While it is accepted that paired NiLi and LiNi antisite defects are present in the important family of NMC cathode materials with the general formula Li(NixMnyCoz)O2, their formation mechanism and influence on properties are not well understood due to the difficulty of accurately quantifying defects. In this work, novel high-precision powder diffraction methods have been used to elucidate the dependence of defect concentration on NMC composition. Formation energies for paired antisite defects (calculated under the assumption of equal state degeneracy) are observed to vary from about 320 to 160 meV, contradicting the constant defect formation energy that would be expected based on the previously proposed atomistic defect formation mechanism (size similarity of Ni2+ and Li+ cations). The present data support an alternative mechanism in which the equilibrium defect concentration is determined by the average size of transition-metal sites and thus suggest a new route by which chemical substitutions can be used to tune defect concentrations to optimal levels.
Bibliographical noteFunding Information:
This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy (DOE) through the Advanced Battery Materials Research (BMR) program and the Battery500 Consortium under Contract No. DE-SC0012704. Use of the Advanced Photon Source at the Argonne National Laboratory was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. A portion of this research used resources at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. Y.S.M. and C.F. thank Dr. Bao Qiu from Ningbo Institute of Materials Technology and Engineering NIMTE for providing a BASF 333 sample. Support and training from NOMAD beamline team members including Katharine Page, Michelle Everett, and Joerg C. Neuefeind are gratefully acknowledged, as is the work of Jonathan Denney in writing automated codes to verify f* diagram calculations.
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