Mechanical degradation and resultant capacity fade in high-capacity electrode materials critically hinder their use in high-performance rechargeable batteries. Despite tremendous efforts devoted to the study of the electro–chemo–mechanical behaviours of high-capacity electrode materials, their fracture properties and mechanisms remain largely unknown. Here we report a nanomechanical study on the damage tolerance of electrochemically lithiated silicon. Our in situ transmission electron microscopy experiments reveal a striking contrast of brittle fracture in pristine silicon versus ductile tensile deformation in fully lithiated silicon. Quantitative fracture toughness measurements by nanoindentation show a rapid brittle-to-ductile transition of fracture as the lithium-to-silicon molar ratio is increased to above 1.5. Molecular dynamics simulations elucidate the mechanistic underpinnings of the brittle-to-ductile transition governed by atomic bonding and lithiation-induced toughening. Our results reveal the high damage tolerance in amorphous lithium-rich silicon alloys and have important implications for the development of durable rechargeable batteries.

Continuum models describing ideal nematic solids are widely used in theoretical studies of liquid crystal elastomers. However, experiments on nematic elastomers show a type of anisotropic response that is not predicted by the ideal models. Therefore, their description requires an additional term coupling elastic and nematic responses, to account for aeolotropic effects. In order to better understand the observed elastic response of liquid crystal elastomers, we analyse theoretically and computationally different stretch and shear deformations. We then compare the elastic moduli in the infinitesimal elastic strain limit obtained from the molecular dynamics simulations with the ones derived theoretically, and show that they are better explained by including nematic order effects within the continuum framework.

Over the past decade, there has been a significant advancement in understanding the mechanics of silicon (Si) electrodes in lithium (Li)-ion batteries. Much of this interest in Si electrodes as ideal anode materials for high-capacity Li-ion batteries stems from its theoretical specific capacity of 4200 mAh g⁻¹, which is an order-of-magnitude higher than that of conventional graphite electrodes (372 mAh g⁻¹). However, the high capacity of Li ions is also accompanied by a ∼300% volume expansion of the Si electrode during Li intercalation, which results in massive cracking of the electrode and capacity fade. In this review article, we summarize recent progress in elucidating the underlying fracture and failure mechanics of Si electrodes using multiscale computations and experiments, spanning the quantum, atomistic, microscopic, and macroscopic length scales. We focus on four fundamental mechanics issues: (i) the mechanical properties and fracture behavior of lithiated Si electrodes; (ii) the interfacial mechanics between Si thin-film electrodes and current collectors; (iii) the deformation and failure mechanics of the solid electrolyte interphase; and (iv) the design of Si electrodes for improved mechanical performance. Current challenges and possible future directions for the field of mechanics of materials in pursuit of high-capacity rechargeable batteries are also discussed.