| Supercapacitor is a new-style energy storage device with performance between conventional capacitors and secondary batteries.With the development of miniaturization,intelligence and portability of electrochemical energy storage devices,researching and developing flexible supercapacitors has become the trend of the times.As the key component of supercapacitor,electrode material is undoubtedly the focus of research.Therefore,the key point of research in this field is to select appropriate flexible current collectors and synthesize high performance flexible electrodes with reasonable composition and stable structure.In this paper,flexible conductive graphite felt(GF)was used as the substrate,cobalt hydroxyl carbonate(Co2(OH)2CO3)was directly grown on it by solvothermal method,and then modify it by electrodepositing nickel phosphate(Ni2P)on the surface of Co2(OH)2CO3,expecting that the specific capacity and the rate performance of the composite electrode material will be improved.Specific contents of this study are as follows:(1)The preparation of Co2(OH)2CO3@GF electrode material.SEM,FTIR and XRD results showed that the Co2(OH)2CO3 with nanowhisker array structure was successfully synthesized on the GF.The electrochemical performances of as-prepared electrode were optimized by adjusting the hydrothermal temperature,reactant ratio and the ratio of alcohol to water in the solvent.Three-electrode system was used to test its electrochemical properties.The results show that the specific capacity of Co2(OH)2CO3?GF is 1022 mF cm-2 at 1 mA cm-2.When current density increases by 20 times,its rate capability is 47.0%.After cycling for 3000 times at 20 mA cm-2,the retention is 91.7%of its initial specific capacity,showing a good cyclic stability.All the results illustrate that Co2(OH)2CO3 is promising for supercapacitors.(2)The modification of Co2(OH)2CO3@GF by electrodepositing Ni2P.Ni2P@Co2(OH)2CO3@GF composite electrode was obtained through electrodepositing Ni2P on the surface of Co2(OH)2CO3.SEM,TEM,XRD,XPS and other characterization techniques show that Ni2P@Co2(OH)2CO3 were nanowhisker arrays with core-shell structure and the amorphous Ni2P was uniformly coated on Co2(OH)2CO3@GF.The specific capacity of optimized Ni2P@Co2(OH)2CO3@GF electrode is 1360 mF cm-2,which is 133%of Co2(OH)2CO3@GF.Its capacity retention ratio is 72.8%with the current density rising from 1 to 20 mA cm-2,54.9%higher than Co2(OH)2CO3@GF electrode.Moreover,the composite electrode exhibits better cycling stability,capacity decreases by only 4%after 3000 cycles.Thus,electrodeposition of Ni2P can improve the electrochemical performance of Co2(OH)2CO3@GF electrode as a whole.(3)The assembly of flexible symmetric supercapacitors.Using self-made KOH-PVA(polyvinylalcohol)gel as solid electrolyte,Ni2P@Co2(OH)2CO3@GF//KOH-PVA//Ni2P@Co2(OH)2CO3@GF and Co2(OH)2CO3@GF//KOH-PVA//Co2(OH)2CO3@GF symmetrical flexible supercapacitor devices were assembled,respectively.The electrochemical test results are as follows:The specific capacity of Co2(OH)2CO3@GF//KOH-PVA//Co2(OH)2CO3@GF is 138.1 mF cm-2 at 1 mA cm-2.Its energy density is 32.7 Wh kg-1 at a power density of 533.3 W kg-1,and its specific capacity keeps 85.7%after 2500 cycles of charge-discharge at a higher current density of 10 mA cm-2.After Ni2P modification of the electrode material,the specific capacity of the Ni2P@Co2(OH)2CO3@GF//KOH-PVA//Ni2P@Co2(OH)2CO3@GF flexible device is 197.5 mF cm-2,and its energy density is up to 46.8 Wh kg-1 at the same power density.Compared with the device before modification,energy density is increased by 43.1%.Futhermore,the devices shows good stability with?92.9%capacitance retention after 2500 cycles(increased by 8.4%),exhibiting a higher energy density and a better cycling stability.Above-mentioned results show that Co2(OH)2CO3@GF can be used as electrode material for flexible supercapacitors,and subsequent modification of Ni2P on Co2(OH)2CO3 surface can effectively improve its supercapacitor performance of the materials. |
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