Novel microporous manganese phosphonate-derived metal oxides as prospective cathode materials for superior flexible asymmetric micro-supercapacitor device

Developing high-power supercapacitors is tremendously relevant to the current energy demand and implementation of renewable energy storage. The template-free microporous organic-inorganic hybrid material manganese phosphonate (MnPIm) and their derivatives heteroatom doped manganese oxides (NP/MnO₂500, NP/MnO₂700, NP/MnO₂900) are synthesized under hydrothermal condition and following the pyrolysis at different temperatures. Due to heteroatoms doped on material, a significant synergistic effect enhances the electrochemical performance in supercapacitor applications. The unique globular morphology with a hollow structure of materials possesses a high surface area, leading to extraordinary specific capacitance. Among these, NP/MnO₂700 electrode material displays the superior specific capacitance value of 1362 F g⁻¹ at 1 mV s⁻¹ in three-electrode assembly with 99.6 % retention of its initial capacitance up to the 2000th cycle. It demonstrates the exceptional specific capacitance of 263 F g⁻¹ in two electrode asymmetric device with an energy density of 72.6 Wh kg⁻¹ at the power density of 1306 W kg⁻¹. The NP/MnO₂700 material is used to fabricate a flexible asymmetric micro-supercapacitor device (MSC) with an areal capacitance of 32.8 mF cm⁻². The energy density of MSC is estimated to be 18.2 μWh cm⁻² at the power density value of 65.6 μW cm⁻² with 84.2 % retention up to the 5000th cycle.