Preparation and Electrochemical Properties of Li(3)V(2)(PO(4))(3−x)Br(x)/Carbon Composites as Cathode Materials for Lithium-Ion Batteries

Li(3)V(2)(PO(4))(3−x)Br(x)/carbon (x = 0.08, 0.14, 0.20, and 0.26) composites as cathode materials for lithium-ion batteries were prepared through partially substituting PO(4)(3−) with Br(−), via a rheological phase reaction method. The crystal structure and morphology of the as-prepared composites were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and electrochemical properties were evaluated by charge/discharge cycling and electrochemical impedance spectroscopy (EIS). XRD results reveal that the Li(3)V(2)(PO(4))(3−x)Br(x)/carbon composites with solid solution phase are well crystallized and have the same monoclinic structure as the pristine Li(3)V(2)(PO(4))(3)/carbon composite. It is indicated by SEM images that the Li(3)V(2)(PO(4))(3−x)Br(x)/carbon composites possess large and irregular particles, with an increasing Br(−) content. Among the Li(3)V(2)(PO(4))(3−x)Br(x)/carbon composites, the Li(3)V(2)(PO(4))(2.86)Br(0.14)/carbon composite shows the highest initial discharge capacity of 178.33 mAh·g(−1) at the current rate of 30 mA·g(−1) in the voltage range of 4.8–3.0 V, and the discharge capacity of 139.66 mAh·g(−1) remains after 100 charge/discharge cycles. Even if operated at the current rate of 90 mA·g(−1), Li(3)V(2)(PO(4))(2.86)Br(0.14)/carbon composite still releases the initial discharge capacity of 156.57 mAh·g(−1), and the discharge capacity of 123.3 mAh·g(−1) can be maintained after the same number of cycles, which is beyond the discharge capacity and cycleability of the pristine Li(3)V(2)(PO(4))(3)/carbon composite. EIS results imply that the Li(3)V(2)(PO(4))(2.86)Br(0.14)/carbon composite demonstrates a decreased charge transfer resistance and preserves a good interfacial compatibility between solid electrode and electrolyte solution, compared with the pristine Li(3)V(2)(PO(4))(3)/carbon composite upon cycling.