Despite the extraordinary gravimetric energy densities, Li-O₂ batteries are still facing a technological challenge;[1] limited round trip efficiency leading to insufficient cycle life. Recently, carbonaceous electrode materials were found to be one of the primary origins of the limited cycle life,[2] as they produce irreversible side products during discharge. A few investigations based on noncarbonaceous materials have demonstrated largely suppressed accumulation of irreversible side products,[3] but such studies have focused mainly on the materials themselves rather than delicate morphology control. As such, here, we report the synthesis of mesoporous titanium nitride (m-TiN) with a 2D hexagonal structure and large pores (>30 nm), which was templated by a block copolymer with tunable chain lengths, and introduce it as a stable air-cathode backbone. Due to the well-aligned pore structure and decent electric conductivity of TiN, the battery reaction was quite reversible, resulting in robust cycling performance for over 100 cycles under a voltage cutoff condition. Furthermore, by protecting the Li metal with a poreless polyurethane separator[4] and engaging a lithium iodide redox mediator[3], the original capacity was retained for 280 cycles under a consistent capacity condition (430 mAh/g). This study reveals that when the appropriate structure and material choice of the air-cathode are coupled with an advanced separator and an effective solution-phase redox mediator, the cycle lives of Li-O₂ batteries can be enhanced dramatically.

References:

[1] J. W. Choi, D. Aurbach, Nat. Rev. Mater. 1 (2016) 16013.

[2] M.M. Ottakam Thotiyl, S.A. Freunberger, Z. Peng, P.G. Bruce, J. Am. Chem. Soc.135 (2013) 494−500.

[3] N. Feng, P. He, H. Zhou, Adv. Energy Mater. 6 (2016) 1502303.

[4] B.G. Kim, J. Kim, J. Min, Y. Lee, J.H. Choi, M.C. Jang, S.A. Freunberger, J.W. Choi, Adv. Funct. Mater. 26 (2016) 1747-1756.