Micro porous forming of polyimide composite membrane with temperature and humidity control and its application Evaluation in lithium-ion batteries

Abstract

The safety concerns pose significant challenges to the development of a new generation of high-energy-density lithium-ion batteries. To avoid short circuiting, it is important to ensure that the separator does not shrink in case of battery overheating. We have developed a process for manufacturing composite membranes by dip-coating polyimide (PI) with polyethylene terephthalate (PET) non-woven fabric as the base film for future continuous mass production. This processing technique, vapor-induced and immersion precipitation phase separation to modulate the pore structure of the PI layer, obtained a PI-PET composite membrane with a porosity of 58 %, a pore size distribution between 25 and 90 nm, and an average pore size of about 65 nm. Additionally, the composite membrane exhibits excellent thermal stability, with a T_d5 of 420 °C and no shrinkage after being heated at 250 °C for 1 h. The capacity retention of a LiNi_0.5Co_0.2Mn_0.3O₂|| graphite (NCM523||C) pouch battery assembled with the PI composite membrane is 60.4 % after 1000 cycles at 1C, comparable to the performance of pouch battery with the commercial Al₂O₃/PE/Al₂O₃ separator. In addition, the pouch battery assembled with the PI composite membrane passes destructive tests such as folding, needling, etc., and it continues to discharge for approximately 10 h after the corners are cut, demonstrating excellent safety features.