Interface Control Of Bismuth-based Nanomaterials And Study On The Performance Of Aqueous Ni//Bi Batterials

At present,under the strategic needs of national carbon neutrality and carbon peaking,higher requirements are put forward for the development of energy storage devices.Although the energy storage system represented by lithium-ion batteries has been widely used in the fields of power batteries and large-scale energy storage,its problems such as high cost,low energy density,and serious safety hazards are no longer in line with the development direction of new energy storage devices in the future.In contrast,aqueous batteries using water-in-salt as electrolytes have obvious advantages in terms of cost,safety and environmental protection,as well as higher theoretical capacity and faster ion/charge transport capabilities,thus becoming an important choice for the next generation of new batteries.Among them,nickel//metal aqueous batteries have attracted extensive attention of researchers due to their abundant electrode material resources,low redox potential,and excellent rate performance.However,the research on nickel//metal aqueous batteries has always focused on the development and improvement of cathode materials,and the lack of suitable anode materials limits the further improvement of its energy density,cycle stability and other properties.Therefore,this paper chooses bismuth oxide as the research object,and adopts a variety of optimization and modification strategies,including defect engineering,heterostructure,composite design and other methods,in order to obtain high-performance anode materials and further improve the application potential of aqueous batteries such as Ni//Bi batteries.The specific work contents and research results are as follows:(1)Preparation and electrochemical performance of NiCo₂S_4-x/NiCo₂O_4-x//Bi/Bi₂O_3-x aqueous alkaline batteries:Based on modification strategies of defects engineering and heterostructures,defect-rich Bi/Bi₂O_3-x hierarchical composites were synthesized on carbon paper substrates via simple hydrothermal,calcination and reduction treatments.Benefiting from the introduction of a large number of vacancy defects,the intrinsic conductivity of the material is effectively enhanced,and the interfacial synergistic effect exerted by the heterogeneous interface between different components promotes the diffusion of ions,thereby realizing fast electrochemical reaction kinetics.Under this multi-method synergistic optimization strategy,the electrochemical performance test results of Bi/Bi₂O_3-x show that,at the current density of 6 A g^-1,the specific capacity of Bi/Bi₂O_3-xis 262.5 m A h g^-1,and when the density is increased to 20 A g^-1,the initial capacity retention rate reaches an ultra-high 88%,showing excellent capacities and rate performance.In addition,defect-rich NiCo₂S_4-x/NiCo₂O_4-x multiphase composites were prepared via the same synthetic route and modification strategy,and the electrochemical test results also showed excellent electrochemical performance.On this basis,the Ni//Bi aqueous alkaline battery was assembled with Bi/Bi₂O_3-x as the anode and NiCo₂S_4-x/NiCo₂O_4-x as the cathode.After testing,at a power density of 2.1 k W kg^-1,the energy density of the battery can reach up to 97.1 W h kg^-1,and the battery still retains nearly80%of its initial capacity after 2500 cycles.(2)Preparation and electrochemical performance of NiCo₂S₄@PPy//Bi₂O₃@PPy aqueous alkaline batteries:Based on the surface and interface chemical modification strategies of composite design,the Bi₂O₃ nanosheet arrays grown on carbon paper substrate was treated to one-step electrodeposition,and the core-shell Bi₂O₃@PPy composite material uniformly coated by conductive polymer was obtained.The loading of PPy on the active material was changed via adjusting the electrodeposition time to study effect on the electrochemical performance.The electrochemical test results show that when the electrodeposition time is 500 s,the electrochemical properties of Bi₂O₃@PPy reach the best,and its the specific capacity is 459.7 m A h g^-1 at a current density of 5 A g^-1.The specific capacity is almost four times that of the original Bi₂O₃ under the same condition.In addition,the NiCo₂S₄@PPy cathode material was synthesized via the same route and also showed the ultra-high capacity performance.This is mainly because the effective combination of PPy and active materials enhances the surface conductivity of the composites,which greatly improves the originally sluggish reaction kinetics,thereby significantly improving the electrochemical performance.On this basis,the Ni//Bi aqueous alkaline battery was assembled with Bi₂O₃@PPy as the anode material and NiCo₂S₄@PPy as the cathode material.After testing,the energy density and power density of the battery are respectively up to 88.3 W h kg^-1 and 4.3 k W kg^-1,and more than 80%of the initial capacity is still retained after 4000 cycles.