Shear and Solvent-Mediated Fabrication of Layered Double-Hydroxide Superstructures for High-Rate Supercapacitor Cathodes

The development of sustainable energy economies is blocked by the lack of stable electrical energy sources with high power and energy densities. Next-generation supercapacitors utilizing 2D layered double hydroxides (LDHs) promise to fill this need in hybrid and standalone architectures; however, despite their high power and energy densities, LDH supercapacitors have poor stability. New methods for creating robust LDH electrodes are necessary to prevent this degradation. Herein, the recently developed annular microreactor is used to synthesize defect-rich NiCoLDH nanocrystals. A simple, solvent-based method is used to rationally generate binder-free, superstructured thin films on Ni foam electrodes. Control over crystallite size, thinness, and orientation improves contact with the conductive substrate, increases reactivity, and improves structural stability. Optimized electrodes are fabricated with specific capacitances from 3000 to 5000 F g(-1) at charging rates as high as 1000 A g(-1), a performance that is retained after 20 000 cycles. This is twice as stable at 5000 times the current density of the most stable reported Ni-based supercapacitor. Ultimately, this study addresses key concerns in electrode development, introduces new approaches through reactor technology and solvent-mediated assembly, and opens new ground for more fundamental inquiries into the mechanisms of electron transport in 2D systems.