Energy storage performance of hybrid aqueous supercapacitor based on nano-Li2MnSiO4 and activated carbon

Abstract

Novel asymmetric supercapacitor (ASC) composed of nanocrystalline Li2MnSiO4 (LMS) and activated carbon (AC) in aqueous electrolyte is investigated. ASC is tested in three different electrolytes, viz. 2 M KOH, 2 M LiOH, and 2 M Li2SO4. The aqueous solution of 2 M KOH is found to be an appropriate electrolyte in terms of better capacitance, cyclability, and rate capability probably due to a smaller hydration sphere radius and larger ionic conductivity of K+ ions. The electrochemical performance of ASC is examined using cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) cycling, and results are complimented with electrochemical impedance spectroscopy (EIS). Novel ASC exhibits the specific capacitance of 60 (±5) F g−1 at 3 mV s−1 in 2 M KOH. The excellent cyclability (till 5000 cycles) is also observed. The improved supercapacitive properties are mainly ascribed to the unique morphology of LMS (surface area ∼30 m2 g−1 and homogenous meso-pore distribution) which provides easy percolation of electrolytic ions to provide better formation of electric double layer with minor redox behavior. The ex situ X-ray diffraction (XRD) measurement was carried out on a cycled electrode to support the plausible reaction mechanism.