Designing CoHCF@FeHCF Core-Shell Structures to Enhance the Rate Performance and Cycling Stability of Sodium-Ion Batteries.

Prussian blue analogs are well suited for sodium-ion battery cathode materials due to their cheap cost and high theoretical specific capacity. Nax CoFe(CN)6 (CoHCF), one of the PBAs, has poor rate performance and cycling stability, while Nax FeFe(CN)6 (FeHCF) has better rate and cycling performance. The CoHCF@FeHCF core-shell structure is designed with CoHCF as the core material and FeHCF as the shell material to enhance the electrochemical properties. The successfully prepared core-shell structure leads to a significant improvement in the rate performance and cycling stability of the composite compared to the unmodified CoHCF. The composite sample of core-shell structure has a specific capacity of 54.8 mAh g-1 at high magnification of 20 C (1 C = 170 mA g-1 ). In terms of cycle stability, it has a capacity retention rate of 84.1% for 100 cycles at 1 C, and a capacity retention rate of 82.7% for 200 cycles at 5 C. Kinetic analysis shows that the composite sample with the core-shell structure has fast kinetic characteristics, and the surface capacitance occupation ratio and sodium-ion diffusion coefficient are higher than those of the unmodified CoHCF.

What about electrochemical behaviors for aurivillius-phase bismuth tungstate? Capacitive or pseudocapacitive.

Researchers mainly explore the mechanism of pseudocapacitance through studying electrode materials with Faraday pseudocapacitive behavior. Here, we found that Bi2WO6, a typical Aurivillius phase material with pseudo-perovskite structure, showed nearly ideal pseudocapacitive behavior. The cyclic voltammetry curve is approximately rectangular in shape, with no redox peaks, which is similar to that of carbon materials. And the shape of the galvanostatic charge-discharge curve is close to an isosceles triangle. In addition, the kinetic analysis demonstrated that the electrochemical process of the A-Bi2WO6 electrode is dominated by surface processes, not diffusion. The A-Bi2WO6 electrode material presents a great volumetric specific capacitance of 466.5 F cm-3 at 0.5 A g-1. These electrochemical properties confirm that the Bi2WO6 material can serve as an ideal support material to explore pseudocapacitive energy storage. This work also provides guidance for the development of new pseudocapacitive materials.

Enhancing the Kinetic Process in Biphasic Crystalline NiWO4 /Amorphous Co-B Electrode Materials toward Energy Storage with Ultrahigh Rate Performance.

Here, we report a two-phase crystalline NiWO4 /amorphous Co-B nanocomposite as an electrode material for supercapacitors, which is effectively synthesized via a simple hydrothermal method and chemical precipitation method. The obtained NiWO4 /Co-B exhibits crystal-amorphous contact, which makes it have more active sites than other crystalline-crystalline phase boundaries, thereby enhancing electron transport. The NiWO4 /Co-B electrode with the best mass ratio of crystalline and amorphous exhibits a great specific capacitance and excellent cycle durability. Compared to individual Co-B and NiWO4 , it also shows enhanced rate capability Besides, NiWO4 /Co-B/activated carbon supercapacitor device can provide a good specific capacitance and a maximum energy density of 10.92 Wh kg-1 at 200 W kg-1 . This work provides new insights to develop novel electrode materials for energy storage and conversion.

Boosting the performance of cobalt molybdate nanorods by introducing nanoflake-like cobalt boride to form a heterostructure for aqueous hybrid supercapacitors.

Binary transition metal oxides have received extensive attention because of their multiple oxidation states. However, due to the inherent vices of poor electronic/ionic conductivities, their practical performance as supercapacitor material is limited. Herein, a cobalt molybdate/cobalt boride (CoMoO4/Co-B) composite is constructed with cobalt boride nanoflake-like as a conductive additive in CoMoO4 nanorods using a facile water bath deposition process and liquid-phase reduction method. The effects of CoMoO4/Co-B mass ratios on its electrochemical performance are investigated. Remarkably, the CoMoO4/Co-B composite obtained at a mass ratio of 2:1 shows highly enhanced electrochemical performance relative to those obtained at other ratios and exhibits an optimum specific capacity of 436 F g-1 at 0.5 A g-1. This kind of composite could also display great rate capacity (294 F g-1 at 10 A g-1) and outstanding long cycle performance (90.5% capacitance retention over 10 000 cycles at 5 A g-1). Also, the asymmetric supercapacitor device is prepared by using CoMoO4/Co-B composite as the anode with the active carbon as the cathode. Such a device demonstrates an outstanding energy density of 23.18 Wh kg-1 and superior long-term stability with 100% initial specific capacity retained after 10,000 cycles. The superior electrochemical properties show that the CoMoO4/Co-B electrode material has tremendous potential in energy storage equipment applications.