Perhaps the biggest hurdle to the widespread uptake of electric cars is not their comparatively short range, but the long time it takes to re-charge the batteries. If a car like the Nissan Leaf manages only an 80-90 mile range as this test suggests (as against the manufacturers’ 108 miles from a tank of sparks) you at least want to know you can re-charge and continue your journey, as with an internal combustion engine. In practice though, a Leaf takes seven to eight hours for a full charge using a 240V – 16A outlet as in the UK. Public quick-charging points are said to give an 80% charge in about 30 minutes. That’s OK if you want to have a cup of coffee and read the papers, but you don’t want to be doing that every 80 miles on a longer journey. So faster charging that would allow, say, a 2-minute turnaround similar to refueling a conventional car could open up use of cars like the Leaf to mainstream rather than just city users.
Well, research at the University of Illinois holds out just that promise, according to an article by the Economist. Their most successful experiment has recharged to almost 100% in two minutes. In addition, the technology applies equally well to nickel hydride batteries as to lithium ion. As the article explains, a battery has two electrodes, an anode and a cathode, that are connected by an electrically conductive materialâ€generally a liquidâ€called an electrolyte. Under normal discharge conditions, negatively charged electrons flow from the anode to the cathode providing a source of electric current. To balance the circuit, positively charged ions flow from the anode to cathode to balance the charges. During recharging, an external source of electrons flows in the opposite direction replacing the positively charged ions ready for discharge again in the future. The speed at which a battery recharges depends on the surface area of contact between the electrolyte and the cathode, but crucially, the amount of energy a battery can hold is dependent on the volume of the electrodes. What is needed is both a high volume and a high surface area for cathode and anode.
Dr. Paul Braun at the university has developed a process to achieve just such an outcome. His starting material is made of closely packed polystyrene spheres about 0.001 millimeters (0.00004 inches) in diameter. The next stage is to fill the gaps between the spheres with nickel by electro-deposition, similar to nickel-plating a piece of steel. After that, the material is heated, to melt the polystyrene and leave a sponge made of metallic nickel. This creates an electrically conductive framework suitable for coating with materials normally used to make cathodes such as a substance called nickel oxyhydroxide for the nickel-metal hydride version of the battery and lithium ion-spiked manganese dioxide for the lithium ion version.
The result is a charging rate 10 to 100 times faster than a normal commercial battery, but with an increase in production costs estimated to be only 20-30 percent more than current methods. 20-30 percent is not to be dismissed, as the battery is a very significant part of the cost of new electric vehicles, but for the convenience of internal combustion “refueling rates, it may be a price worth paying over the life of the car.
How far Dr. Braun’s technology is from commercial application is unclear, but if the wall of money that has poured into new battery technologies is anything to go by, there is no lack of enthusiasm out there to find just such a solution to improving charging rates.