Honestly curious: I'm not a battery or even energy person, but this is interesting.

The charge/discharge efficiencies and rates could just mean we build networks of mixed types? "Trickle" charge/discharge via a slower battery that handles more cycles and is probably way cheaper to build (that's the premise of Na+, right?), but have those batteries back up a more expensive high-rate bank for when power is needed in a burst? Probably a switching problem at that point, which I imagine we already deal with having solar/hydro/fossil/etc.

A Na+ bank sized to handle regular use and charge a Lithium bank when underused so that one is ready for spikes seems like a way to go.