Preparation And Electrochemical Performance Of Transition Metal Oxide/porous Graphene Anode Materials For Lithium-ion Batteries

Transition metal oxides such as Fe₂O₃,NiO and Co₃O₄,usually have high theoretical specific capacity,and attract extensive interest as anode materials for Lithium ion batteries.Nevertheless,the transition metal oxides usually suffer from poor electrical conductivity and large volume expansion in the electrochemical reaction process,which limits its application in LIBs.The most intuitive and commonly used method is to construct the composite of transition metal oxides on carbon support for the enhancement of rate capability.Holey graphene is a promising candidate to enhance the electrochemical properties of metal oxide-based composites because of excellent electron conductivity,superior specific surface area and greatly shorten the Li ions diffusion distance.We synthesized several composite materials of metal oxide and holey graphene through heat treatment process and in-situ etching method.As anode materials for Lithium ion batteries,their electrochemical properties have been studied.Specific research contents are as follows:1.Integrating nanoscale active materials on conductive holey reduced graphene oxide?graphene?framework is an effective strategy to synthesize composite electrode materials for advanced lithium-ion batteries.Herein,a composite of?-Fe₂O₃nanoparticles stabilized by the engineered holes on graphene was successfully synthesized by using a facile in-situ etching route,which exhibited high lithium storage performance.The fundamental insight of its enhancement mechanism was discussed.This work offers a newly route to synthesize the composite of holey grapheneconfined metal oxide nanoparticles for the applications in lithium ion batteries and beyond.2.Utilization of the Kirkendall effect,a composite of holey graphene confined hollow nickel oxide nanocrystals?H-NiO/H-graphene?is designed and successfully fabricated using an in-situ etching approach.As an anode electrode material for Lithium ion battery,the H-NiO/H-graphene shows good cycle stability and rate performance due to the stable hollow structure of NiO nanocrystals and the well conductivity of holey graphene.After 200 cycles at 0.2 A g^-1 current density,the discharge capacity of H-NiO/H-graphene is 732 mA h g^-1.3.As we all known,the rate performance of lithium ion batteries is closely related to the diffusion rate of lithium ions.Therefore,the development of an electrode material that can shorten the diffusion distance of lithium ions is the key to the rapid diffusion of lithium ions and the rate of lithium ion batteries.A novel architecture of hollow Co₃O₄nanocrystals in situ anchored on holey graphene is successfully fabricated,and individual hollow Co₃O₄ nanocrystal is located around one etched hole on graphene sheets.This novel architecture is demonstrated to greatly shorten Li ion diffusion distance for enhancement of Li ion transport,resulting in the best rate performance(751 mA h g^-1 at 5A g^-1,631 mA h g^-1 at 10 A g^-1)among previously reported composites of Co₃O₄ and graphene.Its discharge capacity reaches as high as 1015 mA h g^-11 even after 250th cycles at the current density of 0.2 A g^-1.