November 2, 2010 20:41 by Ty
Researchers at Ohio State University are studying why aged batteries don’t maintain their full charging capacity and lose their charge as they get older. Lithium-ion batteries are being focused on because they have been the best choice for use in electric vehicles and hybrid vehicles. The Li-ion batteries are being tested in various conditions ranging from hot desert temperatures to cold sub zero temperatures. Different battery loads of charge / discharge rates are also being tested. All battery tests are being done to mock real world situations with temperatures and load in a controlled environment.
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After extensive testing and battery aging was completed and battery capacity began to drop, the Li-ion batteries were then opened up and researched at a microscopic level.
When the batteries died, the scientists dissected them and used a technique called infrared thermal imaging to search for problem areas in each electrode, a 1.5-meter-long strip of metal tape coated with oxide and rolled up like a jelly roll. They then took a closer look at these problem areas using a variety of techniques with different length scale resolutions (e.g. scanning electron microscopy, atomic force microscope, scanning spreading resistance microscopy, Kelvin probe microscopy, transmission electron microscopy) and discovered that the finely-structured nanomaterials on these electrodes that allow the battery rapidly charge and discharge had coarsened in size.
Additional studies of the aged batteries, using neutron depth profiling, revealed that a fraction of the lithium that is responsible, in ion form, for shuttling electric charge between electrodes during charging and discharging, was no longer available for charge transfer, but was irreversibly lost from the cathode to the anode.
"We can clearly see that an aged sample versus and unaged sample has much lower lithium concentration in the cathode," said Rizzoni, director of the Center for Automotive Research at OSU. "It has essentially combined with anode material in an irreversible way." (Source: How Batteries Grow Old)
Discovering why there is a lower lithium concentration and preserving or reversing the natural reaction could be the key in future Li-ion battery manufacturing to produce longer lasting and more power batteries.