Study Shows How Lithium-Ion Batteries Age & Degrade

Chevy Volt battery photo

Photo: GM, Chevy Volt lithium-ion battery.
Understanding Why So We Can Hopefully Do Something About It
Researchers at the Ohio State University have been testing lithium-ion batteries, the kind used in the latest electric and hybrid vehicles, to find out how and why their performance degrades with age and use. The OSU lab is set up so that the batteries can be charged and discharged many times in difference conditions (hot like Arizona, cold like Alaska) over many months, mimicking real-world usage patterns as closely are possible.
Chevy Volt battery photo

Photo: GM, Chevy Volt lithium-ion battery.
Slicing and Dicing
Once the batteries were sufficiently aged and degraded, the researchers opened them up to see what was going on inside at the 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. (source)

It turns out that there is a much lower lithium concentration in the cathode after the battery has aged. The researchers think that knowing better what is happening there "could point battery manufacturers in the right direction for making durable batteries with longer lifetimes."

Via Newswise, ABG
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