Lithium (fluorosulfonyl)(nonafluorobutanesulfonyl)imide (LiFNFSI) as conducting salt to improve the high-temperature resilience of lithium-ion cells

A novel lithium salt, lithium (fluorosulfonyl)(nonafluorobutanesulfonyl)imide (LiFNFSI), is investigated as a conducting salt to improve the high-temperature resilience of lithium-ion cells. It shows better thermal stability than LiPF6. The electrolyte having 1.0 M LiFNFSI in a mixture of ethylene carbonate (EC)/ethyl methyl carbonate (EMC) (3:7, v/v) shows high conductivity comparable to LiClO4, good electrochemical stability, and does not corrode aluminum. At both room temperature (25 °C) and elevated temperature (60 °C), the graphite/LiCoO2 cells with LiFNFSI exhibit better cycling performances than those with LiPF6. Particularly, at 60 °C, the capacity fading rate of the LiFNFSI-based cell without any additive is 37% after 100 cycles, while the cell with LiPF6 fails rapidly. These outstanding properties of LiFNFSI make it an attractive candidate to overcome the rapid capacity fading of lithium-ion batteries at elevated temperatures.