To improve the energy/power density of energy storage materials, numerous efforts have focused on the exploration of new structure prototypes, in particular metal-organic fameworks, Prussian blue analogues, open-framework oxides, and polyanion salts. Here we report a novel pyrochlore phase that appears to be useful as a high-capacity cathode for Li and Na batteries. It is an iron fluoride polymorph characterized by an intersecting tunnel structure, providing the space for accommodation and transport of Li and Na ions. It is prepared using hydrolyzable ionic liquids, which serve as reaction educts and structure-directing agents not only as far as the chemical structure is concerned but also in terms of morphology (shape, defect structure, electrode network structure). A capacity higher than 220 mA h g(-1) (for Li and Na storage) and a lifetime of at least 300 cycles (for Li storage) are demonstrated.

Open framework materials as battery electrodes are drawing much more attention recently in view of the requirement on further improving energy storage and power densities, as well as use of a nonlithium cation (such as Na + and Mg 2+ ) transport. In this work, we show a novel top-down approach to prepare fluoride-based open framework (HTB-type FeF 3 •0.33H 2 O) as Liand Na-storage cathode material, characterized by a topotactically solid−solid phase transformation and particle nanosizing with a 100% conversion yield. During this process, the typical Fe-based octahedral chains which are isolated in FeF 3 •3H 2 O precursor are well preserved but are connected with each other, triggered by the alleviated release of hydration water in an ionic liquid (IL) ambience. A comprehensive IL-based scenario to synthesize nanostructured open framework fluorides involving dissolution−precipitation, ionothermal and solid−solid breakdown methods is discussed, mainly depending on how the FeF 6 octahedra are produced and linked.

The magnetic coupling interaction of Mn2+–Mn2+ in Mn2+-included phosphors could induce a shorter emission decay time, compared with that of isolated Mn2+, which could overcome the photoluminescence (PL) saturation when stimulated by a high photon flux due to the long lifetime of the Mn2+ excited state. However, few studies have directly proved the Mn2+–Mn2+ coupling effect on the PL decay. In this paper, the effect on PL of CsMnCl3 (CMC) and its hydrates is revealed by photomagnetism results, excluding the interference effects of site symmetry and phonon energy. The antiferromagnetic interaction of the CMC is larger when Mn2+ at a photoexcited state than at a dark state, which is contrary to the hydrates with weak Mn2+–Mn2+ interaction. This research not only helps researchers to understand the fundamental optical process but also is instructive for designing high performance Mn2+-doped phosphors in the field of displays and lighting.

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Exploring novel structure prototype and mineral phase, especially open framework material, is crucial to developing high-performance Na-ion battery cathodes in view of potentially faster intrinsic diffusion of Na + in lattices. Perovskite phases have been widely applied in solar cells, fuel cells, and electrocatalysis; however, they are rarely attempted as energy storage electrode materials. This study proposes pre-expanding perovskite iron fluoride (KFeF 3 ) framework by stuffing large-sized K + as a channel filler, which is advantageous over Na + , NH 4 + , and H 2 O molecule filler in terms of structure robustness, symmetry, and connectivity. K + stuffing leads to the preservation of a more "regular" cubic phase with fast isotropic 3D diffusion as a consequence of no distortion of FeF 6 octahedra during K-Na electrochemical exchange and following Na-insertion cycling. High-rate Na-storage is achievable with a reversible capacity of 110, 70, and 40 mAh g −1 at 0.1, 2, and 10 C, respectively, for this open framework fluoride cathode, benefiting from solid solution electrochemical behavior and high intrinsic diffusion coefficient. It is thought that this rate performance is currently the best among Na-storage fluoride materials.