An anion-sorted Li-ion electrolyte and flexible MnVO@SWCNT hybrid electrode for an efficient supercapacitor system

Portable and wearable electronics create a wide application opportunity for flexible energy storage materials. This study focuses on electrode and electrolyte modification to fabricate a highly flexible energy storage device with exceptional performance characteristics. Herein, a binary transition metal oxide (BTMO), leveraging the combined advantages of manganese (Mn) and vanadium (V) with their diverse oxidation states, was selected as the electrode material. To construct a flexible and efficient hybrid electrode (MnVO@SWCNT), the BTMO was integrated in the mesh of highly conductive and ductile single-walled carbon nanotubes (SWCNT). Consequently, the impact of electrolyte anions, such as OH⁻, SO₄²⁻, Cl⁻, and NO₃⁻, on the electrochemical efficiency of a MnVO@SWCNT electrode was analyzed in detail to boost the supercapacitor performance. The selection of anion species strongly influenced the fundamental capacitance due to the dissimilarities in ionic mobility and size of anions. As a result, the hybrid electrode operating in an aqueous electrolyte containing Li⁺and OH⁻ions exhibited superior capacitive performance and attained a maximum areal capacitance of 1886 mF cm⁻². To demonstrate the high application potential of such a material, a free-standing binder-free hybrid electrode devoid of an extra counter electrode was used to synthesize a flexible planar supercapacitor, MVO//OH@SWCNT (FpSC), which offered 718 mF cm⁻²capacitance and 105.79 µWh cm⁻²energy density.