Synthesis And Electrochemical Properties Of Vanadate Micro/nano Structures

Lithium-ion batteries as a new generation of energy storage equipment have been widely used in our daily life.However,the problems of high cost and limited lithium sources are becoming more serious,and lithium-ion batteries' cost will be increased in the future.Therefore,it is very important to find the other energy storage equipment to instead of the lithium-ion batteries.Sharing the similar working principle with lithium-ion batteries,sodium-ion batteries are considered one of the most promising alternatives due to their low cost and enormous abundance.Vanadium oxides as electrode materials with abundant source and high energy density have gained many achievements in lithium-ion batteries.So many researchers have tried to apply them to the sodium-ion batteries.The traditional vanadium oxides structure are not stable when they used as the electrode materials in sodium-ion batteries.Improving the electrochemical performance of vanadium oxides in sodium-ion batteries become an important research topic.The aim of this paper is to improve the electrochemical properties of vanadium oxides,mainly based on the materials composting,materials nanosizing and metal ions doping.The main research contents and results are as follows:1.the K2V8O21 and K2V8O21/rGO materials were synthesized by a simple hydrothermal method and their electrochemical properties were investigated in sodium-ion batteries for the first time.Through a series of characterization methods,we can find that the pure K2V8O21 are microspheres and the K2V8O21/rGO are nanoribbons.From the results of electrochemical performance test,a certain amount of graphene can effectively improve the electrochemical performance of K2V8O21.After 50 cycles,the capacity of K2V8O21/rGO is 91.2 mAh g-1 at the current density of 50 mA g-1.The improvement of K2V8O21 performance is attributed to the high strength and toughness of graphene,and graphene can protect the structure of K2V8O21 when charging and discharging well.2.the K doped(NH4)2V3O8/rGO composites were successfully synthesized by using graphene oxide as the oxidant and the materials were applied to the negative electrode materials of sodium-ion batteries for the first time.From the characterization results,the pure(NH4)2V3O8/rGO are nanospheres and each nanosphere diameter about to 500 nm.Meanwhile,the K doped(NI4)2V3O8/rGO showed as nanosheets which the lateral sizes of these nanosheets are typically about 250 nm.From the electrochemical performance,we can find that K doped(NH4)2V3O8/rGO materials showed longer cycle life and higher capacity.The capacity still had 235.4 mAh g-1 after 100 cycles at the current density of 100 mA g-1.Meanwhile,the capacity of pure(NH4)2V3O8/rGO only had 144.7 mA h g-1 after 100 cycles at the current density of 100 mAg-1 This is attributed to the K-doped(NH4)2V3O8 own more interlayer space that benefit for Na+ movement and faster electron transfer rate.