Integrating inorganic Zn-ion conductor with nanocellulose towards separator-free and long-life aqueous zinc ion batteries.

Aqueous zinc-ion batteries (AZIBs) have emerged as a promising energy storage system due to their inherent safety, cost-effectiveness, large power density, and environmental sustainability. However, the widespread adoption of AZIBs is impeded by critical challenges associated with zinc anodes, including uncontrolled dendrite growth, hydrogen evolution, and corrosion, as well as the reliance on thick separators that reduce the battery's energy density. To overcome these limitations, this study introduces a separator-free AZIB design featuring a multifunctional protective coating composed of zinc monofluorophosphate and nanocellulose on the Zn electrode. The hybrid coating with a low thickness of 15 μm serves a dual purpose, not only mitigating dendrite formation and parasitic reactions but also eliminating the need for conventional separators. The electrochemical characterization reveals that the hybrid coating enables superior corrosion resistance, extended electrochemical stability window, improved Zn ion transport, facilitated desolvation process, lowered overpotential, and uniformized Zn deposition. Thanks to these benefits, the Zn//Zn cell offers a long life span up to 1200 h at 10 mA cm and 2 mAh cm, and the full battery delivers great rate capability and cycling stability even under a low negative-to-positive capacity ratio. This work provides an appropriate solution to the development of high-energy-density and durable AZIBs.