A high throughput mass production of separator is proposed using a well-established unique in-house process of roll-to-roll atmospheric atomic layer deposition. An ultra-thin conformal layer of Al2O3 is deposited over the commercial Celgard (PE/PP/PE) using multi-slit gas source head. Overall 10 nm increase is incurred in the thickness, while maintaining the porosity to 48%. The entire process of fabrication was performed at very low temperature of 90 degrees C. The high thermal stability of as-modified separator is achieved at of 180 degrees C. The separator was analyzed using X-ray photoelectron spectrometer, electrochemical impedance spectra, and field emission scanning electron microscope. The as-developed separator showed excellent wettability due to the surface medication in addition to robust flexibility, high conformity, and minimal thermal shrinkage. The Lithium cobalt oxide (LCO)/Graphite cells with atomic layer deposition (ALD) Celgard (Al2O3 deposited) separator delivered remarkable discharge capacity with 79.5% capacity retention after 100 cycles at 1 C as compared to the uncoated-separator(Celgard separator), which yielded relatively less retention of 70%. Moreover, the LCO/Graphite cells with the ALD-Celgard separator delivered the discharge capacity of 140 mAh/g at elevated temperature (up to 80 degrees C).