Chloride Chemistry in Multivalent‐Metal Batteries: From Interphase to Bulk Phase

Rechargeable magnesium (Mg) batteries are promising candidates for next-generation energy storage due to their high energy density, intrinsic safety, and earth-abundant Mg resources. However, their practical application is limited by sluggish desolvation and slow diffusion of divalent Mg²⁺. Here, amine-hydrochloride-based Mg electrolytes are designed to form favorable interphases and chloride-based channels. A ligand exchange strategy is proposed to simultaneously promote fast desolvation on interphases and rapid Mg²⁺ diffusion within cathodes. Detailed analysis reveals that the formation of the chloride-containing cathode-electrolyte interphases and the MgH₂-containing anode-electrolyte interphases are found to facilitate the desolvation process of solvated Mg²⁺. Moreover, the chloride-based channels significantly reduce the diffusion barriers of Mg²⁺ in Mo₆S₈ from 0.712 to 0.517 eV, demonstrating rapid Mg²⁺ diffusion kinetics. Consequently, Mo₆S₈-based full cells achieve a capacity retention of over 80% after 100 cycles at 1 C. Furthermore, this strategy is compatible with chloride-free electrolytes, the full-cells consisted of activated Mo₆S₈ cathode delivers a high specific capacity exceeding 90 mA h g^-1 and 80.3% retention after 900 h of cycling. It is also applicable to organic cathodes and Mo₆S₈-based calcium-metal full-cells. Overall, this work presents a generalizable strategy for designing high-energy-density rechargeable multivalent-metal battery systems.