David Ashby1 Christopher Choi1 Bruce Dunn1

1, University of California, Los Angeles, Los Angeles, California, United States

Although photo-patterning has been used extensively in the semiconductor industry for the fabrication of low cost structures, it has hardly been utilized in the battery community. The photo-patterning of solid electrolytes offers several potential advantages as the ability to achieve spatial control with micron and sub-micron resolution enables one to form electrolytes in non-planar geometries as well as to develop new battery fabrication routes, especially ones that offer better integration with microelectronics and on-chip batteries. The present paper describes our work in photo-patterning two different lithium-ion conducting electrolytes, silica-based ionogels and an epoxy-based gel electrolyte.

Ionogels are pseudo-solid-state electrolytes in which an ionic liquid electrolyte confined in a mesoporous inorganic matrix leads to a material that possesses the electrochemical properties of the ionic liquid despite being a macroscopic solid. In the work reported here, we used UV cross-linking to induce hydrolysis and condensation of a sol-gel silica network. The resulting materials retained the ion transport and electrochemical stability of the confined ionic liquid electrolyte and demonstrated photolithographic patterning of simple structures. The photoresist used in this study, SU-8, was modified with LiClO4 to form a gel electrolyte. The presence of the lithium salt reduces the degree of cross-linking during UV exposure, leading to increased conductivity but without sacrificing photo-patterning properties. The material also exhibits good thermal and electrochemical stability, excellent mechanical integrity and micron-scale patterning. Thin films of both UV cross-linked electrolytes were evaluated in electrochemical half cells and exhibited good interfacial stability.