Eli5: Given their location on the periodic table and the abundance of sodium compared to lithium, why aren’t we using sodium-ion batteries?
In: 12
Sodium is more reactive than lithium **per atom**, but a sodium atom weighs 3 times as much and is much bigger than a lithium atom.
As such the energy *density* of a sodium-ion battery (whether in kWh/kg or in kWh/L) turns out to actually be less than half that of a lithium-ion battery.
When you’re designing something small like a phone battery, that difference in energy density is a very big deal.
For purposes where the size of the battery isn’t such a concern, sodium-ion batteries actually are in use already – for the reasons you posited they’re significantly cheaper per kWh of energy storage.
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