Elucidating the atomistic mechanisms underpinning plasticity in Li-Si nanostructures

作     者：Xin Yan Afif Gouissem Pradeep R. Guduru Pradeep Sharma 

作者机构：Department of Mechanical Engineering University of Houston Texas 77004 USA School of Engineering Brown University Providence Rhode Island 02912 USA Department of Physics University of Houston Texas 77004 USA Material Science and Engineering Program University of Houston Texas 77004 USA 

出 版 物：《Physical Review Materials》 (Physic. Rev. Mat.)

年 卷 期：2017年第1卷第5期

页      面：055401-055401页

核心收录：

基　　金：United States Department of Energy EPSCoR, (DE-SC0007074) National Science Foundation, NSF, (1463205) National Science Foundation, NSF 

主　　题：Mechanical deformation Plasticity Energy materials Nanostructures Multiscale modeling 

摘      要：Amorphous lithium-silicon (a-Li-Si), especially in nanostructure form, is an attractive high-capacity anode material for next-generation Li-ion batteries. During cycles of charging and discharging, a-Li-Si undergoes substantive inelastic deformation and exhibits microcracking. The mechanical response to repeated lithiation-delithiation eventually results in the loss of electrical contact and consequent decrease of capacity, thus underscoring the importance of studying the plasticity of a-Li-Si nanostructures. In recent years, a variety of phenomenological continuum theories have been introduced that purport to model plasticity and the electro-chemo-mechanical behavior of a-Li-Si. Unfortunately, the micromechanisms and atomistic considerations underlying plasticity in Li-Si material are not yet fully understood and this impedes the development of physics-based constitutive models. Conventional molecular dynamics, although extensively used to study this material, is grossly inadequate to resolve this matter. As is well known, conventional molecular dynamics simulations can only address phenomena with characteristic time scales of (at most) a microsecond. Accordingly, in such simulations, the mechanical behavior is deduced under conditions of very high strain rates (usually, 108s−1 or even higher). This limitation severely impacts a realistic assessment of rate-dependent effects. In this work, we attempt to circumvent the time-scale bottleneck of conventional molecular dynamics and provide novel insights into the mechanisms underpinning plastic deformation of Li-Si nanostructures. We utilize an approach that allows imposition of slow strain rates and involves the employment of a new and recently developed potential energy surface sampling method—the so-called autonomous basin climbing—to identify the local minima in the potential energy surface. Combined with other techniques, such as nudged elastic band, kinetic Monte Carlo and transition state theory, we assess the b