CuInS₂ Nanospheres and Nanowhiskers Enhancing the Electrochemical Properties of Sodium-Ion-Conducting Gel Polymer Electrolytes

Herein, the authors report sodium-ion-conducting GPEs dispersed with and without copper indium disulfide (CuInS 2 ) nanoforms. The standard solution casting technique has been used to design sodium-ion-conducting GPEs containing the skeleton of the poly(methyl methacrylate) polymer, sodium tetrafluoroborate as the ionic conducting source, and ethylene carbonate as the plasticizer, while nanospheres and nanowhiskers CuInS 2 served as fillers. The performance of fabricated GPEs has been investigated using electrochemical, infrared, and thermal studies. Ac impedance studies reveal that the optimized GPE with 1 wt % nanowhiskers displays the highest ionic conductivity of 0.19 mS cm –1 at room temperature due to its more porous structure and symmetric variation of the number of particles with particle size. Dielectric and modulus investigations have been used to explore qualitative ion dynamics at varied frequencies. The total ion transport number is found to be >88%, while the confirmation of sodium-ion movement during anodic and cathodic cycles has been established using cyclic voltammetry (CV). The CV technique also indicates an operating voltage range of 3.4 V for the optimized GPE system. Fourier transform infrared spectroscopy (FTIR) revealed significant molecular interactions among CuInS 2 nanoforms, polymer matrix, solvent, and sodium salt. Thermal studies using differential scanning calorimetry (DSC) analysis indicate that the optimized GPE system retains the gel phase up to 388 K, while the thermogravimetric analysis (TGA) experiment suggests a considerably lesser weight loss of 9% when the temperature is ∼470 K. Overall, the introduction of porous CuInS 2 nanoforms within GPEs significantly improves the electrochemical properties while maintaining decent thermal properties.