Structural Amorphization and Ionic Transport Behavior of Phytagel–NaClO₄ Biopolymer Electrolytes

1  Introduction

Rising global energy demand, particularly in renewable and high-technology applications, has accelerated research into advanced energy storage systems. Among these, sodium-ion batteries (SIBs) have emerged as promising alternatives to lithium-ion batteries due to the natural abundance, low cost, and non-toxicity of sodium [1,2]. SIBs exhibit an energy density range of 100–160 Wh·kg−1, making them suitable for large-scale applications, including grid storage and portable electronics. Despite their cost-effectiveness, SIBs still face limitations in achieving long-term stability and high conductivity, as these properties depend strongly on the development of suitable electrolytes [3].

Polymer electrolytes have been extensively studied due to their flexibility, compatibility with electrodes, and ability to provide safe ion transport [4]. More recently, biopolymer electrolytes have attracted increasing attention due to their biodegradability, eco-friendliness, and abundance from renewable resources [5,6]. Unlike synthetic polymers, biopolymers have a lower environmental impact and align with sustainability goals, including SDG 7 (Affordable and Clean Energy) and SDG 12 (Responsible Consumption and Production). However, their application as polymer electrolytes is often limited by inherently low ionic conductivity, arising from restricted polymer chain flexibility and limited ion mobility associated with their semi-crystalline nature [7]. To address this limitation, salt doping is commonly employed to disrupt crystalline domains, increase the amorphous phase, and enhance ionic transport.

In addition to polymer structure, salt characteristics play a crucial role in ion transport. Salts with high lattice energy dissociate poorly, whereas those with lower lattice energy promote greater ion dissociation and increase the concentration of free charge carriers [8]. In this context, sodium perchlorate (NaClO4), owing to its relatively low lattice energy and high solubility, facilitates efficient ionic dissociation, enhances the availability of free Na+ ions, and further suppresses polymer crystallinity [9]. Meanwhile, Phytagel, a biopolymer derived from Sphingomonas Elodea fermentation, exhibits relatively low crystallinity and structural flexibility, which can be further enhanced by salt doping [10,11]. Therefore, combining Phytagel with NaClO4 offers a promising approach to enhance ionic conductivity and structural stability in biopolymer electrolytes for sodium-ion batteries.

In this work, Phytagel is employed as the host biopolymer while NaClO4 is introduced as a dopant salt to develop sodium-based biopolymer electrolytes. Structural analysis using X-ray Diffraction (XRD) is performed to evaluate changes in crystallinity, while Electrochemical Impedance Spectroscopy (EIS) is used to investigate the ionic conductivity of the prepared electrolyte systems.

2  Experimental Sections

2.1 Materials

Phytagel (Mw: ~500,000 g·mol−1), a high-purity gelling polysaccharide derived from Sphingomonas elodea fermentation, was procured from Sigma-Aldrich (USA). Sodium perchlorate (NaClO4, Mw: 122.44 g·mol−1, ≥98%) was obtained from Merck (Germany) and used as the dopant salt. All chemicals were of analytical grade and used without further purification in the preparation of Phytagel–NaClO4 biopolymer electrolytes.

2.2 Preparation of Biopolymer Electrolytes

Host biopolymer Phytagel (0.5 g) was first dissolved in DMSO with continuous magnetic stirring at 60°C for 12 h, followed by the incorporation of various weight percentages of sodium perchlorate (NaClO4) (ranging from 10 to 50 wt.% in 10 wt.% intervals) and further stirring until a clear solution was formed. The resulting homogeneous solutions were cast into glass Petri dishes and dried in an oven at 60°C for 17 h. The dried polymeric films were then peeled off for subsequent characterization.

2.3 Characterization of Biopolymer Electrolytes

2.3.1 Structural Study

The structural characteristics of the prepared Phytagel–NaClO4 biopolymer electrolyte films were analyzed using X-ray diffraction (XRD) to evaluate their degree of crystallinity and amorphous nature. XRD measurements were carried out using a Bruker AXS diffractometer equipped with CuKα radiation (λ = 1.5418 Å). The diffraction patterns were recorded at room temperature over a 2θ range of 5° to 90°.

