The effects of anion structure of lithium salts on the properties of in-situ polymerized thermoplastic polyurethane electrolytes

Thermoplastic polyurethane (TPU) electrolytes with lithium salts were prepared by an in-situ polymerization method. Three different lithium salts were used to study the effects of the anion structure on the properties of polyurethane electrolytes: LiCl, LiClO4, LiN(SO2CF3)2 (LiTFSI). The effects of the anion structure on monomer (PTMG) prior to polymerization and on the properties of TPU electrolytes post polymerization were investigated. The anion structure of lithium salt has a significant influence on the ionic conductivity, thermal stability and tensile property of TPU electrolytes. The TPU electrolytes with LiTFSI demonstrated a high ionic conductivity up to 10−5 S/cm at 300 K. The ionic conductivity of polyurethane electrolytes with lithium salts is in the order: LiCl < LiClO4 < LiTFSI. It was found that the lithium salts with larger anions were easily dissociated in TPU and had stronger interaction with TPU, which provided more charge carriers and gave higher ionic conductivity.