Microscopy and Spectroscopy of Lithium Nickel Oxide-Based Particles Used in High Power Lithium-Ion Cells

D. P. Abraham,^a R. D. Twesten,^b M. Balasubramanian,^c J. Kropf,^a D. Fischer,^d J.McBreen,^c I. Petrov,^b and K. Amine^a

^aChemical Technology Division, Argonne National Laboratory, Argonne, Illinois 60439, USA
^bCenter for Microanalysis of Materials, University of Illinois at Urbana-Champaign, Urbana, Illinois, 61801, USA
^cMaterials and Chemical Sciences Division, Brookhaven National Laboratory, Upton, New York 11973, USA
^dMaterials Science and Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA

Structural and electronic investigations were conducted on lithium nickel oxide-based particles used in positive electrodes of 18650-type high-power Li-ion cells. K-edge X-ray absorption spectroscopy (XAS) revealed trivalent Ni and Co ions in the bulk LiNi_0.8Co_0.2O₂ powder used to prepare the high power electrode laminates. Using oxygen K-edge XAS, high resolution electron microscopy, nanoprobe diffraction, and electron energy-loss spectroscopy, we identified a <5 nm thick modified layer on the surface of the oxide particles, which results from the loss of Ni and Li ordering in the layered Rm structure. This structural change was accompanied by oxygen loss and a lowering of the Ni- and Co-oxidation states in the surface layer. Growth of this surface layer may contribute to the impedance rise observed during accelerated aging of these Li-ion cells.

J. Electrochem. Soc., Volume 150, Issue 11, pp. A1450-A1456 (November 2003)

Copyright © 2003, Electrochemical Society, Inc.

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