Facile and One-Step in Situ Synthesis of Pure Phase Mesoporous Li₂MnSiO₄/CNTs Nanocomposite for Hybrid Supercapacitors

In material sciences, synergistic effect and nanostructuring are the two factors which enable researchers to look beyond the conventionally defined categories of the materials. Here, we report the synthesis mechanism of pure phase mesoporous Li₂MnSiO₄ (LMS) with a high specific surface area by varying the concentration of metal precursors and solvents in one-step hydrothermal technique. Furthermore, the effect of MWCNTs addition on the electrochemical performance of LMS is studied. The quantitative contribution of current generating from EDLC and/or the surface pseudocapacitance reactions, and the current caused by diffusion-controlled redox reactions in the total current is also evaluated. The pure phase LMS/CNTs nanocomposite with 2% MWCNTs (abbreviated as LMS2C) is found to be the best supercapacitor material among studied nanocomposites as it exhibits specific capacitance of ∼290 F g^-1 @ 1 A g^-1, good rate capability, small relaxation time constant (τ = 87 ms), and higher diffusion coefficient of electrolytic cations (D_k ⁺ = 9.4 × 10^-9 cm² s^-1) in 2 M KOH aqueous electrolyte. A hybrid supercapacitor cell (HSC) designed using LMS2C as positive and activated carbon as negative electrodes shows the maximum energy density of 31 W h kg^-1, which is much higher than several recently reported hybrid supercapacitor systems. Two series connected HSCs can power a drone motor and light up 8 red LEDs for more than 3 min, indicating practical applicability of our designed hybrid supercapacitor system.