Construction Of Anode Materials And Study Of Electrolyte For Sodium Ion Batteries

As a new type of secondary battery,sodium ion battery has the advantages of abundant sodium resources,excellent high-low temperature performance and high safety,showing a favourable application prospect in large-scale energy storage field.However,the energy density of sodium-ion batteries is limited due to the higher relative atomic mass of sodium and the higher potential of standard electrodes compared with lithium.Therefore,how to improve the electrochemical energy storage characteristics of sodium-ion batteries is the main challenge.Electrode materials and electrolyte,as the key components of the battery,have a significant impact on the energy density and cycle life of the sodium ion battery.Therefore,the development of high specific capacity electrode materials and the optimization of electrolyte system are the key to promote the rapid development and application of sodium ion battery technology.Firstly,graphite intercalated compound electrode is taken as the research object,and the intrinsic sodium storage capacity of electrode material is improved by adjusting the spacing and electronic structure between graphite layers.Second,the local high concentration electrolyte was taken as the research object,and the compatibility between electrolyte and electrode material was improved by regulating the Na⁺solvation structure and solid electrolyte interface（SEI）in the electrolyte,so as to construct a sodium ion battery with high energy density and long cycle performance.The main research contents are as follows:Bi Cl₃-GICs was prepared by mixing method using graphite as matrix and Bi Cl₃ as intercalation agent.The effect of reaction conditions on the Bi Cl₃ intercalation structure was investigated.It was found that with the increase of reaction temperature,the content of Bi Cl₃intercalation firstly increased and then decreased.The Bi Cl₃-GICs synthesized at 200 ^oC is mainly second-order intercalated phase with the content of Bi Cl₃ up to 54.5%.The Bi Cl₃intercalation extends the interlayer spacing of graphite to 1.26 nm.Thanks to the large layer spacing and high Bi Cl₃ intercalation amount,it shows high specific capacity(213 m Ah g^-1@1A g^-1)and excellent rate performance(170 m Ah g^-1@5 A g^-1)as the electrode material for sodium ion batteries.In situ Raman spectroscopy was used to investigate the structure change and electron interaction mechanism of the material during the first discharge process,which further revealed the sodium storage mechanism of Bi Cl₃-GICs.Using Na FSI as sodium,DME as solvent and BTFE as diluent,a local high-concentration electrolyte system was constructed.The solvation structure of the electrolyte was determined by Raman spectroscopy.It was found that the local high concentration electrolyte retained the local coordination environment of high concentration salt-solvent cluster,and its solvation structure changed compared with the low concentration electrolyte,forming contact ion pairs and anion and anion aggregates.The introduction of diluent reduces the total salt concentration of electrolyte,improves the ionic conductivity of electrolyte,and enhances the wettability between electrolyte and diaphragm and electrode material,which significantly improves the battery performance.In the local high concentration electrolyte,Mesoporous carbon electrodes exhibit excellent specific capacity(170 m Ah g^-1@1 A g^-1)and cycle stability（85%@700 cycles）,superior to the current commercial Na PF₆ electrolyte.SEI composition on the surface of electrode material was analyzed and determined by depth XPS,and the formation mechanism and action mechanism of SEI in local high concentration electrolyte was further explored.