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Abstract
The poor discharge and charge capacities, and the cycle performance of current Li–air batteries represent critical obstacles to their practical application. The fabrication of an integrated structural air electrode with stable parallel micropore channels and excellent electrocatalytic activity is an efficient strategy for solving these problems. Herein, a novel approach involving the synthesis of nitrogen-doped carbon nanotube (N-CNT) arrays on a carbon paper substrate with a conductive carbon-black layer for use as the air electrode is presented. This design achieves faster oxygen, lithium ion, and electron transfer, which allows higher oxygen reduction/evolution reaction activities. As a result, the N-CNT arrays (N/C = 1:20) deliver distinctly higher discharge and charge capacities, 2203 and 186 mAh g−1, than those of active carbons with capacities of 497 and 71 mAh g−1 at 0.05 mA cm−2, respectively. A theoretical analysis of the experimental results shows that the parallel micropore channels of the air electrode decrease oxygen diffusion resistance and lithium ion transfer resistance, enhancing the discharge and charge capacities and cycle performance of Li–air batteries. Additionally, the N-CNT arrays with a high pyridinic nitrogen content can decompose the lithium peroxide product and recover the electrode morphology, thereby further improving the discharge–charge performance of Li–air batteries.
Highlights
Metal–air batteries, such as Li–air batteries, have high theoretical energy and power densities, making them ideally suitable for novel electric vehicle and portable power applications [1,2,3]
The results indicated that the discharge and charge capacities of the Li–air battery with the active carbon were extremely low in the second cycle, whereas those of the nitrogen-doped carbon nanotube (N-carbon nanotube (CNT)) array battery remained relatively high until the fifth cycle
Controlled preparation of N-CNT arrays was performed on a carbon paper substrate with a conductive carbon-black layer via catalyst seed-impregnated chemical vapor deposition (CVD) technology, and showed strong electrochemical performance in Li–air battery applications
Summary
Metal–air batteries, such as Li–air batteries, have high theoretical energy and power densities, making them ideally suitable for novel electric vehicle and portable power applications [1,2,3]. Long-standing previous research has shown that the air electrode is the key component in terms of improving the performance of a Li–air battery, mainly because the oxygen electro-reduction/electro-oxidation processes occur at this component. Lithium ions, and electrons are simultaneously transferred in the air electrode, and resistance to the transfer of these components can severely hinder the oxygen reduction/evolution reaction (ORR/OER) kinetics [10,11,12]. Any residual solid lithium peroxide (Li2O2) product that accumulates in the pores of the air electrode observably restricts the intrinsic kinetics of the oxygen electro-reduction/electro-oxidation processes and the transfer dynamics of oxygen, and greatly increases the transfer resistance of lithium ions and electrons [13]. Improving the air electrode remains a significant challenge in the commercialization of Li–air batteries [14]
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