A comparison of ionic conductivity, thermal behaviour and morphology in two polyether-LiI-LiAl5O8 composite polymer electrolytes

Two polymer hosts have been used to prepare composite electrolytes, i.e. PE O (M-w = 1 x 10(6)) and a triblock copolymer [poly(propylene glycol-ethylen e glycol-propylene glycol)] with M-w = 2000. The effect of the LiAl5O8 addi tion on the properties of electrolytes prepared with polyether-LiI was stud ied. The aluminate ceramic powder was prepared by coprecipitation and calci ned at 1150 degreesC. The main goal of the present investigation is to comp are the two classes of composite electrolytes with polyether-LiI with a com position fixed at n = molar ratio of [O]/[Li] = 20. LiAl5O8 powder was disp ersed by ultrasound in the electrolyte matrix in a range of concentrations up to 20 wt%. Differential scanning calorimetry curves indicated that all m aterials are semi-crystalline, and the triblock composites show a smaller g lass transition (T-g = - 28 degreesC at 20 wt% of ceramic) than that of PEO electrolytes ( - 16 degreesC at 20 wt% of ceramic). Thermomechanical analy ses were performed using penetration mode and the composite electrolytes ex hibited a significant increase in mechanical stability. The ionic conductiv ity of both systems (PEO and triblock-LiI-LiAl5O8) is 5 x 10(-4) S/cm at 80 degreesC. The triblock composite shows a conductivity of one order of magn itude higher than that of the PEO material near room temperature as a conse quence of the decrease in crystallinity after a first heating. This result raises the interest in the development of composites based on a triblock po lyether. (C) 2001 Elsevier Science Ltd. All rights reserved.