Mechanistic Investigation of Functional-Solvent-Based Electrolytes for High-Voltage Lithium Batteries

To meet the growing demand for high energy density battery systems, pairing nickel-rich layered cathodes like LiNi₀.₈Mn₀.₁Co₀.₁O₂ (NMC811) with lithium metal anodes can push specific energy beyond 350 Wh/kg. 1 However, the practical deployment of lithium metal batteries (LMBs) is hindered by major challenges, particularly short cycle life and safety risks stemming from interfacial instability and dendrite formation. 2 These issues are exacerbated under high-voltage operations due to parasitic reactions at the electrolyte-electrode interfaces. 3 Among these, the electrolyte plays a vital role in governing battery stability. Conventional carbonate-based electrolytes decompose at high voltages, accelerating cathode degradation, transition metal dissolution, 4 and unstable cathode-electrolyte interphase (CEI) formation. 5 To address these challenges, electrolyte engineering has emerged as a key strategy, such as fluorinated-solvent-based electrolytes that offer improved oxidative stability and promote robust interphase formation due to the electron-withdrawing fluorine groups. 6, 7 In parallel, silicon-containing solvents are gaining attention for their non-flammability and excellent chemical and thermal stability. 8, 9 In this work, we systematically explored fluorinated and silicon-containing solvents both as single-solvent and co-solvent systems to develop high-performance electrolytes for Li/NMC811 based LMBs. Figure 1a displays voltage profiles as a function of cycling of a Li/NMC811 battery cell using one of the silicon-containing-solvents (Si1) based electrolyte, demonstrating a high initial discharge specific capacity of >210 mAh/g at 4.5 V charge cutoff voltage and C/4 rate and a robust long-term cycle life with >80% capacity retention and >99% Coulombic efficiency after 200 cycles at 1C. Figure 1b shows rate capability test for various functional-solvent-based electrolytes, highlighting the excellent rate capability of the Si1-electrolyte based battery cell. We will discuss the roles of each solvent played in the observed battery performance using density functional theory (DFT) calculations and various analytical and electrochemical characterizations including X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy, cyclic anodic Li and cathodic oxidation stabilities using symmetric cells. Acknowledgement This work was supported by the following funding sources. The Larry and Linda Pearson Endowed Chair at the Leslie A. Rose Department of Mechanical Engineering, South Dakoda School of Mines & Technology. The Naval Air Warfare Center Weapons Division, China Lake, CA under Contract No N6893622C0017. Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the Naval Air Warfare Center Weapons Division, China Lake, CA. The SDBOR Governor Research Center for the Electrochemical Energy Storage, and NASA EPSCOR-80NSSC23M0072. References : Tian, Y.; Zeng, G.; Rutt, A.; Shi, T.; Kim, H.; Wang, J.; Koettgen, J.; Sun, Y.; Ouyang, B.; Chen, T., Promises and challenges of next-generation “beyond Li-ion” batteries for electric vehicles and grid decarbonization. Chemical reviews 2020, 121 (3), 1623-1669. 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Journal of Colloid and Interface Science 2021, 595 , 35-42. Figure 1