Preparation and electrochemical investigation of Li 2CoPO 4F cathode material for lithium-ion batteries

Abstract

In this paper, we report the electrochemical characteristics of a novel cathode material, Li 2CoPO 4F, prepared by solid-state reactions. The solid-state reaction mechanism involved in synthesizing the Li 2CoPO 4F also is analyzed in this paper. When cycled between 2.0 V and 5.0 V during cyclic voltammetry measurements, the Li 2CoPO 4F samples present one, fully reversible anodic reaction at 4.81 V. When cycled between 2.0 V and 5.5 V, peaks occurring at 4.81 V and 5.12 V in the first anodic scan evolved to one broad oxidative, mound-like pattern in subsequent cycles. Correspondingly, the X-ray diffraction (XRD) pattern of the Li 2CoPO 4F electrode discharged from 5.5 V to 2.0 V is slightly different from the patterns exhibited by a fresh sample and the sample discharged from 5.0 V to 2.0 V. This difference may correspond to a structural relaxation that appears above 5 V. In the constant current cycling measurements, the Li 2CoPO 4F samples exhibited a capacity as high as 109 mAh g −1 and maintained a good cyclability between 2.0 V and 5.5 V vs. Li/Li +. XRD measurements confirmed that the discharged state is Li 2CoPO 4F. Combining these XRD results and electrochemical data proved that up to 1 mol Li + is extractable when charged to 5.5 V.