高电压正极材料Li_(1-x)CoO_2(x=0.75)的电子结构

Electronic Structures of High Voltage Cathode Material of Li_(1-x)CoO_2(x=0.75)

进一步提高目前成熟的锂离子电池电极材料LiCoO_2的容量是一个重要的研究方向.本文采用基于密度泛函理论的第一性原理方法研究了高脱锂量材料Li1-xCoO_2(x=0.75)的电子结构和晶体结构性质,为深入理解该高电压材料的电子结构提供基础.计算表明,LiCoO_2材料中Co是以正常的价态+3价的形式存在的.少量脱锂时,小部分Co3+由于进一步失去电子而从+3价变成+4价.当深度脱锂(x=0.75)时,不仅有很多的Co3+再变价,而且部分O-2p轨道也会失去电子,产生2种氧离子O1和O_2,其中O1离子占O变价总数的1/3,而O_2离子占2/3.不同价态的Co与不同氧离子之间的键长有明显的区别.与Co3+相比,Co4+和氧离子之间聚集了更多的电子,它们之间的相互作用力也将强于Co3+与氧离子之间的相互作用力.

To further increase the capacity of the well-developed cathode material LiCoOz for lithium ion batteries is an important di- rection of electronic-structure research.In this paper,first-principle calculations based on the density functional theory has been performed to investigate the geometric and electronic structures of Li1-x CoO2 （x = 0. 75）with high amount of deintercalation of Li, in the purpose of providing information for understanding the nature of electronic structures of this high-voltage material.Calculations show that Co is valence ＋3 in material LiCoOz.When a small amount of Li is extracted from LiCoO2 ,a portion of Co3＋ is trans- formed to Co4＋ owing to the loss of an electron.When a large amount of Li （x=0.75） is extracted,however,part of electrons of O- 2p orbital are also lost,except for the valence change from Co3＋ to Co4＋ .Therefore, two different oxidation states of oxygen, O1 and 02, appear.The O1 oxygen takes 1/3 of the total oxidized oxygen, while 02 oxygen takes up the remaining 2/3. There are obvious differences in bond lengths between different valence states of Co and different types of oxygen.More electron accumulation between Co4＋ and O ions are found,as compared with those between Co3＋ and O ions.Interactions between Co4＋ and O ions are also stronger than those between Co3＋ and O ions.