Vanadium-boride air is also a promising chemistry (http://phys.org/news/2013-09-molten-air-battery-storage-capacity-highest.html http://phys.org/news/2013-09-mo

Vanadium-boride air is also a promising chemistry (http://phys.org/news/2013-09-molten-air-battery-storage-capacity-highest.html http://phys.org/news/2013-09-molten-air-battery-storage-capa...). For aircraft, I'm not sure it would be practical, but in theory you could jettison the spent batteries (which now weigh more thanks to the air adsorption) after takeoff, at which point they would fly/glide themselves to a nearby reprocessing station.