Researchers from Ruhr-Universität Bochum, the Helmholtz Institute Ulm and the Karlsruhe Institute of Technology (KIT) have identified a previously unconfirmed mechanism that contributes to the aging of lithium-metal batteries, revealing that lithium ions become permanently trapped within the copper current collector during battery operation.
The findings, published in Advanced Energy Materials, suggest that this hidden lithium loss may play a larger role in battery capacity degradation than previously recognized, particularly in next-generation lithium-metal and anode-free battery technologies.
Lithium Becomes Trapped in Copper Collector
Using atom probe tomography, the research team directly observed lithium ions penetrating the copper current collector during repeated charging and discharging cycles.
The three-dimensional imaging technique enabled the scientists to map individual chemical elements with sub-nanometer resolution, allowing them to identify the precise locations where lithium accumulated within the copper structure.
According to the researchers, every lithium ion that becomes permanently bound inside the copper collector is no longer available to participate in the battery’s electrochemical reactions, reducing the cell’s overall capacity and contributing to performance degradation over time.
The study found that lithium begins accumulating at grain boundaries and internal interfaces within the copper foil during the very first charge-discharge cycle.
As cycling continues, the surface of the current collector gradually transforms into a nanocrystalline structure while also undergoing oxidation. These structural changes create additional defects that trap even more lithium and oxygen beneath the surface, while accelerating degradation of the copper collector itself.
Findings Challenge Existing Assumptions
The researchers said their observations challenge the long-standing assumption that lithium interacts only minimally with copper current collectors.
Instead, the results indicate that lithium loss to the current collector has likely been underestimated as a contributor to capacity fade in lithium-metal and anode-free battery cells.
These battery technologies are considered promising candidates for achieving significantly higher energy densities than conventional lithium-ion batteries, making a better understanding of their aging mechanisms increasingly important.
Implications for Future Battery Development
The findings come as research institutions and manufacturers continue investing in next-generation battery technologies.
The researchers noted that improved knowledge of lithium degradation mechanisms could help optimize future battery designs and manufacturing processes for high-energy-density cells.
One example is the Fraunhofer Research Production Battery Cell (FFB) facility in Münster, which is developing large-scale research infrastructure to evaluate emerging battery chemistries and production methods.
The team said identifying and mitigating lithium loss within current collectors could play an important role in extending battery life and improving the commercial viability of lithium-metal and anode-free batteries as they move toward industrial-scale production.
