Boosted sodium ion storage performance in MnO 2 : Understanding the bond angle-mediated orbital overlap in MnO 6 units for fast charge transfer

Symmetric six oxygen-coordinated Mn structural units (MnO 6 ) in MnO 2 with small Mn–O orbital overlap hamper electron transfer rates during energy storage. Herein, we report a novel bond angle modulation strategy to manipulate Mn–O orbital overlap in MnO 2 through the construction of Mn vacancies (MnO 2 -V Mn ), aiming at expediting electron transfer, and thus enhancing energy storage performance. Both experimental and theoretical results disclose that the amplification of Mn–O–Mn bond angles exclusively augments the Mn ( dx 2 - y 2 )-O ( py ) orbital overlap and triggers the electron redistribution in MnO 2 -V Mn, inducing an augmented Mn dx 2 - y 2 electron occupation. This heightened presence of active electrons in the Mn dx 2 - y 2 orbital paves the way for accelerating electron transfer and ion transfer in MnO 2 -V Mn. Notably, MnO 2 -V Mn delivers an improved specific capacitance of 425 F g −1 at 1 A g −1 and a superior rate capacity of 265 F g −1 at 20 A g −1. Furthermore, an asymmetric supercapacitor (MnO 2 -V Mn //AC ASC) was fabricated, exhibiting a high energy density of 64.3 Wh kg −1 at a power density of 1000 W kg −1. Furthermore, theoretical insights uncover the profound implications of metal–oxygen–metal bond angle regulation on interatomic orbital overlap modulation. These revelations illuminate pathways for the design of advanced energy storage materials.