In Situ, Operando Lithium K-edge Energy-loss Spectroscopy of Battery Materials

Development of next-generation safe, high energy lithium (Li)-batteries requires better understanding how electrodes function by characterizing electrochemical reaction and the associated ionic transport in anodes, cathodes and the involved interfaces/interphases.Such characterization is preferentially applied in the in situ, operando conditions, at relevant length scales.Most of the available techniques, such as those based on hard X-ray scattering, are suited for bulk measurement at electrode level, but very often have no adequate spatial resolution to probe local structural changes in single particles or interfaces [1].Highresolution scanning/transmission electron microscopy (S/TEM)electron energy-loss spectroscopy (EELS) is powerful, not only because of its high spatial resolution, but also the unparalleled analytical capability in imaging, diffraction, spectroscopy within a single instrument [2].However, directly probing Li, the "main player" in Li-batteries, poses a great challenge to traditional X-ray, electron diffraction and high-resolution S/TEM imaging due to its weak elastic scattering power and vulnerability to radiation damage.Here, we show that Li K-edge EELS can be a unique tool for probing Li, both of its spatial distribution and chemical state in the radiation-sensitive Li-battery materials [3][4], and may also be applied in situ, for tracking lithium ion transport in an operating battery electrode [5][6].