2, University of Tennessee, Knoxville, Knoxville, Tennessee, United States
3, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Development of high performance and reliable energy storage devices that are lightweight and flexible with improved safety are imperative for next generation energy storage technologies, including lithium (Li)-ion batteries, supercapacitors, fuel cells, and many others. High-performance solid state electrolytes have the potential to address various challenges in these electrical energy storage devices, especially if they can meet requirements of (i) high ionic conductivity; (ii) sufficient mechanical strength or modulus to suppress dendrites formation; (iii) high transference number; and (iv) wide electrochemical stability window. However, dry solid-polymer electrolytes lack sufficient ion conductivity to meet cell power requirements, being typically around 10-5-10-9 S/cm. On the other hand, while gel polymer electrolytes can provide adequate ion conductivity, their weak mechanical properties diminish advantage over traditional liquid electrolytes, and limit their utilization. This project focuses on cultivating the fundamental understanding for the development of novel gel polymer electrolytes simultaneously providing high conductivity and tailored mechanical modulus. In the first system, mechanically robust crosslinked PEO membranes were synthesized and doped with sodium triflate and tetraglyme. The relationships between ion conductivity (reached up to 10-4-10-3 S/cm at r.t.) and salt/gel content, glass transition temperature (Tg) and decoupling are investigated. In the second system, mechanically tailored novel single-ion conducting polymer electrolytes (SCPEs), poly[(4-styrenesulfonyl) (trifluromethane-sulfonyl)imide] (poly(STF)) and their copolymers were successfully synthesized. The SCPEs were synthesized by covalently attaching anionic moieties to the polymer that only allows specific cations, such as lithium ions, to move freely and provide ionic conductivity, i.e. the transference number is close to 1. The novel SCPE membrane includes a membrane with PDMS as polymer backbone to afford mechanical robustness and flexibility, and poly(STF) as a side chain to provide single-ion conductivity. The effect of the monomer type, the degree of polymerization of the side chain, and different cations is also studied. The obtained polymer membrane showed 100% elongation and 10-4 S/cm single-ion conductivity (no salt) at 30 oC after doped with propylene carbonate.