Effects of the surface treatment of the Al2O3 filler on the lithium electrode/solid polymer electrolyte interface properties

The lithium deposition–dissolution process in solid polymer electrolytes containing Al2O3 filler treated under different conditions has been investigated comparing with the ionic conduction behavior of the electrolyte. The composite electrolytes were prepared from poly(ethylene oxide) (PEO), LiBF4 and α-Al2O3 filler by using a dry process, where the surface of α-Al2O3 was beforehand modified by a wet process. The exchange current densities, i0, of the lithium electrode process in P(EO)20LiBF4 with and without Al2O3 filler were determined by a micro-polarization method. The temperature dependence of i0 provided similar values for activation energy, ca. 25 and 70 kJ mol−1 in both temperature regions above and below 60 °C, respectively. The effect of the surface treatment of the filler on the lithium electrode process gave a different tendency from that on the ionic conductivity. The Al2O3 surface treated by alkali solution enhanced the electrode process to the largest extent among the fillers used here, while it led to rather poor cycling stability in voltammetry. The enhanced reaction rate at the lithium electrode/solid polymer electrolyte interface has probably resulted in the improved ion dissociation by the surface groups of the Al2O3 filler.