Na-ion diffusion and electrochemical performance of NaVO${}_3$ anode in Li/Na batteries

We study Na ion diffusion and electrochemical performance of NaVO${}_3$ (NVO) as anode material in Li/Na–ion batteries with the specific capacity of $\approx$350 mAhg${}^{-1}$ at the current density 11~mAg${}^{-1}$ after 300 cycles. Remarkably, the capacity retains $\ge$200~mAhg${}^{-1}$ even after 400~cycles at 44~mAg${}^{-1}$ with Coulombic efficiency $>$99%. The deduced diffusion coefficient from galvanostatic intermittent titration technique (GITT), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) measurements for NVO as anode in Li–ion battery is in the range of 10${}^{-10}$–10${}^{-12}$~cm${}^2$s${}^{-1}$. In case of Na-ion batteries, the NVO electrode exhibits initial capacity of 385~mAhg${}^{-1}$ at 7~mAg${}^{-1}$ current rate, but the capacity degradation is relatively faster in subsequent cycles. We find the diffusion coefficient of NVO–Na cells similar to that of NVO–Li. On the other hand, our charge discharge measurements suggest that the overall performance of NVO anode is better in Li–ion battery than Na-ion. Moreover, we use the density functional theory to simulate the energetics of Na vacancy formation in the bulk of the NVO structure, which is found to be 0.88~eV higher than that of the most stable (100) surface. Thus, the Na ion incorporation at the surface of the electrode material is more facile compared to the bulk.