Photolithography has been extensively used to define features and create patterns for devices in the semiconductor industry. Technological advances of photolithography allow for the fabrication of more complex patterns including high aspect ratio (HAR) and tilted geometries with spatial and thickness control, potentially at submicron scales. The use of microfabrication techniques in the production of batteries has not really been considered, but it can open up new fabrication routes especially for integrated on-chip energy storage devices. One important consideration for the development of on-chip batteries is to fabricate a mechanically rigid solid electrolyte with spatial and thickness control from their photopatterning functionality.
In this study, the photopatterning of a lithium-ion conducting solid electrolyte is demonstrated. The approach is taken by modifying a negative photoresist SU-8 with LiClO4, and the resulting lithium modified SU-8 electrolyte is evaluated as a promising gel polymer electrolyte with a room temperature ionic conductivity of 52 μS cm-1.1 Half-cell testing and electrochemical analysis validate its potential use in lithium-ion batteries. Electrochemical impedance spectroscopy shows an increase in the charge transfer resistance after the first cycle due to the reduction of ether linkages that can form a passivation layer at the solid electrolyte interphase (SEI).2 However, the interface becomes very stable and the charge transfer resistance remains constant after 30 charge-discharge cycles. The stable cyclic voltammetry result further validates that there are no other side reactions once the initial SEI forms. The modified SU-8 electrolyte also possesses excellent mechanical integrity, is thermally stable up to 250 °C and can be photopatterned with micron-scale resolution. From this advance in materials design, there is the unique opportunity to incorporate semiconductor processing technology into battery fabrication.
1. C. Choi et al., Adv. Mater., accepted (2017).
2. D. Aurbach et al., J. Electrochem. Soc., 135, 1863, (1988).