Mechanically robust, nonflammable and surface cross-linking composite membranes with high wettability for dendrite-proof and high-safety lithium-ion batteries

Abstract

The separator plays a pivotal role to guarantee the safety and improve the electrochemical properties of lithium batteries. However, poor thermal stability and nonpolar surface of commercial polyolefin separator seriously restricted the development of the high-performance lithium battery. A "hydrophilic and cross-linking" strategy is proposed here to modify and enhance porous flame retardant poly(arylene ether nitrile) (PEN) polymer membrane to obtain high safety and heat resistant lithium batteries. The resultant PEN@PDA-PEI composite separator exhibits three-dimensional porous structure, superior thermal stability (no shrinkage up to 200 °C). Furthermore, the abundant polar groups (cyano group, amino group, hydroxyl group, etc.) from the composite membrane endow it with super electrolyte affinity (the contact angle is 0°) and the highly enhanced electrolyte uptake (from 400% to 618%). It is worth noting that the introduction of the PDA-PEI cross-linked structure on the surface of PEN membranes significantly improves the mechanical properties of PEN porous membrane. The composite membrane presents good lithium metal interface compatibility and high ionic conductivity (1.5 mS cm −1 ). As expected, the LiFePO 4 /Li battery based on PEN@PDA-PEI separator displays better rate and cycle performance than that of commercial polyolefin separator at elevated temperature. Significantly, the surface high-polarity and uniform pore structure of composite separators prevent the growth of lithium dendrite in cycle term, resulting an interesting 3D spherical morphology on Li metal anode. This work provides a new strategy for the preparation of high-performance and high-safety lithium-ion battery separator, it also paves a facile surface crosslinking strategy reinforce the mechanical strength of various porous membranes. • PDA-PEI crosslinking structure is used to modify the flame retardant PEN membrane for Li metal batteries. • Crosslinking structure with abundant polar groups improves the electrolyte affinity and mechanical strength of PEN separator. • The PEN@PDA-PEI separator shows good thermal and shrinkage stability at 200 °C. • Li ion distribution can be well regulated due to the uniform pore structures and the polar groups on PEN@PDA-PEI. • Batteries with PEN@PDA-PEI separator maintains stable cycling performance at high temperature.