Electrospun nanofiber-based tri-layer separators with CuO/TiO2 nanowires for high-performance and long-cycle stability of lithium-ion batteries

The tri-layer nanofiber membranes of (PAN containing CuO/TiO2 nanowires) / (PVDF-HFP + PMMA) / (PAN containing CuO/TiO2 nanowires) as separator in lithium-ion battery were manufactured by electrospinning technique. PVDF-HFP with excellent mechanical properties hinders the mobility of lithium ions because of its high crystallinity. By blending the amorphous PMMA polymer with PVDF-HFP, the crystallinity of PVDF-HFP + PMMA composite nanofiber was lowered, while high mechanical strength was maintained due to the dipole-dipole interaction between two polymers. The (PVDF-HFP + PMMA) nanofiber membrane was employed as the middle layer. The PAN nanofiber membranes containing CuO/TiO2 nanowires were prepared as top and bottom layers. The electrochemical properties and performance of the manufactured tri-layer membrane were evaluated, and it showed superior performance than polyolefin-based membranes. The tri-layer membrane maintained stable voltage changes for 700 h during galvanostatic cycling. Furthermore, it exhibited excellent performance in terms of rate capability and life cycle performance. The PE separator maintained a capacity retention of 67 % after 400 cycles, while the tri-layer membrane separator showed a capacity retention of 87 %. These results suggest the potential utility of tri-layer membrane separators as high-performance separators required in the lithium-ion battery.