Preparation And Electrochemical Properties Of Cobalt-based Hybrid Supercapacitor Electrode Materials

In recent years,supercapacitors have gradually become popular energy storage devices in many fields such as industry,transportation and new energy industry due to their advantages such as short charging time,high power density,long life span,high safety and low production cost.At present,based on the defect that the energy density of supercapacitors is less than that of secondary batteries,the research about supercapacitors mainly focuses on boosting the electrochemical performance of their electrode materials.Including increasing the specific capacity of electrode materials,optimizing the cycle stability and improving the rate performance.Among them,cobalt-based materials are favored by researchers due to their merits such as large theoretical specific capacity,numerous oxidation reduction states and abundant electrochemical active sites.My work is focused on the design and preparation of cobalt compound nanomaterials.The main research results of this paper show as follows:1)In order to improve the specific capacity of Co（CO₃）_0.35Cl_0.2（OH）_1.1·1.74H₂O（CCCH）nanoneedles,a novel two-step activation method was used to change the morphology of Co（Co₃）_0.35Cl_0.2（OH）_1.1·1.74H₂O（CCCH）nanoneedles.The CCCH precursor was obtained by a facile one-step hydrothermal method,then the smooth nanoneedles array was converted into rough and porous structure by the first-step activation technology,which was named CCCH-P75.Finally,the second-step activation procedure transformed the porous structure of CCCH-P75 into nanosheets and labeled as CCCH-P75N50.The specific surface area of the material is increasing obviously,and the internal resistance decreased.The results show that the specific capacity of CCCH-P75N50 electrode is 3.83 F cm^-2 at the current density of 10m A cm^-2,which is larger than that of CCCH-P75(1.74 F cm^-2)and CCCH(0.54 F cm^-2).In addition,the CCCH-P75N50 electrode maintains 83.1%of the initial capacity after 3000cycles of charge and discharge at the current density of 40 m A cm^-2.CCCH-P75N50 is assembled into an asymmetric supercapacitor device CCCH-P75N50//CC HSC,which exhibits a power density of 37.5m W cm^-3 and an energy density of 2.75m Wh cm^-3.The capacitance of the device maintained 88.9%of the initial capacity after charge and discharge for 6000 cycles.2)The second metal iron was introduced and the selenium element was doped to the core-shell hetrogeneous Co Fe₂Se₄@Co Ni-CH composite.Firstly,Co Fe₂Se₄/CC core was grown on blank carbon cloth（CC）substrate by an electrodeposition technology,and then loading Co Ni-CH/CC layer on the core by a hydrothermal method.The results show that the three-dimensional skeleton structure can not only accelerate the electron transfer speed but also shorten the diffusion path of ions.Thus,the internal resistance of the material is reduced and the specific surface area is increased.The specific capacity of the Co Fe₂Se₄@Co Ni-CH electrode obtains 218.6 m Ah g^-1 at 1 A g^-1,and keeps 65.5%of the initial capacity at 20 A g^-1.Co Fe₂Se₄@Co Ni-CH electrode performs as a positive electrode and porous carbon（derived from barley）as a negative electrode,assembled into a drainage alkaline hybrid supercapacitor（HSC）device,providing a energy density of 67.3 Wh kg^-1 at 765.9 W Kg^-1.3)For further optimize the electrochemical performance of the material,the double core-shell heterogeneous Fe_0.4Co_0.6Se₂@Ni Co-P composite was constructed by doping nonmetallic phosphorus on the basis of bimetallic selenides.The Fe_0.4Co_0.6Se₂/CC core layer and Ni Co-P/CC shell layer were grown on blank carbon cloth（CC）substrate by two-step electrodeposition procedures.Fe_0.4Co_0.6Se₂@Ni Co-P electrode exhibits more desirable performance comparing with pure Fe_0.4Co_0.6Se₂/CC and Ni Co-P/CC electrodes in the aspects of specific surface area,electrical conductivity,electrode dynamics and structural stability.Fe_0.4Co_0.6Se₂@Ni Co-P electrode acquires a Cm of 202.3 m Ah g^-1 at the current density of 1A g^-1.Additionally,it shows a good rate performance(144.6 m Ah g^-1 at 20 A g^-1).A Fe_0.4Co_0.6Se₂@Ni Co-P/CC//RPHPC HSC device is assembled,which provides 64.4Wh kg^-1of energy density at 715.9 W Kg^-1 power density.