Nanoconfinement geometry of pillared V2O5 determines electrochemical ion intercalation mechanism, storage sites and diffusion pathways

Improving 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 nanoconfined 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 interaction, as well associated electrochemical mechanisms remain poorly understood. Herein, a series of bilayered V2O5 host materials pillared with alkyldiamines of different lengths is systematically studied, resulting in tunable nanoconfinement geometry with interlayer spacings in the range of 1.0-1.9 nm. We discover that the electrochemical Li+ intercalation capacity is increased from approx. 1 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 co-intercalation in V2O5 with the largest interlayer spacing. The work systematically reveals 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.