KAIST professor Park Sun-a (from left), and POSTECH students Park Geun-chan, Lee Gyu-won and Kim Gang-min, who conducted the research. [KAIST]
KAIST professor Park Sun-a (from left), and POSTECH students Park Geun-chan, Lee Gyu-won and Kim Gang-min, who conducted the research. [KAIST]

Researchers have developed a new electrode material that turns protons — long considered a source of battery degradation — into an additional energy storage carrier.

The advance raises the prospect of commercializing next-generation aqueous zinc-ion batteries capable of storing more energy while charging and discharging rapidly.

KAIST announced Wednesday that a research team led by chemistry professor Park Sun-a has developed a new electrode material using a two-dimensional conductive metal-organic framework (MOF) — a structure in which metal atoms and organic molecules are linked to form tiny pores — that stores zinc ions and protons in sequence, with both contributing to energy storage inside the battery.

Aqueous zinc-ion batteries use a water-based electrolyte, the substance that allows ions to move within a battery. Because they carry a relatively low fire risk, cost less and impose a lighter environmental burden, they are drawing attention as a next-generation candidate for large-scale energy storage system (ESS) applications that store large amounts of electricity for use on demand.

Zinc ions carry a high charge, which makes them slow to move through an electrode and limits how much energy can be stored at fast charge-discharge rates. Protons, by contrast, are small and fast-moving, but excessive proton reactions generate byproducts that obstruct zinc-ion transport. For that reason, protons have until now been treated as a disruptive element that degrades battery performance, and research has focused on suppressing their reactions.

Rather than eliminating proton reactions, the research team chose to control the sequence in which zinc ions and protons are stored, allowing both to contribute to energy storage.

To achieve this, the team introduced amine functional groups — a type of binding site that captures protons — inside the electrode's tiny pores. By designing the amine groups to store protons at a specific voltage, the electrode first takes in zinc ions and then stores protons as an additional step.

A schematic of the new electrode material that stores zinc ions and protons in sequence. [KAIST]
A schematic of the new electrode material that stores zinc ions and protons in sequence. [KAIST]

In practice, zinc ions are stored first at higher voltages, and protons are stored additionally as the voltage drops further. In the team's electrode material, Cu₃(HHTATP)₂, zinc ions and protons participate in energy storage in sequence across distinct voltage ranges.

The electrode material recorded a high storage capacity of 368.7 mAh g⁻¹ at a current density of 0.5 A g⁻¹ — meaning a small amount of electrode material can store a large quantity of electricity.

Particularly notable is that even when the charge-discharge rate was increased 16-fold, the material retained 46.9 percent of its initial storage capacity — close to half. While batteries generally store less energy as charge-discharge speeds increase, this electrode maintained strong storage performance under fast cycling conditions. It also demonstrated stable performance after more than 500 rapid charge-discharge cycles.

"The design strategy proposed in this research can be applied not only to aqueous zinc-ion batteries but also to a wide range of aqueous energy storage systems," Park said. "In particular, the ability to use fast-moving protons as an additional charge carrier means this approach could be applied to high-power energy storage devices, large-scale power storage systems and next-generation eco-friendly battery development."

The findings were published in Chem, an international chemistry journal.


nbgkoo@heraldcorp.com