Atomistic simulation of the early stages of solid electrolyte interphase formation in lithium ion batteries

Lithium ion batteries have fueled a technological revolution in consumer electronics, power tools, and electric vehicles. Further advancements of this technology to improve charge times and capacity while maintaining safe operability, however, require a deeper fundamental understanding of electrode and electrolyte materials as well as their interfaces. In particular, interfacial stability between the high energy anode and the electrolyte represents one of the greatest hurdles to improving current-generation batteries as well as moving onto next-generation technologies like lithium metal or silicon. Despite the commercial availability of lithium ion batteries for more than a decade, there is no intrinsically stable electrolyte which is able to satisfy the design requirements of a commercial device. Instead, a protective layer formed during the first charge cycle known as the solid electrolyte interphase (SEI) is relied upon to ensure stable operation over subsequent charge/discharge cycles. Despite being critical to battery operability, the SEI and the process by which it forms remains poorly understood. As the SEI is only several to tens of nm thick and decomposes in ambient conditions, its study through experiments presents many challenges. However, computational tools can easily access the size- and time-scales required to elucidate the processes which govern the formation of the SEI. This dissertation presents a computational framework by which reductive decomposition of the electrolyte during the early stages of SEI formation may be studied through atomistic simulations including classical molecular dynamics and density functional theory. Additionally, fundamental descriptions of several reaction and diffusion processes involved in the formation of the SEI from a conventional electrolyte on a graphite electrode are presented. This methodology may be later applied to more complex electrolytes or other electrodes like silicon, but also lays the groundwork for exploring later stages of the SEI formation and growth.