Challenges and advances regarding LiVPO4: From HR-STEM & EELS to novel scanning diffraction techniques

Recent advances in electron microscopical techniques now enable valuable insights into ion
transport chemical and crystallographic processes of in battery materials. Influences The
influence of battery cycling on the local crystal behavior structure and chemistry was
successfully shown on LiFePO4 cathodes at the atomic level, [1] using utilizing the electron
dose efficient integrated Differential Phase Contrast (iDPC) Imaging in a scanning
transmission electron microscope (STEM) (iDPC) [2], as well asin combination with Electron
Energy Loss Spectroscopy (EELS) in combination withand Selected Area Electron Diffraction
(SAED) [1,2]. For the more complex and way more beam sensitive, polycrystalline LiVPO4,
which exhibits polycrystalline behavior with crystals in ranging in the size offrom 10 nm to
100 nm, the usage application of these techniques is less straightforward. Orientation of
individual phases is rather problematic due to the main challenges lie in the small crystal size
and their rapid amorphization under electron beam illumination. We therefore employ 4DScanning
Confocal Electron Diffraction (4D-SCED) [3] for analyzing local crystal phases in
combination with High-Resolution and spectroscopic techniques. [3]. This technique is well
suited even for very beam sensitive materials, combining both the signal-to-noise ratio of
SAED with the high lateral resolution of conventional Nanobeam-Diffraction in the range of
~1 nm while still retaining low local electron dose requirements. Combining 4D-SCED with
zero-loss filtering allows for even better signal to noise ratio in k-space imaging. We further
discuss the advantages of 4D-SCED regarding the possibility of real-space phase mapping
as well as combination with other imaging techniques and show these advantages on triedand-
tested materials such as LiFePO4.