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

Abstract

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.

submitted