Porous polyamine/PEO composite solid electrolyte for high performance solid-state lithium metal batteries

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 LiNi0.8Co0.1Mn0.1O2 (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.