Low-loading ionic liquid regulates Li+ coordination and TFSI− association in PEO-based polymer electrolytes for lithium metal batteries

Poly(ethylene oxide) (PEO)-based solid polymer electrolytes are attractive for energy storage, especially for solid-state lithium metal batteries, but their use is hindered by slow Li + transport and unstable Li interfaces. Here, we report a low-loading ionic liquid (IL)-assisted local solvation strategy by incorporating a highly concentrated LiTFSI/sulfolane component and a small amount of Py14TFSI into PEO. Spectroscopy and DFT calculations show that Py14TFSI acts as a coordination regulator rather than a simple plasticizer, decreasing Li + -TFSI − contact ion pairs from 58% in PS to 41% in PSP and promoting more weakly coordinated TFSI − species. The optimized PSP electrolyte delivers an ionic conductivity of 0.116 mS cm −1 at 30 °C, an activation energy of 28.55 kJ mol −1 , and a Li + transference number of 0.40. Consequently, Li||PSP||Li cells cycle for 250 h at 1 mA cm −2 , and LFP||Li cells retain 97% capacity after 150 cycles. Graphical abstract