A recent study published in Communications Materials explored how carrageenan (CARR), a polysaccharide derived from red algae, can enhance the performance of lithium-sulfur (Li-S) batteries. By utilizing water as a solvent and dispersant instead of toxic alternatives, the proposed electrode fabrication process offers a more scalable and eco-friendly approach.
Image Credit: Black_Kira/Shutterstock.com
Background
Li-S batteries could replace Li-ion batteries. They have a higher energy density, improved storage potential, and extended cycle life. However, technical challenges, such as the shuttling of soluble polysulfide intermediates between the sulfur cathode and lithium metal anode, have delayed their commercial readiness.
Binders play a crucial role in Li-S battery performance, facilitating electrode assembly while participating in electrochemical reactions. Traditional binders like polyvinylidene fluoride (PVDF) have limitations, including low conductivity, poor binding properties, and reliance on harmful solvents like N-methyl pyrrolidone.
Alternative binders such as carboxymethylcellulose and biopolymers like alginates, chitosan, CARR, gelatin, and guar gum have recently gained attention. These materials are environmentally friendly, work with water-based synthesis, and avoid toxic solvents. This study focused on the impact of CARR as a binder for improving Li-S battery performance.
Methods
Electrodes were prepared by combining specific proportions of sulfur, carbon, and binder materials. The resulting slurry was spread onto aluminum foil, forming cathodes in the shape of 14 mm discs.
Button cells (CR2032-type) were assembled in an argon-filled glovebox, with stainless steel terminals. The separator and positive electrode were soaked in an electrolyte solution containing 0.25 M LiNO3 and 0.75 M bis(trifluoromethane)sulfonimide lithium). Lithium metal was used as the negative electrode.
Li-polysulfide standards were prepared for X-ray absorption spectroscopy (XAS) by mixing sulfur powder and lithium metal in stoichiometric amounts with dried tetrahydrofuran as the solvent. For sulfur (S) and lithium sulfide (Li2S) standards, commercially available chemicals were combined with boron nitride in an 80:20 ratio by weight.
The morphology and elemental composition of the electrodes were analyzed using scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Electrochemical performance was evaluated through a series of tests, including cyclic voltammetry, rate capability assessments, and long-term cycling experiments on the assembled cells.
Results and Discussion
SEM images revealed that electrodes with lower CARR ratios exhibited more fractures, with the 10 wt.% CARR electrode showing greater cracking compared to its PVDF counterpart. The 7 wt.% CARR electrode displayed a sponge-like structure with optimal porosity, leading to improved rate capability.
Elemental mapping indicated that sulfur distribution was more uniform in electrodes containing 7 and 10 wt.% CARR compared to PVDF-based samples. However, a higher CARR concentration led to sulfur aggregation. The CARR binder also interacted with sulfur particles, as evidenced by sodium and potassium deposits near sulfur clusters. XPS analysis confirmed that CARR formed a thin layer over sulfur and carbon particles, unlike PVDF, which remained localized on sulfur patches.
Electrodes with 10 wt.% PVDF exhibited over ten times the resistance of those with the same concentration of CARR. Importantly, both insufficient (5 wt.%) and excessive (15 wt.%) amounts of CARR increased electrode resistance, highlighting the importance of optimizing binder concentration.
In rate capability tests, PVDF-based electrodes experienced a steep capacity decline, especially at higher cycling rates (C-rates), due to their inelastic nature and low sulfur utilization. In contrast, 7 and 10 wt.% CARR electrodes demonstrated superior sulfur utilization, with the 10 wt.% CARR electrode retaining 30 % capacity at 2 C, compared to only 8.6 % for its PVDF counterpart.
Overall, the results demonstrated that electrodes with 10 wt.% CARR outperformed PVDF-based electrodes in specific discharge capacity, sulfur utilization, and long-term stability. CARR’s ability to chemically interact with polysulfides reduced active material loss, making it a sustainable and effective binder for enhancing Li-S battery performance.
Journal Reference
Zalka, D., et al. (2025). Improving lithium-sulfur battery performance using a polysaccharide binder derived from red algae. Communications Materials. DOI: 10.1038/s43246-025-00734-1, https://www.nature.com/articles/s43246-025-00734-1
Disclaimer: The views expressed here are those of the author expressed in their private capacity and do not necessarily represent the views of AZoM.com Limited T/A AZoNetwork the owner and operator of this website. This disclaimer forms part of the Terms and conditions of use of this website.