Lithium-sulfur (Li-S) batteries are strong contenders, boasting a high theoretical energy density and leveraging the abundant and inexpensive element, sulfur. However, their widespread adoption has been hampered by challenges, particularly their incompatibility with common carbonate-based electrolytes and the need for large electrolyte volumes. A groundbreaking study published in Communications Materials by Francisco J. García-Soriano, Fernando Cometto, Sofia Raviolo, Tim Slosar, Elena Tchernychova, Boštjan Genorio, Robert Dominko, Maria Victoria Bracamonte, and Alen Vizintin presents a significant leap forward: using biocarbon derived from olive pomace, an agricultural byproduct, as a sulfur host in Li-S batteries operating with carbonate-based electrolytes.

Traditionally, research in Li-S batteries has focused on ether-based electrolytes to avoid issues with polysulfide dissolution, which leads to capacity fading and a shortened cycle life. This new approach, however, utilizes microporous carbons to encapsulate sulfur, enabling the use of more widely available carbonate electrolytes and promoting a solid-state sulfur conversion mechanism. This solid-state conversion is key to achieving long-term cyclability. The researchers employed two potassium hydroxide (KOH) activation methods—liquid and solid—to precisely control the porosityPorosity of biochar is a key factor in its effectiveness as a soil amendment and its ability to retain water and nutrients. Biochar’s porosity is influenced by feedstock type and pyrolysis temperature, and it plays a crucial role in microbial activity and overall soil health. Biochar More and surface properties of the biocarbon. The solid-activated biocarbon proved superior, exhibiting higher surface area, increased micropore volume, and a greater concentration of sp2 carbon. These characteristics are crucial for efficient sulfur confinement and facilitating the desired solid-state sulfur conversion.

The electrochemical performance of the resulting sulfur cathodes was impressive, demonstrating remarkable stability regardless of sulfur loading or electrolyte volume. The solid-activated biocarbon cathode achieved a discharge capacity of 850 mAh gs−1​ with a sulfur loading of 4 mgs​cm−2 and a lean electrolyte-to-sulfur ratio of 5 μL mgs−1​. This performance is particularly noteworthy because the electrolyte-to-sulfur ratio is a critical factor for Li-S batteries to compete with conventional Li-ion batteries, with a target of less than 5 μL mgs−1​. Furthermore, these electrodes maintained excellent performance at high current densities, delivering a capacity of 620 mAh gs−1​ at 1 C and 360 mAh gs−1​ at 5 C. This indicates the material’s robustness and stability under varying operational conditions.

The study confirmed that the activation method is vital to the material’s suitability for sulfur hosting. The increased sp2 carbon content and enhanced graphitization in the solid-activated biocarbon, as revealed by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), significantly contribute to improved electronic conductivity. This enhanced conductivity facilitates more efficient electrochemical processes within the cathode. The researchers also observed stable cycling, with both liquid and solid activated biocarbon cathodes maintaining their initial capacities for approximately 300 cycles with Coulombic efficiencies of 99.99%. This remarkable stability underscores the potential of olive pomace-derived biocarbon as a cost-effective and sustainable solution for next-generation energy storage systems.

While highly promising, the research also highlighted challenges. The lithiation process, where lithium ions are incorporated into the material, required higher overpotentials as the cell became more lithiated, indicating increasing difficulty. Conversely, the delithiation process, while kinetically more favorable in its early stages, demanded extreme overpotentials to fully delithiate the material at high states of charge (above 80%). Additionally, dendrite formation on the lithium anode was observed, especially under high sulfur loading conditions. These issues emphasize the need for continued research into electrolyte optimization and anode protection strategies to further enhance the practicality and long-term cycling of these systems. This work represents a significant step towards realizing high-performance, sustainable Li-S batteries using readily available biomassBiomass is a complex biological organic or non-organic solid product derived from living or recently living organism and available naturally. Various types of wastes such as animal manure, waste paper, sludge and many industrial wastes are also treated as biomass because like natural biomass these More.

Source: García-Soriano, F. J., Cometto, F., Raviolo, S., Slosar, T., Tchernychova, E., Genorio, B., Dominko, R., Bracamonte, M. V., & Vizintin, A. (2025). Biocarbon from olive pomace residue as a sulfur host for carbonate-based lithium-sulfur batteries. Communications Materials, 6(122).