NANOCOMPOSITE POLYMER ELECTROLYTES FOR LITHIUM BATTERIES

Ionically conducting polymer membranes (polymer electrolytes) might en hance lithium-battery technology by replacing the liquid electrolyte c urrently in use and thereby enabling the fabrication of flexible, comp act, laminated solid-state structures free from leaks and available in varied geometries'. Polymer electrolytes explored for these purposes are commonly complexes of a lithium salt (LiX) with a high-molecular-w eight polymer such as polyethylene oxide (PEO). But PEO tends to cryst allize below 60 degrees C, whereas fast ion transport is a characteris tic of the amorphous phase. So the conductivity of PEO-LiX electrolyte s reaches practically useful values (of about 10(-4) S cm(-1)) only at temperatures of 60-80 degrees C. The most common approach for lowerin g the operational temperature has been to add liquid plasticizers, but this promotes deterioration of the electrolyte's mechanical propertie s and increases its reactivity towards the lithium metal anode. Here w e show that nanometre-sized ceramic powders can perform as solid plast icizers for PEG, kinetically inhibiting crystallization on annealing f rom the amorphous state above 60 degrees C. We demonstrate conductivit ies of around 10(-4) S cm(-1) at 50 degrees C and 10(-5) S cm(-1) at 3 0 degrees C in a PEO-LiClO4 mixture containing powders of TiO2 and Al2 O3 with particle sizes of 5.8-13 nm, Further optimization might lead t o practical solid-state polymer electrolytes for lithium batteries.