Boudjenane, M. N.MLZ*

2025

Abstract: Among organic cathode candidates for Aqueous Zinc-Ion Batteries (AZIBs), polyaniline (PANI)offers unique advantages owing to its high theoretical capacity, reversible redox chemistry, andintrinsic electronic conductivity [1]. However, its practical implementation is fundamentally hinderedby humidity-driven structural degradation and unstable electrochemical behavior in aqueousenvironments [2,3]. In this work, we investigate the design of fully organic, humidity-resilientPANI-based cathodes, employing cellulose derivatives as green binders to regulate water–polymerinteractions and stabilize electrochemical performance. Composite films were prepared using carboxymethylcellulose (CMC) reinforced with TEMPO-oxidized cellulose nanofibrils (CNFs). Thetotal binder ratio was fixed to 10 wt%, and the CNF content was systematically varied between0-2.5 wt%. Despite their low concentration relative to the active polymer, CNFs were found tomarkedly alter the composite’s hydration behaviour, morphology, and water dynamics, as confirmedthrough a comprehensive multiscale characterization. Cyclic Voltammetry (CV) revealedthat the CMC-only film ensured stable but moderate redox reversibility, whereas the additionof even 1 wt% CNFs effectively tripled the current density and improved peak reproducibility,consistent with enhanced ionic accessibility and film cohesion. At 2 wt% CNFs, the currentresponse notably decreased due to reduced electronic percolation, confirming the existence of anoptimal CNF threshold for maximizing performance. Environmental SEM imaging showed thatthe CMC-only film exhibited up to ∼ 10% lateral swelling at 97% relative humidity (RH), aphenomenon largely suppressed by CNF incorporation. Raman spectroscopy confirmed a stronghumidity-dependent increase in the protonation band as well as quinoid vibrational bands forthe CMC only film indicating the alteration of the protonation state of PANI in the presence ofwater as well a possible overoxidation, an effect which was substantially attenuated in the CNFcontainingsamples, signifying restricted water access and preserved polymer integrity. ComplementaryQuasi-Elastic Neutron Scattering (QENS) measurements quantified the nanoscalewater dynamics, showing that CNFs introduced an additional diffusive water population withhigh mobility. While this led to a favorable diffusion coefficient and water mobility at optimalloading, excessive CNF concentration resulted in highly restricted water domains and slowerdiffusion, correlating with the observed performance drop. Together, these results demonstratethat minor CNF additions (≥ 1 wt%) profoundly influence the hydration behavior, moleculardynamics, and electrochemical response of PANI-based electrodes. Cellulose derivatives thusact as dual regulators offering mechanical stability by limiting humidity-induced deformationand controlling hydration and protonation dynamics. This multiscale understanding establishesa foundation for optimizing fully organic electrode architectures for durable, high-performanceaqueous zinc ion batteries.

Keyword(s): Energy (1st) ; Materials Science (2nd) ; Soft Condensed Matter (2nd)

1. MLZ (MLZ)
2. RESEDA (RESEDA)

1. Measurement at external facility