DC8 will obtain a series of functional nanoporous separators from polyelectrolyte membranes using a facile and upscalable wet-chemical process and having tailored and enhanced properties (e.g. thickness < 25 μm, porosity > 50 %, tensile strength-MD >100 MPa, TD >10 MPa, high liquid electrolyte wettability, enhanced effective conductivity (i.e. reduced membrane tortuosity) and (electro)chemical stability enabling increased cyclability of Na-ion cells. The corresponding structure-property correlations between membrane structure (polymer chemical structure, pores size, pores surface functionality and charge) and electrochemical performance in Na-ion batteries (reduction of the impedance, enhanced effective conductivity, rate capability and cycle life) will be established and used as a guideline for further optimisation of separators functional properties. Na-ion cells (up to 100 mAh in pouch) will be assembled using scaled-up nanoporous separators (i.e. 1 m2) in collaboration with CSIC and KIT.