| Li-O2 batteries have become excellent candidates for a new generation of power energy because of their very high theoretical energy density.At present,the main problems of Li-O2 faced are:the discharging product Li2O2 has a poor conductivity make it easy to accumulate on the surface of the cathode material,resulting in a great electrochemical polarization,thus hindering the further discharge reaction;However,the decomposition of discharging product Li2O2 often requires a charge voltage higher than 4 V?vs Li/Li+,the same below?,resulting in low energy conversion efficiency and cycle life.Thus,researchers have been working over the past few years to reduce the charging potential of Li-O2 batteries in a variety of ways.In this paper,the semiconductor WO3,g-C3N4,CoWO4 with photocatalytic activity is introduced into the cathode material of Li-O2 battery,which constitutes a new type of photo-assisted Li-O2 battery.Using the photo-generated holes favor the decomposition of the Li2O2,meanwhile,the photo-generated electrons is transferred to the anode to reduce Li+to Li metal and the generated photovoltage is utilized to compensate the required charging voltage,thus reducing the charging potential of the lithium-oxygen battery.The main research contents are as follows:1?The precursor of WO3 nanowire array was prepared on the surface of carbon cloth by hydrothermal synthesis method,then,the precursor was heat treatment in three different ways.Photoelectrochemical measurements and a series of structural characterization of WO3 nanowires obtained under three different heat treatment conditions were carried out,and the results showed that the obtained WO3 nanowire array which obtained in the calcination process is performed at 450°C for2 h in air and then at 550°C for 2 h in N2 atmosphere shows typically monoclinic phase and its photoelectrochemical performance is the most excellent.The electrochemical properties of the cathode material used as a Li-O2 battery are tested,in which the charging process is carried out under visible illumination,the discharging process is carried out in the dark state,and the current density is 0.06 mA cm-2.The test shows that the charging potential under illumination can be reduced to 3.55 V and 100laps in a stable cycle compared to the charge potential 4.4 V in the dark state.2?Using NH4Cl as a gaseous template to heat dicyandiamide to obtain ultra-thin g-C3N4nanosheets,and load them onto the WO3 nanowires prepared in the first chapter by simple spraying method to construct WO3@g-C3N4 heterojunction structure.By testing the WO3@g-C3N4 of different g-C3N4 loads by photoelectrochemical performance test,the WO3@g-C3N4 exhibit the best performance when the g-C3N4 load is 0.6mg.The charge and discharge tests of WO3@g-C3N4 under different current densities were carried out.The test results show that compared with pure WO3,WO3@g-C3N4 has a large decrease in charge and discharge overpotential at high current density.The WO3@g-C3N4heterojunction at 0.6 mg g-C3N4 loading was used as the positive electrode material of the Li-O2 battery,and its electrochemical performance was tested at a current density of 0.1 mA cm-2,wherein the charging process was performed under light-assisted,the discharge is carried out in a dark state.After charging to 59 cycle numbers,its charging potential can still be maintained at 3.85 V.The photo-assisted charging potential of WO3@g-C3N4 is reduced by 0.35 V compared with the charging potential of 4.2 V in the full dark state;the charge-discharge over-potential is reduced by 0.5V compared with the performance of pure WO3 at the same current density.The overpotential at large current densities has been greatly improved.3?The NiCo2O4 nanowire array was successfully prepared on the surface of carbon cloth by hydrothermal synthesis,and then immersed in different concentrations of ammonium metatungstate precursor solution,and the CoNiO2@CoWO4 composites were obtained by further heat treatment after removal from the solution.The photoelectric properties of CoNiO2@CoWO4 composites were tested,and the results showed that the CoNiO2@CoWO4 composites showed excellent photochemical properties,in particular,the CoNiO2@CoWO4 obtained by soaking 0.0226 mol L-1 concentration showed the best photoelectrochemical properties.The CoNiO2@CoWO4 composite material was used as a cathode electrode material for a Li-O2 battery,in which charging was performed under light assistance,and discharge was performed in a dark state.The electrochemical potential was measured at a current density of 0.06 mA cm-2.The charge potential of the first lap was 3.73 V,and the discharge potential was 2.74 V.After 50 cycles,the charge potential was maintained at 3.77 V and the discharge potential was 2.82.V.Compared with NiCo2O4,its charge-discharge over-potential is reduced by 1 V,and the overall performance of the battery has been greatly improved. |
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