Study On Preparation,modification And Electrochemical Properties Of Copper-nickel Bimetallic Complexes

In recent years,new energy vehicles and mobile electronic equipments have rapidly developed,lithium ion batteries（LIBs）get a significant status in the development and utilization of new sources due to their environmental friendliness,high energy density and long cycle life.The electrode materials will expand to result in pulverization and to reduce the cyclic stability of LIBs during charge-discharge reactions,and it will also cause safety risks.In order to have practical applications,we have to improve energy density,durability and rate performance of LIBs,thus the development and application of new electrode materials are crucial for LIBs.Metal organic coordination polymers are a type of complexes formed by central metal ions and organic ligands connected with coordination bonds by self-assembly.Their unique skeleton structures and large specific surface areas are beneficial to the insertion and extraction of Li⁺.In this work,3 kinds of metal organic coordination polymers are synthesized by a hydrothermal method,we improve the conductivity and cyclic stability of complexes by compounding with graphene and high-temperature sintering.Following results were obtained after characterizations and electrochemical tests:Copper and nickel are the main coordination centers,and 3 kinds of metal organic polymers were successfully prepared by a hydrothermal method（two of them have crystal structures）.The one is copper-lithium bimetallic coordination polymer whose molecular formula is C₂H₈CuLi₂O₉P₂（named HPCuLi）;the other one is a nickel-based complex whose molecular formula is C₁₈H₂₈Ni₄O₂₅（named BTCNi）.The structures,morphologies and compositions of 3 polymers are characterized by single crystal X-ray diffraction（S-XRD）,powder X-ray diffraction（P-XRD）,scanning electron microscopy（SEM）,energy dispersive spectroscopy（EDS）and thermogravimetric analysis（TG）.3 kinds of complexes as anodes,respectively,are made into button batteries to test the electrochemical performances,HPCuLi can maintain the charge specific capacity of 164.9mAh/g after 100 cycles at a current density of 50 mA/g;HPNi can maintain the charge specific capacity of 158.9 mAh/g after 100 cycles at a current density of 50 mA/g;the charging specific capacity of BTCNi is kept 462 mAh/g after 100 cycles at a current density of 100 mA/g,BTCNi exhibit the best electrochemical performance among the 3complexes.HPCuLi/G which is obtained by compounding HPCuLi with graphene shows better battery performances and rate performances than HPCuLi because graphene which has layered structure and good conductivity can improve electrochemical performances of complexes.HPCuLi/G can maintain the charge specific capacity of 369.5 mAh/g after 100cycles at a current density of 50 mA/g,and can also maintain the charge specific capacity of 167.1 mAh/g at a current density of 800 mA/g.Two nickel-based complexes（HPNi and BTCNi）are sintered at 400℃,500℃and600℃for 2 h in air.With sintering temperatures increasing,the surfaces of polymers happen to change,and the organic ligands are constantly decomposed to provide carbon sources,which can improve the conductivity of oxides.It is interesting that both oxides treated at 500℃have better cyclic stabilities and rate performances.HPNi500 can maintain the charge capacity of 466.5 mAh/g after 150 cycles at a current density of 100mA/g,indicating nickle oxides synthesized by using MOF as a sacrificial template shows good electrochemical performance;whereas BTCNi500 can maintain the charge capacity of 907.3 mAh/g after 50 cycles at a current density of 100 mA/g,and it shows that the synergistic effect of metal nickel and nickel oxide can make electrode materials to maintain better electrochemical performances.