Electrochemical Lithium Insertion Behavior of β-LixV2O5 (0 < x ≤ 3) as the Cathode Material for Secondary Lithium Batteries

Abstract

Electrochemical lithium insertion/extraction reaction in the β-LixV2O5 phase (0 < x ≤ 3) as the cathode material for rechargeable lithium batteries was examined. Of interest is the rigid 3D host lattice of the monoclinic tunnel-like β lithium bronze that shows desirable structural reversibility upon high Li uptakes (∼3 mol per formula unit), and a remarkable discharge capacity exceeding 330 mA h g−1 during 50 cycles were obtained at 10 mA g−1 in the 4.0/1.8 V potential range. Owing to the complicated ordering processes of crystallographic site occupancy, the pure Li-inserted β phase exhibits rather complex electrochemical properties. New Li diffusivity data within the entire concentration range were obtained by electrochemical impedance spectroscopy and galvanostatic intermittent titration. The slow diffusion kinetics at the deeply discharged state (x > 2.0) is mainly responsible for the large polarization during the process as well as a notable capacity drop (around 24% of the initial low-rate capacity) at a higher rate (50 mA g−1). Further, an abrupt decline in the kinetics of charge-transfer during 0.33 < x ≤ 1.0 is discovered, which results from the re-arrangement of the inserted Li+ among the various interstatial sites in the tunnel framework as lithiation proceeds.