Large-scale electric energy storage is fundamental to the use of renewable energy. Recently, research and development efforts on room-temperature sodium-ion batteries (NIBs) have been revitalized, as NIBs are considered promising, low-cost alternatives to the current Li-ion battery technology for large-scale applications. Herein, we introduce a novel layered oxide cathode material, NaNiMnO. This new compound provides a high reversible capacity of 138 mAh g and an average potential of 3.25 V vs Na/Na with a single smooth voltage profile. Its remarkable rate and cycling performances are attributed to the elimination of the P2-O2 phase transition upon cycling to 4.5 V. The first charge process yields an abnormally excess capacity, which has yet to be observed in other P2 layered oxides. Metal K-edge XANES results show that the major charge compensation at the metal site during Na-ion deintercalation is achieved via the oxidation of nickel (Ni) ions, whereas, to a large extent, manganese (Mn) ions remain in their Mn state. Interestingly, electron energy loss spectroscopy (EELS) and soft X-ray absorption spectroscopy (sXAS) results reveal differences in electronic structures in the bulk and at the surface of electrochemically cycled particles. At the surface, transition metal ions (TM ions) are in a lower valence state than in the bulk, and the O K-edge prepeak disappears. On the basis of previous reports on related Li-excess LIB cathodes, it is proposed that part of the charge compensation mechanism during the first cycle takes place at the lattice oxygen site, resulting in a surface to bulk transition metal gradient. We believe that by optimizing and controlling oxygen activity, Na layered oxide materials with higher capacities can be designed.

Atomic layer deposition (ALD) is a commonly used coating technique for lithium ion battery electrodes. Recently, it has been applied to sodium ion battery anode materials. ALD is known to improve the cycling performance, Coulombic efficiency of batteries, and maintain electrode integrity. Here, the electrochemical performance of uncoated P2-NaNiMnO electrodes is compared to that of ALD-coated AlO P2-NaNiMnO electrodes. Given that ALD coatings are in the early stage of development for NIB cathode materials, little is known about how ALD coatings, in particular aluminum oxide (AlO), affect the electrode-electrolyte interface. Therefore, full characterizations of its effects are presented in this work. For the first time, X-ray photoelectron spectroscopy (XPS) is used to elucidate the cathode electrolyte interphase (CEI) on ALD-coated electrodes. It contains less carbonate species and more inorganic species, which allows for fast Na kinetics, resulting in significant increase in Coulombic efficiency and decrease in cathode impedance. The effectiveness of AlO ALD coating is also surprisingly reflected in the enhanced mechanical stability of the particle which prevents particle exfoliation.

X-ray microscopy can provide unique chemical, electronic, and structural insights into perovskite materials and devices leveraging bright, tunable synchrotron X-ray sources. Over the last decade, fundamental understanding of halide perovskites and their impressive performance in optoelectronic devices has been furthered by rigorous research regarding their structural and chemical properties. Herein, studies of perovskites are reviewed that have used X-ray imaging, spectroscopy, and scattering microscopies that have proven valuable tools toward understanding the role of defects, impurities, and processing on perovskite material properties and device performance. Together these microscopic investigations have augmented our understanding of the This article is protected by copyright. All rights reserved. 2 internal workings of perovskites and help steer the perovskite community toward promising directions. In many ways, X-ray microscopy of perovskites is still in its infancy, which leaves many exciting paths unexplored including new super-resolution, multimodal, in situ, and operando experiments. To explore possibilities, pioneering X-ray microscopy along these lines is briefly highlighted from other semiconductor systems including silicon, CdTe, GaAs, CuIn x Ga 1-x Se 2 , and organic photovoltaics. An overview is provided on the progress made in utilizing X-ray microscopy for perovskites and present opportunities and challenges for future work.

The mechanical properties of π-conjugated (semiconducting) polymers are a key determinant of the stability and manufacturability of devices envisioned for applications in energy and healthcare. These propertiesincluding modulus, extensibility, toughness, and strengthare influenced by the morphology of the solid film, which depends on the method of processing. To date, the majority of work done on the mechanical properties of semiconducting polymers has been performed on films deposited by spin coating, a process not amenable to the manufacturing of largearea films. Here, we compare the mechanical properties of thin films of regioregular poly(3-heptylthiophene) (P3HpT) produced by three scalable deposition processesinterfacial spreading, solution shearing, and spray coatingand spin coating (as a reference). Our results lead to four principal conclusions. (1) Spray-coated films have poor mechanical robustness due to defects and inhomogeneous thickness. (2) Sheared films show the highest modulus, strength, and toughness, likely resulting from a decrease in free volume. (3) Interfacially spread films show a lower modulus but greater fracture strain than spin-coated films. (4) The trends observed in the tensile behavior of films cast using different deposition processes held true for both P3HpT and poly(3butylthiophene) (P3BT), an analogue with a higher glass transition temperature. Grazing incidence X-ray diffraction and ultraviolet−visible spectroscopy reveal many notable differences in the solid structures of P3HpT films generated by all four processes. While these morphological differences provide possible explanations for differences in the electronic properties (hole mobility), we find that the mechanical properties of the film are dominated by the free volume and surface topography. In field-effect transistors, spread films had mobilities more than 1 magnitude greater than any other films, likely due to a relatively high proportion of edge-on texturing and long coherence length in the crystalline domains. Overall, spread films offer the best combination of deformability and charge-transport properties.

Conventional processes for depositing thin films of conjugated polymers are restricted to those based on vapor, liquid, and solution‐phase precursors. Each of these methods bear some limitations. For example, low‐bandgap polymers with alternating donor–acceptor structures cannot be deposited from the vapor phase, and solution‐phase deposition is always subject to issues related to the incompatibility of the substrate with the solvent. Here, a technique to enable deposition of large‐area, ultra‐thin films (≈20 nm or more), which are transferred from the surface of water, is demonstrated. From the water, these pre‐solidified films can then be transferred to a desired substrate, circumventing limitations such as solvent orthogonality. The quality of these films is characterized by a variety of imaging and electrochemical measurements. Mechanical toughness is identified as a limiting property of polymer compatibility, along with some strategies to address this limitation. As a demonstration, the films are used as the hole‐transport layer in perovskite solar cells, in which their performance is shown to be comparable to controls formed by spin‐coating.