We have developed silica-composite nonwovens using polyolefin fiber and nanosize silica powder. The silica-composite nonwoven showed better wettability than the polyolefin-based microporous membrane and nonwoven. It was found that the Gurley value of the silica-composite nonwoven has to be higher than 200 s 100 cm(-3) in order to suppress a microshort of battery. It was confirmed that the silica-composite nonwovens showed higher maximum power than that of the Celgard membrane by instantaneous discharging test. The cells with the silica-composite nonwovens showed better cycling performances than that of the Celgard membrane at a moderate C-rate of 0.5. A hot-oven test using charged cells up to 4.2 V exhibited that the cells with the silica-composite nonwovens are thermally stable at 150 degrees C, whereas the cell with the Celgard membrane showed a short circuit probably due to thermal shrinkage of the separator. (C) 2008 The Electrochemical Society.