Lithium-metal battery with capacity retention of 88% over 1,000 cycles

Lithium-metal batteries are widely considered one of the most promising successors to today’s lithium-ion technology. With the potential to deliver significantly higher energy density, they could unlock longer-range electric vehicles and more compact energy storage systems. However, safety and long-term stability have historically limited their commercial viability.

Researchers in Germany now report a significant step forward. Scientists from the Karlsruhe Institute of Technology (KIT) and the Helmholtz-Institut Ulm (HIU) have developed a lithium-metal battery configuration that achieves 88 percent capacity retention after 1,000 charge cycles and an energy density of 560 watt-hours per kilogram.

This combination of high energy density and long cycle life addresses two of the most persistent barriers in lithium-metal battery development.

Why Lithium-Metal Batteries Matter

Lithium-metal batteries replace the graphite anode used in lithium-ion batteries with pure lithium metal. This change dramatically increases theoretical energy density, making lithium-metal systems attractive for electric vehicles, aviation, and advanced energy storage.

Despite this promise, lithium-metal batteries often suffer from instability at the electrode interfaces. Side reactions, dendrite growth, and structural degradation reduce cycle life and raise safety concerns. Solving these issues is essential for moving lithium-metal batteries from laboratory prototypes to commercial products.

The Role of Nickel-Rich NCM88 Cathodes

The German research team based their battery on a low-cobalt, nickel-rich layered cathode known as NCM88, a member of the nickel manganese cobalt oxide (NMC) family.

Nickel-rich cathodes are known for delivering high energy density, but they are also more chemically reactive and mechanically fragile. In conventional electrolytes such as LP30, these cathodes often develop particle cracks during cycling. According to HIU professor Stefano Passerini, the electrolyte penetrates these cracks, triggering destructive reactions that form thick, moss-like lithium-containing layers on the cathode surface.

These reactions degrade structural integrity and are a key reason why nickel-rich lithium-metal batteries struggle to achieve long cycle life.

Why Conventional Electrolytes Fall Short

Traditional organic electrolytes, such as LP30, are widely used in commercial lithium-ion batteries but are not optimized for lithium-metal systems. Their volatility and chemical reactivity can accelerate degradation when used with high-voltage cathodes and lithium-metal anodes.

This instability is one of the main factors preventing lithium-metal batteries from reaching technical and commercial maturity. Addressing electrolyte behaviour is therefore just as important as improving electrode materials.

Introducing a Dual-Anion Ionic Liquid Electrolyte

To overcome these challenges, the research team replaced conventional electrolytes with a low-volatility, non-flammable ionic liquid electrolyte (ILE). Ionic liquid electrolytes are known for their thermal stability, reduced flammability, and strong electrochemical performance.

The newly developed electrolyte incorporates two anions:

• bis(fluorosulfonyl)imide (FSI)
• bis(trifluoromethanesulfonyl)imide (TFSI)

This dual-anion design plays a critical role in stabilizing both the cathode and the lithium-metal anode during repeated cycling.

How the CEI Layer Improves Stability

One of the most important outcomes of the new electrolyte formulation is the formation of a stable cathode-electrolyte interphase (CEI) layer on the NCM88 cathode surface.

This protective CEI layer shields the cathode from harmful reactions with the electrolyte, preventing microcrack formation and structural degradation. By maintaining the cathode surface's integrity, the battery can cycle repeatedly without significant capacity loss.

The dual-anion ionic liquid electrolyte also shows strong compatibility with lithium metal, reducing unwanted side reactions at the anode and improving overall cell efficiency.

Performance Results That Mark a Breakthrough

The resulting lithium-metal battery demonstrated impressive electrochemical performance. According to the research team, the cell achieved an initial specific capacity of 214 mAh g⁻¹ and maintained 88 percent capacity retention after 1,000 cycles.

The battery also delivered an average Coulombic efficiency of 99.94 percent, indicating highly efficient charge and discharge behaviour with minimal energy loss.

High Coulombic efficiency is especially critical for lithium-metal batteries, as even small inefficiencies can lead to rapid degradation over time. These results suggest the new electrolyte significantly reduces structural changes in the nickel-rich cathode and stabilizes long-term performance.

Implications for Future Energy Storage

If scalable, this lithium-metal battery architecture could significantly impact next-generation energy storage. High energy density, combined with long cycle life, enables lighter electric vehicles with extended driving range and fewer battery replacements over their lifetimes.

Improved safety from non-flammable electrolytes further strengthens the case for lithium-metal batteries in demanding applications. As battery research continues to focus on performance, safety, and sustainability, electrolyte innovation will remain a critical driver of progress.

Organizations focused on advanced energy storage solutions closely monitor breakthroughs like this as part of the broader evolution beyond conventional lithium-ion technology.

Final Thoughts

Lithium-metal batteries have long promised superior energy density, but instability and degradation have hindered their commercialization. The work by KIT and the Helmholtz-Institut Ulm demonstrates that combining nickel-rich cathodes with advanced ionic-liquid electrolytes can significantly improve cycle life and efficiency.

At LINIOTECH, developments such as these underscore the importance of material innovation, electrolyte engineering, and system-level design in shaping the future of energy storage. As lithium-metal technology continues to mature, breakthroughs like this bring high-performance, long-life batteries closer to real-world deployment.

FAQs

What makes lithium-metal batteries different from lithium-ion batteries?

Lithium-metal batteries use pure lithium metal as the anode rather than graphite, thereby significantly increasing energy density. This allows batteries to store more energy in less space, making them attractive for electric vehicles and advanced energy storage systems. However, lithium-metal batteries require advanced materials and electrolytes to maintain long-term stability and safety.

Why is capacity retention necessary in lithium-metal batteries?

Capacity retention shows how well a battery maintains its ability to store energy over repeated charge cycles. High capacity retention means the battery degrades more slowly, lasts longer, and delivers more consistent performance. Achieving 88 percent retention after 1,000 cycles represents a significant improvement for lithium-metal technology.

How does the new electrolyte improve lithium-metal battery performance?

The ionic liquid electrolyte used in this research reduces unwanted chemical reactions between the electrolyte and the electrodes. Its low volatility and non-flammable nature enhance safety, while the dual-anion design facilitates the formation of a stable protective layer on the cathode. This prevents microcracks and structural damage that typically reduce battery lifespan.

Are lithium-metal batteries safe for commercial use?

Lithium-metal batteries have historically faced safety challenges due to dendrite formation and electrolyte instability. Advances such as non-flammable ionic-liquid electrolytes and stable interphase layers significantly enhance safety. While more scaling and testing are needed, these developments move lithium-metal batteries closer to safe commercial deployment.

How does this research impact future energy storage solutions?

This research demonstrates that lithium-metal batteries can achieve both high energy density and long cycle life when paired with the right materials. For companies like LINIOTECH, such breakthroughs signal meaningful progress toward next-generation energy storage systems that are lighter, longer-lasting, and more efficient than current lithium-ion technologies.