Luo Ningjing, Feng Lianggang, Yin Huimin, Stein Andreas, Huang Shuping, Hou Zhufeng, Truhlar Donald G
College of Chemistry, Fuzhou University, Fuzhou, Fujian 350108, China.
Department of Chemistry, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455-0431, United States.
ACS Appl Mater Interfaces. 2022 Jul 6;14(26):29832-29843. doi: 10.1021/acsami.2c06173. Epub 2022 Jun 23.
In Li-excess transition metal-oxide cathode materials, anionic oxygen redox can offer high capacity and high voltages, although peroxo and superoxo species may cause oxygen loss, poor cycling performance, and capacity fading. Previous work showed that undesirable formation of peroxide and superoxide bonds was controlled to some extent by Mn substitution, and the present work uses density functional calculations to examine the reasons for this by studying the anionic redox mechanism in LiMnO. This material is obtained by substituting Mn for Sn in LiSnO or for Zr in LiZrO, and we also compare this to previous work on those materials. The calculations predict that LiMnO is stable at room temperature (with a band gap of 3.19 eV as calculated by HSE06 and 1.82 eV as calculated with the less reliable PBE+U), and they elucidate the chemical and structural effects involved in the inhibition of oxygen release in this cathode. Throughout the whole delithiation process, only O ions are oxidized. The directional Mn-O bonds formed from unfilled 3d orbitals effectively inhibit the formation of O-O bonds, and the layered structure is maintained even after removing 3 Li per LiMnO formula unit. The calculated average voltage for removal of 3 Li is 3.69 V by HSE06, and the corresponding capacity is 389 mAh/g. The high voltage of oxygen anionic redox and the high capacity result in a high energy density of 1436 Wh/kg. The Li-ion diffusion barrier for the dominant interlayer diffusion path along the axis is 0.57 eV by PBE+U. These results help us to understand the oxygen redox mechanism in a new lithium-rich LiMnO cathode material and contribute to the design of high-energy density lithium-ion battery cathode materials with favorable electrochemical properties based on anionic oxygen redox.
在富锂过渡金属氧化物阴极材料中，阴离子氧氧化还原可提供高容量和高电压，尽管过氧和超氧物种可能导致氧损失、循环性能差和容量衰减。先前的工作表明，通过锰取代可在一定程度上控制过氧化物和超氧化物键的不良形成，而本工作使用密度泛函计算通过研究LiMnO中的阴离子氧化还原机制来探究其原因。这种材料是通过在LiSnO中用Mn取代Sn或在LiZrO中用Mn取代Zr获得的，并且我们还将其与先前对那些材料的研究进行比较。计算预测LiMnO在室温下是稳定的（通过HSE06计算的带隙为3.19 eV，使用不太可靠的PBE+U计算为1.82 eV），并且阐明了该阴极中抑制氧释放所涉及的化学和结构效应。在整个脱锂过程中，只有O离子被氧化。由未填充的3d轨道形成的定向Mn-O键有效地抑制了O-O键的形成，并且即使在每个LiMnO化学式单元去除3个Li之后仍保持层状结构。通过HSE06计算，去除3个Li的平均电压为3.69 V，相应的容量为389 mAh/g。氧阴离子氧化还原的高电压和高容量导致1436 Wh/kg的高能量密度。通过PBE+U计算，沿轴的主要层间扩散路径的锂离子扩散势垒为0.57 eV。这些结果有助于我们理解新型富锂LiMnO阴极材料中的氧氧化还原机制，并有助于设计基于阴离子氧氧化还原且具有良好电化学性能的高能量密度锂离子电池阴极材料。
