Ultrafast self-assembly of supramolecular hydrogels toward novel flame-retardant separator for safe lithium ion battery.

[Display omitted] • Low-cost melamine-boric acid (MBA) supramolecular hydrogels are self-assembled with a superfast speed in dozens of seconds under room temperature. • In-situ real-time observation of the nucleation and growth of MBA supramolecules is constructed by using polarizing microscope. • The boron nitride and bacterial cellulose (BN/BC) composite aerogel shows excellent flame-retardant performance, electrolyte-wetting ability and high mechanical property. • The BN/BC composite aerogel as the separator enable the derived lithium ion battery with excellent electrochemical property and high safty. Traditional polyolefin separators for lithium-ion batteries (LIBs) often experience limited thermal stability and intrinsic flammability, resulting in great safety risks during their usage. Therefore, it is highly important to develop novel flame-retardant separators for safe LIBs with high performance. In this work, we report a flame-retardant separator derived from boron nitride (BN) aerogel with a high BET surface area of 1127.3 m2 g−1. The aerogel was pyrolyzed from a melamine-boric acid (MBA) supramolecular hydrogel, which was self-assembled at an ultrafast speed. The in-situ evolution details of the nucleation-growth process of the supramolecules could be observed in real-time using a polarizing microscope under ambient conditions. The BN aerogel was further composited with bacterial cellulose (BC) to form a BN/BC composite aerogel with excellent flame-retardant performance, electrolyte-wetting ability and high mechanical property. By using the BN/BC composite aerogel as the separator, the developed LIBs exhibited high specific discharge capacity of 146.5 mAh g−1 and excellent cyclic performance, maintaining 500 cycles with a capacity degradation of only 0.012% per cycle. The high-performance flame-retardant BN/BC composite aerogel represents a promising candidate for separators not only in LIBs but also in other flexible electronics. [ABSTRACT FROM AUTHOR]