Preparation And Electrochemical Performance Of Carbon Cloth Self-supporting Metal Phosphide Electrode Material

Supercapacitors,as one of new type energy storage devices,have the specific power density and the energy density between the lithium-ion batteries and the conventional capacitors.They have been widely applied in many energy-storage fields due to their advantages including fast charge-discharge rate,long life-span,high security and wide operating temperatures,etc.As an important part of supercapacitors,electrode material has attracted widespread interest from researchers.For the extensively researched oxides,their performances at high charge-discharge current densities are seriously impeded by the poor intrinsic conductivity.Thus,seeking novel electrode materials with high intrinsic conductivity is the key to promote the development of high electrochemical performance supercapacitors.Transition metal phosphides with the properties similar to metal alloy,can transfer charge rapidly and exhibit the excellent rate performance during the electrochemical processes at the high current density.Despite transitional metal phosphides have high theoretical capacities,the actual performance is dissatisfactory because of the huge volume expansion and the low availability of transitional metal phosphides electrode materials.Hence,the energy storage mechanisms of different kinds of electrode materials and their research progress are briefly introduced in this paper.Compositing the high conductive material and metal phosphide obtained via different synthesis methods is proposed to the effective way to prepare the electrode materials with high performance.The influence of morphologic structure,electrical conductivity,element component and coating layer of as-prepared materials for the electrochemical performance were studied in the article.The main research contents are presented as follow:?1?Nickel phosphide materials with the nickel-rich outer layer were synthesized using one-pot hydrothermal method.Nickel phosphide materials with different morphologies were obtained subsequently via dissolving the metallic nickel with diluted hydrochloric acid Compared with Ni-P@Ni HL/CC,Ni-P@Ni HL/CC-0.5h and Ni-P@Ni HL/CC-2h,Ni-P@Ni HL/CC-1h electrode presents the outer layer in the form of nanoflakes.It can expose more active sites,and is favorable to the specific capacity.Ni metal in the composites can simultaneously improve the electric conductivity and structural stability.The electrochemical results show that Ni-P@Ni HL/CC-1h presented high specific capacity(280.8 C g^-1),excellent rate(280.8 C g^-1)and cycling performance.Based on the activated process of the electrodes during the cycling,research results reveal that the morphology of Ni-P@Ni HL/CC-1h electrode with stable structure has slightly changed,and the volume expansion was effectively restrained after the cycling.The assembled Ni-P@Ni HL/CC-1h//AC asymmetric capacitor delivered a high energy density(27.6 Wh kg^-1)at a power density of 942.8 W kg^-1.?2?The NiCo precursors with three morphologies?nanoflower,urchin-like and hollow?were synthesized by a solvothermal method on the carbon cloth substrate.Electrochemical results show that the precursor with nanoflower and urchin-like morphologies presented high electrochemical performance.Subsequently,the nickel cobalt phosphides with carbon coating were successfully synthesized via a facile immersion method and the phosphorization process.The structural,morphology and element content of the corresponding samples were investigated.The urchin-like NiCo-based materials consisting of abundant 1D nanoneedles and 2D nanosheets,were uniformly grown on the carbon cloth and form the good conductive network,which can increase the effective utilization of active materials.After phosphorization,the specific surface area and porosity of the materials obtained are increased a lot.Furthermore,the carbon coating materials maintain the integrated morphology of the precursors,having the more concentrated pore size distribution and more the specific surface area than the precursors.EIS results show that the phosphides present the highest electric conductivity and the fastest charge transfer rate among the four ULAs electrode materials.Furthermore,the carbon coating layer is beneficial to improve the conductivity of the NiCoP samples.NiCo P@C-ULAs exhibits the fast ion-diffusion kinetics,thus it has more advantages in the field of electrochemical energy storage and conversion,compared with NiCoP-ULAs,NiCoP-ULAs and NixCo1-xO@C-ULAs electrodes.The assembled Ni CoP@C-ULAs//AC all-solid-state device delivers a high specific capacity of 168.5 C g^-1,outstanding rate and long cycling life,and a high energy density of 37.1 W h kg^-1 at a power density of 792.8 W kg^-1.