Challenges for Li-Ion Batteries Working at High Temperatures

Li-ion batteries working at high temperatures (from 80 to 110 ºC) are thought to be implemented in hybrid electric heavy vehicles. The high working temperature of the battery would facilitate faster charge and discharge rates, allowing the power demands of such an application to be easily reached. Furthermore, sharing a cooling system between the battery pack and other drive train components, such as power electronics, would simplify the thermal management in the hybrid electric vehicle.

Working at higher temperatures could potentially open the possibility of using electrode materials that do not normally work at room temperature due to kinetic limitations. Solid polymer and ionic liquid electrolytes could also be used, as the ionic conductivity and viscosity are improved at high temperatures. Unfortunately, increasing the working temperature of the battery will also present drawbacks. Secondary reactions kinetics are also improved when increasing the temperature, affecting the coulombic efficiency of the cell. Due to safety considerations, liquid electrolytes that are normally used in ambient temperature Li-ion batteries would have to be replaced by safer solid polymer or ionic liquid electrolytes. Finally, issues like the cold-start of hybrid vehicles and prediction of batteries life-time also need to be addressed.

We will present the work done at Uppsala University on high temperatures Li-ion batteries within the Swedish HT-LIB project. Different materials have been tested in half-cells in order to study their cycling performance at 80 ºC. Iron-based cathode materials (LiFePO₄ and Li₂FeSIO₄) were chosen as they are cheap and environmentally friendly, while titanium-based anode materials (Li₄Ti₅O₁₂ and TiO₂) were chosen due to their high working potential versus lithium. The later is beneficial as there is less solid electrolyte interphase formation at those potentials and there is no risk for lithium plating. Finally, cycling of Li-ion whole cells at 80 ºC will be presented.

High Temperature Lithium-ion Batteries (HT-LIB) is a project funded by the Swedish Energy Agency and the collaboration between Chalmers University of Technology, Lund University, Uppsala University and Scania CV AB was created within the Swedish Hybrid Vehicle Centre.