Effect of intercalated anion in nickel-cobalt-layered double hydroxide on its supercapacitive properties

Abstract

Layered double hydroxides (LDHs), a class of 2D lamellar intercalating materials, is a promising candidate for high-performance supercapacitors, while its poor cycling stability has always been its Achille’s heel. Although doping metal ions into the host layer is proved to be an effective way to improve the weakness, the effects of intercalated anions on cycling performance have been rarely studied and highly underestimated. In this paper, we prepared a group of NiCo-LDHs with different intercalated anions, including NO3−, Cl−, SO42−, MoO42− and WO42−, which expand the interlayer spacing from 0.73 to 1.07 nm. Interestingly, although expanding the interlayer spacing could increase the specific capacity by providing more electrochemical active sites, it could not guarantee the improvement in cycling performance and rate capability. The correlation between interlayer spacing and cycling performance exhibits a “volcano” plot. The MoO42− intercalated NiCo-LDH with a 0.96 nm interlayer spacing delivers a high specific capacity of 795 C g−1 and the best cycling stability with 80% capacity retention after 20,000 cycles, which is better than NiCo-LDH-NO3 (0.73 nm, 50% after 3000 cycles) and NiCo-LDH-WO4 (1.07 nm, 64% after 20,000 cycles). By combining the results with the DFT method, the effects of intercalated anion on cycling performance are illustrated. In addition, the asymmetric supercapacitor also exhibits an excellent cycling stability with ∼100% capacity retention after 10,000 cycles. This study provides new insight to the compositional design of LDH-based electrodes for long-lifespan supercapacitors.