Preparation And Lithium/Sodium Storage Performances Investigation Of Ni-Sb-Bi-Based Compounds/MXene Composites

Lithium-ion batteries and sodium-ion batteries are extremely important energy storage devices in the transformation of human energy structure.The energy density,rate performance and cycle stability are the main parameters to evaluate the quality of batteries.Anode is an important part of lithium/sodium-ion batteries.Therefore,developing anode materials with high capacity,superb rate and excellent stability is of great significance for the construction of high-performance lithium/sodium-ion batteries.This thesis starts with the transformation material Ni S,and then investigates the high theoretical specific capacity of Sb₂S₃,Bi₂S₃ and Bi₂Se₃anode materials with both transformation and alloying reactions.The charge-discharge voltage platform of the metal Sb anode is low,which make it suitable material for enhancing the energy density of the full battery.The theoretical capacities of the above materials are high,but all of them have the shortcomings of easy powdering and falling off due to volume expansion and poor electrical conductivity.In this thesis,five kinds of composite materials were prepared by nanometerization,doping modification or structural control methods and combined with highly conductive MXene.The properties of those composites for lithium and sodium storage were studied in detail.Co-Ni S/MXene composite was prepared by interfacial self-assembly method.The driving force of interfacial self-assembly method was the oleylamine layer on the surface of Co-Ni S.In the Co-Ni S/MXene composite,the Co-Ni S nanorods are 15-25 nm in length and 6-9 nm in width and nanorods are uniformly dispersed on the surface of MXene.The stacking of Co-Ni S nanorods was suppressed and MXene can provide electrical conductivity as an excellent conductor of electrons in the structure.The composite exhibits excellent performance for Li/Na storage.When it worked as an anode for Li-ion batteries,it can reach a reversible discharge capacity of 911 m Ah g^-1 at the current density of 0.1 A g^-1.As for of sodium-ion batteries,the reversible capacity at the current density of 0.1 A g^-1 is as high as 541 m Ah g^-1.The theoretical specific capacity of Sb₂S₃ is high.L-tartaric acid,citric acid and triethanolamine are used as ligands to help Sb³⁺disperse and adsorb on MXene uniformly.Subsequently,a uniform and monodisperse amorphous Sb₂S₃ material was grown on the surface of MXene by sulfuration.The morphology characterization shows that the morphologies of Sb₂S₃ obtained by L-tartaric acid,triethanolamine or citric acid as ligands are nanospheres with particle size of 200 nm,flowers with particle size of 500 nm and ultrasmall spheres with particle size of 150 nm,respectively.The spherical Sb₂S₃/MXene-C prepared with citric acid as ligand shows the best sodium storage performance(the specific capacities at 0.1 A·g^-1 and 5 A·g^-1 are840 m Ah·g^-1 and 552 m Ah·g^-1,respectively).Bi has a larger atomic radius than Sb,which is more conducive to the rapid intercalation and deintercalation of Li/Na for getting better rate performance.Therefore,Bi₂S₃ material is studied in the thesis.Utilizing the difference in saturated vapor pressure of water and oleylamine at room temperature,the method of creating vacuum environment is used to translate MXene out from water system into oleylamine solution.Then,Bi-O-Cl nanosheets were constructed on the surface of MXene in oleylamine solution and vulcanized by thioacetamide（TAA）subsequently.It is found that low proportion of TAA will make Bi₂S₃ grow into round and hexagonal flakes and high proportion of TAA will curl Bi₂S₃ into rolls.The roll-like Bi₂S₃/MXene composite exhibits a high specific capacity of 849 m Ah g^-1 at a current density of 0.1 A g^-1,and it could retain 541 m Ah g^-1 after 600 cycles at a high current density of 1 A g^-1.Selenide has lower band gap and higher conductivity than sulfide,and the radius of Se atom is larger,which is more suitable for store alkali metal ions in terms of kinetics.The Sb doped Bi₂Se₃ nanoflowers was grown on the surface of MXene by a wet-chemical method with sodium selenide sulfate as the Se source and then coated with N-doped C.The doping of Sb can inhibit the loss of Se element and keep the structure stable.Furthermore,the MXene and N doping of C can serve as the support and protect active material.The Sb_0.4Bi_1.6Se₃/MXene@NC shows excellent lithium/sodium storage performance.It could deliver ultrahigh reversible capacity(572 and 846 m Ah g^-1 at 0.1 A g^-1 for sodium ion batteries（SIB）and lithium ion batteries（LIB）),outstanding rate performances(438 and 583 m Ah g^-1 at 5 A g^-1 for SIB and LIB)and impressive long-term cycling stability(364 m Ah·g^-1 retention after 2000 cycles at 1 A g^-1 for SIB,495 m Ah·g^-1 retention after 2000 cycles at 5 A g^-1 for LIB).Part of the capacity of metal sulfides and selenides comes from a higher voltage platform,while Sb has a lower voltage platform and is an ideal anode material.MXene was modified by carbon coating.Subquently,Sb₂O₃ nanoparticles were grown on its surface by hydrothermal method.Then,MXene@NC/Sb composites with extremely small particle size Sb were prepared by PH₃ in-situ reduction.Benefiting from this,the MXene@NC/Sb material exhibits excellent cycling stability for sodium storage(the capacity of 190 m Ah g^-1 is maintained after 20000cycles at a high current of 10 A g^-1).In addition,the MXene@NC/Sb composite also possesses excellent lithium storage cycling stability(a capacity of 200 m Ah g^-1 is maintained after 5000cycles at the current density of 10 A g^-1).