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New Type of 'Flow Battery' Can Store 10 Times the Energy of the Next Best Device (sciencemag.org)
sciencehabit writes: Industrial-scale batteries, known as flow batteries, could one day usher in widespread use of renewable energy—but only if the devices can store large amounts of energy cheaply and feed it to the grid when the sun isn't shining and the winds are calm. That's something conventional flow batteries can't do. Now, researchers report that they've created a novel type of flow battery that uses lithium ion technology—the sort used to power laptops—to store about 10 times as much energy as the most common flow batteries on the market. With a few improvements, the new batteries could make a major impact on the way we store and deliver energy. The research, from the National University of Singapore, has one big flaw in particular: speed. It's 'very innovative' work, says Michael Aziz, a flow battery expert at Harvard University. But he adds that even though the novel battery has a high energy density, the rate at which it delivers that power is 10,000 times slower than conventional flow batteries, far too slow for most applications. Wang and his colleagues acknowledge the limitation, but they say they should be able to improve the delivery rate with further improvements to the membrane and the charge-ferrying redox mediators.
When does the battery become capacitor?
When the voltage across it is directly proportional to percentage of charge.
And they already did, many years ago. That's what "supercapacitors" are: Electrochemical cells where the charge is stored by migrating, but not ionization-state-changing, ions in a solution (rather than by migrating electrons within two conductors (one metal, the other metal or conductive liquid) separated by an insulator, as in a conventional or electrolytic capacitor, or ionization-state-changing ions in the cells of a conventional battery,where the voltage only changes slightly with state of charge until nearly full discharge.
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They chose one of the more expensive commercially available battery technologies for their flow battery?
It's still a useful milestone. If you can up the theoretical limit with exotic materials then you can study it and try to replicate it with less exotic materials. Many of our advances in a variety of areas like semiconductors, batteries, superconductors, and a large host of other areas started out with exotics before figuring out how to replicate it with cheaper components. Granted your second argument is valid where with the exception of cars and mobile devices, energy density is usually not a huge concern, it's still nice to know what is possible and with a 10x density increase, the exotics have to be at least 10x more expensive for them not to be competitive.