Why batteries lose their ability to hold a charge as they age

Wednesday, October 20, 2010

WASHINGTON - Scientists have found that batteries lose their ability to hold a charge as they age because the finely structured nanomaterials present in the battery get coarsened in size.

Researchers at the Ohio State University had been trying to study why batteries lose their ability to hold a charge as they age-specifically lithium-ion batteries, which have generated a lot of buzz for their potential to power the electric cars of the future.

Yann Guezennec and Giorgio Rizzoni of OSU developed new experimental facilities and procedures to charge and discharge commercially-available Li-ion batteries thousands of times over many months in a variety of conditions designed to mimic how these batteries are actually used by hybrid and all-electric vehicles.

To understand the results of this testing, Bharat Bhushan, Suresh Babu, and Lei Raymond Cao studied the materials inside of the batteries to help determine how this aging manifests itself in the structure of the electrode materials.

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 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 of the Center for Automotive Research at OSU.he researchers suspect that the coarsening of the cathode may be behind this loss of lithium.

The results were presented at the AVS 57th International Symposium and Exhibition, in New Mexico. (ANI)

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