| Lithium-ion batteries have the advantages of higher specific energy,lighter weight,higher voltage,and longer cycle life,lithium-ion batteries have been rapidly developed and widely used in portable electronic devices and electric vehicles.However,with the continuous development of large-scale energy storage systems,potential problems such as high lithium-ion battery manufacturing costs and limited lithium resource storage will limit the large-scale development of lithium-ion batteries.Sodium and lithium are the same main group elements,have similar chemical and physical properties,and the sodium resources are rich in global reserves,evenly distributed,and have lower development costs.Therefore,the sodium ion battery may be considered as a future energy storage system to replace the lithium ion battery.However,compared with existing mature technologies for lithium-ion battery research,the study of sodium-ion batteries is still not mature.The sodium ion battery is an integrated system composed of several parts,and the negative electrode material is one of the most important components of the sodium ion battery,which plays a crucial role in the electrochemical performance of the sodium ion battery.However,the negative electrode material of sodium ion batteries currently has the following problems:The larger ion radius of sodium ions makes it difficult to perform deintercalation in the electrode material,and the negative electrode material easily undergoes a large volume expansion during the electrochemical reaction and affects the cycle stability of sodium ion battery,the negative electrode material has poor electrical conductivity and makes it difficult to maintain a high capacity.In this paper,NaTi2(PO4)3 was synthesized by hydrothermal method and used as a precursor.Then,NaTi2(PO4)3 was coated with carbon by two different carbon sources and used as a negative electrode material for sodium ion batteries,to study their electrochemical performance.The research content is mainly divided into the following aspects:(1)In the second chapter of the paper,we used hydrothermal method to prepare NaTi2(PO4)3,then used oleic acid as carbon source,NaTi2(PO4)3@C composite material was obatained by mixing NaTi2(PO4)3 with oleic acid and annealing.The structure of NaTi2(PO4)3 and NaTi2(PO4)3@C porous cubes and the electrochemical properties of the negative electrode materials of sodium ion batteries were further analyzed.The test results show that the NaTi2(PO4)3 cubes have a diameter of about 80 nm,and their morphology is uniform.After carbon coating,their dispersibility and morphology are not changed,and the surface of carbon thickness is about 3 nm.The performance test results show that with the carbon coating of NaTi2(PO4)3,its specific capacity,rate performance and cycle stability are improved,and the electrochemical performance is good.(2)In the third chapter of the paper,we used the same method to synthesize NaTi2(PO4)3.Unlike the previous work,we used oleic acid and zinc acetate for grinding,high-temperature treatment and hydrochloric acid post-treatment to prepare porous carbon,and the porous carbon material was mixed with NaTi2(PO4)3 and annealed at high temperature to obtain a NaTi2(PO4)3/C porous cube.We characterized the morphologies and structures of the synthesized carbon materials,NaTi2(PO4)3 and NaTi2(PO4)3/C by SEM,TEM and XRD.The electrochemical test results show that the carbon-coated NaTi2(PO4)3/C composite materials can improve the rate performance,specific capacity and cycle stability of a single NaTi2(PO4)3 anode material. |
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