Towards Room Temperature Rechargeable Fluoride-Ion Batteries

Since the commercial introduction of lithium-ion batteries (LIBs) by Sony in the early 1990s, LIBs become preferred power sources in portable electronics due to their high energy density. LIBs are being slowly introduced in the electric vehicles (EVs) and for grid storage applications. These high energy density LIBs use cobalt or nickel-rich layered cathode materials, which pose several issues. To meet the growing demands, high energy, sustainable, and safe battery technologies that are beyond LIBs are urgently required. Fluoride-ion batteries (FIBs) offer a potential next-generation electrochemical energy storage device that has a higher energy density and safety when compared with state-of-the-art LIBs. Upon realization of its full potential, FIBs would transform the automotive sector and other energy storage sectors beyond LIBs. Currently, FIBs are operated at high temperatures limited by the use of low fluoride-ion conducting solid electrolytes. The development of suitable liquid electrolytes has the potential to bring out the hidden potential of rechargeable fluoride-ion batteries.

Controlling the reactivity of fluoride in solution is vital to develop non-aqueous liquid electrolytes. Earlier electron-deficient boron complexes were used to bind the fluoride ions and control its reactivity. However, boron-based molecules bind fluoride ions too strongly and will not release the fluoride ions to the electrodes in electrochemical cells; therefore, these complexes are not suitable for electrolytic applications.

A series of organic molecules have identified that control the reactivity of the fluoride ions in solution, and at the same time, they would release the fluoride ions to the electrode in electrochemical cells (predicted based on the binding energy). Such molecules will enable the development of advanced liquid electrolytes for FIBs. In an alternative approach, the PI has also proposed to develop new 'quasi non-aqueous' fluoride transporting liquid electrolytes. These two types of liquid electrolytes will be used to build and investigate FIBs with various metal/metal fluoride combinations.

The main objectives of the project are to develop suitable fluoride-ion-transporting non-aqueous and quasi-non-aqueous liquid electrolytes and to ensure that fluoride ion batteries perform under room temperature with high energy and safety.

Potential applications and benefit: The primary outcome of the project will enable the rapid development of room temperature FIBs and will pave the way for the realisation of high energy rechargeable FIBs with applications in portable electronics, grid, and EVs.