Regulating Crystalline Phase/Plane of Polymer Electrolyte for Rapid Lithium Ion Transfer

Electronic-rich functional groups and flexible segments have long been perceived to be the decisive factors influencing lithium-ion transfer in polymer electrolytes, while crystallinity is regarded as the great scourge. Actually, the research on the influence of crystalline phase and crystalline plane is still in scarcity. Herein, taking poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP) as an example, new (111/201) crystal planes (belonged to β-phase) are regulated by dissolving process and clarified by Synchrotron radiation X-ray diffraction and X-ray diffraction. Density functional theory calculation indicates that the newly exposed (111/201) crystal planes provide higher binding energy with lithium ions and are conducive to provide more ion transport channels. ⁷Li nuclear magnetic resonance of new crystalline planes contained PVDF-HFP based electrolyte shows lower field and sharper peak intensity, further proves the rapid lithium ion transfer. Therefore, a high ionic conductivity of 6.42×10^-4 S cm^-1 and a large lithium-ion transfer number of 0.7 are achieved. This study offers a new insight into the influence of crystalline phase and crystalline plane on the transfer of lithium ion for polymer electrolytes.