Superionic Lithium Argyrodite Electrolytes by Bromine-Doping for All-Solid-State Lithium Batteries

High energy density all-solid-state rechargeable batteries with excellent safety are considered as reliable alternative to the current lithium-ion battery. The major challenge of all-solid-state rechargeable batteries is to develop new electrolyte material with high conductivity and good stability against lithium. In this work, the argyrodite electrolytes Li 5.4 PS 4.4 Cl 1.6− x Br x (0 ≤ x ≤ 0.8) are synthesized through wet-milling method. Benefit from higher concentration of Br and the lattice softening of crystal structure, Li 5.4 PS 4.4 Cl 1.2 Br 0.4 electrolyte with the highest lithium ion conductivity of 8.17 mS cm −1 is realized. The Li/Li 5.4 PS 4.4 Cl 1.2 Br 0.4 /Li symmetric battery can stable cycle for 2500 h at 0.1 mA cm −2 , showing favorable stability against lithium. The assembled LiCoO 2 /Li 5.4 PS 4.4 Cl 1.2 Br 0.4 /Li battery delivers an initial reversible capacity of 122.4 mAh g −1 with a capacity retention of 82.8% after 100 cycles. These results demonstrate a promising argyrodite electrolyte Li 5.4 PS 4.4 Cl 1.2 Br 0.4 with high ionic conductivity and favorable electrochemical stability for all-solid-state lithium battery.