Study On Preparation And Modification Of Fe-Sb₂O₃/rGO Composites For Lithium/Sodium Ion Batteries Applications

Lithium-ion batteries（LIBs）are increasingly being used in various industries due to the growing demand for electronic devices and electric vehicles.The negative electrode material of LIBs is crucial in determining its performance.However,the current negative material for commercial lithium-ion batteries,graphite,cannot meet the ever-increasing demand for lithium-ion batteries due to its limited theoretical capacity of 372 m Ah g^-1.This calls for the development of anode materials with both high specific capacity and good cyclic stability.One such promising material is Sb₂O₃,which boasts of high theoretical specific capacity,good safety performance,and low cost,which has attracted the attention of anode material researchers.However,Sb₂O₃practical application presents several challenges.Firstly,it has poor conductivity,leading to unsatisfactory ratio performance.Secondly,the charging and discharging process comes with large volume expansion of up to 260%,resulting in quick capacity attenuation and significant reversible capacity loss during the first cycle.Therefore,researchers must address the challenges for Sb₂O₃ to achieve its full potential in LIB applications.Based on the aforementioned issues,this thesis aims to address the conductive deficiency of Sb₂O₃ through transitioning metal and nitrogen doping modification and graphene composite implementation.Additionally,to address the excessive volume expansion issue,a high-performance lithium/sodium ion battery anode material was synthesized using a well-conceived experimentation approach,which is as follows:Fe-Sb₂O₃/rGO composites doped with Fe³⁺were synthesized by means of a one-step hydrothermal method,using Sb₂O₃ as the antimony source,GO as the carbon source,and Fe Cl₃·6H₂O as the iron source.The impact of the preparation process parameters and the amount of Fe³⁺on the microstructure,phase composition,electrochemical performance of the composites,and the mechanism behind the strengthening were investigated.It was observed that the usage of r GO composites improves the electrical conductivity of Sb₂O₃,and that an appropriate amount of Fe³⁺doping enhances the uniform anchoring of Sb₂O₃ particles on the graphene’s surface,hence effectively ameliorating the volume expansion of the composites throughout the electrochemical cycle.This reduced the reaction energy barrier during the process of lithium/delithium and improved the electrochemical performance of the composites.Hydrothermal treatment of the 4.7 wt.%Fe³⁺content at 120℃×12 h led to the best electrochemical performance of the Fe-Sb₂O₃/r GO composites:at a current density of200 m A g^-1 and for storing lithium,the first reversible specific capacity was 997.7 m Ah g^-1;the first cyclic coulo efficiency（ICE）was 61.31%;the reversible specific capacity was 926.06 mAh g^-1 for 200 cycles,and the capacity retention rate was a high 96.04%.When stored with sodium and at a current density of 100 m A g^-1,the reversible capacity was 1050.7 m Ah g^-1 for the first time,the ICE was 45.75%,the reversible specific capacity was 321.25 m Ah g^-1 after 200 cycles,and the capacity retention rate was63.13%.To improve the low ionic conductivity efficiency（ICE）of Fe-Sb₂O₃/r GO composites,the present study employed a one-step solvothermal method to prepare Fe and N co-doped composites Fe-Sb₂O₃/N-r GO（FS/N-r GO）by utilizing urea as the nitrogen source.The study investigated the effects of preparation parameters and nitrogen doping amount on the microstructure,phase composition and ICE properties of the composites and their strengthening mechanism.Results revealed that the optimum ICE and first reversible specific capacity of the composite were obtained by solvent heat treatment at 120℃×12 h when nitrogen content reached 35 wt.%.The first reversible specific capacity was 1268.7 m Ah g^-1 when storing lithium,and ICE increased to 69.93%at a current density of 200 m A g^-1.For sodium storage,the first reversible capacity reached 500.63 m Ah g^-1 at a current density of 100 m A g^-1,while ICE increased to 57.92%.The mechanism study demonstrated that the improved performance was due to a further increased number of active sites of the composite through N doping,which effectively reduced the residual oxygen-containing functional groups,thereby mitigating the irreversible consumption of lithium/sodium ions on the r GO nanosheets and enhancing the specific capacity of the first reversible and ICE.