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Gel Polymer Electrolytes Based on an Interconnected Porous Matrix Functionalized with Poly(ethylene glycol) Brushes Showing High Lithium Transference Numbers for High Charging-Rate Lithium Ion Batteries

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journal contribution
posted on 04.04.2022, 20:04 by Chih-Hsiang Chang, Ying-Ling Liu
Gel polymer electrolytes (GPEs) with a high ionic conductivity and a high lithium transference number (tLi+) are highly expected for lithium ion batteries to exhibit high lithium ion conduction efficiency and depression on lithium dendrite formation. In this work, a 3-dimensional interconnected porous poly­(vinylidene difluoride) (PVDF) membrane grafted with brush-like poly­(ethylene glycol) (PEG) segments on pore walls has been prepared and utilized as the porous polymer matrix for GPEs. The interconnected porous structure and grafted PEG segments form conduction channels and interfacial transport pathways for ions, contributing to high ionic conductivities. The brush-like PEG structure obstructs the anion motion in the ion-conduction channels, bringing high tLi+ values to the resulting GPEs. The prepared GPEs exhibit an ionic conductivity and a tLi+ value of 2.39 mS cm–1 and 0.82, respectively. Consequently, the batteries employing the GPEs exhibit noteworthy cell performance including a capacity of 95 mAh g–1 under 15C, an initial capacity retention above 72.5%, and a Coulombic efficiency of 99.2% after a 400-cycle test at 2C. Moreover, the cells could stably work for more than 600 h at a constant current density of 0.2 mA cm–2 with overpotential values lower than 15 mV. The result indicates the extreme stability and subtle voltage polarization without short circuiting contributed from the restriction of lithium dendrite growth. A structure design concept for high performance GPEs has been demonstrated.