An Atomic View of Cation Diffusion Pathways from Single‐Crystal Topochemical Transformations

Abstract

The diffusion pathways of Li‐ions as they traverse cathode structures in the course of insertion reactions underpin many questions fundamental to the functionality of Li‐ion batteries. Much current knowledge derives from computational models or the imaging of lithiation behavior at larger length scales; however, it remains difficult to experimentally image Li‐ion diffusion at the atomistic level. Here, by using topochemical Li‐ion insertion and extraction to induce single‐crystal‐to‐single‐crystal transformations in a tunnel‐structured V2O5 polymorph, coupled with operando powder X‐ray diffraction, we leverage single‐crystal X‐ray diffraction to identify the sequence of lattice interstitial sites preferred by Li‐ions to high depths of discharge, and use electron density maps to create a snapshot of ion diffusion in a metastable phase. Our methods enable the atomistic imaging of Li‐ions in this cathode material in kinetic states and provide an experimentally validated angstrom‐level 3D picture of atomic pathways thus far only conjectured through DFT calculations.

Does Water Enhance Mg Intercalation in Oxides? The Case of a Tunnel Framework

“…V 2 O 5 is arguably the most studied compound for this reaction, particularly its layered polymorph. ,,,,− However, such layered structure would introduce confounding effects from possible bulk cointercalation . Recently, a new metastable polymorph with a tunnel structure, ζ-V 2 O 5 , has also been reported to reversibly intercalate Mg 2+ . , Its capacity for Mg storage remained modest in comparison with Li systems, so any enhancements induced upon introducing H 2 O in the electrolyte would serve to evaluate the intrinsic ability of the oxide to intercalate Mg 2+ and its practical limits, adding further motivation for this study. The assessment was carried out by cycling ζ-V 2 O 5 at 110 °C in MgTFSI 2 –PY14TFSI ionic liquid mixtures containing different amounts of H 2 O, labeled as dry IL and wet IL hereafter.…”