■ Title: " Morphological Evolution of Discharge Products in Li-Air and Na-Air Batteries "
■ Speaker : Prof. Carl V. Thompson, Massachusetts Institute of Technology
■ Date & Time : 2015. 06. 29 (Monday) 11:00 -12:00
■ Venue : KI Bldg.(E4) 3F. Lecture Room B301
■ Host: Prof. Jihun Oh (T. 1726)
Rechargeable metal-air (metal-oxygen) batteries are the subject of intense interest as possible alternatives to lithium ion batteries, owing to their potential to provide significantly higher gravimetric energies. However, many challenges to the development of efficient metal-air batteries with high rate capability and cyclability remain. I will review our recent work on Li-air batteries, highlighting both accomplishments and challenges. I will then focus on the morphological evolution of the Li2O2 discharge product. Control of this evolution is likely to be the key to improving rate capability, and may also provide insight into ways of controlling side reactions that lead to reduced cyclability, and to reducing the charge potential in order to improve round-trip efficiency. We have used carpets of free-standing carbon nanotubes as cathode electrodes to achieve near-ideal gravimetric capacities. These electrodes are also well suited for studies of structure and dispersion of discharge products, and of how these properties depend on the discharge rate. We find, in particular, that the rate of nucleation of Li2O2 particles increases with the discharge rate, in such a way as to quickly coat the electrode and limit gravimetric charge capacity. Also, we find that at low discharge rates, Li2O2 particles are toroidal in shape and are composed of aligned nanocrystals, suggesting a mesocrystallization growth process. We have recently carried out parallel studies of Na-air batteries in order to gain insight into differences and similarities in morphological evolution of discharge products.