Preparation And Electrochemical Properties Of Sodium Titanate Flexible Electrode Materials

Sodium ion batteries have received extensive attention in recent years due to the richness and low cost of sodium sources.It is still a big challenge to develop anode materials suitable for sodium ion batteries with high energy density and good cycle performance although some cathode materials with good electrochemical properties have been proposed.Among most of cathode materials,Na₂Ti₃O₇ has the most development prospect because of its high specific capacity and low charge-discharge voltage platform.However,the structural instability and low conductivity of Na₂Ti₃O₇limit its further practical application.Due to the large specific surface area of the nanostructured Na₂Ti₃O₇,the unique material structure compensates for its shortcomings of poor conductivity and small sodium ion diffusion coefficient.However,it still needs to be modified to improve its electrochemical performance.In this paper,the hydrothermal method is used to explore the reaction temperature of the ultra-long Na₂Ti₃O₇nanobelts,and then Na₂Ti₃O₇/RGO composite electrode film can be prepared by the sheet is modified by inserting RGO into the Na₂Ti₃O₇ film.Then,using foam nickel as a matrix,Na₂Ti₃O₇ is grown on its surface in situ to form a Na₂Ti₃O₇/Ni composite electrode material,and finally through the relevant physical characterization and electrochemical performance tests,the mainresults can be obtained as follows:?1?Pure Na₂Ti₃O₇ nanobelt film was synthesized by hydrothermal method.The relationship between temperature and the morphology of Na₂Ti₃O₇was explored.The results show that the optimal reacted temperature and time are 220?and 24 h,respectively.Under SEM characterization,it was observed that the prepared ultra-long Na₂Ti₃O₇nanoribbons had a width of about 150 nm and a length of tens of microns.It has a porous network structure and regular stripsbetween the nanobelts.The Na₂Ti₃O₇nanobelt flexible self-supporting electrode material can be obtained by a self-assembly process.The electrochemical test results show that under a voltage range of 0.01-2.5 V and a current density of 100 m A·g^-1.The initial specific discharge capacityis 143.27 m Ah·g^-1,and the specific discharge capacity is only 42.43 m Ah·g^-1after 100 cycles.The results show that phase Na₂Ti₃O₇nanobelt film have poor cycle performance and multiplier performance due to their poor conductivity.?2?The Na₂Ti₃O₇/RGO composite electrode film was prepared by hydrothermal method supplemented by vacuum suction filtration method.The effect of different proportions of graphene content on the electrochemical performance of the sample was studied.The SEM results revealed that the morphology of the Na₂Ti₃O₇ nanobelts did not be changed during the prepared process,and the RGO sheet was well dispersed into the Na₂Ti₃O₇ nanobelt film.The electrochemical performance results show that the composite material with a graphene ratio of 25%has the best electrochemical performance in the range of 100 m A·g^-1 and 0.01-2.5 V.Compared with Na₂Ti₃O₇ nanobelt film,its first discharge specific capacity increased from143.27 m Ah·g^-1 to 374.33 m Ah·g^-1 and the discharge specific capacity increased from42.43 m Ah·g^-1 to 123.52 m Ah·g^-1 after 100 cycles,which indicates that the electrochemical performance of the composite material was significantly improved.It was found that the charge transfer impedance of the composite material was reduced to about 590?through AC impedance test analysis,indicating that the RGOs improve the electronic conductivity and charge migration rate.So that it has an excellent electrochemical performance.?3?Na₂Ti₃O₇/Ni composite electrode material was prepared by hydrothermal method.It can be seen from the SEM image that the Na₂Ti₃O₇ nanobelts grow well on the surface of the nickel foam,its length is about 20 micron,which is shorter than the pure phase Na₂Ti₃O₇nanobelts.From its electrochemical results,it is found that the discharge specific capacities at the second and 100 th cycles are 185 m Ah·g^-1 and 114m Ah·g^-1under a current density of 100 m A·g^-1 and a voltage window of 0.01-2.5 V,respectively.Its capacity retention rate is 62%.It is observed that the charge-discharge potential platform corresponds well to the potential of CV curve redox peak.The results from the cycle performance and rate performance show that the composite material has a cycle stability.The introduction of foamed nickel played a crucial role to improve the electrochemical performance of Na₂Ti₃O₇.