Shear and Solvent-mediated Fabrication of Layered Double Hydroxide Superstructures for High Rate, Stable 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 two-dimensional 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. In this study, the recently developed annular microreactor is used to synthesize defect-rich NiCo LDH 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, increase reactivity and improve structural stability. Optimized electrodes are fabricated with specific capacitances from 3,000-5,000 F/g at charging rates as high as 1,000 A/g, a performance that was retained after 20,000 cycles. This is twice as stable at 5,000 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.