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REPORT OF THE BASIC RESEARCH NEEDS WORKSHOP New and emerging electron microscopy techniques to benefit energy storage research: Recent advances in electronics and optics have stimulated the development of new experimental microscopy techniques. Integrating and optimizing these emerging techniques so that they may be applied to energy storage research will remain an area of significant interest. One of the most important instrument advances in recent years has been the invention of direct electron detectors, which enable high-speed imaging with a frame rate of over 4,000 frames per second. Such fast imaging has significantly enhanced the temporal resolution for in situ characterization and has also improved low-dose imaging capabilities.24 One significant advantage of these fast cameras is that they enable dramatically improved ptychographic imaging.25,26 Scanning transmission electron microscopy- based ptychography records a full series of “ronchigram” (or convergent beam electron diffraction) patterns as a function of the probe position, resulting in four-dimensional datasets, two in reciprocal space and two in real space. Such 4D datasets have recently been used to reconstruct internal electric or magnetic fields in a specimen at atomic resolution.27 This means that with the integration of in situ electrochemical cycling, electron microscopy may be able to map local electric potential simultaneously with chemical and structural analysis at the atomic scale. This new capability will significantly enhance our understanding of the behavior of solid-solid interfaces and boundaries, where multiple, simultaneous phenomena spanning chemical, electrochemical, mechanical stability, and space charge effects contribute to the overall performance. It must also be mentioned that interfaces are three-dimensional, non-centrosymmetric structures, and their spatial and temporal behavior must be interrogated in 3D at the nanometer to atomic scale. As a result of newly developed atomic-scale tomography, reconstructing the 3D atomic structures of such embedded features is now feasible,21 and dynamic, nanometer-scale chemical tomography has also been demonstrated.28 Thus, it may eventually be possible to combine determinations of both the local electric potential and the 3D atomic structure under in situ cycling. As a result, state-of-the-art scanning and transmission electron microscopy methods will allow us to develop a comprehensive microscopic understanding of the critical interfacial phenomena at the same spatial and temporal coordination, under in situ electrochemical conditions. STEM EELS bcd a Annular bright field – STEM in-situ non-volatile cell Si NW Li Lithiation in-situ volatile cell ac Conducting Epoxy Au Rod A SnO2 Nanowires IL Potentiostat LiCoO2 Au Rod L12 L10 O-K 540 560 580 Energy Loss (eV) 1 nm EDX Sample Electron Beam EELS spectrometer or fast camera Figure 3.6.1. State-of-art and emerging STEM-based techniques and their applications to battery research. STEM = scanning transmission electron microscopy; EELS = electron energy loss spectroscopy; EDX = energy dispersive X-ray analysis; LAADF = low-angle annular dark field; ABF = annular bright field; DPC = differential phase contrast; HAADF = high-angle annular dark field. From Refs. 13, 17, 20-22. Image on upper right from Ref. 23, with permission of American Chemical Society. Future development of electron microscopy techniques: Despite these recent technique developments, the fundamental limits of spatial, energy, and temporal resolution, as well as dose, speed, and chemical sensitivity, have not yet been fully realized. Future microscopy development is needed to address grand scientific challenges in electrical energy storage research. For example, simultaneous high spatial and temporal resolution cannot be achieved, and thus the transport of charge carriers cannot be traced directly at the atomic scale. Energy resolution is not sufficient to probe intermediate electronic states, which dictate 148 PANEL 6 REPORT a pristine b fully charged 1 nm 4-D electron ptychography Atomic scale tomography b L12 [001] [100] L12 Pt Fe [100] [010] L12 [001] fcc A1 L10 [010] L10 L10 L12 L12 Intensity (a.u.)PDF Image | Next Generation Electrical Energy Storage
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