2.3.2 Ionic Conductivity Study

The ionic conductivity of the prepared biopolymer electrolytes was evaluated using a HIOKI 3532-50 LCR Hi-Tester over the frequency range of 100 Hz to 1 MHz. The biopolymer electrolyte thin film was sandwiched between two stainless steel current collectors and evaluated at room temperature (300 K). For selected electrolyte compositions, temperature-dependent electrochemical impedance spectroscopy (EIS) measurements were conducted over the temperature range 303–333 K to investigate the influence of temperature on ionic mobility and conductivity. The thickness of the electrolyte films was determined using a digital thickness gauge. The ionic conductivity, σ, of the electrolytes was calculated using the equation:

σ=tRbA(1)

where t is the thickness of the electrolyte film, A is the surface contact area (cm2), and Rb is the bulk resistance obtained from the impedance plot.

2.3.3 Dielectric Study.

The dielectric constant, εr, represents the ability of the Phytagel–NaClO4 biopolymer electrolyte to store electrical energy upon polarization under an applied alternating electric field. The real and imaginary components of the dielectric constant were calculated from the impedance data using the equation:

εr=−ZiωC0(Zr2+Zi2)(2)

The dielectric loss, εi, indicates dielectric loss caused by ion movement and energy dissipation during polarization. It was calculated using the equation:

εi=ZrωC0(Zr2+Zi2)(3)

Zr and Zi denote the real and imaginary parts of impedance, respectively; ω = 2πf is the angular frequency, and C0 = ε0 A/t is the vacuum capacitance. Here, ε0 is the permittivity of free space (8.854 × 10−12 F·m−1), A is the electrode area, and t is the thickness of the electrolyte film.

The real modulus, Mr, and Mi were computed using the equations:

Mr=εr(εr2+εi2)(4)

Mi=εi(εr2+εi2)(5)

2.3.4 AC Conductivity Study

AC conductivity, σac, is one of the most important parameters for interpreting charge transport mechanisms in solid-state materials, particularly polymer electrolytes. The AC conductivity typically follows Jonscher’s universal power law, as in the equation:

σac(ω)=σdc+Aωs(6)

where ω is the angular frequency, A is a temperature-dependent parameter, s is the power law exponent, and σac is the frequency-independent DC conductivity. The exponent’s value is determined from the slope of the linear plot of ln εi vs. ln ω. By taking the natural logarithm of both sides of the equation, a linearized form is obtained, as expressed in the equation:

lnεi=−s ln ω+lnC(7)

where s is the exponent of frequencies, which describes the degree of interaction between charge carriers and the lattice.

3  Results and Discussion

3.1 Structural Analysis

Fig. 1 presents the XRD pattern of pure Phytagel powder. A broad diffraction halo is observed in the 2θ range of 15°–25°, with no sharp or well-defined peaks, indicating that Phytagel exhibits predominantly amorphous characteristics despite its semicrystalline nature, as commonly reported for polysaccharide-based biopolymers [12]. The absence of distinct diffraction peaks confirms the lack of long-range crystalline order within the Phytagel matrix. Broad and low-intensity peaks in XRD patterns are typically associated with amorphous structures, which enhance the segmental motion of polymer chains and facilitate ion mobility in polymer electrolytes [13]. This amorphous nature is advantageous for polymer electrolyte applications because amorphous regions promote polymer chain flexibility and support efficient ionic transport. This baseline structural characteristic serves as an important reference for comparison with Phytagel–sodium perchlorate (NaClO4) electrolyte films, which are expected to undergo structural modifications upon salt incorporation.

Figure 1: XRD pattern of pure Phytagel biopolymer.

