In situ and ex situ carbon coated Zn2SnO4 nanoparticles as promising negative electrodes for Li-ion batteries

Abstract

Zinc stannate, Zn₂SnO₄ nanoparticles are successfully synthesized by a facile hydrothermal method. Subsequently, a layer of carbon is coated on Zn₂SnO₄ nanoparticles by both in situ and ex situ methods using glucose as a carbon source. The phase purity, carbon content, oxidation state and morphological features are characterized by various techniques. The percentage of carbon present in the Zn₂SnO₄ is calculated using thermogravimetric analysis. The core–shell structure of Zn₂SnO₄@C is revealed through high resolution transmission electron microscope images. The electrochemical performance of the Zn₂SnO₄@C is examined by dQ/dV, charge–discharge, rate capability and electrochemical impedance spectroscopy analysis. Among these, the ex situ carbon coated Zn₂SnO₄ shows superior cycling stability and it delivered a stable specific discharge capacity of 533 mA h g⁻¹ at 700 mA g⁻¹ over 50 cycle. The EIS analysis indicates that the obtained low charge transfer resistance (R_ct) and solid electrolyte interphase (SEI) film resistance (R_SEI) of the ex situ carbon coated Zn₂SnO₄ controls the SEI film thickness on the outer surface of the active material. Overall, the electrochemical analysis elucidates that the ex situ carbon coated Zn₂SnO₄ shows an excellent cycling stability and good electronic conductivity compared with carbon free and in situ carbon coated Zn₂SnO₄.