Pectin Extracted by a Recyclable Molecular Mixture: A Promising Material for Porous Membranes in Quasi-Solid-State Na-Ion Batteries

In this work, we explored a solvent-based extraction of pectin from apple pomace and evaluated the extracted pectin as a precursor for porous quasi-solid-state Na-ion battery membranes, alongside testing hard carbon derived from commercial pectin as an electrode material. A screening of 10 distinct ionic liquids (ILs) and 6 different antisolvents revealed that N,N-dimethylbutylammonium acetate ([DMBA][OAc]), combined with ethanol, was highly effective in pectin extraction, while the same IL with 1-butanol as antisolvent yielded a purer form of the pectin product. Additionally, [DMBA][OAc] did not behave as an IL and resembled a molecular mixture based on1H NMR and conductivity measurements. A two-level fractional design was employed with four factors, considering temperature, solid loading, acid-to-base ratio (ABR), and water content of ILs, where temperature and solid loading were significant factors. The optimized conditions for the pectin extraction were at 80 °C, 1 h, with 15 wt % of solids loading, an ABR of 1.1, and 30 wt % of water content (IL), which yielded 9.6 wt % of pectin. The resulting quasi-solid-state Na-ion half-cell exhibited a capacity of ∼130 mAh g–1at C/20, making it an excellent candidate for energy storage applications.