The aprotic Li-O2 battery has attracted a great deal of interest because, theoretically, it can store far more energy than today's batteries. Toward unlocking the energy capabilities of this neotype energy storage system, noble metal-catalyzed high surface area carbon materials have been widely used as the O2 cathodes, and some of them exhibit excellent electrochemical performances in terms of round-trip efficiency and cycle life. However, whether these outstanding electrochemical performances are backed by the reversible formation/decomposition of Li2O2, i.e., the desired Li-O2 electrochemistry, remains unclear due to a lack of quantitative assays for the Li-O2 cells. Here, noble metal (Ru and Pd)-catalyzed carbon nanotube (CNT) fabrics, prepared by magnetron sputtering, have been used as the O2 cathode in aprotic Li-O2 batteries. The catalyzed Li-O2 cells exhibited considerably high round-trip efficiency and prolonged cycle life, which could match or even surpass some of the best literature results. However, a combined analysis using differential electrochemical mass spectrometry and Fourier transform infrared spectroscopy, revealed that these catalyzed Li-O2 cells (particularly those based on Pd-CNT cathodes) did not work according to the desired Li-O2 electrochemistry. Instead the presence of noble metal catalysts impaired the cells' reversibility, as evidenced by the decreased O2 recovery efficiency (the ratio of the amount of O2 evolved during recharge/that consumed in the preceding discharge) coupled with increased CO2 evolution during charging. The results reported here provide new insights into the O2 electrochemistry in the aprotic Li-O2 batteries containing noble metal catalysts and exemplified the importance of the quantitative assays for the Li-O2 reactions in the course of pursuing truly rechargeable Li-O2 batteries.
Multiporous MnCo2O4 microspheres are fabricated via the solvothermal method followed by pyrolysis of carbonate precursor to demonstrate excellent bifunctional catalytic activity toward both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Because of this multiporous structure, the resulting MnCo2O4 microspheres show an efficient electrocatalytic performance in LiTFSI/TEGDME electrolyte-based Li–O2 batteries. MnCo2O4 microspheres as the air cathode deliver better performance during the discharging and charging processes and good cycle stability compared with that of the Super P. This preliminary result manifests that multiporous MnCo2O4 microspheres are promising cathode catalysts for nonaqueous Li–O2 batteries.
The addition of HO, even trace amount, in aprotic Li-O batteries has a remarkable impact on achieving high capacity by triggering solution mechanism, and even reducing charge overpotential. However, the critical role of HO in promoting solution mechanism still lacks persuasive spectroscopic evidence, moreover, the origin of low polarization remains incompletely understood. Herein, by in situ spectroscopic identification of reaction intermediates, we directly verify that HO additive is able to alter oxygen reduction reaction (ORR) pathway subjected to solution-mediated growth mechanism of LiO. In addition, ingress of HO also induces to form partial LiOH, resulting in reduced charging polarization due to its higher conductivity; however, LiOH could not contribute to O evolution upon recharge. These original results unveil the complex effects of HO on cycling the aprotic Li-O batteries, which are instructive for the mechanism study of aprotic Li-O batteries with protic additives or soluble catalysts.
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