Air is composed of 78%
Air is composed of 78% nitrogen, 21% oxygen. Boiling point of liquid nitrogen is -196 C (-320F). Using solar power, do the heavy lifting on the ground to liquify nitrogen from the air. Liquid oxygen boils at -183 C (-297 F). As the air cools, the oxygen may be drained off before the nitrogen liquifies. As it continues to cool, the remainder is almost pure nitrogen liquid. Density of liquid nitrogen is 0.807 g/ml, that of nitrogen gas is approximately 1/750 of that amount. So, an enormous volume of nitrogen gas coil be created from a small amount of nitrogen liquid. No heat would need to be drawn from the batteries because the atmospheric temperature is going to be far higher than the boiling point of liquid nitrogen. Seems like this would be the propellant of choice. Atmospheric pollution equals zero; you simply return the nitrogen back to the atmosphere as you propel the plane using electric turbines. Exactly how this might be done would require engineering. Seems like you might want to draw in warm atmospheric air in using the turbines, and then apply a mist of liquid nitrogen as the gas exits the plane. The expanding nitrogen would create enormous thrust.