Seaweed-Derived Additive Tames Water and Boosts Zinc Flow in Hydrogel Batteries

Aqueous zinc-ion batteries have long promised a safer, cheaper alternative to lithium-ion technology, but a stubborn trio of problems has kept them out of everyday devices: sluggish ion transport, parasitic water-driven reactions at the electrode surface, and uneven zinc deposition that slowly chokes the anode. Now, a team at Nanjing University of Science and Technology reports a surprisingly elegant fix drawn from one of nature’s most abundant raw materials. By blending oxidized sodium alginate, a derivative of brown seaweed, into a polyacrylamide hydrogel electrolyte, the researchers engineered a gel that moves zinc ions faster, restrains rogue water molecules, and keeps zinc plating remarkably smooth. The work, published in the journal Ionics, demonstrates that a modest tweak to the electrolyte’s molecular architecture can deliver outsized gains in battery lifetime and reliability.

The central challenge the team confronted is the peculiar double life that water leads inside a zinc battery. Water is indispensable: it dissolves the zinc salts that carry charge between the electrodes, giving aqueous electrolytes ionic conductivities that organic solvents simply cannot match. Yet the very water molecules that enable fast transport also swarm the zinc anode, where they participate in hydrogen evolution reactions that waste charge, build up gas pressure, and corrode the metal. Free water also encourages the formation of dendrites, needle-like zinc structures that grow unevenly during charging and can eventually pierce separators or detach from the electrode entirely. The trick, therefore, is not to remove water but to discipline it, binding enough of it into the polymer network so that it can no longer mediate destructive side reactions while leaving sufficient mobility for ions to travel freely.

Oxidized sodium alginate turned out to be an unusually capable disciplinarian. Sodium alginate is a polysaccharide extracted from brown algae, and when it is oxidized, the sugar rings in its backbone are opened to create dialdehyde groups along the chain. These aldehyde-bearing chains are chemically versatile: they can form dynamic covalent bonds, participate in hydrogen bonding, and coordinate metal ions. In the new study, the researchers introduced the oxidized alginate into a polyacrylamide matrix, the workhorse polymer of hydrogel electrolytes, and systematically varied the loading. At an optimized dose of 0.9 grams per batch, the resulting gel, dubbed PAM OSA-0.9 GEL, developed a more open and porous microstructure with noticeably improved wettability, meaning electrolyte solutions spread through and saturate the gel far more effectively than in the pristine polyacrylamide control.

The performance numbers tell a striking story. Ionic conductivity, the measure of how easily charge-carrying ions move through the electrolyte, climbed from 16.2 to 28.6 millisiemens per centimeter, an increase of more than 75 percent. Even more consequential was the change in the apparent zinc-ion transference number, which rose from 0.47 to 0.76. This parameter describes the fraction of total current carried by zinc ions rather than by other mobile species such as protons or sulfate anions. A higher transference number means that when current flows, it is predominantly zinc ions doing the work, which translates directly into more uniform zinc deposition and less concentration polarization near the electrode surface. In parallel, the electrochemical stability window widened from 2.47 to 2.64 volts, giving the electrolyte more headroom before it begins to decompose electrochemically.

The researchers attribute these gains to the way oxidized alginate reorganizes the water inside the gel. The aldehyde and hydroxyl groups along the alginate chains form extensive hydrogen-bonding networks with surrounding water molecules, converting a portion of the free, reactive water into bound water that is far less available for hydrogen evolution or zinc corrosion. At the same time, the alginate’s carboxylate groups coordinate zinc ions, reshaping the solvation shells that surround each ion as it migrates. Solvation structure is a recurring theme in modern electrolyte design, because how zinc ions are dressed in coordinating molecules determines how easily they shed that dressing when they arrive at the anode and join the growing metal deposit. By tuning both the water state and the zinc coordination environment simultaneously, the oxidized alginate addresses two failure modes with a single additive.

The consequences for the zinc anode were immediately visible in the electrochemical tests. Hydrogen evolution and zinc corrosion, the twin scourges of aqueous zinc chemistry, were both alleviated in the modified gel. Nucleation and deposition of zinc became more uniform, with the metal plating as dense, even layers rather than the patchy, dendritic growth that plagues conventional electrolytes. Uniform deposition matters enormously for cycle life: when zinc plates evenly, the electrode surface stays flat and the effective area remains constant, whereas dendritic growth creates dead metal, exposes fresh surface to corrosion, and progressively degrades the cell. The improved wettability and porosity of the OSA-modified gel also help by distributing zinc ion flux more evenly across the electrode interface, preventing the local current hotspots where dendrites preferentially nucleate.

