基于氟化金属-有机框架材料的功能化隔膜设计及其在锂金属电池中的应用

Design of Functionalized Separators Based on Fluorinated Metal-Organic Framework and Their Application in Lithium Metal Batteries

摘要:

开发高能量密度的锂电池是满足先进储能系统需求日益增长的关键。锂金属电池因理论比容量高而备受关注，但不均匀的锂离子通量和锂枝晶等问题限制了其进一步应用。因此，采用氟化金属-有机框架材料（Metal-organic frameworks，MOFs）修饰聚丙烯（Polypropylene，PP）隔膜的新策略来克服上述挑战。通过合成氟化金属-有机框架材料，并将其涂覆在PP隔膜表面，成功制备出基于氟化金属-有机框架材料的功能化隔膜（MOF-4F@PP）。MOF-4F的电负性纳米孔道和均一多孔结构可限制溶液中阴离子的移动，并加速锂离子的传输。实验结果表明，相比于未改性的PP隔膜，MOF-4F@PP隔膜具有优异的电解液润湿性、高的离子电导率（0.96 mS·cm^-1）和锂离子迁移数（0.62）。所以，MOF-4F@PP隔膜能实现更均匀的锂离子通量，形成更稳定的界面层，有效抑制锂枝晶的生长。电化学性能研究进一步表明，使用MOF-4F@PP隔膜组装的Li//Cu和Li//Li电池的循环寿命显著提升，实现了超过1 000 h的循环。MOF-4F@PP隔膜在锂沉积/剥离过程中展现出优异的稳定性，为锂金属电池的长期运行提供了可靠的保障。此外，采用MOF-4F@PP隔膜组装的Li//LiFePO₄电池也呈现出优异的倍率和循环性能，在1 C下经过200次循环后放电容量仍高达125 mAh·g^-1。结果表明，氟化金属-有机框架材料的功能化隔膜对调控离子的传输起到了至关重要的作用，为提升锂金属电池性能提供了新的途径和可能性。

Abstract:

The development of high-energy density lithium secondary batteries is key to meeting the increasing demand for advanced energy storage systems. Lithium metal batteries have attracted attention due to their high theoretical specific capacity， but issues such as uneven lithium ion flux and lithium dendrite formation have limited their further application. Herein， we report a new strategy of modifying polypropylene （PP） separator with fluorinated metal-organic framework （MOF） to overcome these challenges. By synthesizing fluorinated MOF and coating them on the surface of the PP separator， we successfully prepared a functionalized separator based on fluorinated MOF （MOF-4F@PP）. The electronegative nanochannels and uniform porous structure in MOF-4F restrict the movement of anions and accelerate the transport of Li⁺. Experimental results show that compared to the unmodified PP separator， the MOF-4F@PP separator exhibits excellent electrolyte wettability， high ionic conductivity （0.96 mS cm^-1）， and Li⁺ transference number （0.62）. Therefore， the MOF-4F@PP separator can achieve a more uniform lithium ion flux， form a more stable interface layer， and effectively suppress the growth of lithium dendrites. Further studies indicate that the use of the MOF-4F@PP separator significantly improves the cycle life of Li//Cu and Li//Li batteries， achieving over 1 000 h of cycling. The MOF-4F@PP separator demonstrates excellent stability during lithium deposition/stripping processes， providing reliable protection for the long-term operation of lithium metal batteries. Additionally， Li//LiFePO₄ batteries assembled with the MOF-4F@PP separator exhibit outstanding rate capability and cycling performance， with a discharge capacity of 125 mAh·g^-1 after 200 cycles at 1 C rate. These results suggest that fluorinated metal-organic frameworks play a crucial role in regulating ion transport， offering new pathways and possibilities for enhancing the performance of lithium metal batteries.