Synthesis And Electrochemical Performance Of Graphene-based Antimony Composites

With the vigorous development and application of electric vehicles,human society is increasingly demanding lithium-ion batteries（LIBs）.However,lithium resource in earth crust is quite meager and decreased every day,so the price of Li materials and LIBs rise fast and severely.Sodium ion batteries（SIBs）exhibit similar working mechanism with LIBs,own abundant reserves,widespread distribution and low cost,so SIBs have considered as an appealing alternative to LIBs.However,the radius of sodium ion is much larger than that of lithium ion,making the sodiation/desodiation processes and the transmission of sodium ion are much more difficult than lithium ion during the electrochemical process.Hence,selecting suitable electrode materials and designing new electrode structures are the key points for the development of high performance SIBs.Supercapacitors have high power density and long cycle life compared to batteries,so it is becoming an important device for energy storage.The traditional carbon materials provide double layer capacitors,which have good cycle stability but low capacitance.Metal materials and conductive polymers provide pseudocapacitance,which possess large capacitance but poor stability.Hybrid supercapacitors,which own the advantages of double layer capacitors and pseudocapacitance,have become the key point on supercapacitors research.In this thesis,in terms of coating surface with carbon layers,nanonization of active materials,establishing sandwich-like structure/porous structure and alloying/heteroatom doping,three kinds of graphene-based antimony composites were prepared.Carbon coated graphene/antimony composite（G@Sb@C）was first prepared,in which graphene as a supporting substrate.The carbon layer can restrain the exposed Sb nanoparticles between the graphene sheets and carbon layers,reduce the particle sizes and enhance the uniformly distributed loading.Then,the graphene-based antimony/antimony iron composite（G@Sb/FeSb₂）with a unique sandwich-like structure was prepared.The introduced Fe₄Sb matrix can further enhance the electronic transmission and buffer the volume expansion of active materials.At last,the N-doped graphene-based antimony/antimony iron composite（N-G@Sb/FeSb₂）with a mesoporous structure was prepared.The incorporation of nitrogen atoms can enhance the electronic conductivity and increase the active sites on the graphene surface,thus improve the rate performance and the adsorption capacity of ions and charges.Moreover,the mesoporous structure can facilitate the contact between the electrode and Na⁺/the electrolyte.The as-prepared composites were characterized and tested for SIBs/supercapacitors,and the relationships among the components,structures,and electrochemical performance wrer also investigated.The main contents of this thesis are listed as follows:（1）G@Sb@C was prepared by the hydrolysis and in situ growth of the antimony salt on graphene surface,and followed in situ polymerization and thermal reduction processes,in which graphene as a supporting substrate.The graphene framework and carbon layer can buffer the volume change,reduce the aggregation and enhance the electronic conductivity.As an anode material for SIBs,the G@Sb@C electrode charges and discharges at a current density of 0.1 A g^-1 and delivers a high reversible capacity of 569.5 mAh g^-1,the capacity retains about 98.4%after 200 cycles.Moreover,the capacity reaches 433 mAh g^-1 even at a high current density of 5.0 A g^-1.（2）G@Sb/FeSb₂ was prepared by the hydrolysis and in situ growth of the antimony salt and iron salt on graphene surface,and followed thermal reduction processes,in which graphene as a supporting substrate.The nanoparticles are uniformly deposited on graphene sheets,and the composite shows a sandwich-like structure.The nanometerized Sb/FeSb₂particles can enhance the contact area with sodium ion,and the graphene interlayer can buffer the volume change,reduce the aggregation and enhance the electronic conductivity.As an anode material for SIBs,the G@Sb/FeSb₂ electrode charges and discharges at a current density of 0.1 A g^-1 and delivers a high reversible capacity of 535 mAh g^-1,the capacity retains about 96.3%after 200 cycles.Moreover,the capacity reaches 253 and 175mAh g^-1 even at high current densities of 5.0 and 10 A g^-1,respectively.（3）N-G@Sb/FeSb₂ with a mesoporous structure was prepared by the hydrolysis of the antimony salt and iron salt on the graphene surface and coordination with conducting polymers,and followed by thermal reduction processes,in which graphene as a supporting substrate.N-G@Sb/FeSb₂ composite not only possesses the advantages of G@Sb/FeSb₂composite,but also exhibits its own unique advantages:The doping of N can enhance the electronic conductivity,increase the active sites on the graphene surface,thus improve the rate performance and the adsorption capacity of Na⁺;the mesoporous structure can not only benefit the ion transport,but also can effectively accommodate the volume changes of electrode materials during cycling.As an anode material for SIBs,the N-G@Sb/FeSb₂electrode charges and discharges at a current density of 0.1 A g^-1 and delivers a high reversible capacity of 462 mAh g^-1,the capacity retains about 95.6%after 200 cycles.Moreover,the capacity reaches 271 and 219 mAh g^-1 even at high current densities of 5.0and 10 A g^-1,respectively.（4）Due to the unique structure and components of G@Sb/FeSb₂ and N-G@Sb/FeSb₂composites,they can also be applied to supercapacitors.For G@Sb/FeSb₂ composite,the Sb/FeSb₂ particles are uniformly deposited on graphene sheets and contact with electrolyte well,thus the utilization of reactive metal particles is improved;the graphene interlayer can enhance the electronic conductivity and provide double layer capacitors.For N-G@Sb/FeSb₂,the mesoporous structure facilitates the contact between the electrode and the electrolyte,ensures the smooth of the transmission channels;the doping of N can increase the active sites on the graphene surface,thus raise the rate performance and the adsorption capacity of charges.As an electrode material for supercapacitors,the G@Sb/FeSb₂ electrode charges and discharges at a current density of 10 A g^-1 and exhibits a high capacitance of691.1 F g^-1,and the capacitance retention maintains at 98%after 10000 cycles.In addition,the N-G@Sb/FeSb₂ electrode exhibits a high capacitance of 575.5 F g^-1 at the same current density,and the capacitance retention maintains at 99%after 10000 cycles.Moreover,when the current densities increase to 40 and 50 A g^-1,the specific capacitances of G@Sb/FeSb₂electrode can reach 300 and 250 F g^-1,and the specific capacitances of N-G@Sb/FeSb₂electrode can reach 373.1 and 346.1 F g^-1,respectively.