If you add more lithium to the positive electrode of a lithium-ion battery, it can store much more charge in the same amount of space, theoretically powering an electric car 30 to 50 percent farther between charges. But these lithium-rich cathodes quickly lose voltage, and years of research have not been able to pin down why—until now.
Lithium-rich cathodes consist of layers of lithium sandwiched between layers of transition-metal oxides—elements like nickel, manganese, or cobalt combined with oxygen. When lithium-rich cathodes charge, several things happen: lithium ions move from the cathode into the anode, transition-metal atoms take their place, and oxygen atoms release electrons.
In this work, collaborators from Berkeley Lab, SLAC National Accelerator Laboratory, Stanford University, and Samsung created a comprehensive picture of how the chemical processes that lead to high capacity are linked to changes in atomic structure that sap performance.
At the ALS, researchers probed the material’s oxygen chemistry using an advanced form of soft x-ray resonant inelastic x-ray scattering (iRIXS) at Beamline 8.0.1 and scanning transmission x-ray microscopy (STXM) at Beamlines 11.0.2 and 188.8.131.52. At Stanford Synchrotron Radiation Lightsource (SSRL), hard x-rays were used to probe structural changes. The cathodes were made by the Samsung Advanced Institute of Technology, and theoretical modeling was done at Berkeley Lab’s Molecular Foundry.
The results illuminate a promising pathway for optimizing the performance of lithium-rich cathodes by controlling the way their atomic structure evolves as a battery charges and discharges.
Publication: W.E. Gent, K. Lim, Y. Liang, Q. Li, T. Barnes, S.-J. Ahn, K.H. Stone, M. McIntire, J. Hong, J.H. Song, Y. Li, A. Mehta, S. Ermon, T. Tyliszczak, D. Kilcoyne, D. Vine, J.-H. Park, S.-K. Doo, M.F. Toney, W. Yang, D. Prendergast, and W.C. Chueh, “Coupling Between Oxygen Redox and Cation Migration Explains Unusual Electrochemistry in Lithium-Rich Layered Oxides,” Nat. Commun. 8, 2091 (2017), doi:10.1038/s41467-017-02041-x.
Adapted from the Berkeley Lab press release, “X-Rays Provide Key Insights on Path to Lithium-Rich Battery Electrode,” and the SLAC press release, “Scientists Discover Path to Improving Game-Changing Battery Electrode.”