Preparation And Lithium Storage Performance Of Carbon-based Metal Compound Composite Materials

With the development of human society,the continuous consumption of traditional energy and the increasingly prominent environmental problems have made it an inevitable trend to find renewable and clean energy.Wind energy,solar energy or geothermal energy has gradually become a form of new energy that mankind depends on.However,these energy sources are primary energy sources and are usually converted into electrical energy for use.In the process of developing and utilizing renewable energy,electric energy storage technology plays an important role.Among them,in chemical energy storage,lithium-ion batteries are used as energy storage devices in many fields due to their high energy density and coulomb efficiency.In terms of energy density,the capacity of lithium-ion batteries is gradually approaching their theoretical limit,but the energy density is still very low in commercial applications,especially in some portable devices.Therefore,it is very necessary to develop a new type of high energy density lithium ion battery anode material.Various metal compounds（such as metal oxides,metal selenides,etc.）have attracted attention due to their high theoretical capacity.Most of the metal compounds have low conductivity and significant volume effect.They are used as electrode materials for lithium-ion batteries.It often exhibits low cycle stability.The component and structure control of metal compounds has become a research hotspot and development trend of electrode materials for lithium-ion batteries.In particular,carbon-based composite materials can significantly improve the conductivity of materials,reduce material costs,and have advantages such as large room for regulation and control,which have become an ideal trend for industrialization research.This paper designs three-dimensional composite materials by combining carbon with transition metal oxides and selenides.The materials are characterized by scanning microscope,transmission electron microscope,thermogravimetric analyzer and other means,and the lithium storage performance is studied.The results show that the prepared A series of composite materials exhibit high capacity and good cycle stability.Because the three-dimensional structure of the material we prepare has a larger specific surface area,it can provide more active sites,can provide more paths for the transfer of electrons and ions,and can also well alleviate the volume effect during charging and discharging.The specific work is as follows:（1）A three-dimensional Mn O/C nanomaterial was synthesized by a simple route of immersion and calcination.This material combines the excellent lithium storage performance of Mn O and the good stability of carbon.At the same time,the carbon content and morphology of the sample are adjusted by adjusting the calcination temperature.Because Mn O is embedded in the carbon substrate,it provides excellent lithium storage performance by alleviating the volume effect during charging and discharging.The sample Mn O/C-750（Calcined at 750℃）still has a specific capacity of 1067.95 m Ah g^-1 after 200 cycles at a current density of 0.2 A g^-1.The rate performance is 840.04 m Ah g^-1,625.55 m Ah g^-1,510.71 m Ah g^-1,364.61 m Ah g^-1,116.92 m Ah g^-1 and 826.94 m Ah g^-1.After 50 cycles of different rate current densities,they can still reach 826.94 m Ah g^-1 at a current density of 0.2 A g^-1,indicating that it has good rate performance.It still has 722.32 m Ah g^-1 after 600 cycles at a current density of 1 A g^-1.（2）Mn O microspheres were synthesized by a combination of hydrothermal method and template method,Si O₂ and carbon-nitrogen layer were wrapped on the surface of the microspheres,and finally Si O₂ was etched away to obtain a new type of Mn O@Void@NC composite material.The carbon-nitrogen structure of the outermost layer can improve the conductivity of the material and avoid direct contact between the inner layer of Mn O and the electrolyte,which is beneficial to the formation of a stable SEI film.The internal void space protects the volume change of Mn O during charging and discharging,and also protects the carbonitride coating from cracking.This composite material allows lithium ions to be embedded and released quickly during the charge and discharge process,and provides excellent lithium battery performance.The final lithium ion battery test results show that the prepared Mn O@Void@NC has better performance than Mn O and Mn O@NC,and its specific capacity remains at 1143.93 m Ah g^-1 after 200 cycles at a current density of 0.2 A g^-1.The specific capacity of 632.69 m Ah g^-1 is still maintained after 500 cycles at a high current density of 1 A g^-1.（3）The honeycomb-shaped 3D Co Se_x composite material was prepared by freeze-drying and high-temperature calcination.In the experiment,by adjusting the amount of cobalt nitrate,the decomposition of cobalt nitrate and the thermal decomposition of gelatin combined to form different morphologies and structures during the calcination process.Among them,the pore structure produced by the decomposition of cobalt nitrate can reduce the path of lithium ion transmission,the large amount of carbon in the sample can alleviate the volume change of the active material during the charge and discharge process,and its honeycomb three-dimensional structure also provides more reaction sites.So that the material has excellent capacity and rate performance.The sample Co Se_x/C-1.0 has a specific discharge capacity of 1088.01 m Ah g^-1 after 100 cycles at a current density of 0.2 A g^-1,and discharge specific capacity of 779.38 m Ah g^-1after 300 cycles at a high current density of 1 A g^-1.