A New Battery Separator Engineering Could Unlock Faster, More Stable Lithium-Metal Cells

Can a thin layer of material that sits between a battery’s electrodes help overcome two of the biggest obstacles facing next-generation lithium-metal batteries, preventing dangerous dendrite growth at the anode while allowing lithium ions to move quickly enough to improve the performance of high-nickel cathodes?

Researchers at South Korea’s Hanbat National University say they have found evidence that it can, developing a cellulose-based separator infused with the zeolite mineral bikitaite that they say improved the high-rate performance of lithium-metal batteries while stabilizing the lithium-metal anode.

The findings, published in Advanced Functional Materials, come as battery makers and researchers continue to seek higher energy density without sacrificing charging speed, durability and safety.

Lithium-ion batteries have become the dominant technology for electric vehicles and energy storage, but the industry is investigating alternatives and modifications that could store more energy in less space. Global deployment of lithium-ion batteries across applications increased more than sixfold between 2020 and 2025, according to the International Energy Agency, underscoring the scale of the market that researchers are seeking to improve.

Nickel-rich nickel-manganese-cobalt, or NMC, cathodes are attractive because they generally offer higher energy density than lithium iron phosphate batteries. The IEA said the latest NMC batteries can reach about 265 watt-hours per kilogram, compared with up to 205 Wh/kg for LFP cells, although LFP has captured more than half of the global electric-vehicle battery market because of its lower cost and other advantages.

Lithium-metal anodes offer an even larger theoretical capacity advantage over conventional graphite. But the technology has long been held back by instability at the lithium surface, including the formation of dendrites, needle-like structures that can damage the protective solid-electrolyte interphase, consume active lithium and, in some circumstances, penetrate the separator and trigger an internal short circuit. Researchers have studied separator engineering as one way to regulate lithium-ion movement and make lithium deposition more uniform.

The Hanbat team, led by Professor Sun-Yul Ryou of the university’s Department of Chemical and Biological Engineering, developed a separator called CBT by combining cellulose with bikitaite zeolite.

The researchers say the cellulose provides a porous and mechanically flexible structure, while bikitaite helps create pathways for lithium-ion transport and improves the separator’s interaction with the electrolyte. The paper was first published online on May 28, 2026, according to Wiley, and appears in Volume 36, Issue 54 of Advanced Functional Materials.

The CBT separator had an ionic conductivity of 3.45 × 10^-3 siemens per centimetre and a lithium-ion transference number of 0.742, according to the study. The authors said the combination helped reduce polarization and improve charge-transfer kinetics.

“Our results show that battery performance can be improved not only through new cathode and anode materials, but also through separator engineering,” Prof. Ryou told Impact Newswire.

The difference became larger as the discharge rate increased.

At 1C, cells using the CBT separator and a conventional polyethylene separator each delivered about 197 milliampere-hours per gram. At 2C, the figures were 187 and 165 mAh/g respectively. At 4C, the NCM90 cathode delivered 163 mAh/g with CBT, compared with 115 mAh/g with the conventional separator, an improvement of about 42%, the researchers said.

The result is significant because high-rate operation is one of the challenges for lithium-metal cells. Increasing the rate at which a battery is charged or discharged can intensify uneven ion transport and other electrochemical effects that degrade performance.

The researchers also examined what happened at the lithium-metal anode. They reported that cells using the CBT separator showed no visible dendrite growth during real-time observation. Instead, lithium formed a smoother and more compact layer, with more uniform stripping during discharge.

In lithium-metal/NCM90 full cells subjected to 2C charging and 4C discharge conditions, the cells retained about 60% of their capacity after around 2,500 cycles, according to the study. The separator also retained about 68.9% of its initial capacity after 150 cycles at minus 25 degrees Celsius, while maintaining its structural integrity at 200 degrees Celsius.

“What was particularly interesting was that the effect of the modified separator extended beyond the lithium-metal anode and significantly improved the high-rate performance of the NCM90 cathode,” explains Prof. Ryou.

The findings reflect a broader shift in battery research toward components that can improve several aspects of a cell at once. Separators have traditionally been viewed primarily as physical barriers that prevent the positive and negative electrodes from touching while allowing ions to pass through. But research has increasingly shown that their chemistry, pore structure and interaction with electrolytes can affect ion transport, rate performance, cycle life and safety.

That could make separator modifications an attractive development path because they may avoid some of the manufacturing changes required when replacing a cathode or anode material entirely. Ceramic-coated separators and other functional separator technologies are already being explored and used in commercial battery manufacturing.

Still, the Hanbat research remains at the laboratory stage. The study did not demonstrate commercial-scale manufacturing, and tests in larger formats such as pouch or cylindrical cells will be needed to determine whether the performance can be reproduced outside laboratory conditions.

Lithium-metal batteries have faced commercialization challenges for decades, despite their theoretical energy advantages. The underlying problem is not simply storing more lithium. It is maintaining stable interfaces and predictable ion transport over thousands of operating cycles.

“Functional separators should not be viewed only as barriers that separate the two electrodes or as a means of protecting the lithium-metal anode. By controlling ion transport across the cell, they could become an important design element for simultaneously achieving high energy density and high-rate operation in next-generation batteries,” Prof. Ryou explained.

The findings suggest that the next gains in battery performance may not come from continually redesigning the electrodes themselves. By changing how lithium ions move through the separator, researchers can potentially influence both sides of the cell at once, improving high-rate performance at the cathode while reducing the instability that has long complicated lithium-metal anodes. That makes separator engineering an increasingly important part of the push for batteries that combine higher energy density with faster operation and longer life.

But the path from a laboratory cell to a commercial battery remains a long one. The CBT separator still needs to demonstrate that its performance can be reproduced in larger, more complex cells and under the demanding conditions of mass production and everyday use. 

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