Enable High Energy-Density Lithium-Ion Battery Conversion Cathodes Based on Iron Fluorides Using Integrated in Situ Experimental and Computational Approaches

The large-scale deployment of renewable energy technologies critically depends on solving the intermittency of energy production methods with scalable and inexpensive energy-storage solutions. Lithium-ion battery (LIB) technology has been widely considered as the technology of choice to meet the future energy challenge. Conversion cathode materials represented by inexpensive iron fluorides (FeF₂ and FeF₃) and oxyfluorides hold the promise to significantly increase the energy density of current LIBs. However, despite significant experimental and theoretical efforts in recent years, this promise has yet to be realized due to the challenges of fast capacity decay and a large voltage hysteresis. Solving these challenges requires a better understanding of the electrochemical reaction mechanisms during battery operation, especially during recharge, which however has been surprisingly under-researched. Here I will report our comprehensive and integrated experimental and theoretical studies into the mechanisms controlling the nanoscale electrode conversion/reconversion. By holistically evaluating the results from operando 2D X-ray absorption near-edge structure spectroscopy (XANES) microscopy, operando X-ray absorption spectroscopy, in situ scanning transmission electron microscopy (STEM) and electron diffraction (ED), ex situ TEM/ED, and density functional theory simulations, we will present new insights into the conversion mechanisms of these materials. We will also discuss our recent progress in developing long-cycle-life nanostructured iron fluoride conversion cathodes, which is built on the insights gleaned from the integrated experiments and modeling above.