Striping modulations and strain gradients within individual particles of a cathode material upon lithiation

Abstract

The insertion of Li-ions within cathode materials during the discharging of a battery oftentimes brings about one or more structural transformations. The spatiodynamic propagation of phase transformations within a matrix of particles is determined by highly localized intercalation phenomena rather than the global voltage profile. Multiscale inhomogeneities resulting from variations in electrode reactions strongly influence the proportion of actively intercalating electrode materials, define local “hot-spots” wherein the current is greatly amplified during charge/discharge processes, and consequently dictate localized energy dissipation profiles. Multiphasic domains further give rise to localized stress gradients that can induce electrode degradation. However, a clear picture of chemical and stress inhomogeneities remains to be developed for most cathode materials. Here we demonstrate compositional striping modulations between Li-rich and Li-poor domains along the edges of individual nanowires of Li-ion-intercalated V₂O₅ based on analysis of hyperspectral X-ray microscopy data. Analysis of scanning transmission X-ray microscopy data using singular value decomposition and principal component analysis provides a means to map compositional inhomogenieties across individual nanowires and ensembles of nanowires alike. The compositional maps are further transformed to stress and strain maps, which depict the localization of tensile stress and strain within individual nanowires of Li_xV₂O₅. The core–shell and compositional striping modulations manifested here and the resulting strain gradients point to the need to design cathode materials and electrode architectures to mitigate such pronounced local inhomoegeneities in Li-ion intercalation and diffusion.