Facile synthesis of pseudocapacitive Mn₃O₄ nanoparticles for high-performance supercapacitor

In this work, a facile method to produce the ultrafine (4–14 nm) and mixed valence Mn₃O₄ nanoparticles from low-cost MnSiO₃ (manganese silicate) particles were introduced. The best NaOH concentration in hydrothermal treatment has been determined after a series of experiments. Also, the as-synthesized Mn₃O₄ material with good specific capacitance has been investigated attentively at a high mass loading (∼3 mg cm⁻²). The particles size and the pore size distribution is found to be refined and optimized, respectively. This increased the crystallinity and the capacitive contribution in the energy process. Thereby improving the rate capability and cycling stability, which result in significant improvement of specific capacitance (401 F g⁻¹ at 10 mV s⁻¹). The aqueous asymmetric supercapacitor device AC//Mn₃O₄ with a stable working voltage window up to 2.0 V has been fabricated, and it is found to have an energy density of 40.2 W h kg⁻¹ at 500 W kg⁻¹ power density. This could sustain 5000 cycles galvanostatic charge/discharge with 96.9% retention.