Solution chemistry of extremely concentrated electrolyte solutions

2023 Fiscal Year Final Research Report

• Project/Area Number: 21K05115
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 34020:Analytical chemistry-related
• Research Institution: Kagoshima University
• Principal Investigator: KANZAKI Ryo 鹿児島大学, 理工学域理学系, 准教授 (50363320)
• Project Period (FY): 2021-04-01 – 2024-03-31
• Keywords: 電解質溶液 / リチウムイオン電池 / 電位差滴定 / 熱量滴定 / 溶媒和 / 水和 / 高分子電解質

Outline of Final Research Achievements

Focusing on extremely concentrated lithium bis(trifluoromethanesulfonyl)amide (LiTf2N) aqueous solutions, the reaction thermodynamics of acid-base equilibria were investigated, and the influence by concentrated Li+ and Tf2N- ions was quantified in order to clarify the differences from conventional dilute aqueous solutions. The results revealed that (1) the solvation state of the Tf2N- anion contributes to the reaction Gibbs energy of the solute ions through entropy, (2) the practical proton carrier in such extremely concentrated LiTf2N solutions possesses high internal energy, and (3) LiTf2N is classified as an electrolyte of a structure breaker. Both the tendencies and the extent of the changes are different from those of conventional concentrated inorganic electrolyte solutions, indicating the necessity for the development of a new electrolyte solution theory.

Free Research Field

溶液化学

Academic Significance and Societal Importance of the Research Achievements

LiTf2Nによる超濃厚電解質水溶液は，リチウムイオン電池のような高い作動電位でも利用できる水系電解液として，まさに注目されている物質である．その理由として，従来は「自由水」の枯渇によるものとして定性的な説明がなされてきたが，本研究によって，その影響をエネルギーの観点から定量化できることとなった．さらに，似た構造の超強塩基性陰イオンであるトリフルオロメタンスルホン酸（TfOH）の性質も明らかにした．2つのリチウム塩を組み合わせた「water in bisalt（WIBS）」の応用を促進し得る．加えて，従来の無機系濃厚電解質溶液との比較から，新しい電解質溶液論の構築の必要性が示された．