New design paves way for cheaper, safer solid-state batteries

Batteries play a critical role in everyday life, from powering smartphones to enabling electric vehicles.

Despite their importance, today's batteries still come with major drawbacks, including high costs and the risk of fires or explosions. 

All-solid-state batteries have long been viewed as a safer alternative, but progress has been slowed by the challenge of balancing safety, performance, and affordability. 

Now, a research team in South Korea has shown that battery performance can be significantly improved through smart structural design alone, without relying on expensive metals.

On 7 January, KAIST announced a breakthrough by a research team led by Professor Dong-Hwa Seo from the Department of Materials Science and Engineering. 

Researchers developed a new design approach for key all-solid-state battery materials that uses inexpensive raw ingredients while maintaining strong performance and a lower risk of fire or explosion.

Why solid electrolytes are safer but harder to optimise
Traditional lithium-ion batteries depend on a liquid electrolyte that allows lithium ions to move between electrodes. All-solid-state batteries replace this liquid with a solid electrolyte, which greatly improves safety. 

However, lithium ions move more slowly through solids, and past efforts to speed them up often depended on costly metals or complicated manufacturing techniques.

Using crystal chemistry to speed up lithium movement
To solve this problem, the researchers focused on improving how lithium ions travel through solid electrolytes. Their strategy centred on the use of "divalent anions" such as oxygen and sulphur. 

These elements influence the crystal structure of the electrolyte by becoming part of its fundamental framework, which can change how ions move inside the material.

The team applied this idea to low-cost zirconium (Zr)-based halide solid electrolytes. By carefully introducing divalent anions, they were able to precisely adjust the internal structure of the material. 

This approach, known as the "Framework Regulation Mechanism," expands the pathways available to lithium ions and reduces the energy needed for them to move. 

As a result, lithium ions can travel more quickly and efficiently through the solid material.

Performance gains using inexpensive materials
Tests showed that adding oxygen or sulphur to the electrolyte increased lithium-ion mobility by two to four times compared with conventional zirconium-based electrolytes. This improvement indicates that solid-state batteries can reach performance levels suitable for real-world use without relying on expensive materials.

At room temperature, the oxygen-doped electrolyte achieved an ionic conductivity of about 1.78mS/cm, while the sulphur-doped version reached approximately 1.01mS/cm. 

Ionic conductivity measures how easily lithium ions move through a material, and values above 1 mS/cm are generally considered adequate for practical battery applications at room temperature.

Shifting battery innovation toward smarter design
Professor Dong-Hwa Seo explained the broader significance of the work, saying, "Through this research, we have presented a design principle that can simultaneously improve the cost and performance of all-solid-state batteries using cheap raw materials. 

“Its potential for industrial application is very high." 

Lead author Jae-Seung Kim emphasised that the study highlights a shift in battery research, moving attention away from simply choosing new materials and toward designing better structures.