Modeling of volume change phenomena in a Li-air battery

Volume change can occur in a lithium-air cell due to Li metal oxidation (reduction) in anode during discharge (charge) and due to solubility of reaction product (lithium peroxide) in the electrolyte at cathode. A mathematical model is developed to study the performance of lithium-air batteries considering the significant volume changes at the anode and cathode sides. Moving boundary technique is used to obtain the governing equations for transport of lithium ions and oxygen as well as for liquid phase potential. A numerical method is introduced to solve the moving boundary problem, and the electrical performance of lithium-air cell is obtained for various load conditions. Results obtained from this model are validated with experimental results for Lithium-air cell. Numerical results indicate that volume changes significantly affect the functioning of lithium-air cells. The high solubility of lithium peroxide in the electrolyte can reduce the passivation in the cathode, but it can also reduce the effective reaction area in the anode. However, the benefit of the former outweighs the detriment of the later phenomenon. On the other hand, if lithium peroxide is insoluble in electrolyte, electrolyte leakage can take place due to decrease in total available space for electrolyte.