LiMn_(0.8)Fe_(0.2)PO_4/C纳米复合材料的制备与电化学性能研究  

Preparation and Electrochemical Properties of LiMn_(0.8)Fe_(0.2)PO_4/C Nanocomposite

作　　者：苏婧[1] 吴兴隆[1] 郭玉国[1] 

机构地区：[1]中国科学院化学研究所分子纳米结构与纳米技术院重点实验室,北京100190

出　　处：《无机材料学报》2013年第11期1248-1254,共7页Journal of Inorganic Materials

基　　金：国家杰出青年科学基金(51225204);国家重大科学研究计划项目(2012CB932900);国家863计划(2012AA110407);新能源汽车产业动力电池创新项目((2012)1110号)~~

摘　　要：结合溶胶-凝胶和高温固相合成方法成功制备了橄榄石结构的LiMn0.8Fe0.2PO4/C固溶体材料, X射线粉末衍射（XRD）、扫描电子显微镜（SEM）和透射电子显微镜（TEM）表征结果表明纳米尺度的LiMn0.8Fe0.2PO4颗粒均匀分散于原位形成的碳导电网络中。将该纳米复合材料用作锂离子电池正极材料时, 充放电曲线中除了对应于Fe3＋/Fe2＋电对的较短平台（-3.5 V vs Li＋/Li）外, 更高电压的长平台（-4.1 V vs Li＋/Li）对应于LiMn0.8Fe0.2PO4晶格中Mn随Li＋脱出嵌入的氧化还原反应, 该高的电压平台可明显提高相应锂离子电池的能量密度。此外, 使用恒电流间歇滴定技术（GITT）和电化学阻抗谱（EIS）详细研究了LiMn0.8Fe0.2PO4/C电极中锂的化学扩散行为, GITT和EIS所得的锂化学扩散系数DLi分别为5×10-15 - 1×10-14 cm2/s和1.27×10-13 - 2.11×10-13 cm2/s。研究结果表明, DLi值随测试温度的升高而增加, 因此可以通过提高工作温度来改善该类材料的电化学性能。Olivine-structured LiMn0.8Fe0.2PO4/C solid solution was successfully prepared by a Sol-Gel approach combined with a high-temperature solid-state reaction, and characterized by X-ray diffraction （XRD）, scanning electron microscope （SEM） and transmission electron microscope （TEM）. The results revealed that LiMn0.8Fe0.2PO4 nanoparticles were evenly dispersed in the in-situ formed carbon conductive network. When the nanocomposite served as a cathode material for lithium-ion batteries （LIBs）, except a short plateau （~3.5 V vs Li＋/Li） ascribed to Fe3＋/Fe2＋ couples in the charging/discharging profile, the long plateau at higher voltage （~4.1 V vs Li＋/Li） is corresponding to the redox reaction of Mn during the Li＋ extraction/insertion in the LiMn0.8Fe0.2PO4 lattice, and this high voltage plateau can significantly enhance the energy density of relevant LIBs. In addition, the chemical diffusion behavior of lithium in the LiMn0.8Fe0.2PO4/C electrode was investigated in detail using galvanostatic intermittent titration technique （GITT） and electrochemical impedance spectroscope （EIS）, and the chemical diffusion coefficients of lithium, DLi, obtained by GITT and EIS were 5×10-15 -1×10-14 cm2/s and 1.27×10-13- 2.11×10-13 cm2/s, respectively. The results indicate that the value of DLi increases with elevated test temperature, and it can be inferred that the electrochemical properties of such materials can be improved by raising the working temperature.

关 键 词：LiMn0 8Fe0 2PO4 C纳米复合材料 恒电流间歇滴定技术 电化学阻抗谱 锂化学扩散系数 锂离子电池 

分 类 号：TQ174[化学工程—陶瓷工业]