Preparation And Electrochemical Characteristic Of Bismuth-based Nanocomposites As Anode For Lithium-ion Batteries

The gravimetric capacity of bismuth is 386 mA h g-1, which is comparable to that of the commercial carbon anode (372 mA h g-1).While Bi has a quite high volumetric capacity of about 3765 mA h cm-3 and moderate operating voltage (ca. 0.8 V versus Li+/Li), making it promising potential anode materials for LIBs. However, like other transition metal, the practical application of Bi in anodes is still hindered by some problems. The drastic volumetric and structural changes(?215%) during the repeated lithium insertion/extraction process gives rise to pulverization of the electrode materials and gradual aggregation of active materials, resulting in fast capacity fading and poor rate capability.One of the most effective methods to overcome the mentioned problems of Bi requires a combination of carbon hybridization and nanostructuring design. This is because carbon nanomaterials can greatly enhance the conductivity of the composite, and besides, the elastic carbon materials can effectively relieve the strain caused by the volumetric change during insertion/extraction process, protect the Bi from chemical corrosion and agglomeration, improving their cycling stabilityIn this study, graphene aerogels coated Bi2O2CO3 composites are synthesized by hydrothermal method. Here, the three-dimensional flower Bi2O2CO3 is dispersed in the pore structure and the surface of the lamellae in graphene aerogels, which greatly increases the specific surface area of the material and enhances the electrochemical properties of the anode material. The results show that the sample presents a high capacity of 800.3 mA·h·g-1 at 200 mA·g-1 after 570 cycles, while is 3 times of that of Bi2O2C03.In addition, the graphene aerogels coated Bi2O3-Bi2O2C03 composites and graphene aerogels coated Bi composites were prepared by heating graphene aerogels coated Bi202C03 composites at different temperature. Through the structural and electrochemical test, it was found that graphene aerogels coated Bi203-Bi202CO3 composites maintain the original microstructure of the composites, and the capacity of the composites can reach 765 mA h g-1 after 500 cycles at 200 mA g-1 current density. In the graphene aerogels coated Bi composites, Bi nanoparticles are uniformly dispersed on the pore structure and the surface of the lamellae in graphene aerogels. Electrochemical tests showed that the materials was capable of reaching 236 mA h g-1 after 700 cycles at a current density of 200 mA g-1.Rose-like Bi@N-doped carbon nanocomposite was fabricate for the first time by a facile hydrothermal method, following by polydopamine coating for different time and subsequent carbonization. Structural and morphological characterizations reveal that the Bi@N-doped carbon nanocomposite have a uniform rose-like structure, with well crystallized Bi nanoparticles embedded homogeneously in the carbon matrix. These Bi@carbon nanocomposite used as anode materials for rechargeable lithium-ion batteries (LIBs) show that the Bi@carbon nanocomposite reaction for 48h presents a reversible capacity of 712 mA h g-1 for initial cycle at 200 mA g-1 and exhibits excellent cyclability with a capacity of 535 mA h g-1 after 450 cycles at a current density of 200 mA g-1. The excellent lithium storage performance of the Bi@N-doped carbon nanocomposite can be ascribed to the synergetic effects of several factors including the unique rose-like structure, nano-sized Bi and nitrogen doping carbon matrices.