| Sodium-ion batteries as a promising alternatives to lithium-ion batteries for large scale grid energy storage because the abundance,wide distribution and low cost of sodium.Antimony has recently attracted great interest as a promising anode material because of its high theoretical capacity of 660 mAh g-1 and superior electronic conductivity.However,it generally shows poor cycling stability because of its huge volume changes(?390%)during repeat sodium insertion/extraction,resulting in pulverization of the antimony particles and electrical disconnection from the current collector.Previous studies demonstrate that antimony-based sodium ion battery anode material performance improvement can be achieved by reducing the size of antimony particles and coating carbon.Beside,nitrogen-doped carbon materials have been proved as a very effective strategy to enhance the electrochemical performance for the carbon-based materials anodes.Ionic liquids are considered as a new type of precursors for the preparation of nitrogen-doped carbon materials with the advantages of non-flammability,satisfactory electrochemical stability,and excellent electronic conductivity.Based on the above results,we have prepared three kinds of antimony/nitrogen doped composites by thermal decomposition of ionic liquids with antimony and antimony trichloride mixture respectively and systematically studied their sodium storage properties.First,we synthesized an antimony-cyano-based ionic liquid-derived nitrogen-doped carbon(Sb-CNC)hybrid by ball-milling and subsequent pyrolysis treatment.The carbon matrix is obtained by carbonizing[MCNIm]Cl,and Sb nanoparticles are uniformly dispersed in the carbon network.The formation of Sb-N-C bonds between Sb and the cyano-based ionic liquid-derived nitrogen-doped carbon matrix guarantee good structural integrity.Moreover,the presence of nitrogen-doped carbon in the hybrid material serves as a robust protective cover and an electrical highway,buffering the substantial volume expansion of Sb nanoparticles and ensuring the fast electron transport for stable cycling operation.Second,we fabricated a composite of chemical bonding Sb nanoparticles in ionic liquid-derived nitrogen-enriched carbon(Sb@NC)via pyrolysis of a SbCl3/Emim-dca mixture under an Ar/H2 atmosphere.The Sb@NC composite in the half cell of sodium-ion batteries exhibits a high reversible capacity of 440 mAh g-1 at a current density of 100 mA g-1 after 100 cycles,superior rate performance of 285 and 237 mAh g-1 at high current densities of 2 and 5 A g-1,respectively.Furthermore,In the full cell,the energy density of Sb@NC//Na3V2(PO4)3/C is approximately 147 Wh kg-1 at a power density of 50 W kg g-1.Even at 2.37 kW kg-1,an energy density of around 65 Wh kg-1 is still retained.The remarkably improved electrochemical performance could be assigned to the synergistic effect of nanoscale size,uniform distribution,and chemical coupling effect between Sb and ionic liquid-derived nitrogen-enriched carbon.Last,we have demonstrated the synthesis of a novel nitrogen-doped reduced graphene oxide-bonded Sb nanoparticles(denoted as Sb@N-rGO)through ball-malling,freeze-drying and subsequent Ar/H2 thermal decomposition by using Emim-dca as nitrogen sources.Dopping nitrogen atoms can increase the welting property of rGO,electrolyte more easily penetrate the electrode material.In addition,the strong bonding between Sb and pyrrolic nitrogen in nitrogen-doped reduced graphene oxide buffer large volume variation of antimony during cycling.As an anode material for sodium-ion batteries,the Sb/N-rGO composite manifests enhanced high capacity cycling stability and rate performance. |
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