Three-Dimensional Structure And Sodium Storage Mechanism Of Fe₃S₄ Anode Material

As one of the most promising substitutes for lithium-ion batteries,sodium-ion batteries have attracted a lot of research interest due to their rich and cheap sodium resources.They are committed to developing advanced anode materials to improve the battery performance of sodium-ion batteries.However,despite similar principles between SIB and LIB,many challenges are encountered in the search for suitable electrode materials for SIBs.In particular,considering that most battery anode materials undergo significant volume expansion,slow diffusion of sodium ions,and electron conduction path loss during electrochemical cycling,developing an effective strategy to inhibit microstructural changes and performance degradation for sodium ion batteries is critical.In recent years,microstructure design such as porous or three-dimensional nanostructures has proven to be an effective strategy to address these challenges.By creating a larger surface area,the 3D microstructure allows more electrolyte to enter,shortens the sodium ion diffusion path,and achieves rapid sodium kinetics.In addition,the three-dimensional microstructure can also accommodate volume expansion or contraction and reduce internal strain in multiple directions,which keeps the overall microstructure intact during long-term cycling.Although the microstructure design can buffer volume changes and improve ion transport,its contribution to improving electron conductivity is limited.Considering that the above individual strategies may not solve these problems,it is very necessary to propose a simple and effective strategy to solve the above challenges at the same time.In this work,taking advantages of its abundant resources and highly theoretical capacity,Fe₃S₄ is proposed as a model material for SIBs anode to investigate the synergistic strategy to improve sodium ion storage performance.In particular,Fe₃S₄ can be expected to present excellent cyclic stability based on its inherent excellent electronic conductivity,which can ensure the continuous electronic conductivity pathway even volume change occurs.Firstly,the 3D flower-like Fe₃S₄ hierarchitectures composed of nanosheets was synthesized by one-step hydrothermal method,and the growth mechanism of 3D flower-like Fe₃S₄ was studied by controlling the reaction time.The 3D flower-like Fe₃S₄ was used as the anode of sodium ion batteries showed an ultra-high reversible capacity of 762mA h g^-1,close to the theoretical value,and an impressive first coulombic efficiency of up to 96.3%.In addition,it had significant long-cycle stability with a specific capacity of442 mA h g^-1 after 500 cycles at a large magnification of 400 Ag^-1.Beyond the materials synthesis and performance evaluation,we paid more attention on understanding the underlying mechanism for the excellent electrochemical performance by the coupling surface chemistry,3D microstructure and ion/electronic transport pathways.By Constant Current Charge and Discharge Test,Electrochemical impedance spectroscopy?EIS?,Transmission Electron Microscopy?TEM?,Scanning Electron Microscopy?SEM?,X-ray Photoelectron Spectroscopy?XPS?,Transmssion X-ray microscopy?TXM?,it was analyzed and verified that the ether-based electrolyte forms a thin and stable SEI layer to adjust the surface chemical stability.At the same time,combined with the high electron conductivity inherent in Fe₃S₄,the 3D microstructure created a continuous ion/electron pathway that contributed to excellent coulombic efficiency and electrochemical cycle stability.Believe our insights into the 3D nanostructure design and the methodology can promote the progress of developing advanced anode materials for SIBs.