Evidence of transition-metal accumulation on aged graphite anodes by SIMS

Abstract

In cells containing Li1.05 (Ni13 Co13 Mn13)0.95 O2 -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. © 2008 The Electrochemical Society.