Unlocking Sustainable-by-Design Li-Metal Batteries by Recycled PVB in Blend Polymer Electrolytes

In today's sustainability-driven society, the circular economy has emerged as a guiding principle for responsible resource use, aiming to transform production by prioritizing reuse, repair, and recycling, thus extending product lifecycles and reducing waste. Herein, the impact of the circular economy on upcycling, focusing on poly(vinyl butyral) (PVB), widely used as an interlayer in laminated glass, recovered from automotive waste via a patented mechanochemical process, is investigated. For the first time, this process is applied in an innovative closed-loop design for solid polymer electrolytes (SPEs) in Li-metal batteries (LMBs). A green, solvent-free method produces polymer blends of PVB, ensuring outstanding mechanical properties, and poly(ethylene oxide) (PEO) as the ion-conductive matrix. PVB effectively reduces PEO crystallinity, improving ionic conductivity, mechanical strength, and oxidative stability. The resulting SPEs exhibit stable lithium stripping/plating and reduced interfacial resistance in symmetric cells, confirming excellent lithium compatibility. Lab-scale lithium metal polymer cells with a high-loading LiFePO₄-based catholyte (13 mg cm^{- 2}) achieve near-theoretical capacities at low C-rates (154.4 mAh g^-1 at C/5) and excellent rate performance at 65 °C. By promoting a holistic approach to sustainable resource use, PVB contributes to the development of high-performance, environmentally sustainable polymer electrolytes for next-generation LMBs.