Balancing loading mass and gravimetric capacitance of NiCo-layered double hydroxides to achieve ultrahigh areal performance for flexible supercapacitors

Delivering high areal capacitance (CA) at high rates is crucial but challenging for flexible supercapacitors. CA is the product of areal loading mass (MA) and gravimetric capacitance (CW). Finding and understanding the balance between MA and CW of supercapacitor materials is significant for designing high-CA electrodes. Herein, we have systematically studied the correlation between MA and CW of the nanosheet arrays of NiCo-layered double hy-droxide (NiCo-LDH), which were electrodeposited on carbon cloth with different heights to adjust the MA, accompanied by the interlayer distance regulation to improve the CW. The optimal CW performance is achieved at the best charge transfer kinetics for each of MA series. The NiCo-LDH electrode with the suitable MA (2.58 mg cm-2) and the relatively high CW (1918 F g-1 at 5 A g-1 and 400 F g-1 at 150 A g-1) present a high CA of 4948 mF cm-2 at 12.9 mA cm-2 and a record-high 1032 mF cm-2 among LDHs-based flexible electrodes at an ultrahigh current density of 387 mA cm-2. The corresponding flexible supercapacitor coupled with activated carbon de-livers a high energy density of 0.28 mWh cm-2 at an ultrahigh power density of 712 mW cm-2, showing great potential applications.