Synthesis And Electrochemical Performance Study Of LiFePO₄Synthesized Using The Iron Sludge As Start Material

LiFePO4is a very promising cathode material for rechargeable lithium-ironbatteries, because of its low cost, environmental benignity, cycle stability, lowtoxicity and relatively high safety, with a theoretical capacity of170mAh/g and a3.4V discharge plateau vs. Li+/Li.FePO4·2H2O and Fe2O3are recovered from iron sludge and then used as ironsources of LiFePO4/C, which is synthesized via carbothermal reduction method. Thecomposition analysis of the materials is carried out with Inductive Coupled PlasmaEmission Spectrometer (ICP); the number of the crystal water is measured viaThermogravimetric (TGA); Crystal structure and morphology is observed via X-rayDiffraction (XRD), and morphology is observed via Field-emission Scanning ElectronMicroscopy (FE-SEM) and Transmission Electron Microscopy (TEM);electrochemical performance is examined via galvanostatic charge/discharge andCyclic Voltammetry (CV).LiFePO4/C is synthesized via carbothermal reduction method with recoveredFePO4·2H2O, LiOH·H2O and sucrose.The dependence of morphology of FePO4·2H2O on pH is investigated and theoptimal pH is2.1. The number of the crystal water is measured via TGA. AnotherLiFePO4/C sample is synthesized using FePO4·2H2O prepared from commercialreagents under the same condition as a comparison. The discharge capacity of theLiFePO4/C synthesized using iron sludge as start material at0.1C is146.6mAh/g,which is a little bit low, but it has better rate performance and cyclic stability.The process route of recovering Fe2O3from iron sludge is studied and theas-prepared Fe2O3is then used as iron source for synthesizing LiFePO4/C. As a result,the LiFePO4/C using a ball-milled and without HNO3treated Fe2O3as iron sourceshows better rate performance and cyclic stability, with a first cycle dischargecapacity of142.2mAh/g at0.1C and capacity retention of94.2%,84.4%at0.5C and1C, respectively.Fe powder is used as reductant for synthesizing LiFePO4/C. SEM images showthat the particles are of great aggregation. The LiFePO4/C has a low cyclic stability atlow current rate and high cyclic stability but low capacity at high current rate. Zn, Mn and W doped LiFePO4/C are synthesized and tested, with a low capacity of101.72mAh/g,76.20mAh/g and95.10mAh/g at0.1C respectively. The LiFePO4/C showpoor cyclic stability at low current rate and high cyclic stability but low capacitance athigh current rate.