Preparation And Supercapacitor Performance Of Mn-Ni-based Hydroxide Composite

Supercapacitor(SC),a newfashioned energy storage/conversion device,has attracted extensive attention due to the superior power density,high cycling stability,wide operating temperature range.However,it should also be noted that the limitations of charge stagnate on the surface(or near surface)make the capacity and energy density of SCs much lower than the theoretical values.As a new electrode material,transition metal layered hydroxide(LDH)has become a research hotspot due to its excellent performance and unique structure.This article is mainly based on Ni Mn-based hydroxide as the research object,by preparing different transition metal sulfides as its growth substrate,and exploring different methods to improve its electrochemical performance.The central research contents are as follows:(1)Selecting different transition metals,various sulfides such as Co₃S₄,Mn S,Ni₃S₂and Fe S were prepared through simple hydrothermal reaction at different temperatures.The results showed that the Co₃S₄exhibited perfect dendritic morphology at 140?,Mn S and Ni₃S₂showed unique cubic and flocculent morphology characteristics at 120?,however,Fe S exhibited unobservable morphology at different temperatures.Furthermore,the above-mentioned sulfides were used as the substrate for the growth of hydroxides,Ni Mn hydroxides were prepared by selecting different hydrothermal reaction times,and the electrochemical performance was analyzed.The results showed that Co₃S₄,Mn S and Ni₃S₂substrate can improve the specific capacitance and cycle stability of Ni Mn-LDH,while the Fe S was not benefits to the electrochemical performance of Ni Mn-LDH.(2)Taking the flocculent Ni₃S₂as the matrix,Ni Mn-LDH nanosheets were grown on the surface by hydrothermal method and used as the electrode material of the supercapacitor.The unique nano-layered structure of Ni₃S₂/Ni Mn-LDH can not only increase the specific surface area of the electrode material,but also increase the active sites,which can effectively shorten the ion transport path,enhance the ion conversion efficiency,and accelerate the redox reaction.Through the electrochemical performance test,Ni₃S₂/Ni Mn-LDH has relatively ideal capacitance,rate and cycle stability.The specific capacitance of Ni₃S₂/Ni Mn-LDH composite material is 2028.38m F cm^-2at current density of 1 m A cm^-2,and the specific capacitance is still 1080.48m F cm^-2at current density of 10 m A cm^-2.After 5000 cycles of charging and discharging,its specific capacitance can still maintain 69.53%,reflecting excellent electrochemical performance.(3)The surface of Ni₃S₂/Ni Mn-LDH nanosheets was coated with an amorphous carbon layer by hydrothermal method to obtain C/Ni Mn-LDH/Ni₃S₂composite material.This special structure provides conditions for electrolyte penetration and rapid ion/mass transfer and effectively improving electrical conductivity.In addition,the amorphous carbon layer can prevent the electrolyte from corroding the electrode material,guarantee the structure strength and cycling stability.The result clearly indicate that the unique structure can effectively enhance the conductivity and cycling life of LDHs.The specific capacitance of C/Ni Mn-LDH/Ni₃S₂/NF electrode could reach 3490 m F cm^-2at a current density of 2 m A cm^-2and retains 84.25%capacitance after 5000 continuous cycles.Besides,the two-electrode device assembled by C/Ni Mn-LDH/Ni₃S₂/NF and activated carbon(C/Ni Mn-LDH/Ni₃S₂/NF//AC)shows an excellent energy density of 64.46 Wh kg^-1at 1279.96 W kg^-1.(4)Using thiourea as the sulfur source,Ni₃S₂with flake morphology was prepared,and then Co was added on the basis of Ni Mn-LDH to prepare C@Mn Ni Co-OH/Ni₃S₂/NF composite material as electrode material.Ni₃S₂intricate weed-like and ultra-thin Mn Ni Co-OH nanosheets synthesized hybrid heterogeneous core-shell structure has outstanding electrical conductivity,can expand the active site,improve the charge transfer rate and redox reaction.The specific capacitance of C@Mn Ni Co-OH/Ni₃S₂/NF electrode could reach 2332 m F cm^-2at a current density of1 m A cm^-2and retains 89.45%capacitance after 5000 continuous cycles.Besides,the two-electrode device assembled by C@Mn Ni Co-OH/Ni₃S₂/NF and activated carbon(C@Mn Ni Co-OH/Ni₃S₂/NF//AC)shows an excellent density of 73.84 Wh kg^-1at799.95 W kg^-1.