The magnesium–sulfur battery holds great promise for energy storage due to its high energy density and low cost of materials. Unfortunately, current Mg–S electrolytes are found to enable severe self-discharge, leading to poor battery shelf-life.

A major goal of next-generation battery development is the engineering of nonflammable solid-state electrolytes with high enough ionic conductivity to compete with traditional liquid electrolytes. Composite polymer electrolytes (CPEs), which combine inorganic fillers or electrolytes with a polymer matrix, are seen as a strategy to boost the ionic conductivity of flexible polymer electrolytes while overcoming the brittle aspect of inorganic electrolytes. In this work, we examine the impact of polymer backbone chemistry on Li + ion conduction within crosslinked single-ion conducting gel polymer electrolytes (SIPEs) that contain a lithium ion-conducting glass ceramic electrolyte (LICGC). Certain SIPE compositions based on poly(tetrahydrofuran) diacrylate (PTHFDA) crosslinking macromonomers exhibit a significant increase in conductivity with the inclusion of LICGC, a result unexpected from prior literature. With the use of Raman spectroscopy, small angle X-ray scattering, and particle-induced gamma-emission spectroscopy (PIGE), it is proposed that the enhanced conductivity comes from the formation of percolated LICGC particles sheathed in an ion-rich domain. This region develops in the pre-polymer solution due to interactions between the LICGC particle surface and the ionic comonomer, much like the formation of space-charge regions in soggy-sand liquid electrolytes, and persists post-polymerization to yield a CPE of enhanced conductivity. The particle−ionic monomer interactions are modulated by the crosslinking macromonomer polarity, polymer casting solvent, and particle surface area. While there is ample room for continued optimization, the best SIPEs in this study are capable of Li metal dissolution/deposition, and they reach Li + conductivities greater than 2 × 10 −4 S/cm at 25 °C, surpassing the practical use threshold.

Magnesium-sulfur batteries are currently researched for their potential as beyond Li-ion electrochemical energy storage devices. Despite the theoretical high volumetric energy capacity of magnesium metal anodes, sulfur is not very dense and many reports on magnesium-sulfur batteries use configurations with low active material loading and high carbon content at the cathode and high electrolyte content. Thus, the overall energy density of demonstrated magnesium-sulfur batteries is not very high. However, there may be potential for magnesium-sulfur batteries to be competitive in grid scale storage applications. In this presentation, we will report on our investigations related to magnesium polysulfide flow batteries as supported by an Amazon Catalyst at ECS award.