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The instability of sulfide solid electrolytes to Li anode and high‐voltage LiNi0.8Mn0.1Co0.1O2 (NMC811) cathodes limits the cyclic performance of all‐solid‐state lithium battery (ASSLB). Herein, the stability of Li6PS5Cl against Li anode is enhanced by mixing a small amount (0.32 wt%) of CuF2‐LiNO3 (CL) into Li6PS5Cl electrolyte layer to in‐situ form a mixed‐conductive‐lithiophobic and self‐healing LiF‐Li3N‐Cu solid electrolyte interphase (SEI) at Li6PS5Cl‐CL/Li interface. The critical current density (CCD) of Li6PS5Cl‐CuF2‐LiNO3 increases to 1.4 mA cm–2/1.4 mAh cm–2 at room temperature, which is much higher than that of pristine Li6PS5Cl (0.4 mA cm–2/0.4 mAh cm–2) even though mixing 0.32 wt% CL into Li6PS5Cl slightly reduces the ionic conductivity from 2.9 × 10–3 to 1.5 × 10–3 S cm–1. The compatibility of Li6PS5Cl‐CL electrolyte to single‐crystalline NMC811 (S‐NMC811) is further enhanced by adding a small amount (0.02 wt%) of AlF3 into Li6PS5Cl‐CL forming Li6PS5Cl‐CuF2‐LiNO3‐AlF3 (Li6PS5Cl‐CLA) as a cathode electrolyte and by doing Cl– on S‐NMC811 (Cl@S‐NMC811) surface. The Cl@S‐NMC811‐Li6PS5Cl‐CLA|Li6PS5Cl‐CL|Li cells with areal capacity of 2.55 mAh cm‐2 achieve a capacity retention of 69.4% after 100 cycles at 1C (1C = 200 mAh g‐1). Adding a small amount of SEI and cathode/electrolyte interphase (CEI) former into the sulfide electrolytes with minimal reduction (48.3%) of ionic conductivity is an effective method to enhance the performance of ASSLB. [ABSTRACT FROM AUTHOR]