Previous studies have shown that NaClO4 doping significantly alters the structural characteristics of biopolymer electrolytes. In NaCMC-based systems, broad diffraction peaks near 13° and 21° shift or diminish upon the addition of NaClO4·H2O, indicating polymer–salt complexation and the formation of new structural arrangements that reduce crystallinity and enhance ionic conduction [14].

To obtain a clearer understanding of the local structural variations and to quantify the crystalline and amorphous contributions, peak deconvolution was performed on the XRD data. The deconvoluted profiles (Fig. 2) resolve individual Gaussian components embedded within the broad diffraction envelopes. The salt-free sample (0 wt.%) exhibits a relatively low FWHM value of 1.27, indicating a comparatively higher degree of crystallinity in the Phytagel matrix. Upon incorporation of NaClO4, the FWHM increases significantly, reaching a maximum of 4.50 at 40 wt.% before slightly decreasing to 2.72 at 50 wt.%. In general, a larger FWHM indicates greater amorphous content, which enhances polymer segmental flexibility and promotes ionic conductivity [15]. This trend reflects the progressive disruption of crystalline domains, the emergence of structural disorder, and increased chain mobility. Such an enhanced amorphous environment facilitates ion hopping, thereby improving ionic conductivity [16].

Figure 2: XRD deconvolution of Phytagel-based biopolymer electrolyte containing NaClO4 (a) 0 wt.%, (b) 10 wt.%, (c) 20 wt.%, (d) 30 wt.%, (e) 40 wt.% and (f) 50 wt.%.

Fig. 3a shows that the maximum FWHM at 40 wt.% corresponds to the highest amorphous content in the system, a condition commonly linked to enhanced ionic conductivity. Similar trends have been observed in sodium alginate–NaClO4 electrolytes, where peak broadening was associated with the highest conductivity at ~60 wt.% salt loading [17]. At 50 wt.%, the slight reduction in FWHM may be attributed to ion aggregation or the formation of microcrystalline domains, which restricts further structural disorder. This behavior is consistent with observations in PEO–LiTFSI systems, where amorphous content and conductivity decrease beyond a critical salt concentration due to ionic cluster formation, as indicated by XRD data [17].

Figure 3: Influence of NaClO4 concentration on the structural parameters of Phytagel-based biopolymer electrolytes, illustrating the variation in (a) FWHM, (b) crystallite size, and (c) degree of crystallinity with the addition of salt (0–50 wt.%).

Fig. 3b represents the size of the crystallites based on the FWHM values obtained by using the Scherrer equation:

L=0.9λFWHM cos⁡θ(8)

where λ is the X-ray wavelength, which is fixed at 1.5406 Å, and θ is Bragg’s diffraction angle.

As anticipated, the crystallite size decreases rapidly with increasing salt concentration, hence, a greater degree of amorphization occurs, down to 18.01 Å at 40 wt.% compared to 63.66 Å at 0 wt.%. However, at 50 wt.%, the crystallite size increases again to 29.86 Å, consistent with partial recrystallization or ion clustering at higher salt content. The negative correlation between FWHM and crystal size indicates a structural transformation in the Phytagel–NaClO4 system and underscores the crucial role of salt concentration in structuring the material to enhance its electrochemical performance.

The degree of crystallinity, Xc, is an essential parameter for determining the structural order of polymer electrolytes, as it strongly influences ionic transport properties. The deconvoluted XRD patterns of all Phytagel–NaClO4 samples were used to calculate the areas corresponding to the crystalline, Ac and amorphous, Aa components. The Xc was then determined from the XRD data using the equation:

XC=AcAc+Aa×100% (9)

Table 1 summarizes the peak parameters and the corresponding degree of crystallinity for each composition. As expected, the pure Phytagel sample (0 wt.%) exhibits the highest crystallinity at 88.58%, reflecting its highly ordered structure. The introduction of NaClO4 progressively reduces crystallinity by disrupting the regular packing of polymer chains, thereby enhancing segmental motion and facilitating ion hopping, both of which are essential for improved ionic conductivity.

