Toward sustainable spent battery recycling: Unveiling the impact of polyvinylidene fluoride impurities on cathode materials regeneration

Binders are common impurities introduced during the wet metallurgical regeneration process of spent lithium-ion battery cathodes. Previous studies mainly focus on removing impurities such as aluminum and copper. However, the effects of non-metallic impurities like those from polyvinylidene fluoride (PVDF) binders are less investigated. In this study, lithium-rich cathode materials containing 0–10 wt% PVDF impurities are synthesized via a sol-gel method. High-temperature in-situ X-ray photoelectron spectroscopy (XPS) reveals that fluorine atoms from PVDF enter the cathode lattice and bond with metals during sintering. Small amounts of PVDF impurities (5 wt%) favor an expanded c-axis according to X-ray diffraction (XRD). Scanning electron microscopy (SEM), XPS and high-resolution transmission electron microscopy (HRTEM) indicate the surface-enriched spinel phase induced by PVDF. The 5 wt% PVDF sample exhibits comparable initial capacity and superior capacity retention to the pristine sample after 100 cycles. Galvanostatic intermittent titration technique (GITT), cyclic voltammetry (CV) and electrochemical in-situ XRD demonstrate that PVDF impurities enhance lithium-ion diffusion kinetics and structural stability during charge/discharge, which is attributed to the mitigation of polarization and the suppression of oxygen release. This work reveals the positive role of PVDF impurities in regenerating high-performance spent cathodes.