Batteries have become an essential part of modern life, powering smartphones, electric vehicles, and countless other devices. Despite their importance, traditional batteries face significant challenges: high costs, as well as the risk of fire or explosion. Solid-state batteries have long been considered a safer alternative, but their widespread adoption has been limited by the need to balance safety, performance, and affordability.

Recently, a research team from South Korea demonstrated that the performance of solid-state batteries can be significantly improved through thoughtful structural design, without resorting to expensive metals.

Breakthrough in Solid-State Battery Design

On January 7, KAIST announced a major achievement by a team led by Professor Dong-Hwa Seo from the Department of Materials Science and Engineering. Researchers from Seoul National University, Yonsei University, and Dongguk University also participated in the project. Together, they developed a new approach to designing key materials for solid-state batteries, enabling the use of affordable components without compromising performance or safety.

Why Solid Electrolytes Are Safer but Harder to Optimize

Conventional lithium-ion batteries use a liquid electrolyte that allows lithium ions to move quickly between electrodes. In solid-state batteries, this component is replaced by a solid material, which greatly enhances safety. However, lithium ions move more slowly through solids, and previous attempts to speed up this process often required expensive metals or complex technologies.

Crystal Chemistry to Accelerate Lithium Movement

To address this challenge, the scientists focused on improving the movement of lithium ions through solid electrolytes. Their strategy involved introducing so-called "divalent anions"—such as oxygen and sulfur. These elements become part of the crystal structure of the electrolyte, allowing researchers to alter the pathways for ion movement within the material.

The team applied this approach to affordable zirconium-based halide solid electrolytes. By carefully adding divalent anions, the researchers were able to precisely tune the internal structure of the material. This "framework regulation mechanism" widens the channels for lithium ion movement and lowers energy barriers, enabling ions to travel faster and more efficiently.

Modern Methods to Confirm Effectiveness

To verify the structural changes and their impact on lithium ion mobility, the team used advanced analytical techniques:

• High-energy synchrotron X-ray diffraction (Synchrotron XRD)
• Pair distribution function (PDF) analysis
• X-ray absorption spectroscopy (XAS)
• Density functional theory (DFT) modeling to study electronic structure and diffusion

These methods allowed for a detailed examination of how the crystal structure changes and how this affects lithium ion mobility.

Boosting Performance with Affordable Materials

Tests showed that adding oxygen or sulfur to the electrolyte increased lithium ion mobility by 2–4 times compared to standard zirconium electrolytes. This demonstrates that solid-state batteries can achieve the performance levels needed for practical use without relying on costly materials.

At room temperature, the oxygen-enhanced electrolyte reached an ionic conductivity of about 1.78 mS/cm, while the sulfur version achieved around 1.01 mS/cm. Values above 1 mS/cm are considered sufficient for real-world battery applications.

Moving Toward Smarter Battery Design

Professor Dong-Hwa Seo noted that this research offers a design principle that can simultaneously improve the cost and performance of solid-state batteries using inexpensive raw materials. According to him, the potential for industrial application is very high. Lead author Jae-Seung Kim emphasized that this work marks a shift in battery research—from simply choosing new materials to creating more advanced structures.

In summary, this innovative approach to structural design paves the way for the development of safe, efficient, and affordable solid-state batteries for widespread use.