Fluoride-based solid electrolyte surpasses voltage limits

In a major advancement for energy storage technology, Professor Yoon Seok Jung and his team at Yonsei University reveal a new fluoride-based solid electrolyte that enables all-solid-state batteries (ASSBs) to operate beyond 5 volts safely.

Their paper, published in Nature Energy, addressed a long-standing barrier in battery science, achieving high voltage stability without sacrificing ionic conductivity.

As Prof. Jung explains, “Our fluoride solid electrolyte, LiCl–4Li₂TiF₆, opens a previously forbidden route for high-voltage operation in solid-state batteries, marking a true paradigm shift in energy storage design.”

For decades, battery engineers have sought to enhance energy density by increasing voltage, but conventional solid electrolytes, such as sulfides and oxides, tend to break down above 4 V.

The team overcame this limitation by developing a fluoride solid electrolyte (LiCl–4Li₂TiF₆) that remains stable beyond 5 V and exhibits a Li⁺ conductivity of 1.7 × 10^-5 S/cm at 30°C, one of the highest in its class.

This innovation allows spinel cathodes such as LiNi_0.5Mn_1.5O₄ (LNMO) to operate safely and efficiently, even under demanding cycling conditions. When applied as a protective coating on high-voltage cathodes, LiCl–4Li₂TiF₆ effectively suppresses interfacial degradation between the cathode and the electrolyte.

The result showed a battery that retains over 75% capacity after 500 cycles and supports an ultrahigh areal capacity of 35.3 mAh/cm², a record-setting figure for solid-state systems. The team also demonstrated practical adaptability in pouch-type batteries. This is the same format used in electric vehicles and consumer electronics, showing exceptional performance consistency.

Beyond material innovation, the work lays the foundation for a transformative battery design model. The fluoride-based shield introduced by the researchers not only enhances electrochemical stability but also allows compatibility with cost-effective halide catholytes such as Zr-based systems.

This combination could drastically reduce material costs while improving safety and longevity, which are two of the biggest challenges for commercial ASSB technology.

In conclusion, this research holds immense potential—from enabling electric vehicles with longer driving ranges to advancing large-scale renewable energy storage. By utilizing abundant and low-cost materials, it supports the global shift toward sustainable, carbon-neutral energy systems.

Prof. Jung notes, “This research goes beyond a single material; it defines a new design rule for building safe, durable, and high-energy batteries that can truly power the future.”

This breakthrough represents a significant leap toward cleaner and more resilient energy solutions, bridging the gap between laboratory innovation and real-world applications, and laying the groundwork for the next generation of sustainable technology.