Preparation And Lithium-storage Properties Of Carbon-based Metal Compound Composites

The rapid development of today's society has put forward higher requirements for energy storage devices,requiring them to have higher energy density,higher power density,and longer cycle life.As a mature high-efficiency energy storage device,the structural properties of the anode material of lithium-ion batteries have a critical impact on the overall battery performance.Metal compounds have relatively high theoretical specific capacity and become a promising anode material for new generation lithium-ion batteries.However,its large volume expansion and poor electrical conductivity severely limit their development.In this paper,metal compounds(iron oxides and cobalt oxides)are combined with carbon-based conductive materials(graphene oxide and carbon nanotubes)to alleviate the problems of large volume expansion and poor electrical conductivity of metal compounds,and to investigate the relationship between their structural composition and lithium storage performance in order to reveal the synergistic mechanism between the components and the potential reasons for the excellent electrochemical performance.The main work can be summarized as follows:(1)The unique porous skeleton structure of Co-MOF was grown through the carbon nanotubes with excellent electrical conductivity as well as mechanical properties by a simple continuous ultrasonic method,or the carbon nanotubes were completely encapsulated in Co-MOF skeleton to form an amber-like composite.There are also some extra pure carbon nanotubes to build a three-dimensional conductive network with these Co-MOF grown carbon nanotubes to form Co-MOF@CNT three-dimensional network composites.Among them,the carbon nanotube penetrating structure and the surrounding 3D carbon nanotube network can improve the overall electrical conductivity of the composite while effectively buffering the volume change during the charging and discharging of Co-MOF derivatives,thus greatly improving the rate performance and cycling performance of the composite.The Co₃O₄@CNT three-dimensional network composite obtained after heat treatment used as the anode of Li-ion battery has well exploited the synergistic effect between the components and exhibited an enhanced lithium storage capability(up to 1468 m A h g^-1 and 1550 m A h g^-1 after 100 and 120 cycles at current densities of 1.0 A g^-1 and 2.0 A g^-1,respectively)and excellent structural stability.(2)A general method for the preparation of rGO-based flexible self-supporting film electrodes by rapid reduction is proposed.The method provides a faster and more economical preparation process than previous rGO-based composite preparation methods,and can also avoid the use of conductive agents and binders,thus effectively increasing the battery energy density.In addition,the method can be compounded with different materials to prepare rGO-based flexible self-supporting film electrodes with different architectures and different loadings.The electrochemical performance of Fe₃O₄@rGO flexible self-supported films was evaluated when used as anode for Li-ion batteries,showing excellent cycling stability(523 m A h g^-1after 200 cycles at 1.0 A g^-1).Even at a high area loading of 6.0 mg cm^-2,the Fe₃O₄@rGO flexible film electrode exhibited high capacity of 396 m A h g^-1 after 100 cycles at 1.0 A g^-1.(3)Using the method of rapidly preparing rGO-based flexible self-supporting film electrodes,CoO@rGO flexible self-supporting film composite embedded with hollow CoO structure were rapidly prepared by compounding Co-MOF with graphene oxide via the etching effect of ammonium sulfide on Co-MOF and the subsequent heat treatment process.This unique hollow porous structure can effectively shorten the ion transport path and provide more active sites for lithium ions.The high conductivity of reduced graphene oxide further facilitates the rapid charge transfer and provides sufficient buffer space for the hollow Co-MOF nanocubes.This strategy and the related synergistic effect of hollow porous structure and 3D reduced graphene oxide network would open a new way for synthesizing hollow porous structured rGO-based self-supported flexible electrodes.