Flexible, high-wettability and thermostable separator based on fluorinated polyimide for lithium-ion battery

To meet the booming demands for lithium-ion battery (LIB), it is practically significant to promote its electrochemical performance and safety. In our work, a novel kind of flexible membrane as separator for LIB is prepared via phase inversion method with soluble polyimide (SPI) containing trifluoromethyl substituent, which is synthesized from 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene (6FAPB) and 4,4′-oxydiphthalic anhydride (ODPA). The SPI separator shows 5% weight loss temperature (Td5%) of 535 °C and maintains intrinsic dimension even after heating at 200 °C. The SPI membrane depicts a sponge-like structure with abundant interconnected pores and delivers a dominant porosity (67%). The SPI membrane displays desired electrolyte wettability, validated by contact angle tests (16.2° and 46.8° for SPI membrane and PE separator, respectively) and electrolyte uptake tests (420 and 132% for SPI membrane and PE separator, respectively). The LIB with SPI membrane as separator exhibits nice ionic conductivity (0.92 mS cm−1) than that with PE separator (0.30 mS cm−1), and therefore affords better electrochemical performance, such as cycling stability and rate capability.