The microstructure of the active material of Li‐ion batteries has a crucial influence on local ion‐transport processes but is not yet well characterized. Atom probe tomography (APT), a method combining sub‐nanometer spatial resolution with sub‐parts‐per‐thousand chemical resolution is well suited for 3 D microstructural characterization. Herein, the results of the characterization of lithium (nickel)manganese oxides [L(N)MO] with APT are presented. Structural and chemical defects of different dimensions such as the segregation of Na impurities to grain boundaries and the appearance of a Ni‐rich foreign phase are detected. Furthermore, a lamellar microstructure correlated to fluctuations in the local Li content was observed, and its influence on Li transport in the material is discussed. In defect‐free regions, the lattice planes of LMO are reconstructed for the first time, and the high spatial resolution of APT is revealed. Thus, the results demonstrate the potential of APT for the 3 D microstructural characterization of LMO.

lithium manganese oxide spinel, tetragonal Li 2 Mn 2 O 4 , EELS, twinning, defects, interface, lithiation Spinel lithium manganese oxide (Li x Mn 2 O 4 ) is used as an active material in battery cathodes. It is a relatively inexpensive and environmentally friendly material, but suffers from capacity fade during use. The capacity losses are generally attributed to the formation of the tetragonal phase (x > 1) due to overpotentials at the surfaces of the micron-sized particles that are used in commercial electrodes. In this study, we investigate the mechanisms of tetragonal phase formation by performing electrochemical lithiation (discharging) in-situ in the transmission electron microscope (TEM) utilizing diffraction and high resolution as well as spectroscopy. We observe a sharp interface between the cubic spinel (x = 1) and the tetragonal phase (x = 2), that moves under lithium diffusion-control. The tetragonal phase forms as a complex nanotwinned microstructure, presumably to relieve the stresses due to expansion during lithiation. We propose 2 that the twinned microstructure stabilizes the tetragonal phase, adding to capacity loss upon deep discharge.

A method to characterize open-cell nanoporous materials with atom probe tomography (APT) has been developed. For this, open-cell nanoporous gold with pore diameters of around 50 nm was used as a model system, and filled by electron beam-induced deposition (EBID) to obtain a compact material. Two different EBID precursors were successfully tested-dicobalt octacarbonyl [Co2(CO)8] and diiron nonacarbonyl [Fe2(CO)9]. Penetration and filling depth are sufficient for focused ion beam-based APT sample preparation. With this approach, stable APT analysis of the nanoporous material can be performed. Reconstruction reveals the composition of the deposited precursor and the nanoporous material, as well as chemical information of the interfaces between them. Thus, it is shown that, using an appropriate EBID process, local chemical information in three dimensions with sub-nanometer resolution can be obtained from nanoporous materials using APT.

Atom probe tomography is routinely used for the characterization of materials microstructures, usually assuming that the microstructure is unaltered by the analysis. When analyzing ionic conductors, however, gradients in the chemical potential and the electric field penetrating dielectric atom probe specimens can cause significant ionic mobility. Although ionic mobility is undesirable when aiming for materials characterization, it offers a strategy to manipulate materials directly in situ in the atom probe. Here, we present experimental results on the analysis of the ionic conductor lithium-manganese-oxide with different atom probe techniques. We demonstrate that, at a temperature of 30 K, characterization of the materials microstructure is possible without measurable Li mobility. Also, we show that at 298 K the material can be deintercalated, in situ in the atom probe, without changing the manganese-oxide host structure. Combining in situ atom probe deintercalation and subsequent conventional characterization, we demonstrate a new methodological approach to study ionic conductors even in early stages of deintercalation.

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An inGeenious Programm:The GEENI programme (https://www.tu‐braunschweig.de/forschung/zentren/nff/geeni) in Lower Saxony in Germany on energy storage devices and electric mobility was set up to identify potential solutions how electric mobility can be best achieved without using fossil fuels. The challenges addressed start at the development of the electrode material and end at the test of full cells regarding their application in electric vehicles. More specifically, the challenge being addressed is to significantly increase the understanding of the processes in lithium batteries at various size scales through new, or enhanced, preparation, analytical, and numerical methods. This Special Issue provides an overview of the research jointly conducted at five Universities in Lower Saxony and the MEET Battery Research Center at the University of Münster with the aim to expand the current knowledge base relating to transport processes (ion, electron, and heat flow), material mechanical stresses, and manufacturing processes to substantially improve battery systems. The cover art illustration shows lithium manganese oxide particles, a commonly used electrode material. One of the long‐standing challenges is the microstructural characterization of the electrode material itself and identifying the influence of the different microstructures on the (de)intercalation of Li ions. Using atom probe tomography, it was possible to identify different phases, phase segragation as well as a lamellar microstructure and their effect on charging/discharging. Using this information, it should be possible to further improve electrode materials. You can read more in the Full Paper by Johannes Maier et al. at the University of Göttingen on page 1565 in Issue 12, 2016 (DOI: 10.1002/ente.201600210).

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