Untangling a Strange Phenomenon that Both Helps and Hurts Lithium-Ion Battery Performance

Estimated reading time: 4 minutes

But imagine in the sponge relay that with every subsequent soak, the structure of the sponge changes: the fibers stiffen and bundle together, eating up the empty space that makes the material so efficient at absorbing water. Oxygen oxidation does something similar. The authors’ previous study, published in Nature Communications, showed that every time lithium ions cycle out of the cathode into the anode, some transition metal atoms sneak in to take their place and the atomic structure of the cathode becomes a little messier. The layered structure essential to the cathode’s performance slowly falls apart, sapping its voltage and capacity.

In this new study, the researchers showed that this is because yanking the electron from oxygen makes it want to form another bond and transition metal atoms have to move around to accommodate that bond, changing the atomic structure.

“This is the first paper that provides a complete model as to why these things are related and where a lot of the lithium-rich cathode’s unusual properties come from,” says Jihyun Hong, a Stanford and SLAC postdoc, now at the Korea Institute of Science and Technology (KIST).

Harnessing the Effect

Toney says it took the combination of theory and many experimental methods, done at SLAC’s Stanford Synchrotron Light Source (SSRL) as well as Berkeley Lab’s Advanced Light Source (ALS) and Molecular Foundry, to disentangle this complicated problem.

This combination allowed the team to conclusively demonstrate the strong driving force behind changes in the cathode’s bonding configuration during oxygen oxidation. The next step, Toney says, is to find ways to produce those changes without totally disrupting the cathode’s crystal structure.

“Because oxygen oxidation gives rise to extra energy density, being able to understand and control it is potentially a game changer in electric vehicles,” says William Chueh, Assistant Professor of Materials Sciences at Stanford, who co-led the study. “So far, progress in this space has been largely incremental, with improvements of only a few percent per year. If we can find a way to make this work, it would be a huge step forward in making this technology practical.”

The research team also included researchers from the University of California, Berkeley and DOE’s Argonne National Laboratory. SSRL, ALS and the Molecular Foundry are DOE Office of Science user facilities. This research was supported by the DOE offices of Science and Energy Efficiency and Renewable Energy Office of Vehicle Technologies, Battery Materials Research Program.

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