Preparation and electrochemical investigation of Li2CoPO4F cathode material for lithium-ion batteries

In this paper, we report the electrochemical characteristics of a novel cathode material, Li2CoPO4F, prepared by solid-state reactions. The solid-state reaction mechanism involved in synthesizing the Li2CoPO4F also is analyzed in this paper. When cycled between 2.0 V and 5.0 V during cyclic voltammetry measurements, the Li2CoPO4F 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 Li2CoPO4F 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 Li2CoPO4F 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 Li2CoPO4F. Combining these XRD results and electrochemical data proved that up to 1 mol Li+ is extractable when charged to 5.5 V.

Research highlights▶ Li2CoPO4F samples present one, fully-reversible anodic reaction at 4.81 V. ▶ The Li2CoPO4F samples exhibited a capacity as high as 109 mAh/g and maintained a good cyclability between 2.0 V and 5.5 V vs. Li/Li+.