Engineering the Low-Temperature Performance of Li-S Batteries

Abstract

For the last few decades, lithium-ion batteries employing insertion-compound cathodes and graphite anodes have become the standard in consumer electronics and have even become commonplace in applications with extreme-operating environments, such as missions to space.1 As such missions increase in complexity and applications continue to require increasingly greater specific energy, the energy density of secondary batteries needs to similarly increase. Lithium-sulfur (Li-S) batteries have the potential to offer significant improvements due to the sulfur cathode’s high theoretical capacity of 1,672 mA h g-1 and system’s theoretical energy density of 2,500 W h kg-1.2 Conventional lithium-ion batteries experience a sharp loss in energy and power density at temperatures below 0˚C, which significantly impacts design parameters for applications like space missions. During charge and discharge, low temperatures kinetically impede all steps of mass transfer of lithium ions through the battery, particularly through the increasingly viscous electrolyte as well as the electrode-electrolyte interface. This ultimately leads to reduced capacity and utilization of active material.3 In this work, we show that many of these same trends hold true for Li-S batteries at low temperatures. Not only is there a severe drop in accessible capacity with decreasing temperatures, but this loss is primarily exhibited by a shortening in length of the second voltage plateau.4 This plateau corresponds to the formation of the insoluble Li2S discharge product, and from the low temperature behavior, we see that the nucleation and growth of this species is a primary kinetically limiting barrier to low temperature operation of Li-S cells. This presents opportunities for investigation into the kinetic behavior of sulfur reduction and the dynamic interplay between soluble and insoluble species in nonaqueous solvents at low temperatures. We explore this behavior in detail and discuss our efforts in electrolyte co-solvent and additive engineering towards designing a Li-S battery capable of operating at low temperatures. Acknowledgement: This work was supported by a NASA Space Technology Research Fellowship.