Formation Accelerated Side-Reactions Test: A Technique to Study Anode Passivation during Lithium-Ion Cell Formation

High Resolution Image Download MS PowerPoint Slide This study investigates the formation and properties of the solid electrolyte interface (SEI) in lithium-ion batteries under varying salt concentrations (0.4, 0.8, 1.2M) and varying formation temperatures of 20, 30, and 40 °C. This method, focusing on the lowest temperature and salt concentration, was used as a formation accelerated side-reactions test (FAST) to evaluate the impact of different solvent blends and additives on anode passivation using the reduction rate of linear carbonates or nitriles seen in the differential capacity as a SEI performance metric. Electrolytes containing a mixture of vinylene carbonate and ethylene sulfate showed superior passivation, while a 3:7 mixture of fluoroethylene carbonate and ethyl methyl carbonate proved to be the most effective at passivating. Furthermore, the low-viscosity solvent methyl acetate significantly decreased EMC reduction at the anode during formation, resulting in a smaller irreversible increase in the thickness of the anode, perhaps due to a decrease in solvent cointercalation into graphite. Since our differential capacity method can be used to test SEI passivation, the passivation metric is also likely to correlate with long-term cycling performance. These results provide valuable insights into the efficient design of a formation accelerated side-reaction test (FAST) that could accelerate the discovery of high-performance electrolytes through rapid monitoring of SEI passivation during formation.