Lithium-O₂ battery as a novel energy conversion and storage device has attracted increasing attention ^[1]. However, it’s still facing great challenges for practical applications, including of large over potentials, poor cycling life ^[2]. Many reports have shown that a suitable cathode catalyst may could solve these problems ^[3]. Herein, metal sulfide (NiCo₂S₄) nanotube arrays on carbon paper were synthesized through a two-step hydrothermal method and then applied as a freestanding, binder-free cathode for lithium-O₂ batteries directly. This novel air electrode could deliver a high initial discharge capacity of 12348.5 mAh g^-1 with coulomb efficiency of 88.9% (Fig. 1a). Specifically, the discharge/charge over-potentials gap has been reduced to 0.73V, which is much lower than that of the counterpart metal oxide catalyst (NiCo₂O₄ NWs, 1.24 V)(Fig. 1b). Furthermore, this NiCo₂S₄ NTs@CFPs air electrode shows excellent long cycling life (485 cycles). This novel air electrode also exhibited great stability and reversibility. Interestingly, the discharge product of the air electrode with NiCo₂S₄ NTs is film-like amorphous Li₂O₂, which owns higher charge-transport properties and could be decomposed at a much lower potential than the common crystalline Li₂O₂. The excellent cell performances could be ascribed to the intrinsic properties of NiCo₂S₄, including high electrical conductivity and redox activity, the special hollow nanotubes structure, which could provide larger specific surface area and more active sites as well as enough space to accommodate the discharge products. The numerous pores distributed on the nanotube wall could also facilitate the transport of oxygen and electrolyte during the cell operation. This novel freestanding, binder-free air electrode sheds light on the application of metal sulfides not only on Lithium-air batteries, but also other metal-air batteries and fuel cells.

This work was supported by National Natural Science Foundation of China (21673153, 21303114，51272167 and 51572181 ), National Key Research and Development Program of China (2016YFB0100200), Natural Science Foundation of the Higher Education Institutions of Jiangsu Province, China (15KJB480001) and Natural Science Foundation of Jiangsu Province, China (BK20161207).

 

References:

 1. Bruce P.G., Freunberger S.A., Hardwick L.J., Tarascon J.M. (2012). Li-O₂ and Li-S batteries with high energy storage. Nat. Mater., 11, 19-29.

2. Li F.J., Zhang T., Zhou H.S. (2013). Challenges of non-aqueous Li-O₂ batteries: electrolytes, catalysts, and anodes. Energy Environ. Sci., 6, 1125-1141.

3. Shao Y.Y., Park S., Xiao J., Zhang J.-G., Wang Y., Liu J. (2012). Electrocatalysts for nonaqueous lithium-air batteries: status, challenges, and perspective. ACS Catal., 2, 844-857.