Application Of Metal Bismuth Electrode In Lithium/Sodium Ion Batteries

Lithium-ion batteries and sodium-ion batteries,as various types of portable electronic products,have been diffusely applied in various fields on account of more ascendant,for instance high energy density,slow self-discharge rate and capacity retention during discharge-charge cycles,no memory effect.With excellent performance,it has been steadily attacking the high-end market of batteries,and is considered to be the most likely method for power storage in the future.The current commercial ion batteries cannot meet the performance requirements of high energy density,long life and high rate,so the development of high performance lithium/sodium ion batteries is urgently needed.The composition and structure of anode materials have a decisive influence on the electrochemical activity of batteries.Among many updated materials,transition metals and their compounds,such as bismuth and its sulfides,have attracted attention thanks to high theoretical capacity and suitable operating voltage and green non-toxicity.Unfortunately,as a negative electrode material for lithium/sodium ion batteries,pure elemental substances and compounds will produce the phenomenon of volume expansion and particles aggregation with the increase of cycle times,which lead to a large loss of capacity.There is an urgent need to recommend a new synthetic method and to prepare composite materials to effectively alleviate these disadvantages.Recently,Metal organic frameworks?MOFs?have gradually entered the field of vision as structurally stable porous materials.MOFs with structural diversity are used in fuel transportation and storage,medicine,fluorescence and catalysis.At present,MOFs and its derivatives have been successfully applied to energy storage fields such as fuel cells,supercapacitors and secondary batteries.In view of the presence of central metal ions with redox behavior and organic ligands with charge storage and transfer ability,these materials have potential application value in the field of battery electrode materials.However,when MOFs is used alone in electrochemical materials,there are some some inevitable shortcomings,for example low specific capacity and poor conductivity.In this paper,MOFs was used as a precursor to prepare battery electrode materials,and their electrochemical properties were investigated.Experiments have shown that a series of derivatives prepared by this synthetic method have shown favorable electrochemical activity.Here,Bi-BTC is selected as the bismuth source to compound pure bismuth Bi and bismuth compounds?focusing on Bi₂S₃?.On this basis,Bi/C and Bi₂S₃/C are synthesized with porous carbon by organic ligand H₃BTC as the carbon source.After that,Bi₂O₃,Bi₂Se₃ and Bi₂Te₃ are formed successively,and are characterized and tested.The main research of this thesis includes three aspects:?1?Preliminary test with Bi-BTC as precursor.The reduction of Bi-BTC was carried out using three reductants.Firstly,the TPR test of Bi-BTC is proceed,getting the reduction temperature at 400?.Thence,the reduction of the MOF with H₂is realized by controlling the temperature.In addition,hydrazine hydrate and phenylhydrazine are used to reduce Bi-BTC at room temperature.It was found from XRD that elemental Bi is successfully prepared by the three reducing agents.The Bi with H₂ as a reducing agent?denoted as Bi-1?has a relatively regular spherical appearance and a small particle diameter.When the three bismuths are used as anode materials for lithium ion batteries,the electrochemical activity of Bi-1 is superior to that of the other two.Nevertheless,the specific capacity of pure bismuth has not reached our goal,on this basis,carbon source H₃BTC is utilized to make the Bi/C composite for improve the overall electrochemical performance of the Bi.Bi/C?diameter about 29 nm?is formed by Bi microsphere distribution in the carbon frame.The arrival of carbon effectively suppresses the aggregation of particles and the volume expansion of Bi,providing a channel for the ions insertion and extraction and promoting the reaction,and thus improving the overall electrochemical performance of the material.When employed as the anode material for Lithium storage,the Bi/C composite exhibits excellent cycle stability after 150 cycles(515 m Ah g^-1).?2?The main test with Bi-BTC as the precursor.Bi₂S₃ is prepared by sealing with Bi-BTC as sulfur source and sublimated sulfur as sulfur source.material had good lithium storage performance at 400?.Investigating the effect of temperature on electrochemical activity,it is concluded that the material has good lithium storage performance at 400?.Then Bi₂S₃/C with the H₃BTC as carbon source and its lithium storage performance is obtained.The Bi₂S₃/C has a rod shape and is only 60 nm in diameter.In addition,Bi₂S₃ and Bi₂S₃/C are applied to sodium storage.And RGO is employed as the other carbon to compound with Bi₂S₃,and the electrochemical stability of the three electrodes is compared.?3?Extended test with Bi-BTC as precursor.It is calcined at 400? to obtain Bi₂O₃.Bi₂Se₃ and Bi₂Te₃ are obtained with selenium and tellurium powder as the sources in the same way as bismuth sulfide.The electrochemical properties of bismuth compounds are compared and the Bi₂S₃ delivers out-bound cycling stability among the four,which confirms the potential as a anode material for lithium ion batteries.