Symmetric zinc-zinc cells, in which two identical zinc electrodes are cycled against each other, provided the most direct test of anode stability. Cells built with the PAM OSA-0.9 GEL electrolyte operated continuously for 1300 hours at a current density of 1.0 milliampere per square centimeter and an areal capacity of 1.0 milliampere-hour per square centimeter. For a hydrogel-based system, sustaining plating and stripping for well over fifty days without short-circuiting or catastrophic voltage drift is a demanding benchmark, and it reflects the cumulative benefit of faster ion transport, suppressed side reactions, and homogeneous deposition working in concert.

Full cells pairing the zinc anode with a sodium vanadate cathode, specifically NaV3O8·xH2O, showed that the electrolyte improvements carry through to complete devices. At a moderate rate of 1.0 ampere per gram, the full cells retained 79 percent of their initial capacity after 220 cycles. More impressively, when the researchers pushed the cells to a demanding 5.0 amperes per gram, roughly a fivefold faster charge-discharge regime, the cells still held 58 percent of their capacity after 3500 cycles. Fast-charging stability is where many aqueous zinc systems falter, because high rates amplify concentration gradients and accelerate dendrite formation, so the endurance at 5.0 amperes per gram suggests the gel’s enhanced zinc-ion transport genuinely relieves the kinetic bottlenecks that normally sabotage rapid cycling.

What makes the result particularly appealing is its simplicity and sustainability. Oxidized sodium alginate is derived from abundant, renewable seaweed biomass, and alginate chemistry is already well established in fields ranging from wound dressings to drug delivery, where oxidized alginates are prized for their biodegradability and controllable gelation. The literature on alginate oxidation dates back well over a decade, and the material’s behavior, including how oxidation degree governs degradability and crosslinking, is well characterized. Repurposing this biomedical staple as an electrolyte engineer for grid-scale batteries illustrates how cross-disciplinary materials knowledge can accelerate energy research. The work also aligns with a broader trend in the field: rather than chasing exotic synthetic additives, several recent studies have turned to polysaccharides such as cellulose, chitosan, and alginate, whose dense arrays of oxygen-containing functional groups are naturally suited to binding water and coordinating metal ions.

The road to commercial aqueous zinc batteries still has distance to travel. Cathode dissolution, particularly of vanadium-based materials, remains a concern, and the capacity retention figures, while strong for a hydrogel system, indicate that degradation has not been eliminated. Scaling hydrogel electrolytes from laboratory coin cells to large-format pouch cells introduces additional challenges in mechanical robustness, manufacturing throughput, and long-term water retention. Nevertheless, the Nanjing team’s demonstration that a single seaweed-derived polymer can simultaneously raise conductivity, sharpen ion selectivity, widen the stability window, and calm the anode offers a compelling template. If future designs can stack multiple such molecular strategies, pairing alginate-type water regulators with zincophilic interfaces and optimized cathodes, the vision of safe, inexpensive, water-based batteries for grid storage and flexible electronics moves a meaningful step closer to reality.

Subject of Research: Oxidized sodium alginate-modified polyacrylamide hydrogel electrolytes for stable aqueous zinc-ion batteries

Article Title: Oxidized sodium alginate regulates water state and Zn²⁺ transport in polyacrylamide hydrogel electrolytes for stable aqueous zinc-ion batteries

Article References: Chen, M., Huo, X., Tan, G., Wang, C., Wang, J., & Zhong, Q. (2026). Oxidized sodium alginate regulates water state and Zn²⁺ transport in polyacrylamide hydrogel electrolytes for stable aqueous zinc-ion batteries. Ionics. https://doi.org/10.1007/s11581-026-07523-x

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07523-x

Keywords: aqueous zinc-ion batteries, hydrogel electrolyte, oxidized sodium alginate, polyacrylamide, zinc-ion transport, zinc dendrites, hydrogen evolution, solvation structure, ionic conductivity, transference number, sodium vanadate cathode, energy storage