Lithium-metal batteries promise very high energy density, especially when paired with high-nickel cathodes such as NCM90. The bottleneck, however, is operation at high C-rates, where both the Li-metal anode and cathode suffer from transport limitations and polarization.
CBT: a cellulose–zeolite ion-guiding separator
A team led by Prof. Sun-Yul Ryou at Hanbat National University has developed a cellulose-based separator infused with bikitaite zeolite, termed CBT. The design combines:
- the porous network of cellulose, and
- the ion-conducting channels of bikitaite zeolite
to form interconnected pathways for Li⁺ transport across the separator. The CBT separator exhibits an ionic conductivity of 3.45 × 10⁻³ S/cm and a Li⁺ transference number of 0.742, enabling fast and more uniform ion flux, reduced polarization and improved reaction kinetics under high-rate conditions.
Dual benefit: cathode power and anode stability
In Li‖NCM90 cells, the impact on the cathode becomes more pronounced as the rate increases:
- 1C: CBT vs. PE – both ≈ 197 mAh/g
- 2C: CBT – 187 mAh/g, PE – 165 mAh/g
- 4C: CBT – 163 mAh/g, PE – 115 mAh/g → ~42% improvement
On the Li-metal side, in situ observation revealed no visible dendrite growth with CBT. Lithium deposited as a smoother, denser layer and was stripped more uniformly, indicating a stabilized solid electrolyte interphase (SEI) and more homogeneous current distribution.
The improved transport and interfaces translate into long-term durability. Under 2C charge / 4C discharge, Li‖NCM90 cells with CBT retained about 60% capacity after ~2,500 cycles. At −25°C, they preserved ≈68.9% of initial capacity after 150 cycles. The CBT separator also maintained structural integrity at 200°C.
A practical lever for future cell design
Unlike entirely new cathode or anode chemistries, functional separator modification is already compatible with commercial manufacturing (e.g., ceramic-coated separators). The work suggests that ion-transport-regulating separators like CBT could be a practical route to higher power and energy density in next-generation lithium-metal batteries, without overhauling existing electrode materials.
Source: Phys.org
