UV-cured Solid-State Composite Polymer Electrolytes for Flexible/Safer Lithium-Ion Batteries

Abstract

Lithium-ion batteries (LIBs), as a compelling portable power source, have dominated the portable device market due to their high energy density, high voltage window and long cyclability. Flexible LIBs have received great attention as a key component to enable future flexible electronic devices as roll-up displays, touch screens, conformable active radio-frequency identification tags, wearable sensors and implantable medical devices. A number of designs for flexible LIBs have been reported in recent years. In this study, a new class of UV (ultraviolet)-cured mechanically-compliant, dendrite growth-suppressing and thermally-stable composite polymer electrolytes (CPEs) are developed for use in flexible LIBs. These new CPEs are fabricated through an elaborate combination of UV-cured ethoxylated trimethylolpropane triacrylate macromer (serving as a mechanical framework) and Al2O3 nanoparticles (as a functional filler) under the presence of liquid electrolyte (1M LiPF6 in ethylene carbonate/propylene carbonate = 1/1 v/v or succinonitrile-mediated plastic crystal electrolyte (PCE)). A salient structural feature of the CPE is the close-packed Al2O3 nanoparticles in the liquid electrolyte-swollen ETPTA macromer matrix. Owing to this unique morphology, the CPE provides significant improvements in the mechanical bendability and suppression of lithium dendrite growth during repeated charge/discharge cycling of cells. In addition, the CPE precursor mixture (i.e., prior to UV irradiation) with well-tailored rheological properties, via collaboration with UV-assisted imprint lithography technique, enables the generation of micropatterned CPE with tunable dimensions. Notably, the cell incorporating the self-standing PCE based CPE, which acts as thermally-stable electrolyte and also separator membrane, maintains stable charge/discharge behavior even after exposure to thermal shock condition (= 130 ℃/0.5 h), while a control cell assembled with carbonate-based liquid electrolyte and polyethylene separator membrane loses electrochemical activity. We envision that the material/structural concept used for the CPEs is simple and versatile, which thus holds a great deal of promise as a platform electrolyte strategy for next-generation flexible LIBs.