Controllable Construction Of Ternary Fe-based Functionalized Nanomaterials For Energy Storage Applications

The development of efficient,advanced and matched energy storage technologies is imperative for better use of new clean energies,such as solar,wind or tidal power,etc.Among them,Ni/Fe-Biaqueous batteries are competitive in energy storage devices due to their low cost,high safety and large power density.However,their further progress has been impeded by the low specific capacity,short-term cyclic stability and other problems.In contrast,no-aqueous Li-S batteries possess promising application prospects in electrochemical energy-storage applications thanks to their ultra-high theoretical capacity,energy density,low cost and environmental friendliness.Nevertheless,they still face challenges coming from S cathode,like poor electrical conductivity,insufficient actives utilization and intractable polysulfde dissolution in organic electrolytes.In this regard,we plan to design and develop ternary Fe-based nanomaterials(BiFeO₃,NiFe₂O₄)with specific structures,compositions and fuctionality.Due to their unique merits,we aim to solve the problems of aqueous/no-aqueous batteries aforementioned.For Ni/Fe-Bibattery systerms,the BiFeO₃cathode owns attractive advantages of low cost,rich valence states,high theoretical specific capacity and wide operating voltage window.As for no-aqueous Li-S batteries,the NiFe₂O₄ addtives possess high conductivity,large tap density and great Li₂S_nadsorption/catalysis abilities.Based on above considerations,we herein have designed and prepared two kinds of functionalized ternary Fe-based nanomaterials.They are used as active substances or nanocatalysts to improve corresponding electrochemical properties of distinct battery systerms.In addition,their evolution process and electrochemical behaviors are further studied/analyzed.Meanwhile,their potential in practical energy-storage applications has also been explored.The main research contents involve:1.Synthesis of BiFeO₃@carbon nanorods as anodes of Ni/Fe-Biaqueous batteries:BiFeO₃ nanorod precursors are initially made by a simple hydrothermal method.Then,BiFeO₃@carbon nanorods are prepared by in-situ dopamine polymerization and high-temperature calcination treatments.During the synthesis of BiFeO₃ nanorods,the Fe element is successfully introduced into Bi-based anode systerms,realizing the combination of Fe-and Bi-related advantages.On one hand,both Biand Fe components in the ternary composites can exert redox reaction behaviors and make considerable capacity contributions,enhancing the specific capacity of overall cathodes.On the other hand,the yielded strong electrovalent interactions between Biand Fe(in BiFeO_x)could delay bismuthic reduction reactions to an upper temperature over 500°C,making it possible to produce carbon-encapsulated BiFeO_x nanomaterials.Attributing to their advantageous combination/complementation,admirable carbon encapsulation/protection configurations,and fast-reacting kinetics,the as-made BiFeO₃@carbon nanorods can showcase superior anodic performances to traditional bismuthic anodes,including excellent electrochemical activity(both Bi-and Fe-based components act as faradaic redox reaction sites),excellent rate capabilities,and impressive capacity retention(⁸3.4%after 2000 cycles).We furthermore probe the anodic phase changes/capacityfading mechanism during a long-term cyclic period.2.Synthesis of NiFe₂O₄ quantum dots as catalyst for cathodes of Li-S batteries:NiFe₂O₄quantum dots are primarily preparaed by hydrothermal methods.And then they are introduced into S cathode systems as afordable additive substitutes to cut down carbon usage,avoiding the excessive electrolyte consumption and guaranteeing specifc energy parameters.The smart use of NiFe₂O₄ QDs substitutes entails a fact that all involved carbon content in cathodes can be largely decreased to an extremely low level of 5%,thus forming more dense/compact electrodes rather than ones full of internal pores.In addition,NiFe₂O₄quantum dots additives own excellent chemisorption interactions with soluble polysulfde molecules and prominent catalytic properties for Li₂S_n phase conversions and meantime boost the charge-transfer capability/redox kinetics of entire cathode systems.As a consequence,the designed S@CB(?)QDs hybrid cathodes demonstrate outstanding rate behaviors and quite stable cyclic performance in LiNO₃-free electrolytes.