Silvia Porporato1, Hamideh Darjazi1, Matteo Gastaldi1, Alessandro Piovano1, Giuseppina Meligrana1, Giuseppe A. Elia1, Claudio Gerbaldi1 1GameLab Group, Department of Applied Science and Technology, Polytechnic of Turin, Corso Duca degli Abruzzi 24, 10129, Turin, Italy Introduction • Large-scale energy storage systems are becoming fundamental for the modern society, particularly to fully exploit major advantages from renewable energy sources, such as wind and solar light. In this respect, secondary sodium-based batteries may represent the key technology since they possess high energy density, low-cost, simple design and easiness in maintenance. Nevertheless, the state of art of the current materials is rather far from a mass commercialization. Beside electrode materials, an essential role is also played by electrolytes and separators, which are deepened in this work. Indeed, many factors must be considered while selecting the best separator, including electronic insulation, low ionic resistance, mechanical stability, chemical resistance to degradation, wettability and uniform thickness [1]. • In this context, we prepared polyurethane-based membranes starting from polyviniyl butyral (PVB) and diisocyanate, by means of a coagulation bath [2,3]. • The choice of PVB as polymer is related to the European project SUNRISE, which aims to find different recycling pathways for this material, normally used as polymeric interlayer into laminated glasses for construction and automotive. At the moment, the PVB fraction collected after consume, that lacks of optical and mechanical requirements for its original purpose, is incinerated or landfilled, causing tons of losses every year, even though it could find a second life within the energy storage panorama [4]. Electrochemical impedance spectroscopy and plating and stripping processes were evaluated, to demonstrate the practical application of the developed materials in laboratory scale Li-based electrochemical cells at various conditions of current rate, temperature and aging. Preliminary results with dense membranes in combination with lithium are highly encouraging for future tests and measurements with sodium, paving the way to the development of more sustainable electrolytes separators for safe, low cost energy storage devices. Conclusions and future perspectives GPC analysis on commercial PVB: Mn (Average, Da) 15˙800 Mw (Weighted Average, Da) 135˙606 Polydispersity index 8 Porous Membrane Dense Membrane Membrane Preparation 4,4′-methylenebis (cyclohexyl isocyanate) H12MDI Solvent NMP 70 °C – 30 min Coagulation bath 1 h 1. Washing process Depending on the coagulation bath, two different materials can be obtained: Polyvinyl butyrral (PVB) Macroscopically identical, but microscopically and operationally diverse FESEM images 2. Drying at 40°C overnight OH concentration determination through IR using 2-ethyl-1-exanol for calibration curve in CHCl3 as solvent: 0.0172 mol OH in 1 g PVB (963 mg of equivalent KOH) 4000 3500 3000 2500 2000 1500 1000 500 0.00 0.05 0.10 0.15 0.20 PVB commercial Porous membrane Dense membrane H12MDI isocianate ATR (a.u.) Wavenumber (cm-1) 0 100 200 300 400 500 600 700 800 -16 -14 -12 -10 -8 -6 -4 -2 0 Derivative Weight Change (%/°C) T (°C) Commercial PVB Porous Membrane Dense Membrane Physico-chemical Membrane Characterization ATR-IR TGA References [1] Arora, P. et al., Chem. Rev., 2004, 104, 4419 [2] Lian, F. et al., J Memb. Sci., 2014, 456, 42 [3] Lv, Z. et al., Chemical Engineering Journal, 2022, 430 [4] F. Duffner et al., Renewable Sustainable Energy Rev., 2020, 127, 10987 [5] Porporato, S. et al., article under submission This work has received funding from the Italian Government (PRIN funding No 2017MCEEY4) and from the European Union's Horizon 2020 R&I program (grant agreements No 958243). 0 100 200 300 400 500 600 700 800 0 100 200 300 400 500 600 700 800 0 50 0 50 Z''/W OCV 5th cycle 10th cycle 15th cycle 20th cycle Z'/W 0 10 20 30 40 50 60 0 10 20 30 40 50