(Invited) Layered and Spinel Hosts for Li, Na, K and Mg-Ion Batteries

Abstract

Layered and spinel intercalation compounds have proven to be excellent electrode materials for Li-ion batteries. They are also promising electrode materials for Na, K and Mg-ion batteries. The electrochemical properties of an intercalation compound are very sensitive to the host crystal structure and guest cation chemistry. A systematic first-principles study of the electrochemical properties of layered and spinel forms of AxMO2 and AxMS2 was performed where A = Li, Na, K, Mg and where M are different transition metals. Differences in predicted voltage profiles and transport behavior emerge due to variations in guest ion radius and the degree of ionic bonding within the host. Statistical mechanics studies predict that phase stability, ordering tendencies and diffusion mechanisms change dramatically when varying the guest cation. In contrast to Li and Mg, the intercalation of the larger Na and K cations in layered compounds induces numerous stacking sequence phase transformations and results in complex ordering patterns. Variations in composition in layered intercalation compounds containing Na and K are realized by maintaining well-ordered domains that are interrupted by anti-phase boundaries. These ordering patterns have important consequences for diffusion mechanisms. Kinetic Monte Carlo simulations of diffusion show that the topology of the host structure plays an important role in affecting correlated diffusion, which usually leads to significant drops in diffusion coefficients.