Synthesis and electrochemical properties of polyhedron-shaped Li3V2−xSnx(PO4)3 as cathode material for lithium-ion batteries

Sn-doped Li3V2−xSnx(PO4)3/C (x = 0, 0.02, 0.04, 0.08) composites are prepared using an ultrasonic-assisted sol–gel method under a static inert atmosphere. The effects of Sn-doping on the structure and electrochemical performance of Li3V2(PO4)3/C are investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical measurements. The XRD patterns demonstrate that Sn-doping affects the preferred crystal growth direction of Li3V2(PO4)3. The SEM results show that the particles of the Sn-doped samples have a polyhedron shape. The particles are micron-size and present high crystallinity. The Li3V1.98Sn0.02(PO4)3/C sample, which has initial capacities of 122.7 and 117.2 mAh g−1 at 0.2 and 5 C between 3.0 and 4.3 V, respectively, shows the best electrochemical performance among obtained samples. During Li+ de-intercalation and intercalation processes, Sn4+ could functions as a cushion bracket to protect the Li3V2(PO4)3 crystal lattice from shrinking, which greatly improves the rate performance and cycling performance of Li3V2(PO4)3.