Applications of halloysite in separators for secondary batteries

Secondary batteries have received extensive attention due to the increasing demand for electric vehicles, portable electronics, and energy storage systems. A separator, a critical component of a battery, prevents short circuits by physically blocking the anode and cathode while allowing ion transport for electrochemical reactions. Although often underestimated, the separator significantly impacts the electrochemical performance and stable operation of batteries. Halloysite nanotubes (HNTs), a naturally occurring clay material, offer unique structures, surface chemistry, and abundant availability, making them ideal for improving battery separators. This review explores recent studies on HNTs in battery separators, covering preparation and coating methods, and detailed characterizations in both Li-based and non-Li-based secondary batteries. The integration of HNTs in separators offers multiple benefits such as improved thermal stability, enhanced heat conduction, better electrolyte wettability and uptake, and reinforced mechanical strength. Additionally, HNTs effectively mitigate the shuttle effect in Li‑S batteries, suppress organic intermediate migration in Zn-organic batteries, and enhance long-term cycle stability across various battery systems. This comprehensive review demonstrates the significant impact of HNTs on battery technology and paves the way for potential future advancements in energy storage devices.