Study On Organic/Inorganic Transition Metal Compounds As Anode Materials For The Lithium-ion Battery

Li-ion batteries are widely used due to high specific capacity,long cycle life,high safety and friendly environment.At present,graphite（372 mAh/g）as mainly anode material of Li-ion batteries provides limited capacity.Therefore,it is the development direction of lithium ion batteries to search for electrode materials with large capacity and good cyclic stability.Among all inorganic transition metal compounds,the si materials have been widely studied because of large theoretical capacity（4200 mAh/g）,low working potential and abundant reserves.But Si materials will have large huge volume expansion in the cycles,which not only caused the active material layer separated from current collectors and the active material layer breakage hindered the electron transfer,but also unstable SEI film formed during the powdering Si contacted with the electrolyte.The above factors lead to fast capacity degradation and poor cyclic performance of the Si materials.In this paper,the cyclic performance of Si materials was improved by current collectors.Carbon cloth（CC）was used as the base material and the annealed copper coated carbon cloth was made by a two-steps:electrodeposition and annealing at 400℃.It was made into half-cells with nano silicon,the initial capacity of battery was 1250 mAh/g at current density of 210 mA/g,and the capacity retention rate was 98%after 40 cycles.The improvement of cyclic performance is attributed to the hole and Cu-protuberance structure which produced on the nodular type of copper during annealing process.The surface structure provides buffer space for volume expansion of Si materials.Transition metal oxides MxOy（M=Fe,Co,Cu and so on）have the advantages of large theoretical capacity（about 2³ times of graphite）,low working potential and low price,but poor cycle performance.The modification methods for transition metal oxides are mainly from nanoscale design and composites creation.In the case of Cu₂O,this paper used carbon fiber cloth as the base material and took a simple hydrothermal method to grown carbon coated Cu₂O nanoparticles on the surface of the carbon fiber as independent electrode composites（Cu₂O@C/CC）,which can be directly used as anode materials.Cu₂O@C/CC composites provided 580 mAh/g after 60 cycles at current density of 100 mA/g and 280mAh/g of reversible capacity at current density of 1 A/g.The good cyclic performance of Cu₂O@C/CC electrode composites are ascribed to the core-shell structure which inhibited the volume expansion of Cu₂O and the 3D conductive network provided by carbon cloth which promoted the charge transfer.MOFs materials are coordination compounds which form by metal ions as the junction center and organic ligand.Both the metal center and organic ligand of the MOFs materials have the ability to load the charge,so it has the ability to be used to the electrode materials for lithium-ion batteries.Although the MOFs performed good electrochemical performance,the structural stability and poor conductivity are still the problem to be solved.This paper reported a type of new[Mn_1.5（HCOO）₃]_∞MOFs material acted as anode materials for lithium-ion batteries.The physical characterization of[Mn_1.5（HCOO）₃]_∞MOFs show its space structure and surface morphology,and the[Mn_1.5（HCOO）₃]_∞MOFs acted as anode material for lithium-ion batteries to test electrochemical properties.The[Mn_1.5（HCOO）₃]_∞MOFs provided a reversible capacity of 280 mAh/g after 130 cycles at current density of 100 mA/g and 125 mAh/g at 1 A/g.At the same time,the[Mn_1.5（HCOO）₃]_∞electrodes were used to characterize the charged state and discharged state by infrared absorption spectrum to explain the mechanism of charge-discharge and the reason for the stability of the structure.