Owing to its high theoretical capacity, Li-O₂ batteries have attracted much attention during the past decades. However, in the state-of-art, the discharge capacity of a Li-O₂ cell is far behind the theoretical value. The insulating nature of the discharge product Li₂O₂ can be one of the main issues and the maximum distance for electron tunneling through this thin film is less than 10 nm according to first-principle calculation.¹ Nevertheless, the experimental finding of 40 nm Li₂O₂ film by Yang et al. breaks the limitation electron tunneling, which may imply that there may be other factors accounting for the thick Li₂O₂ film.²

In the present work, we simulated the growth of Li₂O₂ thin film during the discharge process of a Li-O₂ battery and studied the influences of catalyst and LiO₂ diffusion rate with a meso-scale model. On the basis of kinetic Monte Carlo method, this model combined a stochastic description of mass transport and a detailed elementary reaction We found that : (1) the interplay between diffusion kinetics and reaction kinetics influenced strongly the ordering of the Li₂O₂ thin film. With the presence of catalyst, the formed Li₂O₂ showed a lower degree of ordering and is more likely to be amorphous owning to the fast kinetics; (2) the mobility of LiO₂ ion pair, which depends largely on the nature of the electrolyte, also has impacts on the homogeneity of the compactness of Li₂O₂ thin film. These results are of high importance to develop a better understanding on the role of catalyst and reaction kinetics in the Li-O₂batteries.

References

[1] Viswanathan, V.; Thygesen, K. S.; Hummelshøj, J. S.; Nørskov, J. K.; Girishkumar, G.; McCloskey, B. D.; Luntz, A. C. J. Chem. Phys.2011, 135 (21), 214704.

[2] Yang, C.; Wong, R. A.; Hong, M.; Yamanaka, K.; Ohta, T.; Byon, H. R. Nano Lett. 2016, 16 (5), 2969–2974.

[3] Blanquer, G.; Yin, Y.; Quiroga, M. A.; Franco, A. A. J. Electrochem. Soc. 2016, 163(3), A329–A337.

[4] Yin, Y,; Zhao, R.; Deng. Y and Franco, A. A. J. Phys. Chem.Lett. (Submitted)