Synthesis And Modification Of The Composite Cathode Material LiMn_1-xFe_xPO₄/C

Abstract:LiMn1-xFexPO4/C composite cathode materials for lithium-ion batteries have the potential advantage of high energy density. However, the materials suffer of poor reversibility of Mn3+/Mn2+redox and Jahn-Teller during the charge-discharge process, which result in poor rate and cycle performances. In this paper, solid-state method and co-precipitation method of LiMn1-xFexPO4/C powders has been investigated in detail.Phase-pure LiMnPO4/C cathode material was synthesized by high temperature solid-state method using MnO, MnC2O4·2H2O, MnCO3and Mn (CH3COO)2powder as manganese source, Li2CO3, NH4H2PO4and glucose as Li+, PO43-and carbon source, respectively. XRD, SEM, TEM technique, galvan charge-discharge and cyclic voltammetry tests were taken. Highly pure LiMnPO4samples with fine crystalline and uniform particle size in200-500nm were abtained by MnC2O4·2H2O mechanical activation method, it showed a comparable energy storage capability having discharge capacity of81mAh/g at0.05C-rate, with a good discharge plateau around3.94V and good cyclic stability. Two-step sintering process was used to modifycation the synthesis method. LiMnPO4/C samples with uniform partical size in100nm were abtained which were coated by a homogeneous carbon layer. The samples showed a comparable discharge capacity of105.3mAhg-1at0.05C-rate.LiMnPO4/C composite was prepared by using MnC2O4·2H2O as raw material. The synthetic conditions of MnC2O4·2H2O were optimized by investigating pH value, which affects the structure, morphology and properties of obtained LiMnPO4/C materials. The LiMnPO4/C samples synthesized from precursors precipitated under pH=5delivers a specific capcity of103mAhg-1.LiMn1-xFexPO4/C were prepared by using Mn1-xFexC2O4·2H2O as raw material. Fe content and pH value effect the structure and morphology of Mn1-xFexC2O4·2H2O. Fe content effects the properties of obtained LiMn1-xFexPO4/C samples. The LiMn0.85Fe0.15PO4/C maintained the discharge capacity of130.8、128.6、23.3、103.0and87.8mAhg-1at0.05、0.1、0.2、0.5、1C, respectively. The Mg doping composite material Li (Mn0.9Fe0.10)0.97Mg0.03PO4/C was prepared by high temperature solid state method, which had discharge specific capacity of129.7.131.0.126.5、120.8、117.6and88mAhg-1at0.05、0.1、0.2、0.5、1and2C, respectively.