Title: Facet Dependent Disorder in the Pristine High Voltage Lithium-Manganese-Rich Cathode Material

Abstract

Defects and surface reconstructions are thought to be crucial for the long term stability of high-voltage lithium-manganese-rich cathodes. Unfortunately, many of these defects arise only after electrochemical cycling which occur under harsh conditions making it difficult to fully comprehend the role they play in degrading material performance. Recently, it has been observed that defects are present even in the pristine material. This study, therefore, focuses on examining the nature of the disorder observed in pristine Li$$_{1.2}$$Ni$$_{0.175}$$Mn$$_{0.525}$$Co$$_{0.1}$$O$$_2$$ (LNMCO) particles. Using atomic resolution Z-contrast imaging and electron energy-loss spectroscopy measurements we show that there are indeed a significant amount of anti-site defects present in this material; with transition metals substituting on Li metal sites. Furthermore, we find a strong tendency of segregation of these types of defects towards open facets (surfaces perpendicular to the layered arrangement of atoms), rather than closed facets (surfaces parallel to the layered arrangement of atoms). First principles calculations identify anti-site defect pairs of Ni swapping with Li ions as the predominant defect in the material. Furthermore, energetically favorable swapping of Ni on the Mn sites were observed to lead to Mn depletion at open facets. Relatively, low Ni migration barriers also support the notion that Ni are the predominant cause of disorder. These insights suggests that certain facets of the LNMCO particles may be more useful for inhibiting surface reconstruction and improving the stability of these materials through careful consideration of the exposed surface.

Authors:

Dixit, Hemant M. ^[1]; Zhou, Wu ^[1]; Idrobo Tapia, Juan Carlos ^[1]; Nanda, Jagjit ^[1]; Cooper, Valentino R. ^[1]

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+ Show Author Affiliations

1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

Publication Date:

Fri Nov 21 00:00:00 EST 2014

Research Org.:

Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Sciences (CNMS)

Sponsoring Org.:

USDOE Office of Energy Efficiency and Renewable Energy (EERE); USDOE Office of Science (SC)

OSTI Identifier:

1185550

Grant/Contract Number:  

AC05-00OR22725

Resource Type:

Accepted Manuscript

Journal Name:

ACS Nano

Additional Journal Information:

Journal Volume: 8; Journal Issue: 12; Journal ID: ISSN 1936-0851

Publisher:

American Chemical Society (ACS)

Country of Publication:

United States

Language:

English

Subject:

25 ENERGY STORAGE; Li-ion battery; antisite defects; Ni segregation; surface; migration barriers