Maybe this is the technology that is desperately needed by solar power farms in order to release electricity overnight, and for wind power in quiet periods. What makes this an excellent solution is that electricity is not stored inside the battery, but in large tanks.

I always find myself worrying, when there is talk about pumps, that the pumping will make the whole process a pointless exercise.

digi_owl, youre comment could be amusing if you were talking about something much bigger, like life itself. almost every mammal has a pulse, created by a pump called a heart.
life can be a pointless exercise yea. but pumps do seem to be pretty efficient. they help move and mix disparate levels of things. heat pumps, chemical pumps, salt pumps. its all about motion, and if you think about a generator as creating a voltage, youre talking about pumping elecriicty.

Why low-energy density, high viscosity slurry? How about using compressed lithium-oxygen gas = high energy density. The gas mixture could be charged and compressed hydraulically as in an accumulator, storing both thermodynamic energy and electrical energy.
http://www.gizmag.com/lithium-air-battery/14720/
The system could be arranged such that a lithium ion-gas accumulator is simultaneously electrically charged and hydraulically pressurized, the compressed charged gas mixture can then be stored in a pressure vessel until needed, at which point a valve can open, releasing the compressed gas accross a flow capacitor, possibly also driving an-air motor generator at the same time = instant electricity!

Hmmmm. Automobiles have pumps and tanks. I wonder if this could be scaled down to provide an alternative to battery packs, assuming you could get the kind of quick response that a vehicle would require for acceleration, etc. The slurry might be regenerated via either a quick plug-in charge, or a trickle charge from an IC-powered generator. But even with a tenfold improvement in slurry charge density it may be too large a system.

This isn't an answer just yet. It has no great energy storage capacity. Why do the creators think the electrolyte slurry have a long life? I couldn't see the answer in the article.

to PeetEngineer:
Wouldn't the fact that the lithium-oxygen gas, being highly compressed result in a lower energy efficiency, as energy must be diverted into running compressors (PV=nRT --> p*(dV)=nr(dT))

lithium-oxygen gas ? sounds absolutely frightening? there was a big fire in Vancouver B.C. rather dangerous big fire. It was a Li battery recycle plant. Tell me why Li and O in gaseous form is not a disaster begging to happen.

What is lithium-oxygen gas? Does it exist?

walt ` what about the explosive properties of gasoline?