Study On Preparation,Modification And Electrochemical Performance Of Lanthanide Metal Coordination Complexes

In this green era,in order to avoid the problem of the greenhouse gas effect and the environmental pollution caused by traditional energy extraction,lithium ion batteries(LIBs)as"green"energy sources have large specific capacity,controllable shape and long cycle life,high power density and other advantages have been widely used in small electronic products,automobiles and other domains.An important part of a LIB is its electrode material.The advantages and disadvantages of the electrode material are mainly its structural stability,specific capacity,and whether it is green or environmentally friendly.At present,the commercially available anode material is graphite,and the lanthanide metal organic frameworks(Ln-MOFs)is crystalline porous material containing rare earth metals combined with organic and inorganic materials.It has considerable potential to be used as an electrode material.In this paper,three kinds of lanthanide-lithium bimetallic coordination polymers,one lanthanide coordination polymer and their related derivatives were prepared by hydrothermal synthesis.The electrochemical properties of these materials for LIBs were studied.The specific research work are as follows:(1)Using pyromellitic acid as a ligand,and using cerium,praseodymium and lanthanum as the main coordination centers,four new lanthanide complexes with different structures were successfully prepared by hydrothermal synthesis methods(CeLipma,PrLipma,LaLipma and Cepma),three of which are lanthanide-lithium bimetallic coordination polymers.the structures,morphologies and compositions of these four different new rare earth metal complexes were analyzed by means of single crystal x ray diffractometer(SXRD),scanning electron microscope(SEM)and energy dispersive spectrometer(EDS).These three lanthanide-lithium bimetallic coordination polymers materials as negative electrode materials were assembled into a cell in a glove box to test the battery performance.Among them,CeLipma has outstanding performance.The charge and discharge cycles are performed at a current density of 100mA/g.CeLipma can increase the specific capacity up to 800mAh/g with the increase of the number of cycles.After 50 cycling,the capacity retention rate reach 91.4%.(2)Using pomelo peel as raw material,three different methods were used to pyrolyze pomelo peel to obtain porous carbon material,and its electrochemical performance was studied and compared.We found that the vacuum-treated carbon material(S1)has a specific discharge capacity close to that of graphite.Its specific surface area is 464.2 m~2/g,and its pore size is 82.2nm.(3)The prepared biochar(S1)was compounded with CeLipma at different mass ratios under hydrothermal conditions.Three composite samples were obtained:CeLipma0.05C,CeLipma0.1C,and CeLipma0.15C.X-ray diffractometer(XRD),electron microscope(SEM),and other test methods were used to analyze the phase,morphology and composition of the three samples,and the three samples were made into button batteries and tested at a current density of 100 mA/g.The performance of Celipma0.05C is outstanding and stable,and the specific capacity after 100 cycles of electrochemical test is 494.3 mAh/g.(4)Modify the cerium-lithium bimetal coordination polymer material with outstanding performance.The sintering temperature of CeLipma in the air was 400°C,500°C,850°C,and sintering for 4h.The corresponding products were named CeLipma400,CeLipma500,and CeLipma850,respectively.The morphology and composition of the three samples were tested by X-ray diffraction(XRD),electron microscope(SEM),and other test methods and take three kinds of samples as anodes to assemble into button batteries for charge and discharge tests at a current density of 100 mA/g.It was found that CeLipma850 was porous.In the electrochemical test,the specific capacity was 206 mAh/g after 400 cycles,showing good electrochemical performance.