在 EC/DMC 中对 LiTDI、LiFSI 和 LiPF6 进行离子关联分析，以获得更好的锂离子电池性能,RSC Advances

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在 EC/DMC 中对 LiTDI、LiFSI 和 LiPF6 进行离子关联分析，以获得更好的锂离子电池性能
RSC Advances ( IF 3.9 ) Pub Date : 2019-02-06 00:00:00 , DOI: 10.1039/c8ra08430k
Christopher L Berhaut _{1,

2} , Daniel Lemordant ₁ , Patrice Porion ₃ , Laure Timperman ₁ , Grégory Schmidt ₂ , Mériem Anouti ₁

Affiliation

新的锂盐，例如双（氟磺酰基）亚胺锂 (LiFSI) 和 4,5-二氰基-2-(三氟甲基)咪唑-1-ide (LiTDI) 锂盐现在正在挑战最常用的电解质盐六氟磷酸锂 (LiPF ₆ )在商用锂离子电池中。因此，现在重要的是在碳酸亚乙酯和碳酸二甲酯的标准溶剂混合物（EC/DMC：50/50 wt%）中比较这些电解质组分。有了这个目标，传输特性，如离子电导率、粘度和⁷对锂自扩散系数进行了深入研究。此外，由于这些性质与离子间相互作用和离子溶剂化的性质直接相关，因此可以更好地了解电解质的结构性质。锂盐浓度在 25°C 时在 0.1 mol L ^-1至 2 mol L ^{-1的范围内变化，在 1 mol L}^-1的固定浓度下工作温度从 20°C 至 80°C 变化。借助 Walden 规则和 Nernst-Einstein 方程，实验结果用于研究盐离子对 (IP) 解离系数 ( α _{D ) 的温度依赖性。}锂阳离子有效溶质半径（r _Li) 已使用 Jones-Dole-Kaminsky 方程与 Einstein 关系对溶液中硬球的粘度和 Stokes-Einstein 方程进行了确定。从α _D和 r _Li随温度的变化可以推断，在 EC/DMC 中，LiFSI 形成溶剂共享离子对（SIP），LiTDI 和 LiPF ₆很可能形成溶剂分离离子对（S ₂ IP) 或 SIP 和 S ₂ IP 的混合。根据α _D的温度依赖性，得到离子对形成的标准吉布斯自由能、焓和熵等热力学参数。除了与变化提供的信息一致α _D和 r _Li，可以得出结论，对于 EC/DMC 中的三种盐，离子对形成过程是放能和吸热的。

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Ionic association analysis of LiTDI, LiFSI and LiPF6 in EC/DMC for better Li-ion battery performances

New lithium salts such as lithium bis(fluorosulfonyl)imide (LiFSI) and lithium 4,5-dicyano-2-(trifluoromethyl)imidazole-1-ide (LiTDI) are now challenging lithium hexafluorophosphate (LiPF₆), the most used electrolyte salt in commercial Li-ion batteries. Thus it is now important to establish a comparison of these electrolyte components in a standard solvent mixture of ethylene carbonate and dimethyl carbonate (EC/DMC: 50/50 wt%). With this aim, transport properties, such as the ionic conductivity, viscosity and ⁷Li self-diffusion coefficient have been deeply investigated. Moreover, as these properties are directly linked to the nature of the interionic interactions and ion solvation, a better understanding of the structural properties of electrolytes can be obtained. The Li salt concentration has been varied over the range of 0.1 mol L⁻¹ to 2 mol L⁻¹ at 25 °C and the working temperature from 20 °C to 80 °C at the fixed concentration of 1 mol L⁻¹. Experimental results were used to investigate the temperature dependence of the salt ion-pair (IP) dissociation coefficient (α_D) with the help of the Walden rule and the Nernst–Einstein equation. The lithium cation effective solute radius (r_Li) has been determined using the Jones–Dole–Kaminsky equation coupled to the Einstein relation for the viscosity of hard spheres in solution and the Stokes–Einstein equation. From the variations of α_D and r_Li with the temperature, it is inferred that in EC/DMC LiFSI forms solvent-shared ion-pairs (SIP) and that, LiTDI and LiPF₆ are likely to form solvent separated ion-pairs (S₂IP) or a mixture of SIP and S₂IP. From the temperature dependence of α_D, thermodynamic parameters such as the standard Gibbs free energy, enthalpy and entropy for the ion-pair formation are obtained. Besides being in agreement with the information provided by the variations of α_D and r_Li, it is concluded that the ion-pair formation process is exergonic and endothermic for the three salts in EC/DMC.

更新日期：2019-02-06

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