Research On Preparation And Properties Of CoNiFe-LDH/multilayer Graphene Composites For Supercapacitor

Supercapacitors have the advantage of high power density,but the energy density is low,thus limiting their development.Layered double hydroxides have a high specific surface area and also have good redox properties,and so have become a key research area for supercapacitors.However,layered double hydroxides have the disadvantage of poor conductivity,which needs to be urgently solved.In this paper,composites of layered double hydroxides loaded on the surface of multilayer graphene were prepared for high specific capacitiance and rate performance.The main research contents are as follows:?1?Cobalt-Iron layered double hydroxides/multilayer graphene composites were prepared by a hydrothermal method.Morphological analysis and electrochemical performance tests were performed on samples with different reaction times of 1,3,and 10 hours.The results show that a lamellar CoFe-LDH?LDH:Layered Double Hydroxides?layer can be formed on the surface of multilayer graphene with a reaction time of 1 hour.Longer reaction times lead to decomposition of LDH.When the reaction time is 10 hours,CoFe-LDH will completely decompose into CoFe oxide.Electrochemical performance tests of the composites showed that the specific capacitance of the samples at 1,3,and 10 hour reaction times were 872.5 F g^-1,462.5 F g^-1,and 82.5 F g^-1,respectively,at a current density of 1 A g^-1.After 5000 cycles of charge and discharge,the specific capacitance were 36.8%,67%,and 41.5%,respectively.The composite material shows good specific capacitance and rate performance,but the cycle performance needs to be improved.?2?Cobalt-Nickel-Iron layered double hydroxides/multilayer graphene composites were prepared by hydrothermal reactions and the corresponding products were tested for electrochemical performance.Keeping the content of cobalt and iron constant,with the increase of nickel content,the lamellar structure of Co NiFe-LDH sheet becomes more and more pronounced.The morphology of CoNiFe-LDH is optimal and the specific capacitance maximum with a molar ratio of Co:Ni:Fe=2:3:2,Microstructure observation shows that the thickness of the lower layer is about 5 nm,and the gap between the layers is about 50 nm.The specific capacitance is 2107.5 F g^-1at a current density of 1 A g^-1,and the specific capacitance can reach 628 F g^-1after 5000 cycles.The influence of the reaction time and temperature on the properties of CoNiFe-LDH/multilayer graphene was studied for Co:Ni:Fe=2:1:1 samples.Studies have shown that as the reaction time increases,the specific capacitance of the sample decreases,and the cycling performance also gradually decreases.As the reaction temperature increases,the specific capacitance of the sample decreases.?3?An asymmetrical supercapacitor was fabricated by assembly of CoNiFe-LDH and activated carbon.The specific capacitance is 75.8 F g^-1in the voltage range 0-1.5V with current density of 1 A g^-1,the power density can reach 6.67 kW kg^-1,and the energy density can reach23.68 W kg^-1.After 1000 cycles at a current density of 1 A g^-1,the specific capacitance remained93.6%of the original value,showing good stability.