PVDF/lithiated sulfonated poly (ether ether ketone) blend coated PE separators for high-performance lithium metal batteries

Ionic conductivity and lithium ion transference number (tLi+) of electrolytes are essential parameters governing the performances of high energy density lithium metal batteries. Although the importance of tLi+ versus ionic conductivity has been theorized by simulation, the systematically experimental study of their respective effects on lithium dendrite suppression and battery performances is rarely carried out. Here, a series of polyvinylidene fluoride and lithated sulfonated poly (ether ether ketone) blend (PVDF/SPEEK-Li) coated polyethylene (PE) separators with exactly the same composition but different pore morphologies are fabricated by vapor and non-solvent induced phase separation. The effects of sulfonate group–ion interaction and pore morphologies on ionic conductivity and tLi+ of the electrolytes are studied. The performances of lithium metal batteries can be obviously improved by subtle increase of the tLi+, especially at high charge rates and even with a decrease in conductivity. Even at a high current density of 3 C, the PVDF/SPEEK-Li coated PE separator assembled lithium metal battery using a LiFePO4 cathode with a mass loading of 10.5 mg cm−2 can run stably for 200 cycles with a capacity retention of 79 %, which is superior to the PE separator assembled battery with a life of only 55 cycles.