Self-Supported Sisal-like CuCo2O4@Ni(OH)2 Core–Shell Composites Grown on Ni Foam for High-Performance All-Solid State Supercapacitors

Nickel Cobaltite: A Positive Electrode Material for Hybrid Supercapacitors

The increased demand of energy due to the recent technological advances in diverse fields such as portable electronics and electric vehicles is often hindered by the poor capability of energy-storage systems. Although supercapacitors (SCs) exhibit higher power density than state-of-the art batteries, their insufficient energy density remains a major challenge. An emerging concept of hybrid supercapacitors (HSCs) with the combination of one capacitive and one battery electrode in a single cell holds a great promise to deliver high energy density without sacrificing power density and cycling stability. This Minireview elaborates the recent advances of use of nickel cobaltite (NiCo₂ O₄ ) as a potential positive electrode (battery-like) for HSCs. A brief introduction on the structural benefits and charge storage mechanisms of NiCo₂ O₄ was provided. It further shed a light on composites of NiCo₂ O₄ with different materials like carbon, polymers, metal oxides, and others, which altogether helps in increasing the electrochemical performance of HSCs. Finally, the key scientific challenges and perspectives on building high-performance HSCs for future-generation applications were reviewed.

A highly conductive Ni(OH)2 nano-sheet wrapped CuCo2S4 nano-tube electrode with a core-shell structure for high performance supercapacitors

The design of microstructures and the optimum selection of electrode materials have substantial effects on the electrochemical performances of supercapacitors. A core-shell structured CuCo2S4@Ni(OH)2 electrode material was designed, with CuCo2S4 nanotubes as the core wrapped by interlaced Ni(OH)2 nano-sheets as the shell. The hydrothermal and electro-deposition processes were adopted to synthesize CuCo2S4@Ni(OH)2 materials. The CuCo2S4 nanotubes can both provide specific capacitance and act as a "superhighway" for electrons due to their highly conductive skeleton structure. The Ni(OH)2 nano-sheets will boost the electrochemically active sites and enhance the specific surface area. Meanwhile, the mutually restricted core-shell CuCo2S4@Ni(OH)2 electrode could regulate the volume deformation to improve its stability. The CuCo2S4@Ni(OH)2 electrode had a maximum specific capacitance of 2668.4 F g-1 at a current density of 1 A g-1 and a superior cycling stability of 90.3% after 10 000 cycles. Moreover, a CuCo2S4@Ni(OH)2//active carbon asymmetric supercapacitor with a maximum energy density of 44 W h kg-1 was assembled, suggesting that CuCo2S4@Ni(OH)2 is a successful binder-free electrode material for high performance supercapacitors.

Three-dimensional hierarchical core-shell CuCo2O4@Co(OH)2 nanoflakes as high-performance electrode materials for flexible supercapacitors

Rational design of composite electrode materials with novel nanostructures plays an important role in improving both high energy density and structure stability of flexible and wearable supercapacitors. Herein, numerous peculiar three-dimensional hierarchical core-shell CuCo₂O₄@Co(OH)₂ nanoflakes directly grown on Ni foam are synthesized via a facile hydrothermal method and subsequent electrodeposition technique. Ultrathin Co(OH)₂ nanosheets arrays vertically anchored on CuCo₂O₄ nanoflakes can not only improve the electrical conductivity, but also provide interconnected channels for ion diffusion and enrich electrochemical active sites to boost faradaic redox reaction, leading to the enhanced electrochemical behavior. Excellent electrochemical performance of CuCo₂O₄@Co(OH)₂ electrode can be reflected on a higher specific capacitance of 1558 F/g and lower resistance compared with that of the pristine CuCo₂O₄ electrode. The asymmetric flexible supercapacitor assembled by the optimized CuCo₂O₄@Co(OH)₂ electrode and activated carbon exhibits high energy density of 62.5 Wh/kg at 893 W/kg, outstanding cycle stability of 88.6% capacitance retention after 10,000 cycles and remarkable mechanical flexibility, performing the best electrochemical behavior among various metal oxides based asymmetric supercapacitors. All above results indicate that the resulted hierarchical core-shell CuCo₂O₄@Co(OH)₂ electrode can be a promising candidate for flexible energy storage devices.

CuCo2O4 nanoparticles wrapped in a rGO aerogel composite as an anode for a fast and stable Li-ion capacitor with ultra-high specific energy

To meet practical application requirements, high specific energy and specific power and excellent cyclability are highly desired.

Fabrication of NiCo2S4/carbon-filled nickel foam complex as an advanced binder-free electrode for supercapacitors

A novel strategy, composed of epoxy-resin filling, carbonization, and hydrothermal growing of NiCo2S4 nanorods, was developed to enlarge the surface area of nickel foam (NF) for loading electrochemically active materials and to successfully fabricate NiCo2S4/carbon-filled NF binder-free electrodes. Due to the certain electrical conductivity of the filled epoxy-resin-derived carbon and the enlarged loading surface area, the targeted electrode possesses outstanding electrochemical energy storage performance, with a maximum specific capacitance of 9.28 F cm-2 at a current density of 4 mA cm-2, more than 6 times the 1.46 F cm-2 of the NF-based electrode formed via directly growing NiCo2S4 on NF, and with a specific capacitance retention of about 60% after 2000 charge/discharge cycles. Our strategy provides a promising avenue for constructing a high-performance NF-based binder-free electrode and our resultant electrode presents great application potential in electrochemical energy storage.