Recycled Red Mud–Decorated Porous 3D Graphene for High-Energy Flexible Micro-Supercapacitor

Flexible micro-supercapacitors, with high energy and power density, and using materials with a low environmental impact are attractive for next-generation energy storage devices. Carbon-based materials are widely used for supercapacitors but can be increased in energy density via combination with metal oxides. Red mud is an iron-oxide-rich by-product of aluminum production, which needs to be more widely utilized to reduce its environmental damage. To achieve a flexible micro-supercapacitor device with increased energy density, a laser-induced graphene (LIG) supercapacitor is realized from a polyimide substrate, decorated with red-mud nanoparticles (LIG-RM), employing a solid-state ionic liquid electrolyte with a mixture of poly(vinylidene fluoride) (PVDF), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMI][TFSI]), and 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF₄]). The fabricated two-electrode flexible device, in an interdigitated planar design, with inkjet-printed silver current collectors, has a high energy of 0.018 mWh cm⁻² at a power of 0.66 mW cm⁻², with 81% of capacitance retained after 4000 cycles and good resistance to bending and flexing. The high energy storage performance, brought about through the combination of graphene and red-mud nanoparticles, which would—if not utilized—be an environmental liability, shows a promise as a material for future energy storage with low environmental impact.