Roll-to-Roll Functionalization of Polyolefin Separators for High-Performance Lithium-Ion Batteries

Abstract

Modified polyolefin separators fabricated via a roll-to-roll system exhibit markedly improved compatibility with lithium ion battery electrolytes. Zwitterionic molecules containing a perfluorophenyl azide functional group were synthesized and covalently bound to the surface of commercial polyolefin separators via UV-activated photochemistry. A roll-to-roll prototype system was constructed allowing for the functionalization of large areas of separator under ambient conditions at low cost. Lithium-ion battery cells containing the modified separators exhibit superior electrochemical performance using a common commercial electrolyte. The modified separators, both monolayer PE and trilayer PP/PE/PP, are wetted instantly upon contact with liquid electrolytes lacking linear carbonates. These electrolytes have been designed for use in batteries with advanced thermal stability properties and/or higher voltage windows, which have previously been hindered by incompatibility with commercial trilayer polyolefin separators. This scalable modification technique is able to meet the rapidly growing demand for low-cost, high-performance separators for safer lithium-ion batteries.