promising applications in energy storage devices meet the multiplying demands regarding high energy densities and safety concerns. [1] As a key part of ASSLBs, the SEs possess merits including decent thermal properties, mechanical strengths, and electrochemical stability windows; high Li transference numbers; and stable ion transports. [2] Among diverse SEs, sulfides show high ionic conductivity comparable to the commercial liquid electrolytes at room temperature, and good deformability favorable for battery assembling, [3] which are prime candidates for practical applications. [4] Nonetheless, sulfide SEs are electrochemically incompatible with metallic Li, which generates electronic conductive interphases. [5] This not only promotes the interfacial reaction of Li/sulfide causing a large interface resistance but also accelerates the Li-dendrites growth, leading to a rapid deterioration of battery performance and finally short circuits. [6] Despite the progress achieved, how to suppress Li dendrites in SEs to date is still a major issue to hinder the practical applications of lithium metal anode. Yet, no significant breakthrough has been achieved. ASSLBs using sulfide SEs and Li metal anode can only work for a few hundred cycles (<300 cycles) at room temperature, even at relatively small current densities (<0.3 mA cm −2 ), while the long-life batteries always use Li composite anodes such as Li-In, [7] Li-C, [8] and Ag-C. [4a] However, considering the high theoretical capacity (3860 mAh/g) and low electrochemical potential (−3.04 V vs SHE), Li metal remains the ultimate choice for Li batteries. [9] Moreover, a Li metal anode is important for developing next-generation Li-S batteries, [10] along with the sulfide SEs to restrain the polysulfide dissolution. It is thus significant to improve the electrochemical stability of sulfide SEs to Li. Many efforts based on external routes have been made so far to successfully mitigate the reactivity of Li/sulfide-SEs, including Li alloying (e.g., In-Li), surface decorations, construction of artificial interfaces, and incorporation of organic/ionic-liquid buffer layers. [6a,11] Combined with these external routes, if the sulfides themselves can be optimized via the intrinsic routes, for example, doping, phase transition, and microstructural modification, the interfacial stability of Li/sulfide is expected to be effectively enhanced.Compared with other sulfide-based SEs, Li-argyrodites Li 7-a PS 6-a X a (X = Cl, Br, I) as an important family member of sulfide-based SEs not only possess a low cost and high ionic A stable interface and preventing dendrite-growth are two crucial factors to realize long-life all-solid-state Li batteries (ASSLBs) using sulfide-based solid electrolytes (SEs) and Li metal anodes. But it remains a challenge to accomplish the two factors simultaneously. Here, an effective strategy is reported to realize this goal in Li-argyrodites via self-engineered metastable decomposition that is enabled by Si doping in Cl-rich argyrodites. It is shown that Cl...
