The Preparation And Application Of Graphite Nanosheets In Primary Lithium Batteries

Since graphene has emerged and received scientific community’sattentions due to its exceptional charge transport, thermal and mechanicalproperties. Graphene is being used in many fields. Especially inelectrochemistry, the application of graphene plays an important role. And thelithium batteries have been one of hot topics in storage equipment industries.In this paper, graphite nanosheets are used as auxiliary materials to enhanceelectric conductivity of graphite fluorides, for the purpose of improvingperformance of primary lithium/graphite fluorides （Li/CFx） batteries.Firstly, Graphite oxide was synthesized through the oxidation of graphite bythe method based on Hummers, and was exfoliated to obtain graphene oxidesheets by means of ultrasonic treatment. Following heat treatment, chemicalreduction of graphene oxide sheets has been performed with sodium citrate toproduce graphite nanosheets. And the produces obtained in each stage werecharacterized by scanning electron microscope （SEM）, Flourier-infraredspectra （FT-IR） and Raman spectroscopy. The result shows that oxygenicfunctional groups nearly are removed after heat treatment and chemicalreduction of graphene oxide, and the disorder degree of graphite nanosheetsincreases and the thickness reduces to nanometers（8¹2nm）. Thus, the resultindicates that graphite nanosheets are successly preparated. However, thethickness of thin films is larger than that of graphene.Secondly, the structure and morphology of commercial graphite fluorides（CFx） were characterized by FT-IR, XRD and SEM in our work. Using CFx and lithium metal disc as the active material of cathode material and anoderespectively, we assembled Li/CFx coin cells （2016 configuration） in whichcathode material was composed of CFx, conductive agent and PVDF. Then theelectrochemical performance of Li/CFx coin cells is measured from differentrespects, such as different ratio of cathode material, conductive agent,thickness of electrode, and current density. The Li/CFx coin cells withacetylene black as conductive agent, exhibited high specific capacity （751mAh/g） and high working voltage （2.62 V）at 0.1 mA cm^-2 current density. Thecurrent density increased to 0.6 mA cm^-2, whereas their specific capacity andoperating voltage decreased.Finally, graphite nanosheets as conductive agent were mixed with theactive material （CFx） to enhance conductivity of CFx using the methods ofaddition without any treatment, mixing by grind and addition from solution.Then Li/CFx coin cells with graphite nanosheets were assembled to test thedischarge performance. The data show that Li/CFx coin cells using themethods of addition without any treatment and mixing by grind exhibited muchlower and unstable operating voltage than that of Li/CFx coin cells withacetylene black as conductive agent. These problems didn’t arise in the Li/CFxcoin cells using the method of addition from solution. The dischargeperformance of these coin cells identified with that of Li/CFx coin cells withacetylene black at 0.1 mA cm^-2current density. However, it shows an obviousadvantage when the current density increased from 0.7 mA cm^-2to 2.0 mA cm^-2,and the Li/CFx coin cells shew satisfactory performance. The operating voltagewas high and stable, and the specific capacity was maintained at a relativelyhigh level and decreased slowly. The Li/CFx batteries, using the same amountof acetylene black and mixture mixed with acetylene black and graphitenanosheets as conductive additives respectively, were completely discharged,and then the impedance for the Li/CFx batteries was performed. Thus, addinggraphite nanosheets from solution effectively increased the cell reaction kinetics of the CFx cathode, and decreased the impedance for the Li/CFxbatteries. In summary the performance of Li/CFx batteries was improved.