[adrian_b]

It is impossible for sodium-ion batteries to reach the same energy density as the best lithium-ion batteries.

So lithium-ion batteries will never be replaced in smartphones or laptops by sodium-ion batteries.

But there are plenty of applications where the energy density of sodium-ion batteries is sufficient. Eventually sodium-ion batteries will be much cheaper and this is why they will replace lithium-ion batteries in all cheap cars and for most stationary energy storage (except when lower auto-discharge is desired).

[rootusrootus]

How much less density are we talking? I'd accept a modest reduction in my smartphone battery capacity if the trade-off was a 10,000 cycle battery.

[adrian_b]

For the same amount of stored energy, one needs a triple mass of sodium vs. lithium.

However, sodium-ion batteries and lithium-ion batteries do not have metal electrodes (because for now it is not known how to ensure that those will survive an acceptable number of cycles), so the actual mass and volume of the electrodes are significantly greater than that of the sodium or lithium that is used.

Because of that, the difference in energy densities is much lower than the mass ratio seems to imply.

The parent article claims that the energy density of the Na-ion batteries is in the same range with that of the LFP batteries (i.e. lower than that of the Li-ion batteries with Ni or Co based electrodes).