Iodine as a Temperature-Responsive Redox Shuttle Additive for Swelling Suppression of Lithium-Ion Batteries at Elevated Temperatures

The swelling issue by gas evolution at elevated temperatures (85–90 °C) is one of the major challenges related to current Li-ion batteries (LIBs). We herein demonstrate that iodine (I2) as a redox shuttle additive, when its dose is properly determined, can suppress the swelling behavior of LiCoO2/graphite Al-pouch cells during storage at 90 °C without sacrificing other cell performances. This approach is based on two findings: 1) swelling during 90 °C storage is severe only when the cells are fully charged, and 2) the shuttling reaction of I2 can be tuned to be activated only when the temperature is as high as 90 °C by employing an appropriate amount of I2. Therefore, when a fully charged cell is exposed to a temperature of 90 °C, the self-discharge by I2 lowers the state of charge of the cell, suppressing the swelling. This temperature-responsive shuttling behavior of I2 is ascribed to the preferential adsorption of I2 on the cathode surface. It is also confirmed that inclusion of the I2 additive does not lead to deterioration in other aspects of cell performance, such as the discharge capacity or long-term cyclability. Along with the improved cell performance, the low-cost and environmental compatibility of I2 makes it a promising electrolyte additive for thermally robust LIBs. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, WeinheimFALS