The Preparation And Electrochemical Properties Of Transition Metal Selenide Composite Materials

The increasing global demand for energy has made the exploration of electrochemical energy storage devices（EESDs）an essential component for energy reform.As the most widely used electrochemical energy storage devices,supercapacitors（SCs）and sodium ion batteries（SIBs）have their own advantages.SCs are ideal for high energy charging and discharging devices,owing to their high energy density,stable cycling performance.Meanwhile,SIBs possess high energy density qualities,which are practical for portable devices.In particular,transition metal selenides are a promising candidate for application in both supercapacitors and sodium-ion batteries,due to their high theoretical specific capacity,abundance,low cost,and high initial coulomb efficiency.This article explores a convenient,low-cost,and environmentally friendly one-step solid-phase synthesis method for electrode material preparation.This method successfully prepared transition metal selenide composite materials including nickel selenide/carbon nanotubes（NiSe₂/CNTs）,nickel-cobalt selenide/carbon nanotubes（NiCo₂Se₄/CNTs）,and cobalt-iron selenide/carbon nanotubes（CoFeSe/CNTs）without the need for protective inert atmospheres.The relationship between the physicochemical properties such as morphology,elemental valence distribution,specific surface area,pore size structure,and electrochemical properties of the relevant composites were also investigated.The prepared composite materials were assembled as electrode materials for mixed supercapacitors and sodium-ion batteries,respectively.（1）A one-step solid-phase synthesis method was employed to prepare NiSe₂ and NiSe₂/CNTs nanocomposites using nickel formate,selenium powder,and multi-walled carbon nanotubes as raw materials.The effects of reaction temperature and carbon nanotube addition on the electrochemical properties of NiSe₂/CNTs nanocomposites were evaluated.The results revealed that NiSe₂/CNTs nanocomposites prepared at450°C,with an addition of 20 mg of carbon nanotubes,exhibited superior electrochemical properties.The prepared NiSe₂/CNTs nanocomposites demonstrated a high specific capacity of 172.7 m Ah g^-1(1381.6 F g^-1)at a current density of 1 A g^-1(and retained up to 108.6 m Ah g^-1 at a current density of 20 A g^-1),indicating high multiplicative performance.The NiSe₂/CNTs nanocomposite was integrated with interconnected hierarchical porous carbon（IHPC）to assemble a hybrid supercapacitor（NiSe₂/CNT//IHPC）,which demonstrated a specific capacity of 57.07 m Ah g^-1 at a current density of 1 A g^-1.It provided an energy density of 42.8 Wh kg^-1 at a power density of 0.84 k W kg^-1 and exhibited 100%capacitance retention after 20,000charge/discharge cycles.As an anode material for sodium-ion batteries,it demonstrated a reversible specific capacity of 415.8 m Ah g^-1 at a small current density of 0.1 A g^-1and a discharge specific capacity of 330 m Ah g^-1 after 360 cycles at a current density of 2 A g^-1,with good cycling performance and high multiplicative capability.it exhibited a reversible specific capacity of 415.8 m Ah g^-1 at a small current density of0.1 A g^-1,and a discharge specific capacity of 330 m Ah g^-1 after 360 cycles at a current density of 2 A g^-1,with good multiplicative performance and cycling performance.（2）NiCo₂Se₄/CNTs composites were synthesized via a one-step solid-phase synthesis method,using nickel acetate,cobalt acetate,selenium powder,and multi-walled carbon nanotubes as starting materials.The effects of reaction temperature and amount of carbon nanotubes on the electrochemical properties of the resulting NiCo₂Se₄/CNTs composites were investigated.The results showed that the composites obtained at 750°C,with an addition of 30 mg of carbon nanotubes,displayed superior electrochemical performance.As supercapacitor electrodes,NiCo₂Se₄/CNTs composites demonstrated a high specific capacity of 133.7 m Ah g^-1(1069.9 F g^-1)at a current density of 1 A g^-1,and exhibited excellent multiplicative performance,retaining up to 88.0%of the specific capacity at a current density of 10 A g^-1.The NiCo₂Se₄/CNTs composite and IHPC were integrated for the assembly of a hybrid supercapacitor（NiCo₂Se₄/CNT//IHPC）,which exhibited a device specific capacity of44.43 m Ah g^-1 at a current density of 1 A g^-1,and provided an energy density of 33.32Wh kg^-1 at a power density of 0.41 k W kg^-1.The hybrid supercapacitor retained 91.6%of its capacitive properties after 20,000 charge/discharge cycles.The prepared NiCo₂Se₄/CNTs composites maintained a high specific capacity when used as anode materials for sodium-ion batteries.After 300 cycles at a current density of 0.1 A g^-1,the reversible specific capacity was 367.1 m Ah g^-1 with a coulomb efficiency of 99.2%,while at a current density of 2.0 A g^-1,the reversible specific capacity was 319 m Ah g^-1 after 500 cycles.It maintained a high specific capacity of 268.6 m Ah g^-1 after 1000long cycles at a high current of 5 A g^-1,indicating its excellent cycling and multiplicative performance.（3）CoFeSe/CNTs nanocomposites were prepared by a one-step solid-phase synthesis method using carbon nanotubes as the conductive matrix,cobalt acetate as the cobalt source,Prussian blue as the iron source,and selenium powder as the selenium source.The prepared CoFeSe/CNTs nanocomposites exhibited high specific capacity and excellent rate performance as negative electrode materials for sodium-ion batteries.After 200 cycles at a current density of 0.1 A g^-1,the reversible specific capacity was 567 m Ah g^-1 and the coulombic efficiency was 97.3%.After 140 cycles at a current density of 2.0 A g^-1,the reversible specific capacity was 333.1 m Ah g^-1.When the current density was increased to 5.0 A g^-1,the reversible specific capacity was 272.4 m Ah g^-1 after 1500 cycles.The material exhibited high cycling stability and high capacity retention rate at high current densities.