MCNTs@MnO<sub>2</sub> Nanocomposite Cathode Integrated with Soluble O<sub>2</sub>-Carrier Co-salen in Electrolyte for High-Performance Li-Air Batteries.
basic_science · Level V
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- Record sourced from PubMed, PMID 28135104.
- Also identified by DOI 10.1021/acs.nanolett.7b00203.
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Abstract
Li-air batteries (LABs) are promising because of their high energy density. However, LABs are troubled by large electrochemical polarization during discharge and charge, side reactions from both carbon cathode surface/peroxide product and electrolyte/superoxide intermediate, as well as the requirement for pure O<sub>2</sub>. Here we report the solution using multiwall carbon nanotubes (MCNTs)@MnO<sub>2</sub> nanocomposite cathode integrated with N,N'-bis(salicylidene)ethylenediaminocobalt(II) (Co<sup>II</sup>-salen) in electrolyte for LABs. The advantage of such a combination is that on one hand, the coating layer of δ-MnO<sub>2</sub> with about 2-3 nm on MCNTs@MnO<sub>2</sub> nanocomposite catalyzes Li<sub>2</sub>O<sub>2</sub> decomposition during charge and suppresses side reactions between product Li<sub>2</sub>O<sub>2</sub> and MCNT surface. On the other hand, Co<sup>II</sup>-salen works as a mobile O<sub>2</sub>-carrier and accelerates Li<sub>2</sub>O<sub>2</sub> formation through the reaciton of (Co<sup>III</sup>-salen)<sub>2</sub>-O<sub>2</sub><sup>2-</sup> + 2Li<sup>+</sup> + 2e<sup>-</sup> → 2Co<sup>II</sup>-salen + Li<sub>2</sub>O<sub>2</sub>. This reaction route overcomes the pure O<sub>2</sub> limitation and avoids the formation of aggressive superoxide intermediate (O<sub>2</sub><sup>-</sup> or LiO<sub>2</sub>), which easily attacks organic electrolyte. By using this double-catalyst system of Co-salen/MCNTs@MnO<sub>2</sub>, the lifetime of LABs is prolonged to 300 cycles at 500 mA g<sup>-1</sup> (0.15 mA cm<sup>-2</sup>) with fixed capacity of 1000 mAh g<sup>-1</sup> (0.30 mAh cm<sup>-2</sup>) in dry air (21% O<sub>2</sub>). Furthermore, we up-scale the capacity to 500 mAh (5.2 mAh cm<sup>-2</sup>) in pouch-type batteries (∼4 g, 325 Wh kg<sup>-1</sup>). This study should pave a new way for the design and construction of practical LABs.