The Investigation of Flexible Lithium-air Battery Cathode Preparation and Device Integration

Author:Yang Xiao Yang

Supervisor:zuo jun min


Degree Year:2019





In the background of highly informational modern society,various kinds of flexible portable electronic devices are gradually appearing in our lives,and changing our modes of production and lifestyle.With the rapid development of science and technology,flexible electronic devices are becoming more and more intelligent,and power consumption is increasing,which presents higher challenges for the matching power supply system.Lithium-air(Li-air)battery has been considered as a promising power supply system for flexible electronic devices due to their high theoretical energy density.However,the developments of Li-air battery are still in its infancy.Moreover,there are few researches on flexible Li-air battery.The lack of high performance flexible cathode materials and backward battery configuration design has greatly hindered the development of Li-air battery flexibility.Based on the above problems,this paper mainly focuses on the preparation of flexible cathode materials for high performance Li-air batteries and the design of flexible Li-air battery device structure.1.Nitrogen-doped carbon nanotubes were grown on stainless steel mesh substrates(N-CNTs@SS)via one-step in situ CVD strategy as an integrated self-standing flexible Li-air battery cathode material.Melamine was used as a solid carbon source and nitrogen source instead of flammable gas,which held the advantages of simple operation and high safety.Thanks to the successful imitation of the highly diffusive structure of capillary tissue,the bionic flexible electrode possesses a large number of multi-level channels and three-dimensional(3D)penetrating space structure,as well as high conductivity,super mechanical stability and structural stability,superhydrophobic characteristics.The electrode exhibits excellent electrochemical properties in Li-air batteries,including a high specific capacity up to 9299 mAh g-1 and long cycle life over 200 cycles.We use N-CNTs@SS as cathode material,by introducing gel electrolyte and ionic liquid electrolyte,we design and assemble a one dimensional(1D)flexible Li-air battery successfully.The flexible Li-air battery with excellent flexibility can operate stably in humid air for a quite long time,which can meet the demand of flexible devices for flexible deformation operation in air.2.Carbon materials are unstable and can decompose during the charging process of Li-air battery,which will cause irreversible side reaction,thus leading to the battery performance decay.In order to overcome this problem,a high-performance flexible cathode for Li-air battery has been prepared via a hydrothermal and electrodeposition process.Firstly,TiO2 nanowire arrays with high-stability were grown on the surface of carbon cloth in situ as a framework,and then a nanolayer of RuO2 with efficient catalytic activity was coated on the surface of TiO2 nanowires uniformly as the cathode materials for Li-air battery.By optimizing the surface properties of the electrodes,RuO2 nanolayers with metal conductivity can not only improve the electronic conductivity of the electrodes,but also increase the active sites on the surface of the electrodes,and change the growth mode of the discharge products.The Li-air battery assembled with this electrode shows excellent electrochemical performance,including high specific capacity,low charge-discharge overpotential,high rate performance and long cycle stability.In addition,using the electrode as a flexible cathode,we successfully assembled two-dimensional(2D)planar flexible Li-air battery by strengthening the anode structure,preparing a special flexible gas diffuse layer for Li-air battery,innovating packaging methods and optimizing the battery structure.3.Although the use of precious metals can reduce the charge-discharge overpotential of Li-air battery to a certain extent,the high price still limits their large-scale application,and the reduction of the charge-discharge overpotential by improving the catalytic activity is also limited.Based on the above,we prepared TiO2/TiN composite bifunctional flexible Li-air battery cathode materials with photoelectric catalytic activity by melamine-assisted nitridation at relatively low temperature.The excellent electrocatalytic activity of TiN and the unique 3D array porous structure of the cathode lead to excellent battery performance.The discharge capacity of the as-prepared cathode is close to 10 000 mAh g-1.At the same time,using the photogenerated hole effect of TiO2 semiconductor,we introduced solar energy into the charging process of Li-air battery.By using the valence band oxidation ability generated by photogenerated hole effect to assist Li2O2 decomposition during charging process,the charge overpotential of the Li-air battery was reduced to-0.02 V,and the charge-discharge overpotential was only 0.19 V.As a proof-of-concept experiment,we assembled a flexible Li-air battery with the cathode and integrated them integrated with a flexible solar cell to design a flexible self-powered energy system that with energy conversion,storage and release functions,which greatly broaden the application scenario of flexible Li-air battery.More importantly,by exploring the decomposition process of the discharge products in Li-air battery,we have proved the feasibility of solar-assisted charging and solar battery-driven charging process in Li-air battery with the dual-function electrode.