The Synthesis,Modification And Electrochemical Performance Of Vanadate Lithium Electrode Materials

Vanadium oxides are considered as promising cathode materials for lithium-ion batteries, due to their attractive properties, such as high capacity, low cost. Of these, LiV3O8and LiV2O5are the most studied ones. However, both materials suffer from certain structural instability during the cycling, thus resulting in serious capacity fading. For this reason, AlF3coating was used to modify the electrochemical properties of LiV3O8. In addition, considering that the synthesis method strongly influences the electrochemical performance of vanadium oxides, two kinds of vanadium sources with different morphologies was employed to fabricate nanostructured LiV2O5by two-step method with the aim of improving its cycling performance, respectively. The main contents and results are summarized as follows:LiV3O8flakes were firstly synthesized by PEG-assisted two-step method, then AlF3coated LiV3O8composites were prepared by chemical precipitation approach. It can be seen clearly that the AlF3was successfully coated on the surface of the LiV3O8by means of SEM and TEM images. XRD results revealed that a little structural change of the cathode material appeared. The electrochemical properties of AlF3/LiV3O8composite were systematically investigated in comparison with the bare one. Note that the A1F3coating can greatly enhance the cycle performance with a specific discharge capacity of204.6mAh g-1remaining after50cycles at150mA g-1, and the corresponding capacity retention is up to93.6%, while that of the bare one is only61%.γ-LiV2O5nanoflakes were synthesized by two-step method using ammonium divanadate nanoflake as precursor. The morphology of as-prepared materials was characterized by SEM and AFM, indicating that the thickness of nanoflakes was about2～4nm and the width was60～350nm. CV analysis demonstrated good reversible lithium insertion/de-insertion ability. The electrode process kinetics of γ-LiV2O5was studied by EIS. The charge transfer resistance (Rct) had a minimum at2.77V. The Li-ion diffusion coefficients was calculated to be10-9cm2·s-1. The nanoflakes delivered an initial specific discharge capacity of242.4mAh g-1at50mA g-1and retained the discharge capacity of145.7mAh·g-1after50cycles.One-dimension γ-LiV2O5nanorods were synthesized using VO2(B) nanorods as precursor. The as-prepared material is characterized by XRD、 XPS、FT-IR、TEM, CV and charge-discharge cycling test. TEM results show that the LiV2O5nanorods are90～250nm in diameter. The nanorods deliver a maximum specific discharge capacity of284.3mAh g-1at15mA g-1and it maintains270.2mAh g-1at the15th cycle. Good rate capability is also observed, with the discharge capacity of250.1and202.6mAh g-1at50and300mA g-1, respectively. The capacity retention was84.2%at300mA g-1over50cycles. Electrochemical performance of as-prepared material here is much better than that in reported literature. The Li+diffusion coefficient of LiV2O5was calculated to be10-10～10-9cm2s-1.