期刊
NANO LETTERS
卷 16, 期 5, 页码 3292-3300出版社
AMER CHEMICAL SOC
DOI: 10.1021/acs.nanolett.6b00870
关键词
Carbon nanotubes; covalent organic framework; lithium polysulfides; lithium-sulfur batteries; micro/mesoporous hierarchical structure; net on net
类别
资金
- Basic Science Research Program through the National Research Foundation of Korea (NRF) - Ministry of Science, ICT, and future Planning [2015R1A2A1A01003474, 2015R1D1A1A01057004]
- [NRF-2014R1ASA1009799]
- National Research Foundation of Korea [2015R1D1A1A01057004] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)
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 Li2Sx. 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.
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