Chemomechanical Simulation of LiF-Rich Solid–Electrolyte Interphase Formed from Fluoroethylene Carbonate on a Silicon Anode

Abstract

Maintaining an electrochemically and mechanically stable solid–electrolyte interphase (SEI) is of fundamental importance to the performance of high-capacity anode materials such as silicon. In this study, a chemomechanical model was developed to analyze the stress and strain in a LiF-particle/polymer system. By chemomechanical simulations, the stress and strain developments in a LiF-rich SEI with an inorganic/organic nanocomposite structure, consisting of LiF particles and poly­(fluoroethylene carbonate) formed on silicon, were investigated. The results revealed that the LiF particle distribution in the SEI has considerable influence on the stress development. The presence of the polymer at the LiF/Si interface significantly reduced the von Mises stress, while the direct bonding of LiF and silicon resulted in increased stress, which caused ductile fracture with fragile void formation. The lateral tensile stress and strain were particularly concentrated at the LiF/polymer interface, suggesting likely ductile fracture of the polymer in this domain. These findings also supported the results of recent in situ atomic force microscopy and time-of-flight secondary ion mass spectrometry studies, which proposed void formation in the SEI when the expansion of the underlying electrode applies tensile strains to the film, accompanied by the formation of Li-containing species inside the void structure, which are associated with capacity losses. The stress and strain concentrations increased with shorter interparticle distances and larger particles. The modeling results indicated that the richness of LiF particles (i.e., particle size or interparticle distance) must be optimized to maintain the stress at the polymer/particle interface within the fracture limit. More broadly, this study provides important guidelines for producing SEI layers that can simultaneously satisfy both electrochemical and mechanical criteria for the long-term passivation of silicon electrode surfaces.

Chemo‐Mechanical Model of SEI Growth on Silicon Electrode Particles**

“…[31,[62][63][64] Several groups developed mechanistic models to describe the mechanical response of the SEI on battery cycling. [14,[64][65][66][67][68][69][70][71][72][73][74][75][76][77][78][79] However, these models focus on SEI mechanics and incorporate at most simple SEI growth models. [14,[65][66][67][68]75,79] In this paper, we develop a detailed electrochemo-mechanical model to describe SEI mechanics and growth on a deforming electrode particle.…”

Potentiostatic lithium plating as a fast method for electrolyte evaluation in lithium metal batteries

“…However, donor numbers of the solvents are generally supposed to be higher than those of the salt in order to ensure dissociation of the electrolyte salt [79]. When FEC is used as an additive, its comparably lower DN serves two purposes: firstly, acting as a diluent to facilitate faster kinetics, but secondly also as a film-forming additive promoting LiF-rich SEI formation [80][81][82]. In the ether-based electrolytes we see higher donor numbers for both solvents (DOL: 21.2 kcal mol − 1 , DME: 20.0 kcal mol − 1 ) and salts (TFSI − : 11.2 kcal mol − 1 , NO 3 − : 22.2 kcal mol − 1 ).…”