Any loss of lithium reduces the capacity and service life of lithium batteries. After the latest research led to the assumption that lithium is lost to the current collector during charging, researchers at Ruhr University Bochum, Germany, working with Professor Tong Li, the Helmholtz Institute Ulm, and a team led by Professor Dominic Bresser at the Karlsruhe Institute of Technology, Germany, took a closer look at this hypothesis. By using atom probe tomography, they were able to verify that lithium are indeed incorporated into the copper current collector. This loss increases with the number of charging cycles. “Understanding these processes is crucial for anode-free batteries of the future,” says Li. The researchers report their findings in the journal Advanced Energy Materials from July 10, 2026.

The copper current collector is a thin copper foil that serves as a substrate for the anode and collects electrons to lead them to the negative terminal. In lithium-metal batteries, lithium can diffuse into the copper current collector during the charge and discharge cycle. “However, it was previously unclear where the lithium ions accumulate,” explains Li. “It is difficult to detect lithium in copper because of a lack of analytical methods for tracing highly reactive and lightweight lithium.”

The research team utilized atom probe tomography, which allows the precise, three-dimensional mapping of any element with sub-nanometer resolution. This revealed that, after just one charge/discharge cycle, lithium is initially incorporated at the grain boundary and boundary junction of the copper foil. After three cycles, the surface of the copper foil becomes nanocrystalline and oxidized. The resulting defects further bind lithium and oxygen beneath the surface, leading to degradation of the copper current collector.

“All this information is important for understanding how the current collector influences the performance of lithium batteries of the future,” explains Li; lithium-metal batteries (LMBs), and recently zero-excess or anode-free LMBs are seen to be the next significant steps on the path toward even higher energy densities. These far surpass the currently prevailing lithium-ion technology. “The general assumption about zero-excess LMBs is that lithium does not diffuse into or interact with the copper current collector,” says Li. “the loss of lithium to the copper collector has been largely overlooked until now, in discussions about the performance degradation of LMBs.”