Elucidating the structure and ion transport mechanism in lithium halospinels and high-entropy lithium metal chlorides solid electrolytes

Lithium metal chloride solid electrolytes are regarded as promising candidate for applying in all-solid-state batteries as they show good ionic conductivities of > 1 mS cm-1 at room temperature and good electrochemical compatibility with 4V class cathode materials. In this project, we developed Zr4+, Al3+, Fe3+ and Mg2+ doped Li2±xSc1-xMxCl4 halospinel with ionic conductivities up to 1.8 mS cm-1. However, the conductivity of Al3+, Fe3+, Mg2+ doped halospinel is < 1 mS cm-1 and lower than computational prediction. We ascribe the reason not only to the different sizes of lattice framework from different sizes of metal dopant, but to a different lithium distribution over the 8a, 16c, 16d and 48f sites. We propose high resolution neutron powder diffraction to elucidate the halospinel structure and especially lithium sublattice at room temperature and 10K. The low temperature data will reduce thermal diffuse scattering and give insights on the origin of high energy 48f site occupancy. We also developped high entropy Li2.05MCl6 (M=Zr, Mg, Ca, Y, Sc, Ho) crystallizing in orthorhombic crystal system, different from the parent structure trigonal Li2ZrCl6, with a 4-fold ionic conductivity boost to 1.6 mS cm-1. All data will be used for Rietveld refinement analysis and combined with negative fourier density map to find all lithium locations, the results will help us elucidating the structure and ion transport mechanism in lithium metal chloride materials.