Solid state batteries show huge promise, but what does that actually mean?

I've been doing some research recently on electric vehicles for our next family car, and I've been pleased to see how much batteries and range have improved since last time I researched them (and ended up bottling out and going for a hybrid).

But then I just read an article about solid state car batteries and now have an idea of how much more things could improve very soon. Toyota has been testing such a battery in concept vehicles for some time, and is expected to officially unveil the technology as early as next year, with a view to commercial release by 2025. Volkswagen is also working on a solid state battery.

Solid state batteries promise to double the range of electric cars (over the lithium-ion batteries currently used by most electric vehicles) and, at the same time, cut charging times to as little as 10 to 20 minutes (as compared to several hours currently). Also, they are not as heavy, and are less affected by cold temperatures. This is, then, a big deal.

But what does solid state actually mean?

Solid state batteries use both solid electrodes and solid electrolytes, as opposed to the liquid (or polymer) electrolytes used by the more traditional lithium-ion batteries. As a result, solid state batteries are less flammable, more stable, and allow for higher energy densities. Polyether and lithium phosphorus oxynitride are two commonly used solid electrolytes in battery development, if that means anything to you, though other oxides, sulphides, phosphates and solid polymers are also candidates. The main challenge appears to be bringing down the production costs.

Exciting times in electric car production, then, but probably not relevant to my next purchase decision (or possibly even the one after).