Addressing Fundamental Problems in Capacitive Energy Storage

The rapidly growing demand for capacitive energy storage systems for applications such as self-powered micro and nanosystems, portable electronic devices, and large-scale stationary applications has inspired much research in an effort to develop devices that can provide high power and energy densities. The important factors affecting the performance of electrochemical capacitors (ECs) are the intrinsic properties of electrode materials and electrolytes, as well as the properties of their interfaces. There is no perfect electrode material and no ideal electrolyte that can meet the performance goal for every application. Therefore, a rational design of these materials is crucial for rapid advancement and widespread implementation of ECs. A large variety of nanostructured carbon materials are available nowadays that can be used as electrode materials. 1 Zero- and one-dimensional nanoparticles, such as onion-like carbon and nanotubes, can provide a high power due to fast ion sorption/desorption on their outer surfaces. 2 Two-dimensional graphene has been receiving an increasing attention due to its higher charge-discharge rates compared to porous carbons and high volumetric energy density. Three-dimensional porous activated, carbide-derived and templated carbon networks, having a high surface area and porosity in the subnanometer or a few-nanometers range, can provide high energy density if the pore size is matched with the electrolyte ion size. 3 While aqueous electrolytes, such as sodium sulfate, are the safest and least expensive, they have a limited voltage window. Organic electrolytes are the most commonly used ones in commercial devices. Non-flammable ionic liquids are attracting an increasing attention due to their low vapor pressure leading to a safe operation in the range from -50°C to at least 100°C and a larger voltage window resulting in a higher energy density compared to other electrolytes. 4 Further advances in development of materials and understanding charged solid-electrolyte interfaces are expected to lead to a wider use of capacitive energy storage at the scales ranging from microelectronics to automobiles and electrical grid. 5,6 This talk will summarize some of the research efforts at Fluid Interface Reactions, Structure and Transport (FIRST) center towards understanding the effects of the structure of the electrode materials and properties of the electrode/electrolyte interfaces on the capacitive energy storage in ECs. References (1) Simon, P.; Gogotsi, Y. Capacitive Energy Storage in Nanostructured Carbon Electrolyte Systems. Acc. Chem. Res. 2012 , 46 , 1094–1103. (2) McDonough, J.; Gogotsi, Y. Carbon Onions: Synthesis and Electrochemical Applications. Electrochem. Soc. Interface 2013 , 12 , 61–66. (3) Presser, V.; Heon, M.; Gogotsi, Y. Carbide-Derived Carbons - From Porous Networks to Nanotubes and Graphene. Adv. Funct. Mater. 2011 , 21 , 810–833. (4) Van Aken, K. L.; Beidaghi, M.; Gogotsi, Y. Formulation of Ionic-Liquid Electrolyte to Expand the Voltage Window of Supercapacitors. Angew. Chemie 2015 , 127 , 4888–4891. (5) Presser, V.; Dennison, C. R.; Campos, J.; Knehr, K. W.; Kumbur, E. C.; Gogotsi, Y. The Electrochemical Flow Capacitor: A New Concept for Rapid Energy Storage and Recovery. Adv. Energy Mater. 2012 , 2 , 895–902. (6) Beidaghi, M.; Gogotsi, Y. Capacitive Energy Storage in Micro-Scale Devices: Recent Advances in Design and Fabrication of Micro-Supercapacitors. Energy Environ. Sci. 2014 , 7 , 867.