Room-Temperature Pseudo-Solid-State Iron Fluoride Conversion Battery with High Ionic Conductivity

• Published in: ACS applied materials & interfaces 2022-12, Vol.15 (1)
• Main Authors: Lapp, Aliya Siegel, Merrill, Laura Christine, Wygant, Bryan Russell, Ashby, David Scott, Bhandarkar, Austin S., Zhang, Alan Chiurun, Fuller, Elliot James, Harrison, Katharine Lee, Lambert, Timothy N., Talin, Albert Alec
• Format: Article
• Language: English
• Subjects: batteries; conversion; ENERGY STORAGE; gel polymer electrolytes; ionogels; iron fluoride; localized high-concentration electrolytes; pseudo-solid state
• ISSN: 1944-8244; 1944-8252

Li-metal batteries (LMBs) employing conversion cathode materials (e.g., FeF3) are a promising way to prepare inexpensive, environmentally friendly batteries with high energy density. Pseudo-solid-state ionogel separators harness the energy density and safety advantages of solid-state LMBs, while alleviating key drawbacks (e.g., poor ionic conductivity and high interfacial resistance). In this work, a pseudo-solid-state conversion battery (Li-FeF3) is presented that achieves stable, high rate (1.0 mA cm–2) cycling at room temperature. The batteries described herein contain gel-infiltrated FeF3 cathodes prepared by exchanging the ionic liquid in a polymer ionogel with a localized high-concentration electrolyte (LHCE). The LHCE gel merges the benefits of a flexible separator (e.g., adaptation to conversion-related volume changes) with the excellent chemical stability and high ionic conductivity (~2 mS cm–1 at 25 °C) of an LHCE. The latter property is in contrast to previous solid-state iron fluoride batteries, where poor ionic conductivities necessitated elevated temperatures to realize practical power levels. Importantly, the stable, room-temperature Li-FeF3 cycling performance obtained with the LHCE gel at high current densities paves the way for exploring a range of architectures including flexible, three-dimensional, and custom shape batteries.