Controlling Gel Morphology for Enhancing the Cation Mobility of Poly(vinylidene difluoride)-Based Gel Electrolytes for Lithium Secondary Batteries

• Published in: Journal of physical chemistry. C Vol. 124; no. 26; pp. 14082 - 14088
• Main Authors: Takeda, Sahori, Saito, Yuria, Yagi, Toshiki, Watanabe, Keisuke, Kobayashi, Shota
• Format: Journal Article
• Language: English
• Published: American Chemical Society 02.07.2020
• Subjects: C: Energy Conversion and Storage; Energy and Charge Transport
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.0c02164

We evaluated the relaxation times (T 2), mobilities, and microviscosities of ionic species in terms of the crystallinity, X c, of the constituent poly­(vinylidene difluoride) (PVDF) polymer of the PVDF-based gel electrolytes through NMR studies to confirm the anomalous features of the location and mobility of ions. Two T 2 components of the anion (T 2(F1) > T 2(F2)) and a significant increase in the longer T 2(F1) of the major component with increasing X c were detected in annealed gels, contrary to the single component of T 2(F) that was short and independent of the X c of quenched gels. This indicated that the anions of annealed gels had two different locations, and their contributions to the anion migration changed with X c. As the PVDF-based gel consists of a mixture of crystalline and amorphous phases, and the crystal domain size depends on X c, T 2(F1) would reflect the sizes of the crystal domains that selectively influence the anion mobility. Furthermore, mobilities and microviscosities of the carrier ions were evaluated to confirm the ion-migration mechanism associated with the interaction between the ion and crystalline polymer in the gel. This revealed the basis for designing polymer gel electrolytes for lithium secondary batteries by controlling the two-phase morphology of the PVDF-based gels.