Solid polymer electrolytes (SPEs) have attracted much attention due to their better safety and flexibility. However, the low ionic conductivity and narrow electrochemical window impede their applications in PEO-based solid-state batteries. Here we report the synthesis of a new SPE comprising PEO with 1 wt% fluoromethyl modified polyamine (PAN-FMP) as a filler that has high ionic conductivity and a wide electrochemical window. The LiFePO₄ (LFP)/SPE/Li cell delivers an initial capacity of 124 mA h g⁻¹ at 1C with a capacity retention of 83% after 1000 cycles. Moreover, the electrochemical stability window of the SPE has been widened up to 4.8 V, which makes it compatible with high voltage cathodes such as LiNi_0.8Co_0.1Mn_0.1O₂ (NMC811). The enhanced ionic conductivity of the SPE originates from the PAN-FMP filler rich in –CF₃ groups that interact with ether oxygen on the PEO segment and make ether oxygen form loose ion pairs with Li⁺ ions, thus inhibiting the rearrangement and crystallization of PEO and enhancing Li⁺ ion transport of the SPE. The long cycle life of the full cell is attributed to the formation of a LiF-rich-solid electrolyte interface (SEI) layer due to PAN-FMP promoting the defluorination of TFSI⁻. The LiF SEI layer enables uniform lithium metal deposition, and prevents the growth of lithium dendrites. The low-cost, simple preparation method and superior electrochemical performance of the SPE with an organic PAN-FMP filler thus provide a new strategy to enable high voltage and high energy density polymer based solid-state batteries.