In-situ multi-scale structural engineering of cathode and electrolyte for high-rate and long-life Mg metal batteries

Abstract

Vanadium pentoxide (V₂O₅) displays the characteristics of high theoretical specific capacity, high operating voltage, and adjustable layered structure, possessing the considerable potential as cathode in magnesium metal batteries (MMBs). Nevertheless, the large charge-radius ratio of Mg²⁺ induces the strong interactions of Mg²⁺ with solvent molecules of electrolyte and anionic framework of cathode, resulting in a notable voltage polarization and structural deterioration during cycling process. Herein, an in-situ multi-scale structural engineering is proposed to activate the interlayer-expanded V₂O₅ cathode (pillared by tetrabutylammonium cation) via adding hexadecyltrimethylammonium bromide (CTAB) additive into electrolyte. During cycling, the in-situ incorporation of CTA⁺ not only enhances the electrostatic shielding effect and Mg species migration, but also stabilizes the interlayer spacing. Besides, CTA⁺ is prone to be adsorbed on cathode surface and induces the loss-free pulverization and amorphization of electroactive grains, leading to the pronounced effect of intercalation pseudocapacitance. CTAB additive also enables to scissor the Mg²⁺ solvation sheath and tailor the insertion mode of Mg species, further endowing V₂O₅ cathode with fast reaction kinetics. Based on these merits, the corresponding V₂O₅||Mg full cells exhibit the remarkable rate performance with capacities as high as 317.6, 274.4, 201.1, and 132.7 mAh g⁻¹ at the high current densities of 0.1, 0.2, 0.5, and 1 A g⁻¹, respectively. Moreover, after 1000 cycles, the capacity is still preserved to be 90.4 mAh g⁻¹ at 1 A g⁻¹ with an average coulombic efficiency of ∼100%. Our strategy of synergetic modulations of cathode host and electrolyte solvation structures provides new guidance for the development of high-rate, large-capacity, and long-life MMBs.