SEPARATOR FOR LITHIUM ION SECONDARY BATTERIES, AND LITHIUM ION SECONDARY BATTERY

This separator is for electrochemical elements, is to be interposed between a pair of electrodes, and includes para-aramid fibers for holding an electrolytic solution. The separator for electrochemical elements is characterized in that the contained amount of fibers having a fiber diameter of 0.03-0.50 μm is 90 mass % or more, the proportion of the number of fibers having a fiber length not less than 0.05 mm but less than 0.20 mm is 20-30%, and the proportion of the number of fibers having a fiber length not less than 0.20 mm but less than 5.00 mm is 70-80%.