(198c) Hierarchical NiCo2O4 Nanosheets on Carbon Nanofiber Films for High Energy Density and Long-Life Li-O2 Batteries

Rechargeable lithium-oxygen (Li-O₂) batteries are unmatched candidates amongst future electrochemical energy storage devices for electric vehicles due to their high theoretical energy density of 3505 Wh kg^−1, which is about 10 times higher than that of conventional Li-ion batteries (360 Wh kg^−1).^{[1, 2]} Despite their superior theoretical storage capacity, constructing a cycling stable Li-O₂ battery cathode is still facing materials challenges.^{[3, 4]} This is traced to the sluggish kinetic of ORR/OER giving the large discharge/charge overpotentials and the random deposition of Li₂O₂ blocking the permeation path for oxygen and electrolyte, leading to low round-trip efficiency, poor rate capability, and short cycling performance.^{[5, 6]} Thus, it is highly demanded to design and develop a light weight cathode with high catalytic ORR/OER activities for realizing the high energy density of Li-O₂ batteries.

Herein, we propose a novel structure of hierarchical NiCo₂O₄ nanosheets on porous carbon nanofiber films (denoted as NiCo₂O₄@CNFs), for high energy density and long-life Li-O₂ batteries. The nanostructured cathode integrates several desirable design rationales for high-performance Li-O₂ batteries based on low-dimensional ultrathin nanosheets, lightweight conductive carbon networks, and a binder-free cathode. With the help of this rational design, the NiCo₂O₄@CNFs cathode exhibits excellent electrochemical performance including a high specific discharge capacity of 4179 mA h g^−1, excellent energy density of 2110 Wh kg^−1, and especially superior cycling stability retaining after 350 cycles. As these results, other metal-oxygen batteries, such as Zn-O₂ batteries, Al-O₂ batteries, and Na-O₂ batteries, can be also used to the rational design of the hierarchical catalyst constructed low-dimensional nanostructure and the lightweight porous carbon nanofiber electrode toward oxygen cathodes.

References

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[2] P. G. Bruce, S. A. Freunberger, L. J. Hardwick, J. M. Tarascon, Nat. Mater. 2012, 11, 19.

[3] N. Feng, P. He, H. Zhou, Adv. Energy Mater. 2016, 6, 201502303.

[4] Y. Li, X. Wang, S. Dong, X. Chen, G. Cui, Adv. Energy Mater. 2016, 6, 201600751.

[5] J. Wang, Y. Li, X. Sun, Nano Energy 2013, 2, 443.

[6] Z. Peng, S. A. Freunberger, Y. Chen, P. G. Bruce, Science 2012, 337, 563.