Preparation Of Mo-based Compound/Ni₃S₂ Composite Material And Its Application In Supercapacitors

The low energy density of supercapacitors(SCs)restricts its wider application.Researchers recently proposed hybrid supercapacitors(HSCs),which have attracted more and more attention due to their combination of the high energy density of batteries and the high power density of electric double layer capacitors.Among them,the development of battery-type electrodes,which plays a decisive role in the energy density of HSCs,has become the current development focus.Chalcogenides,especially Ni₃S₂,as battery-type cathode materials,have significant advantages in improving energy density due to their significant electrochemical activity and high specific capacity.However,its unfavorable reaction kinetics will weaken the electrochemical performance,especially under the fast charge-discharge rate,the structural stability of Ni₃S₂ becomes worse.Combining it with a molybdenum-based compound with strong mechanical properties,through the construction of a unique stable structure,the optimization of the Ni₃S₂ material is achieved,thereby solving the limitations caused by poor cycle performance,and obtaining high capacity and energy density.Based on this,this thesis mainly carried out the following three parts of research content:(1)The self-supported Ni₃S₂/NF-180 nanosheets were synthesized by one-step hydrothermal method.At 5 m A cm^-2,the area specific capacity of the hexagonal nanosheets was 2.1 C cm^-2.The higher capacity may be due to the large space between the nanosheets,which brings sufficient reaction sites,thus speeding up the chemical reaction process.(2)The heterostructure(MoS₂-Ni₃S₂/NF-C)was designed based on the stable MoS₂material.This unique structure can form numerous charge storage active sites,which is conducive to the transfer of interfacial charges,so that MoS₂-Ni₃S₂/NF-C obtains ultra-high capacity and stability.At 5 m A cm^-2,the specific capacity reaches 3.82 C cm^-2.And after 50,000 cycles of discharge,the capacity hardly decays.Obviously,its specific capacity and structural stability are higher than that of a single Ni₃S₂ material.(3)This experiment constructed an amorphous-crystalline nanosheet array structure(Mo₃-Ni₃S₂/NF-0.5)by means of a two-step hydrothermal method.Among them,the disordered structure of amorphous Mo₃ can better adapt to the volume change during discharge,and the unique crystalline Ni₃S₂ sheet structure can achieve rich structural nano-crystallization,revealing a large number of electrochemically active sites.The ingenious synergistic effect between the two makes Mo₃-Ni₃S₂/NF-0.5 play to the advantages of their respective components and exhibit ultra-high specific capacity.At 5m A cm^-2,the area specific capacity is 8.52 C cm^-2.When further assembled into HSCs,the energy density is as high as 4.18 m Wh cm^-2.