Andersson Rassmus, Hernández Guiomar, Mindemark Jonas
Department of Chemistry - Ångström Laboratory, Uppsala University, Box 538, SE-751 21 Uppsala, Sweden.
Phys Chem Chem Phys. 2022 Jul 6;24(26):16343-16352. doi: 10.1039/d2cp01904c.
In the progress of implementing solid polymer electrolytes (SPEs) into batteries, fundamental understanding of the processes occurring within and in the vicinity of the SPE are required. An important but so far relatively unexplored parameter influencing the ion transport properties is the ion coordination strength. Our understanding of the coordination chemistry and its role for the ion transport is partly hampered by the scarcity of suitable methods to measure this phenomenon. Herein, two qualitative methods and one quantitative method to assess the ion coordination strength are presented, contrasted and discussed for TFSI-based salts of Li, Na and Mg in polyethylene oxide (PEO), poly(ε-caprolactone) (PCL) and poly(trimethylene carbonate) (PTMC). For the qualitative methods, the coordination strength is probed by studying the equilibrium between cation coordination to polymer ligands or solvent molecules, whereas the quantitative method studies the ion dissociation equilibrium of salts in solvent-free polymers. All methods are in agreement that regardless of cation, the strongest coordination strength is observed for PEO, while PTMC exhibits the weakest coordination strength. Considering the cations, the weakest coordination is observed for Mg in all polymers, indicative of the strong ion-ion interactions in Mg(TFSI), whilst the coordination strength for Li and Na seems to be more influenced by the interplay between the cation charge/radius and the polymer structure. The trends observed are in excellent agreement with previously observed transference numbers, confirming the importance and its connection to the ion transport in SPEs.
在将固态聚合物电解质（SPEs）应用于电池的过程中，需要对SPE内部及附近发生的过程有基本的了解。影响离子传输性能的一个重要但迄今尚未得到充分探索的参数是离子配位强度。我们对配位化学及其在离子传输中作用的理解在一定程度上受到缺乏合适方法来测量这一现象的阻碍。本文介绍了两种定性方法和一种定量方法，用于评估聚环氧乙烷（PEO）、聚（ε-己内酯）（PCL）和聚（碳酸三亚甲基酯）（PTMC）中基于双（三氟甲基磺酰）亚胺（TFSI）的锂盐、钠盐和镁盐的离子配位强度，并对其进行了对比和讨论。对于定性方法，通过研究阳离子与聚合物配体或溶剂分子配位的平衡来探测配位强度，而定量方法则研究无溶剂聚合物中盐的离子解离平衡。所有方法都一致认为，无论阳离子如何，PEO的配位强度最强，而PTMC的配位强度最弱。考虑到阳离子，在所有聚合物中镁的配位最弱，这表明Mg（TFSI）中存在强离子-离子相互作用，而锂和钠的配位强度似乎更多地受到阳离子电荷/半径与聚合物结构之间相互作用的影响。观察到的趋势与先前观察到的迁移数非常一致，证实了其在SPEs离子传输中的重要性及其相关性。
