Preparation And Electrochemical Storage Mechanism Of Nickelbased Metal-organic Framework Derivatives

In order to cope with the dwindling fossil energy and reduce the global greenhouse effect,mankind's demand for new energy batteries is becoming stronger.Lithium-ion batteries(LIBs)have the advantages of pollution-free,good safety,and reusability,and are favored by people.Therefore,how to further develop LIBs with low cost,long cycle life,and high-rate performance has become a hot research topic.The negative electrode material,as one of the main components of LIBs,greatly limits its development.At present,graphite is mainly used as a commercial negative electrode,but due to the small theoretical capacity of graphite,it cannot meet the requirements of people.Therefore,it is imperative to design a negative electrode with high theoretical capacity and good cycle performance.The carbon composite material was obtained by using porous properties of MOFs and in-situ carbonization under calcination condition.It is helpful to infiltrate electrolyte and construct high-speed channel of electron and ion in LIBs test.Nickel based selenide material is a kind of compound with high theoretical capacity.It will achieve excellent electrochemical performance to prepare nickel-based selenide by Ni-MOF.However,the slow reaction kinetics of single-phase nickel-based selenides and the volume expansion during charge and discharge will lead to the sharp rupture and pulverization of the electrode.Therefore,a unique single metal selenide heterostructure was synthesized by precisely adjusting the mass ratio of Ni-MOF to selenium powder.It was found that this structure can effectively accelerate the electrode reaction kinetics and improve the cycle performance of LIBs.The research is based on Ni-MOF carbonization treatment,in situ construction of a two-phase metal selenide heterostructure with strong interaction,eliminating the interference of heteroatoms,focusing on the study of the influence of heterostructures on the charging and discharging reaction process.In addition,the influence of heterostructures with the same phase types formed by different component contents in the heterogeneous composite on the lithium storage mechanism was further studied.The paper is mainly summarized as follows:(1)Herein,nanosized monometallic selenides heterostructures are developed by precisely controlled selenylation of metal organic frameworks,which are implanted into in-situ formed carbon(Ni Se/Ni Se₂@C).At the same time,as a comparative experiment,Ni Se@C and Ni Se₂@C single-phase carbon composites were also prepared.When applied to LIBs anode materials,Ni Se/Ni Se₂@C exhibits much better lithium storage performance than single-phase carbon composites,with a higher reversible capacity of 1015.5 m Ah g^-1,better rate capacity(500.8 m Ah g^-1 at 4 A g^-1)and excellent long-cycle performance.This excellent electrochemical performance is attributed to the disordered atomic arrangement at the interface of the two phases in the heterostructure,which will cause the redistribution of interface charges and the generation of lattice distortion,thereby promoting the easy adsorption and rapid adsorption of Li⁺during the reaction.Transfer and provide additional active centers.As expected,Ni Se/Ni Se₂@C exhibits lower charge transfer resistance,higher Li⁺diffusion coefficient and reaction kinetics.(2)After carbonizing Ni-MOF to obtain Ni@C,precise selenization is performed to obtain single-metal heterostructures and porous carbon composites with the same composition but different contents(When the ratio of Ni@C:Se is 5:7,Ni₃Se₄/Ni Se₂@C-1 is produced;when the ratio of Ni@C:Se is 5:8,Ni₃Se₄/Ni Se₂@C-2 is produced).At the same time,as a comparative experiment,Ni₃Se₄@C and Ni Se₂@C single-phase carbon composites were also prepared.This paper mainly controls the content of heterostructures through interface engineering,and explores how micro-interfaces can further promote the transfer and storage of electrons and ions in the electrochemical process.When used as an anode electrode material for LIBs,it still maintains a specific capacity of 621.3 m Ah g^-1after 1000 cycles at a current density of 1 A g^-1.And at a high current density of 4 A g^-1,it still has a specific capacity of 363.4 m Ah g^-1 after 2000 cycles.It shows that Ni₃Se₄/Ni Se₂@C-1 has good cycle stability.The advantages of the higher content of heterostructure to accelerate charge transfer and reduce ion adsorption energy further improve the performance of the material,which leads to the further acceleration of reaction kinetics,and the carbon skeleton coating can buffer the volume expansion and reduction of agglomeration.The results show that Ni₃Se₄/Ni Se₂@C-1 with more micro interfaces exhibits excellent electrochemical performance as anode material.