Preparation And Electrochemical Properties Of Metal-Organic Complexes Based Electrode Materials

With the increasing consumption of non-renewable resources such as fossil fuels and the more serious environmental pollution problems,new efficient and environmentally friendly electrochemical energy storage devices such as lithium-ion batteries and supercapacitors have become one of the important strategic choices for the sustainable development of the current society.For energy storage devices,its superiority mainly depends on the electrode material.Therefore,it is urgent to research and prepare electrode materials with the advantages of high specific capacity,good electrochemical stability,and long cycle life.Metal-organic coordination polymer（MOCP）themselves have abundant interpenetrating pore structures,which facilitate the transport of electrons and ions.The complex materials are crystalline materials with highly ordered structures,uniformly dispersed active sites and exposed active sites.It is beneficial to participate in the energy conversion process,and ultimately can effectively improve the electrochemical energy storage performance.In this paper,the hydrothermal method was used to prepare electrode materials and electrode material precursors.These electrode materials mainly include3d-monometallic organic coordination polymers,3d-4f bimetallic organic coordination polymers and organic coordination polymers precursors with special morphologies.The specific content as follows:1.3d-monometallic organic coordination polymers（Mn-MOF,2,4-pdc-Co,Co-MOF）were prepared by hydrothermal method.They were characterized by SXRD,PXRD,XPS and BET.As an electrode material for lithium-ion batteries or supercapacitors,targeted modification is carried out for the shortcomings of poor conductivity and small specific surface area of the original material,and the electrochemical performance of the complex is tested by CV,GCD,EIS,cycle stability test.For Mn-MOF,a small amount of Cu powder was added as a conductive agent for modification（Mn-MOF-Cu）.As an electrode material for supercapacitors,the specific capacitance of Mn-MOF-Cu is 1606 F g^-1,higher than that of Mn-MOF(1106 F g^-1)at the same current density(0.5 A g^-1).In addition,Mn-MOF-Cu also exhibits good cycling stability.For 2,4-pdc-Co,the morphology was mainly modified,and the original bulk crystal was modified into a one-dimensional morphology（2,4-pdc-Co-W）with the same crystal structure.The modified electrode material has a significant increase in specific surface area,and has obvious advantages as an electrode material for supercapacitors.For Co-MOF,the conductivity is also modified.Experiments show that as the electrode material of lithium ion battery,the addition of 20%Cu powder has the most excellent electrochemical performance.However,Co-MOF has the problem of poor structural stability as an electrode material for lithium ion batteries.2.Three 3d-4f bimetallic organic framework（ZnCe-MOF,Cu Ce-MOF and CeCu-MOF）were prepared by hydrothermal method.The complexes were characterized by SXRD,PXRD,XPS and SEM.As an electrode material for lithium-ion batterie or supercapacitor,electropolymerized conductive polymers and compounded with plant carbon are used for targeted modification in view of the poor conductivity of the original materials,and CV,GCD,EIS,cycle stability tests are used to test.For ZnCe-MOF and Cu Ce-MOF,Cu Ce-MOF@PANI-1,Cu Ce-MOF@PANI-2,ZnCe-MOF@PANI-1 and ZnCe-MOF@PANI-2 were obtained by electropolymerization of different amounts of conductive polymers.The experimental results show that Cu Ce-MOF@PANI-1 and ZnCe-MOF@PANI-1 have good electrochemical performance and have certain application potential.For CeCu-MOF,the conductivity was also modified.Four kinds of plant carbons were prepared by different methods,and a carbon material with the best electrochemical performance was screened out as a conductive agent.The addition of plant carbon has the best electrochemical performance.As the electrode material of the supercapacitor,the addition of 20%of the vegetable carbon has the best electrochemical performance.In addition,this experiment also proves that the addition of rare earth elements can effectively solve the problem of poor structural stability of electrode materials in the electrochemical process encountered in the experiments in the previous chapter.3.Two types of metal-organic coordination polymer precursors with special morphologies were prepared by hydrothermal method,and then calcined at high temperature to obtain hollow Ni-Co oxides and flower-likeCeCo oxides.For CeCo oxide,its annealing conditions were explored in the experiment.Among them,the material（CeCo-700）calcined at 700°C has good electrochemical performance as an electrode material for lithium ion batteries.At a current density of 100 m A g^-1,the reversible capacity of CeCo-700 reaches 952 m Ah g^-1after 100 cycles.It is used as the anode material of the full battery and exhibits a specific capacity of 195 m Ah g^-1after 50 cycles at a current density of 200 m A g^-1.After connecting 9 full batteries in series,the"SUT"LED light bulb circuit board can be successfully lit.For the Ni-Co oxides,in which the Ni Co₂O₄/Ni O composite is used as the anode material for Li-ion batteries,the reversible capacity is 659m Ah g^-1after 100 cycles at 100 m A g^-1.As an electrode material for supercapacitors,Ni Co₂O₄/Ni O has a specific capacitance of 708.4 F g^-1at 1 A g^-1,and its capacity retention rate is 94.3%after 10,000 cycles at 10 m A g^-1.These excellent electrochemical performances on Li-ion batteries and supercapacitors are firstly attributed to the synergistic effect between bimetals,and secondly,the modification of a small amount of Ni O in the electrode material,which contributes to the Li⁺storage to a certain extent.To sum up,seven kinds of 3d-monometallic and 3d-4f bimetallic organic coordination polymers with novel structures were prepared and modified according to the shortcomings of different kinds of organometallic coordination polymers.Secondly,the introduction of 4f metal into 3d-organometallic coordination polymer can improve the structural stability of electrode materials in electrochemical process.Finally,the application value of these electrode materials was explored.