A new solid polymer electrolyte (SPE) PEO-LiTFSI-1%LGPS-10%SN is successfully prepared via a convenient method with low cost. The effect of SN on the ionic conductivity of PEO-based electrolyte is systematically investigated. It presents a maximum conductivity of 9.10×10−5 S·cm−1 at 25°C, and a 15-fold ion conductivity enhancement in PEO-LiTFSI. It exhibits wide electrochemical window (0–5.5V) and excellent compatibility with metallic Li. The LiFePO4/Li batteries exhibit a good cycling and rate performance under 40°C, whose maximum discharge specific capacity at 0.1 C is 160.6mAh·g−1, and 94.7% can be retained after 60 cycles. At 0.5C, the maximum discharge specific capacity is 138.4mAh·g−1, and capacity retention close to 90% even after 100 cycles. The reasons of activation process are discussed. This new SPE with outstanding electrochemical performance is a promising solid electrolyte candidate for applications in all-solid-state lithium battery.