Visible Light Photocatalysis Assisted Preparation And Performance Of Cathode Materials For Lithium-air Batteries

Lithium-air batteries have received widespread attention due to their ultra-high theoretical energy density,but in practical applications,problems such as large polarization and poor cycle performance have restricted its development.The introduction of catalyst is an effective means of improvement.Common catalysts have their own advantages and disadvantages.Among them,the transition metal oxide is cheap and stable in structure,which is a good choice,but its catalytic ability is limited.Therefore,this paper introduces the concept of photocatalysis assistance,hoping to use photoelectric double catalysis to speed up the electrode reaction rate and improve battery performance.Ti O2 as a semiconductor material has a stable structure,simple preparation,and low price.It also has photocatalytic and electrocatalytic capabilities,and has applications in lithium-air batteries,photovoltaic devices,and other fields.However,Ti O2 has a wider band gap?3.2 e V?and can only absorb 5% of the ultraviolet light in sunlight,which means that its light utilization rate is low.In response to this problem,combined with photocatalytic auxiliary lithium-air battery,this paper proposes two solutions: Replace Ti O2 with lanthanum cobalt-based perovskite with narrower forbidden band width and photoelectric catalytic ability;The up-conversion luminescent material is compounded with Ti O2 to increase the intensity of ultraviolet light and enhance photocatalysis to promote the performance of the battery.In the first part of the paper,LaCoO₃ and La0.7Sr0.3CoO₃ perovskite materials were prepared by citric acid hydrothermal method and heat treatment.The carrier concentration after doping was increased by three times.Assembled the battery,with a voltage limit of 2 V in the absence of light,and a discharge test at a current density of 0.1 A g-1.Their specific capacities were 17929.9 m Ah g-1 and 19433.1 m Ah g-1,respectively.The capacity was significantly improved after doping.When the light source is introduced during the charging and discharging process,the charging and discharging voltage gap will be significantly reduced,and the material changes after doping are more significant.At a limited capacity of 1000 m Ah g-1 and a current density of 1 A g-1,the cycle stability of the battery was tested under light.Both of them cycled for more than 100 cycles,demonstrating good cycle ability.During the charging and discharging process,gas chromatography was used to determine the oxygen content in the exhaust gas of the battery.Compared with when there is no light,the discharge process consumes more oxygen,and the release process releases more oxygen during the light.Explained that the light accelerated the ORR and OER response of the battery.The second part of the work is to first prepare the up-conversion luminescent materials NaYF₄:Yb3+,Er3+ by hydrothermal method,mechanically mix it with commercial Ti O2 as a positive electrode catalyst for lithium air batteries,and use commercial Ti O2 as a blank group.Through electrochemical tests,we found that NaYF₄:Yb3+,Er3+ have no significant effect on battery performance.In the charge and discharge test of NaYF₄:Yb3+,Er3+/ Ti O2 batteries with a current density of 1A g-1,the discharge voltage increased by 0.071 V and the charge voltage decreased by 0.239 V,which was almost the same as the Ti O2 battery.The analysis may be due to the energy loss caused by the cross-relaxation of luminescent nanoparticles.Then we use NaYF₄:Yb3+,Er3+ particles as the core,and use a solvothermal method to coat a Ti O2 shell layer on the surface to make NaYF₄:Yb3+,Er3+ @ Ti O2 core-shell structure.Assembled the battery for characterization,and found that the battery performance has not been significantly improved.The reason for the analysis may be the problem of the up-converting luminescent material itself.Finally,it is concluded that Er3+,as an activator,cannot convert infrared light to ultraviolet light,so it is almost useless for battery performance.