Extended Data Fig. 1: Characterization of lithium ion diffusivity and charge storage of RS-Nb2O5 and a-Nb2O5 sample.
a, GITT measurements of the RS- and a-Nb2O5 electrodes. b, The logarithmic plot of Li ion diffusivity as a function of voltage by GITT measurements. Overall, RS-Nb2O5 exhibited an order of magnitude higher Li ion diffusivity compared to a-Nb2O5 within the potential window during lithiation. During the cathodic scan, both samples experienced a gradual decrease in diffusivity as more Li+ occupied the vacant sites in the host material. It is worth noting that below 1.1 V, Li+ diffusivity in RS-Nb2O5 slightly increased, concurrent with the ongoing phase transformation upon cycling. Li+ diffusivity in RS-Nb2O5 is also higher than that of other polymorphs of Nb2O5 electrodes. c and d, cyclic voltammograms of RS- and a-Nb2O5 electrodes at varying scan rates. Insights in terms of diffusion and capacitive contribution to Li storage can be obtained by analyzing the peak current (i) dependence on scan rate (ν). For a redox reaction limited by semi-infinite diffusion, the peak current is proportional to the square root of the scan rate (ν1/2); while for a capacitive process it varies linearly with ν44,45. A b value can be obtained by analyzing the power law relationship between i and ν via i = aνb, where a and b are adjustable parameters. It was found that the b values for RS-Nb2O5 and a-Nb2O5 sample were ~0.85 and ~0.80, respectively. The results suggest both electrodes have mixed contribution from diffusion and capacitive process with RS-Nb2O5 electrode having a slightly higher capacitive contribution indicative of a faster kinetic in RS-Nb2O5.
