Reduced Gassing in Lithium-Ion Batteries with Organosilicon Additives

Abstract

The battery industry is constantly seeking to improve battery capacity, lifetime, and safety. Electrolytes are a key development focus in achieving these goals, as traditional carbonate-based electrolytes cause capacity fade and gassing through degradation processes, as well as representing a safety risk due to flammability. The release of gasses through electrolyte decomposition is a problem of prominent concern in the battery industry, due to the negative impact of gassing on cell safety and performance. Studies on battery gassing have been reported for a wide range of battery systems,1-3 but the mechanisms and conditions of gas release are complex and not fully understood. Gaining a greater understanding of gassing mechanisms, and the specific electrolyte components that cause them, will allow for precise design of battery electrolyte formulations that optimize performance and minimize gassing.In addition to understanding traditional electrolyte blends, the investigation of new electrolytes and additives is essential in developing low-gassing batteries. Organosilicon (OS) materials have been developed by Silatronix® as critical high stability additions to conventional carbonate electrolytes to enable next-generation Li-ion batteries. This novel organosilicon chemistry involves the merging of a silane with a Li+ coordinating functionality. For example, the OS3® solvent family contains a nitrile functionality. The adoption of new Li-ion battery electrolyte materials is driven by the desire to deploy higher energy density batteries capable of performing under broader operating conditions of temperature and voltage, and the design of OS solvents results in low molecular-weight molecules that have demonstrated superior thermal and electrochemical stability,4,5 as well as good safety properties with a high flash point and low vapor pressure.Silatronix® has conducted commercially relevant performance testing and fundamental mechanistic studies to investigate gassing phenomena in advanced Li-ion chemistries under both cycling and storage test conditions. In these studies, commercially relevant electrolytes were evaluated as well as electrolytes designed to specifically isolate the effect of selected electrolyte components, including OS3® and other industry-relevant solvents. The dependence of gassing on storage and voltage conditions was investigated, and connections between gas analysis and the electrode surface chemistry are also reported. Gas component analysis was performed with a calibrated dual-column GC-TCD, a similar analytical system to that utilized in previous studies,6 which provides excellent resolution and quantification of every gaseous product. Key experimental results show that all OS3® concentrations reduce gas generation after 60°C storage and higher OS3® content provides greater benefit. Overall, we show that organosilicon additives substantially reduce gassing from carbonate-based electrolytes while maintaining good cell performance. 1. Zhang, S.S., Insight into the Gassing Problem of Li-ion Battery. Frontiers in Energy Research 2014, 2, 59.2. Self, J.; Aiken, C.P.; Petibon, R.; Dahn, J.R., Survey of Gas Expansion in Li-Ion NMC Pouch Cells. Journal of the Electrochemical Society 2015, 162, A796-A802.3. Jung, R.; Metzger, M.; Maglia, F.; Stinner, C., Chemical vs Electrochemical Electrolyte Oxidation on NMC111, NMC622, LNMO, and Conductive Carbon. The Journal of Physical Chemistry Letters 2017, 8, 4820-4825.4. Guillot, S.L.; Peña-Hueso, A.; Usrey, M.; Hamers, R.J., Thermal and Hydrolytic Decomposition Mechanisms of Organosilicon Electrolytes with Enhanced Thermal Stability for Lithium-Ion batteries. Journal of the Electrochemical Society 2018, 164, A1907-A1917.5. Chen, X.; Usrey, M.; Peña-Hueso, A.; West, R.; Hamers, R.J., Thermal and Electrochemical Stability of Organosilicon Electrolytes for Lithium-Ion Batteries. Journal of Power Sources 2013, 241, 311-319.6. Xiong, D.J.; Ellis, L.D.; Petibon, R.; Hynes, T.; Liu, Q.Q.; Dahn, J.R., Studies of Gas Generation, Gas Consumption and Impedance Growth in Li-Ion Cells with Carbonate or Fluorinated Electrolytes Using the Pouch Bag Method. Journal of the Electrochemical Society 2017, 164, A340-A347.