Waste shells and plant compounds inspire a biochar coating for more durable zinc-iodine batteries
image: Biomaterial-derived porous carbon doped with heteroatoms as a separator coating for high-energy–density Zn-I batteries
Credit: Shanshuai Chen, Liu Tian, Xiaoqiang Feng, Huanyu Bao & Hongliang Wang
A study published in Biochar reports a sustainable strategy for improving zinc-iodine batteries by turning biomass-derived materials into a functional coating for battery separators. The research team developed a nitrogen and phosphorus co-doped porous carbon, made from chitin and phytic acid, that helps address several major barriers facing zinc-iodine battery technology, including poor iodine utilization, polyiodide “shuttling,” slow reaction kinetics, and zinc dendrite growth.
Zinc-iodine batteries are attracting growing attention as promising energy-storage systems because zinc is relatively abundant, low-cost, and safer than many materials used in conventional batteries. Iodine also offers high theoretical capacity and favorable electrochemical properties. However, in practical batteries, iodine-based reaction intermediates can dissolve into the electrolyte and migrate between electrodes. This shuttle effect causes capacity loss, reduces efficiency, and shortens battery life. Meanwhile, uneven zinc deposition can produce dendrites, needle-like structures that may damage the battery and raise safety concerns.
To tackle these challenges, the researchers designed a biochar-based separator coating using two abundant and renewable sources: chitin, commonly found in shrimp and crab shells, and phytic acid, a phosphorus-rich compound found in plants. Through carbonization and activation, the team prepared porous carbon nanosheets co-doped with nitrogen and phosphorus, referred to as NP-PC. This material was then coated onto a glass fiber separator to form an NP-PC@GF composite separator.
“Our goal was to show that sustainable biomass resources can do more than reduce waste,” said the research team. “By carefully designing the structure and chemistry of biochar, we can create functional materials that improve battery performance and support the development of safer, higher-energy storage systems.”
The coating works in several complementary ways. Its porous structure provides pathways for ion transport and offers physical sites to trap iodine-related species. The nitrogen and phosphorus atoms introduce polar active sites that strengthen chemical interactions with polyiodides, helping prevent them from diffusing through the battery. The coating also improves electrolyte wettability and supports more uniform zinc deposition, reducing dendrite formation on the zinc anode.
Electrochemical tests demonstrated the advantages of the NP-PC@GF separator. A zinc-iodine battery using the coated separator delivered an initial discharge capacity of 7.8 mAh cm⁻² at a high current density of 20 mA cm⁻² and retained 4.6 mAh cm⁻² after 190 cycles. Under high iodine loading, the battery achieved an initial specific capacity of 8.9 mAh cm⁻² and maintained about 5.1 mAh cm⁻² after 174 cycles. Compared with separators coated with nitrogen-doped carbon alone, the nitrogen and phosphorus co-doped biochar coating showed improved long-cycle stability, lower polarization, and better control of zinc deposition.
Microscopy results further supported the electrochemical findings. After cycling, zinc paired with the NP-PC@GF separator showed much smoother deposition and no obvious vertical dendrite growth, while the comparison separator showed irregular dendritic structures. UV-visible adsorption experiments also confirmed that the NP-PC material could strongly adsorb polyiodide species, helping explain its ability to reduce the shuttle effect.
The study highlights a new route for using underutilized biomass resources in advanced energy-storage devices. By combining sustainability with electrochemical functionality, the biochar-derived separator coating provides a promising design strategy for high-performance zinc-iodine batteries and other next-generation rechargeable battery systems.
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Journal Reference: Chen, S., Tian, L., Feng, X. et al. Biomaterial-derived porous carbon doped with heteroatoms as a separator coating for high-energy–density Zn-I batteries. Biochar 6, 99 (2024).
https://doi.org/10.1007/s42773-024-00399-y
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About Biochar
Biochar (e-ISSN: 2524-7867) is the first journal dedicated exclusively to biochar research, spanning agronomy, environmental science, and materials science. It publishes original studies on biochar production, processing, and applications—such as bioenergy, environmental remediation, soil enhancement, climate mitigation, water treatment, and sustainability analysis. The journal serves as an innovative and professional platform for global researchers to share advances in this rapidly expanding field.