Polymer electrolytes plasticized with hyperbranched polymer for lithium polymer batteries

Hyperbranched polymers (HBPs) with different terminal groups and different ethylene oxide (EO) chain lengths were prepared, and the influence of the HBP structures including molecular weights and molecular weight distribution on the ionic conductivity and the mechanical property of the composite polymer electrolytes composed of poly (ethylene oxide) (PEO), HBP, BaTiO₃ as a ceramic filler, and LiN(CF₃SO₂)₂ as a lithium salt were investigated. It was found that the molecular weights of the HBP do not affect significantly the ionic conductivity, but the molecular weight distribution might affect it, and also further branching at the terminals of the HBP led to a decrease in the ionic conductivity. The HBP with longer EO chain length was effective for enhancement of the ionic conductivity in comparison with the HBP with shorter one. The increase in cross-linkable groups (acryloyl group) at the terminals of the HBP improved the tensile strength, but caused the ionic conductivity to decrease. Loosely cross-linked composite polymer electrolyte showed higher ionic conductivity and higher tensile strength than no cross-linked one. Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14 – 18, 2004.