| As an anode material for lithium ion batteries,NaLiTi3O7 has attracted the attention of researchers because of its stable structure,low voltage platform?1.25 V?and high specific capacity(281.6 mA·h·g-1).In order to study the effect of the structure of the material on its properties.In this paper,NaLiTi3O7 materials with different features were synthesized and the relationship between the structure and electrochemical properties of the materials were investigated.Firstly,the pure phase NaLiTi3O7 material was obtained by simple solid phase method using titanium dioxide with different morphology,and the effect of different morphology of titanium source on the morphology and electrochemical properties of the product was studied.The electrochemical test shows that the NaLiTi3O7 material with the morphology of the nanoparticles has the best electrochemical performance.The results of EIS show that the lithium ion diffusion coefficient of NLTO-S-3 is the largest,which is2.21×10-1616 cm2·s-1.As the size of the material is small and the migration path of lithium ion is short,the sample NLTO-S-3 of nanoparticles has relatively high specific capacity when charging and discharging at different current density.In particular,the specific capacity of 75.3 mA·h·g-1 can be reached under the large current density of 2.8 A·g-1.It is difficult to maintain the same morphology as the titanium source because of the simple solid phase method.In order to solve this problem,a one-step solvothermal synthesis method is used directly.Ammonium hydrogen carbonate was used as a soft template.The effects of calcination temperature and ammonium hydrogen carbonate dosage on the morphology and electrochemical properties of the material were studied respectively.The results show that the microspheres,which is composed of particles with particle size of about 200 nm and the diameter is about 23?m,can be obtained under suitable calcination temperature and the amount of ammonium hydrogen carbonate.And it exhibits good cycling stability and rate performance.The reversible specific capacity of the sample under the current density of 50,140,280,560,1400 and 2800 mA·g-1 are242.8,195.2,170.6,149.6,123.2 and 99.6 mA·h·g-1,respectively.The sample can still maintain 93 mA·h·g-1 after 500 cycles at the high current density of 2.8 A·g-1.The test results of EIS also proved that the materials with porous graded microspheres exhibited excellent electrochemical properties.In order to further improve the electrochemical properties of the materials,a simple non template solvothermal method was used to prepare a NaLi Ti3O7 material with two-dimensional flakes structure.The structural characterization and electrochemical performance of the samples showed that the sample of NLTO-2 had the best electrochemical performance,which is due to the two-dimensional nano-flakes has a shorter lithium ion and electron transport distance in the vertical plane,and the larger surface area.The reversible specific capacity of the sample under the current density of50,140,280,560,1400 and 2800 mA·g-1 are 276.9,229,206.1,193.2,163.3 and 139.4mA·h·g-1,respectively.Under the high current density of 2.8 A·g-1,the specific capacity of 104 mA·h·g-1 can still be reached after 1000 cycles.The results of EIS show that the impedance of the sample of NLTO-2 is the smallest,and the lithium ion diffusion coefficient is 6.26×10-1414 cm2·s-1,higher than the other three samples.The above results further indicate that the design and regulation of the structure and morphology of nanomaterials by appropriate strategies will effectively improve the electrochemical performance of the materials. |
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