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

Abstract

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] 4d¹⁰) 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-e_g, culminating in a strengthened Mn (e_g)–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.