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.

Cation reordering instead of phase transitions: Origins and implications of contrasting lithiation mechanisms in 1D ζ- and 2D α-V 2 O 5

“…Mitigating the constraints and degradation mechanisms that limit cathode materials from realizing their full potential requires consideration of the dynamical evolution of structure across multiple length scales ( 8 , 9 ). In this work, we directly interrogate the role of lattice structure by comparing electrochemical lithiation/delithiation mechanisms in two distinct polymorphs of V 2 O 5 , which differ in atomic connectivity but have the same composition ( 10 – 13 ). By using particles of similar dimensions, we seek to disentangle the role of specific structural motifs and atomistic diffusion pathways in each polymorph by mapping the dynamical evolution of lithiation-induced structural modifications using operando synchrotron X-ray diffraction (XRD) measurements and ex situ scanning transmission X-ray microscopy (STXM) and by correlating the observed structure evolution to electrochemical performance and the coupling of electrochemistry with mechanics.…”

Curvature-Induced Modification of Mechano-Electrochemical Coupling and Nucleation Kinetics in a Cathode Material

“…[62][63][64] Indeed, recent lithiation/delithiation studies of single crystals of z-V 2 O 5 even suggest that Li ions prefer a specific ordering of crystallographic sites upon lithiation (b/b 0 /C site fill in a specific order), but Li is removed from all sites at the same time during delithiation. 65 It is expected that the evolution of stress derived from compositional inhomogeneity would be exacerbated during delithiation owing to increased rates of delithiation from hot spots formed during lithiation. 62 Mitigating stress during delithiation (charging) provides further motivation for incorporating geometric curvature into the mesoscale design of cathode materials.…”

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

“…Crystal structure data is summarized in Table 1 and details of unit cell parameters, refinement parameters, and atom positions are denoted in Tables S1-S24, as well as crystal information and CCDC deposition numbers. [31] Scanning electron microscopy (SEM) images showing the cracking patterns on the single-crystalline surface of topochemically treated crystals are shown in the Supporting Information in Figures S1 and S2. Figure S3 shows the atomic labeling scheme, which has been held constant across the topochemically modified structures.…”