Isotopic Labeling of Carbonate Solvents to Understand Gas Generation in Li-Ion Batteries and Gas Reduction by Fluorinated Organosilanes

Abstract

Battery aging processes from cycling or storage at high temperatures, high voltages, and long times lead to significant degradation of the lithium-ion electrolyte, including decomposition to gaseous species. Gassing in battery pouch cells causes swelling, negatively impacting cell safety and performance. Development of electrolyte formulations that increase stability and reduce gassing is critical for next-generation battery applications and requires a greater understanding of the mechanisms of gas generation and reduction.Fluorinated organosilicon (OS) materials have been developed by Silatronix® to improve high temperature performance with significantly reduced gassing in high Ni battery systems.1 Utilization of a calibrated GC-TCD system allows the specific gas species to be identified and quantified but did not provide information on the mechanisms responsible for producing each species. To provide that information, studies using isotopically labeled carbonate solvents were conducted to identify the source for each gas species using a calibrated GC-MS system.2,3 Beyond identifying the gas species that evolve from particular carbonate solvents, these studies showed that the fluorinated organosilicon (OS) compounds reduce gassing (50-80% reduction depending on the specific OS formulation) by addressing all observed sources of gas during high temperature storage.2,3 The use of isotopically labeled carbonate solvents is extended within this study to provide insight into the origin of gas products and the nature of gas reduction by various OS materials under diverse aging conditions, including high temperature and fast charge cycling, as well as high temperature storage. This investigation includes multiple 13C-labeled electrolyte components including diethyl carbonate (DEC) and dimethyl carbonate (DMC) in addition to ethylene carbonate (EC). Carbonate-only electrolytes are compared to electrolytes containing OS compounds to gain insight into gas reduction mechanisms. Where possible, comparisons are made between different OS structures and popular commercial additives.Overall, this study builds on previous work to detail the origins of gassing from three common commercial carbonate solvents when combined in a complex electrolyte formulation under multiple test conditions and demonstrates that OS materials are highly effective gas-reducing components.