Significant Role of Al in Ternary Layered Double Hydroxides for Enhancing Electrochemical Performance of Flexible Asymmetric Supercapacitor

The Al effect on the electrochemical properties of layered double hydroxides (LDHs) is not properly probed, although it is demonstrated to notably promote the capacitive behavior of LDHs. Herein, ternary NiCo2Alx layered double hydroxides with varying levels of Al stoichiometry are purposely developed, grown directly on mechanically flexible and electrically conducting carbon cloth (CC@NiCo2Alx-LDH). Al plays a significant role in determining the structure, morphology, and electrochemical behavior of NiCo2Alx-LDHs. At an increasing level of Al in NiCo2Alx-LDHs, there is a steady evolution from 1D nanowire to 2D nanosheets. The CC@NiCo2Al-LDH at an appropriate level of Al and with the nanowire-nanosheet mixed morphology exhibits both significantly enhanced electrochemical performance and excellent structural stability, with about a 2.3-fold capacitance of NiCo2-OH. When applied as the anode in a flexible asymmetric supercapacitor (ASC), the CC@NiCo2Al-LDH gives rise to a remarkable energy density of 44 Wh kg(-1) at the power density of 462 W kg(-1), together with remarkable cyclic stability with 91.2% capacitance retention over 15 000 charge-discharge cycles. The present study demonstrates a new pathway to significantly improve the electrochemical performance and stability of transition metal LDHs, which are otherwise unstable in structure and poorly performing in both rate and cycling capability.