Projection Micro Stereolithography of Skin Layered Microporous Polymer Membranes As a Separator for Li-Ion Batteries

Abstract

Commercial liquid electrolyte lithium-ion batteries (LIBs) traditionally incorporate microporous polymer membranes, or separators, to isolate electrode contact and enable ionic transport. Although they do not actively participate in cell chemistry, well-designed separators can influence cell performance and safety, and thus, are essential components of a cell. Current separator manufacturing processes include "wet" or "dry" mechanical stretching , phase inversion, and evaporation-induced phase separation. However, these processes have limited morphological control of geometry and layered structures. Additive manufacturing techniques have been used to rapidly prototype materials that have both high customizability and fine microstructural control. We investigate hexanediol diacrylate (HDDA) as a polymer system using projection micro-stereolithography, a layer-by-layer photopolymerization technique, to develop separators with controlled microstructures for Li-ion batteries. We successfully fabricate a unique polymer architecture of alternating nanometer thin skin layers and microporous network. The fine control of printing parameters (i.e., printing platform, skin layers, and exposure time), results in tunable porosity and morphology. This unique approach to manufacturing LIB separators provides hierarchical homogeneity for more uniform Li-ion transport. It’s potential as a LIB separator is explored by characterizing its electrolyte wettability, thermal tolerance, electrochemical properties, and mechanical stability. Finally, lithium symmetric cells using the HDDA microporous membranes are evaluated against Celgard 2325 separators. This work provides a promising new route for developing separators using additive manufacturing techniques to enable high performance Li-ion batteries.