Study On Sodium Storage Performance And Mechanism Of Antimony-Based Multi-Component Self-Supporting Nanoarrays

Sodium-ion batteries have attracted significant attention owing to the abundant availability of sodium and low cost.Sb-based materials exhibit promising potential for sodium-ion batteries applications due to their high capacity and favorable Na alloying potential.However,their practical deployment is impeded by rapid capacity decay resulted from drastic volume fluctuations during Na alloying/dealloying processes.Therefore,how to reduce the adverse effects of volume changes and improve the cycle stability of the electrode has become the core problem and focus of research on Sb-based electrodes.This dissertation aims are to develop high-performance Sb-based multi-component arrays for SIBs.Building upon the construction of a 3D self-supporting array structure,a series of Sb-based alloy materials with excellent performance were prepared by incorporating control strategies such as heterointerface construction,thermal treatment-coupled modification,and concentration gradient design.The sodium storage processes were explored through in situ/ex situ characterization techniques,while the mechanisms behind the enhancement of the battery performance via different modification methods were extensively investigated through density functional theory calculations and finite element analysis.The following are the main research contents and conclusions:（1）Self-supported nanowall arrays composed of Sb Bi-Sb₂Se₃-Bi₂Se₃ were directly deposited on Cu substrates.During the electrodeposition,Sb,Bi and Se have been simultaneously integrated into the 3D nanowalls,giving rise to a structure with uniformly distributed phases of Sb Bi,Sb₂Se₃ and Bi₂Se₃.Because of such a unique construction,the electrode demonstrated exceptional long-term stability for sodium storage.DFT calculation results confirmed that the heterostructured interfaces could enhance the Na-ion diffusion,in-situ temperature sensing revealed that this distinctive heterostructure demonstrates excellent thermal stability.Ex-situ XPS analysis confirmed that this electrode facilitates the formation of a highly durable solid electrolyte interphase film,and ex-situ XRD and TEM analysis were used to not only study its sodium storage mechanism,but also prove the persistence of this unique structure and composition advantage.（2）The previous composite involving Bi yielded a relatively low capacity and failed to fully demonstrate the high-capacity characteristics of Sb.To maximize the high-capacity advantage of the alloy,the higher-capacity Sn was introduced into Sb to fabricate a self-supporting Sb Sn alloy array.This binary alloy exhibits a distinct pyramid-like structure,and the subsequent thermal annealing process forms an“alloy glue”at the root of the arrays,establishing a robust connection between the Sb Sn and the Cu.When employed directly as the anode material for sodium storage,such an alloy nanoarray demonstrated a capacity of 679 m Ah g^-1 at 0.2 C and exceptional cycling stability of 511m Ah g^-1 over 800 cycles at 2 C.DFT calculation results suggest that the alloy provides more favorable Na diffusion compared to the individual metals,and the“alloy glue”enhances the interaction between the Cu and Sb Sn.Based on FEA,such a unique construction of the pyramid-like nanostructure offers a uniform distribution and effective dissipation of stress.（3）Based on the previous work,the rate performance of the electrode should be further improved by shortening the electron/ion transport path.Inspired by the multilayered structure of the pine trees,3D hierarchical multilayered Sn doped Sb nanoarray coated with a thin C layer is prepared,where the voids between the multilayered could not only buffer the volume change during alloying/dealloying,but also provide ample assess to the electrolyte.While the outer C layer offered extra structural protection against internal stress,giving rise to a highly robust array that could efficiently confine the structural strain.DFT calculation suggested that in comparison to the control samples of pure Sb and Sb（Sn）,the Sn dopant could effectively confine the volume variation.This has been verified by FEA,where Sb（Sn）@C demonstrated more uniform von Mises stress distribution,and smaller displacement during Na alloying than the dense nanoarray without the hierarchical multilayered structure.（4）From the above work,it can be found that if the stress accumulated during the sodium storage process can be effectively dissipated,the possibility of electrode failure will be minimized.To further simplify the material preparation process and regulate the stress distribution within the electrode to improve cycle stability,the 3D coral-like array structure with gradient distributions of Sb and Cu was synthesized.The array features a bottom rich in Sb and a Cu-rich top with decreasing Sb and increasing Cu concentrations from bottom to top.The former provides high capacity,whereas the latter acts as a protective component to prevent the structure from collapse.The gradual transition in composition of the electrode introduces a laddered-type volume expansion effect,facilitating a uniform distribution and effective release of stress,thereby promoting mechanical stability.The sodium storage mechanism was deeply analyzed through in-situ XRD,EIS and ex-situ TEM,and it was found that the amorphous intermediate state formed during the sodium storage process not only helps buffer volume changes and promotes charge transport.