Enhancing structural, optical and electrical properties of carboxymethyl cellulose/sodium alginate hybrid polymer films with CoCl2 for solid-state battery applications

In the present work, carboxymethyl cellulose (CMC) and sodium alginate (SA) polymer composites containing varying concentrations of cobalt chloride (CoCl₂) were synthesized by the solution-casting method. The structural, optical, and electrical properties of the fabricated films were investigated. The surface morphology was studied using field-emission scanning electron microscopy (FE-SEM). X-ray diffraction (XRD) analysis revealed that CoCl₂ incorporation induced partial crystallinity within the intrinsically amorphous CMC/SA matrix. In contrast, Fourier-transform infrared (FTIR) analysis confirmed the interaction of the polymer film components. The optical properties of CMC/SA polymer composite films were notably improved upon CoCl₂ doping. As the CoCl₂ content increased to 80 wt%, the indirect and direct optical band gaps decreased to 2.04 eV and 3.78 eV, respectively. A noticeable reduction in the optical band gap values pointed to enhanced optoelectronic characteristics. Ultraviolet-visible (UV-Vis) analysis revealed enhanced optical absorption, attributed to the coexistence of Co²⁺ ions in mixed octahedral and tetrahedral coordination environments. Broadband dielectric spectroscopy (BDS) showed substantial improvements in electrical conductivity and dielectric permittivity. From the BDS measurement, the highest DC conductivity value at room temperature (25 °C) was 5 × 10^-5 S/cm for the composite containing 50 wt% CoCl_2. The findings demonstrate that CoCl₂ incorporation enhanced the optical and electrical performance of the fabricated films. Among all the compositions tested, the CMC/SA composite film containing 50 wt% CoCl₂ exhibited the most favorable characteristics, particularly in terms of electrical conductivity, highlighting its potential as a solid polymer candidate for use in solid-state batteries, optoelectronic devices, and energy-storage systems.