I understand charge time is a concern, but it is'nt the theoretical limitation of really any battery technology. From the computing parlance it's embarrassingly parallel. More, smaller cells allows for more current => faster charge times. theoretical limitations: energy density, number of cycles economics limitation: material and manufacturing costs. infrastructure limitations: grids to power these charge rates at scale Sodium Ion is promising because it drastically lowers the material cost. Cheap batteries can help solve the infrastructure problems as energy reservoirs, but I am more or less not swayed by the fast charge time break through. I can show doubling charge time with some AAs.