KAIST Develops Next-Generation Battery Component Using Protons

Protons, once considered 'troublemakers' within batteries, have become the key to energy storage. A research team led by Professor Park Sun-ah from the Department of Chemistry at KAIST announced on the 19th that they have developed an electrode material that sequentially stores zinc ions and protons by utilizing a two-dimensional conductive metal-organic framework (MOF). This research presents an approach to simultaneously increase the storage capacity and charge-discharge performance of aqueous zinc-ion batteries, which use water-based electrolytes.

Aqueous zinc-ion batteries are attracting attention as next-generation batteries for large-scale energy storage systems (ESS) due to their low fire risk, low cost, and minimal environmental burden resulting from the use of water-based electrolytes. However, zinc ions have a weakness: their large charge makes it difficult for them to move rapidly inside the electrode. Conversely, small and fast-moving protons would generate byproducts if they reacted excessively, blocking the movement of zinc ions. Consequently, existing research has focused on inhibiting proton reactions.

The research team flipped this approach. Instead of blocking protons, they regulated the storage sequence of zinc ions and protons, utilizing both ions for energy storage. They introduced amine functional groups to trap protons within the microscopic pores of the electrode, designing it so that protons are stored at a specific voltage. As a result, a structure was implemented where zinc ions are stored first in the high-voltage range, and protons are stored additionally when the voltage drops. By storing large zinc ions first and filling the remaining space with small protons, the electrode's storage efficiency was enhanced. In particular, the key is reducing the byproducts generated by premature proton reactions, preventing the storage processes of the two ions from interfering with each other. The research team also confirmed through various X-ray analyses that zinc ions are stored first, followed by protons, and that the storage and release of protons are repeatable.

The performance was also verified. The electrode material 'Cu₃(HHTATP)₂' developed by the team recorded a high storage capacity of 368.7 mAh g⁻¹ under 0.5 A g⁻¹ conditions. Even when the charge-discharge speed was increased 16-fold, it maintained 46.9% of its initial capacity, and it demonstrated stable performance even after repeating fast charge-discharge cycles over 500 times.

The results of this study were published in the international academic journal 'Chem' on the 7th of last month. The research overcame the limitation of simultaneously realizing high storage capacity and rapid ion movement in porous electrodes, demonstrating that the storage sequence of different ions can be controlled through molecular-level design.

"We have shown that protons, which were previously considered 'troublemakers' that could lower battery performance, can actually be utilized to store more energy," said Professor Park Sun-ah of the KAIST Department of Chemistry. "We expect to develop batteries that can store more energy quickly by applying this principle to various electrode materials."