One-pot synthesis of boron-doped cobalt oxide nanorod coupled with reduced graphene oxide for sodium ion batteries.

Heteroatom doping is one of the feasible strategies to improve electrode efficiency. Meanwhile, graphene helps to optimize structure and improve conductivity of the electrode. Here, we synthesized a composite of boron-doped cobalt oxide nanorods coupled with reduced graphene oxide by a one-step hydrothermal method and investigated its electrochemical performance for sodium ion storage. Because of the activated boron and conductive graphene, the assembled sodium-ion battery shows excellent cycling stability with a high initial reversible capacity of 424.8 mAh g-1, which is maintained as high as 444.2 mAh g-1 after 50 cycles at a current density of 100 mA g-1. The electrodes also exhibit excellent rate performance with 270.5 mAh g-1 at 2000 mA g-1, and retain 96% of the reversible capacity upon recovery from 100 mA g-1. This study shows that boron doping can increase the capacity of cobalt oxides and graphene can stabilize structure and improve conductivity of the active electrode material, which are essential for achieving satisfactory electrochemical performance. Therefore, the doping of boron and introduction of graphene may be one of the promising means to optimize the electrochemical performance of anode materials.

Mini-Review on the Redox Additives in Aqueous Electrolyte for High Performance Supercapacitors.

Supercapacitors, also known as electrochemical capacitors, are attracting much research attention owing to their high power density, long-term cycling stability, as well as exceptional safety compared with rechargeable batteries, although the globally accepted quantitative benchmarks on the power density, cycling stability, and safety are yet to be established. However, it should be noted that the supercapacitors generally exhibit low energy density, which cannot satisfy the demands where both high energy density and power density are needed. To date, various methods have been employed to improve the electrochemical performances of supercapacitors. Among them, introducing redox additives (or redox mediators) into conventional aqueous electrolyte is regarded as one of the most promising strategies. The redox additives in aqueous electrolyte are widely demonstrated to be able to increase the charge storage capability via redox transformation and thus enhance the electrochemical performances. Herein, we present a brief review on the classification, state-of-the-art progress, challenges, and perspectives of the redox additives in aqueous electrolyte for high performance supercapacitors.

Formation of needle-like porous CoNi2S4-MnOOH for high performance hybrid supercapacitors with high energy density.

Seeking for suitable electrode materials and designing rational porous structures are great challenges for developing high performance supercapacitors. Herein, needle-like porous CoNi2S4-MnOOH (denoted as NCS-MO) were prepared via a simple two steps solvothermal method and used as battery-type electrode of supercapacitor for the first time. Owing to the multiple oxidation states of needle-like porous NCS-MO and the inherent porous structure, the electrode delivers outstanding electrochemical capacitive properties with a high gravimetric specific capacitance of 1267.7 F g-1 at the scan rate of 1 mV s-1. To further assess the practical electrochemical performances, we assembled a hybrid supercapacitor using the as-synthesized porous NCS-MO as cathode and active carbon as anode. The device exhibits excellent performance with a high energy density of 47.1 Wh kg-1 at the power density of 998 W kg-1 in an extended voltage range of 1.6 V and outstanding cycling stability. These results demonstrate that the needle-like porous NCS-MO could be promising potential electrode material for high performance supercapacitor.