Description of the Silicon Voltage Hysteresis with a Visco-Elastoplastic SEI Model

Abstract

The solid-electrolyte interphase (SEI) plays a crucial role in the performance and lifespan of lithium-ion batteries. Despite ongoing research, key aspects of this passivation layer remain unclear. Our study focuses on understanding SEI growth mechanisms and the mechanical behavior to improve battery lifetime and performance, contributing to more sustainable energy storage. In advanced lithium-ion batteries, capacity fade during open-circuit storage results mainly from SEI growth. We investigate electron and solvent diffusion mechanisms to describe SEI growth, considering the observed capacity loss depending on state-of-charge (SOC) and time. Our simulations reveal that electron diffusion explains both SOC dependence and time behavior, while solvent diffusion reproduces only one aspect [1]. This detailed understanding, including self-discharge effects, can also describe experiments with significant capacity fades. Looking ahead to applications such as aviation, the development of next-generation of lithium-ion batteries with increased storage capacity is imperative. Silicon, with its high theoretical capacity, is a promising candidate for future anodes. However, silicon anodes undergo substantial volume expansion that the SEI has to withstand. Consequently, significant strains and plastic flow emerge within the SEI [2]. Moreover, silicon exhibits an open-circuit voltage hysteresis, posing challenges due to detrimental heat generation and for accurately estimating the state-of-charge. While previous explanations focused on plastic models for silicon thin films and large particles, amorphous silicon nanoparticles were not considered. Our chemo-mechanical model of a silicon nanoparticle and SEI successfully replicates the observed open-circuit potential hysteresis in experiments [3]. In addition, viscous behavior of the SEI explains the voltage difference between slow cycling and the relaxed voltage in GITT experiments. 1. Köbbing, L.; Latz, A.; Horstmann, B. J. Power Sources 2023, DOI: 10.1016/j.jpowsour.2023.232651. 2. Kolzenberg, L.; Latz, A.; Horstmann, B. Batter. Supercaps 2022, 5, DOI: 10.1002/batt.202100216. 3. Köbbing, L.; Latz, A.; Horstmann, B. ArXiv Preprint. 2023, DOI: 10.48550/arXiv.2305.17533.