Molecular level modeling of batteries

Abstract

Our study points to the key roles played by bonding covalency and structural disorder in giving rise to brittle and ductile regimes over the course of cycling a-Si electrode. Additionally, a novel reactive atomistic model is developed to study the continuum regimes of chemo-mechanical crack growth in brittle amorphous regimes, using a modified Lennard-Jones based pairwise force field. Finally, a combined molecular dynamics and Monte Carlo approach towards simulating key redox mechanisms of deposition and dissolution at battery interfaces is implemented, with design MD simulations to study minimum model of charge/discharge of an electrochemical cell.

Rechargeable batteries are integral to the portable, entertainment, computing, and telecommunication equipment required by today's information-rich, mobile society. As of today we still fall short of completely comprehending several key nanoscale phenomena that hinder the performance of different types of batteries. Computer simulations have become useful tools to enrich our understanding of these phenomena and corresponding failure mechanisms. These include instabilities arising from mechanical, and coupled electro-chemical, chemo-mechanical processes that consistently lead to poor battery performance. In this thesis, we have studied some of the most significant stumbling blocks like growth of dendritic projections, delamination due to volume expansion, interfacial stress build-up, and chemo-mechanically coupled crack propagation. Surface diffusion characteristics have been analysed as a predictive indicator of dendrite growth in lithium and potassium electrodes. The dynamic stress evolution in a lithiated silicon electrode is studied, and an alternative to avoid volume expansion-induced cracking is demonstrated by engineering a van der Waals “slippery” interface between the Si film and the current collector. Furthermore, in order to understand the mechanical instability more fundamentally, the structural transformation in amorphous silicon (a-Si) during lithiation and delithiation cycles is analyzed.