Understanding structural stability of monoclinic LiMnO2 and NaMnO2 upon de-intercalation.
Although many strategies for Li-ion batteries have been successfully transplanted in Na-ion batteries, distinctions between these two kinds of secondary batteries are still clear. For example, monoclinic-NaMnO2 demonstrates high structural stability during charging and discharging, but its iso-structured LiMnO2 transforms to a spinel upon de-lithiation and the specific capacity fades quickly with cycling. In this work, first-principles calculations were carried out to have a better understanding of their difference in structural stability upon de-intercalation. Our studies show that the Mn-ions migrate into the Li layer of LiMnO2via an interstitial tetrahedral O atom when a triple-vacancy of the Li-ion is produced. This process follows a double-vacancy mechanism and results in blocking of the diffusion of other Li-ions. In contrast, it is very difficult for the Mn-ions to migrate into the Na layer in NaMnO2 even when triple-vacancies are generated. The drastic differences between LiMnO2 and NaMnO2 in charge distribution and in the length of the Mn-O bond are believed to be responsible for the Mn-ion migration in them. These findings provide revelations for understanding the de-intercalation behaviors of electrode materials for Li- and Na-ion batteries as well as insights into the structural stability of LiMnO2vs. NaMnO2 upon alkali metal ion de-intercalation.
Key Laboratory for Renewable Energy, Chinese Academy of Sciences, Beijing Key Laboratory for New Energy Materials and Devices, Beijing National Laboratory for Condense Matter Physics, Institute of Physics, Chinese Academy of Sciences, P. O. Box 603, Beijing 100190, China. zxwang@iphy.ac.cn.
Meng
M
Tian
Yurui
Y
Gao
Zhaoxiang
Z
Wang
Liquan
L
Chen