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

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.