Sodium atoms have a much higher molecular weight (22.99 u) than Lithium atoms (6.94 u). This alone makes Lithium more competitive by weight in the long run. Th

Sodium atoms have a much higher molecular weight (22.99 u) than Lithium atoms (6.94 u). This alone makes Lithium more competitive by weight in the long run. The ideal battery consists of two electrodes where one consists purely of the alkali metal in the charged state and the other one is weightless at the charged state but then collects the metal oxide when discharging. The oxygen is ideally taken from the air. Currently we are far from that ideal since the electrodes contain additional matrix materials, between the electrodes an electrolyte is present, the oxidizing agent is stored inside the battery requiring yet other chemicals to keep it stable. Then the battery needs a casing which adds more weight.