Electrospun polyacrylonitrile microfiber separators for ionic liquid electrolytes in Li-ion batteries

Despite much recent progress in the development of room temperature ionic liquid (RTIL) electrolytes for lithium-ion batteries (LIBs), relatively little work has been done in terms of investigating commercially applicable separator materials capable of accommodating RTILs. In this work, we demonstrate an electrospun polyacrylonitrile (PAN) microfiber separator. The PAN microfiber separators show high degrees of porosity (∼83%), wettability, and mechanical strength (σ_UTS = 16.98 MPa and E = 5.95 MPa). The physical properties of our electrospun separators lead to impressive electrochemical performance, showing an apparent MacMullin number (N_M) of <5 when combined with the PYR₁₃FSI (1.2M LiFSI) electrolyte. These results are validated by superior rate performance and the exhibition of a high capacity full-cell utilizing a PAN microfiber separator in combination with the PYR₁₃FSI (1.2M LiFSI) RTIL electrolyte. Such work represents significant progress in the advancement of RTIL electrolytes for LIBs, indicating that nonwoven separators are a commercially viable solution to the previous lack of separator materials for RTIL electrolytes.