Electron paramagnetic resonance imaging for real-time monitoring of Li-ion batteries

Batteries for electrical storage are central to any future alternative energy paradigm. The ability to probe the redox mechanisms occurring at electrodes during their operation is essential to improve battery performances. Here we present the first report on Electron Paramagnetic Resonance operando spectroscopy and in situ imaging of a Li-ion battery using Li 2 Ru 0.75 Sn 0.25 O 3 , a high-capacity (>270 mAh g −1 ) Li-rich layered oxide, as positive electrode. By monitoring operando the electron paramagnetic resonance signals of Ru 5+ and paramagnetic oxygen species, we unambiguously prove the formation of reversible (O 2 ) n − species that contribute to their high capacity. In addition, we visualize by imaging with micrometric resolution the plating/stripping of Li at the negative electrode and highlight the zones of nucleation and growth of Ru 5+ /oxygen species at the positive electrode. This efficient way to locate ‘electron’-related phenomena opens a new area in the field of battery characterization that should enable future breakthroughs in battery research. It is important as well as challenging to in situ probe redox mechanisms occurring at battery electrodes. Here, the authors develop an in situ electron paramagnetic resonance imaging technique and provide measurements on the nucleation growth of the anionic and cationic redox species at a battery electrode.