Provided is a separator for a power storage device that combines high permeability and battery safety at high temperature. The separator for a power storage device has an inorganic content layer that contains inorganic particles and polyolefin resin. In a cross section of the inorganic content layer, a ratio b of the area occupied by the inorganic particles is 9-35% [inclusive], the ratio of the area occupied by vacancies is 20-60% [inclusive], and a TD direction heat shrinkage a at 150° C. of the separator for a power storage device is 4% or less.

A separator for power storage devices includes a synthetic resin film having minute pore portions, the separator having an air resistance of 30 sec/100 mL/16 μm or more and 100 sec/100 mL/16 μm or less, and a first scattering peak in a stretching direction measured by small-angle X-ray scattering measurement (SAXS) present in a range where a scattering vector is 0.0030 nm.sup.−1 or more and 0.0080 nm.sup.−1 or less.

In an electrolytic capacitor having a capacitor element housed inside a body case where the capacitor element has a first electrode member and a second electrode member wound up with a separator in between and where the capacitor element holding an electrolyte solution, there is provided, between the first and second electrode members, a conductive polymer particle band in which conductive polymer particles of a conductive polymer in a dense state are disposed to extend in the longitudinal direction of the separator, the conductive polymer particle band contains a cellulose derivative, and the conductive polymer particle band is provided to cover, within at least one of regions on opposite sides of the center line of the separator in its lateral direction, one half or more of the region in the lateral direction.

In an electrolytic capacitor having a capacitor element housed inside a body case where the capacitor element has a first electrode member and a second electrode member wound up with a separator in between and where the capacitor element holding an electrolyte solution, there is provided, between the first and second electrode members, a conductive polymer particle band in which conductive polymer particles of a conductive polymer in a dense state are disposed to extend in the longitudinal direction of the separator, the conductive polymer particle band contains a cellulose derivative, and the conductive polymer particle band is provided to cover, within at least one of regions on opposite sides of the center line of the separator in its lateral direction, one half or more of the region in the lateral direction.

Disclosed is a functional layer for an electrochemical device that comprises inorganic particles and a particulate polymer, wherein the functional layer comprises a particle-detached portion, in a plan view of a surface of the functional layer, a ratio of an area of the particle-detached portion in a total area of the particulate polymer and the particle-detached portion is 0.1% or more and 40.0% or less, and a volume-average particle diameter of the particulate polymer is larger than a thickness of an inorganic particle layer comprising the inorganic particles.

A thin separator for electrochemical elements, which has achieved chemical stability, while maintaining a good balance among short-circuit resistance, resistivity, electrolyte solution impregnability and electrolyte solution retainability of the separator. A separator for electrochemical elements, which is interposed between a pair of electrodes so as to separate the electrodes from each other, and which holds an electrolyte solution. This separator for electrochemical elements is composed of beaten cellulose fibers and thermoplastic synthetic fibers, and has a thickness of 5.0-30.0 μm and a density of 0.50-0.75 g/cm.sup.3; and the thickness X (μm) and the air resistance Y (second/100 ml) of this separator for electrochemical elements satisfy formula 1:
Y≥0.01X.sup.2−0.6X+11.5.

A thin separator for electrochemical elements, which has achieved chemical stability, while maintaining a good balance among short-circuit resistance, resistivity, electrolyte solution impregnability and electrolyte solution retainability of the separator. A separator for electrochemical elements, which is interposed between a pair of electrodes so as to separate the electrodes from each other, and which holds an electrolyte solution. This separator for electrochemical elements is composed of beaten cellulose fibers and thermoplastic synthetic fibers, and has a thickness of 5.0-30.0 μm and a density of 0.50-0.75 g/cm.sup.3; and the thickness X (μm) and the air resistance Y (second/100 ml) of this separator for electrochemical elements satisfy formula 1:
Y≥0.01X.sup.2−0.6X+11.5.

Disclosed is a separator including inorganic particles and a binder resin. The separator may be used as a free standing type separator including no separator substrate, such as a polymer resin film, and thus causes no problem of heat shrinking. In addition, the separator includes an elastomer to provide a small change in dimension and high elongation, and thus is prevented from being damaged by external impact.

A heat-resistant separator for an electrochemical element in which the thickness of the separator is reduced while maintaining the balance between the short circuit resistance, resistance, electrolyte impregnation performance, and electrolyte retention performance of the separator. A separator for an electrochemical element includes beaten cellulose fibers, wherein the value obtained by dividing the average value for the distance between the center point of a cellulose stem fiber constituting part of the separator and the center point of another cellulose stem fiber nearest to said cellulose stem fiber by the thickness of the separator is 0.80 to 1.35.

A heat-resistant separator for an electrochemical element in which the thickness of the separator is reduced while maintaining the balance between the short circuit resistance, resistance, electrolyte impregnation performance, and electrolyte retention performance of the separator. A separator for an electrochemical element includes beaten cellulose fibers, wherein the value obtained by dividing the average value for the distance between the center point of a cellulose stem fiber constituting part of the separator and the center point of another cellulose stem fiber nearest to said cellulose stem fiber by the thickness of the separator is 0.80 to 1.35.