Development of superionic halide electrolytes for solid state iron fluoride conversion cathodes

Abstract

Li-ion rechargeable batteries enjoy tremendous success in powering our daily lives, yet they face significant challenges in safety, performance, and cost for their applications in transportation electrification and grid storage. Solid-state batteries (SSBs) are considered a promising alternative due to the potential improvements in safety, energy and power densities. The utilization of inorganic solid electrolytes in an SSB can also enable high-energy, low-cost battery chemistries that are not compatible with conventional lithium-ion batteries based on liquid electrolytes. In this thesis, we aim to develop superionic halide solid electrolytes to address the performance limitations of solid-state conversion-type iron fluoride (FeF3) cathodes, which can potentially double the energy density of today’s lithium-ion cathodes with low-cost, earth-abundant elements. Combining material synthesis, materials characterization and electrochemical measurements, we investigate the effects of halide composition on their ionic conductivity and (electro)chemical stability. The research enabled us to develop a Zr-substituted lithium yttrium chloride (Li3YxZr1-xCl6) solid electrolyte that exhibits a high ionic conductivity of 0.9 mS·cm-1 as well as excellent compatibility with FeF3 cathodes, exhibiting over 100 cycles of stable performance. The excellent performance of the solid electrolyte having been demonstrated in a solid-state battery with FeF3 cathode and lithium-indium anode paves the way for the practical application of solid-state iron fluoride cathodes for next-generation battery technologies.