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

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 gamma-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 1500 F g(-1) at 1 A g(-1), with 70.3% retention at 10 A g(-1) in 2 M 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 1.8 V, and exhibits a high specific capacitance of 115 F g(-1) and a high energy density of 52 W h kg(-1) at 1 A g(-1) as well as an excellent cycling stability. (C) 2015 Elsevier B.V. All rights reserved.