Preparation Of （Bi,Sb）₂S₃ Composites And Study Of Their Potassium Storage Properties

The rechargeable lithium-ion battery is widely used in mobile electronic equipment and electric vehicles because of its high energy density.However,due to the scarcity and uneven geographical distribution of lithium resources,lithium-ion batteries cannot meet the requirements of large-scale energy storage.Potassium has been favored by researchers in recent years due to its abundant reserves and similarity to lithium in terms of electrochemical properties and redox potential.However,the large radius of potassium ions makes the chemical kinetics of the anode material de-intercalation process slow and leads to large changes in the volume of the material,which limits the development of potassium-ion batteries.Therefore,it is necessary to find a suitable anode material to accommodate large potassium ions.（Bi,Sb）₂S₃ material combines the high theoretical capacity of Sb(660m Ah g^-1)and the large layer spacing of Bi,making it a potential anode material.However,（Bi,Sb）₂S₃ materials have the disadvantages of poor electrical conductivity,poor cycle stability and poor interface compatibility,resulting in poor rate and cycle performance of the battery.In view of the above shortcomings,this paper starts from optimizing the microstructure,composition,interface properties and decreasing energy storage barrier of the material to improve the potassium storage performance of the anode material.The research content is as follows:Firstly,the Bi Sb S₃/NPC-OBA composites were prepared by solvothermal method.The rod-shaped Bi Sb S₃ with a 1:1 Sb/Bi ratio was embedded in the conductive network of porous carbon（NPC）and organic matter（E）-4,4’-（（diazene-1,2-diylbis（4,1-phenylene））bis（azanediyl））bis（4-oxobutanoic acid）（OBA）.By introducing multiple active sites,an organic-inorganic composite electrode material with excellent interface compatibility was constructed.Among them,OBA combines with NPC through P-O bonding and hydrogen bonding to prevent organic materials detaching from current collection during potassium storage.NPC contains N and P heteroatoms that can improve the conductivity of the material and provide nucleation sites for Bi Sb S₃ crystal nuclei.The porous structure of NPC helps buffer the volume expansion of Bi Sb S₃.The active sites contained in OBA can not only provide additional potassium storage capacity,but also fix FSI^-,promote the formation of solid electrolyte interface film（SEI）rich in inorganic components,thereby improving the interface compatibility between electrode and electrolyte.Furthermore,it can promote the desolvation of K⁺,improve potassium storage kinetics and rate and cycling performance of potassium-ion batteries.Through theoretical calculations,it is confirmed that the conductive network of NPC-OBA can promote electron delocalization and improve the transport efficiency of electrons and K⁺,so that reduces the potassium storage barrier.The Bi Sb S₃/NPC-OBA composite was assembled into the battery for electrochemical performance test and the results showed that it had good potassium storage performance.The charging capacity was 739.4 m Ah g^-1 at a current density of 0.05 A g^-1 and the first-round coulombic efficiency could reach 81.2%.The capacity retention rate was 75.6%after500 cycles at a 2 A g^-1 current density.In order to further improve the structural stability and wide temperature adaptability of the anode material,poly 3,4-ethylene dioxythiophene（PET）was used as a conductive matrix and the organic substance thioctic acid（TA）was added.The Bi_0.67Sb_1.33S₃/PET@TA composite with an Sb/Bi ratio of 2:1 was prepared by template method and solvothermal method.The added TA can polymerize in situ under the effect of electrolyte and Bi_0.67Sb_1.33S₃ to form PTA,obtaining Bi_0.67Sb_1.33S₃/PET@PTA composite with a more stable structure eventually.Compared with the rod-like Bi Sb S₃ prepared in the previous system,Bi_0.67Sb_1.33S₃ is a smaller nanoparticle that is tightly embedded in PET@PTA supramolecular polymer network,which can effectively alleviate the problem of volume expansion.Due to the doping of protic acid,the energy state of theπelectrons of the PET polymer chain changes,making it have strong conductive ability.The hollow structure of PET allows the electrolyte to fully infiltrate the electrode material.The supramolecular network composed of PET and PTA two cross-linked polymers makes the composite have high mechanical strength,tensile properties and thermodynamic stability,which can improve the high temperature adaptability of the electrode.The excellent fixation ability of anionic FSI^-can further improve the K⁺transport kinetics and improve the low-temperature adaptability of the electrode.The dynamic hydrogen bond network can finely regulate the interface of the material,so that the material can show strong self-healing ability and excellent electrochemical performance in extreme temperature environments.The discharge capacity of Bi_0.67Sb_1.33S₃/PET@PTA composites can reach 475.2 m Ah g^-1 after100 cycles of the cycle at a current density of 0.5 A g^-1.When the current density increases to 2 A g^-1,the capacity can be maintained at 223.7 m Ah g^-1 after 500 cycles.The capacity retention rate of Bi_0.67Sb_1.33S₃/PET@PTA//PTCDA battery at-40°C and 70°C was 66%and84%of the capacity at 25°C,respectively,reflecting superior cycling performance.Furthermore,the potassium storage mechanism of composites was explored by ex-situ XRD and ex-situ XPS.