Decomposition of the fluoroethylene carbonate additive and the glue effect of lithium fluoride products for the solid electrolyte interphase: an ab initio study
Decomposition of the fluoroethylene carbonate additive and the glue effect of lithium fluoride products for the solid electrolyte interphase: an ab initio study
复制标题
DOI：
10.1039/c5cp07583a
复制
发表时间：
2016-03-28
影响因子：
3.3
通讯作者：
Tateyama, Yoshitaka
中科院分区：
文献类型：
--
作者：
Okuno, Yukihiro;Ushirogata, Keisuke;Tateyama, Yoshitaka
锂离子电池（LIB）电解质溶液中的添加剂对阳极上形成的固体电解质界面（SEI）的性能具有很大影响，并且是LIB稳定性和耐久性的关键。我们从理论上研究了氟代碳酸亚乙酯（FEC），一个代表性的添加剂，最近引起了相当大的关注，为提高硅电极的循环稳定性和改善钠离子电池的可逆性的影响。首先，我们深入研究了还原分解开环，氟化氢（HF）消除，形成碳酸亚乙烯酯（VC）添加剂和FEC在碳酸乙烯酯（EC）电解质中的分子间化学反应，通过使用密度泛函理论（DFT）为基础的分子动力学和蓝月亮系综技术的自由能分布。结果表明，FEC还原分解最可能的产物是氟化锂（LiF），并且与VC添加剂相比，FEC对阴离子自由基的反应性呈惰性。我们还通过使用两个模型系统研究了生成的LiF对SEI的影响;（1）LiF分子分布在有机SEI膜组分（SFC）的模型聚集体中，以及（2）与SFC聚集体接合的LiF聚集体。DFT计算表明，F原子与多个有机SFC分子中的Li原子形成了强的键合，起到了连接它们的作用。在后一种界面体系中，LiF聚集体通过F-Li键吸附有机SFCs。这些结果表明，LiF部分在SEI膜内的有机SFC中起到胶的作用。我们还检查了LiF聚集体和锂化硅阳极之间的界面结构，发现它们牢固结合。这种强结合可能与FEC添加剂在用于硅阳极的电解质中的有效性有关。
Additives in the electrolyte solution of lithium-ion batteries (LIBs) have a large impact on the performance of the solid electrolyte interphase (SEI) that forms on the anode and is a key to the stability and durability of LIBs. We theoretically investigated effects of fluoroethylene carbonate (FEC), a representative additive, that has recently attracted considerable attention for the enhancement of cycling stability of silicon electrodes and the improvement of reversibility of sodium-ion batteries. First, we intensively examined the reductive decompositions by ring-opening, hydrogen fluoride (HF) elimination to form a vinylene carbonate (VC) additive and intermolecular chemical reactions of FEC in the ethylene carbonate (EC) electrolyte, by using density functional theory (DFT) based molecular dynamics and the blue-moon ensemble technique for the free energy profile. The results show that the most plausible product of the FEC reductive decomposition is lithium fluoride (LiF), and that the reactivity of FEC to anion radicals is found to be inert compared to the VC additive. We also investigated the effects of the generated LiF on the SEI by using two model systems; (1) LiF molecules distributed in a model aggregate of organic SEI film components (SFCs) and (2) a LiF aggregate interfaced with the SFC aggregate. DFT calculations of the former system show that F atoms form strong bindings with the Li atoms of multiple organic SFC molecules and play as a joint connecting them. In the latter interface system, the LiF aggregate adsorbs the organic SFCs through the F-Li bindings. These results suggest that LiF moieties play the role of glue in the organic SFC within the SEI film. We also examined the interface structure between a LiF aggregate and a lithiated silicon anode, and found that they are strongly bound. This strong binding is likely to be related to the effectiveness of the FEC additive in the electrolyte for the silicon anode.