Preparation Of Nano Bi₂O₃/C Composite Material And Its Research On Electrochemical Lithium-storage Properties

Currently,Bi₂O₃ has been considered as a potential candidate for new anode material of next generation lithium ion batteries,due to its high theoretical capacity(690 m Ah g^-1),as well as friendly environment,low cost and abundant resources.However,the poor electrical conductivity and severe volume expansion of Bi₂O₃ during charge and discharge process restrict its application in lithium storage.In order to overcome the disadvantages of Bi₂O₃ mentioned above,we designed and prepared some Bi₂O₃/C nanocomposites with different microstructures and improved its lithium-storage performance via the dynamic advantage of nanostructure and interface control strategy.XRD,SEM,TEM,Raman,nitrogen adsorption-desorption,galvanostatic charge and discharge,EIS and other characterization methods were carried out to investigate the formation mechanism,microstructure characteristic and electrochemical lithium-storage performance of the as-prepared composite material.Bi₂O₃@C composite material was obtained by hydrothermal carbonization method.In the Bi₂O₃@C composite,the dimension of Bi₂O₃ sphere is 100⁵00 nm,while the thickness of carbon layer is about 4 nm.Carbon coating layer can enhance the electrical conductivity of Bi₂O₃ and inhibit its aggragation during charge and discharge process.In addition,carbon layer facilitates to form stable SEI film through invoiding the direct contact between Bi₂O₃ and electrolyte.Bi₂O₃@C composite has improved electrochemical lithium-storage performance compared to Bi₂O₃ nanospheres.Remarkably,Bi₂O₃@C has an initial discharge capacity of 887 m Ah g^-1,first irreversible capacity loss of 40 % and a stable cycle performance of 357 mAh g^-1?reversible capacity retention rate of 67 %?at a current density of 300 mA g^-1 after 100 cycles.Meanwhile,even at a current density of 6000 mA g^-1,the composite obtains a discharge capacity of 196 m Ah g^-1.Bi₂O₃@N-doped graphene composite was prepared by hydrothermal reaction.In the Bi₂O₃@N-doped graphene composite,Bi₂O₃ particles are encapsulated by N-doped graphene.Compared with carbon coating layer,N-doped graphene facilitates to improve the electrical conductivity of electrode material and wettability of electrolyte.In addition,porous N-doped graphene facilitates to enhance the migration speed of Li+.Therefore,the composite has excellent electrochemical lithium-storage performance.The composite has an initial discharge capacity of 890 m Ah g^-1,first irreversible capacity loss of 32 % and a stable cycle performance of 399 mAh g^-1?reversible capacity retention rate of 66 %?at a current density of 300 mA g^-1 after 100 cycles.Even at a current density of 6000 mA g^-1,the composite shows a discharge capacity of 249 m Ah g^-1.On the basis of the above mentioned mechanism of carbon coating and graphene modification,Bi₂O₃@C@nitrogen-doped graphene composite was prepared by ‘one-pot method' based on in-situ hydrothermal carbonation strategy.Bi₂O₃@C@N-doped graphene composite has the combined lithium-storage merits of the above mentioned two modification methods.Moreover,the further reduced dimension of Bi₂O₃ facilitates to reduce the transport path of electron and Li+.The composite demonstrates an initial discharge capacity of 900 mAh g^-1,first irreversible capacity loss of 30 % and a stable cycle performance of 427 mAh g^-1?reversible capacity retention rate of 68 %?at a current density of 300 mA g^-1 after 100 cycles.Even at a current density of 6000 mA g^-1,the composite demonstrates a discharge capacity of 270 m Ah g^-1.PPy-coated Bi₂O₃@CMK-3 composite was prepared by nano-casting method.The carbon skeleton of CMK-3 effectively inhibits the aggragation and growth of Bi₂O₃ particles,and the PPy coating controls the stability of interface.In this composite,unique mesoporous channels further enhance the transportation rate of Li+.By optimizing the lithium-storage merits of above mentioned three kinds of composites,polypyrrole-coated Bi₂O₃@CMK-3 composite shows the most excellent electrochemical performance.Impressively,the composite has an initial discharge capacity of 949 m Ah g^-1,first irreversible capacity loss of 26 % and a stable cycle performance of 492 mAh g^-1?reversible capacity retention rate of 70 %?at a current density of 300 m A g^-1 after 100 cycles.Even at a current density of 6000 m A g^-1,the composite provides a discharge capacity of 321 mAh g^-1.