Influence of the Halogen in Argyrodite Electrolytes on the Electrochemical Performance of All-Solid-State Lithium Batteries

All-solid-state lithium batteries (ASSLBs) are considered as an alternative solution to lithium-ion batteries, because of their safety and high theoretical energy density. Argyrodite-based solid-electrolytes (SEs), Li6PS5X (X = Cl, Cl0.5Br0.5 or Br), are promising candidates for ASSLBs. Most of the previous reports have used Li6PS5Cl as the default SE composition. Here, the electrochemical behavior of three different argyrodites with Cl- or Br-, or both, as the halogen is systematically studied. Using LiNi0.6Co0.2Mn0.2O2 as a model cathode, the behavior of these SEs in ASSLB cells is also studied. SEs containing Br show higher near-room-temperature ionic conductivity (>2 mS cm(-1)) and the critical current density (>= 1 mA cm(-2)) during Li plating/stripping, and are stable up to 5 V versus Li/Li+. Li6PS5Br gives the best electrochemical performance in terms of C-rate and long-term cycling among the three samples. Specifically, the cathode delivers an initial reversible capacity of 156 mAh g(-1), with approximate to 27% irreversible capacity loss and 90% capacity retention over 100 cycles, and >99% Coulombic efficiency. It delivers approximate to 56 mAh g(-1) at 10C, 36% of its initial capacity at 0.2C, whereas Li6PS5Cl and Li6PS5Cl0.5Br0.5 deliver only 20 and 46 mAh g(-1) at 10C.