Electrochemical phase reconstruction of biomimetic MnO2 structure to enhance sodium-ion storage kinetics in aqueous systems

The application of conventional manganese dioxide (MnO2) materials in sodium-ion supercapacitors (Na-SCs) is considerably limited by their low conductivity and structural instability. Biomimetic morphology engineering can optimize the electrochemical performance of MnO2. Here, based on the metal-organic frameworks (MOFs)-derived method and electrochemical reconstruction, a coral-like MnO2 structure integrated with a functional nitrogen-doped carbon (NC) coating is designed for Na-SC application. The bioinspired coral-like structure captures numerous electrolyte ions and increases the Na+ concentration on the electrode surface, which is beneficial for optimizing the Na+ transport pathway and accelerating the electrode reaction kinetics. Moreover, the coral-like crosslinked structure effectively enhances the mechanical properties, enabling the maintenance of the structure of MnO2-based electrodes during long-term operation. Furthermore, in/ex-situ characterizations are performed to elucidate the mechanism of lattice transformation during electrochemical phase reconstruction. Additionally, the theoretical calculation and simulation results reveal the ion/electron dynamics in the fabricated electrode. The prepared electrode demonstrates excellent capacitance storage ability (340.7 F g−1 at 0.5 A g−1) and cycling stability (85.1 % capacitance retention after 10,000 cycles). The assembled hybrid device exhibits exceptional life-span (82.0 % capacitance retention after 10,000 cycles) and exceptional energy density (36.5 Wh kg−1). This study provides a reliable biomimetic morphology design strategy for MnO2 cathodes, paving the way for the fabrication of high-performance Na-SCs.