Application of soluble aromatic polyamide as a binder for LiFePO4 cathodes in lithium-ion batteries

초록

To evaluate aromatic polyamides as binders for lithium-ion batteries (LIBs), a high molecular weight poly(3,4 '- oxydianiline terephthalamide) (POTA) was synthesized and applied to lithium iron phosphate (LFP) cathodes. POTA was designed to be soluble in polar aprotic solvents by incorporating an asymmetric unit and a flexible ether linkage, enabling solution processing. Compared with PVDF, POTA-based slurries exhibited superior dispersion stability, attributable to stronger polymer-solid interactions. Among the POTAs with different molecular weights, the LFP-POTA-47 (Mn= 473,700 g/mol) electrode showed exceptional adhesion strength to Al current collectors by balancing inter-and intramolecular interactions, yielding a steady-state peel force of 15.05 N cm-1, approximately 86 times higher than the LFP-PVDF electrode (0.175 N cm-1). LFP-POTA-47 electrode also achieved the best electrochemical performance, providing 155.1 mA h g-1 at 0.2C and 120.2 mA h g-1 at 5C (77.5% retention), with 96.2% capacity retention after 300 cycles. Electrochemical impedance spectroscopy (EIS) showed that the LFP-POTA-47 electrode had the lowest charge transfer resistance, and the Li+ diffusion coefficients estimated from EIS and cyclic voltammetry were the highest among all electrodes tested.

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