Preparation And Energy Storage Mechanism Of Nickel-Cobalt Phosphide/Hydroxide With Hierarchical Core-Shell Structure

Transition metal phosphides（TMPs）,which exhibits excellent conductivity and electrochemical activity,and transition metal hydroxides,with large surface area and regulated charge,are promising materials for supercapacitor.However,structure collapse and reuniting hinder the application for TMP and transition metal hydroxides,respectively.In view constructing hierarchical core-shell structure is an effective way to improve the electrochemical activity of materials.In this essay,we are committed to fabricate materials with high energy density and long cycle life by constructing hierarchical core-shell structure based on nickel-cobalt phosphide/hydroxide.The main contents are as follows:（1）First of all,the NiCoP nanowires is synthesized by hydrothermal and phosphating method.Then the NiCoP/NiAl-LDH core-shell structure is constructed by secondary hydrothermal method.The effects of secondary hydrothermal time and temperature on the structure and performance of materials were studied.And the optimal one shows high specific capacitance(2324 F g^-1)and wide voltage window（0-0.55 V）.After that,we prepared NiCoP@C/NiAl-LDH triple material to improve the conductivity,which remains 69%of the initial specific capacitance after 2000 cycles.（2）Adjustments have been made to the material and structural design according to the previous exploration.On one hand,we prepared 3D hierarchical NiCoP nanoarrays which provides better mechanical stability and more channels for electron transfer.On the other,the NiCoP with high electrochemical activity is combined with Co（OH）₂ with superior stability exhibits remarkable cycle life and rate capability.Therefore,NiCoP/Co（OH）₂ electrode exhibits remarkable electrochemical performance with specific capacity of 2190 F g^-1 at 1 A g^-1 and retains 80%of the initial capacity at 20 A g^-1.Furthermore,the as-fabricated asymmetric supercapacitors display outstanding long-term cycle life with 87%retention after 6000 cycles at 10 A g^-1 and high energy density/power density.（3）MnCo/NiCo-LDH composite materials are prepared by hydrothermal and electro-deposition.We investigate the effect of element ratio of NiCo-LDH on electrochemical properties of composites.The construction of hierarchical core-shell structure significantly improves the cycle life and charge storage capacity,which is4.53 F cm^-2(at 2 A cm^-2).The MnCo/NiCo-LDH/AC asymmetric supercapacitor exhibits high power density of 48.4 Wh^-11 at an energy density of 750 W kg^-1,and remains 82%of the initial specific capacitance after 10,000 cycles.