Heat-resistant Al2O3 nanowire-polyetherimide separator for safer and faster lithium-ion batteries

Poor heat/flame-resistance of polyolefin (e.g., polyethylene and polypropylene) separators and high flammability of organic electrolytes used in today's lithium-ion batteries (LIBs) may trigger rare yet potentially catastrophic safety issues. Here, we mitigate this challenge by developing a heat-resistant and flame-retardant porous composite membrane composed of polyetherimide (PEI) and Al2O3 nanowires (NWs). The membranes are fabricated based on an industrially scalable non-solvent-induced phase separation process, which results in an intimately interconnected porous network of Al2O3 NWs and PEI. The produced composite membranes exhibit excellent flexibility, thermal stability, and flame-retardancy. Importantly, the composite membranes exhibit minimal thermal shrinkage and superior tensile strength (16 MPa) at temperatures as high as 200 °C, significantly exceeding the performance of conventional polyolefin separators. Compared with commercial separators, their superior wettability and higher ionic conductivity (by up to 2.4 times) when filled with the same electrolyte, larger electrolyte uptake (∼190 wt.%), as well as improved cycle and rate performance demonstrated in LiNiMnCoO2 (NCM)-based LIBs make them attractive choices for a variety of electrochemical energy storage devices.