Na-ion diffusion and electrochemical performance of NaVO3 anode in Li/Na batteries
Abstract
We study Na ion diffusion and electrochemical performance of NaVO3 (NVO) as anode material in Li/Na--ion batteries with the specific capacity of ≈350 mAhg-1 at the current density 11~mAg-1 after 300 cycles. Remarkably, the capacity retains 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~cm2s-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.