Fundamental Linkage Between Structure, Electrochemical Properties, and Chemical Compositions of LiNi1- x- yMn x Co y O2 Cathode Materials

Jiangtao Hu; Qinchao Wang; Bingbin Wu; Sha Tan; Zulipiya Shadike; Yujing Bi; M Stanley Whittingham; Jie Xiao; Xiao-Qing Yang; Enyuan Hu

doi:10.1021/acsami.0c18942

Fundamental Linkage Between Structure, Electrochemical Properties, and Chemical Compositions of LiNi_{1- x- y}Mn _x Co _y O₂ Cathode Materials

ACS Appl Mater Interfaces. 2021 Jan 20;13(2):2622-2629. doi: 10.1021/acsami.0c18942. Epub 2021 Jan 7.

Authors

Jiangtao Hu¹, Qinchao Wang², Bingbin Wu¹, Sha Tan², Zulipiya Shadike², Yujing Bi¹, M Stanley Whittingham³, Jie Xiao^{1

4}, Xiao-Qing Yang², Enyuan Hu²

Affiliations

¹ Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, Washington, 99354 United States.
² Chemistry Division, Brookhaven National Laboratory, Upton, New York, 11973 United States.
³ Materials Science & Engineering, Binghamton University, Binghamton, New York, 13902 United States.
⁴ Department of Chemistry & Biochemistry, University of Arkansas, Fayetteville, Arkansas, 72701 United States.

PMID: 33410655
DOI: 10.1021/acsami.0c18942

Abstract

LiNi_1-x-yMn_xCo_yO₂ (NMC) is an important class of high-energy-density cathode materials. The possibility of changing both x and y in the chemical formula provides numerous materials with diverse electrochemical and structural properties. It is highly desirable to have guidance on correlating NMC structural and electrochemical properties with their chemical composition for material designing and screening. Here, using synchrotron-based X-ray diffraction, X-ray absorption spectroscopy, electrochemical characterization, and literature survey, the content difference between Mn and Co (denoted as x-y in NMC) is identified as an effective indicator to estimate Li/transition metal (Li/TM) cation mixing ratio and first-cycle Coulombic efficiency (CE). In addition, a linear relationship between oxygen position "z" and the size difference between Li⁺ and TM cation (normalized by the c-axis length) is found, and such linearity can be used to accurately predict the oxygen position in NMC materials by considering the average TM cation size and c-axis length. It is also concluded that the shortest O-O distance in the bulk of NMC materials could not be shorter than 2.5 Å even at a highly charged state. Therefore, oxygen release is not likely to take place from the bulk if the structure maintains the R3 ̅m symmetry.

Keywords: LiNi1−x−yMnxCoyO2; cation mixing; chemical composition; first-cycle Coulombic efficiency; oxygen position.