Advanced polyimide separator via co-precursor method for lithium-ion batteries with low thermal runaway risks

Separator is an important component in lithium-ion batteries, and it plays a critical role in ensuring the overall thermal safety and electrochemical performance of a battery. To date, the development of safe and robust lithium-ion batteries is still hindered by the commercial polyolefin membrane due to its poor thermal stability and inferior electrolyte wettability. Thus, to address this shortcoming, an advanced polyimide aerogel separator was designed by simple one-pot reaction via co-precursor and cross-linking methods in this work. Based on molecular structure designation and gelation time control, the as-prepared polyimide aerogel separator (C-PI separator) possessed high porosity, good flexibility, excellent thermal stability, and superior electrolyte wettability, which are essential attributes of a high-performing separator. LiFePO4|Li metal battery was later assembled with C-PI separator, and the cell demonstrated outstanding long-term cyclic performance (>1000 cycles at 1C with 93.6 % retention). Compared with PE separators, the NCM523-graphite pouch cell assembled with C-PI separators exhibited high thermal stability with a higher thermal runaway temperature (204.9 °C vs. 140.4 °C) and a lower maximum temperature rise (0.06 °C/min vs. 8 °C/min), demonstrating its application potential in scenarios with high requirements for safety. Furtherly, the thermal runaway mechanisms of the full cells were explored and explained in this work.