| In recent years,the increasingly serious environmental and energy problems have promoted the development of new clean energy storage devices.Supercapacitors(electrochemical capacitors),one of the energy storage devices,have been a hotspot of current research,due to its advantages of long cycle life,high power and energy densities,fast charge-discharge and low cost.Given this,the development of electrode materials with excellent electrochemical properties has become an important research direction.Nickel-based materials have attracted extensive attention,ascribing to their high theory capacitance,wide range resources,low-cost and environmental friendly.In this paper,nickel-based double hydroxide and nickel-based phosphide as substrates were compounded with other materials respectively to prepare composite materials with unique microstructure,in order to modify and enhance their capacitance performance.The main results are as follows:(1)Preparation of Ni/Al-LDH and carbon cloth(CC)composites(Ni/Al-LDH/CC)and their capacitance performance study.The composite flexible electrode materials,Ni/Al-LDH directly growing on CC surface,were synthesized via facile one-step hydrothermal method.Their unique 3D open structures supply larger contact between electrolyte and electrode materials,enabling the electrochemical active materials to be fully utilized.Meanwhile,Ni/Al-LDH/CC can be used as working electrode without binders or conductive additions,helpful for the decrease of interface resistance and enhancement of electrochemical transfer rate.The electrochemical measurements reveal that the composites possess good electrochemical performances:the specific capacitance(Csp)is 359.2 F·g-1 at the current density 0.3 A·g-1 and increases by 5.9%after 3000 galvanostatic charge-discharge(GCD)cycles.Furthermore,the asymmetric supercapacitor,Ni/Al-LDH/CC and activated carbon(AC)as the positive and negative electrodes respectively(Ni/Al-LDH/CC/AC),was assembled.Its voltage can be up to 1.6 V,as well as high energy density 20.9 Wh·kg-1 at 0.27 kW·kg-1 power density.Meanwhile,83.9%retention of Csp after 3000 GCD cycles is achieved at the current density 0.5 A·g-1.(2)Preparation of Ni-P@Ni-Co composites and their electrochemical behavior research.The micro/nano-structure core/shell composites,Ni-Co nanocoposites uniformly coating on micrometer spherical Ni-P precursors,were prepared by two-step hydrothermal method,in order to improve materials stability.Meanwhile,nickel-based phosphide capacitance performance was optimized by the synerfistic effect between Ni and Co.The results show that Ni-P@Ni-Co has a high specific surface area 74.2 m2·g-1 and good capacitance performances when used as supercapacitor electrode materials.Its Csp can reach 1121.1 F·g-1 at 1 A·g-1 current density,and still retain 879.2 F·g-1 at 20 A·g-1.At the same time,the retention of Csp is 95.8%after 5000 GCD cycles at 2 A·g-1 current density.Furthermore,an asymmetric,Ni-P@Ni-Co as positive electrode and AC as negative electrode(Ni-P@Ni-Co//AC),was assembled with 1.6 V working voltage.The Ni-P@Ni-Co//AC delivers a high energy density of 28.9 Wh·kg-1 at the power density of 0.4 kW·kg-1,together with 89.1%Csp retention after 5000 GCD cycles at the current density of 1 A·g-1,and nearly 100%Coulombic efficiency. |
