Understanding the interplay between ion association, desolvation, and electric double layer (EDL) structure is crucial for designing high-performance energy storage devices with concentrated electrolytes. However, these dynamics in water-in-salt electrolytes within the nanopores of carbon electrodes are not fully understood. This study explores the ion association in water-in-salt LiTFSI electrolyte in more detail, classifying various ion pairs as a function of concentration. Based on Raman spectroscopy data of electrolyte and electrochemical investigations on non-porous electrodes, modification in the classical Gouy-Chapman-Stern (GCS) model has been proposed by incorporating ionicity to estimate Debye length. The modified model shows a sharp Debye length decrease as the concentration rises from 1 to 10 mol∙kg⁻¹ but an increase beyond 10 mol∙kg⁻¹ due to ion pairing. The modified model accurately reflects differential and experimental EDL capacitance values obtained from cyclic voltammetry and electrochemical impedance spectroscopy. The data obtained for non-porous electrodes was adjusted by dividing it with the MacMullin number of the carbon electrode to estimate the Debye length in pores. Further, introducing the MacMullin number into the Stokes-Einstein equation enabled the estimation of ionic radii within pores, which was subsequently utilized to calculate extent of ion desolvation/dehydration in micro- and mesopores. The concentration-dependent ionic association governs the Debye length trends in pores, which correlate with confined ionic radii, ion desolvation, and resulting EDL charging dynamics. Our findings highlight 5 mol∙kg⁻¹ LiTFSI as optimal for faster charging rates and 10 mol∙kg⁻¹ for higher energy density, providing critical insights for developing efficient electrolytes and porous carbon electrodes.

中文翻译：

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拉曼光谱和电化学方法制备多孔碳电极中盐包水电解质的双电层结构


了解离子缔合、脱溶剂和双电层 （EDL） 结构之间的相互作用对于设计具有浓电解质的高性能储能设备至关重要。然而，碳电极纳米孔内盐包水电解质中的这些动力学尚不完全清楚。本研究更详细地探讨了盐包水 LiTFSI 电解质中的离子关联，将各种离子对分类为浓度的函数。基于电解质和无孔电极电化学研究的拉曼光谱数据，提出了对经典 Gouy-Chapman-Stern （GCS） 模型的修改，方法是结合电离度来估计德拜长度。修改后的模型显示，当浓度从 1 mol∙kg⁻¹ 上升到 10 mol∙kg⁻¹ 时，德拜长度急剧减少，但由于离子对，德拜长度增加超过 10 mol∙kg⁻¹。修改后的模型准确地反映了从循环伏安法和电化学阻抗谱获得的差分和实验 EDL 电容值。通过将无孔电极的数据除以碳电极的 MacMullin 数来调整无孔电极的数据，以估计孔中的德拜长度。此外，将 MacMullin 数引入 Stokes-Einstein 方程中，可以估计孔隙内的离子半径，随后用于计算微孔隙和中孔隙中离子脱溶剂化/脱水的程度。浓度依赖性离子键合控制着孔隙中的德拜长度趋势，这与局限离子半径、离子脱溶剂化和由此产生的 EDL 电荷动力学相关。 我们的研究结果强调 5 mol∙kg⁻¹ LiTFSI 是更快充电速率的最佳选择，而 10 mol∙kg⁻¹ LiTFSI 是更高能量密度的最佳选择，为开发高效的电解质和多孔碳电极提供了重要见解。