Synthesis And Performance Of Cobalt-Nickle Based Composites For Supercapacitors

Since the 21st century,the rapid consumption of fossil fuels has led to the shortage of existing fossil energy and the destruction of the environment.Therefore,there is an urgent need to develop an energy storage/conversion technology that is efficient,clean,and renewable.Among them,supercapacitors have attracted much attention due to their fast charge-discharge,high power density,and long cycle life.The capacitive properties of electrode materials have a profound impact on the energy density of supercapacitors.However,most of the current electrode materials still suffer from insufficient specific capacitance and volume expansion during charging and discharging,which leads to insufficient stability.In order to improve the above shortcomings,in this thesis,cobalt-nickel-based oxides,hydroxides and MOF electrode materials with different morphologies were synthesized mainly from the perspectives of structure regulation and sulfidation modification.The specific research results are as follows:（1）NiCo₂O₄ nanoneedles were synthesized on the conductive carbon cloth substrate by hydrothermal method and calcination method.And the Ni Co₂O₄/Ni Mo O₄ hierarchical composite structure was synthesized by the secondary hydrothermal reaction,which the electrode was optimized by controlling the time of the secondary hydrothermal reaction.The optimized Ni Co₂O₄/Ni Mo O₄ hierarchical structure electrode exhibits a high areal specific capacity of 0.67 m A h·cm^-2 at the current density of 4 m A·cm^-2,and the corresponding areal specific capacitance is 3.75 F·cm^-2.And showed better cycling stability than NiCo₂O₄ and NiMoO₄ monomers,respectively.The constructed asymmetric supercapacitor NCM-8//AC has a satisfactory energy density of 38.69 Wh·kg^-1 at 228.56 W·kg^-1 power density,and the capacity retention rate is 90.88%after 5000 cycles at 4 m A·cm^-2 current density.It shows its potential application value in energy storage devices.（2）CuO@NiCoMn-LDH nanowire/nanosheet array composite with 3D core-shell structure was synthesized on Cu foam conductive substrate by wet chemical method,annealing,and electrochemical deposition methods for high-performance supercapacitors.The morphology of the composites was mainly controlled by adjusting the content of Mn,and the effect of the core-shell structure on the electrochemical performance of the composites was investigated.The Cu O@Ni Co Mn-LDH electrode can achieve a high areal specific capacity of2.66 m A h·cm^-2(10 m A·cm^-2).When the current density was increased to 30 m A·cm^-2,there was still 78.3%capacitance retention.In addition,under the condition of 30 m A cm^-2,after3000 cycles,there is an initial capacity retention rate of 94.82%.（3）CoNi-MOF was synthesized on nickel foam by hydrothermal and wet chemical methods,and then carbonized.Then it was modified by low-temperature vulcanization,and the 8 h was determined as the optimal vulcanization time.In 2 M KOH alkaline electrolyte,the electrode exhibits excellent capacitive performance,reaching a high areal specific capacity of 0.93 m A h·cm^-2 at the current density of 3 m A cm^-2,which corresponds to the mass specific capacity of 176.93 m A h·g^-1.In addition,the asymmetric supercapacitor constructed with the electrode and activated carbon material has a capacity retention rate of 85.61%after 4500charge and discharge cycles.