PEG高温固相法合成-英文

Journal of Alloys and Compounds456(2008)

461–465

A soft chemistry synthesis routine for LiFePO4–C

using a novel carbon source

L.N.Wang a,X.C.Zhan a,Z.G.Zhang a,K.L.Zhang a,b,∗

a College of Chemistry and Molecular Sciences,Wuhan University,Wuhan430072,China

b Centre of Nanoscience and Nanotechnology Research,Wuhan University,Wuhan430072,China

Received17August2006;received in revised form13February2007;accepted20February2007

Available online23February2007

Abstract

As a novel carbon source,polyethylene glycol(PEG;mean molecular weight of10,000)was adopted to prepare LiFePO4–C cathode material by a very simple soft chemistry method,which was called rheological phase reaction by us.X-ray diffraction(XRD)reveal that the crystallized LiFePO4powder can be synthesized easily by rheological phase reaction at a relative low temperature(400◦C).Scanning electron microscopy (SEM)results indicate that after the decomposition of PEG,active material and porous structure carbon were left in the resultant products.An initial discharge capacity of162and139mAh g−1was achieved for500◦C sample at room temperature with C rates of0.06C(10mA g−1)and1C (170mA g−1),respectively.The satisfactory initial discharge capacity and superior rate capacity should attribute to the porous conductive carbon structure and the soft synthesis process.

©2007Elsevier B.V.All rights reserved.

Keywords:Cathode material;LiFePO4;PEG;Rheological phase reaction

1.Introduction

Due to its overwhelming advantages of low toxicity,good thermal stability and relatively high theoretical capacity,olivine type LiFePO4,which wasfirst introduced as a lithium batteries cathode material by Padhi et al.appears as a potential candidate to be used as positive electrode in next generation of Li-ion batteries[1–5].

As a material,however,LiFePO4is an insulator,which seri-ously limits its rate capability in lithium cells.It shows high electrochemical properties only at low charge–discharge rates owing to its low electronic conductivity and low lithium ion motion ability[6,7].Therefore,research on this insulating com-pound was up to now mostly devoted to enhance the composite’s conductivity by metal doping[8,9]or coating with the electron-ically conductive like carbon,metal and metal oxide[10–12].

Other possible means of improving the rate performance of LiFePO4materials are those of enhancing its ionic/electronic conductivity by optimization of particles with suitable prepara-tion procedures.In addition to the traditional solid-state reaction

∗Corresponding author.Tel.:+862787218484;fax:+862768754067.

E-mail address:klzhang@(K.L.Zhang).synthesis routine,alternative synthesis processes including sol–gel,hydrothermal,co-precipitation,microwave heating,etc. have developed continually[11,13–15].

In this work,an example of preparing LiFePO4material with nano-sizedfine particles by employing a novel carbon source of polyethylene glycol(PEG)with a very simple soft chem-istry method—the rheological phase reaction method[16–19]is provided.The solid reactants are fully mixed in a proper molar ratio,made up by adding the required amount of water or other solvent to a solid–liquid rheological body in which the solid particles and liquid substance are uniformly distributed.Then after reaction under suitable conditions,the product is obtained. Under the solid–liquid rheological state,many substances have new reaction properties.The resultant powders prepared by this method often show excellent electrochemical performance. The microstructure and the rate performance of the as-prepared LiFePO4–C were investigated.Also,an excellent organic carbon source—PEG was introduced.

2.Experimental

Li2CO3,FeC2O4·2H2O,NH4H2PO4and polyethylene glycol(mean molec-ular weight of10,000)powders were used as the starting materials by rheological phase reaction.They were mixed thoroughly by grinding.Then appropriate

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