Synthesis, characterization, and electrochemical performance of LiFePO _4/C cathode materials for lithium ion batteries using various carbon sources: Best results by using polystyrene nano-spheres

摘要

Olivine LiFePO _4/C cathode materials for lithium ion batteries were synthesized using monodisperse polystyrene (PS) nano-spheres and other carbon sources. The structure, morphology, and electrochemical performance of LiFePO _4/C were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), galvanostatic charge-discharge tests, electrochemical impedance spec-troscopy (EIS) measurements, and Raman spectroscopy measurements. The results demonstrated that LiFePO _4/C materials have an ordered olivine-type structure with small particle sizes. Electrochemical analyses showed that the LiFePO _4/C cathode material synthesized from 7 wt.% PS nano-spheres delivers an initial discharge capacity of 167 mAh g ~(-1) (very close to the theoretical capacity of 170 mAh g ~(-1)) at 0.1 C rate cycled between 2.5 and 4.1 V with excellent capacity retention after 50 cycles. According to Raman spectroscopy and EIS analysis, this composite had a lower I D/I G, sp ~3/sp ~2 peak ratio, charge transfer resistance, and a higher exchange current density, indicating an improved electrochemical performance, due to the in-creased proportion of graphite-like carbon formed during pyrolysis of PS nano-spheres, containing functionalized aromatic groups.