Layered materials have been extensively studied due to their facile ability to reversibly incorporate ions within interlayer sites and the pronounced modification to the electronic structure upon functionalization of their active sites. Unfortunately, little is still understood about the electronic structure changes experienced with structural and chemical modifications. In this talk, I will focus on the use of scanning transmission X-ray microscopy (STXM) as a probe to evaluate the changes of the electronic structure in layered materials. First, STXM observations indicate that the formation of lithiation gradients in individual nanowires of V2O5 arise from electron localization and local structural distortions(Fig1a,b). Electrons localized in the V2O5 framework couple to a local distortion, giving rise to polarons(Fig1c,d). In addition, we evaluated a cluster of interlaced LixV2O5 nanoparticles. Increased heterogeneity at the interface between particles suggests the exchange of Li-ions, implying a particle-by-particle lithiation(Fig2a). Next, I will present the first direct visualization of compositional inhomogeneities within cathode materials during electrochemical discharge. Two distinct patterns are evidenced: core—shell separation and striping modulations of Li-rich and Li-poor domains within individual particles(Fig2b,c). 3D compositional maps have been developed and translated to stress and strain maps, providing a hitherto unprecedented direct visualization of stress and strain inhomogeneities(Fig2d,e). Finally, I will discuss my current work on the canonical MXene Ti3C2Tx and description of the electronic structure with topochemical functionalization.

Comprehensive nanoscale evaluation of layered materials by X-ray microscopy

2019 Fall National Meeting

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