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.