Dendrite Formation and Self‐Healing Mechanism in Ionic Liquid‐Based Magnesium Batteries

Magnesium (Mg) is set as a viable alternative battery material to lithium (Li) owing to its cost, natural abundance, and safety. Nevertheless, the formation of dendrites on Mg anodes remains controversial. While some studies refute their existence, others report contradictory findings influenced by current density and the insufficiently understood roles of electrolyte formulation, additives, and temperature. In this work, these parameters are systematically investigated using symmetric Mg|Mg and asymmetric Mg|TiS$_2$ cells with tailored ionic-liquid-based electrolytes. Furthermore, operando optical microscopy is employed to visualize nucleation and dendritic growth at different current densities. At low current densities (0.1–0.5 mA cm$^{−2}$), non-uniform island-like Mg deposits evolved into soft dendrites, finally leading to short-circuiting. Contrary, higher current densities (1–5 mA cm$^{−2}$) promote uniform, spherical deposits and facilitate stable cycling over 700 cycles. In Mg|TiS2 asymmetric cells, enhanced cycling stability is observed at 50 mA g$^{−1}$, whereas soft dendrite formation at 10 mA g$^{−1}$ leads to cell failure within 30 cycles. ... mehrTaking advantage of Mg's safety, cycling of symmetric cells are continued even beyond dendrite-forming to study morphological and mechanical recovery. Notably, our analysis reveales self-healing due to dendrite fusion in previously short-circuited cells. These findings reveal conditions affecting Mg dendrite behavior, highlighting the key roles of current density and temperature in developing stable, rechargeable Mg batteries, and reporting self-healing in Mg batteries for the first time.