Alkali-Etched NiCoAl-LDH with Improved Electrochemical Performance for Asymmetric Supercapacitors

Abstract

Hydrotalcite, first found in natural ores, has important applications in supercapacitors. NiCoAl-LDH, as a hydrotalcite-like compound with good crystallinity, is commonly synthesized by a hydrothermal method. Al3+ plays an important role in the crystallization of hydrotalcite and can provide stable trivalent cations, which is conducive to the formation of hydrotalcite. However, aluminum and its hydroxides are unstable in a strong alkaline electrolyte; therefore, a secondary alkali treatment is proposed in this work to produce cation vacancies. The hydrophilicity of the NiCoAl-OH surface with cation vacancy has been greatly improved, which is conducive to the wetting and infiltration of electrolyte in water-based supercapacitors. At the same time, cation vacancies generate a large number of defects as active sites for energy storage. As a result, the specific capacity of the NiCoAl-OH electrode after 10,000 cycles can be maintained at 94.1%, which is much better than the NiCoAl-LDH material of 74%.

Nickel Hydroxides: Requirements, Targeted Construction and Choice of Characteristics and Industrially Applicable Synthesis for Targeted Use in Electrochemical Devices

“…For example, β-modification in the form of ultrafine β-Ni(OH) 2 , [65] β-Ni(OH) 2 with nano-architectures, obtained by solvothermal synthesis, [132] microporous β-Ni(OH) 2 nanorods, [131] mesoporous β-Ni(OH) 2 , [131] β-Ni(OH) 2 nanospheres prepared by a facile electrochemical synthesis, [63] one-dimensional β-Ni(OH) 2 nanostructures, obtained by ionic liquid etching, [133] of two-dimensional Co 2 + -doped β-Ni(OH) 2 , prepared by in situ sol-gel synthesis using nickel complex, [134] uniform pompon-like β-Ni(OH) 2 hollow microspheres, [135] β-Ni(OH) 2 Hierarchical Hollow Microspheres, [136] prepared by l-lysine assisted synthesis, and also β-Ni(OH) 2 /carbon nanotube composite, [137] including those obtained by the hydrothermal method. [138] Supercapacitors use a more active α-modification of nickel hydroxide, [6,8,79,139] including layered double hydroxides: nanosized Ni-Al-Co-Cu LDH, [140] NiÀ Al LDH, [141] Porous NiÀ Co LDH, [142] metal-organic frameworks on NiÀ Co hydroxides hollow prisms [143] , Hierarchical NiÀ Mn LDH Hollow Spheres, [144] MnS/Ni-LDH [145] and nickel foam supported hierarchical NiCo2S4@Ni-Fe LDH [146] heterostructures, Ni-Ti-Al LDH [147] and Ni-Co-Al LDH, prepared by alkali etching, Ni-Co-Mn LDH with a hollow polyhedron [149] and spherical trimetallic Ni-Zn-Co LDH prepared with application MOF (metal-organic framework).…”

Layered Double Hydroxides as the Unique Product of Target Ionic Construction for Energy, Chemical, Foods, Cosmetics, Medicine and Ecology Applications

“…LDHs based on hydroxides of electrochemically active Mguests (Ni(OH) 2 or Co(OH) 2 ) are used as active substances of the Faraday electrode of hybrid supercapacitors. [45,46] Due to the high rate of charge/discharge (oxidation/reduction), the electrochemical process is localized on the surface and in a thin near-surface layer of particles. Therefore, for use in this area, hydroxides (including LDHs) must meet special requirements.…”