Co2GeO4 nanocomposites with reduced graphene oxide and carbon nanotubes as high-performance anodes for Na-ion batteries

Abstract

Heterostructure nanomaterials have attracted attention as potential anodes for sodium-ion batteries (NIBs), owing to their outstanding properties. In this work, a single-step facile hydrothermal route was adopted for the synthesis of Co₂GeO₄, Co₂GeO₄/rGO, and Co₂GeO₄/MWCNT nanocomposites. The X-ray diffraction analysis reveals the spinel phase formation of Co₂GeO₄, Co₂GeO₄/rGO, and Co₂GeO₄/MWCNTs. Scanning and transmission electron microscopy results depict the growth of pristine Co₂GeO₄ and Co₂GeO₄/rGO nanocomposites in the nanoscale size with sharp-edge plate-like morphology, while plate-like particles in Co₂GeO₄/MWCNT nanocomposites are grown on the surface and inside MWCNTs. The chemical bonding, oxidation state of elements in the composition, and the presence of rGO and MWCNTs are confirmed by X-ray photoelectron spectroscopy. The galvanostatic measurements reveal that Co₂GeO₄, Co₂GeO₄/rGO, and Co₂GeO₄/MWCNT electrodes exhibit specific capacities of 314, 425 and 475 mA h g⁻¹ respectively at a rate of 0.05C. The rate capability and long cycle testing results show higher specific capacity and structural stability of Co₂GeO₄/MWCNT nanocomposites. Co₂GeO₄/MWCNT nanocomposites show a specific capacity of 108 mA h g⁻¹ at a high current density of 6.4C. Sodium diffusion coefficient was calculated using a galvanostatic intermittent titration technique and values were calculated in the range of 10⁻¹⁴ to 10⁻¹⁶ cm² s⁻¹ and 10⁻¹³ to 10⁻¹⁶ cm² s⁻¹ for Co₂GeO₄/rGO, and Co₂GeO₄/MWCNTs, respectively, which are greater than the values of pristine Co₂GeO₄ (10⁻¹⁵ to 10⁻¹⁷ cm² s⁻¹). This indicates the improved sodium-ion diffusion kinetics of Co₂GeO₄/rGO and Co₂GeO₄/MWCNT nanocomposites, indicating their superior electrochemical performance to pristine Co₂GeO₄.