Kanzaki R., Hidaka T., Kodamatani H., Tomiyasu T., Fujii K. . Proton-transfer reaction thermodynamics in highly concentrated electrolytes for advanced aqueous lithium-ion batteries . J2025 · 担当区分： 筆頭著者, 責任著者 記述言語： 英語 掲載種別： 研究論文（学術雑誌） 出版者・発行元： Journal of Molecular Liquids We have studied proton-transfer reactions in highly concentrated aqueous electrolytes focusing on lithium bis(trifluoromethanesulfonyl)amide (LiTf2N) for potential applications in advanced aqueous lithium-ion batteries. In 20 mol kg−1 LiTf2N aqueous solution, the autoprotolysis constant pKW increased significantly to 16.2, indicating a reduction in ionization compared to bulk water (pKW = 14 at infinite dilution), and the H+ concentration is lower than in dilute aqueous solutions. This was mainly attributed to the increase in the activity coefficient of H+ (γH) with increasing LiTf2N concentration. Calorimetric measurements revealed that the increase in pKW is driven by an increase in the autoprotolysis enthalpy, suggesting that H+ is enthalpically unfavorable in concentrated LiTf2N solutions. In contrast, the autoprotolysis entropy showed no significant contribution to the pKW variation. We extended this study to the acid-base reaction of acetic acid as a model system in highly concentrated electrolyte solutions. The pKa value of acetic acid (or the corresponding ionization Gibbs energy) showed little dependence on the LiTf2N concentration. In contrast, the corresponding ionization enthalpy and entropy increased significantly with increasing LiTf2N concentration. Due to the enthalpy–entropy compensation effect, the pKa value resulted in limited variation even under highly concentrated conditions. The obtained enthalpy values for the ionization processes support that proton carriers lie in an enthalpically unstable state. These findings provide new insights into the fundamental behavior of protons in highly concentrated aqueous electrolytes, which is critical for the design and optimization of aqueous lithium-ion batteries and other electrochemical systems. DOI： 10.1016/j.molliq.2025.127388 Scopus
