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Why lithium-ion cells go bad

Research work recently conducted by several engineering faculty members at Ohio State University may eventually lead to lithium-ion batteries that last longer.

Researchers Giorgio Rizzoni, the Director for OSU's Center for Automotive Research, and Mechanical Engineering Professor Yann Guezennec, created experimental facilities and procedures that mimicked the environment in which hybrid and all-electric vehicles, using lithium-ion batteries, operate.

In the midst of all the charging and discharging of batteries, Professor Bharat Bhushan and Assistant Professor Lei Raymond Cao, both of the mechanical and aerospace engineering department, and Associate Professor Suresh Babu, materials science engineering, began to investigate how the aging of the batteries' electrode materials influenced battery life. Using infrared thermal imaging and a number of other methods, it became apparent that the coarsening of nanomaterials on electrodes is likely behind the degradation of lithium-ion batteries.

The researchers recently described their work in a paper presented at the AVS 57th International Symposium & Exhibition in Albuquerque. They say they have identified and tested a set of experimental techniques for multi-scale characterization of the cathode in the Li-ion batteries. The electrical properties are studied using the electrochemical impedance spectroscopy and scanning spreading resistance microscopy. The structural degradation is studied using the infrared thermal imaging (meters), a scanning electron microscope (micro), X-ray diffraction (micro), atomic force microscope (micro to nano), transmission electron microscope (micro) and electron energy loss spectroscopy.They also came up with a relatively new neutron depth profiling technique to study the transport and concentration of lithium within the few microns of the cathode thickness.

They used these techniques to check out an unaged and an aged LiFePO4 based Li-ion battery. They found that a fraction of the lithium ions responsible 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. All in all, the aged sample had much lower lithium concentration in the cathode. The lithium had combined with anode material irreversibly.

More info: http://mae.osu.edu/news/2010/10/infrared-thermal-imaging-used-study-lithium-ion-battery-life

http://www.avssymposium.org/Open/SearchPapers.aspx?PaperNumber=AS-TuP-9

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