Enhanced sodium ion storage in MnO₂ through asymmetric orbital hybridization induced by spin-paired ion doping

Manganese dioxide (MnO2), due to its considerable theoretical capacitance, is emerging as a promising contender in the search for effective electrode materials. However, its practical application is hampered by its inherently low conductivity. Herein, we propose a unique methodology-employing a spin-paired ion doping strategy-to bolster the orbital hybridization between Mn 3d and O 2p, thus enhancing electron transfer during Na+ storage. The experimental and calculation results indicate that spin-paired Sn4+ ions ([Kr] 4d(10)) engage in weak orbital hybridization with neighbouring oxygen atoms. This weak interaction promotes an increased count of solitary electrons within adjacent O atoms. Importantly, these solitary electrons in the O 2p orbital are confirmed to be relocated to the Mn 3d-eg, culminating in a strengthened Mn (eg)-O (2p) orbital hybridization. The resultant Sn-MnO2 exhibits a significant elevation in specific capacitance to 323.0 F g(-1) at 1 A g(-1). In addition, the fabricated asymmetric supercapacitor delivers a peak energy density of 42.3 W h kg(-1 )at a power density of 1620.0 W kg(-1). This work illustrates a novel pathway to manipulate the electronic structure of MnO2 by enhancing the Mn (3d-e(g))-O (2p) orbital hybridization, which can be extrapolated to the design of other cutting-edge energy materials.