Secondary FeF 2 -Li Batteries in Ionic Liquid Electrolytes

Conventional intercalation Li-ion batteries are physico-chemically limited in their energy density and exhibit a restricted temperature operation range. To further increase energy density limit and enable reversible battery cycling at elevated temperatures, the exploitation of new cell chemistry is required. Conversion-type transition metal fluorides (TMFs) can store multiple Li-ions per metal center and thus increase the theoretical energy density by 200% to 300% compared to intercalation compounds. [1] Ionic liquids (ILs) are liquid salts (below 100°C) with improved thermal stability due to the ionic nature of its constituents, little to no flammability, and a low vapor pressure. Combining a TMF cathode with an IL electrolyte and a metallic lithium anode can provide an energy-dense, safe energy storage alternative with a broader operating temperature range and additional versatility for applications in the military, oil, and aerospace sector. [2] In my talk, I will discuss our progress on the development and characterisation of a secondary FeF 2 -IL-Li-metal battery. We studied the impact of active material morphology and carbon-composite preparation techniques on the electronic conductivity and electrochemical performance in a bis(fluorosulfonyl)imide based IL electrolyte. In addition, we investigated different IL formulations for their applicability with TMFs and Li-metal. Both the cathode and anode electrolyte interphases were studied at different temperatures and their role in a full cell setup is elucidated. [1] Olbrich, L. F., Xiao, A. W. & Pasta, M. Conversion-type fluoride cathodes: Current state of the art. Current Opinion in Electrochemistry 30, 100779 (2021). [2] Lin, X., Salari, M., Arava, L. M. R., Ajayan, P. M. & Grinstaff, M. W. High temperature electrical energy storage: Advances, challenges, and frontiers. Chemical Society Reviews 45, 5848–5887 (2016). Figure 1