A slight decrease in crystallinity is observed at 10 wt.% (86.01%), followed by further reductions at higher salt contents, 79.61% at 20 wt.%, 75.38% at 30 wt.%, and a pronounced drop to 28.12% at 40 wt.%. This sharp decline indicates a major structural transition to an amorphous phase, coinciding with the highest ionic conductivity measured in this system. This is consistent with the increase in amorphous fraction and reduction in crystalline domains at this concentration. Interestingly, crystallinity increases again, reaching 74.05% at 50 wt.%, suggesting partial recrystallization or the formation of ionic clusters at high salt loadings. Such clustering can hinder ion mobility and reflect the nonlinear relationship between salt concentration and structural disorder. Fig. 3c illustrates this trend, showing a clear minimum in crystallinity at 40 wt.%, the composition at which effective biopolymer–salt complexation produces the most favorable amorphous structure.

3.2 Ionic Conductivity Analysis

Electrochemical impedance spectroscopy (EIS) was used to evaluate electrical properties, including ionic mobility and interfacial behavior, in the Phytagel–NaClO4 biopolymer electrolytes. The conductivity (Fig. 4) increased from 2.97 × 10−5 S·cm−1 at 0 wt.% to a maximum of 2.41 × 10−4 S·cm−1 at 40 wt.%, reflecting enhanced NaClO4 dissociation and greater sodium-ion mobility, which is consistent with the reduced crystallinity observed from XRD analysis. At this composition, the bulk resistance was also the lowest, indicating improved charge transport. However, beyond the optimum, the conductivity declined to 2.83 × 10−5 S·cm−1 at 50 wt.%. Despite the relatively low crystallinity at this concentration, excessive salt promotes ion aggregation via strong electrostatic interactions, forming neutral ion pairs and clusters that reduce the number of free, mobile ions available for charge transport and, consequently, limit ionic conduction within the polymer matrix [18]. Despite a reduction in conductivity at excessive salt loading, the value remains higher than that of the salt-free system, primarily because dissociated ions remain available to act as charge carriers. The salt-free system, lacking mobile ionic species, exhibits inherently poor ionic conduction. These results show that salt concentration strongly influences ionic conductivity, with 40 wt.% NaClO4 identified as the optimal composition.

Figure 4: Room-temperature ionic conductivity of Phytagel–NaClO4 biopolymer electrolytes at salt concentrations of 0, 20, 30, 40, and 50 wt.%.

Fig. 5 schematically illustrates the mechanism of sodium-ion transport in the phytagel-based biopolymer electrolyte. Upon salt dissolution, sodium perchlorate (NaClO4) dissociates into mobile sodium ions (Na+) and perchlorate anions (ClO4−). The Na+ ions coordinate with electron-rich oxygen atoms along the polymer backbone and migrate between coordination sites through a hopping process facilitated by the segmental motion of the polymer chains. Among the available functional groups, the negatively charged carboxylate (–COO−) provides strong electrostatic interactions and likely serves as the primary coordination center, while ether and hydroxyl oxygens act as secondary pathways for ion transport. The high density of oxygen-containing groups in phytagel provides abundant coordination sites, and the incorporation of NaClO4 enhances ionic conductivity by increasing the charge-carrier concentration and promoting effective salt dissociation within the polymer matrix.

Figure 5: Mechanism of ionic conduction of NaClO4-Phytagel.

Following the concentration-dependent conductivity analysis, the influence of temperature on ionic transport in the Phytagel–NaClO4 biopolymer electrolytes was further investigated. Temperature plays a crucial role in governing ionic conductivity in biopolymer electrolyte systems, as it directly influences ion mobility and polymer chain dynamics. Polymer hosts are typically semicrystalline, comprising crystalline and amorphous regions, with the latter providing the primary pathway for ion transport due to its greater structural disorder and chain flexibility. As temperature increases, thermal energy promotes the expansion of these amorphous domains, thereby creating a more favorable environment for ionic conduction [19,20]. However, a slight initial decrease in conductivity was observed, which may be attributed to transient ion association and localized polymer-chain rearrangements that temporarily restrict charge-carrier mobility. With further increases in temperature, increased thermal energy facilitates polymer segmental motion and promotes ion dissociation, thereby increasing the population of free ions available for conduction. Consequently, all samples exhibit thermally activated transport behavior, as evidenced by the overall increase in conductivity with temperature, as summarized in Table 2.

