Microstructured electrodes for electrochemical energy storage
Lithium-ion batteries and electric double-layer capacitors are two types of electrochemical energy storage devices that are characterized by high energy density and high power density, respectively. While these technologies have been successfully applied in applications such as personal electronics and electric vehicles, the potential for microscale energy storage devices remains unrealized. In this dissertation novel materials and processing methods are introduced for the fabrication of microscale lithium-ion batteries and electric double-layer capacitors. In the area of electric double-layer capacitors, carbon electrodes are fabricated by electrophoretic deposition and self-assembly and paired with a novel solid-state ionogel electrolyte. We successfully fabricate an on-chip electric double-layer capacitor that is just 0.14 mm2 in electrode area, which is about 40 times smaller than any device so far reported in the literature. Microscale lithium-ion battery electrodes are prepared by micro-molding techniques. The composition of the anode and cathode are tuned to maximize mechanical durability, electronic and ionic conductivity. SU-8 photoresist is presented as a novel electrolyte material for conformally patterning 3D anode arrays. Both 2D and 3D lithium-ion batteries using SU-8 are presented. Initial results suggest that a working 3D microbattery based on SU-8 electrolyte is feasible. Finally, more fundamental research is presented on the sol-gel encapsulation of lithium-polysulfide liquid catholytes. By carefully tuning the non-hydrolytic sol-gel reaction, water-reactive lithium-polysulfides are successfully encapsulated to form a polysulfide gel that retains its lithium storage activity. This polysulfide gel is used to fabricate a fully solid-state lithium-sulfur battery.