The key mechanism of twin-mediated microcracks in enhancing Mg anodes’ discharge behavior

Abstract

Optimizing the microstructural features of Mg anodes serves as a vital strategy to innovate high-performance Mg-air batteries. In this investigation, AZ31 magnesium anodes with different microstructures were prepared at four annealing temperatures, and their discharge behavior and surface morphology were systematically compared. The results indicated that, owing to its higher content of tensile twins, the sample heat-treated at 350 °C demonstrated superior discharge characteristics. When tested at a current density of 10 mA·cm −2 , this specific anode delivered a mean discharge voltage of 1.072 V alongside a 57.6% anode efficiency. Such enhanced performance was primarily linked to the proliferation of surface microcracks induced by tensile twins. These microcracks accelerated the reaction between the electrolyte and the underlying magnesium substrate, allowing more unreacted magnesium matrix to participate in the discharge process. In contrast, increased double twins caused a “block effect”, significantly degrading the discharge performance of the Mg anode. In addition to twins, a fine grain structure, non-basal grain orientation, low dislocation density, trace amounts of strip-like β-Mg 17 Al 12 phase, and a weakened basal texture all contributed positively to the discharge performance. The findings establish a theoretical basis for the microstructure design of high-performance magnesium anodes and contribute positively to the development of green energy storage technology.