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

TL;DR

This study investigates NaVO$_3$ as an anode material in Li/Na-ion batteries, demonstrating promising capacity retention and diffusion properties, with better performance in Li-ion batteries and insights from DFT on Na vacancy energetics.

Contribution

The paper provides comprehensive electrochemical characterization of NaVO$_3$ in Li/Na-ion batteries and explores Na vacancy formation energetics using density functional theory.

Findings

NaVO$_3$ retains ≥200 mAhg$^{-1}$ after 400 cycles in Li-ion batteries.

Diffusion coefficients are in the range of 10$^{-10}$–10$^{-12}$ cm$^2$s$^{-1}$ for both Li and Na systems.

NaVO$_3$ performs better in Li-ion batteries than in Na-ion 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.