On the safety of the Li4Ti5O12/LiMn2O4 lithium-ion battery system

The aim of this work is to investigate the inherent safety characteristics of the Li4Ti5O12/LiMn2O4 cell chemistry in a real battery. For this purpose, the reactivity of the Li4Ti5O12 anode material with the electrolyte was first studied upon its electrochemical lithiation in a Li-metal half-cell. Results obtained by differential scanning calorimetry show that the total heat associated with this reaction increased when the lithium amount inserted in Li4Ti5O12 increased, with no noticeable change in the onset temperature (125 degrees C ). It was also found that the total heat of the fully lithiated Li4Ti5O12 (383 J/g) was much smaller compared to that of the fully lithiated graphite (2700 J/g), the latter having a lower onset temperature (100 degrees C). The thermal and structural stability of Li6.5Ti5O12 and Li0.2Mn2O4 phases was investigated after the chemical lithiation of Li4Ti5O12 with butylithium and the chemical delithiation of LiMn2O4 with nitronium tetrafluoroborate. Data from thermal gravimetric analysis show that the Li0.2Mn2O4 cathode released less than 2 wt % oxygen below 400 degrees C, while the Li6.5Ti5O12 anode gained 4 wt % at the same temperature. The accelerated rate calorimetry test performed on 18650- cells containing Li4Ti5O12/LiMn2O4 chemistry showed no thermal runaway, explosion, or fire. These results clearly demonstrate that the Li4Ti5O12/ LiMn2O4 battery could be one of the safest Li- ion battery systems. (c) 2007 The Electrochemical Society.