Grain boundary phenomena in LiI-P(EO)-Al2O3-based composite solid electrolytes

Ion conducting polymers have attracted worldwide attention due to their high potential for use in lithium rechargeable batteries, as well as in other electrochemical devices. In the present communication LiI-P(EO)(n)-high surface area -Al2O3-based composite solid electrolytes (CSE, n less than or equal to 3) have been characterized with the use of DSC, AC impedance and SEM techniques. According to DSC thermograms at T<70-90 degrees C CSEs with n less than or equal to 3 are almost solid. Al2O3 increases CSE ionic conductivity to a maximum of 1-2*10(-4) S*cm(-1) at 6%v/v Al2O3. Grain boundary resistance (ROB) was found to be a dominant impedance component in CSEs under investigation. It should be reduced before these CSEs can be used in high power lithium batteries at moderate temperatures. Al2O3 and CaI2 increase RGB, decrease COB associated with the impairment of interparticle contact. It was established that the values of ROB at T<90 degrees C can be decreased by a factor of three to ten by small additions of EC and PEGDME and hot pressing of CSE, According to SEM micrographs, LiI-P(EO)(n)-Al2O3, CSEs consist of units whose size is of the order of hundreds of microns. EC and PEGDME do not change the unit size, but cause the separation of Al2O3 and its accumulation on the surface and unit boundaries.