Kinetic insight into the electrochemical sodium insertion-extraction mechanism of the puckered γ′-V2O5 polymorph

Abstract The kinetics of the electrochemical Na reaction in the γ′-V2O5 polymorph prepared by the carboreduction route is investigated by electrochemical impedance spectroscopy. This cathode material with puckered layer structure is capable of delivering a high discharge capacity of 143 mAh g−1 at a relatively high operating voltage of 3.3 V vs. Na+/Na. In spite of a good cyclability, a low efficiency of the first charge process limits yet the value of the stable capacity of this material upon cycling. The present study intends to give further insight into the sodium insertion-extraction mechanism in γ′-V2O5 by achieving a picture of the main kinetic parameters as a function of Na uptake in γ-NaxV2O5 electrodes (0 ≤ x ≤ 0.97). We show that the evolution of cathode impedance, charge transfer resistance, double layer capacity and apparent chemical Na diffusion coefficient are highly correlated to the structural changes induced upon sodiation. A faster Na diffusion is revealed in the richest 0.6