High-Performance β-MnO2-Based Flexible and Binder-Free Asymmetric Supercapacitor

Achieving high specific capacitance is a key objective in realizing high energy density supercapacitor. In this work, morphology-controlled β-MnO₂ spheres are synthesized using a simple co-precipitation process, and binder-free electrodes are prepared and employed in an asymmetric supercapacitor (ASC) fabrication. The as-prepared β-MnO₂ spheres showed an excellent specific capacitance of ≈394 F g⁻¹ at a current density of 0.37 A g⁻¹ in KOH electrolyte. Remarkably, β-MnO₂ spheres in KOH electrolytes showed highly improved performance than that of other electrolytes. Further, to ensure the practical viability of the as-prepared β-MnO₂, β-MnO₂||Activated Carbon (AC) ASC prototype is fabricated, and its supercapacitor properties are characterized. ASC device showed an excellent cycle life with capacitance retention and coulombic efficiency of 72 and >95%, respectively, up to 10,000 cycles, indicating the good practical viability of the ASC in alkaline electrolytes. The ASC delivered a specific energy of 26.6 Wh kg⁻¹ at a specific power of 175 W kg⁻¹; the maximum power-delivering ability is also evidenced by getting 4.55 kW kg⁻¹ at 7.55 Wh kg⁻¹. Thus, the obtained unlocked specific capacitance of the morphology-controlled β-MnO₂ electrode will be considered as a potential candidate for ASC applications as a positive electrode in alkaline electrolyte.