No abstract

3833 mAh cm −3 nearly double that of lithium (2062 mAh cm −3 ), and exhibits a relatively negative reduction potential of −2.4 V versus standard hydrogen electrode (SHE). [6][7][8][9] Despite of these intriguing merits, the practical employment of RMBs is hampered by several main hurdles. First, clumsy Mg 2+ intercalation is the primary limitation for the choice of competent cathode materials, because the strong Coulombic interactions between the divalent Mg 2+ ions and the anions in the host materials often result in sluggish diffusion kinetics and slow interfacial charge transfer. [10][11][12][13] Second, to design appropriate electrolytes for Mg plating/ stripping with high Coulombic efficiency, wide electrochemical window, and good compatibility with the cathodic materials is another great challenge. [14,15] Therefore, to develop advanced cathode materials capable of rapid Mg 2+ insertion/extraction in suitable electrolytes for reversible Mg plating/stripping is highly desirable. Since the pioneering work of Chevrel phase compounds (Mo 6 S 8 ) reported by Aurbach et al. in 2000, [16] tremendous efforts have been devoted to develop cathode materials for RMBs, including transition metal oxides (MnO 2 , V 2 O 5 , Mn 3 O 4 , WO 3 , Co 3 O 4 ), [17-21] polyanionic compounds (Mg 1.03 Mn 0.97 SiO 4 , MgCoSiO 4 ), [22,23] and transition metal dichalcogenides (TMDs, such as TiS 2 , MoS 2 , WSe 2 ). [24][25][26][27][28] However, most oxides and polyanionic compounds suffer from low capacity and poor cycling performance owing to the strong interactions between divalent Mg 2+ and O 2− in the hosts. [25,29] On the contrary, TMDs are deemed to be a class of promising cathode materials with more favorable kinetics, attributing to the relatively weaker MgS or MgSe bonds than MgO bond. [25,28,30] Nevertheless, layered TMDs also suffer from slow Mg 2+ ion diffusion due to the narrow interlayer spacing and the high polarity of Mg 2+ . [31] Recently, it was reported that the interlayer distances of TMDs could be expanded by intercalating guest molecules (water or organic molecules), enlarging the dimension of ion diffusion channels and shielding the Coulombic interactions between Mg 2+ and the lattice anions of hosts. 13,27 In addition, the intercalated molecules served as interlayer pillars are conducive to maintain the framework of host materials for prolonged cycles. [32,33] Rechargeable magnesium batteries (RMBs) are attractive candidates for large-scale energy storage owing to the high theoretical specific capacity, rich earth abundance, and good safety characteristics. However, the development of desirable cathode materials for RMBs is constrained by the high polarity and slow intercalation kinetics of Mg 2+ ions. Herein, it is demonstrated that 2-ethylhexylamine pillared vanadium disulfide nanoflowers (expanded VS 2 ) with enlarged interlayer distances exhibit greatly boosted electrochemical performance as a cathode material in RMBs. Through a one-step solution-phase synthesis and in situ 2-ethylhexylamine intercalatio...

No abstract