New Battery tech: Fast charging, No loss of capacity

A breakthrough in Lithium battery tech at MIT has enabled scientists to construct batteries that charge and discharge orders of magnitude faster than existing ones. The only change is the way that the battery material is constructed.  

The new batteries also lose capacity slower. In some experiments, the capacity was actually found to increase over several charge/discharge cycles. This could lead to smaller, lighter batteries. Expected in a phone near you within two to three years. [Link]

Traditionally, scientists have thought that the lithium ions responsible, along with electrons, for carrying charge across the battery simply move too slowly through the material.

About five years ago, however, Ceder and colleagues made a surprising discovery. Computer calculations of a well-known battery material, lithium iron phosphate, predicted that the material's lithium ions should actually be moving extremely quickly.

"If transport of the lithium ions was so fast, something else had to be the problem," Ceder said.

Further calculations showed that lithium ions can indeed move very quickly into the material but only through tunnels accessed from the surface. If a lithium ion at the surface is directly in front of a tunnel entrance, there's no problem: it proceeds efficiently into the tunnel. But if the ion isn't directly in front, it is prevented from reaching the tunnel entrance because it cannot move to access that entrance. 

Also, at Ars Technica: [Link]

At low discharge rates, a cell prepared from this material discharges completely to its theoretical limit (~166mAh/g). As the authors put it, "Capacity retention of the material is superior." Running it through 50 charge/discharge cycles revealed no significant change in the total capacity of the battery.

But the truly surprising features of the cell came when the authors tweaked the cathode to allow higher currents to be run into the cell. Increasing the rate by a factor of 100 dropped the total capacity down to about 110mAh/g, but increased the power rate by two orders of magnitude (that's a hundred-fold increase) compared to traditional lithium batteries. Amazingly, under these conditions, the charge capacity of the battery actually increased as it underwent more charge/discharge cycles. Doubling the charge transport from there cut the capacity in half, but again doubled the power rate. At this top rate, the entire battery would discharge in as little as nine seconds. That sort of performance had previously only been achieved using supercapacitors. 

However, 

A more significant problem is that these batteries may wind up facing an electric grid that was never meant to deal with them. A 1Wh cell phone battery could charge in 10 seconds, but would pull a hefty 360W in the process. A battery that's sufficient to run an electric vehicle could be fully charged in five minutes—which would make electric vehicles incredibly practical—but doing so would pull 180kW, which is most certainly not practical.