Lithium Difluorophosphate Additive Engineering Enabling Stable Cathodic Interface for High‐Performance Sulfide‐Based All‐Solid‐State Lithium Battery

Coupling with high‐voltage oxide cathode is the key to achieve high‐energy density sulfide‐based all‐solid‐state lithium batteries. However, the complex interfacial issues including the space charge layer effect and undesirable side reaction between sulfide solid‐state electrolytes and oxide cathode materials are the main constraints on the development of high‐performance all‐solid‐state lithium batteries, which lead to the continuous decay of electrochemical performance. Herein, different from the complicated coating procedure, a LiPO 2 F 2 additive engineering was proposed to achieve high‐performance all‐solid‐state lithium batteries. With the introduction of LiPO 2 F 2 additive, a protective cathode–electrolyte interphase consisting of LiP x O y F z , LiF, and Li 3 PO 4 could be in situ formed to improve the interfacial stability between LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) and Li 5.5 PS 4.5 Cl 1.5 (LPSC). Benefiting from this, the NCM811/LPSC/Li all‐solid‐state lithium battery exhibited impressive cyclic stability with a capacity retention of 85.5% after 600 cycles (at 0.5 C). Diverse and comprehensive characterization, combined with finite element simulation and density functional theory calculation fully demonstrated the effective component, interfacial stabilization function and enhanced kinetic of LiPO 2 F 2 ‐derived cathode–electrolyte interphase. This work provides not only a feasible and effective method to stabilize the cathodic interface but also worthy insight into interfacial design for high‐performance all‐solid‐state lithium batteries.