Accordingly, conductivity measurements were carried out over the temperature range of 303–333 K for electrolytes containing 0, 40, and 50 wt.% NaClO4. Interestingly, the 50 wt.% electrolyte exhibited a pronounced increase in conductivity from the 10−5 to 10−4 S·cm−1 range with a slight temperature rise from 300 to 303 K, which can be attributed to thermally activated ion transport consistent with Arrhenius-type behavior. As temperature increases, enhanced segmental motion of the polymer chains generates greater free volume, facilitating ion hopping between coordination sites and thereby improving ionic conductivity [21]. Similar behavior has been reported in agarose-based biopolymer electrolytes, where increased chain flexibility at elevated temperatures promotes ion transport [22].

Among the investigated compositions, the electrolyte containing 40 wt.% NaClO4 demonstrates the highest ionic conductivity, reaching a maximum value of 2.11 × 10−3 S·cm−1 at 333 K. This result indicates that ion transport is most efficient at this optimal salt concentration due to enhanced amorphous content and increased availability of mobile charge carriers. In contrast, the salt-free electrolyte (0 wt.%) exhibits the lowest conductivity over the temperature range due to the absence of mobile sodium ions. Although the 50 wt.% NaClO4 shows higher conductivity than the salt-free system; however, its performance remains inferior to that of the 40 wt.% sample, likely due to ion aggregation and reduced ion mobility at excessive salt loading. These findings confirm that an optimal salt concentration is necessary to balance charge-carrier density and polymer segmental motion for efficient ionic transport.

3.3 Dielectric Studies

Fig. 6 illustrates the frequency dependence of the dielectric constant of the Phytagel–sodium perchlorate biopolymer electrolyte at different temperatures (303–333 K). As shown in Fig. 6, εr exhibits very high values at low frequencies, particularly at 323 K, which is attributed to the accumulation of mobile Na+ ions at the electrode–electrolyte interface, resulting in strong interfacial (space-charge) polarization. With increasing frequency, εr decreases sharply because ions and dipoles cannot follow the rapidly oscillating electric field, thereby reducing polarization [23]. In addition, εr increases with temperature due to enhanced segmental motion of polymer chains and increased ionic mobility, peaking at 323 K, indicating optimal conditions for ionic transport.

Figure 6: Temperature dependence of the dielectric constant for Phytagel-based biopolymer electrolyte containing 40 wt.% NaClO4 in the temperature range of 300–333 K.

Fig. 7 shows the variation of the dielectric constant with frequency at different temperatures. Higher εi values are observed at low frequencies, particularly at 323 and 333 K, indicating increased dielectric loss due to ion accumulation at the electrode–electrolyte interface. As frequency increases, εi decreases markedly because the ions cannot respond to the rapidly changing electric field, thereby reducing energy dissipation. The increase in εi with temperature in the low-frequency region reflects enhanced ionic mobility and polymer chain flexibility. The highest εi values at 323 K suggest stronger ion–polymer interactions and more effective ionic motion within the electrolyte system.

Figure 7: Temperature dependence of the dielectric loss for Phytagel-based biopolymer electrolyte containing 40 wt.% NaClO4 in the temperature range of 300–333 K.

The results indicate that the dielectric constant and dielectric loss of this biopolymer electrolyte system are strongly dependent on both frequency and temperature. At low frequencies and elevated temperatures, interfacial polarization and ionic motion dominate the dielectric response of the system. The observed non-Debye relaxation behaviour, together with the enhanced values of εr and εi at 323 K, confirms the significant role of thermal activation and ion-hopping mechanisms in governing the dielectric properties of the phytagel–NaClO4 biopolymer electrolyte.

