F and N Rich Solid Electrolyte for Stable All‐Solid‐State Battery

Abstract The instability of sulfide solid electrolytes to Li anode and high‐voltage LiNi_0.8Mn_0.1Co_0.1O₂ (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.