UV- and/or thermally-cured electrolyte membranes for aging resistant lithium polymer batteries

Polymer electrolytes exhibit unique characteristics such as mechanical stability, facile fabrication methods in desirable size and shape, lightweight, possibility to fabricate an intimate electrode/electrolyte interface and leak free assembly, safety and economic packaging structure. Free radical photo-polymerization (UV-curing) can be an interesting alternative process to produce polymer electrolytes for Li-ion batteries (LIBs). It can be carried out at ambient temperature where a liquid polyfunctional reactant with a photo-initiator undergo polymerization to obtain a cross-linked film. It is an excellent technique due to its easiness in processing and eco-friendliness as the solvents are not used. Hereby, ion conducting, self-standing and tack-free ethylene oxide based polymer electrolytes encompassing a room temperature ionic liquid (RTIL) and/or tetraglyme (G4) with specific amounts of lithium salt are successfully prepared via a rapid UV curing process. All materials are characterized in terms of their physical, chemical and morphological properties, following galvanostatically cycling in lab-scale lithium batteries. Tensile analysis confirmed that the UV-irradiated membranes showed an average Young’s modulus E of 0.2 ± 0.05 MPa. It is interesting to note that more than 50 wt.% of ionic liquid is generally incorporated, thus these are encouraging values. The SPE showed the thermal stability > 300 °C under inert conditions, and such remarkable results is interesting for safer Li-ion batteries application. X-ray diffraction analysis (XRD) confirmed the role of UV-curing process in obtaining a nearly fully amorphous state. The SPE exhibited excellent ionic conductivity (>10–4 S cm–1 at ambient temperature), electrochemical stability (>5V vs. Li+/Li), and optimum interfacial stability. At 20 °C the ionic conductivity value is equal to 2.5×10-4 S cm-1. The lab-scale Li-polymer cell assembled demonstrated stable charge/discharge characteristics (130 mAh g-1) without any capacity fading upon > 2000 cycles. The overall performance of the SPEs encourages the possibility of effective implementation in the next generation of safe, durable and high energy density all-solid Li-metal polymer batteries working at ambient and/or sub-ambient temperatures.