Patent ID: 8679200

Claim:
A method for reducing the self discharge rate and the variability in the self discharge rate of an electrochemical cell comprising inserting a porous separator between a cathode and an anode of said cell and wherein said porous separator comprises a nanoweb that further comprises a plurality of nanofibers wherein the nanofibers consist essentially of a fully aromatic polyimide comprising monomer units derived from pyromellitic dianhydride and oxy-dianiline and the fully aromatic polyimide has a degree of imidization greater than 0.51 where degree of imidization is the ratio of the height of the imide C—N absorbance at 1375 cm −1 to the C—H absorbance at 1500 cm −1 and wherein in a measurement of self discharge capacity in open circuit, the standard deviation of the seven day open circuit percent self discharge capacity divided by the average percent self discharge capacity in the same measurement measured on six samples is 0.125 or less.