The mineral manaksite, KNaMnSi₄O₁₀, as a supercapattery-type electrochemical energy storage material

The manaksite mineral KNaMnSi₄O₁₀ was synthesized and used to fabricate electrodes, which were investigated for electrochemical energy storage (EES) application using cyclic voltammetry (CV), galvanostatic charge and discharge (GCD), and electrochemical impedance spectroscopy (EIS). Optimum weight percentages (wt%) of electrode components were established as 10 wt% polytetrafluoroethylene (PTFE) binder, 15 wt% RuO₂ and 5 wt% carbon black. RuO₂ was added to improve electrical conductivity. A ratio of 13 : 3 for KNaMnSi₄O₁₀ : RuO₂ was used in the fabrication of the electrode. A study of the suitable electrolyte and corresponding concentration to use was done using NaOH and KOH, both at concentrations of 1 M, 3 M and 6 M, with 3 M NaOH as the optimum electrolyte and concentration. The KNaMnSi₄O₁₀ yielded a specific capacity of 106 mA h g^-1. An investigation into the energy storage mechanism from a plot of log I(ν) vs. log ν, where I is current and ν is the scan rate gave a b value parameter of 0.8; that is, in-between 0.5 obtained for a pure battery material and 1.0 for a pure capacitor material. Accordingly, KNaMnSi₄O₁₀ exhibited a battery-supercapacitor duality phenomenon consistent with supercapattery materials. The KNaMnSi₄O₁₀ electrochemical system involved both capacitive and diffusion-controlled processes and was found to have good cyclic stability. It is concluded that KNaMnSi₄O₁₀ is a potential electrochemical energy storage material.