Silicon-Doped Argyrodite Solid Electrolyte Li6PS5I with Improved Ionic Conductivity and Interfacial Compatibility for High-Performance All-Solid-State Lithium Batteries

Argyrodite-type sulfide solid electrolytes (SEs) Li6PS5X (X = Cl, Br, I) have attracted considerable interest lately by providing a promising lithium-ion transport capability for its application in all-solid-state lithium batteries (ASSLBs). However, other than Li6PS5Cl and Li6PS5Br, Li6PS5I shows poor ionic conductivity of 10–7 S cm–1, which is originated from the I–/S2– site ordered arrangement in its structure. Herein, we report a silicon-doped solid electrolyte Li6+x P1–x Si x S5I in this sulfide class, which can remarkably increase the conductivity to 1.1 × 10–3 S cm–1 and lower the activation energy to 0.19 eV as a consequence of changing the structural unit in the argyrodite network. The Li6+x P1–x Si x S5I solid electrolytes are employed in ASSLBs with Li­(Ni0.8Mn0.1Co0.1)­O2 (NCM-811) as cathode and Li metal as an anode to evaluate the electrochemical performance. With x = 0.55, the battery displays an initial discharge capacity of 105 mA h g–1 at a rate of 0.05C and achieves high Coulombic efficiency. Moreover, chemical reactions occurring on the interfaces of the NCM/SE and Li/SE in regard to the degradation of cell performance are also investigated.