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<p>In this study, we investigate the underlying causes of degradation in Li<sub>4</sub>Ti<sub>5</sub>O<sub>12</sub>//LiMn<sub>2</sub>O<sub>4</sub> cells with an <i>N</i>/<i>P</i> ratio of 0.9 utilizing 19.44&#xa0;m LiN(SO<sub>2</sub>CF<sub>3</sub>)<sub>2</sub> and 8.33&#xa0;m LiN(SO<sub>2</sub>CF<sub>2</sub>CF<sub>3</sub>)<sub>2</sub> (Li(TFSI)<sub>0.7</sub>(BETI)<sub>0.3</sub>∙2H<sub>2</sub>O), 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 LiMn<sub>2</sub>O<sub>4</sub> cathode and rapid self-discharge at room temperature. To address these challenges, we apply a calcium fluoride (CaF<sub>2</sub>) coating to the electrodes, designed to scavenge HF by reacting to form calcium bifluoride (Ca(HF<sub>2</sub>)<sub>2</sub>). This reaction underscores the unique quasi-non-aqueous nature of Li(TFSI)<sub>0.7</sub>(BETI)<sub>0.3</sub>∙2H<sub>2</sub>O, which facilitates chemical processes not possible in traditional aqueous electrolytes. Electrochemical evaluations demonstrate that the CaF<sub>2</sub>-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)<sub>0.7</sub>(BETI)<sub>0.3</sub>∙2H<sub>2</sub>O 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.</p> Graphical Abstract <p></p>

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Addressing electrode degradation issue in high negative to positive electrode capacity ratio lithium-ion batteries using water-in-salt electrolyte

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年6月14日

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  • Orynbay Zhanadilov,
  • Aktilek Akhmetova,
  • Junehyuk Son,
  • Jun Ho Yu,
  • Mingony Kim,
  • Kyung Yoon Chung,
  • Hee Jae Kim,
  • Zhumabay Bakenov,
  • Hitoshi Yashiro,
  • Seung-Taek Myung

摘要

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.

Graphical Abstract