2, Institute for Basic Science, Seoul, , Korea (the Republic of)
Solid electrolyte materials have attracted immense interest owing to their stability and wide voltage windows needed for high energy density all-solid states batteries. From the solid electrolyte, achieving ionic conductivity higher than the liquid electrolytes is crucial for high power and high energy density of the battery. Li7P3S11 has been considered as promising with high Li ionic conductivity comparable to that of a liquid electrolyte at room temperature. However, due to its structural complexity from low symmetry, its structural properties that enhance ionic diffusivity are still unknown.
Here, we demonstrate various new (meta-)stable Li ions interstitial sites using ab-initio molecular dynamics calculations. Moreover, from these new sites, a ground state configuration different from the previously reported ground state configuration with new Li+ ordering was found. To understand the Li+ diffusion mechanism near the anode and the cathode, defect formation energies are calculated based on the new ground structure. Diffusivities at the various defect concentrations are estimated using AIMD calculation.
These results suggest that the PS43-(thiophosphate) and pyrothiophosphate(P2S74-) which construct the frame in the Li7P3S11 form unique local environment that offer diffusion mechanism of Li ions close to the liquid-like behavior and allow ultrahigh conductivity. We suggest that our conclusion opens up the new possibility for high performance superionic conductors having the liquid-like diffusion behavior.