gap between existing circuit capacitors and supercapacitors. The outcomes of this study will in addition enhance understanding in the areas of related materials and devices.