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

Lithium argyrodite electrolytes(Li6PS5X(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 Li6PS5I in solid-state batteries have not been fully investigated yet.Here,we unravel the synthetic process for the Li6PS5I phase with the mechanical milling route,in which the argyrodite phase appears after 500 r·min-1 for 12 h.The pure Li6PS5I 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 Li6PS5I is applied with both the pristine and LiNbO3-coated LiNi0.7Mn0.2Co0.1O2 cathodes in solid-state batteries.The coated LiNi0.7Mn0.2Co0.1O2 material delivers higher dis-charge 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 LiNi0.7Mn0.2Co0.1O2 electrode exhibits potential operation at-20℃.In situ/ex situ electrochemical impedance spectrum(EIS)are applied to unravel the resistance evaluation of solid-state batteries(SSBs)at dif-ferent temperatures,which show that the low electrolyte conductivity and the slow lithium-ion mobility across the interface are the major bottlenecks for good electrochem-ical performance.