Solid‐state lithium metal batteries (LMBs), constructed through the in‐situ fabrication of polymer electrolytes, are considered a critical strategy for the next‐generation battery systems with high energy density and enhanced safety. However, the constrained oxidation stability of polymers, such as the extensively utilized polyethers, limits their applications in high‐voltage batteries and further energy density improvements. Herein, an in‐situ fabricated fluorinated and crosslinked polyether‐based gel polymer electrolyte, FGPE, is presented, exhibiting a high oxidation potential (5.1 V). The fluorinated polyether significantly improves compatibility with both lithium metal and high‐voltage cathode, attributed to the electron‐withdrawing ‐CF3 group and the generated LiF‐rich electrolyte/electrode interphase. Consequently, the solid‐state Li||LiNi0.6Co0.2Mn0.2O2 batteries employing FGPE demonstrate exceptional cycling performances of 1000 cycles with 78% retention, representing one of the best results ever reported for polymer electrolytes. Moreover, FGPE enables batteries to operate at 4.7 V, realizing the highest operating voltage of polyether‐based batteries to date. Notably, our designed in‐situ FGPE provides the solid‐state batteries with exceptional cycling stability even at practical conditions, including high cathode loading (21 mg cm‐2) and industry‐level 18650‐type cylindrical cells (1.3 Ah, 500 cycles). This work provides critical insights into the development of oxidation‐stable polymer electrolytes and the advancement of practical high‐voltage LMBs.
