Biorenewable Calcite as an Inorganic Filler in Ionic Liquid Gel Polymer Electrolytes for Supercapacitors

Supercapacitors play a crucial role in the global shift toward cleaner, renewable energy and away from fossil fuels. Ionic liquid electrolytes have a larger electrochemical window than some organic electrolytes and have been mixed with various polymers to make ionic liquid gel polymer electrolytes (ILGPEs), a solid-state electrolyte and separator combination. One way to improve the conductivity of these electrolytes is to add inorganic materials such as ceramics and zeolites to increase their ionic conductivity. Herein, we incorporate a biorenewable calcite from waste blue mussel shells as an inorganic filler in ILGPEs. ILGPEs composed of 80 wt % [EMIM][NTf₂] and 20 wt % PVdF-co-HFP are prepared with various amounts of calcite to determine the effect on the ionic conductivity. The optimal addition of calcite is 2 wt % based on the mechanical stability of the ILGPE. The ILGPE with calcite has the same thermostability (350 °C) and electrochemical window (3.5 V) as the control ILGPE. Symmetric coin cell capacitors were fabricated using ILGPEs with 2 wt % calcite and without calcite as a control. Their performance was compared using cyclic voltammetry and galvanostatic cycling. The specific capacitances of the two devices are similar, 110 and 129 F g^-1, with and without calcite, respectively.