Structural, optical, and electrochemical evaluation of LiNO₃-doped karaya gum solid polymer electrolytes for energy storage applications

Biopolymer electrolytes are increasingly explored for their ability to enhance the efficiency and stability of electrochemical and optoelectronic devices. In the present study, lithium nitrate–doped Karaya gum–based polymer electrolytes are fabricated via the solution casting technique. Structural characteristics are examined using X-ray diffraction, revealing modifications in the polymer matrix upon salt incorporation. Thermal behavior is evaluated through differential scanning calorimetry, from which the glass transition temperature is identified. Impedance spectroscopy measurements indicate that the electrolyte composition containing 1 g of Karaya gum and 0.3 g of LiNO₃ exhibits the highest ionic conductivity, reaching 1.08 × 10^–3 Scm⁻¹ at room temperature. Analysis of temperature-dependent conductivity further shows that this composition (KLN 3) possesses the lowest activation energy of 0.10 eV, which suggests the facilitated ion transport. The charge transport behavior of KLN 3 follows the overlapping large polaron tunnelling (OLPT) model, as supported by its temperature-dependent conduction characteristics. Optical investigations performed using UV–visible spectroscopy reveal noticeable changes in the absorption edge, optical band gap, and related optical parameters, indicating alterations in the electronic structure of the electrolyte films due to salt addition. A symmetric supercapacitor is fabricated using KLN 3 as the solid polymer electrolyte and activated carbon as both electrodes, and its performance is evaluated by CV and GCD. The combined electrochemical and optical findings demonstrate that the prepared biopolymer electrolytes are promising candidates for solid-state applications, including rechargeable batteries, electrochromic devices, and photonic systems.