Sodium-Ion-Conducting Alginate-Based Electrolyte Material for Energy Storage Applications

A green pseudosolid polymer electrolyte is prepared using sodium alginate and sodium polyphosphate via a sustainable solution-cast method with water as the medium. The amorphous anionic polymer backbone enables easy cationic movement, enhancing ionic conductivity. This water-in-salt electrolyte exhibits an electrochemical stability window of 3.2 V and a cationic transport number of 0.90%. Thermal analysis confirms stability up to 150 degrees C, making it suitable for high-temperature applications. X-ray diffraction analysis verifies its amorphous nature, facilitating smooth ion transport, while scanning electron microscopy reveals a smooth morphology with well-defined pores, improving electrode interface stability. At room temperature, the electrolyte displays electrical conductivity around 10-5 S cm-1, increasing to 10-4 S cm-1 above 40 degrees C. The drift ionic velocity is approximate to 10-5 m s-1, with ionic mobility of 10-7 mV s-1. Cage-type hopping dominates ionic movement, requiring a low activation energy of 0.158 eV. Incorporating an ionic liquid as a plasticizer further enhances conductivity to 10-3 S cm-1. Additionally, the material exhibits dielectric relaxation due to polar group orientation. Its high capacitance with minimal electrode contribution makes it a promising candidate for energy storage applications, offering excellent electrochemical and thermal stability, along with superior electrode-electrolyte interface properties.