Fig. 8 illustrates the frequency dependence of the real part of the modulus. The Mr values remain relatively low across the frequency range, particularly at lower frequencies, a characteristic of materials with high dielectric permittivity and indicative of the dominance of electrode polarization effects. As the frequency increases beyond log f ≈ 4.5, Mr begins to rise due to the reduction of space-charge polarization and the emergence of bulk relaxation processes. The enhancement in Mr is more pronounced at 313 K, suggesting improved segmental motion of the polymer chains that facilitates ion migration. At higher temperatures (323 and 333 K), the Mr curves exhibit gentler slopes, possibly indicating more homogeneous ionic relaxation behavior resulting from increased thermal activation.

Figure 8: Temperature dependence of the real part of the modulus for Phytagel-based biopolymer electrolyte containing 40 wt.% of NaClO4 in the temperature range of 300–333 K.

Fig. 9 presents the frequency dependence of the imaginary part of the modulus. At low frequencies (log f < 4.0), the Mi values are nearly temperature-independent and approach zero, implying negligible electrode polarization effects and the dominance of long-range ion transport. With further increases in frequency, a sharp rise in Mi is observed, marking the onset of dielectric relaxation as ions begin to hop between coordination sites. The most prominent increase in Mi occurs at 313 K, where a sharp upward trend is evident around log f ≈ 5.0, indicating a reduced relaxation time and enhanced ionic mobility. At elevated temperatures (323 and 333 K), the increase in Mi shifts toward slightly lower frequencies, reflecting the thermally activated nature of the relaxation process.

Figure 9: Temperature dependence of the imaginary part of the modulus for Phytagel-based biopolymer electrolyte containing 40 wt.% of NaClO4 in the temperature range of 300–333 K.

The results indicate that the Mr and Mi analyses reveal strongly thermally activated ionic conductivity at 40 wt.% Phytagel–sodium perchlorate system. The temperature-induced shift of the frequency-dependent Mi response toward lower frequencies, together with the increase in Mr, demonstrates that higher thermal energy enhances ion dynamics by promoting ion hopping and polymer segmental mobility. These observations confirm that ionic transport in this system proceeds predominantly through a thermally assisted hopping mechanism and is strongly governed by polymer chain flexibility and temperature.

3.4 AC Conductivity Analysis

Fig. 10 shows the AC conductivity, σac, of the samples measured over the frequency range 100 Hz to 1 MHz at four temperatures (303, 313, 323, and 333 K). At all temperatures, σac increases with frequency, particularly in the high-frequency region, which is consistent with a hopping-based conduction mechanism. The conductivity is also thermally activated, increasing with temperature. Notably, at 323 K, a relaxation anomaly is observed in the frequency range of log f ≈ 4.6–5.0. Similar features have been attributed to electrode polarization and Maxwell–Wagner–Sillars (MWS) interfacial polarization effects in systems with porous electrodes [24] and nanocomposite oxides [25]. In addition, electrode polarization is often associated with a reduced conductivity exponent and the appearance of conductivity dips, as reported in dielectric studies of perovskite materials [26]. These observations suggest that the anomaly originates from interfacial charge dynamics, which are likely responsible for the observed decrease in σac.

Figure 10: Frequency-dependent AC ionic conductivity of Phytagel-based biopolymer electrolyte containing 40 wt.% of NaClO4 in the temperature range of 300–333 K.

Fig. 11 presents the ln εi vs. ln ω plots for the Phytagel–NaClO4 biopolymer electrolyte at temperatures between 300 and 333 K. The plots exhibit good linearity, indicating power-law behavior characteristic of dielectric relaxation in disordered polymer systems. The slope decreases with increasing temperature, from −0.667 at 300 K to −0.406 at 323 K, suggesting that dielectric loss becomes less frequency-dependent as thermal energy increases ionic mobility and polymer segmental flexibility. This behavior is consistent with non-Debye relaxation and Jonscher’s universal dielectric response reported for solid polymer electrolytes, in which charge-carrier hopping and interfacial polarization dominate the dielectric response [27].

