Development of a Janus cellulose separator with dielectric effect modulation using 2D perforated titania nanosheet for zinc batteries

Aqueous zinc-ion batteries (AZIBs) are promising candidates for grid-scale energy storage owing to their inherent safety, low cost, and use of environmentally benign materials. However, the practical deployment of Zn metal anodes remains hindered by dendritic growth, hydrogen evolution, and passivation effects, which compromise cycling stability and coulombic efficiency. Herein, we report the development of a Janus-structured cellulose-based membrane functionalized with 2D perforated holey titania (HT) nanosheets to address these persistent challenges. The symmetric membrane architecture, with HT nanosheets imbedded in polymethylcellulose (PMC) scaffold, combines the advantages of high dielectric constant modulation and directional Zn ²⁺flux regulation. Electrochemical analysis revealed that the incorporation of HT on Janus-structured cellulose-based membrane enhanced its interfacial stability, lower overpotential, and suppressed Zn dendrite formation. The content of HT (1 %,2 % and 3 %) was evaluated and the results showed that 2 % HT membrane exhibit uniform Zn plating/stripping for over 5000 h in symmetric Zn||Zn cells at 2 mA cm ⁻², outperforming both pristine PMC and higher HT-loading variants. Furthermore, Zn//V ₂O ₅full cells with the Janus separator deliver excellent rate capability and long-term cycling retention, demonstrating 98 % coulombic efficiency over 2000 cycles at 0.5 A g ⁻¹. This work highlights the synergistic impact of dielectric tuning and interface engineering in separator design and provides a scalable strategy for realizing durable aqueous Zn metal batteries.