Understanding the thermal instability of fluoroethylene carbonate in LiPF6-based electrolytes for lithium ion batteries
Understanding the thermal instability of fluoroethylene carbonate in LiPF6-based electrolytes for lithium ion batteries
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DOI：
10.1016/j.electacta.2016.12.126
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发表时间：
2017-01-20
影响因子：
6.6
通讯作者：
Choi, Nam-Soon
中科院分区：
文献类型：
--
作者：
Kim, Koeun;Park, Inbok;Choi, Nam-Soon
研究了LiCoO2(LCO)-LiNi0.5Co0.2Mn0.3O2(NCM)/沥青涂层硅合金-石墨(Si-C)电池以碳酸乙烯(EC)和碳酸氟乙烯(FEC)为基础的电解液在高温下的循环和储存性能。过量的FeC(在基于LiPF6的电解液中用作助溶剂)在电极上形成固体电解质界面(SEI)层期间未被完全消耗，在存在Lewis酸(如PF5)的情况下容易发生脱氟；此反应在高温下会产生不需要的HF和各种酸(H3OPF6、HPO2F2、H2PO3F、H3PO4)。我们的研究表明，在高温下，FeC分解形成的HF和酸性化合物导致过渡金属离子(从LCO-NCM阴极)大量溶解到电解液中，结果是，由于溶解的金属离子沉积在阳极上，整个电池的可逆容量降低。此外，我们通过模型实验论证了高温下LiPF6基电解液中FeC热不稳定性的可能机制。(C)2016爱思唯尔有限公司。保留所有权利。
The cycling and storage performances of LiCoO2 (LCO)-LiNi0.5Co0.2Mn0.3O2 (NCM)/pitch-coated silicon alloy-graphite (Si-C) full cells with ethylene carbonate (EC)-based and fluoroethylene carbonate (FEC)-based electrolytes are investigated at elevated temperatures. Excess FEC (used as a co-solvent in LiPF6-based electrolytes), which is not completely consumed during the formation of the solid electrolyte interphase (SEI) layer on the electrodes, is prone to defluorination in the presence of Lewis acids such as PF5; this reaction can generate unwanted HF and various acids (H3OPF6, HPO2F2, H2PO3F, H3PO4) at elevated temperatures. Our investigation reveals that the HF and acid compounds that are formed by FEC decomposition causes significant dissolution of transition metal ions (from the LCO-NCM cathode) into the electrolyte at elevated temperatures; as a result, the reversible capacity of the full cells reduces because of the deposition of the dissolved metal ions onto the anode. Moreover, we demonstrate possible mechanisms that account for the thermal instability of FEC in LiPF6-based electrolytes at elevated temperatures using model experiments. (C) 2016 Elsevier Ltd. All rights reserved.