The Functionalized Graphene Nanosheets For Electrode Materials

One of the biggest challenges facing the wireless mobile community today is providing efficient,low-cost,and environmentally friendly energy storage media for increasingly diverse applications.Lithium-ion batteries have gradually developed into representatives of energy storage and conversion because of their clear advantages and decades of research results.With the demand for higher quality of battery performance in recent years,electrode materials and conductive agents for the lithium ion batteries need to be re-developed.Since the addition of the conductive agent can improve the conductivity of the material,how to select an appropriate conductive agent is an urgent problem to be solved.At present,carbon black,acetylene black,carbon cellulose,and modified carbon nanotubes are commonly used in conductive agents,and their composites cannot achieve effective connection of particles to cause poor conductivity.Graphene has high conductivity and high electronic quality,With its high electrical conductivity,it can build a three-dimensional conductive network of "points,lines,and surfaces" with the help of carbon nanotubes and carbon black,which effectively improves battery capacity and rate performance.However,most of the preparation methods cannot process high quality graphene in large quantities,which limits its application in lithium ion batteries.Therefore,how to find an efficient,green,and simple method to produce high-quality graphene in large scale and apply it to lithium-ion batteries has become a research hotspot and a difficult point.In this paper,graphite is used as a raw material,and the exfoliation method of supercritical CO₂ assisted with fluid shear is used to prepare graphene on a large scale.This method is found effective for the exfoliation of graphite.The Raman spectroscopy and X-ray diffraction result show the process causes few damages to the structure of graphene.And the test reveals that graphene exhibits excellent conductivity.The prepared graphene is mixed with carbon nanotubes and carbon black,the optimal mixing ratio of three phases is discussed,and the uniform graphene-based conductive slurry is prepared.The results show that they form a three-dimensional conductive network of "point,line,and plane",which can fully reduce the agglomeration of carbon nanotube and graphene,reduce electrode polarization and lithium ion transfer resistance,and increase the reaction kinetic rate of the electrode.Then it greatly improves electrochemical performance.In order to investigate the influence of three phases on the capacity and rate performance of battery,different mass ratios and sizes in the conductive additives were used.It was found that when mass ratio between the carbon nanotubes,graphene and carbon black was 4:2:4,it has better performance than others.The cycle performance and low temperature performance of the battery were then tested and compared with commercial carbon black as the conductive agent.The results show that the battery has better performance than the commercial carbon black as the conductive agent.This is an important step for the application of graphene in the large-scale production of lithium ion batteries.