Evaluation of Electropolymerization as a Versatile Approach for Applying Conformal Polymer Electrolyte Films on Complex Micro-Scale Silicon Architectures

Abstract

Application of conformal thin polymer electrolyte coatings on architecturally complex conductive electrode surfaces in various microdevices presents a significant technical challenge using conventional thin-film deposition techniques. In this study, electro-grafting combined with electropolymerization is investigated as a more versatile technique for applying these electrolyte coatings in order to advance the development of 3D microbatteries. Gel polymer electrolyte (GPE) films of several micrometers of thickness are electrochemically polymerized on cylindrical silicon micropillars employed as the anode in a lithium-ion battery. This in-situ electrochemical method allowed greater control of polymer film formation by applying a suitably negative potential for a designated duration. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy is used to analyze the surface and cross sections of polymer-coated silicon micropillars to evaluate film formation as a function of applied potential and electrodeposition time. Discrete robust GPE samples, with the same composition as those prepared by electropolymerization, are also prepared to simplify characterization. The polymer electrolyte exhibits good thermal and electrochemical stability, high discharge capacity, and excellent capacity retention at high rates when evaluated in a coin cell. These results suggest that the electrochemical electrolyte coating technique holds promise for fabricating small-scale lithium-ion batteries with complex electrode architectures.