Crystallographic design of intercalation materials

Abstract

Intercalation materials are promising candidates for reversible energy storage and are, for example, used as lithium-battery electrodes, hydrogen-storage compounds, and electrochromic materials. An important issue preventing the more widespread use of these materials is that they undergo structural transformations (of up to ∼ 10% lattice strains) during intercalation, which expand the material, nucleate microcracks, and, ultimately, lead to material failure. Besides the structural transformation of lattices, the crystallographic texture of the intercalation material plays a key role in governing ion-transport properties, generating phase separation microstructures, and elastically interacting with crystal defects.In this review, I provide an overview of how the structural transformation of lattices, phase transformation microstructures, and crystallographic defects affect the chemo-mechanical properties of intercalation materials. In each section, I identify the key challenges and opportunities to crystallographically design intercalation compounds to improve their properties and lifespans. I predominantly cite examples from the literature of intercalation cathodes used in rechargeable batteries, however, the identified challenges and opportunities are transferable to a broader range of intercalation compounds.

Multivariate hyperspectral data analytics across length scales to probe compositional, phase, and strain heterogeneities in electrode materials

“…The most significant stress experienced by the test particle coincides with phase boundaries, reflecting the sharp changes in lithiation and elastic misfit strain at the α-Li 0.1 V 2 O 5 and ε-Li 0.45 V 2 O 5 interface. 62 A complete picture of lithiation-induced stresses is provided in Figure S13 , wherein the complex stress state is deconvoluted into the von Mises, normal, and shear stress components under fixed and free boundary conditions. Here, the choice of boundary conditions is intended to capture the likely varying interactions, in a real electrode, between the active primary particles and the surrounding electrode, which can significantly influence the stress state of a given particle.…”

“…Secondary areas of elevated von Mises stress coincide with highly lithiated nanowire tips; lithiation-induced local compression of the crystal lattice likely alters the local diffusion rate, exacerbating lithiation differences and driving additional coherency strain. 24 , 62 A full profile of stress calculations from FEA is shown in Figure S15— which provides a rich picture of lithiation-induced stress gradients. For the particle fragments shown in Figure 4 , interparticle diffusion is limited, and the thermodynamic driving forces for phase separation are accommodated by intraparticle lithiation gradients.…”