Synthesis and characteristics of Li3V2(PO4)3 as cathode materials for lithium-ion batteries

Monoclinic lithium vanadium phosphate, Li3V2(PO4)3, was synthesized by carbon-thermal reduction (RTC) under Ar atmosphere. The influence of sintering temperatures on the synthesis of Li3V2(PO4)3 has been investigated using X-ray diffraction (XRD), SEM and electrochemical methods. XRD patterns show that the Li3V2(PO4)3 compound with monoclinic crystal structure begins to appear at the temperature of less than 900 °C. As the temperature was ≥ 900 °C, pure monoclinic Li3V2(PO4)3 phase can be obtained. SEM results indicate that the particle size of as-prepared samples increased with the sintering temperature increase, as well as the presence of minor carbon particles on the surface of the sample particles, which are very useful to enhance the electronic conductivity of Li3V2(PO4)3. Charge/discharge tests show the 900 °C-sample exhibits the highest initial discharge capacity of 119.3 mAh/g at 10 mA/g in the voltage range of 3.0–4.2 V with good capacity retention. CV experiment exhibits that there are three anodic peaks at 3.61, 3.69 and 4.09 V on lithium extraction as well as three cathodic peaks at 3.58, 3.66 and 4.03 V on lithium reinsertion at 0.05 mV/s between 3.0 and 4.3 V. It is suggested that the optimal sintering temperature is 900 °C in order to obtain pure monoclinic Li3V2(PO4)3 with good electrochemical performance by CRT method, and the monoclinic Li3V2(PO4)3 can be used as candidate cathode materials for lithium-ion batteries.