GIST Develops Electrolyte Technology That Dramatically Improves the Lifespan of Aqueous Zinc Batteries

Professor Sangryun Kim's Chemistry Team Collaborates with Ewha Womans University

Complex Hydride Additive Forms Hydride-Based Protective Layer on Electrode Surface

Gwangju Institute of Science and Technology (GIST) announced on August 11 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 defined a new principle for electrolyte design that can suppress electrode degradation and improve the lifespan of 'aqueous zinc metal batteries' using complex hydrides.

(From left) Professor Sangryun Kim of GIST Department of Chemistry, Heejeong Oh, Integrated Master-PhD Program Student. Provided by GIST

The team presented a novel electrolyte (the liquid inside the battery through which ions move) design strategy capable of simultaneously enhancing both 'electrode stability' and 'long-term charge/discharge performance,' which had previously been difficult to address together.

Recently, as the significance of large-scale Energy Storage Systems (ESS) increases, 'aqueous zinc metal batteries' with advantages in safety and cost-effectiveness have been drawing attention as next-generation secondary batteries. These batteries use a water-based electrolyte instead of volatile and toxic organic solvents, which improves safety; they also utilize zinc as an electrode, leveraging its low price and large storage capacity. However, repeated charging and discharging causes reactions between water and zinc, resulting in hydrogen evolution and the formation of byproducts such as zinc oxide (ZnO). In addition, uneven deposition of zinc on the electrode surface gradually damages the electrode, limiting its long-term stable operation.

The research team addressed these issues by adding complex hydrides to the aqueous zinc metal battery electrolyte and analyzing changes occurring at the zinc metal surface and in the electrolyte during charge/discharge cycles. The complex hydride (Zn(B12H12)) used in this study dissociates into zinc ions and complex anions upon dissolving in water. These complex anions interact weakly with water and surrounding ions, leaving the main properties of the original electrolyte—such as structure, ion conductivity, and viscosity—largely unchanged. (Complex anion: a negatively charged polyatomic ion structure in which a central atom is surrounded by multiple molecules or ions.)

However, once charge/discharge begins, the complex anion reacts on the zinc electrode surface to form a 'hydride-rich interphase,' or a hydride-based protective layer.

Analysis results of the hydride-based interfacial layer formed on the zinc electrode surface. Provided by GIST

While the electrolyte itself remains unchanged, this protective interphase forms only on the zinc surface during charge/discharge processes. The protective layer suppresses the direct reaction between water and zinc, thereby reducing both the hydrogen evolution reaction* and zinc oxidation that cause electrode damage, and further promotes uniform deposition of zinc onto the electrode surface.

The team verified the formation and distribution of this hydride-based interfacial layer using X-ray Photoelectron Spectroscopy (XPS) and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). XPS analysis, which explores chemical bonding states, showed that boron-hydrogen bonds derived from the complex hydride appeared on the zinc surface from the very first charge/discharge cycle and were still present after 100 cycles, demonstrating stable formation of the hydride-based interfacial layer. ToF-SIMS analysis, which examines surface composition distributions, also confirmed that hydride-derived components were concentrated on the zinc surface, supporting the existence of the hydride-based interfacial layer.

Professor Sangryun Kim commented, "This research is significant in that it elucidates the mechanism for forming complex hydride-based interphases in aqueous electrolytes, thereby expanding complex hydride research into aqueous electrochemistry and offering a new direction for electrolyte design in next-generation aqueous metal batteries."

This research, supervised by Professor Sangryun Kim (who also holds a joint appointment at the School of Energy Convergence) with Heejung Oh, Integrated Master's and Doctoral Program Student, as the first author, received support from the following programs: ▲ the Korea Technology Commercialization Promotion Agency's 'Fast-Track Commercialization of Next-Generation Promising Seed Technologies', ▲ Ministry of Education and Gwangju Metropolitan City's 'Regional Innovation-centered University Support System (RISE)', ▲ the Ministry of Trade, Industry and Energy and the Korea Institute for Advancement of Technology's 'Industrial Technology Innovation Program', and ▲ the Ministry of Science and ICT and National Research Foundation of Korea's 'Excellent·Young Research (Type B)'. The research results were published online on July 26 in the international journal Chemical Engineering Journal, specializing in materials science and chemistry.

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