Hybrid supercapacitor based on non-flammable deep eutectic solvent electrolytes with sodium trifluoroacetate

Sodium-ion capacitors are considered an alternative to lithium-ion batteries due to their high cost-effectiveness and superior performance in terms of power output and energy density. Generally, organic electrolytes are used in hybrid capacitors. However, due to safety problems, deep eutectic solvent electrolytes are increasingly being considered as alternatives. Nevertheless, commonly used electrolyte salts have drawbacks in terms of stability and cost. In this study, a deep eutectic solvent electrolyte is synthesized using sodium trifluoroacetate (NaTFA). The result confirms that this electrolyte is non-flammable and that the TFA⁻ anion provides improved electrochemical stability when synthesized with methyl carbamate. Symmetric cell operation with the synthesized electrolyte demonstrates a capacitance retention of 78 % after 8000 cycles at 1 A g⁻¹. In addition, NaTi₂(PO₄)₃/C is used as the anode, resulting in energy density of 88.8 Wh kg⁻¹ at a power density of 125 W kg⁻¹ and 32.1 Wh kg⁻¹ at 2500 W kg⁻¹ in the hybrid cell. These results suggest that NaTFA interacts with amides to form deep eutectic solvents, which are likely to be used for electrochemical applications as electrolytes.