On the safety of the LiM ₄Ti ₅O ₁₂/LiMn ₂O ₄ lithium-ion battery system

The aim of this work is to investigate the inherent safety characteristics of the Li4 Ti5 O12 LiMn2 O4 cell chemistry in a real battery. For this purpose, the reactivity of the Li4 Ti5 O12 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 Li4 Ti5 O12 increased, with no noticeable change in the onset temperature (125°C). It was also found that the total heat of the fully lithiated Li4 Ti5 O12 (383 Jg) was much smaller compared to that of the fully lithiated graphite (2700 Jg), the latter having a lower onset temperature (100°C). The thermal and structural stability of Li6.5 Ti5 O12 and Li0.2 Mn2 O4 phases was investigated after the chemical lithiation of Li4 Ti5 O12 with butylithium and the chemical delithiation of LiMn2 O4 with nitronium tetrafluoroborate. Data from thermal gravimetric analysis show that the Li0.2 Mn2 O4 cathode released less than 2 wt % oxygen below 400°C, while the Li6.5 Ti5 O12 anode gained 4 wt % at the same temperature. The accelerated rate calorimetry test performed on 18650-cells containing Li4 Ti5 O12 LiMn2 O4 chemistry showed no thermal runaway, explosion, or fire. These results clearly demonstrate that the Li4 Ti5 O12 LiMn2 O4 battery could be one of the safest Li-ion battery systems.