Tuning Ni/Al Ratio to Enhance Pseudocapacitive Charge Storage Properties of Nickel-Aluminum Layered Double Hydroxide

Compared with batteries, the advantages of capacitive energy storage include high power, fast charging kinetics, and long cycling stability. Owing to their layered structure and tunable transition metal charge, layered double hydroxides (LDHs) have great potential to be applied as pseudocapacitor materials. Here, a systematic experimental study is reported on the impact of the Ni/Al ratio on the structure, morphology, ion transport kinetics, interlayer phenomena, and performance of NiAl-LDH supercapacitor electrode materials, in which three NiAl-LDH materials with Ni/Al ratios of 2, 3, and 4, are synthesized using a hydrothermal method. The increase of the Ni/Al ratio results in more open interlayer space resulting in faster ion diffusion kinetics. Although an increase in the Ni/Al ratio introduces more redox active sites, it leads to degradation in crystallinity and morphology, which has a significant negative impact on pseudocapacitance. Electrochemical tests suggest that at Ni/Al = 3, the NiAl-LDH electrode exhibits optimum specific capacitance of 2128 F g(-1) at 1 A g(-1) with long cycle stability. This work highlights the complex interplay among compositional and structural factors on the kinetic and performance behaviors of NiAl-LDH materials. Subtle compositional modification is an effective strategy to enhance the pseudocapacitive charge storage property of NiAl-LDH pseduocapacitor materials.