Evidence of Transition-Metal Accumulation on Aged Graphite Anodes by SIMS

In cells containing Li(1.05)(Ni(1/3)Co(1/3)Mn(1/3))(0.95)O(2)-based positive and graphite-based negative electrodes, a significant portion of cell impedance rise on aging is known to be from the negative electrode. One possible reason for this impedance rise is the dissolution of transition-metal elements from the oxide electrode that accumulate and create a high-impedance layer at the negative electrode electrolyte interface. This article details dynamic secondary ion mass spectrometry (SIMS) measurements, which provide a relative comparison of Mn, Co, and Ni contents on fresh, formed, and aged graphite electrodes. The data clearly indicate that these transition-metal elements accumulate at the electrode surface and diffuse into the electrode during cell aging. (C) 2008 The Electrochemical Society. [DOI: 10.1149/1.2987680] All rights reserved.