Passage 3 All Pumped Up
新式电动汽车 《经济学人》

[00:00]Prototypes of new electric vehicles that are soon to go on sale show lots of promise.
[00:09]They are clean, quiet and provide nippy performance.
[00:14]But even with advances in power systems and improved lithium-ion batteries,
[00:21]their range on a single charge is limited-and recharging can take hours.
[00:27]However, a team of German engineers thinks it may be possible to produce a battery
[00:34]for an electric car which can be recharged in minutes,
[00:39]in a manner similar to refueling a car with petrol.
[00:44]The technology that Jens Noack and his colleagues at the Fraunhofer Institute
[00:50]for Chemical Technology in Pfinztal are experimenting with is called a flow battery.
[00:58]All batteries work by converting electrical energy into chemical energy during charging,
[01:08]and then converting it back into electricity as the battery is discharged.
[01:15]Traditional batteries store the chemical energy in two solid electrodes;
[01:22]flow batteries store it in the liquid electrolyte in which the electrodes are immersed.
[01:30]The electrolyte is stored in an external tank
[01:34]and pumped through the battery's cells to convert chemical energy into electricity.
[01:42]When the electrolyte has been discharged, it can be pumped back through again
[01:48]while a current is applied in order to recharge it.
[01:52]There is, though, another way to recharge a flow battery:
[01:58]pump out the discharged electrolyte
[02:01]and replace it with a solution that has been recharged elsewhere.
[02:06]In a car, says Mr Noack, this process could be done at a garage
[02:12]in not much more time than it takes to fill up a conventional car with petrol.
[02:19]Such batteries are already in use,
[02:23]but mainly in stationary applications.
[02:27]So-called "redox" flow batteries are sometimes used to balance grid power
[02:35]and store energy from wind turbines or solar panels.
[02:41]The term "redox" refers to the electrochemical potential between two different electrolytes.
[02:50]These are pumped through a cell, separated by a membrane. Ions passing through the membrane,
[02:59]as one solution is reduced and the other oxidized,
[03:04]create a current which powers an external circuit.
[03:09]One of the most efficient redox flow batteries was developed in the 1980s
[03:16]at the University of New South Wales in Australia.
[03:22]It uses vanadium in both electrolytes.
[03:26]Vanadium can exist in solution in several different oxidation states.
[03:34]Using the same element in both electrolytes avoids contamination problems.
[03:41]Another advantage of a vanadium redox flow battery is that its capacity is limited
[03:50]only by the size of the tanks used to store its electrolytes.