The Electrochemical Performances Of Vanadate-based Cathode Nanomaterials By A Sol-gel Route

Vanadate as the cathode materials has the advantages of stability, high theoretical capacity, high-rate capability and so on. When the silver vanadium oxides are used as the cathode materials, the batteries have very poor cycling capability, which constrain their applications just in the primary batteries. Sodium vanadates have an excellent cyclic stability, but they are hard to be synthetized. This work is focus on synthesizing nanostructured silver vanadates and sodium vanadates by a sol-gel route, which have enhanced cycling and high-rate performances. As follows:(1) The oxalic acid is used as the chelating agent and the carbon resource to synthesize the Agi.2V3O8nanobelts and nanorods as a cathode material by a sol-gel route. The testing results show, the electrochemical performances are largely relied on the morphologies and the calcinated temperatures. With the increasing of temperature, the crystallinity would increase and the sizes of particles grow. The thickness of nanobelts prepared at450℃is around200nm. Suggesting by the charging/discharging results, the product prepared at500℃has a excellent cyclic stability and high-rate capability with the initial capacities of215,198, and174mAh/g at the current density of50,100, and200mA/g respectively. After100cycles, the capacity has a gradually arising process instead of fading. It is the first time that SVOs can be applied as the second battery.(2) The oxalic acid is used as the chelating agent and the carbon resource to synthesize the Ag4V2O7nanorods as a cathode material by a sol-gel route. Suggested by many researches on SVOs, the content of Ag plays a great role on the electrochemical performances. When the ratio of Ag/V is bigger than1/2, the material would have poor the cycling capability. The product synthesized at300℃discharge a initial capacity of215.8mAh/g at the current density of100mA/g whose Warburg impedance is only50Ω. This is the first time that Ag4V2O7nanorods synthensized by a sol-gel route can be used as a high-performance cathode material.(3) The citric acid is used as the chelating agent and the carbon resource to synthesize the Ago.33V205nanorods as a cathode material by a sol-gel route. The Ag0.33V2O5has well cycling properties:The products calcined at different temperatures (300,350, and400℃) can deliver capacities of268.6,247.0, and219.6mAh/g at the current density of100mA/g. After30cycles, they remain the capacities of205.5,211.2, and192.6mAh/g.(4) Sodium vanadium oxide (Na1.25V3O8) nanobelts have been successfully prepared by a facile sol-gel route with subsequent calcinations in air. The thickness and the crystallinity of the Na1.25V3O8nanobelts increase with the calcinations temperatures. For comparison, bulk Na1.25V3O8particles are also prepared using conventional high-temperature solid-state method. As cathode materials for lithium ion batteries, they exhibit much higher capacity than that for the Na1.25V3O8bulk particles. Moreover, the morphology and the crystallinity of the nanobelts are found to have a great effect on the electrochemical performance. The Na1.25V3O8nanobelts synthesized at400℃shows relatively high specific discharge capacity of225mA h g-1and excellent stability at100mA g-1. When evaluated at200mA g-1, the nanobelts retain94%of the initial capacity even after450cycles.