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 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) cathodes limits the cyclic performance of all‐solid‐state lithium battery (ASSLB). Herein, the stability of Li 6 PS 5 Cl against Li anode is enhanced by mixing a small amount (0.32 wt%) of CuF 2 ‐LiNO 3 (CL) into Li 6 PS 5 Cl electrolyte layer to in‐situ form a mixed‐conductive‐lithiophobic and self‐healing LiF‐Li 3 N‐Cu solid electrolyte interphase (SEI) at Li 6 PS 5 Cl‐CL/Li interface. The critical current density (CCD) of Li 6 PS 5 Cl‐CuF 2 ‐LiNO 3 increases to 1.4 mA cm –2 /1.4 mAh cm –2 at room temperature, which is much higher than that of pristine Li 6 PS 5 Cl (0.4 mA cm –2 /0.4 mAh cm –2 ) even though mixing 0.32 wt% CL into Li 6 PS 5 Cl slightly reduces the ionic conductivity from 2.9 × 10 –3 to 1.5 × 10 –3 S cm –1 . The compatibility of Li 6 PS 5 Cl‐CL electrolyte to single‐crystalline NMC811 (S‐NMC811) is further enhanced by adding a small amount (0.02 wt%) of AlF 3 into Li 6 PS 5 Cl‐CL forming Li 6 PS 5 Cl‐CuF 2 ‐LiNO 3 ‐AlF 3 (Li 6 PS 5 Cl‐CLA) as a cathode electrolyte and by doing Cl – on S‐NMC811 (Cl@S‐NMC811) surface. The Cl@S‐NMC811‐Li 6 PS 5 Cl‐CLA|Li 6 PS 5 Cl‐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.