Structural evolution and ion transport characteristics of potassium carbonate doped chitosan solid polymer electrolytes for potassium-ion energy storage systems

Potassium-ion batteries are emerging as cost-effective alternatives to lithium-based systems due to the abundance and low cost of potassium. In this study, potassium carbonate (KC) was incorporated into a biodegradable chitosan (CH) matrix to develop solid polymer electrolytes with salt concentrations ranging from 0 to 40 wt% via solution casting. Among all compositions, the electrolyte with 30 wt% KC exhibited the best performance, showing the lowest bulk resistance (55 Ω) and highest ionic conductivity (2.64 × 10⁻⁵ S/cm). This enhancement is attributed to optimal salt dissociation and increased potassium ion mobility, while higher salt content led to ion aggregation and reduced conductivity. The conductivity followed Arrhenius behavior, indicating thermally activated ion hopping through the polymer matrix. DSC analysis revealed a shift in glass transition temperature, suggesting improved polymer chain flexibility and ion transport. FTIR results confirmed the formation of polymer–salt complexes, indicating strong interactions between chitosan functional groups and potassium ions. The electrolyte also demonstrated a high ionic transference number (0.99), confirming dominant ionic conduction. Cyclic voltammetry indicated good electrochemical reversibility and suitability for electric double-layer capacitors (EDLCs). Additionally, the material exhibited electrochemical stability up to 2.75 V, highlighting its potential for safe and sustainable energy storage applications.