Silicon-Doped Argyrodite Solid Electrolyte Li₆PS₅I with Improved Ionic Conductivity and Interfacial Compatibility for...

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^-/S^2- site ordered arrangement in its structure. Herein, we report a silicon-doped solid electrolyte Li₆₊P_1-SiS₅I 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₊P_1-SiS₅I solid electrolytes are employed in ASSLBs with Li(Ni_0.8Mn_0.1Co_0.1)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.