Zichao Yan

Sandwich-like cobalt sulfide–graphene composite – an anode material with excellent electrochemical performance for sodium ion batteries

Recently, sodium-ion batteries have been considered alternatives to lithium-ion batteries. However, the poor cycling performance and unsatisfactory rate capability of existing anodes hinder the development of sodium-ion batteries. Here we fabricate a sandwich-like cobalt sulfide–reduced graphene oxide (CoS/rGO) composite using a hydrothermal method as the anode material for sodium ion batteries. According to the SEM analysis, CoS nanoparticles anchor on both sides of the reduced graphene oxide nanosheets in such a way that the nanoporous structure with a large amount of void spaces can be prepared. And the cycling performance of the sandwich-like CoS/rGO composite is drastically enhanced compared with that of the bare CoS nanoparticles. After 100 cycles, the discharge capacity of CoS/rGO still remains at 230 mA h g−1, while the specific capacity of the bare CoS nanoparticles at the first cycle is 601 mA h g−1, dropping rapidly to 68 mA h g−1 after only 40 cycles. Furthermore, CoS/rGO gives an excellent rate capability even up to a large current of 2 A g−1. It is noted that the synergistic effect between CoS and graphene can contribute to the improved electrochemical performance.

The excellent cycling stability and superior rate capability of polypyrrole as the anode material for rechargeable sodium ion batteries

Polypyrrole with a submicrostructure has been successfully synthesized via a simple chemical oxidative polymerization. As characterized by X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM), the submicron polypyrrole shows a fluffy structure comprised chains composed of submicron particles. The submicron polypyrrole shows excellent electrochemical performance as the anode material for sodium ion batteries, which is much better than bulk polypyrrole. It displays a stable discharge capacity of 183 mA h g−1 at 400 mA g−1 after 100 cycles, whereas only 34.8 mA h g−1 for bulk polypyrrole under the same conditions. Furthermore, the submicron polypyrrole shows an extremely stable storage capacity during long term cycling even at super high rates. Except the irreversible capacity for the first cycle, the specific capacity remains stable and still maintains at 84 mA h g−1 after 500 cycles at 14 400 mA g−1. The remarkable electrochemical performance greatly suggests that the submicron polypyrrole is an advanced anode material for sodium ion batteries.