Computational Investigations of Charge Transport in Non-Aqueous Li-O2 Batteries

Despite their great promise, there are significant challenges to developing practical Li−air batteries. One is the electrical passivation of the cathode during discharge.[1,2] This occurs because insoluble and insulating Li₂O₂ produced during discharge builds up as a deposit on the cathode surface and ultimately inhibits charge transfer to the Li₂O^₂−electrolyte interface where the electrochemistry occurs. This manifests itself as a “sudden death” (rapid drop in the output potential U) of the discharge at some maximum discharge capacity, Q_max.

In this talk, we will discuss the dependence of the maximum discharge capacity Q_maxon the current density, j.[3]  We show that a wide range of experiments can be rationalized using a model that accounts for charge transport through tunneling and polarons.  We further show that tunneling dominates at the current density of interest.

References

[1] P. Albertus, G. Girishkumar, and B. McCloskey, J. Electrochem. Soc. (2011) 158, A343-A351.

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

[3] A. C. Luntz, V. Viswanathan, J. Voss, J. Varley, J. K. Nørskov, R. Scheffler and A. Speidel, J. Phys. Chem. Lett., (2013) 4, 3494-3499.

Fig 1: (a) Experimental Li−O₂ galvanostatic discharge curves (U versus capacity) observed in a bulk electrolysis cell on a ∼1 cm² area GC cathode with 1 M LiTFSI in DME as the electrolyte, ∼1 bar O2 pressure, and at T = 20 and 40 °C. The various curves for different discharge currents and T are labeled at the side. (b) Theoretical galvanostatic discharge curves (U versus the average thickness of the film d) under the same conditions as (a) and based on the simple model described in ref. [3].