Preparation And Electrochemical Performance Of Co-based And Mobased Transition(Dual) Metal Oxide(Sulfide)

With the gradual depletion of fossil energy and aggravation of environmental pollution,the development of clean,environmental-friendly and energy-efficient new energy sources has attracted widespread attention.The lithium ion battery has been regarded as one of the most promising energy storage devices due to its advantages of high specific capacity,long cycle life,no memory effect and green environmental protection and so on.In recent years,lithium ion battery is widely used in portable electronic products such as notebook computers,digital cameras,mobile phones,and it also shows very broad application prospect in the field of high power devices of electric vehicles,smart grid and electric cars.It is one of the key factors to improve the performance of lithium ion battery by developing anode materials with high ratio energy and high specific power.Among them,transition（dual）metal oxides（sulfides）have high theoretical specific capacity,low cost,abundant resources and are easy to be prepared on a large scale.Therefore,it has became one of the research hotspots for lithium ion battery anode materials.However,there are also some problems that need to be solved,such as poor conductivity and large volume effect,which lead to poor rate performance and low cycle stability.In this paper,the nanotransition metal compounds are combined with carbon materials and the self-supporting bimetallic sulfide is synthesized on the conductive base foam nickel,which can effectively improve the electrochemical properties.The main research contents and conclusions are as follows:（1）Preparation and electrochemical performance of Co₃O₄@NC composites.Melamine is used as the carbon and nitrogen sources,cobalt acetate as the cobalt source and ammonium oxalate as the precipitant.The precursor material is prepared by precipitation method,followed by high-temperature carbonization and low-temperature oxidation treatment to obtain the Co₃O₄@NC（cobalt tetroxide@nitrogen-doped carbon）composites material.By optimizing the amount of cobalt source（25mmol）,the starfish-like Co₃O₄@NC-2 composite was obtained.The structural characterization shows that it is a secondary micro-nano structure with consisting of cobalt tetroxide nanoparticles and being coated with a carbon layer on the surface.The electrochemical test results show that the discharge specific capacity shows 747.6 mA h/g with the capacity retention ratio of 85.1%,after 100 cycles at a current density of200 mA/g.The discharge specific capacity retains 596.4 mA h/g,after 300 cycles at a current density of 500 mA/g.The excellent cycling performance is attributed to the uniform coating of N-doped carbon on its surface.（2）In-situ construction and electrochemical properties of three-dimensionalInterconnected MoS₂/NPC-NCNTs composite.Melamine is used as the carbon and nitrogen sources,silica as the mesoporous template.First,melamine-formaldehyde resin is prepared by microemulsion method.Then,catalysis is simultaneously in progress during the carbonization of the resin to form a 3D carbon substrate network structure by N-doped carbon nanotubes and amorphous carbon.Finally,MoS₂/NPC-NCNTs（molybdenum disulfide/nitrogen-doped porous carbon-carbon nanotube）composite is obtained through hydrothermal method.The structural characterization finds that the three-dimensionally connected N-doped porous carbon-carbon nanotube network carbon substrate is similar to the reinforced concrete structure,NPC and NCNTs are entwined and interconnected each other and MoS₂ are firmly anchored into the substrate.When it is used as anode materials for lithium-ion batteries,the discharge specific capacity is as high as 1056.4 mA h/g and the capacity retention ratio is 86.7%at a current density of 200 mA/g for 100 cycles.After 400 cycles at a current density of 1000 mA/g,the discharge specific capacity still can be retained at 526.1 mA h/g.Even at a high current density of 4000 mA/g,a high specific capacity of 452.2 mA h/g can still be achieved.The excellent cycle and rate properties are attributed to the unique structure of the material,the introduction of conductive carbon substrate and the characteristic of nitrogen doping.（3）Preparation and electrochemical performance of self-supporting CoMoS₄.Firstiy,using sodium molybdate and cobalt acetate as raw material,CoMoO₄ is successfully grown on foam nickel substrate by the hydrothermal method and heat treatment technology.Then,it is sulfided in the sodium sulfide solution to finally obtain self-supporting CoMoS₄ electrode.Structural characterization shows that CoMoO₄ nanosheets are uniformly grown on foam nickel substrate.After sulfuration,the morphology has been changed to form honeycomb-like CoMoS₄.It has excellent electrochemical performances.At the current density of 100 mA/g,the initial charge-discharge capacity are 1678.3 mA h/g and 1914.8 mA h/g,the initial coulomb efficiency is 87.6%.After 40 cycles at a current density of 200 mA/g,the specific capacity is 1184 mA h/g,which is much higher than that of the CoMoS₄ powder sample.Honeycomb-like CoMoS₄ electrode also exhibits excellent performance in sodium-ion batteries.Even at a current density of 1000 mA/g,the specific capacity is as high as944.3 mA h/g.The self-supporting electrode of foam nickel substrate has a key effect for the improvement of rate performance.The improvement of initial coulomb efficiency is attributed to the fact that nickel promotes the conversion reaction of the active material with the lithium（sodium）.In this paper,we provide a simple method for the preparation of carbon coated porous secondary nanostructures and a feasible strategy for constructing three-dimensional nitrogen doped porous carbon-carbon nanotube network carbon substrate in situ and also provide an idea for the improvement of electrochemical properties of lithium anode materials for transition metal compounds,especial ly the first coulomb efficiency.Furthermore,we also have laid a good foundation for the further development of lithium（sodium）anode materials.