Energy Storage Research Of Molybdenum Disulfide Compound Materials

Supercapacitors have high power density and long cycle life,electrode material is the core research content of supercapacitor.As a typical transition metal sulfide,MoS₂ has been widely studied for its excellent cyclic stability and lower volume expansion rate.However,compared with carbon materials such as graphene,MoS₂ has low electronic conductivity with 3.3*10^-7 S cm^-1and poor rate performance.At the same time,the actual specific capacitance of MoS₂remains limited.Therefore,in order to solve the problems and improve the electrochemical performance of MoS₂,researchers often use other materials with high electrochemical activity and high conductivity to modify MoS₂ to improve it's performance.In this paper,FeS₂,CoS₂,and Fe-CoS₂ were used to modify MoS₂.Firstly,FeS₂ with high capacitance was used to modify MoS₂.FeS₂ has a higher theoretical capacitance(894 m A h g-1),FeS₂/MoS₂crosslinked nanosheets prepared introduced pseudocapacitance due to the occurrence of redox reaction of FeS₂/FeS₂OH in alkaline electrolyte,thus improving the specific capacitance of FeS₂/MoS₂.Secondly,MoS₂ electrode material was modified by CoS₂octahedral particles with high conductivity.CoS₂ has excellent electrical conductivity(6.7*10³S cm-1 at 300 K),The rate performance of the prepared CoS₂/MoS₂ compounds can be significantly improved.Thirdly,multi-metal synergistic effect of Fe-CoS₂ nanoparticals modified MoS₂.Partial doping of Fe²⁺ions in CoS₂ can expose more active sites of redox reaction of CoS₂,thus improve the specific capacitance.Meanwhile,Fe-CoS₂ can retain the high conductivity of CoS₂ and improve the rate performance of Fe-CoS₂/MoS₂ electrode material.Therefore,modification of by Fe-CoS₂ could not only improve the specific capacitance of MoS₂,but also improve the rate performance.This paper mainly completes the following work:(1)Preparation and electrochemical properties of FeS₂/MoS₂ electrode materials.MoO_x was prepared by anodic oxidation and MoS₂ was prepared by hydrothermal sulfuration.Then,FeS₂/MoS₂ electrode material was prepared by placing MoS₂ in a Teflon-lined autoclave containing ferric chloride,sodium dodecyl sulfate and thiourea for 12 h at 180?.FeS₂/MoS₂ presents nanoporous structures formed by vertically arranged cross-linked nanosheets.This structure is conducive to the effective diffusion of electrolyte ions and provides sufficient reaction interfaces for electrolyte ions.Electrochemical tests were carried out in 3.0 M KOH and 0.5 M Na₂SO₄ electrolyte.The specific capacitance of FeS₂/MoS₂ at the current density of 1 m A cm^-2was 495 m F cm^-2 and 394 m F cm^-2,respectively.When the current density increases from 1 m A cm^-2 to 10 m A cm^-2,the rate performance in alkaline and neutral electrolytes increases from 71%and 57.8%of MoS₂ to 75.6%and 76.14%of FeS₂/MoS₂,the rate performance was improved.At the same time,the cyclic stability test results indicated that the FeS₂/MoS₂ had excellent cyclic stability.An asymmetric solid-state supercapacitor is constructed using FeS₂/MoS₂ anode,the exfoliated graphite carbon paper cathode and Na Mo O₄-Na₂SO₄-PVA gel electrolyte.At 1.0 m A cm^-2,the specific capacitance is 1.88 F cm^-3,energy density is 0.936 mwh cm^-3at the power density is 15.83 mw cm^-3.At the current density of 5.0 m A cm^-2,the capacity retention rate was97.8%after charging and discharging for 5000 times,indicating that FeS₂/MoS₂ electrode can be used as a good supercapacitor material.(2)Preparation and electrochemical properties of CoS₂/MoS₂ electrode materials.CoS₂/MoS₂ electrode material was prepared by reaction of cobalt nitrate hexahydrate and thiourea in aqueous solution with MoS₂ as precursor for 12 hours at 200?.CoS₂octahedral particles with a diameter about 500 nm,smooth surface and uniform particle size are coated on MoS₂nanosheets.CoS₂ particles with high conductivity can increase the active site of electrochemical reaction,improve the material conductivity and enhance its electrochemical activity.When the current density is 1 m A cm^-2,the specific capacitance of CoS₂/MoS₂ in alkaline and neutral electrolytes is 387.55 m F cm^-2 and 605.77 m F cm^-2,respectively.The specific capacitance is greatly increased at neutral electrolyte.When the current density increases from 1 m A cm^-2 to 10 m A cm^-2,the capacitance retention rate of CoS₂/MoS₂ is 84.8%and 82.8%in alkaline and neutral electrolytes,respectively,which proves that the modification of CoS₂significantly improves its rate performance.An asymmetric solid-state supercapacitor is constructed using CoS₂/MoS₂ anode,Mn O₂/ACP-10 cathode and Na Mo O₄-Na₂SO₄-PVA gel electrolyte.At 1.0 m A cm^-2,the specific capacitance is 4.32 F cm^-3,energy density is 1.944 mwh cm^-3at the power density is 18 mw cm^-3.The device can light yellow LED lights,proving it's high working voltage and energy density.(3)Preparation and electrochemical properties of Fe-CoS₂/MoS₂ electrode materials.Using MoS₂ as the precursor,Fe-CoS₂/MoS₂ anode were prepared by reacting for 12 hours in an aqueous solution containing cobalt nitrate,ferrous chloride and thiourea at 180?.The surface of MoS₂ nanosheets are covered with a layer of nano-cone-shaped Fe-CoS₂,which is evenly distributed to form Fe-CoS₂/MoS₂.The multi-metal synergistic effect of Fe-CoS₂nanoparticles has good conductivity and rich electrochemistry active sites.When the current density is 1 m A cm^-2,the specific capacitance of Fe-CoS₂/MoS₂ in alkaline and neutral electrolytes is 507.39 m F cm^-2 and 602.33 m F cm^-2,respectively.The increase of specific capacitance was obvious in both electrolytes.When the current density increased from 1 m A cm^-2 to 10 m A cm^-2,the capacity retention rate of Fe-CoS₂/MoS₂ was 80.92%and 82.75%respectively,indicating that the rate performance of Fe-CoS₂/MoS₂ was significantly improved.An asymmetric solid-state supercapacitor is constructed using CoS₂/MoS₂ anode,Mn O₂/ACP-10 cathode and Na Mo O₄-Na₂SO₄-PVA gel electrolyte.When the current density at1.0 m A cm^-2,the specific capacitance is 4.42 F cm^-3,energy density is 1.989 mwh cm^-3.The device can light red LED lights and successfully drive small fans,proving that Fe-CoS₂/MoS₂electrode material can be used as excellent anode material for supercapacitor.