Al掺杂的尖晶石型LiMn_2O_4的结构和电子性质  

Structural and electronic properties of Al-doped spinel LiMn_2O_4

作　　者：高潭华[1] 刘慧英[2] 张鹏[3] 吴顺情[3] 杨勇[4] 朱梓忠[3,5] 

机构地区：[1]武夷学院电子工程系,武夷山354300 [2]集美大学理学院,厦门361021 [3]厦门大学物理系,厦门361005 [4]厦门大学固体表面物理化学国家重点实验室,厦门361005 [5]福建省理论与计算化学重点实验室,厦门大学,厦门361005

出　　处：《物理学报》2012年第18期467-475,共9页Acta Physica Sinica

基　　金：国家重点基础研究发展计划(批准号:2011CB935903);福建省自然科学基金(批准号:2008J04018)资助的课题~~

摘　　要：采用基于密度泛函理论的第一性原理方法,在广义梯度近似(GGA)和GGA+U方法下对尖晶石型LiMn_2O_4及其Al掺杂的尖晶石型LiAl_(0.125)Mn_(1.875)O_4晶体的结构和电子性质进行了计算.结果表明:采用GGA方法得到尖晶石型LiMn_2O_4是立方晶系结构,其中的Mn离子为+3.5价,无法解释它的Jahn-Teller畸变.给出的LiMn_O_4能带结构特征也与实验结果不符.而采用GGA+U方法得到在低温下的LiMn_2O_4和其掺杂体系LiAl_(0.125)Mn_(1.875)O_4的晶体都是正交结构,与实验一致.也能明确地确定Mn的两种价态Mn^3+/Mn^(4+)的分布并且能够说明Mn^3+O_6的z方向有明显的Jahn-Teller畸变,而Mn^(4+)O_6则没有畸变.LiMn_2O_4的能带结构与实验比较也能够符合.采用GGA+U方法对Al掺杂体系的LiAl_(0.125)Mn_(1.875)O_4的研究表明,用Al替换一个Mn不会明显地改变晶体的电子性质,但可以有效地消除Al^3+O_6八面体的Jahn-Teller畸变,从而改善正极材料LiMn_2O_4的性能,这与电化学实验的观察结果相一致.The structural and electronic properties of spinel LiMn204 and its A1 doping system LiAlo.125Mnl.s75Oa are investigated within the density functional theory in both the generalized gradient approximation （GGA） and the GGA with Hubbard U correc- tion （GGA＋U）. The results from the GGA method suggest that LiMn204 has a cubic structure and the valences of Mn ions are all ＋3.5, which is unable to explain the John-Teller distortions in the material. The band structure of LiMn204 predicted by the GGA method is also inconsistent with experimental result. With the GGA＋U method, the low temperature structures of LiMn204 and its A1 doping system LiAlo.125Mnl.s7504 are shown to be orthogonal, the two different valence states of Mn, i.e., Mn3＋/Mn4＋ ions, are then determined, which is then able to explain the John-Teller distortion in octahedron Mna＋O6 and the non-existence of distortion in octohedron Mn4＋O6. These results are in good accordance with experimental data. Their band structures by GGA＋U calculations are also consistent with experimental results. The GGA＋U calculations on the LiAlo.125Mnl.s7504 indicate that with the replacement of an Mn by A1, the crystal structure and electronic properties are not significantly changed, but the John-Teller distortion in octahe- dron A13＋O~ can be effectively eliminated, which could improve the performance of the anode materials based on LiMn204. The phenomenon is in consistent with the electrochemical experiments.

关 键 词：LiMn_2O_4 AL掺杂 电子结构 第一原理计算 

分 类 号：O469[理学—凝聚态物理]