A newly-developed heat-resistance polyimide microsphere coating to enhance the thermal stability of commercial polyolefin separators for advanced lithium-ion battery

Polymer separators with high-temp dimensional stability is strongly demanded for high-safety lithium-ion batteries (LIBs). In this study, a novel polyimide (PI) microsphere coating slurry was prepared and then plated on Celgard polypropylene (PP) separator, producing PP@PI microsphere composite separator with excellent thermal stability, flame retardancy, high liquid retention capacity and high ionic conductivity by a simple blade-coating process. The results show that the thermal stability and liquid retention capacity of the PP@PI microsphere composite separator are significantly improved. Compared with the pure commercial PP separator which sharply shrank at 150 degrees C, the PI microsphere composite separator shows negligible shrinkage over 150 degrees C. The obtained PP@PI microsphere composite separators exhibited excellent thermal stability and fire-resistance properties. At the same time, the peel strength of composite separator reached 138.6 N.m(-1), with excellent adhesion. The surface density of PP@PI microsphere composite separator is 16.62 g.m(-2), which is lower than 30.22 g.m(-2) of ceramic coated composite separator. Electrochemical characterizations indicate that the discharge capacity and capacity retention rate of the battery assembled with PP@PI microsphere composite separator are significantly higher than those assembled with the pure PP separator. The half-cell assembled with this composite separator shows a high capacity of 144.3 mAh.g(-1) at 5C, which is much higher than the 117.8 mAh.g(-1) of the commercial PP separator equipped battery. Moreover, the lithium-ion batteries assembled with the PP@PI microsphere composite separator show excellent cycle stability after 200 cycles at 1C. More importantly, the lithium-ion battery assembled with PP@PI microsphere composite separator has excellent safety at high temperature. These features demonstrate the potential of PP@PI microspheres composite membrane as high-security separator for LIBs.

Automated summary

In this study, a PP@PI microsphere composite separator with excellent thermal stability, flame retardancy, and high ionic conductivity was prepared by a simple blade-coating process. The composite separator showed improved thermal stability, liquid retention capacity, and adhesion compared to the pure commercial PP separator. The lithium-ion battery assembled with this composite separator exhibited higher discharge capacity and cycle stability, as well as excellent safety at high temperatures.