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

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 & nbsp;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 LiFePO4/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.

隔膜对于保障锂电池的安全性以及提升其电化学性能起着关键作用。然而，商业聚烯烃隔膜较差的热稳定性和非极性表面严重限制了高性能锂电池的发展。本文提出了一种“亲水和交联”策略来改性和增强多孔阻燃聚芳醚腈（PEN）聚合物膜，以获得高安全性和耐热的锂电池。所得的PEN@PDA - PEI复合隔膜呈现三维多孔结构，具有优异的热稳定性（在200°C时无收缩）。此外，复合膜中丰富的极性基团（氰基、氨基、羟基等）使其具有超强的电解液亲和性（接触角为0）以及大幅提高的电解液吸收量（从400%提高到618%）。值得注意的是，在PEN膜表面引入PDA - PEI交联结构显著提高了PEN多孔膜的机械性能。该复合膜具有良好的锂金属界面相容性和高离子电导率（1.5 mS/cm）。正如预期的那样，基于PEN@PDA - PEI隔膜的LiFePO₄/Li电池在高温下比商业聚烯烃隔膜表现出更好的倍率性能和循环性能。重要的是，复合隔膜的表面高极性和均匀的孔结构在循环过程中阻止了锂枝晶的生长，使得锂金属负极呈现出有趣的三维球形形态。这项工作为制备高性能和高安全性的锂离子电池隔膜提供了一种新策略，也为增强各种多孔膜的机械强度提供了一种简便的表面交联策略。