Solid-state NMR Study On The Structure And Molecular Motion Of PEO/Li~+ Amorphous Polymer Electrolyte

In this thesis,we prepared a series of amorphous PEO/Li⁺samples,in which the amorphous PEO/Li⁺complex structures were located on the surfaces of PEO crystal lamella.Varied advanced solid-state NMR techniques were applied to study the phase structure and molecular dynamics in the samples.Combined with electrochemical performance,the influences of lithium ion motion on the ionic conduction mechanism were investigated.1.An amorphous PEO/Li⁺complex structure rich in chain ends was constructed on the PEO crystal surface by the immersion method.Two different lithium ions in PEO/Li⁺system were assigned by ⁷Li NMR.The motion of chain segments and chain ends in amorphous phase was analyzed by ¹³C NMR.Finally,the activation energy required for lithium ion exchange motion is obtained through the 2D ⁷Li exchange NMR.The exchange dynamics of the lithium ions provide a molecular mechanism of the ion transportation in the surface of PEO crystal lamella,which is further correlated with the ionic conduction mechanism of the PEO/Li⁺complex structure.2.Based on the work in the first part,the chemical structure of the PEO chain end was changed,and the influence of the PEO chain ends on the PEO/Li⁺complex structures on the surface of the PEO wafer was studied.It was found by DSC that the complete amorphous state of this type of material was temporarily stable,which would gradually transform into a stable composite containing PEO crystal phase.⁷Li and ¹³C solid-state NMR were used to investigated the distribution and motion of the lithium ions in the transient and stable states,and the diffusion motion of the lithium ions in stable state was investigated by ¹H-⁷Li WISE NMR.Finally,the distribution of lithium ions in the amorphous phase and the relationship between lithium ion motion and conductivity are discussed.