Sodium ion batteries, because of their sustainability attributes, could be an attractive alternative to Li-ion technology for specific applications. However, it remains challenging to design high energy density and moisture stable Na-based positive electrodes by implementing the anionic redox process that has recently boosted the capacity of Li-rich layered oxides.Here, we report the first anionic-redox active O3-NaLi1/3Mn2/3O2 phase obtained through a ceramic process by carefully controlling the delicate balance between synthesis conditions and stoichiometry. It shows a sustained reversible capacity of 190 mAh g −1 by redox processes on oxygen and manganese ions as deduced by combined HAXPES and mRIXS spectroscopy techniques. Remarkably, unlike any other anionic-redox layered oxides so far reported, O3-NaLi1/3Mn2/3O2 electrodes do not show voltage fade upon cycling. This finding is due to switching from the interlayer to intralayer migration of the Mn cations promoted by Li + displacement towards the alkali layer upon first Na + de-insertion. Another practical asset of this material stems from its moisture stability, hence facilitating its handling and electrode processing. Besides providing insightful fundamental findings pertaining to anion redox, this work offers future directions towards designing high energy density electrodes for advanced Na-ion batteries.
Metal-organic frameworks (MOFs) are promising multifunctional materials which can combine the properties of porous materials (catalysis, shape-selective absorption, gas storage, and purification) with those of dense inorganic phases (magnetism and optics). The performances of the new class of micro-and mesoporous metal-organic frameworks favorably compare with zeolites [1,2] in terms of either CO 2 capture, [3,4] hydrogen sorption, [5][6][7] or capabilities to host a wide variety of aqueous or nonaqueous solvent molecules for energy applications. These properties arise from the presence of large-size tunnels or cages within their skeleton, built up from organic (often polycarboxylates) and inorganic moieties of variable dimensionalities (clusters, chains, or slabs). Herein we report the first use of these materials as rechargeable intercalation electrodes with promise for application in the positive electrode in Li-based batteries.Despite these properties, the insulating nature of MOFs would appear to preclude their applicability for electrochemical intercalation. Nevertheless, the success of carboncoated LiFePO 4 insulating particles [8,9] recently showed that the search for electrode materials could be extended to compounds without a particularly high electronic conductivity, or a high diffusion coefficient for lithium ions. Yet, three unsuccessful attempts aimed at using MOFs as energy-storage electrodes have been reported. The first reports on Lielectrochemical reduction of a Ni-based microporous phosphate led to the irreversible decomposition of the solid into a nanocomposite electrode made of Ni nanoparticles embedded into a Li 2 O matrix through a conversion process. [10] Following the same line, the second example is related to the Ga-V phosphonate framework featuring redox-active oxovanadyl centers.[11] Very recently, Li et al. studied the electrochemical Li reactivity of a Zn-based MOF [12] in the presence of lithium ions and found, in accordance with a previous study, the decomposition of the precursor into a Znbased nanocomposite matrix containing Li 2 O. It was stated by the authors that this material was "not suitable for application in reversible lithium storage."One possible way to bypass these poorly reversible conversion/decomposition reactions is to use MOFs that are based on earlier (3d) transition metals to take advantage of the lower occupation of 3d-electron orbitals (higher oxidation states) and therefore higher M À O bond stability with respect to charge variations, and to bring about some long-range electron delocalization through the stabilization of class II or class III mixed-valence states associated with a doubleexchange mechanism. In recent years, such attempts to induce mixed valence in zeolite or MOFs have failed. The richer chemistry of MOFs, and the numerous organicinorganic combinations it allows, including the incorporation of either 3d or rare-earth metals, seemed more attractive for checking the feasibility of inducing the proper structural configuration to favor a delocali...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.