Insights into the Lithium Solvation Environments of Localized High Concentration Electrolytes by NMR and Effects on NMC811/Gr Cell Performance
Authors: Guillot Sarah Lucienne , Usrey Monica Lee , Du Peng , Sriramulu Suresh 
Published: December 2024

Advanced battery technologies require advanced electrolytes to support high voltage and long cycle life at a wide range of temperatures and charging rates, and enhanced safety. The lithium solvation environment within the electrolyte can have a large impact on cell performance, influencing ion transport in the electrolyte as well as ion transfer at the electrode-electrolyte interfaces.1 By optimizing lithium-ion solvation, cell kinetics can be improved to facilitate low temperature and fast charge performance, while also promoting stable electrode interfaces during high temperature operation. Localized high concentration electrolytes (LHCEs)- composed of lithium salt(s), solvents, and a non- or minimally-solvating diluent -are designed to enhance the local concentration of salt around the lithium ion. These anion-involved lithium solvation environments can increase ion transport in the electrolyte and lead to more stable, inorganic-rich interfacial species.2 While LHCEs have shown promise in improving performance for lithium metal, high voltage, fast charge, and low temperature applications,2,3 further understanding of solvation in LHCEs and development of new diluent molecules is needed. The development of diluents should include solvation and physical property characterization, as well as performance testing in battery cells.

Previous studies have demonstrated that nuclear magnetic resonance spectroscopy (NMR) can be used to provide insight into the solvation environments of electrolytes with standard carbonate solvents as well as novel solvent species.4,5 In this work, we utilized NMR to build understanding of the cation (Li: 7Li-NMR), anion (PF6: 19F-NMR), and solvent (carbonates: 13C-NMR) solvation environments of standard electrolytes as a function of salt concentration. We then applied this understanding to NMR analysis of electrolytes with a known diluent to establish a baseline of how solvation changes for LHCEs. Finally, this body of knowledge was used to investigate a novel fluorinated ether species, KDC-403, proposed as a diluent for LHCEs. Furthermore, we demonstrate improved low temperature cycling and more stable fast charge cycling with reduced lithium plating in electrolytes containing KDC-403, supporting previous studies that conclude LHCEs can provide superior battery performance.

References:

Hou, T.; Fong, K.D.; Wang, J.; Persson, K. The Solvation Structure, Transport Properties and Reduction Behavior of Carbonate-based Electrolytes of Lithium-ion Batteries. Chemical Science 2021, 12, 14740.

Cao, X.; Jia, H.; Zu, W.; Zhang, J-G. Review—Localized High-Concentration Electrolytes for Lithium Batteries. Journal of the Electrochemical Society 2021, 168, 010522.

Yang, J.; Shi, X.; Wang, W.; Liu, Z.; Shen, C. Localized High-Concentration Electrolyte (LHCE) for Fast Charging Lithium-Ion Batteries. Batteries 2023, 9(3), 155.

Yang, L.; Xiao, A.; Lucht, B.L. Investigation of Solvation in Lithium Ion Battery Electrolytes by NMR Spectroscopy. Journal of Molecular Liquids 2010, 154, 131.

Usrey, M. L.; Peña-Hueso, A.; Du, P.; Zhou, L.; Johnson, T.; West, R.; Hamers, R.J. Understanding the Unique Solvation Structure of Organosilicon-based Electrolytes for Lithium-ion Batteries. 233rd Electrochemical Society Meeting Presentation, May 13th 2018.

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