MCNTs@MnO₂ Nanocomposite Cathode Integrated with Soluble O₂-Carrier Co-salen in Electrolyte for High-Performance Li–Air Batteries

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 O2. We here report the solution using multi-wall carbon nanotubes (MCNTs)@MnO2 nanocomposite cathode integrated with N,N'-bis(salicylidene)ethylenediaminocobalt(II) (Co II -salen) in electrolyte for LABs. The advantage of such a combination is that on one hand, the coating layer of δ-MnO2 with about 2-3 nm on MCNTs@MnO2 nanocomposite catalyzes Li2O2 decomposition during charge and suppresses side reactions between product Li2O2 and MCNT surface. On the other hand, Co II -salen works as a mobile O2-carrier and accelerates Li2O2 formation through the reaciton of (Co III -salen)2-O2 2-+ 2Li + + 2e -→ 2Co II -salen + Li2O2. This reaction route overcomes the pure O2 limitation and avoids the formation of aggressive superoxide intermediate (O2 -or LiO2), which easily attacks organic electrolyte. By using this double-2 catalyst system of Co-salen/MCNTs@MnO2, the lifetime of LABs is polonged to 300 cycles at 500 mA g -1 (0.15 mA cm -2 ) with fixed capacity of 1000 mAh g -1 (0.30 mAh cm -2 ) in dry air (21% O2). Furthermore, we up-scale the capacity to 500 mAh (5.2 mAh cm -2 ) in pouchtype batteries (~4 g, 325 Wh kg -1 ). This study should pave a new way for the design and construction of practical LABs.Lithium-air batteries (LABs) have recently attracted extensive academic and technological interest due to their high theoretical energy density of ~3600 Wh kg -1 based on the electrochemical reaction pathway of 2Li + + O2 + 2e − ↔ Li2O2. [1][2][3][4][5] However, LABs still suffer from three critical issues. The first one is insufficient catalytic activities towards Li2O2 formation/decomposition, leading to large electrochemical polarizition during discharge and charge. The second one is side reactions not only between nonaqueous electrolyte and superoxide intermediate but also between carbon cathode surface and product Li2O2, [6][7][8][9] resulting in short cycling life. The third one is slow diffusion and large concentration polarization of oxygen in electrolyte, giving rise to the requirement for high-purity O2. The cathode reactions include the formation of superoxide intermediate (LiO2 or O2 -) and Li2O2 product in discharge and the decomposition of Li2O2 in charge. [10][11][12][13][14] The superoxide intermediate easily decomposes the organic electrolyte; while, the insoluble Li2O2 product that is deposited on carbon cathode tends to oxidize the defects and oxygen-containing radicals on carbon cathode surface. The inexpensive method to increase catalytic activities towards Li2O2 formation/decomposition is worth developing. However, the report on costeffective methods to prevent carbon cathode surface from side reactions and avoid the formation of superoxide intermediate is still limited.During reversib...

3D Hollow α‐MnO2 Framework as an Efficient Electrocatalyst for Lithium–Oxygen Batteries

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