Research On The Performance And Mechanism Of Lithium Metal-graphene Paper Composite Anode

The mileage upgrade of electric vehicles greatly raised the requirement of high-energy-density lithium batteries,in which metallic lithium is a promising anode candidate for the future.As anode,metallic Lithium has the highest theoretical capacity?3860 mAh/g?and the lowest electrochemical potential?-3.04 V?in the candidates.However,serious safety issues and rapid capacity fade severely impede its practical applications.The modification research of lithium metal anode properties has recently captured increasing attentions.In this thesis,based on graphene paper?GP?,a high performance lithium composite anode has been designed for lithium metal batteries.GPs were prepared by flow-induced filtration of electrochemical exfoliated graphene sheets.The results showed that the sheet thickness of graphene was highly related with electrolyte?K₂SO₄?concentration.By adjusting the concentration of solution,we found graphene sheets fabricated in 0.1 M K₂SO₄ have the thinnest average thickness.Uniaxial in-plane tensile tests operated in the self-developed in situ scanning electron microscopy?SEM?tensile system showed that the thickness of graphene sheets has strong impact on the fracture strength of corresponding graphene papers.And the GP formed by thinnest graphene sheets has the best fracture strength of 192 MPa.This is due to that the thickness decrease of exfoliated graphene will increase the quantity of interlayer crosslinks,thus improving the mechanical properties of GPs.Lithium metal-GP composite electrode was fabricated by electrodeposition method.The results showed deposited lithium appeared at the surface and inside of GP which led to an increase in the thickness of GP.This phenomenon was further confirmed by in-situ,real-time and dynamic SEM observation of the lithium deposition process.In order to evaluate the modification method which GP was used as the skeleton,pure lithium,lithium-10 h?hours?-GP and 50 h-lithium-GP were used to assemble symmetrical batteries for measurements,respectively.The results showed that the composite of lithium and GP effectively reduces the internal resistance and improve the cycling performance.This is because that the GP skeleton inhibits the growth of lithium dendrites and stabilizes the SEI layer during cycling process.