Tailoring morphology of cobalt-nickel layered double hydroxide via different surfactants for high-performance supercapacitor.

Tailoring the morphology of cobalt-nickel layered double hydroxide (LDH) electrode material was successfully achieved via the process of cathodic electrodeposition by adding different surfactants (hexamethylenetetramine, dodecyltrimethylammonium bromide (DTAB) or cetyltrimethylammonium bromide). The as-prepared Co0.75Ni0.25(OH)2 samples with surfactants exhibited wrinkle-like, cauliflower-like or net-like structures that corresponded to better electrochemical performances than the untreated one. In particular, a specific capacitance of 1209.1 F g-1 was found for the cauliflower-like Co0.75Ni0.25(OH)2 electrode material using DTAB as the surfactant at a current density of 1 A g-1, whose structure boosted ion diffusion to present a good rate ability of 64% with a 50-fold increase in current density from 1 A g-1 to 50 A g-1. Accordingly, the asymmetric supercapacitor assembled by current LDH electrode and activated carbon electrode showed an energy density as high as 21.3 Wh kg-1 at a power density of 3625 W kg-1. The relationship between surfactant and electrochemical performance of the LDH electrode materials has been discussed.

Nanocrystalline LaOx/NiO composite as high performance electrodes for supercapacitors.

Nanocrystalline LaOx/NiO composite electrodes were synthesized via two types of facile cathodic electrodeposition methods onto nickel foam followed by thermal annealing without any binders. Scanning electron microscopy and transmission electron microscopy investigation revealed that LaOx nanocrystalline particles with an average diameter of 50 nm are uniformly distributed in the NiO layer or alternately deposited with the NiO layer onto the substrate. It is speculated that LaOx particles can participate in the faradaic reaction directly and offer more redox sites. Besides this, the unique Ni/La layered structure facilitates the diffusion of ions and retards the electrode polarization, thus leading to a better rate capability and cycling stability of NiO. As a result, the obtained electrodes display very competitive electrochemical performance (a specific capacitance of 1238 F g-1 at a current density of 0.5 A g-1, excellent rate capability of 86% of the original capacitance at 10 A g-1 and excellent cycling stability of 93% capacitance after 10 000 cycles). In addition, asymmetric coin devices were assembled using LaOx/NiO as the positive electrode and active carbon as the negative electrode. The assembled asymmetric devices demonstrate a high energy density of 13.12 W h kg-1 at a power density of 90.72 W kg-1.

Metal Oxide Nanostructures Generated from In Situ Sacrifice of Zinc in Bimetallic Textures as Flexible Ni/Fe Fast Battery Electrodes.

An "in situ sacrifice" process was devised in this work as a room-temperature, all-solution processed electrochemical method to synthesize nanostructured NiOx and FeOx directly on current collectors. After electrodepositing NiZn/FeZn bimetallic textures on a copper net, the zinc component is etched and the remnant nickel/iron are evolved into NiOx and FeOx by the "in situ sacrifice" activation we propose. As-prepared electrodes exhibit high areal capacities of 0.47 mA h cm-2 and 0.32 mA h cm-2 , respectively. By integrating NiOx as the cathode, FeOx as the anode, and poly(vinyl alcohol) (PVA)-KOH gel as the separator/solid-state electrolyte, the assembled quasi-solid-state flexible battery delivers a volumetric capacity of 6.91 mA h cm-3 at 5 mA cm-2 , along with a maximum energy density of 7.40 mWh cm-3 under a power density of 0.27 W cm-3 and a maximum tested power density of 3.13 W cm-3 with a 2.17 mW h cm-3 energy density retention. Our room-temperature synthesis, which only consumes minute electricity, makes it a promising approach for large-scale production. We also emphasize the in situ sacrifice zinc etching process used in this work as a general strategy for metal-based nanostructure growth for high-performance battery materials.