Classically, late transition-metal organometallic compounds promote multielectron processes solely through the change in oxidation state of the metal centre. In contrast, uranium typically undergoes single-electron chemistry. However, using redox-active ligands can engage multielectron reactivity at this metal in analogy to transition metals. Here we show that a redox-flexible pyridine(diimine) ligand can stabilize a series of highly reduced uranium coordination complexes by storing one, two or three electrons in the ligand. These species reduce organoazides easily to form uranium-nitrogen multiple bonds with the release of dinitrogen. The extent of ligand reduction dictates the formation of uranium mono-, bis- and tris(imido) products. Spectroscopic and structural characterization of these compounds supports the idea that electrons are stored in the ligand framework and used in subsequent reactivity. Computational analyses of the uranium imido products probed their molecular and electronic structures, which facilitated a comparison between the bonding in the tris(imido) structure and its tris(oxo) analogue.

Sodium-ion intercalation pseudocapacitance promises fast energy storage that is cheaper than lithium-ion-based systems. MoS 2 is an attractive sodium-ion host due to its large van der Waals gaps, high Na + mobility, and high electronic conductivity in the 1T phase. In this paper, we have quantified high levels (>90%) of pseudocapacitive charge storage in 30 μm thick MoS 2 nanocrystal-based composite electrodes, which can be charged to almost 50% of their 1C capacity in just under 40 s. In addition, very little decay is observed in the delivered capacity (retention of 97%) after 1800 cycles at a rate of 20C. Synchrotron-based operando X-ray diffraction shows that the pseudocapacitive performance is enabled through suppression of the trigonal 1T-MoS 2 to triclinic Na x MoS 2 phase transition in MoS 2 nanocrystals during charge−discharge.

Conventional cathodes for Li-ion batteries (LIBs) are reaching their theoretical capacity limits. One way to meet the growing demands for high-capacity LIBs is by developing so-called Li-rich cathode materials that greatly benefit from additional capacities from anionic moieties in the structure. Li-rich materials are intrinsically subject to higher degrees of (de)­intercalation, leaving the particles more prone to fractures and thus rapid capacity fade. Alkali-rich LiNaFeS2 reversibly cycles with capacities exceeding 300 mAh g–1, but its capacity fades faster than an isostructural material Li2FeS2. Using synchrotron-based transmission X-ray microscopy (TXM), we demonstrate that the capacity fade of LiNaFeS2 stems from particle fractures in the first charge cycle. We improve the cycling performance of LiNaFeS2 by means of cryomilling, which enhances capacity retention at cycle 50 by 76%. Through crystallographic and morphological characterization techniques, we confirm that cryomilling not only decreases particle and crystallite size while increasing microstrain but also prevents particles from fracturing. Cryomilling is a powerful tool to engineer nanoscale battery materials, and TXM allows the direct observation of morphological changes of the particles, which can be leveraged to develop next-generation cathode materials for LIBs.