Solid polymer electrolyte is advantageous for use in batteries as opposed to the standard liquid electrolyte due to the safety benefit of eliminating the volatile, flammable liquid components from the batteries. Furthermore, solid polymer electrolytes have advantages over solid inorganic electrolytes in that they have better mechanical properties, being less fragile and brittle, and have lower interfacial resistance while in contact with the battery electrode, thus not limiting the specific energy that can be delivered as much as inorganic electrolytes do. Sulfur copolymers are favorable compared to elemental sulfur for use in an all-solid metal-sulfur battery cathode due to being more tunable in terms of sulfur distribution and being able to directly attach oligomeric ion transport channels to sulfur. The devised metal-sulfur batteries have a potentially high energy density which could be used to power trucks and airplanes. In this work, we synthesize the copolymer poly(Sulfur-r-Styrene-r-PEG Styrene) via reported methods of inverse vulcanization and dynamic covalent polymerization to obtain a sulfur cathode material attached to a poly(ethylene oxide)-based ion transport channel. We report on this synthesis for implementation of the sulfur copolymer in a lithium-sulfur battery as well as the characterization of the bulk material properties of the copolymer and the overall composite cathode. These characterizations include differential scanning calorimetry for determining the glass transition temperature to examine the existence of unincorporated elemental sulfur in the synthesized copolymer, dielectric / impedance spectroscopy for characterizing ionic conductivity in this copolymer system, absorption spectroscopy for evaluating the absorption of the electrochemical reaction intermediate lithium polysulfides (LixSy) into the polar region of the polymers, and Raman spectroscopy during cycling of the battery for gaining information on the charge / discharge reaction pathways with sulfur and polysulfide speciation along with the ionic interactions that impact cation transport in the solid state.

Characterizing sulfur copolymer composite cathodes for all-solid batteries

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