An Approach to 12 V Lead-Free Batteries: Tolerance toward Overcharge of 2.5 V Battery Consisting of LTO and LAMO

The 2.5 V 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 terms of tolerance toward overcharge in voltages up to 5.2 V. LTO can be cycled with ca. 225 niAh g(-1) of rechargeable capacity in voltages ranging from 0 to 2 V in a Li/LTO cell. The fatal damage was not observed even after LTO at 0 V was stored at 25 degrees C for 2 weeks. LAMO can be cycled with ca. 120 mAh g(-1) of rechargeable capacity in voltages ranging from 3 to 5.2 V in a Li/LAMO cell without a dramatic capacity fading during 52 cycles. Because the 12 V batteries consist of five 2.5 V cells connected in series, occasional 26 V input is possible for the 12 V batteries. X-ray diffraction measurements on the positive and negative electrodes under overcharged conditions are also performed and show that both LTO and LAMO are resistive against overcharge. From the results, we discuss whether or not the materials selection based on a spinel-framework structure is correct for the 12 V lead-free batteries. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3176875] All rights reserved.