Aging of a Commercial Graphite/LiFePO4 Cell

The aging behavior of a commercial 2.3 Ah graphite/LFP cell during a year of cycling or storage at either 25 or 45 degrees C is investigated. The performance decline of the cells during the aging period is monitored by non-destructive electrochemical techniques and is discussed in detail. An in-depth analysis of the aging results reveals that aging manifests itself more in terms of capacity loss rather than in terms of impedance increase, regardless of the cycling or storage conditions and of the temperature. The capacity fade is larger at 45 degrees C than at 25 degrees C, regardless of the cycling or storage conditions, and at a same temperature, cycling conditions are always more detrimental to capacity fade than storage conditions. The loss of cyclable lithium is identified as the main source of capacity fade in all cases, and for the cells aged at 45 degrees C, a partial loss of graphite active material is suspected as well towards the end of the aging period. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3614529] All rights reserved.