Silatronix (United States)

Lithium-ion batteries (LIBs) with nonaqueous liquid electrolytes are prone to gas generation at elevated voltages and temperatures, degrading battery performance and posing serious safety risks. Organosilicon (OS) additives are an emerging candidate solution for gassing problems in LIBs, but a detailed understanding of their functional mechanisms remains elusive. In this work, we present a combined computational and experimental study to elucidate the gas-reducing effects of OS additives. Cell volume measurements and gas chromatography-mass spectrometry reveal that OS additives can substantially reduce gas evolution in LIBs, particularly CO2 regardless of source. Through density functional theory calculations, we identify multiple plausible pathways for CO2 evolution, including (1) nucleophile-induced ring-opening of ethylene carbonate (EC) and the subsequent electro-oxidation and (2) direct electro-oxidation of lithium carbonate (Li2CO3). Correspondingly, we find that OS additives function via two primary mechanisms: (1) scavenging of nucleophiles such as superoxide (O2•-), peroxide (O22-), and carbonate ion (CO32-); (2) oligomerization with ethylene carbonate oxide ion and ethylene dicarbonate ion. Moreover, we discover that OS additives possess strong lithium coordination affinity, which helps further reduce the nucleophilic reaction energies and hence increases their nucleophile-scavenging efficiency. Finally, we provide a mechanistic interpretation for the enhanced gas-reduction effects observed with fluorinated OS compounds, corroborated by surface analysis results from X-ray photoelectron spectroscopy. Our study offers the first molecular-level insights into how OS additives contribute to reduced gas formation in LIBs, paving the way for improved safety and performance of LIBs.

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.

Organosilicon (OS) electrolytes have been developed as a viable alternative to conventional carbonate electrolytes for lithium ion batteries.1,2 A recent trend in the Li-ion industry toward adoption of new materials is driven by the desire to deploy larger capacity batteries under broader operating conditions. New advanced Li-ion chemistries to meet these requirements often require electrolytes with enhanced thermal and electrochemical stability that provide performance across a wide temperature range. Silatronix has developed and synthesized an entirely new class of OS molecules with superior thermal, chemical, and electrochemical properties. The leading candidate from this new class is OS3 which showcases greatly enhanced stability and performance attributes in Li-ion batteries. Specifically, OS3 provides benefits such as lower anode and cathode impedance and reduced gas generation in multiple Li-ion chemistries. The role of the Li+ solvation structure in the determination of electrolyte performance, including the formation, stability, and performance of the SEI layer, has been investigated using multiple analytical techniques. These techniques include FTIR spectroscopy, Raman spectroscopy4, NMR spectroscopy3, and electrospray ionization mass spectrometry (ESI-MS)5. In this work, we focus on understanding the unique role that OS3 plays in the Li+ solvation sheath with NMR spectroscopy using multiple nuclei to simultaneously probe the anion, cation, and solvent environments. Data collected for electrolytes containing solvents with a variety of functional groups finds that the NMR response to Li+ coordination is identical for multiple solvents with the same coordinating functionality (e.g., carbonate, nitrile, etc). Therefore, the solvation behavior of multiple solvents in complex electrolytes can be deconvoluted and individually understood. The strong participation of OS solvents in the Li+ solvation sheath, including the displacement of strong carbonate solvents such as EC. has been demonstrated in multiple electrolytes using NMR spectroscopy and ESI-MS. *RJH and RW have a financial interest in the outcome of this work.

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