KAIST

< Members of the research team, from left: Prof. Sarah Sunah Park, KAIST; Geunchan Park, doctoral student, POSTECH(co-first author); master graduate Gyuwon Lee, POSTECH (co-first author); Kangmin Kim, POSTECH (second author) >

Batteries that use water-based electrolytes have a relatively low risk of fire and are inexpensive, but they have faced limitations in storing large amounts of energy. KAIST researchers have succeeded in using a reaction previously regarded as a “troublemaker” that degrades battery performance to store more energy instead. This achievement opens up the possibility of next-generation water-based batteries capable of storing more energy while charging and discharging rapidly.

KAIST (President Choongsik Bae) announced on the 19th that a research team led by Sarah S. Park from the Department of Chemistry has developed a new electrode material that sequentially stores zinc ions (Zn²⁺) and protons. The material is based on a two-dimensional conductive metal–organic framework (MOF), a structure in which metals and organic molecules are connected to form microscopic pores.

Aqueous zinc-ion batteries use water-based electrolytes. An electrolyte is a substance that allows ions to move inside a battery. Because aqueous zinc-ion batteries have a relatively low risk of fire, are inexpensive, and impose a low environmental burden, they are attracting attention as a next-generation option for large-scale energy storage systems (ESS).

Because zinc ions carry electrical charge, are divalent ions and slow movement inside electrodes, making it difficult to achieve both high capacity and fast charge–discharge performance at the same time. Protons, by contrast, are extremely small and can move very quickly, making them an ideal charge carrier. However, when too many protons enter an electrode, byproducts form on the electrode surface, interfering with the movement of zinc ions and lowering battery performance. For this reason, protons have traditionally been regarded as “troublemakers” that degrade battery performance, and research has focused on suppressing their reactions.

< Figure 1. Conceptual diagram illustrating high-capacity energy storage achieved through sequential storage of zinc ions and protons within a 2D conductive MOF >

The research team took a different approach. Instead of suppressing proton reactions, the research team precisely controlled the order in which zinc ions and protons are stored so that both could be used for energy storage.

To accomplish this, they introduced amine functional groups into the micropores of a two-dimensional conductive MOF, designing the material so that it would react with protons only when a certain voltage was reached. By designing the amine functional groups to store protons only at a specific voltage, the researchers enabled zinc ions to be stored first, followed by the additional storage of protons.

The principle is similar to first placing large pebbles in an empty bottle and then filling the gaps between them with fine sand. The electrode is used more efficiently by storing the relatively large zinc ions first and then adding the smaller protons.

In practice, zinc ions were stored first in the higher-voltage range, while protons were additionally stored as the voltage decreased. In the Cu₃(HHTATP)₂ electrode material developed by the research team, zinc ions and protons participated in energy storage sequentially in different voltage ranges.

The sequence is particularly important. If protons react too early, by-products may form and obstruct the movement of zinc ions. By enabling protons to react only after the zinc ions had been stored, the researchers reduced interference between the two storage processes.

The newly developed electrode material achieved a high storage capacity of 368.7 mAh g⁻¹ at 0.5 A g⁻¹. In simple terms, this means that a small amount of electrode material can store a large amount of electricity.

Even when the charging and discharging rate was increased sixteenfold, the electrode retained 46.9% of its initial storage capacity—nearly half. Batteries generally store less energy as their charging and discharging rates increase, but the new electrode maintained substantial storage capacity even under rapid charging and discharging conditions. It also demonstrated stable performance after more than 500 rapid charge–discharge cycles.

Using various X-ray analysis techniques, the research team confirmed that zinc ions were stored first, followed by additional proton storage. The researchers also found that the process of storing and subsequently releasing protons could be repeated.

< Figure 2. Conceptual illustration of the research (AI-generated image) >

This study is significant because it overcomes the difficulty of simultaneously achieving high capacity and rapid ion transport in porous electrode materials. In particular, it presents a new direction for developing next-generation aqueous zinc-ion batteries by demonstrating that the storage sequence of different ions can be controlled through molecular-level design.

The findings present a new design approach that could enable safe and economical aqueous zinc-ion batteries to store more energy while charging and discharging rapidly. The approach is expected to help improve the performance of water-based batteries used in applications such as large-scale energy storage systems.

Professor Sarah S. Park from KAIST said, “This study demonstrates that protons, previously regarded as ‘troublemakers’ that could degrade battery performance, can instead be used to store more energy. We expect that applying this principle to various electrode materials will lead to the development of batteries capable of rapidly storing larger amounts of energy.”

POSTECH doctoral student Geunchan Park and master student Gyuwon Lee, participated as co-first authors. The study was published in the international chemistry journal Chem on July 7.

Paper title: Sequential Zn²⁺–H⁺ Storage in a 2D Conductive Metal–Organic Framework for Advanced Aqueous Zinc-Ion Battery
DOI: 10.1016/j.chempr.2026.103129

Author information: Geunchan Park (co-first author), Gyuwon Lee (co-first author), Kangmin Kim (second author), Sarah S. Park (corresponding author)

This research was supported by the Basic Research Program of the National Research Foundation of Korea and the National Supercomputing Center.