UC Berkeley

Perfluoropolyethers (PFPE) are commercially available non-flammable short chain polymeric liquids. End-functionalized PFPE chains solvate lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt and these mixtures can be used as electrolytes for lithium (Li) batteries. Here we synthesize and characterize a new class of solid PFPE electrolytes. The electrolytes are made by either thermal or UV crosslinking PFPE chains with urethane methacrylate end-groups. For the synthesis of thermally crosslinked electrolytes, polyhedral oligomeric silsesquioxane (POSS) with organic acrylopropyl groups was used as crosslinker agent, while for UV cured electrolytes a photoinitiatior was used. We present thermal, morphological, and electrical data of the solid electrolytes. We compare these properties with those of the two parent liquids (PFPE with urethane methacrylate end-groups and POSS with acrylopropyl groups) mixed with LiTFSI. The solubility limit of LiTFSI in the PFPE-based solids is higher than that in the liquids. The conductivity data are analyzed using the Vogel–Tamman–Fulcher equation. The concentration of effective charge carriers is a strong function of the nature of the solvent (solid versus liquid) whereas the activation energy is neither a strong function of the nature of the solvent nor salt concentration.