Fabrication Of Self-assembled Ni-Co LDH/sulfonated Graphene Composites For Supercapacitors

Among various energy storage devices,electrochemical supercapacitors have attracted much attention due to their high power density,fast charging and discharging processes,wide voltage range,and long cycle life.It has broad application prospects in mobile electronic devices and electric vehicles.The electrode material is the key to determine the energy storage performance of supercapacitors,so it has been widely studied.This paper mainly studies the preparation of sulfonated graphene,the synthesis of nickel-cobalt layered double hydroxide,and the preparation of self-assembled composites consisting of sulfonated graphene and nickel-cobalt layered double hydroxide,in addition to research the electrochemical characteristics in three-electrode and two-electrode systems.Glucosamine was used as the reducing agent and nitrogen-doping to obtain nitrogen-doped graphene?GGN?,leading to the reduction of graphene oxide along with the immobilization glucosamine to the surface graphene.Afterwards,sulfonated graphene?SGN?was obtained through the sulfonation of GGN using chlorosulfonic acid as a sulfonation with dichloromethane as a solvent.The results show that GGN and SGN have good dispersion properties and rich negative charge groups on the surface,which is conducive to the preparation of self-assembled composite materials.In the three-electrode test system of the prepared SGN80 electrode material.the specific capacitence of SGN80can reach 138.13 F·g^-1 at 1 A·g^-1,with the specific capacitance retention rate of 85.1%(117.5F·g^-1)as the increase of current densities to 10 A·g^-1.Oxidation-induced intercalation was used to prepare the NO₃^-intercalated flower-spherical nickel-cobalt layered double hydroxide?NCLDH?.The valence of metal elements in the host layered structure of NCLDH was controlled by adjusting the amount of oxidant,aiming to to control the interlayer distance.the prepared NCLDH16 material presents a porous flower spherical structure with a layer spacing of 0.79 nm.The flower-spherical structure ensures that the electrode material can provide abundant active sites and adequate diffusion channels of electrolyte ions.The introduction of NO₃^-is capable to promote the exfoliation of NCLDH.In the three-electrode test system.the as-obtained NCLDH16possessed a superior specific capacitence of 1604.4 F·g^-1 at a current density of 1 A·g^-1.Notably,NCLDH16 still achieved a specific capacitence of 1393.6 F·g^-1 at a high current density of 10 A·g^-1,indicating an extraordinary rate capability.NCLDH and functionalized graphene were separated and dispersed in deionized water,and then composite materials were prepared by self-assembly method.The mechanism of self-assembled composite materials was explored,and analyzed the relationship between the structure and electrochemical performance of self-assembled composite materials.The presence of functionalized graphene provided structural support in favor of accelerating electron transfer.The hybrid supercapacitor based on NCLDH16/SGN80 achieved a high specific capacitance of 120.53 F·g^-1 at a current density of 1 A·g^-1.Importantly,the hybrid supercapacitor attained a maximum energy density of 42.86Wh·kg^-1 at a power density of800 W·kg^-1.