Catalytic Oxygen Conversion And Cathode Materials For High Performance Li-O₂ Batteries

Lithium-oxygen batteries have received great attention in the past decade owing to its highest theoretical energy density among the ever-reported chemical batteries,however the sluggish kinetics and the involved unfavorable side reactions severely hinder the battery performance.In this regard,developing superior catalysts is the key to solving the aforementioned issue.Although various catalysts have been developed,the actual battery performance is still far away from being satisfactory.Moreover,it is still unclear on the relation between the adsorption of the superoxide species and the kinetics of the Li-O2 chemistry,especially on the understanding of modulation essence at the atomic levels,which is fundamentally interesting yet challenging.To this end,we have reasonably designed suitable catalysts and cathode structures to promote oxygen conversion reaction kinetics.At the same time,through various operando characteration methods and theoretical calculations,the interaction between the surface structure of the catalysts and the reaction intermediates is deeply analyzed to reveal the mechanism of the catalysts'catalytic oxygen conversion process.In addition,we also systematically studied the performance of typical transition metal carbides and transition metal sulfides when used as oxygen electrodes for lithium-oxygen batteries.The main research work of the paper is summarized as follows:1,probing the relation between the adsorption of the superoxide species and the kinetics of the Li-O2 chemistry is critical for the design of superior oxygen electrodes for Li-O2 battery,yet the understanding of the modulation essence especially at the atomic levels is still very limited.Herein,we reveal the adsorption behaviors of the superoxide species can be well regulated via the core-induced interfacial charge interaction,and find moderate adsorption strength can enable superior rate capability of Li-O2 battery.More importantly,the developed operando X-ray absorption near-edge structure(XANES),operando surface-enhanced Raman spectroscopy(SERS)and electron spin resonance(ESR)provide tools to in-situ monitor the evolution of the superoxide intermediates and the electronic states of the catalysts' metal sites during discharge and charge process,which can be correlated with the surface adsorption states.The concept to tune the adsorption behavior through interfacial charge engineering could open up new opportunities to further advance the development of Li-O2 battery and beyond.2,by introducing vacancies on the MoS2 basal plane and in-situ synthesized method,we demonstrated the excellent catalysis of MoS2-x for oxygen redox kinetics to improve the Li-O2 batteries performance.It is demonstrated that the sulfur defects could effectively increase the intrinsic conductivity and the number of active sites,substantially improving the oxygen conversation catalysis of pristine MoS2.The large number of porous structures in the carbon 3D framework not only serves as ion and gas transport channels,but also helps to increase the specific surface area to expose active sites,and provides enough space for accommodating solid discharge products to achieve a satisfactory battery specific capacity.To the best of the knowledge,the fabricated cathode materials have been regarded as one of the excellent oxygen conversion catalysts from 3D network design and surface modulation,offering an open vision for the designing Li-O2 catalysts and beyond.