Abstract
Li-O2 batteries are attractive thanks to their high theoretical discharge capacity of 1,168 mAh.g-1, and the low cost of their constituent materials. However, Li-O2 batteries face several challenges: stability, low practical capacity, rate capability and cycle life. In my PhD research, I focused on studying transport processes in porous Li-O2 battery electrodes. Transport of oxygen plays a crucial role in defining the battery performance. By improving transport, in principle, we can tackle two of the four aforementioned challenges of Li-O2 batteries, improving practical discharge capacity and rate capability. In my thesis I developed several models. A kinetic Monte Carlo model is developed to study pore size effect on diffusion. A continuum model is used to study electrode pore size effect on discharge capacity of Li-O2 batteries, and then the accuracy of the model is studied. A pore network model is developed to describe electrode mesostructure in detail and to predict the electrode performance in a more accurate way. We show that the pore network model is more accurate in describing pore size effect on battery performance than the continuum model. I conducted Pulsed Field Gradient NMR experiments to measure the evolution of electrode tortuosity along discharge; and we showed the tortuosity decreases along depth of discharge and the rate of decay depends on the electrolyte