Extending Cycle Life of Lithium-Ion Batteries Consisting of Lithium Insertion Electrodes: Cycle Efficiency Versus Ah-Efficiency

Capacity fading of the cell consisting of lithium titanium oxide (LTO; Li[Li1/3Ti5/3]O-4) and lithium aluminum manganese oxide (LAMO; Li[Li0.1Al0.1Mn1.8]O-4) is examined in a three-electrode configuration at 55 degrees C. Capacity fading observed during 400 cycles at 55 degrees C is explained in terms of the state of charge (SOC) of the LTO-negative and LAMO-positive electrodes. At the discharge-end voltage of 0 V for the LTO/LAMO cell, the SOC of LTO is always 0% although LAMO is expected to be 0% in its SOC from the basic research results on Ah-efficiency obtained in Li/LTO and Li/LAMO cells. In order to understand the anomalous capacity fading, the LTO/LTO and LAMO/LAMO cells are fabricated and examined at 55 degrees C, and the current due to the side reactions at the LTO and LAMO electrodes is determined. The current at the LTO electrode is much larger than that at the LAMO electrode, which is in reverse order in our common understanding on LTO and LAMO in non-aqueous lithium cells. From these results, extending cycle life is discussed in terms of the cycle efficiency versus Ah-efficiency. Difficulties to describe cell chemistry underlying the capacity fading are also discussed. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.002112jes] All rights reserved.