Mixed-valent MnSiO₃/C nanocomposite for high-performance asymmetric supercapacitor

In this work, carbon-coated manganese silicate (MnSiO₃/C) nanocomposite with excellent cycling stability was fabricated via a cost-effective process. The carbon coating followed with a CO₂ heat treatment process on the manganese silicate results in mixed-valent hierarchically-porous nanoparticles, which tightly connects with an ultrathin (∼1.5 nm) and ordered carbon coating layer. This composite features rectangular-like cyclic voltammetry curve with two couples of redox peaks, suppressing the irreversible reactions and thus providing a broad and stable working voltage. By fitting the CV curves, the MnSiO₃/C demonstrates a capacitive energy-storage behavior. The as-assembled activated carbon//MnSiO₃/C asymmetric supercapacitor in 1 M Na₂SO₄ aqueous electrolyte is found to have excellent cycling stability, with 95.5% retention of initial after 10,000 cycles. This device could deliver 25.8 W h kg⁻¹ energy density at the power density of 1 kW kg⁻¹ with ∼10 mg cm⁻² high mass loading, suggesting a bright prospect in practical application.