SODIUM ION CONDUCTING SOLID POLYMER ELECTROLYTE FOR RECHARGEABLE BATTERY

Abstract

Polyvinyl alcohol (PVA) based solid polymer electrolytes doped with varying concentrations of sodium tetrafluoroborate (NaBF4) were studied for electrochemical applications. Impedance spectroscopy was employed to analyze the impact of NaBF4 concentration (10, 20, and 30 wt.%) on electrolyte performance. The frequency dependence of the real impedance component was measured at room temperature to understand ionic transport. Ionic conductivity was evaluated as a function of both salt concentration at 30°C and frequency at room temperature, with the 80PVA:20NaBF4 system exhibiting the highest conductivity. The relationship between NaBF4 concentration, frequency, and ionic conductivity provides insights for optimizing these PVA-based electrolytes.

Specification

Description:1. Room temperature impedance spectroscopy of PVA: NaBF4 solid polymer electrolytes (100:0, 90:10, 80:20, and 70:30 weight ratios) reveals how the real impedance varies with frequency. At low frequencies, Z' is high due to the slow response of sodium ions to the alternating field, resulting in lower ion mobility and higher resistance, typical of solid electrolytes with reduced ionic conductivity. Z' decreases with increasing frequency. At high frequencies, Z' may plateau as the ions can no longer follow the field effectively, and the material's resistance dominates.
2. The PVA: NaBF4 system reaches maximum ionic conductivity at a 20 wt.% NaBF4 concentration. Increasing NaBF4 concentration below this level enhances conductivity due to the increased presence of charge-carrying Na⁺ and BF4⁻ ions. At 20 wt.%, an optimal balance is achieved between ion availability and mobility within the PVA matrix. Exceeding this concentration leads to decreased conductivity, attributed to ion clustering or incomplete dissociation, reducing the number of free charge carriers.
3. As shown in Figure 3, conductivity in the polymer electrolytes depends on both frequency and NaBF4 concentration. Higher frequencies and increasing NaBF4 doping (up to 20 wt.%) lead to greater conductivity. At lower frequencies, conductivity starts low but increases with both frequency and doping, possibly due to charge transfer complex formation and decreased crystallinity. A sharp conductivity change at higher megahertz frequencies is attributed to ionic aggregate formation, which impedes ion transport.
, Claims:1. PVA doped with NaBF4 solid polymer electrolytes (SPEs) has been synthesized using a solution casting technique.
2. SPE consists of polymer PVA and sodium salt NaBF4.
3. After the incorporation of 20 wt.% of NaBF4 salt, the ionic conductivity has been improved to 8.47 × 10-7 S/cm at 30 °C.
4. The minimum value of bulk resistance is observed for 80PVA: 20NaBF4 system.

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