Enhanced performance of nickel–aluminum layered double hydroxide nanosheets/carbon nanotubes composite for supercapacitor and asymmetric capacitor

Abstract

Binary composite consisting of nickel aluminum-layered double hydroxides (LDHs) nanosheets and carbon nanotubes (CNTs) is fabricated by a solution method. The CNTs are pre-coated by γ-Al2O3. The structural characterization and morphological observation demonstrate that Ni–Al hydroxide crystals with hydrotalcite structure are in situ deposited on the surface of CNTs. The as-prepared binary composite combines the pseudo-capacitive of Ni–Al LDHs with double-layer capacitive of carbon nanotubes. CNTs can improve the electrical conductivity and decrease the electrochemical polarization of the composite. Electrochemical measurements of the Ni–Al LDHs/CNTs material show a much better electrochemical performance than pure Ni–Al LDHs. It can yield a high specific capacitance of 1500Fg−1 at 1Ag−1, with 70.3% retention at 10Ag−1 in 2M KOH and a good cycling stability. An asymmetric capacitor is assembled with Ni–Al LDHs/CNTs as a positive electrode and activated carbon as the negative electrode. It can cycle reversibly in a potential window of 1.8V, and exhibits a high specific capacitance of 115Fg−1 and a high energy density of 52Whkg−1 at 1Ag−1 as well as an excellent cycling stability.