High ionic conductivity and electrode interface properties of polymer electrolytes based on high molecular weight branched polyether

Ionic conductivity and electrode interface properties of solid polymer electrolytes (SPE) based on high-molecular-weight branched polyethers have been studied for their application to solid state rechargeable lithium batteries. High molecular weight (105–106) comb-shaped polyethers, poly[ethylene oxide-co-2-(2-methoxyethoxy)ethyl glycidyl ether] [P(EO/MEEGE)], allow to give elastic and self-standing polymer electrolyte films without cross-linking. With increasing the MEEGE composition, the conductivity appreciably increases and takes a maximum at MEEGE compositions of 0.2–0.3, due to the fast ion transport assisted by highly mobile ether side-chains. Interfacial resistance (Ri) at the lithium electrode interface decreases with increasing ionic conductivities of the polymer electrolytes, which are affected by the MEEGE composition and lithium salt species complexed with the copolymers. An all-solid lithium polymer battery, Li/P(EO/MEEGE=91/9)-LiClO4/LiCoO2 composite cathode cell, exhibited a discharging life of over 7 h at 0.1 mA/cm2 and a low cell impedance of 96 Ω cm2 after full charge at 60°C.