A new type composite nonwoven separator has been developed by combining a polyacrylonitrile (PAN) nano-fiber nonwoven and ceramic containing polyolefin nonwoven. The physical, electrochemical and thermal properties of the separator were investigated. The separator has mean pore size of about 0.8μm as well as narrow pore-size distribution. Besides, the separator possesses higher porosity and air permeability than a conventional microporous membrane separator. The separator showed tensile strength of 46N5cm−1 at 10% elongation. Any internal short circuit was not observed for cells with the separator during charge–discharge test, and the cells showed stable cycling performance. Moreover, the cells showed better rate capabilities than cells with the conventional one. On a hot oven test at 150°C, the composite nonwoven separator showed better thermal stability than the conventional one. In addition, internal short circuit by thermal shrinkage of separator was not observed for a cell with the separator at 150°C for 1h.