The use of lithium-ion batteries has been rapidly expanding in portable electronic devices, electric vehicles and energy storage systems due to their high energy density and long cycle life.  In lithium-ion batteries, a separator is a critical component which prevents physical contact of the positive and negative electrodes while permitting free ionic transport within the cell.  Most of the separators currently used in lithium-ion batteries are based on microporous polyolefin membranes such as polyethylene (PE) and polypropylene (PP) as well as various combinations of the two [1,2]. Although these separators offer excellent mechanical strength and chemical stability, they shrink and even melt at high temperatures, which causes short circuit between electrodes in the case of unusual heat generation.  Furthermore, the large difference in polarity between the non-polar polyolefin separator and the polar organic electrolyte leads to poor wettability.  In order to solve these problems, ceramic-coated separators have been developed by combining the characteristics of a polymeric separator and ceramic materials.

In this study, we tried to improve the thermal safety and cycling performance of lithium-ion cells by using separators coated by amino-functionalized SiO₂ (A-SiO₂) nanoparticles.  These separators exhibited enhanced thermal stability and melt integrity.  Due to the high affinity of A-SiO₂ with liquid electrolyte, the A-SiO₂ coated separators exhibited good wettability and high ionic conductivity.  Furthermore, A-SiO₂ nanoparticles played a role as HF scavenger, which suppressed HF generation and electrolyte decomposition at elevated temperature.  As a result, the lithium-ion cells assembled with A-SiO₂ coated separator exhibited the improved cycling performance at both ambient temperature and elevated temperature.

References

[1] P. Arora, Z. Zhang, Chem. Rev. 104 (2004) 4419-4462.

[2] S.S.Zhang, J. Power Sources 164 (2007) 351-364.