Controllable Preparation Of Advanced Electrode Materials For Supercapacitors And Study On Their Electrochemical Performances

To find and develop renewable clean energy sources becomes the most effective way to address the problem of energy shortages and environmental degradation.In the process of discovering and utilizing new energy,various energy storage devices are inevitably involved and needed.Thus,supercapacitors?or electrochemical capacitors?have broad application prospects due to the advantages of high power density(>10 kW kg^-1),fast charge/discharge,long cycling stability?>100000 cycles?,safety,ect.However,today's commercial supercapacitors?activated carbon and composite material?with low energy density(3⁶ Wh kg^-1) cannot satisfy the demand of power station peak shaving,industrial equipment,electric vehicles,and so forth.Therefore,it is extremely imminent to research and develop supercapacitors with high energy density.The key to solve this problem is increasing the specific of the electrode materials and widening the voltage window of the device.In this paper,electrode materials with high specific surface area,suitable pore structure and multi-dimensional are prepared by designing a reasonable synthetic route,and studied their electrochemical capacitance properties using cyclic voltammetry,galvanostatic charge-discharge and electrochemical impedance spectroscopy.The details are as follows:?1?A facile two-step strategy was applied to prepare NiCo₂O₄ powder after calcining a precursor[(Ni_1-xCo_x)OH₂](CO₃^2-)_x/2·nH₂O] containing cobalt and nickel,which obtained by hydrolysis reaction,using Ni?NO₃?₂,Co?NO₃?₂ and urea as raw materials.The results of SEM,XRD and BET show that NiCo₂O₄ is a microsphere with diameter of 2³?m and low crystallinity.Its surface has urchin-like morphology and hierarchical structure,and the specific surface area is 224 m² g^-1.The electrochemical test results indicate that the specific capacitance is 1167 F g^-1 at the current density of 1 A g^-1.When the current density is increased to 20 A g^-1,the specific capacitance is 1087 F g^-1 corresponding to 93% capacitance retention rate.After3000 charge/discharge cycles at 10 A g^-1,the specific capacitance is attenuated from 1095 F g^-1 to 967 F g^-1,and the capacitance retention still 88.5%.?2?A binderless NiCo₂O₄/NF electrode was synthesized by in-situ growth of on the surface of foamed nickel by direct hydrothermal method.SEM and XRD results show that the "sesuvium portulacastrum-like" NiCo₂O₄ grows on the surface of foamed nickel,with a length of about 1?m and a width of about 100 nm,which is prove to be spinel phase.The electrochemical test results reveal that the specific capacitance is 1349 F g^-1 at the current density of 1 A g^-1.After 3000 charge/discharge cycles at 10 A g^-1,the specific capacitance of electrode materials is 1152 F g^-1,and the capacitance retention is 85.4%.?3?The litchi shell,as a carbon source,was hydrothermal treated with H₂O₂ and HAc and then carbonized at a high temperature to obtain a litchi shell carbon material.The result of SEM,BET and IR spectra show that the surface of the prepared litchi shell carbon material exhibits a sponge-like morphology,whose specific surface area is about 1037 m² g^-1 and rich in carbonyl and hydroxyl polar groups.The electrochemical test results reveal that the specific capacitance of AC-HAc/H₂O₂ exhibits 228 F g^-1 at the current density of 1 A g^-1,especially after 20000charge/discharge cycles,the capacitance is almost maintained at 100%.Thereafter,the litchi shell carbon material used as negative electrode,NiCo₂O₄ used as positive electrode,and the PVA/KOH sol are used as the electrolyte to assemble an all-solid asymmetric supercapacitor,which energy density is 54 Wh kg^-1 and the power density of 808 W kg^-1.After 15000charge/discharge cycles at 5 A g^-1,the capacity was attenuated to 50% of the initial value.