Addressing electrode degradation issue in high negative to positive electrode capacity ratio lithium-ion batteries using water-in-salt electrolyte
Zhanadilov O. Akhmetova A. Son J. Yu J.H. Kim M. Chung K.Y. Kim H.J. Bakenov Z. Yashiro H. Myung S.-T.
June 2025Springer Science and Business Media B.V.
Advanced Composites and Hybrid Materials
2025#8Issue 3
In this study, we investigate the underlying causes of degradation in Li4Ti5O12//LiMn2O4 cells with an N/P ratio of 0.9 utilizing 19.44 m LiN(SO2CF3)2 and 8.33 m LiN(SO2CF2CF3)2 (Li(TFSI)0.7(BETI)0.3∙2H2O), a hydrate-melt electrolyte. We identify the formation of hydrofluoric acid (HF) during electrochemical reactions as a key factor leading to both Mn dissolution from the LiMn2O4 cathode and rapid self-discharge at room temperature. To address these challenges, we apply a calcium fluoride (CaF2) coating to the electrodes, designed to scavenge HF by reacting to form calcium bifluoride (Ca(HF2)2). This reaction underscores the unique quasi-non-aqueous nature of Li(TFSI)0.7(BETI)0.3∙2H2O, which facilitates chemical processes not possible in traditional aqueous electrolytes. Electrochemical evaluations demonstrate that the CaF2-coated electrode exhibits improved capacity retention and higher coulombic efficiency than their uncoated counterparts. Despite these enhancements, the rapid self-discharge issue remains, indicating that additional factors contribute to this phenomenon and require further investigation. Our findings highlight the potential of water-in-salt systems, particularly the Li(TFSI)0.7(BETI)0.3∙2H2O electrolyte, in advancing lithium-ion battery technology by leveraging their distinct chemical environment. This study provides insights into the mechanisms affecting the stability and performance of hydrate-melt electrolyte for exploiting quasi-non-aqueous systems in energy-storage applications.
CaF2 coating , HF formation , Hydrate-melt electrolyte , Lithium-ion batteries , Mn dissolution , Water-in-salt electrolyte
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Department of Nanotechnology and Advanced Materials Engineering & Sejong Battery Institute, Hybrid Materials Research Center, Sejong University, Seoul, 05006, South Korea
Energy Storage Research Center, Korea Institute of Science and Technology, Hwarang-Ro 14-Gil 5, Seongbuk-Gu, Seoul, 02792, South Korea
Division of Energy and Environment Technology, KIST School, Korea University of Science and Technology, Seoul, 02792, South Korea
Department of Chemical and Materials Engineering, School of Engineering and Digital Sciences, Nazarbayev University, 53 Kabanbay Batyr Ave, Astana, Kazakhstan
National Laboratory Astana, Nazarbayev University, 53 Kabanbay Batyr Ave, Astana, 010000, Kazakhstan
Department of Chemistry and Bioengineering, Iwate University, Ueda 4-3-5, Morioka, Iwate, 020-8551, Japan
Department of Nanotechnology and Advanced Materials Engineering & Sejong Battery Institute
Energy Storage Research Center
Division of Energy and Environment Technology
Department of Chemical and Materials Engineering
National Laboratory Astana
Department of Chemistry and Bioengineering
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