| With the global energy shortage and environmental pollution,the demand for clean energy in world continues to increase.Sodium-ion batteries（SIBs）are on the horizon of researchers due to their abundant reserves and low prices.At present,the main problem in the development of SIBs is to find suitable anode materials.The main problems of current anode materials are low specific capacity and poor cycle stability.Therefore,it is essential to develop anodes for SIBs with high specific capacity and good cycle stability.Alloy-type anode materials with high specific capacity have attracted more and more attention.Among them,bismuth（Bi）has a suitable voltage window and a long and stable voltage plateau,which is beneficial for its practical application in SIBs.However,when Bi is used as the anode materials for SIBs,the volumetric strain happened during the charge-discharge process,which cause the electrode structure to break down,resulting in capacity fading and anode failure.In view of this,this paper uses carbon materials to disperse and coat the nano-Bi particles.The cycling stability and rate performance of Bi anode were improved by microstructure design and regulation.A series of characterization means and electrochemical testing instruments were used to explore the relationship between material structure and properties.The main research contents of this paper are as follows:（1）Using Bi（NO3）3·5H2O as bismuth source and NaBH4 as reducing agent,Bi nanoparticles with particle size distribution of 52-118 nm were prepared by microemulsion method;and bismuth citrate was used as carbon source and bismuth source,and the amorphous carbon-coated nano-Bi（Bi@C）composites were obtained by heat treatment.The microscopic morphology and battery performance of Bi nanoparticles and Bi@C composites were analyzed by various characterization methods combined with various electrochemical tests.And the results showed that the coating of amorphous carbon effectively limited the volume expansion of Bi during the sodium intercalation process,thus The structural integrity of the electrode material is maintained;at the same time,the good electronic conductivity of amorphous carbon accelerates the transfer of electrons;in addition,amorphous carbon can also contribute a certain specific capacity in the composite material.（2）Using graphene oxide（GO）as raw material and ascorbic acid as reducing agent,three-dimensional porous graphene（3DPG）was prepared by hydrothermal method and Bi nanoparticles were loaded on it（Bi/3DPG）.At the same time,the Bi loading in the composites was controlled by changing the ratio of Bi nanoparticles to graphite oxide during the hydrothermal process,and the effect of loading on the pore structure and electrochemical properties of the composites was explored.The results show that the Bi/3DPG-M composite has suitable Bi loading（71.9%）and abundant mesopores（81.6%）when applied to the anode of Na-ion batteries,which can ensure the fast Na+transport and high specific capacity.The highly conductive network provided by 3DPG accelerates ion and electron transfer while limiting the agglomeration and volume expansion of Bi nanoparticles.Benefiting from the rational structural design,the specific capacity of Bi/3DPG-M can reach 270 mAh g-1,after 500 cycles at 0.1 A g-1.In addition,Bi/3DPG-M also exhibits excellent rate capability with a specific capacity of 266.1 mAh g-1 at 5A g-1. |
