Preparation of LiFePO4 added PPy as cathode materials for li-ion battery

Abstract

LiFePO4 is an alternative cathode material for lithium-based battery cells. LiFePO4 demonstrates many advantages such as non-toxicity, low cost, and stable structure. One of the main problems of LiFePO4 is its low electronic conductivity, which results in its poor rate capability due to the poor kinetics of lithium intercalation/deintercalation process. The objective of this study is to increase the electrical conductivity of LiFePO4. An in-situ carbon source such as polypyrrole PPy was applied to prepare LiFePO4/C composites by heat treatment. The nature of polypyrole in the system can be considered not only as carbon source, but also as a structure director. The LiFePO4/C composites were prepared with the addition of PPy which were varied between 2.5, 5, 7.5, 10 and 15 % weight, and graphite also added in the amount of four times the PPy content. The crystal structure, surface morphology, elemental analysis, and conductivity of LiFePO4/C composites were characterized by X-ray diffraction and scanning electron microscopy combined with energy dispersive spectrometry and use of LCR meter, respectively. The XRD patterns of LiFePO4/C composites showed that the LiFePO4/C particles belong to a pure orthorhombic system of olivine-type structure (Pnma, JCPDS: 40-1499). Carbon phase was not found apparently from the XRD pattern, which indicated that it may be present in amorphous form. The particles morphology were composed of primary particles approximately 400 nm in diameter, with homogeneous pores and were agglomerated, while carbon deposition was observed on the surface. The addition of PPy increased the conductivity of materials. The highest conductivity of LiFePO4/C composite was 9.74 × 10−2 S cm−1 reached by the addition of 15% PPy.