Since Whittingham et al. first reported the reversible electrochemical performance of lithium ions intercalated into V2O5 structure in 1976, V2O5 has been used as a cathode material for rechargeable lithium-ion batteries due to its low cost, easy synthesis and high energy density. Extensive research. Vanadium in V2O5 has a valence of +5, while the stable low valence state of vanadium is +2, so the transfer of 3 electrons can theoretically be achieved. The transfer of two electrons can generally be achieved even in the case of limited voltage range. Compared with LiCoO2, LiFePO4, and LiMn2O4, which can only achieve one or less electron transfer, V2O5 has a higher theoretical specific capacity, so it has become a research hotspot. However, during the deep charge-discharge process of Li-ion batteries, the defects of V2O5, such as poor structural stability and low electronic conductivity, severely limit its application in Li-ion batteries. In order to improve the electrochemical performance of V2O5, the current research focus focuses on the preparation of V2O5 nanomaterials with different morphologies. The electrolyte of this type of material can be well diffused into the material, forming more active sites for electrochemical reaction, shortening the diffusion path of lithium ions, thereby realizing the full performance of electrode materials at high rates.
In view of the outstanding performance of V2O5 nanomaterials with different morphologies in improving their electrochemical performance, we have fabricated one-dimensional V2O5 nanomaterials with controllable structures by using electrospinning technique combined with the change of calcination temperature. The prepared V2O5 nanomaterials with different morphologies were used as cathode materials to assemble a simulated battery, the charge-discharge cycle performance and cyclic voltammetry curves were tested, and the charge-discharge of V2O5 nanomaterials with different morphologies as cathode materials were discussed. It is found that the morphology of V2O5 nanofibers has a great influence on its charge-discharge performance.
1. Preparation method of one-dimensional V2O5 cathode material
(1) Synthesis of vanadium acetylacetonate
The synthesis of vanadium acetylacetonate refers to the method reported in the literature. The specific experimental process is as follows: Weigh 5.46g of commercial V2O5 powder and ultrasonically disperse it in 60mL of acetylacetone. Under vigorous stirring, the solution is heated to reflux. After the reaction for 30h, the solution is cooled to room temperature, filtered, and washed with ethanol for 3 times. Store dry for later use.
(2) Preparation of one-dimensional V2O5 cathode material
A certain mass of polyvinylpyrrolidone was weighed, dissolved in N,N-dimethylformamide, and stirred at room temperature for 12 h to prepare a viscous solution with a mass fraction of 17%. Take 3 g of the prepared viscous solution, add 0.3978 g of vanadium acetylacetonate prepared in the above process, and stir at room temperature for 12 h.
The above-mentioned transparent and uniform spinning solution is loaded into a syringe with a stainless steel flattened needle, the syringe with spinning solution is installed on an electrospinning device, and the electrospinning parameters are set to prepare non-woven fibers by electrospinning. film. The specific spinning parameters are as follows: the electrostatic voltage applied between the spinneret and the receiving plate is 15kV, the vertical distance between the spinneret and the receiving plate is 12cm, the advancing speed of the syringe pump is set to 1.0mL/h, and the Foil-covered flat-panel receiver.
The prepared non-woven film was placed in a tube furnace, calcined at a heating rate of 1 °C/min for 12 h at different temperatures in an air atmosphere, and then cooled to room temperature naturally, and the samples were taken out for characterization and performance testing. .
2. Characterization of one-dimensional V2O5 cathode materials
The morphology of the samples was analyzed by FEITacnai G2 transmission electron microscope and HITACHIS4800 field emission scanning electron microscope. The structure of the material was tested with a German BrukerD8 X-ray diffractometer and CuKα rays (λ=1.5406Å; 1Å=10-10m, the same below). The thermal analysis curve of the sample was tested in the air atmosphere by using the STA449F3 thermogravimetric and differential thermal (TG/DSC) synchronous analyzer produced by the German NETZSCH company. The heating rate was 5 °C/min, and the cooling was a natural cooling process.
3. Electrochemical performance test of one-dimensional V2O5 cathode material
The active material, binder (polyvinylidene fluoride, PVDF) and conductive agent (acetylene black) are mixed in a mass ratio of 7:2:1, and N-methylpyrrolidone (NMP) is added and ground for a period of time, so that the mixture is in the grinding process. Mix well in the bowl. It was then coated on an aluminum foil, and then dried at 80°C for 8h. Electrode pieces with a diameter of 12 cm were formed using a punching machine and weighed. A 2025 button cell was assembled in a glove box, using a lithium sheet as the counter electrode and reference electrode, using a Celgard2400 separator, using LiPF6 (1mol/L)/EC:DMC (1:1, mass ratio) as the electrolytic liquid. Cyclic voltammetry and constant current charge-discharge tests were performed on the battery. The cyclic voltammetry test was performed with the VMP3 electrochemical workstation of Biologic Company, and the constant current charge-discharge test was performed with the charge-discharge instrument of Wuhan Blue Electric Company.