Superionic conductivity in lithium argyrodite solid-state electrolyte by controlled Cl-doping

The lithium ion conductivity of lithium argyrodite can be improved by introducing Cl to tailor the S/Cl disorder in the structure. An ultrafast room temperature lithium ion conductivity of up to 6.4 mS/cm was achieved for Li_5.7PS_4.7Cl_1.3. The synthesis parameters for Li_7-xPS_6-xCl_x (x = 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9) are systematically investigated to obtain pure lithium argyrodite phase with high ionic conductivity. AC impedance spectroscopy and ⁷Li spin-lattice relaxation NMR are utilized to show the enhancement of lithium ion conductivity caused by the incorporation of Cl. Ab initio molecular dynamics (AIMD) simulations proved that the introduction of Cl can effectively decrease the energy barriers for lithium ion migration in both short and long diffusion length scales. All-solid-state lithium batteries using LiNbO₃-coated LiNi_0.8Mn_0.1Co_0.1O₂ cathode and Li_5.7PS_4.7Cl_1.3 solid electrolyte display high discharge capacities and excellent cycling performances at relatively high current densities. EIS and galvanostatic intermittent titration technique (GITT) further confirm that the improved electrochemical performance can be attributed to the mitigation of voltage polarization and reduction of the interfacial resistance between the cathode and solid electrolyte.