Synthesis And Electrochemical Performance Of LiMnPO₄for Cathode Material Of Lithium-ion Batteries

Due to the theoretical specific capacity of LiMnPO₄as170mAh/g and a voltageplatform of4.1V vs. Li/Li⁺, the battery with LiMnPO₄as cathode material has a highenergy density. Moreover, due to the low cost and environment friendly, LiMnPO₄hasgood application potential.The LiMnPO₄/C composite was prepared by high temperature solid state methodand sol-gel method, respectively. A suitable heat treatment temperature was selectedby TG-DTA test, the phase structure and morphology of the obtained materials wereinvestigated by x-ray diffraction （XRD）, scanning electron microscopy （SEM）andtransmission electron microscopy （TEM）; the electrochemical performance wasstudied by the charge/discharge test and cyclic voltammetry method（CV）.The phase structure, morphology and electrochemical performance of theLiMnPO₄/C composties was studied, which prepared by high temperature solid statereaction using sucrose and super conductive carbon black BP2000as carbon source.The result indicated that the property of composite add two mixed carbon source isbetter than that add either alone. A series of iron-doped LiMnPO₄materials wereprepared, the quality amount of doped iron was0,0.05,0.1,0.15,0.2, respectively. Itpresented that the solid solution material of LiMn1-xFexPO4/C have high crystallinityand homogeneous particle size. The first discharge specific capacity of iron-dopedsamples achieve at155.5mAh/g（x=0.05）,137.4mAh/g （x=0.1）,153.5mAh/g（x=0.15）,117.3mAh/g（x=0.2）, respectively, which is much higher than the un-doped one of64.3mAh/g. Meanwhile, the doped materials have higher discharge capacity retention.The sol-gel preparation of LiMnPO₄/C using citric acid as complexing agent andthe effect of the precursor concentration and heat-treatment temperature on thestructure and electrochemical performance of LiMnPO₄/C have been explored. Itshowed that the obtained LiMnPO₄/C compostite have small, homogenous size ofabout100nm, a good cycling performance and rate charge-discharge property and thefirst discharge specific capacity of93.2mAh/g at0.1C with the selected precursorconcentration of0.75M and the selected heat-treatment temperature of550℃.