Anionically-reinforced nanocellulose separator enables dual suppression of zinc dendrites and polyiodide shuttle for long-cycle Zn-I2 batteries

As demand grows for safe and sustainable energy storage, zinc–iodine (Zn–I₂) batteries have emerged as a promising candidate due to their fast kinetics and low cost. However, zinc dendrite growth and polyiodide shuttle effects remain major barriers to long-term stability. Now, researchers from Nanjing Forestry University and Nanjing University, led by Prof. Jizhang Chen and Prof. Yagang Yao, have developed a straw-derived, anionically reinforced nanocellulose separator that effectively addresses both challenges.

Why This Separator Matters

• Dual Functional Design: Simultaneously suppresses zinc dendrite formation and polyiodide migration through electrostatic repulsion and enhanced ion transport.
• Sustainable & Scalable: Fabricated from renewable straw biomass using a simple solution-casting method—eco-friendly and cost-effective.
• Ultrathin & Strong: At just 20 μm thick, it offers 147 MPa tensile strength, outperforming conventional glass fiber separators.

Innovative Design and Features

• TOCN-A Structure: Combines TEMPO-oxidized cellulose nanofibers (TOCN) with anionic polyacrylamide (APAM) to boost negative charge density and mechanical integrity.
• Enhanced Zn²⁺ Transport: Achieves a Zn²⁺ transfer number of 0.45 and ionic conductivity of 14.3 mS cm^-1, promoting uniform zinc deposition.
• Polyiodide Blocking: Strong electrostatic repulsion reduces I₃⁻ migration by 81%, significantly improving cathode stability.

Applications and Performance

• Long Cycle Life: Zn//Zn symmetric cells run for >1800 h at 2 mA cm^-2/2 mAh cm^-2, and 300 h under extreme conditions (25 mAh cm^-2).
• High Stability: Zn–I₂ full cells retain 94.2% capacity after 10,000 cycles at 2 A g^-1, with ultralow decay rate of 0.0058‰ per cycle.
• Pouch Cell Validation: Demonstrates 99.4% capacity retention over 300 cycles and successfully powers LED panels and electronic devices.

Conclusion and Outlook

This work presents a multifunctional, biomass-derived separator that tackles both anode and cathode challenges in Zn–I₂ batteries.