Pore-Scale Simulations of Porous Electrodes of Li-O Batteries at Different Saturation Levels.

This study reconstructs pore-scale structures of battery electrodes from scanning electron microscopy images, quantitatively studies the distribution of the electrolyte at various saturations, and simulates the discharge performance of Li-O batteries. This research sheds lights on the critical role of liquid-gas two-phase mass transfer within the porous electrode on the electrochemical performance of batteries. It is found that fully saturated electrodes (100% saturation) have high oxygen-transfer resistance, which will impede the battery performance at typical electrode thickness (∼200 μm). On the contrary, overdried battery (with <50% saturations) electrodes have poor electrochemical performance because dry pores are inactive for electrochemical reactions. In addition, the low electrolyte saturation level leads to low ionic conductivity and high mass transfer resistance of the lithium ion. Carefully designed electrodes with the mixture of lyophilic and lyophobic pores could achieve similar discharge capacity (>7 A h/g) at high current (20 A/m) with lyophilic electrodes that are fully saturated by the electrolyte at low current (1 A/m). The findings from this study enable further research to significantly increase (by orders of magnitude) the operating current and power of the Li-O battery and accelerate its deployment to transport and stationary applications.