Investigating the influence of PVDF binder crystallinity on the performance of LiFePO4 cathode in Li-ion batteries

Abstract

Abstract Poly(vinylidene fluoride) (PVDF) has been widely utilized as a binder material in cathode as well as anode preparation for Li-ion batteries. Recent reports on water-soluble and functional binders have firmly established that even though the binder consists of only a small part of the electrode, it can significantly boost cell performance. However, no previous report has specifically explored the role of PVDF crystallinity on the performance of the LiFePO4 cathode and cell. In the present work, LiFePO4 cathodes with two different binders PVDF 1 (Kynar HSV 900), and PVDF 2 (Solef 5130) have been prepared. The PVDF binder with higher crystallinity showed more viscosity (86.3 Pa.s), higher adhesion strength (11.42 N-cm−1), and minimal electrolyte uptake (11.3%) as compared to the low crystallinity binder (32.8 Pa.s, 1.30 N-cm−1, and 18.88%). Thus, the cell having more crystalline PVDF binder showed a higher initial capacity of ∼146 mAh-g−1 and stable cyclability performance (82% capacity retention after 500 cycles) as compared to the cell with less crystalline binder PVDF (∼136 mAh-g−1 and 64%). The post-mortem analysis performed after 500 cycles of charging and discharging revealed relatively smaller cracks formed in the cathode with higher crystallinity binder, which explains its better cyclability.