Natural Fibers Flax and Wool as Replacements for Synthetic Polymers in Active Masses of Pb/PbO ₂ Systems

The aim of this study was to investigate the effect of natural fiber additives in the negative (NAM) and positive (PAM) electroactive masses on the electrochemical properties of lead – acid cells. Natural, biodegradable fibers (flax and wool) were tested as substitutes for polyester. Conductivity of fiber suspensions in H₂SO₄ differed by only 3–4% from the neat electrolyte, with minor time-dependent drifts attributed to ion leaching. Pastes with flax and wool exhibited higher moisture contents (+20% for flax, +12–17% for wool vs. polyester), which promoted a more open, crystalline microstructure confirmed by SEM. Reactivity tests showed a mass gain upon acid soaking ~69% higher for PAM and ~108% higher for NAM compared to the standard. During formation, fiber-modified positive electrodes reached ~8 Ah capacity in the first cycle, whereas the standard required three cycles. Electrochemical impedance spectroscopy confirmed consistently lower charge transfer resistance (CRT), with wool plates showing a 4–8% reduction relative to the standard. These results demonstrate that natural fibers effectively modify the physicochemical and electrochemical properties of lead – acid battery electrodes, enabling faster formation, lower interfacial resistance, and improved performance while supporting the use of renewable and biodegradable materials.