SnOx/Carbon Core Shell Structure: An Efficient Anode for Rechargeable Sodium Ion Batteries
The major obstacle in realizing NIBs has been the absence of suitable anodes. Most of all, graphite which has been a commercially well-known anode material for LIBs cannot be used as an insertion host for Na ions due to their large ionic size. Moreover, only few noticeable studies on negative electrode materials, e.g., lead and hard carbon have been reported thus far. Metal oxides are considered to be important electrode materials, as they follow a conversion reaction mechanism. However, metal oxides suffer from several problems when used as anode materials which limit their use, such as swelling and shrinking of active material particles upon the insertion and extraction of Li+ or Na+ ions, which can induce poor contact between the active materials and the electron conducting agents, leading to low electric and ionic conductivity.
In this study, we report the electrochemical activity of carbon coated SnOx nanostructures for NIBs. The nanostructured SnOx were synthesized by a hydrothermal method and their surfaces were coated by carbon to improve the electric conductivity. The effect of solvent used for hydrothermal process and annealing temperature on the structure, morphology and Na storage capacity was investigated. The single phase SnO2 was obtained using ethanol solvent, while the blend of SnO and SnO2 was obtained using DI water and ethylene glycol solvents. The transmission electron microscopic images conform the presence of carbon coating on the SnOx nanoparticles. Further, the anodes made of carbon coated SnOx prepared in ethanol solvent exhibited stable cycling performance and attained the capacity of about 443 mAh/g in the first charge. With the help of the conductive carbon, the carbon coated SnO2 delivered more capacity at high rates; 257 mAh/g at the 1 C-rate, 156 mAh/g at the 5 C-rate and 70 mAh/g at the 10 C-rate. The excellent cyclability and high-rate capability are attributed to the formation of a mixed conducting network and the uniform carbon coating formed on the SnO2 nanoparticles.