Sun Zifei, Wang Baichuan, Boebinger Matthew G, Magasinski Alexandre, Jhulki Samik, Zhang Yawei, Fu Wenbin, McDowell Matthew T, Yushin Gleb
School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332, United States.
School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, United States.
ACS Appl Mater Interfaces. 2022 Jul 27;14(29):33447-33456. doi: 10.1021/acsami.2c10851. Epub 2022 Jul 14.
Iron trifluoride (FeF), a conversion-type cathode for sodium-ion batteries (SIBs), is based on cheap and abundant Fe and provides high theoretical capacity. However, the applications of FeF-based SIBs have been hindered by their low-capacity utilization and poor cycling stability. Herein, we report greatly enhanced performance of FeF in multiple types of ionic liquid (IL) electrolytes at both room temperature (RT) and elevated temperatures. The PyrFSI electrolyte demonstrated the best cycling stability with an unprecedented decay rate of only ∼0.023% per cycle after the initial stabilization and an average coulombic efficiency of ∼99.5% for over 1000 cycles at RT. The PyrFSI electrolyte demonstrated the best cycling stability with a capacity decay rate of only ∼0.25% per cycle at 60 °C. Cells using PyrFSI and EMIMFSI electrolytes also showed promising cycling stability with capacity decay rates of ∼0.039% and ∼0.030% per cycle over 1000 cycles, respectively. A protective and ionically conductive cathode electrolyte interphase (CEI) layer is formed during cycling in ILs, diminishing side reactions that commonly lead to gassing and excessive CEI growth in organic electrolytes, especially at elevated temperatures. Furthermore, the increased ionic conductivity and decreased viscosity of ILs at elevated temperatures help attain higher accessible capacity. The application of ILs sheds light on designing a protective CEI for its use in stable SIBs.
三氟化铁（FeF）是一种用于钠离子电池（SIBs）的转换型阴极，它基于廉价且储量丰富的铁，并具有较高的理论容量。然而，基于FeF的SIBs的应用受到其低容量利用率和较差循环稳定性的阻碍。在此，我们报道了FeF在多种离子液体（IL）电解质中，在室温（RT）和高温下的性能都有显著提升。PyrFSI电解质表现出最佳的循环稳定性，在初始稳定后，其前所未有的衰减速率仅为每循环约0.023%，在室温下超过1000次循环的平均库仑效率约为99.5%。PyrFSI电解质在60℃时也表现出最佳的循环稳定性，容量衰减速率仅为每循环约0.25%。使用PyrFSI和EMIMFSI电解质的电池在超过1000次循环中也分别表现出了有前景的循环稳定性，容量衰减速率分别为每循环约0.039%和约0.030%。在ILs中循环时会形成一层保护性且具有离子导电性的阴极电解质界面（CEI）层，减少了通常会导致在有机电解质中产生气体和过度CEI生长的副反应，尤其是在高温下。此外，ILs在高温下离子电导率的增加和粘度的降低有助于获得更高的可利用容量。ILs的应用为设计用于稳定SIBs的保护性CEI提供了思路。
