Sonochemically Prepared Nanodot Magnesium Fluoride‐Based Anodeless Carbon Substrate for Simultaneously Reinforcing Interphasial and Reaction Kinetics for Sulfide‐Based All‐Solid‐State Batteries

“Anodeless” electrodes for all‐solid‐state batteries (ASSBs) have been attracting attention as a solution for achieving high energy density. Recent studies on anodeless electrodes have shown improvements in cycle life and energy density through the stabilization of plated lithium (Li) using Li‐soluble metals (e.g., Ag, Zn, etc.). In this study, magnesium‐based materials (MgF2@C) are introduced for use as an anodeless electrode. Nanodot magnesium fluoride (MgF2) is synthesized onto a carbon black surface via sonochemical synthesis. MgF2 is converted to a Mg‐Li alloy and LiF during lithiation. The Mg‐Li alloy from the MgF2@C anodeless electrode reduces lithiation overpotential and provides a uniform and dense Li layer between the current collector and the anodeless electrode. The ASSB cell assembled with the MgF2@C anodeless electrode exhibits 81.4% capacity retention after 200 cycles at 30 °C. MgF2@C anodeless electrode is prepared for all‐solid‐state batteries. This MgF2@C prepared via sonochemical synthesis achieves enhanced dispersion of nanodot MgF2 on the carbon black surface. Mg‐Li alloy and LiF converted from MgF2 during the lithiation step improve charging kinetics. The anodeless electrode with MgF2@C shows lower overpotentials, and supeorio cycle life and rate capability compared to carbon black.