Nanoconfinement Geometry of Pillared VO Determines Electrochemical Ion Intercalation Mechanisms, Storage Sites, and Diffusion Pathways.

Improving the electrochemical ion intercalation capacity and kinetics in layered host materials is a critical challenge to further develop lithium-ion batteries, as well as emerging cell chemistries based on ions beyond lithium. Modification of the nanoconfining interlayer space within host materials by synthetic pillaring approaches has emerged as a promising strategy; however, the resulting structural properties of host materials, host-pillar interactions as well as associated electrochemical mechanisms remain poorly understood. Herein, we systematically study a series of bilayered VO host materials pillared with alkyldiamines of different lengths, resulting in tunable nanoconfinement geometries with interlayer spacings in the range of 1.0-1.9 nm. The electrochemical Li intercalation capacity is increased from approximately 1.0 to 1.5 Li per VO in expanded host materials due to the stabilization of new storage sites. The intercalation kinetics improve with expansion due to a transition in Li diffusion pathways from 1D to 2D diffusional networks. Operando X-ray diffraction reveals a transition of the intercalation mechanism from solid-solution Li intercalation in VO hosts with small and medium interlayer spacings to solvent cointercalation in VO with the largest interlayer spacing. The work systematically demonstrates the impact of nanoconfinement geometry within bilayered VO on the resulting Li intercalation metrics and mechanisms, providing insights into both the microstructure and associated electrochemistry of pillared materials.