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(Image Credit: Chandler Cruttenden/Unsplash)
Poor crabs. Aqueous zinc-metal batteries could be applicable for grid storage. After all, there is a lot of zinc, and it’s cheaper and safer than lithium. Conventional liquid electrolytes and polymer separators influence dendritic zinc growth and side reactions, affecting cycle life and rate capability. In 2022, researchers at the University of Maryland addressed that issue by developing a zinc-coordinated chitosan gel electrolyte sourced from crustacean shells.
Seafood waste like crab, shrimp, and lobster exoskeletons contains chitosan, which is extracted. The team created a chitosan-Zn gel that functions as both an electrolyte and separator. To do this, they dissolved chitosan in an aqueous solution. Afterward, they added zinc salt to coordinate Zn2+ with the polymer chains, and cast the mixture into a film that forms a cross-linked chitosan-Zn gel electrolyte.
Mechanically robust, the Zn-chitosan network ionically conducts and modulates interfacial deposition. Rather than producing sharp dendrites, zinc deposits as parallel hexagonal platelets that pack densely on the anode surface. By using this approach, the local current hot spots are reduced, lowing the risk of short circuits.
To assess performance, the team tested symmetric Zn||Zn cells to probe plating/stripping stability. Zn||Cu half cells were also tested to measure Coulombic efficiency, along with practical cathodes to evaluate rate capability and cycle life under realistic loading.
It has strong anode reversibility. During half-cell and symmetric cell testing, zinc anodes that have the chitosan-Zn electrolyte achieve approximately 99.7% Coulombic efficiency and sustained over 1,000 cycles at 50mA cm-2. This indicated that stable plating/stripping under aggressive current densities had occurred. Full cells with practical cathodes and high mass loading (around 10mg cm-2) demonstrate high-rate operation up to 20C (≈40mA cm-2). They also preserve capacity over 400 cycles at 2C (4mA cm-2) with areal capacities reaching roughly 2.3mAh cm-2. As a result, the chemistry in the batteries is suitable for high-power, long-term stationary storage.
The team claims these batteries are sustainable. Due to the nonflammable, biopolymer-based electrolyte composition, microbes can biodegrade two-thirds of the cell. The chitosan component fully breaks down within five months. Remnants of the zinc fraction can then be recycled. Researchers say there is more zinc in the crust than lithium, suggesting the chemical is feasible for large-scale deployment from cost and supply perspectives.
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