Temperature Dependence of Fe Nucleation Behavior and Electrochemical Performance in Aqueous Fe Metal Batteries

Aqueous Fe metal batteries are considered promising for electrical energy storage because of their affordability, operational safety, and eco-friendliness. Fe deposition and dissolution at room temperature have been widely studied. Nevertheless, the early nucleation and growth behavior of Fe metal at different temperatures remains largely unexplored. In this work, the nucleation and growth of Fe on a Cu substrate are systematically investigated over a temperature range of 20-60 °C. Low temperature favors the formation of small, dense Fe nuclei with an average equivalent grain size of 0.99 ± 0.46 μm (20 °C). In contrast, elevated temperature induces vertical Fe growth, forming larger particles and facilitating dendrite formation, with the average equivalent grain size increasing to 2.18 ± 0.87 μm (60 °C). Furthermore, increased temperature aggravates the hydrogen evolution reaction and surface oxidation, reducing current efficiency and covering active sites, which leads to a reduction in the cycle life of a Fe || Cu half-cell. The temperature-switching experiments showed that Fe dendrites formed at 60 °C could be effectively eliminated by low-temperature treatment (20 °C), restoring a uniform deposition surface and improving cycling stability. This work provides a fundamental understanding of temperature-dependent Fe electrodeposition and offers a reversible strategy for stabilizing Fe anodes under variable thermal conditions.