Study On Preparation And Electrochemical Properties Of Co-Ni LDHs-based Nanomaterials

Nowadays,with the aggravation of the energy crisis and greenhouse effect,the research of new energy storage devices is imminent and imperative under the situation.And the supercapacitor is a kind of high-performance energy storage device among them,which has been extensively studied.Although supercapacitors have great advantages such as high capacity,high power density,long life,safety and no pollution,the low energy density still further limits their practical application.More importantly,tremendous studies have shown that the energy density is closely correlated with the structure of electrode material,and it can be greatly enhanced by optimizing the structure of electrode material.Layered double hydroxides(LDHs)are regarded as ideal supercapacitor electrode materials due to the large interlayer spacing,adjustable structure,and high theoretical capacity.Especially the theoretical capacity of the hydroxides corresponding to Co and Ni elements are very high,both of which are greater than 3000 F g-1.At present,the research of Co-Ni LDHs electrode materials has received widespread attention.Nevertheless,the serious problems of Co-Ni LDHs with poor conductivity,slow ion transfer rate,and structural instability have affected the application of Co-Ni LDHs in supercapacitor electrode materials,so it must be prerequisite to optimize electrode materials for improving their electrochemical performance.Meanwhile,compared with bulk materials,nanomaterials have larger specific surface area,more active sites,and shorter electron transmission paths,which can improve the electrochemical performance of electrode materials.In addition,structural optimization of electrode materials is also an effective method to solve this problem.For example,the composite structure can increase the specific surface area of the material,effectively reduce the surface energy of the material,and play a synergistic role between the materials to obtain supercapacitor electrodes with excellent performance.In this paper,two preparation routes were designed to obtain novel hierarchical structure petaloid Co-Ni LDHs microsphere powder and Fe(OH)3/Ni(OH)2/Co-Ni LDH nanosheet array composite,respectively.The electrode material of super capacitor with better performance was obtained.The main research contents of the paper are as follows:(1)Study on preparation and electrochemical properties of Co-Ni LDHs microspheres composed of novel ultra-thin nanosheets:Precursor was prepared by hydrothermal method,and then annealed in a closed container with NaH2PO2·H2O at a lower temperature(200?)for 3.5 h to prepare layered structure petaloid Co-Ni LDHs microspheres,such microsphere structure composed of ultra-thin nanosheets not only prevents the nanosheets from agglomeration with a larger specific surface area,but also exposed more active sites to participate in the redox reaction,thus shows excellent electrochemical performance.In this regard,the experiment explored the influence of Co/Ni molar ratio,the amount of NaH2PO2·H2O and the time of secondary annealing on the final product morphology as well as performance,specifically analyzed its growth process,further determined the optimal reactant ratio and reaction time.In this case,when Co/Ni molar ratio is 3:2,NaH2PO2·H2O is 200 mg,Co-Ni LDHs-3:2 produced by reacting at 200? for 3.5 h has the best capacitance performance.At 1Ag-1,the specific capacitance was 996.4 F g-1,and 84.7%of the initial specific capacitance was maintained after 2500 cycles,showing good cycle stability.(2)Combined with Celgard membrane-assisted hydrothermal method and electrochemical deposition method,Fe(OH)3/Ni(OH)2 and Co-Ni LDHs composite nanosheet array electrode material(Fe(Ni)/Co-Ni LDHs)was successfully prepared on a nickel foam substrate,obtaining superb electrochemical performance.Moreover,the effect of electrodeposition time on the morphology and properties of Fe(Ni)/Co-Ni LDHs was explored.The results show that Fe(Ni)/Co-Ni LDHs-15 prepared by electrodeposition for 15 min has the highest surface capacitance,which has been as high as 14.499 F cm-2 at a current density of 5 mA cm-2,much higher than most of the reported work.Even after 3000 cycles,there is still a capacitance retention rate of 69.74%,exhibiting better cycle stability.