Next-generation Mg-ion batteries design: do Cl-anions favor the Mg2+deposition?

Understanding the behavior of Mg(II) complexes in chloride-containing environments is essential for advancing magnesium-based electrochemical systems. In this study, we propose a model to elucidate the fundamental behavior of Mg(II) complexes near a pristine Mg(0001) surface in tetrahydrofuran (THF), with a focus on the role of Cl^-anions. We investigate the stability and deposition behavior of three representative coordination species: [Mg(THF)₅]²⁺, [MgCl(THF)₃]⁺, and [MgCl₂(THF)₂]. Our findings demonstrate that Cl^-shifts deposition potentials without significantly affecting kinetics at high concentrations, while trace amounts of Cl^-may slightly inhibit deposition. The proposed mechanism provides new insights into the speciation and electrochemical behavior of Mg(II) in chloride-containing THF, contributing to the development of more efficient Mg battery electrolytes.