Structure and Performances of xLiFePO4/C·(1 − x)Li3V2(PO4)3/C Cathode for Lithium‐Ion Batteries by Using Poly(vinyl alcohol) as Carbon Source

Abstract

Poly(vinyl alcohol), whose pyrolysis carbon possesses high conductivity of 8.88 × 10−1 S/cm, was used to synthesize xLiFePO4/C·(1 − x)Li3V2(PO4)3/C cathode. It was characterized by X‐ray diffraction, scanning electron microscopy, conductivity, cyclic voltammetry, and galvanostatic charge and discharge experiments. Results show that LiFePO4/C and Li3V2(PO4)3/C coexists in the cathode. The particles sizes of 0.75LiFePO4/C·0.25Li3V2(PO4)3/C (x = 0.75) are much smaller than 100 nm due to the role of poly(vinyl alcohol). Its conductivity is 8.79 × 10−2 S/cm. The oxidative and reductive peaks in cyclic voltammetry are sharp and symmetrical. Their low potential gaps indicate that the extractions and insertions of lithium ion possess excellent reversibility. Its discharge capacities at 1 and 5 C are 141.1 and 100.1 mAh/g. The more Li3V2(PO4)3/C in cathode results in the deterioration of electrochemical performances due to its low theoretical capacity. It is concluded that poly(vinyl alcohol) is an effective carbon source in the preparation of xLiFePO4/C·(1 − x)Li3V2(PO4)3/C composite cathode with excellent performances.