Toward Transitioning to Green and Sustainable Supercapacitors

The rapid advancement of supercapacitor technologies has intensified the demand for sustainable electrode fabrication methods that minimize environmental impact. A major challenge arises from the extensive use of the toxic solvent N-methyl-2-pyrrolidone (NMP), which is subject to increasingly stringent regulatory restrictions. We demonstrate that NMP can be effectively replaced with two green solvents, dihydrolevoglucosenone (Cyrene) and N-butyl-2-pyrrolidone (Tamisolve), without compromising electrochemical performance. Electrode formulations were prepared using nitrogen-doped graphene as the active material, in combination with either polyvinylidene fluoride (PVDF), a widely employed fluorinated binder, or polyvinylpyrrolidone (PVP), a non-fluorinated alternative with improved environmental profile. Optimized coatings exhibited high mass loadings exceeding 6 mg cm⁻² while maintaining strong adhesion to current collectors, an often overlooked yet critical parameter for scalable manufacturing. Electrochemical testing revealed that PVDF in Cyrene delivered an energy density of 66.6 Wh kg⁻¹ at a power density of 1.85 kW kg⁻¹, with excellent cycling stability, retaining 91 % of capacitance after 100,000 cycles. PVP in Cyrene provided a more environmentally benign alternative, achieving an energy density of 64.2 Wh kg⁻¹ at 1.80 kW kg⁻¹, with 78 % capacitance retention after 100,000 cycles, thereby highlighting the trade-off between performance and sustainability.