Preparation Of MoSe₂ Composites And Their Application In Electrochemical Energy Storage

In recent years,low-cost sodium-ion batteries have attracted widespread attention and are expected to replace lithium-ion batteries in some areas.However,the development of sodium-ion batteries has been limited by the large radius of sodium ions and slow reaction kinetics.Therefore,it is particularly important to find suitable sodium-embedded materials.Among many materials,Mo Se₂stands out because of its Larger layer spacing and high theoretical capacity.However,Mo Se₂displays some disadvantages,such as poor structural stability and slow kinetics,which make its capacity fade seriously during cycling,resulting in poor rate capability and cycle stability.In view of the above shortcomings,this paper modified Mo Se₂by optimizing the structure,constructing heterojunction and optimizing the composition.The research contents are as follows:Firstly,solid rod-like MoO₃ is used as a template to grow polypyrrole on the surface,followed by partial etching,carbonization and selenization to obtain H-NC/MoO₂@Mo Se₂composites.Among them,MoO₂@Mo Se₂heterostructure can improve the electronic structure,homogenize the distribution of electrode electric field,reduce the diffusion barrier,promote the transfer of ions and electrons,guide the uniform deposition of sodium ions,inhibit the growth of dendritic sodium,and improve the kinetics of electron and ion transfer.The NC in the composite can improve the conductivity of the material.The hollow structure can provide a large specific surface area,which is beneficial to the infiltration of the electrolyte,and can relieve the volume expansion of the Mo Se₂material in the charging and discharging process and improve the stability of the material.Through a series of characterization methods,the H-NC/MoO₂@Mo Se₂composite is successfully prepared,and its electrochemical performance is tested,which showed good sodium storage performance.And that principle of DFT is combine to prove the energy storage superiority of the composite material.At a current density of 50 m A/g,the H-NC/MoO₂@Mo Se₂composite displays a charge capacity of 899.5 m Ah/g and a discharge capacity of 1056.4 m Ah/g,and its first cycle coulombic efficiency is 85.1%.The capacity retention rate can reach 85.7%after500 cycles at the current density of 3 A/g.Considering that the above composites have limited Na⁺attachment points and are easy to powder during cycling,Mo Se₂is combined with L-Cysteine(LC),a flexible and tough organic component,to prepare a LC@Sn_0.2Mo_0.8Se₂@NC composite,which is based on Mo Se₂doped with Sn⁴⁺,composite with nitrogen-rich carbon network structure(NC)and LC.The doping of Sn⁴⁺can produce a large number of defects,increase the active sites,reduce the energy storage barrier,and expand the layer spacing of Mo Se₂to accelerate the ion diffusion.The nitrogen-containing carbon network structure in the composite material can not only provide a large specific surface area,but also alleviate the volume expansion of Mo Se₂and effectively inhibit the shedding of Mo Se₂material during cycling.The addition of the organic component LC can increase the connection sites of Na⁺,inhibit the shuttle effect of selenium,reduce the side reaction between the electrode material and the electrolyte,enhance the stability of the material,and greatly improve the sodium storage capacity.Through a series of characterization means,the successful preparation of LC@Sn_0.2Mo_0.8Se₂@NC composite is proved,and its electrochemical performance is tested,which showed excellent sodium storage performance,as well as combined with DFT calculations,the energy storage mechanism is studied.At a current density of 0.05 A/g,the LC@Sn_0.2Mo_0.8Se₂@NC composite exhibited a first-cycle discharge capacity of 1133.7 m Ah/g and a first-cycle coulombic efficiency of 85.6%.At the current density of 0.1 A/g,the discharge capacity can still reach 711.6 m Ah/g after 100 cycles.When the current density increases to 3 A/g,the capacity retention rate can reach 90%after 500 cycles.Finally,the LC@Sn_0.2Mo_0.8Se₂@NC composite is applied to a hybrid sodium-ion capacitor,and the specific capacitance of the LC@Sn_0.2Mo_0.8Se₂@NC composite could reach 134.6 F/g at a current density of 0.1A/g.A specific capacitance retention of 88.6%is achieved after 5000 cycles at a current density of 3.2 A/g.And the energy density of 77.7 Wh/Kg is achieved at a power density of 16075.9 W/Kg.