Design, Preparation And Electrochemical Properties Of Transition Metal Oxides And Sulfides/Heterogen Doped Carbon Composites

With the growth of energy demand and the increasing environmental pollution,lithium-ion batteries have attracted much attention due to their high energy density,long cycle life and environmental friendliness.Due to the lower theoretical capacity,further development of the commercial graphite anode in lithium/sodium ion batteries have been limited.Owing to high theoretical capacity and low cost,metal oxides/sulfides are considered as potential graphite substitutes.However,the low conductivity and large volume changes during electrochemical process hinder their practical application.In this paper,we prepard different metal oxides/sulfides@heterogeneous element-doped cabon core-shell structure composite materials.Due to the cabon shell,the electrochemical performance of the metal oxides/sulfides have been improved.The main contents and results of this paper are as follows:?1?Nitrogen and sulfur co-doped carbon matrix coated cuprous sulfide?Cu₂S@NSCm?composite:N,S co-doped carbon coated Cu₂S composite was obtained by hydrothermal method,in-situ polymerization and treated at high-temperature calcination with copper nitrate and thiourea as raw materials.When tested as a negative electrode material for lithium ion batteries,the reversible discharge capacity of 790.8 mAh g^-1 and 560.1 mAh g^-11 can be obtained at a current density of 200 mA g^-11 and 1000 mA g^-1,respectively,corresponding to capacity retention of 88.4%and 99%.And it also delivers a reversible capacity of 182.3 mAh g^-1 after 50 cycles at 100 mA g^-1 in SIBs.These properties are significantly superior to pure Cu₂S materials.The excellent electrochemical performance of Cu₂S@NSCm can be attributed to its co-doped structure,which is more conducive to lithium/sodium ion intercalation/extraction,and the carbon-coated structure can buffer the volume expansion during the cycling.?2?Nitrogen-doped carbon carbon matrix coated ferroferric oxide?Fe₃O₄@NCm?composite:N-doped carbon-coated Fe₃O₄ composites were obtained by hydrothermal method,in-situ polymerization and treated at high-temperature calcination with ferric chloride and sodium hydroxide as raw materials,and study the effect of different carbon content on performance.Through various electrochemical characterization analysis,Fe₃O₄@NCm-60 exhibits superior electrochemical performance.When tested at room temperature at current density of 1000 mA g^-1 after500 cycles,Fe₃O₄@NCm-60 delivered a reversible capacity of 950 mAh g^-1,and it exhibited a high reversible capacity of 760 mAh g^-1 after 900 cycles when tested at a current density of 1000 mA g^-11 at a temperature of-17±2°C.The excellent electrochemical performance of Fe₃O₄@NCm-60 can be ascribed to the nitrogen-doped carbon-coated structure to improve conductivity and buffer volume change,and the pseudo-capacitance characteristics of the material can also maintain good performance at low temperatures.?3?Nitrogen-doped carbon coated porous ferroferric oxide@reduced graphene?Fe₃O₄@NC@rGO?composite:Fe₃O₄@NC@rGO is prepared through hydrothermal,in-situ polymerization and high-temperature calcination treatment using ferric chloride and sodium hydroxide as raw materials.Electrochemical test results show that Fe₃O₄@NC@rGO posses excellent lithium/sodium storage performance.When used as anode in lithium ion batteries,it can deliver a reversible capacity of 1571 mA h g^-1 at a current density of 200 mA g^-1 after 100 cycles.When it used as anode in sodium ion batteries,it exhibited a reversible capacity of 270 mAh g^-1 at a current density of 50 mA g^-1 after 100 cycles,which is much higher than pure Fe₃O₄.The excellent electrochemical performance of Fe₃O₄@NC@rGO can be attributed to the nitrogen-doped carbon core-shell structure and the synergistic effect of carbon coating and graphene.