COF-Net on CNT-Net as a Molecularly Designed, Hierarchical Porous Chemical Trap for Polysulfides in Lithium-Sulfur Batteries.
The hierarchical porous structure has garnered considerable attention as a multiscale engineering strategy to bring unforeseen synergistic effects in a vast variety of functional materials. Here, we demonstrate a "microporous covalent organic framework (COF) net on mesoporous carbon nanotube (CNT) net" hybrid architecture as a new class of molecularly designed, hierarchical porous chemical trap for lithium polysulfides (Li2Sx) in Li-S batteries. As a proof of concept for the hybrid architecture, self-standing COF-net on CNT-net interlayers (called "NN interlayers") are fabricated through CNT-templated in situ COF synthesis and then inserted between sulfur cathodes and separators. Two COFs with different micropore sizes (COF-1 (0.7 nm) and COF-5 (2.7 nm)) are chosen as model systems. The effects of the pore size and (boron-mediated) chemical affinity of microporous COF nets on Li2Sx adsorption phenomena are theoretically investigated through density functional theory calculations. Benefiting from the chemical/structural uniqueness, the NN interlayers effectively capture Li2Sx without impairing their ion/electron conduction. Notably, the COF-1 NN interlayer, driven by the well-designed microporous structure, allows for the selective deposition/dissolution (i.e., facile solid-liquid conversion) of electrically inert Li2S. As a consequence, the COF-1 NN interlayer provides a significant improvement in the electrochemical performance of Li-S cells (capacity retention after 300 cycles (at charge/discharge rate = 2.0 C/2.0 C) = 84% versus 15% for a control cell with no interlayer) that lies far beyond those accessible with conventional Li-S technologies.
JongTae
J
Yoo
Sung-Ju
SJ
Cho
Gwan Yeong
GY
Jung
Su Hwan
SH
Kim
Keun-Ho
KH
Choi
Jeong-Hoon
JH
Kim
Korea Packaging Center, Korea Institute of Industrial Technology , Ojeong-gu, Bucheon 14449, Korea.
Chang Kee
CK
Lee
Center for Multidimensional Carbon Materials, Institute for Basic Science (IBS) , Ulsan 44919, Korea.
Sang Kyu
SK
Kwak
Sang-Young
SY
Lee
Carbon nanotubes; covalent organic framework; lithium polysulfides; lithium−sulfur batteries; micro/mesoporous hierarchical structure; net on net