Did you know that one kind of battery can be refilled with a charge in much the same way as a gas tank? It’s not a new idea. One of the most efficient incarnations of what is called a redox flow battery was developed in the 1980s at the University of New South Wales, Australia. Most traditional lead batteries store a charge in solid electrodes submerged in an electrolyte solution. The Australian redox flow batteries store the charge in the electrolyte solution and extract it with vanadium electrodes. The electrolyte solution, being liquid, can be pumped in or out of the battery – meaning that a charge could be replaced simply by pumping in a new load of electrolyte. This is not much different in concept than pumping gas into a tank.

A redox flow battery is a good example of a ‘concept in waiting.’ The idea has been around a while and there are versions in routine use, however, it has not been practical in the context of vehicles. That’s because the current model of a redox battery requires two large tanks to store fresh and discharged electrolyte. These tanks would reduce the amount of charge available in vehicles and thereby reduce the driving range. This driving range could be as low as 25 km, less than a quarter available to current lithium-ion batteries.
 
This is where new research comes into play. Scientists at the Fraunhofer Institute for Chemical Technology in Pfinztal (Germany) believe that the efficiency of a redox flow battery can be increased considerably.  
 

The German researchers are experimenting with other materials in their redox flow cell, including electrodes made from vanadium and bromide ions, and iron and chromium. […they] believe it is possible to build a redox flow battery that would provide a four- or five-fold increase in the range of an electric vehicle compared with one powered by an existing flow battery of a similar size. That would give such a vehicle a range equivalent to one running on a lithium-ion battery, but with the ability to be recharged either by being plugged into the mains or in minutes by swapping electrolytes.
[Source: The Economist]

 
Any technology at the ‘concept’ stage is…speculative. In this case, it may be worth tracking because the idea is patently acceptable. Existing networks of petrol (gas) stations could also dispense charged electrolyte. The time it takes to ‘fill a battery’ is comparable to filling a gas tank. If the range can be increased, and the safety guaranteed, the idea could be ramped-up to large scale production and perhaps become commercially successful. However, that’s still a big IF. Much also depends on the general acceptance of battery driven electrical vehicles, in comparison to say hydrogen driven vehicles. So, while research is underway, this remains just another ‘promising’ avenue for alternative energy storage and use.