Robust polyetherimide fibrous membrane with crosslinked topographies fabricated via in-situ micro-melting and its application as superior Lithium-ion battery separator with shutdown function

With more and more applications of Lithium-ion batteries (LIBs) in electronics, Polyolefin (PO) separators, including Polyethylene (PE) and Polypropylene (PP) separators, cannot meet the increasing requirements of high performance LIBs. Separators with good thermal stability and high electrochemical performance are in great demand. In this paper, Polyetherimide (PEI) fibrous membrane separators with crosslinking network morphologies have been successfully fabricated via electrospinning and in-situ micro-melting technique. The in-situ micro-melting process converts the loose and weak PEI nonwoven membrane to the compact and robust crosslinked fibrous membrane, and then improves the tensile strength of the membrane from 4 MPa to 21 MPa. The crosslinking structure greatly reduces the risk of fibrous membrane disassembling into the loose nonwovens during long-term battery cycling, and consequently improves the stability of LIBs. The results of Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA) show that the crosslinked PEI fibrous membrane presents excellent thermal stability (5% weight loss at about 522.2 °C) and thermal dimensional stability (without shrinkage below 240 °C), better than Celgard-2400 separator. The LIB with this separator shows higher capacity (113.3 mAh g−1, 5 C) than that with Celgard-2400 separator (95.2 mAh g−1, 5 C). More importantly, this PEI separator exhibits thermal shutdown function at 260 °C, which provides LIB with a safe guarantee under high temperature. All above-mentioned properties make crosslinked PEI fibrous membrane a good candidate as a separator of LIB.