Influence of fluoropolymer binders on the electrochemical performance of C-LiFePO4 based cathodes

Abstract

The polymer binder plays a relevant role in the performance of battery electrodes. This work proposes poly(vinylidene fluoride-co-trifluoroethylene), PVDF-TrFE, as a polymer binder for C-LiFePO4 based cathodes and investigates its effect in the electrochemical properties of the cathodes. Morphological, electrical, swelling and electrochemical properties were investigated for this polymer binder and the results were compared with the ones from two other fluoropolymers, poly(vinylidene fluoride), PVDF, and poly(vinylidene fluoride-cohexafluoropropylene), PVDF-HFP, already reported in the literature as binders for CLiFePO4 cathodes. It is demonstrated that cathode morphology and electrical conductivity are similar, independently of the polymer binders, but that the swelling values depend on the selected binder. The voltage difference between the two redox peaks of the C-LiFePO4 based cathodes with PVDF, PVDF-HFP or PVDF-TrFE as binders are 0.46, 0.79 and 0.83 V, respectively. Also, the impedance values show the following order: PVDF < PVDF-HFP ≤ PVDF-TrFE. Finally, the discharge capacities values are 129 mAh.g-1 , 75.5 mAh g-1 and 94.3 mAh.g-1 for PVDF, PVDF-HFP and PVDF-TrFE binders after 50 cycles at Crate. Thus, it is concluded that PVDF-TrFE binder shows good rate capability and cycle performance, being therefore adequate for the development of C-LiFePO4 cathodes in lithium-ion batteries