Lithium-ion batteries are the rechargeable batteries used in most hybrid-electric cars and all-electric cars as well. Inside, lithium ions shuttle back and forth between the anode and cathode of the battery – to the anode when the battery is charging, and back to the cathode when the battery is discharging.
Previously, the researchers determined that, during aging of the battery, cyclable lithium permanently builds up on the surface of the anode, and the battery loses charge capacity.
This latest study revealed that lithium migrates through the anode to build up on the copper current collector as well.
Previously, the researchers used NDP to study the cathodes and anodes of six off-the-shelf lithium-ion car batteries – one new battery and five batteries which they aged themselves in the laboratory – and found that lithium builds up on the anode surface over time.
To understand more about how these batteries degrade, the researchers have been studying the batteries further, at various scales ranging from the millimeter (millionths of a meter) down to the nanometer (billionths of a meter) with different techniques.
In the NDP technique, researchers pass neutrons through a material and capture the charged particles that emerge from the fission reaction between neutrons and lithium in the electrodes. Since different chemical elements emit a certain signature set of particles with specific energies, NDP can reveal the presence of impurities in a material.
In this latest study, NDP detected the presence of lithium in the copper current collector from one of the aged batteries. The detection was measured as a ratio of the number of copper atoms in the collector to the number of lithium atoms that had collected there. The test yielded a ratio of up to 0.08 percent, or approximately one lithium atom per 1250 copper atoms in the collector.
That’s a small number, but high enough that it could conceivably affect the electrical performance of the current collector – and, in turn, the performance of a battery, a researcher said. He hopes that battery makers will further investigate this phenomenon and use the information to design new materials that might prevent lithium from escaping the electrode material.
Next, the researchers will study the impedance, or internal electrical resistance, of lithium-ion batteries on the nanoscale.
This story is reprinted from material from Ohio State University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.