Role of van der Waals Forces in Thermodynamics and Kinetics of Layered Transition Metal Oxide Electrodes: Alkali and Alkaline-Earth Ion Insertion into V2O5

Layered transition metal oxides (LTMOs) have a long tradition of success as effective electrode materials for power storage applications. However, the growing demand for improved technologies has motivated a strong interest in developing new generations of this class of materials. First-principles calculations, in particular density functional theory (DFT), have become an important tool to gain atomic-level understanding and speed up the search of new materials in general. An important structural ingredient of LTMOs is the weak van der Waals (vdW) forces that hold layers together. Unfortunately, conventional DFT approaches have serious shortcomings to treat these dispersion interactions. This is an uneasy position for the role of DFT in describing such layered-type structural materials. Recent exciting developments in DFT allow us now to tackle this problem head on. Here we have employed newly developed vdW-inclusive methods based on improved nonlocal density functionals to thoroughly explore the role of vdW forces in key thermodynamic and kinetic properties of alkali (Li, Na, and K) and alkaline-earth (Mg, Ca, and Sr) ion insertion into alpha-V2O5. We find that vdW forces help to stabilize inserted ions and, therefore, increase average voltages compared to the values obtained with conventional non-vdW-inclusive DFT methods. Added to this, activation energies for ion diffusion significantly increase as a consequence of a proper account for vdW interactions. These results highlight the relevance of vdW forces to ion intercalation and dynamics in LTMOs in general.