Preparation Of Nano-single Crystal NaFeO₂ Cathode Material And Research On Its Sodium Storage Performance

Due to the abundant reserves and wide sources of sodium on the earth,sodium-ion batteries are considered to be one of the sustainable energy storage technologies that can replace lithium-ion batteries for large-scale energy storage.As an important component of the sodium ion battery,the cathode material determines the pros and cons of its electrochemical performance.Layered sodium-containing transition metal oxides have good potential application prospects for sodium ion batteries because of their large theoretical specific capacity,high working voltage,and good cycle stability.Among the layered sodium-containing transition metal oxides,O3-NaFeO₂has the advantages of abundant raw materials,non-toxicity,and low cost,and is considered to be a promising cathode material.However,the reaction conditions for preparing O3-NaFeO₂by the solid-phase sintering method are demanding,requiring the use of expensive Na₂O₂as the sodium source,and the use of inert gas for protection during the sintering.In addition,the obtained products are often accompanied by the formation of?-NaFeO₂with no electrochemical activity.In this thesis,the single crystal O3-NaFeO₂nanoflakes have been synthesized via a facile solvothermal route without using Na₂O₂as sodium source.Through the solvothermal treatment,the inactive a-Fe₂O₃can be converted into active?-Fe₂O₃first and subsequently into the single crystal NaFeO₂nanoflakes via Na⁺/Fe³⁺topochemical ion exchange reaction.A thin layer of carbon is further coated on NaFeO₂nanoflakes to enhance its electrode kinetics and structural stability.The carbon coated NaFeO₂cathode delivers a high reversible specific capacity of 89.6 m Ah g-¹at 0.1 C and exhibits 87.3%capacity retention after 100 cycles at 0.1C,well maintaining the layered O3-structure.By using hard carbon as anode,a carbon coated NaFeO₂//hard carbon full cell is successfully constructed,exhibiting good cyclability with81.9%capacity retention after 100 cycles.The present work provides a novel synthesis strategy for developing O3-NaFeO₂-based cathode for sustainable sodium-ion batteries.