New separator pushes lithium-metal battery capacity 42% higher at 4C, curbs dendrites

A new cellulose separator infused with bikitaite could help lithium-metal batteries handle rapid cycling while improving the performance of high-nickel NCM90 cathodes. Researchers in South Korea found that the separator boosted capacity at high discharge rates and helped prevent dendrite growth on the lithium-metal anode. The separator, called CBT, uses a porous cellulose structure combined with bikitaite, a zeolite mineral. Together, they create pathways that allow lithium ions to move more evenly through the cell. That is important for lithium-metal batteries, which can offer higher energy density than conventional lithium-ion cells but remain difficult to operate at high rates. Uneven lithium deposition can produce dendrites, while electrolyte degradation can reduce performance and increase the risk of short circuits. Researchers led by Professor Sun-Yul Ryou at Hanbat National University found that the modified separator also addressed a problem on the cathode side, where high discharge rates can cause a sharp drop in usable capacity. Ion pathways reshape battery speed The CBT separator recorded an ionic conductivity of 3.45 × 10⁻³ S cm⁻¹ and a lithium-ion transference number of 0.742. The researchers linked these properties to faster and more uniform ion transport, reducing polarization during demanding charge and discharge conditions. At 1C, cells using CBT and conventional polyethylene separators both delivered about 197 mAh g⁻¹. But the gap grew at higher rates. At 2C, CBT delivered 187 mAh g⁻¹, compared with 165 mAh g⁻¹ for the conventional separator. At 4C, the NCM90 cathode with CBT reached 163 mAh g⁻¹, while the conventional separator produced 115 mAh g⁻¹. That represents an improvement of about 42 percent, showing that the separator can influence cathode performance as well as anode stability. “Our results show that battery performance can be improved not only through new cathode and anode materials, but also through separator engineering. 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. Smoother lithium, longer cycling The separator also helped control lithium deposition. Real-time observations showed no visible dendrite growth in cells using CBT. Instead, lithium formed a smoother, more compact layer and was removed more evenly during stripping. The cells retained roughly 60 percent of their capacity after 2,500 cycles at 2C/4C. The separator also maintained about 68.9 percent capacity after 150 cycles at -25 °C (-13°F) and remained stable at 200 °C (392°F). The approach avoids redesigning electrodes and could potentially fit existing battery production lines. However, it still needs testing in commercial pouch and cylindrical cells. “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,” concludes Prof. Ryou. The study was published in the journal Advanced Functional Materials. Get the latest in engineering, tech, space & science - delivered daily to your inbox.With over a decade-long career in journalism, Neetika Walter has worked with The Economic Times, ANI, and Hindustan Times, covering politics, business, technology, and the clean energy sector. Passionate about contemporary culture, books, poetry, and storytelling, she brings depth and insight to her writing. When she isn’t chasing stories, she’s likely lost in a book or enjoying the company of her dogs.