The lithium-ion batteries commonly used in hybrid and electric-only cars could fail earlier than expected because of a newly-discovered problem with the current collector.
Researchers led by Ohio State University engineers examined used car batteries and discovered that over time lithium accumulates beyond the battery electrodes, in the current collector – a sheet of copper which facilitates electron transfer between the electrodes and the car’s electrical system.
“Our study shows that the copper current collector plays a role in the performance of the battery,” says Professor Bharat Bhushan.
Inside a lithium-ion battery, lithium ions shuttle back and forth between the anode and cathode of the battery – and the team had already discovered that, as the battery ages, cyclable lithium permanently builds up on the surface of the anode, affecting the battery’s charge capacity.
Now,though, they’ve found that lithium migrates through the anode to build up on the copper current collector as well.
“We didn’t set out to find lithium in the current collector, so you could say we accidentally discovered it, and how it got there is a bit of a mystery,” says Bushan. “As far as we know, nobody has ever expected active lithium to migrate inside the current collector.”
In tests, thr group found a ratio of the number of copper atoms in the collector to the number of lithium atoms that had collected there of up to 0.08 percent, or approximately one lithium atom per 1250 copper atoms in the collector.
That’s enough, says the team, to affect the electrical performance of the current collector – and, in turn, the performance of a battery. He says battery makers should investigate and design new materials that might prevent lithium from escaping the electrode material.