Lithium Storage Mechanism Of Nanopores In Carbon Materials And Lithium Deposition On Them

Metallic lithium is an ideal anode material for its high specific capacity(3860 mA h g^-1)and low redox potential(-3.04 V vs.SHE).However,issues such as dendritic growth and low Coulombic efficiency prevent its application.This dissertation will focus on the lithium metal storage mechanism in porous carbon materials and the lithium deposition on the carbon current collectors.Porous carbons usually show very high capacities for lithium storage and good cycling performance.However,the controversy on the lithium storage in the nanopores has never been stopped.We investigated the lithium and sodium storage behavior of the pyrolytic carbon in different potential ranges and realized lithium metal storage in the cavities of the carbon nanotubes(CNTs)containing iron carbide.We directly observed the metallic lithium by the cryogenic transmission electron microscope(cryo-TEM)and discussed the conditions of the lithium metal storage in the cavities of CNTs.This provides the possibility to further increase the lithium storage capacity of carbon materials.The commercial CNT sponge was used as a three-dimensional(3D)current collector for dendrite-free lithium deposition.The stable graphitic-amorphous carbon composite structure and enhanced affinity of lithiated graphite with lithium metal improve the Coulombic efficiency and the cycle stability of the lithium metal batteries.The lithium plating/stripping on the sponge is stable for 90 cycles with high coulombic efficiencies.In the commercial LiPF₆-carbonate electrolyte,the presence of metallic lithium can destruct the solid electrolyte interphase(SEI)film on the graphite and the graphite structure without the protection of the SEI film will be destroyed due to co-intercalation of the solvated lithium ions,causing the poor lithium plating/stripping cycling on the graphite.We improve the structural stability of the graphite substrate and the lithium plating/stripping cycling behavior on it by two methods.On one hand,the reduction of the graphite particle size significantly suppresses the particle pulverization and makes the graphite more stable in both the ether and the carbonate electrolytes.On the other hand,we enhance the stability of the SEI film on the graphite substrate for lithium deposition by using lithium bis(fluorosulfonyl)imide(LiFSI)in the carbonate electrolyte,protecting the structure of graphite and improving the lithium plating/stripping cycling on it.