Porous organogel membranes (POMs) composed of electrospun nanofibers with a crosslinking modification have demonstrated great potential as battery separators. As a proof of concept, we fabricated such membranes using electrospun Matrimid nanofibers crosslinked through a room temperature solvent immersion technique. The effects of the crosslinking modification on the chemical structure and mechanical properties of electrospun Matrimid mats were evaluated using Fourier transform infrared spectroscopy and dynamic mechanical analysis tests. Stability was tested on the resulting POMs showing that the crosslinking modification on Matrimid drastically improved fiber chemical and sovothermal resistance. A Matrimid organogel membrane with a 3-day crosslinking modification was tested as separator in a Li-ion battery. When soaked in dimethylformamide (DMF), no thermal shrinkage was observed at temperature up to 180 degrees C. At 190 degrees C and 200 degrees C, Matrimid membranes showed shrinkage of 10% and 20% with respect to their original sample area, respectively. The discharge capacity of the battery was over 93% after 20 cycles with an average Coulombic efficiency above 98%. The membrane retained physical stability and flexibility after being in contact with the electrolyte LiPF6 in EC-DEC-DMC for three weeks of testing and demonstrated great potential as battery separators in applications involving strong solvents and high temperature.