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Abstract

A separator material of the present invention is a sulfonated nonwoven that comprises a polyolefin ultra-fine short fiber having a fineness of less than 0.5 dtex and other polyolefin short fiber(s). The other polyolefin short fibers include a polyolefin thermal bonding short fiber. At least a portion of the polyolefin thermal bonding short fiber is flattened to bond the component fibers together. The nonwoven has a specific surface area in a range of 0.6 m.sup.2/g to 1.5 m.sup.2/g and satisfies the following ranges. (1) A ratio (S/C).sub.E of the number of sulfur atoms (S) to the number of carbon atoms (C) in the nonwoven, as measured by Electron Spectroscopy for Chemical Analysis (ESCA), is in a range of 5.times.10.sup.-3 to 60.times.10.sup.-3. (2) A ratio (S/C).sub.B of the number of sulfur atoms (S) to the number of carbon atoms (C) in the nonwoven, as measured by a flask combustion technique, is in a range of 2.5.times.10.sup.-3 to 7.times.10.sup.-3. (3) A ratio (S/C).sub.E/(S/C).sub.B (depth of sulfonation) of (S/C).sub.E to (S/C).sub.B is in a range of 1.5 to 12. Thus, a separator material that has a high level of self-discharging performance when charge and discharge are repeatedly performed, a high level of process performance when assembling a battery, and a high level of short-circuit withstand capability; a method of producing the same; and an alkali secondary battery separator, are provided.

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