Structural Design And Electrochemical Properties Of Carbon-based Composites

The massive consumption of fossil energy and the environmental pollution caused by it are becoming increasingly serious,which promotes the development of renewable and clean energy such as solar energy and water energy,thus driving the progress of electrochemical energy storage equipment.Among many electrochemical energy storage devices,due to its high operating voltage,no memory effect,high energy density and lightweight quality,Lithium-ion batteries have become an indispensable power supply to maintain daily life.However,most of the high specific capacity anode materials in Lithium-ion batteries used have outstanding problems such as poor conductivity and large volume change during charge and discharge,which seriously affect the capacity performance and cycle life of the batteries.Herein,in order to solve these problems,two kinds of carbon-based composite materials based on graphene were prepared by introducing stable and conductive carbon materials and the design of nanostructure.In addition,the electrochemical performances of these composite materials were studied.The specific contents are as follows:（1）Two-dimensional graphene sheets and Co₉S₈ nanoparticles were all coated with a carbon layer to form a N-C@Co₉S₈@G nanosheet structure.In this nanostructure,graphene can significantly improve the electrical conductivity and structural stability of the composite material.When used as the anode of Lithium-ion batteries,N-C@Co₉S₈@G has high specific capacity(1009 mA h g^-1 at 0.1 A g^-1),excellent rate performance(422 mA h g^-1 at 10 A g^-1)and long cycle life(853 mA h g^-1 after 500 cycles at 1 A g^-1).In addition,the full cell assembled with LiCoO₂ as cathode shows a high reversible capacity of 300 mA h g^-1 at 0.1 A g^-1.（2）Three-dimensional graphene aerogel and Si/carbon nanoparticles were used to form Si@N-C@G aerogel structure by hydrothermal method,and used it as anode material for Lithium-ion batteries.With the help of polydopamine coating,Si nanoparticles were uniformly dispersed in the three-dimensional aerogel structure.The Si@N-C@G sample with optimal graphene content shows a high capacity(712 mA h g^-1 at 0.1 A g^-1)and outstanding cycle stability(420 mA h g^-1 after 1500 cycles at 1 A g^-1).When used as full cell anode,it shows a reversible capacity of 187.6 mA h g^-1 after 80 cycles at 0.1 A g^-1.