Study On The Preparation And Improved Electrochemical Performances Of LiV₃O₈ As Cathode Materials For Secondary Lithium Batteries

Due to the rapid development of science and technology, the electrochemical and energy have attracted more and more attention. As the future electrochemical energy, lithium-ion batteries are considered to be the ideal choice for the devices of the vehicles and energy storage power stations. The high energy density, low cost, high safety, layered LiV3O8 as one of battery materials have the most development potential. However, at the process of the charge/discharge, the destroy of the crystal structure and the dissolution of the materials which lead to the cycle stability to decrease is the bottleneck of the development. Based on this situation, with the fundament of maturely synthesizing the materials through the rheological phase method, we study the materials by the doping and coating. we have synthesized LiV3-xLaxO8 materials, LiV3-xNbxO8 materials, x wt. % Mg3(PO4)2 – LiV3O8 composites materials, x wt. % Ni3(PO4)2 –LiV3O8 composites, and the further characterization of the material and its electrochemical properties, the main contents are as follows:Firstly, the series of LiV3-xLaxO8 materials for different doping proportion were synthesized by a rheological phase method. Among these materials, LiV2.99La0.01O8 materials show the most improved electrochemical performance. At the current rate of 60 mA g–1 in the voltage range of 1.8~4.0 V, the initial discharge capacity reached 309.30 mAh g–1 and the discharge capacity of 251.91 mAh g–1 remains after 50 cycles times. Even if the current density scan enlarged to 240 mA g-1, the materials still exhibits the discharge capacity 248.91 mAh g–1, then after the same cycles times, the discharge capacity of 174.63 mAh g–1, indicating that the material after doping have improved exhibits good rate capability and cycling stability.Secondly, the series of LiV3-x Nbx O8 materials for different doping proportion were synthesized by a rheological phase method. Among these materials, LiV2.99Nb0.01O8 materials show the most improved electrochemical performance. At the current rate of 60 mA g–1 in the voltage range of 1.8- 4.0 V, the initial discharge capacity reached 307.62 mAh g–1 and the discharge capacity of 241.21 mAh g–1 remains after 50 cycles times. Even if the current density scan enlarged to 240 mA g-1, the materials still exhibits the discharge capacity 255.01 mAh g–1, then after the same cycles times, the discharge capacity of 178.30 mAh g–1, indicating that the material after doping exhibits good rate capability and cycling stability.Thirdly, the series of x wt. % Mg3(PO4)2 – LiV3O8 composites for different coating proportion were synthesized by a rheological phase method. Among these composites, 1.0 wt. % Mg3(PO4)2 – LiV3O8 composites show the most improved electrochemical performance. The coating layer is only 24.7 nm. At the current rate of 60 mA g–1 in the voltage range of 1.8~4.0 V, the initial discharge capacity reached 323.93 mAh g–1 and the discharge capacity of 250.93 mAh g–1 remains after 50 cycles times. Even if the current density scan enlarged to 240 mA g-1, the composites still exhibits the discharge capacity 266.49 mAh g–1, then after the same cycles times, the discharge capacity of 170.89 mAh g–1, indicating that the material after coating exhibits good rate capability and cycling stability.Lastly, the series of x wt. % Ni3(PO4)2 – LiV3O8 composites for different coating proportion were synthesized by a rheological phase method. Among these composites, 3.0 wt. % Ni3(PO4)2 – Li V3O8 composites show the most improved electrochemical performance. The coating layer is only 28 nm. At the current rate of 60 mA g–1 in the voltage range of 1.8~4.0 V, the initial discharge capacity reached 298.73 mAh g–1 and the discharge capacity of 240.3 mAh g–1 remains after 50 cycles times. Even if the current density scan enlarged to 240 mA g-1, the composites still exhibits the discharge capacity 224.46 mAh g–1, then after the same cycles times, the discharge capacity of 182.03 mAh g–1, indicating that the material after coating exhibits good rate capability and cycling stability.