Preparation,Characterization And Sodium Storage Properties Of Titanium Phosphate-Based Anode Materials

Aqueous sodium-ion batteries（ASIBs）have attracted widespread attention due to their obvious advantages of low cost,high safety,and high ionic conductivity,and have become a new type of green energy storage device that is developing rapidly.NASICON Na Ti₂（PO₄）₃（NTP）is one of the most competitive anode materials for ASIBs because of its unique three-dimensional open frame structure,large theoretical capacity,and good chemical stability.However,NTP has low electronic conductivity;At the same time,the high reactivity and solubility characteristics of water lead to serious side reactions such as oxygen reduction at the electrode-electrolyte interface and dissolution of the active material.These problems are important factors that limit the practical application of NTP-based ASIBs.To better solve the above problems,this paper proposes a co-regulation strategy for electrode materials and electrolytes:NTP anode materials with high electronic conductivity and stable structure are designed and prepared;And the components and parameters in the water-electrolyte are precisely regulated.Finally,the modified NTP exhibits high rate characteristics and excellent cycling performance in the optimized electrolyte and successfully constructs an aqueous sodium-ion device with high energy density and long cycle life of NTP based.The specific research results are as follows:（1）A porous single crystal NTP（expressed as NTP@C）micro-frame material coated with a conductive carbon nanolayer was successfully prepared by a simple and controllable polymer-stabilized droplet template method and subsequent annealing treatment,which has significantly improved electronic conductivity and structural stability.By further adjusting the dissolved oxygen content and p H value in Na₂SO₄ water-electrolyte,the side reactions can be effectively reduced,and the reversible ability and cyclic stability of ASIBs under high-rate conditions can be significantly enhanced.The results show that the NTP@C anode exhibits high rate capability and significant long-term electrochemical stability in the optimized Na₂SO₄ water-electrolyte with p H=8.0 and N₂ purge deoxygenation.In addition,the assembled NTP@C//Na_0.44Mn O₂Aqueous sodium-ion full battery has a high energy density of about 40.0 Wh kg^-1 and excellent cycle stability.（2）Using Ti₃C₂T_x MXene as the titanium source matrix,a single crystal carbon-coated NTP（expressed as S-NTP@C）cubic material was prepared by simple hydrothermal method and subsequent annealing process,and the electronic conductivity and ion mobility was significantly improved,and excellent electrochemical energy storage was realized.In order to reduce the oxygen content and OH^-diffusion rate in the aqueous electrolyte,and alleviate the occurrence of related side reactions.A Na₂SO₄-Si O₂ hydrogel electrolyte with a unique three-dimensional network structure was prepared,and the introduced silica molecules had interaction forces with water molecules,and finally,Si-O-H-O-H bonds were formed.Na₂SO₄-Si O₂ hydrogel electrolyte effectively limited water activity and inhibited the dissolution of electrode material.In addition,the reduction of dissolved oxygen content can provide a stable chemical reaction environment,which is of great significance for protecting the electrode material and reducing the deterioration of battery performance caused by irreversible side reactions between the electrode material and water and oxygen.The results show that the S-NTP@C anode has a high reversible capacity,excellent rate performance,and long cycle life in Na₂SO₄-Si O₂ hydrogel electrolyte.The assembled S-NTP@C//AC quasi-solid aqueous sodium-ion capacitors perform well under Na₂SO₄-Si O₂ hydrogel electrolyte,providing a reversible specific capacity of about 76.6 m Ah g^-1 at a high rate of 10 C,and an ultra-high capacity retention rate of 99.1%after 18,000 uninterrupted cycles.