Multivalent cation batteries are attracting increasing attention in energy-storage applications, but reversible storage of highly polarizing multivalent cations is a major difficulty for the electrode materials. In the present study, charge-delocalizing Mo3S13 cluster-based materials (crystalline (NH4)2Mo3S13 and amorphous MoSx) are designed and investigated as cathodes for rechargeable magnesium batteries. Both of the cathodes show high magnesium storage capacities (296 and 302 mAh g–1 at 100 mA g–1) and superior rate performances (76 and 80 mAh g–1 at 15 A g–1). A high area loading of 3.0 mg cm–2 could be achieved. These performances are of the highest level compared with those of reported magnesium storage materials. Further mechanism study and theoretical computation demonstrate the magnesium storage active sites are the bridging disulfur groups of the Mo3S13 cluster. The valence state of bridging disulfur decreases/increases largely during magnesiation/demagnesiation along with breaking/formation of the sulfur–sulfur bond, which makes the Mg-association/dissociation highly reversible. The sulfur–sulfur bond breaking and formation provides high reversible capacities. Prominently, the valence state increase and sulfur–sulfur bond formation of the bridging disulfur during charge weakens the bonding with Mg2+, significantly assisting the magnesium dissociation. The present study not only develops high-performance magnesium storage cathode materials but also demonstrates the importance of constructing favorable magnesium storage active sites in the high-performance cathode materials design. The findings presented herein are of great significance for the development of electrode materials for the storage of multivalent cations.
Rechargeable Mg batteries (RMBs) are a promising large-scale energy-storage technology with low cost and high safety, but the performance is limited by the inferior kinetics of Mg-intercalation cathodes. In the present study, an octylamine-supporting interlayer expanded molybdenum diselenide (e-MoSe 2 ) is synthesized and used as cathode for RMBs, in comparison with ordinary crystalline MoSe 2 . The octylamine molecules introduced show a strong interaction with the MoSe 2 layers and increase the layer spacing significantly from 6.46 to 11.5 Å. e-MoSe 2 shows a high Mg-storage capacity of 238 mAh g −1 at 50 mA g −1 and a superior rate performance of 39 mAh g −1 at 10 A g −1 , far advantageous over crystalline MoSe 2 . e-MoSe 2 also shows a considerably high structure stability during repeated magnesiation/demagnesiation, providing an outstanding cycling stability for 1000 cycles. Further electrochemical tests demonstrate the high Mg 2+ diffusion coefficients in e-MoSe 2 . Theoretical computation indicates the interlayer expansion changes the Mg 2+ diffusion paths from “hollow site → hollow site” to “hollow site → Se atom site → hollow site”, largely decreasing the energy barrier and improving the Mg 2+ diffusion kinetics. The present work highlights an efficient strategy for the improvement of Mg-storage performance for RMB cathodes.
Junjun Wang,Ruohan Yu,Jianxiang Wang,Juncai Long,Fan Qiao,Lei Zhang,Guanjie He,Qinyou An,Liqiang Mai
Bismuth has garnered significant interest as an anode material for magnesium batteries (MBs) because of its high volumetric specific capacity and low working potential. Nonetheless, the limited cycling performance (≤100 cycles) limits the practical application of Bi as anode for MBs. Therefore, the improvement of Bi cycling performance is of great significance to the development of MBs and is also full of challenges. Here, Bi nanoparticles encapsulated in nitrogen-doped carbon with single-atom Bi embedded (Bi@NC) are prepared and reported as an anode material for MBs. Bi@NC demonstrates impressive performance, with a high discharge capacity of 347.5 mAh g −1 and good rate capability (206.4 mAh g −1 @500 mA g −1 ) in a fluoride alkyl magnesium salt electrolyte. In addition, Bi@NC exhibits exceptional long-term stability, enduring 400 cycles at 500 mA g −1 . To the best of our knowledge, among reported Bi and Bi-based compounds for MBs, Bi@NC exhibits the longest cycle life in this work. The magnesium storage mechanism of Bi@NC is deeply studied through X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. This work provides some guidance for further improving the cycling performance of other alloy anodes in MBs.
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