化学学报 ›› 2013, Vol. 71 ›› Issue (07): 1029-1034.DOI: 10.6023/A13030294 上一篇    下一篇

研究论文

锂离子电池正极材料LiNi0.5Mn1.5O4金属掺杂的第一性原理研究

杨思七, 张天然, 陶占良, 陈军   

  1. 南开大学化学学院先进能源材料化学教育部重点实验室 天津 300071
  • 收稿日期:2013-03-17 出版日期:2013-07-14 发布日期:2013-04-17
  • 通讯作者: 陈军, E-mail: chenabc@nankai.edu.cn; Tel.: 022-23506808; Fax: 022-23509571. E-mail:chenabc@nankai.edu.cn
  • 基金资助:

    项目受国家自然科学基金重点项目(No. 21231005);科技部973纳米重大科学研究计划(No. 2011CB935900)和高等学校创新引智计划(No. B12015)资助.

First-principles Study on Metal-doped LiNi0.5Mn1.5O4 as a Cathode Material for Rechargeable Li-Ion Batteries

Yang Siqi, Zhang Tianran, Tao Zhanliang, Chen Jun   

  1. Key Laboratory of Advanced Energy Materials Chemistry (Ministry of Education), College of Chemistry, Nankai University, Tianjin 300071, China
  • Received:2013-03-17 Online:2013-07-14 Published:2013-04-17
  • Supported by:

    Project supported by the National Natural Science Foundation Key Project (No. 21231005), 973 (No. 2011CB935900) and 111 (No. B12015).

近来尖晶石相LiNi0.5Mn1.5O4被认为是一种有前景的二次锂离子电池正极材料. 但是其相对较差的循环性能和倍率性能限制了LiNi0.5Mn1.5O4的大规模应用. 金属掺杂被认为是一种提高其电化学性能的有效方法. 然而, 还急需深层次地理解掺杂对材料结构和电化学性质的影响. 采用第一性原理方法, 系统地研究了金属掺杂的LiM0.125Ni0.375Mn1.5O4 (M为Cr, Fe和Co)电极体系的结构与电子性质. 计算结果显示, 少量的过渡金属M取代LiNi0.5Mn1.5O4晶格中的Ni, 能够有效抑制材料在电化学脱嵌锂过程中的体积变化(从锂化相到脱锂相, 体积变化率约为4%, 而未掺杂的情况为4.7%), 提高材料循环性能. 体系态密度表明金属掺杂能够减小体系的带隙, 进而提高材料的电子传导. 另外, 通过Li离子的扩散计算, 我们发现与未掺杂的LiNi0.5Mn1.5O4相比, Co掺杂使得Li在材料中两条不同扩散路径的扩散能垒分别降低了约90 meV和140 meV, 表明Co掺杂有利于Li在材料中的快速扩散.

关键词: 第一性原理, 尖晶石相LiNi0.5Mn1.5O4, 掺杂, 体积变化率, 锂扩散能垒

Spinel LiNi0.5Mn1.5O4 is recently considered as a promising cathode material for rechargeable Li-ion batteries, yet its large-scale application is limited due to relatively poor cycling and rate performance. Metal doping is expected to be an effective approach to improve the electrochemical performance of spinel LiNi0.5Mn1.5O4. However, deeper understanding into doping effects on structural and electrochemical properties of LiNi0.5Mn1.5O4 electrode materials is still ambiguous. In this work, systematic first-principles studies based on the density functional theory (DFT) have been carried out to investigate electronic and structural properties of LiM0.125Ni0.375Mn1.5O4 (where M=Cr, Fe, and Co) cathode. All computations were carried out on the basis of projector augmented wave (PAW) approach as implemented in VASP. The exchange and correlation potential was treated with the generalized gradient approximation (GGA) of Perdew and Wang (PW91). In order to take into account the strong on-site Coulomb interaction (U) presented in the localized d electrons of transition metals, the GGA-U framework was used for evaluating the exchange-correlation energy. Within this framework, the effective single parameters Ueff of 3.5, 4, 5, 5.62 and 5.96 eV were used for Cr, Fe, Mn, Co and Ni, respectively. The electron wave functions were expanded by a high cutoff of 500 eV and the total energy was converged to 10-5 eV. The following electronic states are treated as valence electrons: Li, 2s12p0; O, 2s22p4; Cr, 3d54s1; Mn, 3d64s1; Fe, 3d74s1; Co, 3d84s1; Ni, 3d94s1; Regarding the accurate calculations of total energy and electronic structure, the tetrahedron method with Blöch correction was adopted for structural relaxation and density of state (DOS) analysis. The cell parameters, volume cells, and positions of all the atoms in the primitive cell were fully relaxed until the residual Hellmann-Feynman force on each atom was less than 10-2 eV/Â. It is found that doping a small quantity of metal M atoms into the Ni site results in a decrease in the volume variation during the lithiation/delithiation cycle (ca. 4% from lithiated phase to delithiated phase, whereas 4.7% for the undoped case). Electronic calculations suggested that transition metal doping (Cr-, Fe-, and Co-doping) would effectively improve the electronic conductivity of systems. To evaluate effects of dopants on lithium mobility, we calculated the activation energies for lithium diffusion in M-doped LiNi0.5Mn1.5O4 cathode. Our calculations indicate that doping with Co can potentially reduce lithium diffusion barrier as compared to that of pristine LiNi0.5Mn1.5O4 spinel.

Key words: first-principles, spinel LiNi0.5Mn1.5O4, doping, volume variation, Li diffusion barriers