快离子导体La_(0.8)Sr_(0.2)MnO_3包覆LiMn_2O_4正极材料的结构和电化学性能

Structure and Electrochemical Performance of LiMn_2O_4 Cathode Materials Coated with Fast Ionic Conductor La_(0.8)Sr_(0.2)MnO_3

为进一步提高动力电池正极材料锰酸锂(LiMn_2O_4)的循环稳定性,通过溶胶-凝胶法用快离子导体La_(0.8)Sr_(0.2)MnO_3作为包覆材料对LiMn_2O_4进行表面修饰,探讨了不同包覆量对复合材料电化学性能的影响。采用X射线衍射仪(XRD)、场发射扫描电镜(FESEM)和透射电子显微镜(TEM)对样品的微观结构以及形貌进行表征。结果表明:La_(0.8)Sr_(0.2)MnO_3的包覆并没有改变LiMn_2O_4晶体结构及空间构型;相比纯的LiMn_2O_4样品,La_(0.8)Sr_(0.2)MnO_3包覆后的样品颗粒表面较为粗糙;涂层为薄膜状结构,均匀且完全包覆在LiMn_2O_4颗粒的表面。利用电化学测试方法测试其电化学性能,测试结果表明,当La_(0.8)Sr_(0.2)MnO_3包覆量为5%时,具有较好的电化学性能,首次放电比容量为127.4 m A·h/g(0.1 C),25℃循环400次后容量保持率为91.2%,55℃循环100次后容量保持率为91.1%;与未经表面修饰的样品相比,其首次放电比容量为119.1 m A·h/g(0.1 C),400次的容量保持率为61.9%,100次容量保持率为77.9%,La_(0.8)Sr_(0.2)MnO_3包覆后的样品的电化学性能尤其是循环性能得到明显的提高。

LiMn_2O_4 coated with La_(0.8)Sr_(0.2)MnO_3 fast ionic conductor was synthesized by sol-gel method,and the influence of coating content on the electrochemical performance was explored.X-ray diffractometer(XRD),field emission scanning electron microscope(FESEM) and transmission electron microscope(TEM) were employed to characterize the microstructure and morphology of sample.Results showed that La_(0.8)Sr_(0.2)MnO_3 coating did not change the crystal structure and spatial configuration of LiMn_2O_4.Compared with pure LiMn_2O_4,the sample particles coated with La_(0.8)Sr_(0.2)MnO_3 appeared rougher surface.The coating was membranous structure,and entirely coated the surface of LiMn_2O_4 particles.In addition,the electrochemical performance was evaluated by electrochemical method,and the test showed that when La_(0.8)Sr_(0.2) MnO_3 content was 5%,the sample had better electrochemical performance with 127.4mA ? h/g(0.1 C) of discharge specific capacity of the first cycle,91.2%of capacity retention ratio after 400 times cycle at 25 ℃and 91.1%after 100 times cycle at 55 ℃.By contrast,the initial LiMn_2O_4 without modification had only 119.1 mA ? h/g at 0.1 C,the capacity retention ratios were 61.9%and 77.9%after 400 and100 cycles,respectively.Therefore,the electrochemical performance,especially cycle performance of LiMn_2O_4 coated with La_(0.8)Sr_(0.2)MnO_3 was improved apparently.