Role of Surface Acidity in the Surface Stabilization of the High-Voltage Cathode LiNi0.6Mn0.2Co0.2O2

Nathan D. Phillip, Beth L. Armstrong, Claus Daniel, Gabriel M. Veith

Research output: Contribution to journalArticlepeer-review

9 Scopus citations

Abstract

Metal oxide coatings have been reported to be an effective approach for stabilizing cathode interfaces, but the associated chemistry is unclear. In this work, thin films of TiO2, ZnO, and Cr2O3, which have different surface acidities/basicities, were used to modify the surface chemistry of LiNi0.6Mn0.2Co0.2O2 and study the acidity's role in the cathode/electrolyte interphase composition and impedance under high-voltage cycling (4.5 V vs Li/Li+). Cathodes with more acidic surfaces provided higher initial specific capacity and capacity retention with cycling. More basic surfaces had higher initial impedance and greater impedance growth with cycling. These differences appeared to depend on the degree of LiPF6 salt decomposition at the interface, which was related to acidity, with more neutral surfaces having a LiF/LixPOyFz ratio close to unity, but basic surfaces had substantially more LiF. This chemistry was more significant than the cathode electrolyte interphase (CEI) thickness as the more acidic surfaces formed a thicker CEI than the basic surface, resulting in better capacity retention. These results suggest that the Brønsted acidity of cathodes directly influences electrolyte degradation, ion transport, and thus, cell lifetime.

Original languageEnglish
Pages (from-to)14968-14975
Number of pages8
JournalACS Omega
Volume5
Issue number25
DOIs
StatePublished - Jun 30 2020

Funding

This research at the Oak Ridge National Laboratory, managed by UT Battelle, LLC, for the U.S. Department of Energy (DOE) under contract DE-AC05-00OR22725, was sponsored by the Office of Energy Efficiency and Renewable Energy (EERE) Vehicle Technologies Office (VTO) (Deputy Director: David Howell) Applied Battery Research subprogram (Program Manager: Peter Faguy) (N.D.P., C.D., and G.M.V.). A portion (IEP) was sponsored by the Office of Energy Efficiency and Renewable Energy (EERE) Vehicle Technologies Office (VTO) (Deputy Director: David Howell) Silicon Deep Dive subprogram (Program Manager: Brian Cunningham) (B.L.A.). The authors thank Alex Rogers and Katie Burdette for assistance with zeta potential data interpretation.

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