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

Abstract

Delivering high areal capacitance (C_A) at high rates is crucial but challenging for flexible supercapacitors. C_A is the product of areal loading mass (M_A) and gravimetric capacitance (C_W). Finding and understanding the balance between M_A and C_W of supercapacitor materials is significant for designing high-C_A electrodes. Herein, we have systematically studied the correlation between M_A and C_W of the nanosheet arrays of NiCo−layered double hydroxide (NiCo−LDH), which were electrodeposited on carbon cloth with different heights to adjust the M_A, accompanied by the interlayer distance regulation to improve the C_W. The optimal C_W performance is achieved at the best charge transfer kinetics for each of M_A series. The NiCo−LDH electrode with the suitable M_A (2.58 ​mg ​cm⁻²) and the relatively high C_W (1918 F ​g⁻¹ ​at 5 ​A ​g⁻¹ and 400 ​F ​g⁻¹ ​at 150 ​A ​g⁻¹) present a high C_A 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 delivers a high energy density of 0.28 ​mWh cm⁻² ​at an ultrahigh power density of 712 ​mW ​cm⁻², showing great potential applications.