Preparation And Research Of Bifunctional Electrode Material Na_xMTi?PO₄?₃

With the energy shortage and environmental pollution becoming more and more serious,it's very important to develop and find new clean and sustainable energy sources.As a kind of green,environmental friendly,renewable,high electrochemical capacity,high energy density and good cycle performance,lithium-ion battery has attracted extensive attention.However,due to the high price of lithium resources and the earth resources are limited due to its low level of resources.To meet today energy needs,secondary batteries other than lithium-ion batteries,especially large-scale grid systems,must be considered.In recent years,due to the economy of lithium ion batteries and the availability of intercalated elements,the possibility of replacing lithium ion batteries has attracted more and more attention.As a feasible electrode for sodium ion battery,polyanionic electrode material has shown economic advantage,large capacity and long-term cycling ability.Although some aspects are still challenging,recent findings strongly support the feasibility of bifunctional electrode material;Na_xMTi?PO₄?₃ in the selection of water-based sodium ion batteries.Based on the research progress of polyanions in sodium ion batteries,Na₃MnTi?PO₄?₃bifunctional electrode materials were synthesized by sol-gel method.In the reaction process of Na₃MnTi?PO₄?₃,there are two redox pairs Mn²⁺/Mn³⁺and Ti³⁺/Ti⁴⁺,which can be used as both positive and negative electrode materials,that is,bi-functional electrode materials.In this paper,the addition of cetyltrimethylammonium?CTAB?bromide in the early synthesis process is used to form a smaller structure,which increases the specific surface area and is more favorable to the penetration of electrolyte.The electrochemical performance was improved.The materials of Na₂VTi?PO₄?₃ and Na₃MnTi?PO₄?₃ have similar chemical properties V⁴⁺/V³⁺and Ti³⁺/Ti⁴⁺two redox pairs,which can be represented by the general formula Na_xMti?PO₄?₃.In this paper,a flexible film with a fishing net structure is prepared by the electrostatic spinning technique,and the special fishing net structure is to increase the content of the active material.And the film can be directly made into an electrode without adding a binder and a conductive agent,which can greatly reduce the resistance of the battery and greatly help the improvement of the electrochemical performance.Through cyclic voltammetry,it was observed that there was a significant redox peak and the symmetry was good.Because of the rapid development of the medical technology,it is possible to use the body fluid of human body as the electrolyte,so this paper uses Na₂Vti?PO₄?₃ as the electrode to prepare the symmetrical sodium ion battery,and the original Na2SO4electrolyte is replaced with the NaCl electrolyte and the body fluid of the human body is simulated.And the electrochemical performance of the NaCl solution at different concentrations was tested.As the cell shell implanted in the human body is harmful to the human body and has high requirements for the volume of the battery,the silk fibroin hydrogel is prepared,the flexible film is made into a micro-electrode,and finally,the symmetrical sodium ion full cell is assembled,and the electrochemical test is carried out.The current density is 1 C to reach the capacity of 54.1 mAh·g^-1.After 800 cycles,the coulometric efficiency of the cell reached 100%and the capacity retention rate reached 74%.The possible application of the battery in a human body is demonstrated.