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...

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Rechargeable magnesium batteries (RMBs) based on metal Mg anodes have shown great potential owing to the abundant natural resources, high volumetric capacity, and low safety hazard. Nevertheless, the development of RMBs is hampered by the sluggish kinetics of Mg2+ diffusion and the limited cyclability of cathode materials. Herein, nonstoichiometric copper selenide (Cu2–xSe) are synthesized via a solution‐based method and exploited as a durable cathode material based on ionic displacement mechanism for RMBs. The copper ions in the Se2− based sub‐lattices are reversibly exchanged by Mg2+ ions without causing lattice collapse. Owing to the same face‐centered cubic Se2− sub‐lattices and similar unit cell size of Cu2–xSe and MgSe, the energy barrier for lattice reconstruction during cycling processes is very low, significantly improving the rate performance, structural stability, and cycle life of the Cu2–xSe cathode. Moreover, metal Cu is in situ generated during discharging, thus greatly facilitating electron transport. Comprehensive characterizations confirm that the Cu2–xSe cathode undergoes reversible copper ion extrusion/reinjection during the discharge−charge steps. This work suggests the great potential for exploring high‐performance electrode materials based on ionic displacement mechanism for advanced multivalent‐ion secondary batteries.

Rechargeable lithium metal batteries are of tremendous interest due to the high theoretical capacity and low reduction potential of lithium metal anode. However, the formation of unstable solid electrolyte interphase (SEI) results in lithium dendrite growth and low Coulombic efficiency during Li plating/stripping processes. Herein, we report an effective strategy to stabilize Li metal anode by in situ constructing antimony-based lithiophilic interphase on Li anode (Sb–Li) using antimony triiodide-tetrahydrofuran (THF) solution. The antimony-based lithiophilic interphase is composed of amorphous antimony and lithium compounds, revealed by in-depth X-ray photoelectron spectroscopy. The Sb–Li anode enables dendrite-free Li deposition in both ether- and ester-based electrolytes. As a result, as-assembled lithium–sulfur (Li–S) batteries with Sb–Li anode exhibit an initial capacity of 915 mAh g–1 at 1.0 C and a capacity retention >83% after 400 cycles. Operando Raman analysis confirmed that the antimony-based lithiophilic interphase can prevent parasitic side reactions, and also relieve the shuttle effect of polysulfides. Furthermore, Sb–Li|LiFePO4 cells have also realized high rate performance and stable cyclability. We expect this effective strategy for stabilizing Li metal anode will provide a valuable route to develop high-energy Li metal batteries.