The Preparation And Supercapacitor Properties Of The Co-Al Layered Double Hydroxide Composite Electrode Material

With the increasing depletion of the traditional fossil fuel and the environmental pollution,the new type of energy storage device is of great significance to the utilization and development of the renewable energy.Supercapacitors?SCs?with versatile advantages including high power density,fast charging and discharging capacity,long-term cycling lifespan and environment friendliness have been widely used in various fields of the energy storage system.As a kind of SCs electrode material,Co-Al layered double hydroxide?CoAl-LDH?becomes a potential electrode material because of its high theoretical specific capacity and rich redox activity.However,relatively low conductivity has become a key factor hindering its development.It is found that the carbon material has the characteristics of large specific surface area and good electrical conductivity.The composites with CoAl-LDH and carbon materials can achieve the maximum potential of composite electrode materials by the synergetic effect of each other.In order to improve the conductivity of CoAl-LDH,the composite electrode materials with high specific capacitance,good conductivity and excellent cycle stability have been successfully designed by different preparation methods in this paper.The morphology and material composition of the prepared composite were analyzed by SEM,TEM,XRD and XPS.The electrochemical performance of the composite was studied by cyclic voltammetry?CV?,galvanostatic charge-discharge?GCD?and electrochemical impedance?EIS?.The research process and conclusions are as follows:?1?CoAl-LDH@rGO/NF nanosheets composites were prepared on reduced graphene oxide nickel foam substrate?rGO/NF?by hydrothermal method.The as-synthesized CoAl-LDH@rGO/NF composites exhibites excellent electrochemical performance due to the synergistic effect of CoAl-LDH nanosheets and rGO.The content of NH₄F has a great effect on the morphology and electrochemical properties of CoAl-LDH@rGO/NF composites.The optimum electrochemical performance of the CoAl-LDH@rGO/NF composites electrode was obtained when the amount of NH₄F was 6 mmol.The largest specific capacitance of 1671.4 F g^-1(1 A g^-1)and the ultra-high cycling performance with 97%retention of the original value are achieved even after5000 charge/discharge cycles.A remarkable energy density value of 41.3 Wh kg^-1 at a power density of 408.9 W kg^-1 is achieved in the CoAl-LDH@rGO-6/NF//AC asymmetric supercapacitor?ASC?.Furthermore,the ASC retaines 100%of its original specific capacitance value even after 5000cycles.?2?The Ni₃S₂/CoAl-LDH/rGO/NF composites were successfully prepared by hydrothermal and electrodeposition methods.The synergistic effects of rGO,CoAl-LDH and Ni₃S₂ play an important role in the electrochemical performance of electrode materials.Compared with single CoAl-LDH/rGO and Ni₃S₂ electrodes,the electrochemical properties of Ni₃S₂/CoAl-LDH/rGO/NF composites were improved obviously.Moreover,the influence of the number of electrodeposition circles?loading mass of Ni₃S₂?on the morphology and electrochemical performance of Ni₃S₂/CoAl-LDH/rGO/NF electrode was further studied.The optimum specific capacitance of 2457.5 F g^-1(1 A g^-1)is achieved as the munber of electrodeposition circle is 6?Ni₃S₂/CoAl-LDH/rGO/NF-6?.Furthermore,an ASC device based on the Ni₃S₂/CoAl-LDH/rGO/NF-6composite showes a maximun energy density of 59.8 W h kg^-1(402.8 W kg^-1)and a good long-term stability?retention 91%even after 5000 cycles?.?3?NiMnO_x composites with different Ni/Mn molar ratio were synthesized by one-step hydrothermal method.The electrochemical properties of the prepared composites with different Ni/Mn molar ratios were investigated,and the optimal Ni/Mn molar ratio was determined to be 2:1.Moreover,Co?OH?₂/Ni₂Mn₁O_x/NF nanohybrid with novel porous honeycomb percolation network was designed by electrodeposition Co?OH?₂ on the surface of Ni₂Mn₁O_x/NF.The specific capacitance of Co?OH?₂/Ni₂Mn₁O_x/NF composite electrode material reaches 1898.1 F g^-1 at the current density of 1 A g^-1,which is significantly higher than that of the Ni₂Mn₁O_x/NF electrode.Subsequently,an ASC based on Co?OH?₂/Ni₂Mn₁O_x/NF as a positive electrode and AC as a negative electrode deliveres a high energy density of 47.3 Wh kg^-1 at a power density of 424.7 W kg^-1,making it is a possible contender for supercapacitors in energy storage systems.