Preparation and characterization of LiFePO 4 /graphene-oxide composites
- PDF / 1,841,082 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 94 Downloads / 269 Views
1266-CC03-02
Preparation and characterization of LiFePO4/graphene-oxide composites Hongming Yu, Ruijun Pan, Xuefei Chen, Wentao Song, Jian Xie, Xingbin Zhao* 1 Department of Materials Science and Engineering, Zhejiang University, 38 Zheda Road 310027, Hangzhou, China. ABSTRACT LiFePO4/graphene-oxide (GNO) composites were prepared by co-precipitation method. Their structure and morphology were investigated by X-ray diffraction, Fourier transform infrared spectra, field emission scanning electron microscopy, and transmission electron microscopy. A low content of GNO can be uniformly dispersed in the matrix of LiFePO4 nano particles, while at a higher content, GNO will aggregate severely and has a negative effect on the electrochemical performance of LiFePO4. Further heat treatment can improve the crystallinity of LiFePO4, and improve the electrochemical performance of LiFePO4 with a relatively low content of GNO. INTRODUCTION Ever since olivine structure lithium iron phosphate was proposed as a cathode material for Li-ion batteries by Padhi [1] in 1997, lots of research have been dedicated to this material due to its high safety, high specific capacity (170 mAh g-1), low cost and environmental benignity. Yet its intrinsically low conductivity should be improved before large scale use. By now, several ways such as doping with foreign atoms [2], coating with conductive materials [3, 4], reducing particle size [5], and creating a fast ion-conducting surface phase [6] have been developed to overcome this shortage. Among them, coating with carbon is always an effective way to increase the electronic conductivity of LiFePO4. However, the carbon content should be controlled as low as possible in consideration of energy density loss. Graphene, an intensively studied two-dimensional carbon material [7], possess a remarkable electronic mobility of 15 000 m2 V-1 s-1, which was described as massless Dirac fermins [8]. Although the hydrophobic nature of graphene makes it difficult to form a uniform dispersion in aqueous solution, it can become hydrophilic by adding oxygen-containing groups. The graphene based nanosheet can be obtained by exfoliation of graphite oxide [9]. In this work, a co-precipitation method was adopted to prepare LiFePO4/grphene-oxide (GNO) composites, the effect of GNO content and annealing treatment on the electrochemical performance of LiFePO4 was studied. EXPERIMENT Graphite oxide was prepared by a modified Hmmers’ method. The obtained graphite oxide powers can be easily dispersed in either water or dimethyl sulfoxide (DMSO). Graphene GNO solution was then obtained by exfoliation of graphite oxide through ultrasonication in DMSO solution at concentration of 1 mg ml-1.
A co-precipitation method was used to obtain LiFePO4/GNO composites. An equimolar aqueous solution of 0.1M FeSO4⋅7H2O and 0.1M H3PO4 was mixed together under stirring to form a suspension, into which a certain amount of GNO solution in DMSO was added, and then a 0.3M LiOH⋅H2O solution was added to the mixture with a Li:Fe:P molar ratio of
Data Loading...
