| With the widespread application of lithium-ion batteries(LIBs)in electric vehicles and large-scale energy storage,the limited availability and rising prices of lithium resources have gradually become prominent issues.Potassium and sodium have oxidation-reduction potentials similar to lithium,and are abundant and low-cost resources.Therefore,sodium/potassium-ion batteries(SIBs/PIBs)have become alternatives to LIBs in large-scale energy storage facilities.SIBs/PIBs have similar energy storage mechanism as LIBs,but existing LIB anode electrode materials are not suitable for SIB/PIB systems due to the larger ionic radius of Na+/K+.Therefore,developing high-performance anode electrode materials is crucial for the commercial application of SIBs/PIBs.Bi/Sb-based materials have the advantages of high theoretical Na/K storage capacity and lower reaction potential,making them suitable as anode electrode materials for SIBs/PIBs.However,Bi/Sb-based materials undergo significant volume changes during the Na/K insertion and extraction processes,which can cause active material pulverization and detachment from the current collector,leading to a decline in electrochemical performance.In this thesis,a series of Bi/Sb-based anode materials were prepared using composition and structure design,and methods such as nanoporous structure design and carbon composites.Their Na/K storage behavior and mechanism were systematically studied through electrochemical tests and operando XRD.(1)Mg-In-Bi precursors were prepared by rapid solidification and further dealloying treatment,successfully obtaining np-InBi alloys with a three-dimensional ligament-channel structure.The np-InBi electrode showed a high initial specific capacity of 474.6 mAh g-1(SIBs)and 458.8 mAh g-1(PIBs)in ester-based electrolytes,and excellent cycling stability in etherbased electrolytes.The Na/K storage mechanism of np-InBi as anode electrodes for SIBs/PIBs were revealed using operando XRD.During the cycling process,the phase evolution was reversible alloying-dealloying process,i.e.,InBi+Bi?NaBi+In+Na15IIn27?Na3Bi+Na15In27(SIBs)and InBi+Bi? KBi2+Bi3In5?K3Bi+K8In11(PIBs).(2)The np-BiSb alloys were prepared by dealloying the Al-Bi-Sb precursors,which were synthesized by rapid solidification.The phase evolution mechanism during the dealloying process was investigated using operando XRD.The SEM results showed that the Bi/Sb composition ratio could effectively tune the ligament size and microstructure morphology of np-BiSb.The np-BiSb possesses a three-dimensional bicontinuous ligament-channel structure,which not only enhances the contact area between the electrode and electrolyte and the rate of ion/electron transport,but also alleviates the volume change caused by Na insertion and extraction during charge and discharge processes.Among the three electrode compositions,npBi25Sb75 electrode exhibited the highest initial specific capacity,better cycling stability(340.1 mAh g-1 after 200 cycles),and rate performance(261.1 mAh g-1 reversible capacity at 2 A g-1).In addition,the phase evolution behavior of np-BiSb electrode during cycling was elucidated using operando XRD,revealing the Na storage mechanism.(3)To develop cost-effective and facilely prepared anode materials for SIBs,Fe2.55Sb2/C composites were prepared by solid phase reaction and used as precursors for selective corrosion to obtain Sb/C composites.Both electrodes exhibited excellent cyclic stability because of the carbon matrix served to alleviate volume expansion and improve electron conductivity,with reversible specific capacities of 120.8 and 186.1 mAh g-1 after 1000 cycles at a current density of 1 A g-1.The Sb/C material also provided stable Na storage sites due to its abundant nanoscale pores,defects,and disordered structures.Kinetic studies revealed the pseudocapacitive behavior of the Sb/C electrode,which greatly enhanced the rate performance,maintaining a reversible capacity of 186.1 mAh g-1 at a current density of 10 A g-1. |
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