Research For Energy Storage Mechanism Of The V₃O₇ Nano Arrays And Further Optimized Through Bonding With N-doped Carbon

Supercapacitor is a kind of device that was different from traditional double-layer capacitor and battery.It has been applied in many areas and also advantageous safeguard for energy and environment problems due to its high power density,long cycle life and fast charge/discharge rates.Till now,some materials such as carbon,metal oxides and polymer etc.However,these materials were mainly worked as positive electrodes,but the species of the negative materials are limited and the capacitance of them is unsatisfactory.The unbalance capacity of the positive and negative materials hindered the development of full supercapacitor and the realistic application.Thus,the research of negative material is in urge need.Among the most supercapacitor materials,vanadium oxides possess multiple vanadium oxidation states including V2O5,VO2 and V2O3 etc.They are widely concerned due to its,high capacity and low cost.The theoretical specific capacitance and potential window for vanadium oxides are higher than those for other transition metal oxides.The unique layered structure is very beneficial for the insertion/desertion of some ions and enhanced the capacitance finally.Thus,vanadium oxides have great potential to appllied in society.In this work,we mainly investigated a new material of V3O7 with hybrid valences.We studied its energy storage mechanism and then further optimized by N-doped carbon.The specific content is as following:(1)The nest-like V3O7 self-assembled by porous V3O7 nanowires was fabricated by the method of simple hydrothermal.The formation mechanism of the morphology was sure due to the reduction process of ethanol through control experiment.The energy storage mechanism of V3O7 was investigated at different reaction potentials.It was found that V3O7 was converted to V6O13 at a potential of 0.6 V,and became V2O5 at 0.2 V.The nest-like V3O7 showed a high capacitance of 365.62 F g-1at the current density of 0.5 A g-1.(2)An in situ photopolymerization method was introduced to synthesize V3O7@polypyrrole(PPy)and then,V3O7 nanowires coated with a layer of N-doped carbon were obtained after calcination to enhance the performance in terms of capacitance and stability.This unique N-doped carbon coated nest-like V3O7(NC-V3O7)exhibited a high specific capacitance of 660.63 F g-1 at a current density of 0.5 A g-1 and even reached 187.72 F g-1 at a high current density of 50 A g-1.According to this investigation,the superior performance of NC-V3O7 is attributed to the synergy between N-doped carbon and V3O7,that is,the unique three layer structure(C bonded both to V and N)stabilized V3O7 and supported high-speed ionic and electronic transmission channels.Finally,full symmetric(NC-V3O7//NC-V3O7)and asymmetric(?-MnO2 nanosheets//NC-V3O7)supercapacitor devices were assembled and showed higher power and energy density than those of related reports.