Effects of Preinserted Na Ions on Li-Ion Electrochemical Intercalation Properties of V₂O₅

Na-preinserted V2O5 samples of NaxV2O5 (x = 0.00, 0.005, 0.01, or 0.02) were synthesized through sol-gel and freeze-drying routes and subsequent calcination. X-ray diffraction (XRD) results showed that all of the synthesized materials have typical orthorhombic structures without impurity phases. The lattice parameters were refined via the Rietveld refinement method, and the results suggested that the lattice parameters of preinserted samples increased in comparison with pristine V2O5. X-ray photoelectron spectroscopy (XPS) measurements demonstrated that the V(4+) concentration in the Na-preinserted V2O5 samples gradually increased as amount of sodium increased. Results from both XRD and XPS strongly suggested that Na ions indeed enter the interlamination position in the V2O5 crystal to expand the channels for Li-ion migration. NaxV2O5 samples exhibited improved electrochemical properties compared with those of pristine V2O5. Among all of the samples, Na0.01V2O5 delivered the highest reversible specific capacity, best cycling stability, and excellent rate capability. The analysis and discussion on ion diffusion revealed that the preinserted Na ions benefited the mobility of Li ions to improve the rate capabilities of electrodes.