Preparation Of Vanadium-based Composites And Their Application In Supercapacitors

Wearable and flexible energy storage devices has attracted many attentions by researchers.It is of great significance to develop flexible energy storage devices with small size and high electrochemical performance.As a single crystal polyvalent metal,vanadium is easy to react with oxygen to form oxides of various phases and morphologies,and vanadium oxide with special lamellar structure can make different groups or metal ions intercalate reversibly.The intercalation of lithium(sodium)ions can form lithium(sodium)intercalated compounds with lamellar structure,such as Lix VO₂ and Nax VO₂.LDH owes excellent anion embedding and exchange ability,ideal specific capacitance.It is considered to be an ideal and typical pseudocapacitor material.In this paper,two kinds of vanadium-based carbon composites were prepared.Contents and conclusions are displayed in the following:(1)VO₂(B)@graphene(VO₂(B)@GN)core-shell composites were synthesized from vanadium pentoxide and graphite by one-step hydrothermal method.The addition of graphene not only promotes the conductivity and mechanical properties of compound,but also improves the electrochemical properties of materials and enhance the structural stability of materials.With the augment of GN,the specific capacitance of VO₂(B)@GN increases at first and then decreases.The initial discharge capacity of the composite can reach 197 F g^-1at 0.5 A g^-1and 160 F g^-1at 1 A g^-1,which are both better than rod-like pure phase VO₂(B).In addition,the capacitance loss rate of VO₂(B)@GN-2 composite electrode is 4.51%after 1000 charge-discharge cycles,which is way higher than that of pure VO₂(B)electrode(14.57%).The test results also show that VO₂(B)@GN-2 composite electrode has good cycle stability.VO₂(B)@GN-2electrodes were assembled into supercapacitors by screen printing.Several assembled SCs were connected,and the red LED was found to be able to be lighted,which also illustrates its potential application in food safety intelligent packaging.(2)A novel Ni V-LDH@CNT structural composite was successfully prepared by one-step coprecipitation method.The composite material also owes special structure:hollow tubular carbon nanotubes are inserted between the LDH plates.This special structure not only increases the electron transmission efficiency,but also improves the cyclic stability of the electrode material.The specific capacitance of LDH₃@CNT composites is 1493 F g^-1 at 1 A g^-1 and its specific retention is 71%after 1000 charge-discharge cycles at 50 A g^-1.The above results show that LDH₃@CNT composites possesses excellent advantages as electrode materials.In addition,the screen-printed ASCs were fabricated,whose positive electrode is Ni V-LDH@CNT and negative electrode is activated carbon.The specific capacitance of the ASCs device was 85 F g^-1 at 2 A g^-1,showing ideal electrochemical performance and indicating the potential application of Ni V-LDH@CNT as electrode material in energy storage devices.