Seoul, South Korea – Researchers at Yonsei University have announced a groundbreaking advancement in battery technology, developing a novel fluoride-based solid electrolyte that enables all-solid-state batteries (ASSBs) to safely operate beyond the long-standing 5-volt limit. This breakthrough, led by Professor Yoon Seok Jung and his team, overcomes a critical hurdle in energy storage, paving the way for significantly higher energy density, enhanced safety, and extended lifespan in future batteries for electric vehicles, consumer electronics, and renewable energy systems. The findings were published in the prestigious journal Nature Energy on October 3, 2025.
The Breakthrough: LiCl–4Li₂TiF₆ Fluoride Electrolyte
For decades, battery engineers have grappled with the inherent instability of conventional solid electrolytes, such as sulfides and oxides, which tend to break down at voltages exceeding 4 volts. This limitation has severely restricted the energy density and overall performance of solid-state batteries.
Professor Jung’s team, in collaboration with researchers from Dongguk University and KAIST, engineered a new fluoride-based solid electrolyte, specifically identified as LiCl–4Li₂TiF₆. This innovative material demonstrates remarkable stability, maintaining its integrity and high lithium-ion conductivity even when operating beyond 5 volts. “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,” explained Professor Jung.
Why 5 Volts Matters for Battery Performance
Breaking the 5-volt barrier is a monumental achievement in battery science, directly translating to a substantial increase in energy density. The higher the voltage a battery can safely withstand, the more energy it can store within the same volume or weight. This directly impacts the performance of devices and vehicles:
- Electric Vehicles (EVs): Longer driving ranges and faster charging capabilities become more attainable.
- Consumer Electronics: Devices could feature extended battery life without an increase in size.
- Renewable Energy Storage: More efficient and compact storage solutions for solar and wind power grids are possible.
Enhanced Stability and Durability
Beyond merely achieving high voltage, the new LiCl–4Li₂TiF₆ electrolyte significantly enhances the overall stability and durability of ASSBs. The team found that when applied as a protective coating on high-voltage spinel cathodes, such as lithium nickel manganese oxide (LNMO), the fluoride electrolyte effectively suppresses interfacial degradation between the cathode and the electrolyte. This prevention of detrimental chemical reactions is crucial for maintaining battery longevity and performance over numerous charge-discharge cycles.
In practical tests, batteries incorporating this fluoride electrolyte retained over 75% of their capacity after 500 cycles. Furthermore, they achieved an ultra-high areal capacity of 35.3 mAh/cm², setting a new record for solid-state systems. The innovation also demonstrated practical adaptability in pouch-type batteries—the same format used in electric vehicles and consumer electronics—showing exceptional performance consistency.
A Paradigm Shift in Battery Design
Professor Jung emphasizes that this breakthrough represents more than just a new material; it lays the foundation for a transformative battery design model. The concept of using a fluoride-based solid electrolyte as a protective interface introduces a novel dimension to battery architecture, balancing electrochemical performance with crucial aspects like durability and safety.
The fluoride-based shield not only improves electrochemical stability but also enables compatibility with cost-effective halide catholytes, such as Zr-based systems. This compatibility could lead to a significant reduction in material costs, while simultaneously enhancing safety and longevity, which are critical challenges for the commercialization of ASSB technology.
This research marks a significant stride toward the next generation of energy storage, promising safer, denser, and longer-lasting batteries that could seamlessly integrate into electric transportation, grid storage, and portable electronics.
