Regulation Of Sodium Storage Performance And Mechanism Exploration In V₄C₃T_x MXene-Based Bimetallic Compounds

In the context of the ongoing global energy transition and climate change,there is an urgent need to explore efficient and sustainable solutions for energy storage.Sodium Ion Batteries（SIBs）,with their abundant resources,low cost,and environmental friendliness,are considered strong contenders for the next generation of energy storage systems.Sodium（Na）,being one of the most abundant metallic elements on Earth,not only possesses a high theoretical specific capacity and good electrochemical stability but also renders sodium ion batteries particularly attractive for large-scale energy storage applications.However,practical implementation of sodium ion batteries still faces several challenges,primarily related to enhancing energy density and extending cycle life.These challenges arise from the lower diffusion efficiency caused by larger ionic radius of sodium ions as well as structural instability during insertion and extraction processes in electrode materials.In response to these issues,continuous exploration of new efficient electrode materials remains crucial.In this research field,bimetallic compounds and V₄C₃T_x MXene materials have gained significant attention due to their distinctive physicochemical properties.By combining two metal elements,bimetallic compounds can modulate the electronic structure and catalytic activity,thereby optimizing the electrochemical performance of electrode materials.Particularly in sodium-ion batteries,bimetallic compounds are anticipated to substantially enhance charging and discharging efficiency as well as cycle stability by providing more active sites and facilitating electron/ion transport.As a novel two-dimensional material,V₄C₃T_x MXene offers new possibilities for developing electrode materials for sodium-ion batteries with its excellent conductivity,tunable surface functionalization,and unique layered structure.V₄C₃T_x MXene not only serves as a highly conductive substrate to facilitate rapid electron transport but also interacts with sodium ions through its surface functional groups,thus improving the kinetics of sodium insertion/extraction and enhancing battery performance.This paper combines bimetallic compounds with V₄C₃T_x MXene using a composite material strategy to optimize multiple aspects of sodium-ion battery performance.This approach leverages both the high activity of bimetallic compounds and the high conductivity of MXene while capitalizing on their synergistic effect to further improve structural stability and electrochemical activity of electrode materials.For instance,bimetallic compounds act as active centers promoting rapid sodium insertion while MXene layers provide a fast pathway for electron transport that enhances the contact interface between the electrode and electrolyte,collectively improving charge-discharge performance and cycle stability in sodium-ion batteries.The main achievements include:（1）The design and preparation of sodium-ion battery anode material using a multi-interface combination strategy of C@FCSe@V₄C₃.By combining FCSe（Fe Se₂/Co Se₂）bimetallic selenide nanoparticles with V₄C₃T_x MXene nanosheets,a composite anode material is constructed to enhance the performance of sodium-ion batteries through interface optimization.The FCSe nanoparticles are uniformly grown on the surface of MXene using hydrothermal treatment,chemical vapor deposition,and subsequent heat treatment processes,forming the C@FCSe@V₄C₃ composite material.Detailed analysis of the microstructure and surface properties of C@FCSe@V₄C₃ composite material is conducted through various physical characterization methods,and its sodium-ion storage performance is evaluated through electrochemical tests.The results show that the C@FCSe@V₄C₃ anode material exhibits excellent electrochemical performance in sodium-ion batteries,including high specific capacity,outstanding cycle stability,and good rate performance,attributed to its unique multi-interface combination strategy and effective electron/ion transport channels.（2）The design and preparation of a Capacity-Enhanced Battery（CEB）using a Bi Zn S（Bi₂S₃@Zn S）composite material combined on ultra-large MXene layers.The carefully designed C@Bi Zn S@V₄C₃ material shows a sophisticated dual mechanism response to different current densities,harmonizing the storage and release of sodium ions electrochemically.At lower current densities,the battery behavior is significant,dominated by complex sodium ion alloying and conversion reactions within the Bi Zn S framework,ensuring strong energy retention.As the current density surges,the material’s energy storage mechanism transitions rapidly,displaying distinct supercapacitor characteristics:active sites on MXene and Bi Zn S rapidly adsorb ions,thereby promoting instantaneous energy output.This dual-function mechanism allows the C@Bi Zn S@V₄C₃ composite material to possess an impressive specific capacity of270.4 m Ah g^-1 even under demanding 100 Ag^-1 current density while showing extraordinary endurance over 10,000 cycles at 20 Ag^-1,showcasing unparalleled electrochemical stability and rate capability.This finding elevates the CEB concept to a higher level,indicating the significant research potential of ultra-large MXene composite materials in advanced energy storage systems.（3）The design and preparation of a C@NCS@V₄C₃T_x mixture as an efficient anode material for Sodium-Ion Batteries（SIBs）.Through a synergistic modification strategy of isotope substitution and two-dimensional conductive framework support,a novel(Co_0.5Ni_0.5)S₂@V₄C₃T_x（C@NCS@V₄C₃T_x）anode material with carbon layer coating is successfully prepared.The C@NCS@V₄C₃T_x mixture exhibits extremely high reversible specific capacity and satisfactory long-term cycle stability,thanks to the high conductivity and robustness of the two-dimensional framework V₄C₃T_x MXene.The sodium-ion storage mechanism,particularly the synergistic effect between the high capacity of bimetallic TMS and the metallic conductivity and outstanding stability of V₄C₃T_x MXene,plays a crucial role in achieving high performance.Therefore,the assembled C@NCS@V₄C₃T_x//Na₃V₂（PO₄）₃ full battery displays excellent electrochemical performance,serving as a portable integrated unit for self-powered systems.（4）The design and exploration of the regulation mechanism of exceptional performance of sodium-ion battery（SIBs）bimetallic electrodes through allotrope substitution and d-electron distribution control.Successfully designing and fabricating Fe_xCo_1-xS₂ bimetallic sulfide electrode materials,and through the fine-tuning of tail d-electron distribution,significant alleviation of challenges associated with heterogeneous structures in SIB anodes,such as uneven sodium storage and internal binding instability,was achieved.Especially leveraging the unique capabilities of V₄C₃-MXene as a support limited the growth of bimetallic sulfides,thus enhancing lattice integrity and electrochemical performance.Through targeted substitution strategies,a significant improvement in SIB anode performance was realized,where C@Fe_0.25Co_0.75S₂@V₄C₃ not only showed the best sodium storage performance and cycle stability but also achieved an impressive specific capacity of 751 m Ah g^-1 at a current density of 0.1 Ag^-1.