First-principles Formulation of Spinel-like Structured Li(4-3x)YxCl4 as Promising Solid-State Electrolytes to Enable Superb Lithium Ion Conductivity and Matching Oxidation Potentials to High-voltage Cathodes

Halide solid-state electrolytes (SSEs) have attracted great attention as potential electrolytes for all solid-state batteries (ASSBs) owing to their high oxidation potentials, excellent ductility, and good resilience to humidity. However, to date most reported halide SSEs only demonstrated rather limited ionic conductivities due to lack of effective diffusion channels for fast transportation of lithium ions. Here in this work, we have carried out extensive first principles calculations towards identifying novel candidates as highly attractive halide SSEs, and we find that through tuning the lattice chemistry in the hexagonal Li3YCl6 halide, one is able to open a new avenue in achieving three highly stable compounds with spinel-like cubic structures. The two best cubic compounds, Li2.125Y0.625Cl4 and Li2.5Y0.5Cl4, are able to offer very efficient three-dimensional highways for Li+ transportation, with their being able to offer remarkable room-temperature Li+ conductivities of 6.11 mS cm−1 and 8.42 mS cm−1 at low activation energies (0.247 eV and 0.244 eV), respectively. In addition to ionic conductivities being several times higher than that of the pristine Li3YCl6 phase, they also have remarkably high oxidation potentials above 4.0 V desirable to accommodate high voltage cathode materials electrochemically.