Lab study finds lithium ions cluster in battery electrolytes

For a long time, battery scientists assumed that lithium ions drift through the liquid inside a cell largely alone. A team at Columbia University now reports that they often do not. In a study published in Nature, the researchers found that up to 40% of lithium ions in standard electrolytes group together into multi-ion clusters, and that clustering grows as salt concentration rises.

The electrolyte is the liquid that carries lithium ions between a battery's electrodes. It also drives the formation of the solid electrolyte interphase, a thin protective film on the anode that shapes both how long a battery lasts and how safe it is. Until now, the atomic-level structure behind that film had been difficult to pin down. The study was co-led by Richard Friesner of Columbia's Department of Chemistry, with Alexander Urban, Lauren Marbella and Daniel Steingart of the School of Engineering and Applied Science. The simulations relied on machine learning force field technology provided by Schrödinger Inc., with support from the New York Structural Biology Center.

The simulations showed lithium ions bunching up even without anions, the negatively charged ions that had been assumed to be needed for such groupings. Quantum chemical calculations indicate that these multi-lithium clusters are unusually easy to reduce, meaning they take up electrons readily. That makes them likely candidates for the intermediate steps that build the protective film, which the researchers describe as critical for longevity and safety.

The simulations were only half of the work. Columbia's engineering school ran experiments, and the team reports that its machine learning simulations showed strong agreement with a wide range of experimental data on condensed-phase systems. Friesner stressed that confirming the predicted chemistry in the lab was extremely difficult. This is a laboratory result, and it has not yet been turned into a commercial electrolyte.

For battery chemists designing next-generation electrolytes, the clusters offer a concrete target: a model of what happens at the atomic scale, which the authors say can guide work on performance, stability and charge rates. The team says the insights have the potential to produce higher-capacity, faster-charging and longer-lasting batteries, but it gives no timeline for when that could reach a product. Friesner also argues that the same blend of simulation and experiment could help with biology and materials science more broadly.