UC Berkeley

Supercapacitors represent a critical energy storage device technology for applications which require higher power density and/or cycle lifetime than existing battery technologies. Micro-scale supercapacitors, in particular, can enable novel applications in autonomous, wireless microsensors and microelectronics. If these micro-supercapacitors can be fabricated in a planar, on-chip geometry, the energy storage and the devices to be powered can be integrated on a single chip, improving scalability and reducing cost. The primary components of a supercapacitor are the electrodes and electrolyte. The properties of the electrode and electrolyte materials have a significant effect on device performance, and thus, there is significant opportunity for engineering materials to improve the energy density, power density, cycle lifetime, cost, safety, manufacturability, and harsh environment performance of micro-supercapacitors. Furthermore, these properties could be intelligently tailored for specific applications.

This manuscript provides some background on the principles underlying supercapacitor materials selection and testing, and presents several approaches to engineer these materials. Electrode materials which are investigated include photoresist derived porous carbon, vertically aligned carbon nanotubes, and 3D templated graphene. Electrolytes which are explored include various aqueous salts (and their impact on device cycle lifetime performance) as well as ionic liquid based gels (or ionogels). Furthermore, efforts to fabricate flexible micro-supercapacitors are discussed.

For on-chip energy storage involving high temperature operation, yttria-stabilized zirconia is investigated as the electrolyte. Silicon carbide (SiC)-based material for the electrode and its metal contact stability are also investigated, as the stability of these contacts during operation is an important consideration for the performance of high temperature micro-supercapacitors. Epitaxial graphene growth on SiC thin films is presented as one approach to stabilizing metal-to-SiC contacts.