On the Use of Recycled PVB to Develop Sustainable Separators for Greener Li-Ion Batteries

In this work, sustainable Li-based battery separators are prepared starting from a waste material from the glass industry, viz. polyvinyl butyral (PVB) widely used as a sacrificial interlayer in high impact-resistant windows. First, polymeric membranes are prepared via the phase-inversion method using commercial PVB as the backbone and 4,4′-methylenebis(cyclohexylisocyanate) as a crosslinking agent. They are characterized from a physicochemical viewpoint by thermomechanical analysis, infrared spectroscopy, and scanning electron microscopy, and are successfully tested as separators in Li-metal cells with LP30 electrolyte. Electrical and electrochemical properties are evaluated by impedance spectroscopy and galvanostatic cycling, providing comparable results with commercial Celgard 25 µm monolayer microporous polypropylene separator. As a proof-of-concept, for the first time, recycled PVB-based polymer membranes from wasted car glasses are prepared, adjusting the synthesis protocol to account for the presence of plasticizers and contaminants. They show a dense elastomeric appearance and proved to be compatible with Li metal and stable upon 600 h of Li plating/stripping. The electrochemical window is compatible with the LiFePO₄ cathode, as demonstrated by prolonged galvanostatic cycling (250 cycles) in laboratory-scale cells. Preliminary results are highly encouraging and pave the way to developing novel separators for safe, low-cost, and sustainable energy storage devices.