Synthetic optimization and application of Li-argyrodite Li6PS5I in solid-state battery at different temperatures

Lithium argyrodite electrolytes (Li 6 PS 5 X (X = Cl, Br, I)) have received tremendous attention due to their low cost and high conductivity among sulfide electrolytes. However, the synthesis details and application of Li 6 PS 5 I in solid-state batteries have not been fully investigated yet. Here, we unravel the synthetic process for the Li 6 PS 5 I phase with the mechanical milling route, in which the argyrodite phase appears after 500 r·min −1 for 12 h. The pure Li 6 PS 5 I phase with the highest ionic conductivity (2.1 × 10 −4 S·cm −1 ) is obtained after 20-h milling, and a subsequent annealing process causes a decrease in the conductivity. The Li 6 PS 5 I is applied with both the pristine and LiNbO 3 -coated LiNi 0.7 Mn 0.2 Co 0.1 O 2 cathodes in solid-state batteries. The coated LiNi 0.7 Mn 0.2 Co 0.1 O 2 material delivers higher discharge capacities (211.4 vs. 140.7 mAh·g −1 at 0.05C for the 1st cycle, and 144.0 vs. 66.5 mAh·g −1 at 0.50C for the 2nd cycle) and higher coulombic efficiencies. Moreover, the coated LiNi 0.7 Mn 0.2 Co 0.1 O 2 electrode exhibits potential operation at − 20 °C. In situ/ex situ electrochemical impedance spectrum (EIS) are applied to unravel the resistance evaluation of solid-state batteries (SSBs) at different temperatures, which show that the low electrolyte conductivity and the slow lithium-ion mobility across the interface are the major bottlenecks for good electrochemical performance. Graphical abstract