Dual-ion batteries (DIBs) are emerging as a highly attractive class of batteries as they try to address the shortcomings of the widely used lithium ion batteries. Among the various organic electrolytes used in DIBs, ethyl methyl carbonate (EMC) with LiPF₆ salt is recently being considered as a better electrolyte in comparison to commercially used ethylene carbonate (EC). In this work, we have carried out a comparative study of EMC and EC solvent systems to address the greater stability of EMC in contact with aluminum (Al) and lithiated Al (LiAl) electrode as well as the effect of salt in the solid electrolyte interphase (SEI) formation process with the help of ab initio molecular dynamics (AIMD) simulations. We find that EMC can decompose via 1e^– reduction due to limited charge transfer from the Al surface, whereas 2e^– reduction becomes more favorable with lithiation of the Al anode surface. The limited decomposition observed in EMC compared to EC in contact with the Al electrode surface justifies the enhanced stability of EMC solvent in DIBs with an Al anode. However, the decomposition and SEI formation process can speed up in the presence of LiPF₆ salt as it induces more charge transfer (1.11 |e| for Al and 2.86 |e| for LiAl) from the electrode surface. Nevertheless, the charge transfer is less than in the case of EC solvent (2.54 |e| for Al and 5.42 |e| for LiAl), further justifying the stability of EMC solvent. We also find that the charge transfer to the salt molecule from the electrode surface depends on the position of the salt rather than the composition of the electrode surface. Overall, our study shows that the EMC solvent–LiPF₆ salt combination can serve as an efficient electrolyte for Al anode DIBs.

中文翻译：

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铝阳极双离子电池中固体电解质界面形成的理论见解

由于双离子电池（DIB）试图解决广泛使用的锂离子电池的缺点，因此正成为一种极具吸引力的电池。在DIB中使用的各种有机电解质中，与商业使用的碳酸亚乙酯（EC）相比，带有LiPF ₆盐的碳酸乙基甲基酯（EMC）最近被认为是一种更好的电解质。在这项工作中，我们进行了EMC和EC溶剂系统的比较研究，以解决EMC与铝（Al）和锂化Al（LiAl）电极接触时的更大稳定性以及盐在固体电解质界面中的影响从头算分子动力学（AIMD）模拟的过程（SEI）形成过程。我们发现EMC可以通过1e进行分解^–减少由于从Al表面有限的电荷转移，而图2e ^-还原变得与铝阳极表面的锂化更有利。与与铝电极表面接触的EC相比，EMC中观察到的有限分解证明了具有Al阳极的DIB中EMC溶剂具有更高的稳定性。但是，在LiPF ₆存在下，分解和SEI形成过程可以加快盐会引起更多的电荷从电极表面转移（对于Al而言为1.11 | e |，对于LiAl为2.86 | e |）。然而，电荷转移小于EC溶剂的情况（Al为2.54 | e |，LiAl为5.42 | e |），这进一步证明了EMC溶剂的稳定性。我们还发现，电荷从电极表面转移到盐分子的过程取决于盐的位置，而不是电极表面的组成。总体而言，我们的研究表明，EMC溶剂与LiPF ₆盐的组合可作为铝阳极DIB的有效电解质。