Capacity Maintained at 96% Even After 5,000 Cycles... Extended Lifespan for Aqueous Zinc Batteries [Reading Science]

GIST, KIER, and Ewha Womans University Uncover Principle of Electrolyte That Forms Protective Layer on Zinc Electrodes

A technology has been developed that significantly extends the lifespan of aqueous zinc metal batteries, which use water-based electrolytes, making them less prone to fire hazards and more cost-effective. This was achieved by introducing an electrolyte additive that forms a protective layer on the surface of the zinc electrode, thereby preventing hydrogen generation and electrode damage, which are the main causes of performance degradation.

On August 11, the Gwangju Institute of Science and Technology (GIST) announced that a research team led by Professor Sangryun Kim from the Department of Chemistry, in collaboration with the Korea Institute of Energy Research (KIER) and Ewha Womans University, has identified a new principle for designing electrolytes that utilizes complex hydrides to enhance the electrode stability and long-term charge/discharge performance of aqueous zinc metal batteries.

Structure and Electrolyte Characteristics of the Initiated Hydride. Even with the addition of the initiated hydride, electrolyte characteristics similar to those of the existing electrolyte are maintained, and inside the hydride ion, boron-hydrogen (B-H) and boron-boron (B-B) bonds exist. Provided by the research team.

Aqueous zinc metal batteries use water-based electrolytes instead of volatile and toxic organic solvents. Because they are relatively safe and allow the use of low-cost zinc as an electrode, they are gaining attention as a promising candidate for next-generation secondary batteries for large-scale energy storage systems (ESS).

The problem is that with repeated charging and discharging, water reacts with zinc to generate byproducts such as hydrogen and zinc oxide (ZnO). Zinc also tends to deposit unevenly on the electrode surface, leading to electrode damage and performance decline over long-term use.

The research team added 'Zn(B12H12)', a type of complex hydride, to the electrolyte. In water, this compound dissociates into zinc ions (Zn2+) and anions ([B12H12]2-). It did not significantly alter the existing properties of the electrolyte, such as ionic conductivity or viscosity.

Electrolyte Remains the Same, Only Zinc Surface Gets a 'Protective Layer'

Once charging and discharging began, differences emerged. The anion reacted at the zinc electrode surface, forming a hydride-rich interphase. This principle involves creating a protective layer only on the reactive zinc surface, rather than altering the properties of the entire electrolyte.

This protective layer reduced direct contact between water and zinc, thereby suppressing unwanted hydrogen generation and zinc oxidation. It also helped minimize the uneven deposition of zinc on the electrode surface. Using X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS), the research team confirmed that the protective layer forms and persists even after 100 charge/discharge cycles.

Research team photo. (From left) Professor Sangryun Kim, Department of Chemistry, GIST; Heejung Oh, Integrated Master's and Ph.D. student. Provided by GIST

The performance tests further underscored the additive's effectiveness. Zinc symmetric cells with the complex hydride additive operated stably for up to 3,000 hours. In the zinc–vanadium oxide cells, 96.55% of the initial capacity was maintained even after 5,000 charge/discharge cycles, and Coulombic efficiency reached 99.8%. By comparison, cells using conventional electrolytes retained only 46.40% of their initial capacity under the same conditions. Coulombic efficiency represents the ratio of discharge to charge capacity; the closer to 100%, the less loss occurs during charge/discharge cycles.

Professor Kim stated, "This research is significant as it identifies the mechanism of hydride-based interphase formation in aqueous electrolytes, thereby extending the scope of complex hydride research to aqueous electrochemistry and providing a new direction for designing electrolytes for next-generation aqueous metal batteries."

The findings, with Heejung Oh, an integrated master's and doctoral student in the Department of Chemistry at GIST, listed as the first author, were published online on July 26 in the international journal, Chemical Engineering Journal.

This content was produced with the assistance of AI translation services.