The molecular sieving mechanism of a polysulfide-blocking metal-organic framework separator for lithium-sulfur batteries
The molecular sieving mechanism of a polysulfide-blocking metal-organic framework separator for lithium-sulfur batteries
复制标题
DOI：
10.1039/d1ta04943g
复制
发表时间：
2021-10-07
影响因子：
11.9
通讯作者：
Jung, Sung Chul
中科院分区：
文献类型：
--
作者：
Jeon, Taegon;Jung, Sung Chul
锂硫电池的穿梭效应是制约锂硫电池实用化的关键问题，开发功能性隔膜是抑制锂硫电池穿梭效应的有效途径。金属有机骨架（MOF）已被用作分离器，用于筛出LPS，同时允许Li+离子通过。该研究首次通过检查Li+离子和被1，2-二甲基乙烷（DME）分子溶剂化的LPS渗透到Cu-3（BTC）（2）（BTC =苯-1，3，5-三羧酸酯）MOF纳米片中来阐明MOF在原子水平上的筛分过程。溶剂化的LPS，即，Li 2Sx（DME）（4）（x = 8、6和4）太大而不能进入MOF的孔。部分去溶剂化的LPS，即，Li 2Sx（DME）（2）可以进入孔，但由于1.73-1.99 eV的高渗透势垒而被捕获在孔壁中。然而，部分去溶剂化的Li+离子，即，Li+（DME）（2）可以通过克服0.66eV的低得多的渗透势垒而穿过MOF层，而不会被捕获在孔壁中。此外，Li+（DME）（2）可以在MOF层内快速移动，具有0.32 eV的非常低的扩散势垒。MOF的LPS-阻断能力源于（1）由于孔径不大于LPS的尺寸，LPS和孔壁之间的空间排斥和（2）由于LPS的溶剂化结构不完全被溶剂包围，LPS和孔壁之间形成化学键。本研究中提出的MOF的筛分机理不仅有助于设计用于Li-S电池的有效微孔隔膜，而且有助于理解一般微孔材料的传输。
Development of functional separators that block the migration of lithium polysulfides (LPSs) is an efficient way to suppress the shuttle effect, a critical issue restricting the practical applications of lithium-sulfur (Li-S) batteries. A metal-organic framework (MOF) has been used as a separator for sieving out the LPSs while allowing the Li+ ions to pass through. This study is the first to elucidate the sieving process of the MOF at the atomic level by examining the penetration of Li+ ions and LPSs solvated by 1,2-dimethylethane (DME) molecules into the Cu-3(BTC)(2) (BTC = benzene-1,3,5-tricarboxylate) MOF nanosheet. The solvated LPSs, i.e., Li2Sx(DME)(4) (x = 8, 6, and 4), are too large to enter the pores of the MOF. The partially desolvated LPSs, i.e., Li2Sx(DME)(2), can enter the pores but get trapped in the pore walls due to the high penetration barriers of 1.73-1.99 eV. However, the partially desolvated Li+ ions, i.e., Li+(DME)(2), can pass through the MOF layer by overcoming a much lower penetration barrier of 0.66 eV without getting trapped in the pore walls. Moreover, Li+(DME)(2) can move rapidly within the MOF layer with a very low diffusion barrier of 0.32 eV. The LPS-blocking ability of the MOF results from (1) the steric repulsion between the LPSs and the pore wall due to the pore size not being larger than the size of the LPSs and (2) the formation of chemical bonds between the LPSs and the pore wall due to the solvation structure of the LPSs incompletely surrounded by solvents. The sieving mechanism of the MOF presented in this study will be helpful not only for designing efficient microporous separators for Li-S batteries but also for understanding the transport across general microporous materials.