Nanoconfinement Geometry of Pillared V₂O₅ Determines Electrochemical Ion Intercalation Mechanisms, Storage Sites, and Diffusion Pathways.

Abstract

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 V₂O₅ 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 V₂O₅ 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 V₂O₅ hosts with small and medium interlayer spacings to solvent cointercalation in V₂O₅ with the largest interlayer spacing. The work systematically demonstrates the impact of nanoconfinement geometry within bilayered V₂O₅ on the resulting Li⁺ intercalation metrics and mechanisms, providing insights into both the microstructure and associated electrochemistry of pillared materials.