A recent study published in Advanced Energy and Sustainability Research proposed a biodegradable battery using Mg–Mo electrodes and gelatin-based organic acid electrolytes, such as lactic acid (LA)–gel and citric acid (CA)–gel. The inclusion of organic acids improved the electrolyte’s ionic conductivity and enhanced its interaction with the Mg electrode, boosting battery performance.
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Background
Biodegradable batteries offer an environmentally friendly alternative to conventional batteries by using materials that naturally decompose. These batteries typically incorporate biodegradable metals or metal oxides, including Mg, Mo, Zn, Cu, Fe, W, and MoO3.
Mg-based anodes are widely studied due to their high energy density, stable voltage, and biocompatibility. When paired with Mo cathodes, they provide good stability and low toxicity. Another key component is the electrolyte, where gel polymer electrolytes (GPEs) stand out due to their safety, flexibility, low flammability, and strong interfacial contact with electrodes.
This study evaluated CA- and LA-based electrolytes as representatives of strong and weak organic acids, respectively, in fully biodegradable Mg-based batteries.
Methods
The electrolyte was prepared by mixing commercial gelatin extracted from pig skin with different concentrations of organic acids (0–5 wt.% CA or 0–12 wt.% LA). The solution was molded into 2 × 2 cm films with a 1 mm thickness and dehydrated by sequential immersion in ethanol solutions of increasing concentration (30 %–100 %). The dried samples were then coated with Pt to optimize surface conductivity.
For capacity testing, the battery consisted of a 1 cm2 with an anode made from either 0.3 mm pure Mg or Mg alloy AZ31 and a 0.5 mm Mo cathode. The electrodes were pressed against the electrolyte to form 1 × 1 × 1 mm batteries.
The batteries used in stretchability and wearability tests had different designs. To enhance stretchability, Mg and Mo electrodes with a thickness of 0.1 mm were selected. These electrodes had an area of 6 × 3 cm; a serpentine Kirigami pattern on the electrodes was cut using scissors. The electrolyte was synthesized by pouring 12 wt.% LA–gel liquid into a 6 × 3 cm mold with a depth of 0.8 cm.
After cooling, the electrolyte was detached from the mold, and a serpentine Kirigami pattern, with identical dimensions to the electrodes, was cut through it using a knife. Finally, the Mg–Mo electrodes and LA–gel electrolyte were assembled into a battery through the same process as above.
Results and Discussion
Electrochemical tests showed that adding organic acids significantly increased ionic conductivity. The electrolyte with 12 wt.% LA exhibited four times the conductivity of pure gel. Arrhenius plots confirmed that organic acids reduced activation energy, promoting faster ion movement and lower internal resistance.
Scanning electron microscope images revealed the rough and irregular surface of the organic acid electrolyte, likely providing microscopic pathways for ion conduction. Additionally, batteries with organic acid electrolytes and Mg–Mo electrodes exhibited higher open-circuit voltages (OCV) than those with a gel-only electrolyte, supporting the role of proton concentration in enhancing electrode potential.
Capacity tests showed that organic acid electrolytes supported higher voltage plateaus and improved capacity at higher discharge currents. When using the Mg alloy AZ31 as the anode, the battery did not show significant advantages in acidic electrolyte conditions but improved capacity in neutral gel-based electrolytes due to AZ31’s lower electrochemical activity and higher corrosion resistance than pure Mg.
The stretchable battery, based on the gel-organic acid electrolyte, maintained stable voltage even when stretched to 180 % of its original length, demonstrating excellent mechanical resilience.
Conclusion
This study comprehensively evaluated the performance of Mg–Mo batteries with gelatin-based organic acid electrolytes. Electrochemical tests confirmed the improved ionic conductivity from organic acid incorporation.
The LA–gel electrolyte achieved a maximum conductivity of 2.37 × 10−3 S/cm, while the CA–gel electrolyte exhibited a low activation energy of 11.04 kJ/mol. A simple wearable circuit using the stretchable battery demonstrated its potential for real-world applications. Furthermore, degradation tests showed that both the electrolyte and Mg electrode decomposed in phosphate buffer saline solution, supporting the battery’s biodegradability.
These findings highlight the potential of gelatin–organic acid-based batteries for wearable applications and sustainable energy solutions by reducing electronic waste.
Journal Reference
Liu, J., Lazaris, G., Lee, J., Bhadra, S. (2025). Gelatin–Organic Acid‐Based Biodegradable Batteries for Stretchable Electronics. Advanced Energy and Sustainability Research. DOI: 10.1002/aesr.202400402, https://onlinelibrary.wiley.com/doi/10.1002/aesr.202400402
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