| Lithium-air batteries have been considered as the next-generation power source and storage equipment for the high theoretical specific capacity of 3505 m A h g-1.As known,the discharge product is insulating solid phase,which will retard the electrochemical reaction and further lead to the high charge voltage.As proposed,the preparation of high-performance electrocatalysts,utilization of photo energy and design of novel air battery schemes have been recognized as one of the important ways to achieve the low charge voltage,long cycling stability and high energy efficiency.The main research contents are as follows:1.To achieve the high-performance cathode material with large specific surface area,the CO-MOF/carbon cloth composites were obtained by simple liquid deposition method at room temperature and converted into Co3O4 nanosheets after heat treatment.The growing nanosheets were supported on the surface of the carbon cloth,and the morphology maintained good integrity and consistency during the heat treatment.The self-supported sample possess the cross-linked nanosheets,abundant inner pore structure and large open area,which will facilitate the electron transport,electrolyte infiltration,O2diffusion and discharge products storage.The Co3O4/CT samples,worked as oxygen cathode,possess a larger discharge capacity,higher coulomb efficiency and lower charge/discharge polarization,comparing with CONS powder sample.In addition,using the flexible carbon cloth as current collector,Co3O4/CT sample as positive electrode was assembled into a soft package.The battery can maintain the stability of working voltage under various working conditions,indicating the potential application in flexible devices.2.In order to avoid the volatility and small electrochemical window of organic electrolyte,solid-state electrolyte Li1-xAlxGe2-x（PO4）3（LAGP）was synthesized for alternate,where the conductivity of lithium ion is as high as 4.5×10-4 S cm-1.Combined with MOF-converted nickel cobaltite（Ni Co2O4）,the solid-state lithium-oxygen battery was assembled.The Ni elecment effitively enhanced the electron transport and provided more active sites for electrochemical reaction.With the Ni Co2O4/CT as cathode,the discharge capacity reaches 5534 m A h g-1 at 100 m A g-1 and the coulomb efficiency was as high as96%.Besides,considering that kinetics of solid-liquid reactions is superior to those of solid-solid reactions,the hybrid lithium-oxygen battery was assembled,where the solid discharge product lithium peroxide is changed to lithium hydroxide.Combining with Ni Co2O4 as oxygen cathode,the aqueous battery has a low charge voltage and works for 500 hours.3.Considering that the oxidation kinetics of the charge process is relatively slow,we figure out an ideal to utilize the photo generated hole to oxidize Li2O2 and design the photo-assisted lithium-oxygen battery.To be specific,the discharge process is conducted in the dark and the charge process is in the light illumination.During that,light is applied to the surface of Ti O2,resulting in large amounts of photo-generated electrons and holes on the Ti O2,where the holes can oxidize solid Li2O2.The photogenerated electrons pass through an external circuit and reach the side of the metal lithium electrode under the action of an applied voltage.The lithium ions in the electrolyte are reduced to form a circuit of the battery.By hydrothermal method,the Ti O2 nanorods are grown on the surface of carbon cloth.Under the light condition,the charging potential decreased to 2.86 V,compared with the dark state of 4.31 V.The charge/discharge polarization of the battery was only 0.21 V,and the energy efficiency is as high as 92.7%.In addition,during the test,the photocorrosion of Ti O2 creates many defects which becomes the catalytic active site and promotes the ORR performance during the discharge process.4.In consideration of the electrochemical stability and volatility of organic electrolyte during light illumination,a photo-assisted lithium-oxygen battery was designed in aqueous electrolyte withα-Fe2O3nanorods which possess good visible light absorption performance.It is noted that the photoelectrochemical water oxidation research is successfully integrated into energy storage area with the same electrochemical reaction mechanism.The test results showed that the charging potential is greatly decreased under illumination,and the energy efficiency increased to 81.3%.By photodeposition of Ni OOH,the charging potential of the battery was further reduced to 3.03 V.As a result,the universal strategies for improving the electrochemical property for photo-electrode also have a positive effect on the batteries’performance.5.As the component of the air,we realize the circulation of the aqueous lithium-carbon dioxide battery to investigate the influence of carbon dioxide on the charge/discharge process in the lithium air battery.We regulated the discharge products from the traditional C and lithium carbonate to the soluble HCOOH,where the kinetics of solid-liquid reactions is superior to those of solid-solid reactions.The porous Pd cathode is prepared by electrodeposition method using the triblock copolymer P123 as soft template.As a bifunctional catalyst for formic acid oxidation and carbon dioxide reduction,the electrochemical active area of the porous Pd cathode is up to 37.4 m2 g-1.The electrochemical test shows that the oxidation current of formic acid reached 10 m A cm-2 at 0.44 V（vs.RHE）,which can maintain the stability for a long time.At the same time,the catalyst has excellent CO2 reduction performance in0.1 M Li Cl solution.At the potential of-0.33 V（vs.RHE）,the reduction product was mainly detected to be formic acid and the current reached 16.4 m A cm-2,with the high Faraday efficiency of 85%.At the current density of 0.2 m A cm-2,the charging platform potential maintained at 2.87 V for more than10 hours and the energy efficiency as high as 91%.Its charge potential is lower than that of all reported lithium-carbon dioxide batteries. |
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