A surprising breakthrough could help sodium-ion batteries rival lithium—and even turn seawater into drinking water. Scientists discovered that keeping water inside a key battery material, instead of removing it as traditionally done, dramatically boosts performance. The “wet” version stores nearly twice as much charge, charges faster, and remains stable for hundreds of cycles, placing it among the top-performing sodium battery materials ever reported.
There actually is not a lot of room for improvement. Highest energy will still be limited to lithium chemistry because of the periodic table.
That’s a limit on gravimetric energy density. There are plenty of other parameters that can be improved.