Research On Preparation And Electrochemical Performances Of Bismuth Based Electrode Materials For Supercapacitors

With the excessive consumption of fossil fuels and the increasing deterioration of ecological environment,there are growing demands for the development of sustainable and efficient energy storage devices.Among various electrochemical storage technologies,supercapacitors have a wide application prospect due to their advantages of rapid charge/discharge rates,high power output and high cyclic stability.Therefore,it is very important for supercapacitors to develop highly efficient electrode materials with high specific capacitance and good rate capability.Bi-based compounds are expected to be applied in energy storage due to the characteristics of abundant voids,large dielectric constant,high ionic conductivity and environmental friendliness,etc.In this thesis,a series of Bi-based compounds and their composites have been prepared by simple chemical precipitation or solvothermal method.Furthermore,the corresponding composition,micromorphology and capacitive behavior have been characterized and tested.The main contents are as follows:?1?A series of Bi₁₀Co₁₆O₃₈?BCO?electrode materials have been synthesized by a facile chemical precipitation method at different water-bath temperatures.We have further probed the effects of water-bath temperature on morphology and electrochemical performance of BCO electrode materials.The results show that the reaction temperature affects the thickness and agglomeration of as-prepared BCO nanoplates.Compared with other agglomerated BCO nanoplates,BCO-3 nanoplates prepared at 50°C distribute uniformly and possess homogeneous thickness.Thereinto,BCO-3 based electrode possesses the highest specific capacity of 932.5 C g^-1 at 1.0 A g^-1.Additionally,the capacity retention of BCO-3 based electrode is 70.8%at 10.0 A g^-1,indicating excellent rate capability.As-prepared BCO-3 based electrode possesses the capacity retention of 83.4%at 7.0 A g^-1 even after 2000 cycles,suggesting favorable cyclic life.?2?A series of Bi₁₂NiO₁₉?BNO?materials have been prepared by a simple chemical precipitation method at different water-bath temperatures,and the optimal reaction temperature of 50°C has been selected through electrochemical tests.Subsequently,we have investigated the impact of additive amount of GO nanosheets on the morphology and capacitive behavior of BNO/GO based electrodes prepared at 50°C.The results indicate that GO nanosheets with large surface area can regulate the morphology of BNO materials and alleviate the agglomeration phenomenon to a certain extent.At 1.0 A g^-1,BNO/GO-2based electrode displays the maximum specific capacity of 925.4 C g^-1,which is higher than GO(93.4 C g^-1)and BNO-3(744.3 C g^-1)based electrodes.In addition,compared with single-component electrode,the addition of GO nanosheets can improve the rate capability and cyclic stability of BNO/GO-2 based electrode.?3?A series of Bi₂S₃ electrode materials have been synthesized by a solvothermal method at the same additive amount of CTAB,SDBS and PVP as surfactant,respectively.The electrochemical tests show that PVP as surfactant can greatly improve the electrochemical performance of Bi₂S₃-P electrode materials.Subsequently,we have discussed the influences of the additive amount of PVP on morphology and electrochemical performance of Bi₂S₃ electrode materials by physical characterizations and electrochemical measurements.The result of FE-SEM analysis shows that the morphology and size of Bi₂S₃ can be controlled by adjusting the additive amount of PVP.Thereinto,Bi₂S₃-3 materials prepared at 50.0 mg?4.00 wt%?PVP present micron-sized chrysanthemum structure assembled by nanowires.Additionally,Bi₂S₃ electrode materials prepared at different additive amount of PVP significantly exhibit different electrochemical properties.At 1.0 A g^-1,the specific capacity of Bi₂S₃-3 based electrode(up to 826.6 C g^-1)is higher than those of other Bi₂S₃based electrodes.As the current density increases to 15.0 A g^-1,the specific capacity of Bi₂S₃-3 based electrode remains 91.3%of initial value.At current density of 7.0 A g^-1,Bi₂S₃-3 based electrode possesses outstanding cyclic stability after 2000 cycles.?4?Sea urchin-like CuS/Bi₂S₃?CSBS?composites have been prepared via a simple solvothermal method through adjusting the molar ratio of CuS to Bi₂S₃.The result of FE-SEM analysis shows that,compared to Bi₂S₃ materials with disordered nanoplates and CuS materials with uneven microspheres,as-prepared CSBS-2 composite presents uniform sea urchin-like structure built by nanowires.The results of electrochemical tests show that the specific capacities of single-component CuS and Bi₂S₃ based electrodes are 168.8 C g^-1and 588.3 C g^-1 at current density of 1.0 A g^-1,respectively.With increasing molar ratio of CuS to Bi₂S₃,the specific capacity of CSBS based electrodes increases firstly and decreases later.When the molar ratio of CuS to Bi₂S₃ is 4:6,as-prepared CSBS-2 based electrode exhibits the highest specific capacity of 848.5 C g^-1.At 7.0 A g^-1,the capacity retention of CSBS-2 based electrode is 83.5%even after 2000 cycles,while those of as-prepared CuS and Bi₂S₃ based electrodes are 62.4%and 73.3%,respectively,indicating the improved cyclic stability of CSBC-2 based electrode.In this thesis,a series of Bi-based compounds and their composites have been synthesized through simple preparation process.The electrochemical tests show that Bi₁₀Co₁₆O₃₈nanoplates,Bi₁₂NiO₁₉/GO nanocomposites,chrysanthemum-like Bi₂S₃ materials and sea urchin-like CuS/Bi₂S₃ composites display outstanding capacitive behavior,indicating that as-prepared Bi-based compounds and their composites can be a kind of potential electrode materials for energy storage.