Effects of Operating Temperature on the Electrical Performance of a Li-air Battery operated with Ionic Liquid Electrolyte

Li-air cell operated with ionic liquid electrolytes is a very promising energy storage technology for electric vehicle and plug-in hybrid electric vehicle due to several favorable characteristics of ionic liquids. However, Li-air cells that employ room temperature ionic liquid (RTIL) electrolytes exhibit poor performance due to limited oxygen solubility and low reactant species mobility. To circumvent these aforementioned drawbacks, we investigated the electrical performance of a Li-air cell with ionic liquid electrolytes operating at high temperature. A continuum based model is used to quantify the performance of the Li-air cell, with an ionic liquid (MPPY-TFSI) electrolyte, as a function of operating temperature. Simulations at the atomistic scale, such as molecular dynamics (MD) and density functional theory (DFT) calculations are used to obtain key properties for the continuum model. These properties include electron transfer reaction rate constant, species diffusivity and oxygen solubility. The MD simulations indicate that oxygen solubility in ionic liquid increases with temperature, which is very favorable for high temperature operation. The continuum based cell level simulation results show that the battery performance can be improved significantly by increasing operating temperature. For instance, specific capacity as high as 3000 mAh/g can be achieved at 110 degrees C operating temperature, which is almost 25 times higher than its counterpart at room temperature. Simulation results also reveal that by increasing the operating temperature, the specific capacity can be improved significantly for high load current density, which is one of the most critical drawbacks in RTIL based Li-air battery. We also studied the effect of cathode thickness on the performance of Li-air battery at different operating temperatures. The transport limitation of oxygen and lithium ions can be alleviated at higher operating temperatures, suggesting that even thicker cathode materials can be used to enhance the cell capacity at elevated temperature. (C) 2016 Elsevier Ltd. All rights reserved.