Preparation Of SnO₂ Nanostructured Cathode And Exploration Their Performance In Photo-assisted Lithium-oxygen Batteries

Due to the high theoretical energy density of 3,860 mAh g^-1,lithium-oxygen battery has great application prospects,and is very expected to become the next generation of new energy storage battery.In lithium-oxygen battery,the difficult solubility and low conductivity of lithium peroxide（Li₂O₂）cause a high charging voltage（>4.0 V）,serious battery polarization,bad battery performance,low energy conversion efficiency,and even lead to the premature battery failure.At present,the problem with Li₂O₂ decomposition has not been effectively solved.In view of the above problems,we prepare the gold nanoparticles composite tin dioxide（ASO）mesoporous nanotubes and Sn O₂ nanoparticle compositeα-Fe₂O₃ nanotubes（FS）as the anode in lithium-oxygen batteries,and successfully build an emerging photo-assisted lithium-oxygen battery by introducing light energy into lithium-oxygen battery.Under the visible light,the two structures reduce the composite efficiency of electrons and holes,thus facilitating carrier separation.During the discharged process,the photogenerated electrons promote oxygen（O₂）reduction reaction（ORR）and improve the discharge potential.And during charging process,the photogenerated holes promote the Li₂O₂ to decompose into O₂ and Li⁺,while the photoelectron reduces Li⁺into the metal lithium through the external circuit,therefore the charging potential of the battery is reduced.（1）SnO₂ mesoporous nanotubes（SO）were successfully prepared by template and calcination,and Au NPs was coupled to the surface of SO by self-assembly to obtain metal/semiconductor heterojunction structure named Au/SO（ASO）.Owing to the local surface plasmon resonance（LSPR）effect of Au and the tubular structure of SO,ASO electrodes have excellent UV-visible light absorption.At the current density of100 m A g^-1,the discharged platform can reach to 3.10 V,exceeding the thermodynamic equilibrium voltage of 2.96 V.Meanwhile,the discharge specific capacity of the battery is 10705.2 m Ah g^-1,2.36 times of ASO without illumination.During the charged process,the holes of ASO boost the decomposition of Li₂O₂,making the charged platform decrease to 3.59 V.Therefore,the overpotential is 0.59 V and the round-trip cycle efficiency can be reached to 86%.This work shows that enhancing the efficiency of the charge transfer dynamics can provide a new way for the decomposition of Li₂O₂.（2）The α-Fe₂O₃ nanotubes are prepared by the hydrothermal synthesis process,and then load SnO₂ nanoparticles on their surface to formα-Fe₂O₃/Sn O₂（FS）,an n-n type semiconductor heterojunction composite.Electrochemical tests demonstrate that FS has excellent carrier separation efficiency and photocatalytic activity under the visible light.The FS positive electrode has significant effects in improving the ORR and OER of lithium-oxygen batteries.At the current density of 0.01 m A cm^-2,the discharge platform of the battery is 3.27 V,the charging platform is 3.28 V,and the overpotential is 0.01 V with the energy efficiency of 99%.The battery achieves 252ultra-long cycles at the limit discharge voltage of 3.0 V with the current density of 0.01m A cm^-2,and its capacity efficiency can still reach to 80%after the circulation.At the same time,its rate performance,discharge specific capacity have been steadily improved.It is worth mentioning that the structure and stability of the FS can still be maintained after the super-long cycle,which fully shows that the designed structure of FS is conducive to transmitting ions and electrons.