Manganese Intercalation Enabling High-Performance Aqueous Fe–VO2 Batteries

The aqueous iron ion batteries (AIIBs) are an attractive option for large-scale energy storage applications. However, the inadequate plating and stripping of Fe2+ ions underscore the need to explore more suitable cathode materials. Herein, we optimize the structure of tunnel-like VO2 nanosheets by introducing Mn2+ ion intercalation as a cathode material to enhance their performance in AIIBs. Mn2+ serves as a stabilizing pillar for VO2, which brings some oxygen vacancies to provide extra electrochemically active sites, and accelerates the reversible (de)insertion of Fe2+ ions. In addition, the density functional theory (DFT) calculations show that the introduction of Mn2+ reduces the band gap of VO2 and also decreases the electrostatic interaction between Fe2+ and VO2. Consequently, the VO2 with interlayer Mn2+ pillars (5% MVO) electrodes exhibit a remarkable capacity of 284.32 mAh g-1 at a current density of 0.1 A g-1 and demonstrate excellent cycle life, maintaining 81.7% of their capacity at 1.0 A g-1 after 600 cycles. Therefore, these results offer a promising choice for the cathode material to achieve outstanding electrochemical performance in AIIBs.