Researchers at the University of Illinois have used 3D X-ray tomography of an electrode to better understand what is happening on the inside of a lithium ion battery and build batteries with more storage capacity and longer life.
When a lithium battery is being charged, lithium ions embed themselves into host particles in the graphite anode and are stored there until needed to produce energy during the battery discharge. The graphite particles expand as the lithium ions enter them during charging, and contract when the ions exit them during discharging.
"Every time a battery is charged, the lithium ions enter the graphite, causing it to expand by about 10 percent in size, which puts a lot of stress on the graphite particles," said John Lambros, professor in the Department of Aerospace Engineering and director of the Advanced Materials Testing and Evaluation Laboratory (AMTEL) at the university. "As this expansion-contraction process continues with each successive charge-discharge cycle of the battery, the host particles begin to fragment and lose their capacity to store the lithium and may also separate from the surrounding matrix leading to loss of conductivity.
"If we can determine how the graphite particles fail in the interior of the electrode, we may be able to suppress these problems and learn how to extend the life of the battery. So we wanted to see in a working anode how the graphite particles expand when the lithium enters them. You can certainly let the process happen and then measure how much the electrode grows to see the global strain--but with the X-rays we can look inside the electrode and get internal local measurements of expansion as lithiation progresses."