中国科学院上海高等研究所徐庆研究小组取得进展。他们发现以致密亲锂位为保护层的三维共价有机框架实现高性能锂金属电池。2024年11月5日出版的《德国应用化学》发表了这项成果。

锂金属电池具有显著的能量密度，但由于锂枝晶的累积和循环过程中的死锂，电池寿命短，库仑效率低。

该研究组制备了一种新型三维（3D）共价有机骨架（COF）作为锂金属电池的阳极保护层，该骨架具有致密的亲锂位点（杂原子质量含量为32.32wt%）。研究者采用[6+4]合成策略，通过诱导柔性的6-连接环三磷腈衍生物醛和4-连接卟啉基四苯胺，合成了三维COF。

COF中的磷腈环和卟啉环作为富电子和亲锂位点，增强了它们在三维方向上的均匀Li⁺通量，从而实现了高度光滑和致密的Li沉积。在320次循环中，Li/Por-PN-COF-Cu电池的平均CE达到了创纪录的99.1%。同时，丰富的亲锂位促进了Li⁺的快速传递，Li⁺转移数为0.87，使LiFePO4电池在5℃的严酷速率下也能稳定的剥离/镀过程。

理论计算表明，Li⁺与COF之间的强相互作用力促进了Li⁺从电解质中溶解，1.08 eV的低迁移势垒表明Li⁺离子与π-电子体系之间的相互作用有利。

附：英文原文

Title: Three-dimensional Covalent Organic Framework with Dense Lithiophilic Sites as Protective Layer to Enable High-Performance Lithium Metal Battery

Author: Shuang Zheng, Yubin Fu, Shuai Bi, Xiubei Yang, Xiaoyu Xu, Xuewen Li, Qing Xu, Gaofeng Zeng

Issue&Volume: 2024-11-05

Abstract: Lithium (Li) metal batteries with remarkable energy densities are restrained by short lifetime and low Coulombic efficiency (CE), resulting from the accumulative Li dendrites and dead Li during cycling. Here, we prepared a new three-dimensional (3D) covalent organic framework (COF) with dense lithiophilic sites (heteoatom weight contents of 32.32wt%) as an anodic protective layer of Li metal batteries. The 3D COF was synthesized using a [6+4] synthesis strategy by inducing flexible 6-connected cyclotriphosphazene derivative aldehyde and 4-connected porphyrin-based tetraphenylamines. Both phosphazene and porphyrin rings in the COF served as electron-rich and lithiophilic sites, enhancing a homogeneous Li+ flux via 3D direction towards highly smooth and compact Li deposition. The Li/Por-PN-COF-Cu cells achieved a record average CE of 99.1% for 320 cycles with smooth Li deposition. Meanwhile, the abundant lithiophilic sites can promote fast Li+ transport with Li+ transference number of 0.87, enabling LiFePO4 full cell with stable stripping/plating processes even at a harsh rate of 5 C. Theoretical calculations revealed that the strong interaction force between Li+ and the COF facilitated the dissolution of Li+ from the electrolyte, and the low migration barrier of 1.08 eV indicated a favorable interaction between the Li+ ions and the π-electron system.

DOI: 10.1002/anie.202417973

Source: https://onlinelibrary.wiley.com/doi/10.1002/anie.202417973