Interplay Between Stereochemically Active Lone Pair Repulsions, Sigma Hole Interactions, and Delocalized Redox...

Area of Science:

• Materials Science
• Solid-State Chemistry
• Electrochemistry

Background:

• Topochemical cation insertion/extraction is a common strategy for solid-state material modification.
• Topochemical anion insertion strategies and design principles for hosts are significantly less explored.

Purpose of the Study:

• To explore topochemical anion insertion, specifically fluoride-ion insertion, in periodic solids.
• To decipher the fundamental principles governing reversible fluoride-ion insertion and diffusion in Sn2TiO4.
• To identify design criteria for future anion insertion host materials.

Main Methods:

• X-ray scattering for crystal structure analysis.
• X-ray absorption/emission spectroscopy for electronic structure probing.
• Magnetic susceptibility measurements and first-principles calculations.

Main Results:

• Reversible room-temperature fluoride-ion insertion observed in Sn2TiO4 tunnels.
• Identified key factors: large polarizable tunnels, delocalized redox, lone pair repulsion, and dative interactions.
• Achieved a reversible capacity of 0.5 fluoride ions per Sn2TiO4 formula unit.

Conclusions:

• The interplay between dative interactions and lone pair repulsions is crucial for fluoride-ion insertion thermodynamics and kinetics.
• Designing effective fluoride-ion insertion hosts requires precise control over lattice-ion interactions.
• This work provides a foundation for developing novel anion battery materials.