Figure 11: ln εi vs. ln ω of Phytagel-based biopolymer electrolyte containing 40 wt.% of NaClO4 in the temperature range of 300–333 K.

From the linear fits, the power-law exponent s was extracted and plotted as a function of temperature (Fig. 12). The obtained s values indicate a thermally assisted hopping process, with lower s values corresponding to long-range ionic transport within the electrolyte matrix. Based on Fig. 10, the power-law exponent exhibits an explicit temperature dependence, increasing from 0.3328 at 300 K to a maximum value of 0.5936 at 323 K. This temperature-induced increase in s is consistent with the Correlated Barrier Hopping (CBH) model, which describes ion transport in highly disordered polymer systems as a thermally activated hopping process between localized sites [28]. The rise in s reflects enhanced polymer segmental mobility and reduced effective energy barriers for ion hopping as temperature increases. A slight decrease in s at 333 K suggests the onset of ionic aggregation or clustering, which may restrict high-frequency charge transport and limit ionic mobility. Similar behavior has been reported in molecular dynamics simulations, in which increased thermal energy at elevated temperatures promotes ion aggregation and reduces ion diffusivity [29]. Overall, the temperature dependence of s confirms that ionic conduction in the Phytagel–NaClO4 biopolymer electrolyte follows the CBH mechanism within the investigated temperature range. It is also worth noting that, although the structural and electrical properties of gellan gum (Phytagel)-based NaClO4 biopolymer electrolytes have been previously reported [30], the present work places greater emphasis on systematically correlating structural parameters with ionic transport behavior.

Figure 12: Power exponent law of a Phytagel-based biopolymer electrolyte containing 40 wt.% of sodium perchlorate at different temperatures.

4  Conclusion

Phytagel–NaClO4 biopolymer electrolytes with salt concentrations ranging from 0 to 50 wt.% were successfully prepared by solution casting and systematically characterised using XRD and EIS. Structural analysis revealed that NaClO4 incorporation progressively disrupted the crystalline domains of Phytagel, with the highest amorphous content achieved at 40 wt.% salt loading, as evidenced by peak broadening, increased FWHM, reduced crystallite size, and a significant decrease in crystallinity. This enhanced amorphisation directly correlated with improved ionic conductivity. Electrical measurements showed that the ionic conductivity increased with salt concentration, reaching a maximum at 40 wt.% NaClO4. Dielectric and modulus analyses further confirmed non-Debye relaxation behavior, strong interfacial polarisation, and thermally assisted ion hopping mechanisms, particularly at the optimal salt composition. Overall, the results demonstrate that 40 wt.% NaClO4 provides the optimal balance between structural disorder and ionic mobility, underscoring the strong potential of Phytagel–NaClO4 biopolymer electrolytes for sodium-based sustainable energy storage applications.

Acknowledgement: The authors would like to thank the iMADE Research Laboratory, the Institute of Science, and the Faculty of Applied Sciences, Universiti Teknologi MARA (UiTM), for providing research facilities to carry out this project.

Funding Statement: The authors received no specific funding for this study.

Author Contributions: All authors contributed substantially in accordance with the journal’s authorship criteria. Norlela Manja Ahmad performed the sample preparation and characterizations, data validation, and analysis. Farisha Irdina Muhammad Ridzuan contributed to manuscript editing, organization, technical review, and language refinement. Nur Farisha Sulthan Hussain provided technical guidance on instrument operation and experimental procedures. Siti Zafirah Zainal Abidin conceptualized the research, supervised the experimental design, and contributed to data interpretation. All authors reviewed and approved the final version of the manuscript.

Availability of Data and Materials: The data and code that support the findings of this study are available from the corresponding author upon reasonable request.

Ethics Approval: Not applicable.

Conflicts of Interest: The authors declare no conflicts of interest.

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