(658g) Reversible Control of Electrochemical Properties Using Thermally-Responsive Polymer Electrolytes

Electrical energy storage continues to attract extensive research efforts and federal funding to address the growing demands in transportation and renewable energy generation. Recent progress in batteries and supercapacitors shows tremendous promise for high power, high energy density devices; however, these approaches fail to meet the performance requirements for bulk energy storage while addressing concerns with flammability, reactivity, and thermal runaway. The thermal instability in batteries, particularly Li-ion, creates a major roadblock to implementing large-scale storage systems to support emerging energy sources such as wind and solar, in addition to systems for transportation and consumer end-use. Efforts to mitigate these safety issues typically involve the implementation of low conductivity solid-state materials or irreversible safety devices, which prove problematic for efficient, large-scale energy systems.

Rather than choosing between low-performance devices and wasted batteries, we present a novel approach to thermal control and safety using an electrolyte with properties that can be regulated by temperature. In the proposed system, a polymer electrolyte is designed to decrease conductivity through phase separation at high temperature, where the potential for runaway and thermal failure is high. As the temperature cools to an acceptable level, the initial conductivity is restored as the electrolyte returns to its initial state. The objective of this research is to understand how the properties of responsive polymer electrolytes influence property changes in electrochemical systems. To achieve this goal, copolymers containing a thermally-active polymer, poly(n-isopropylacrylamide) (PNIPAm), and ionic groups were synthesized and evaluated in order to: (1) understand how the thermal response of copolymer electrolytes is affected by the type, composition, and structure of the ionic group, (2) improve the extent to which the electrolyte properties can be switched with temperature, and (3) achieve thermally-responsive polymer behavior in a variety of aqueous and nonaqueous solutions with varying electrolytes. At room temperature, the copolymers will be dissolved in solution providing free ions, whereas at high temperature, the polymer phase separates with its ions. Our proposed system will allows for the use of high conductivity electrolytes with a reversible safety mechanism.