This study addresses the challenge of developing high-performance cathodes for magnesium (Mg) batteries by unlocking the reversible four-electron Te³⁺/Te⁴⁺ conversion in elemental tellurium (Te). The researchers tailored the classic magnesium aluminum chloride complex (MACC) electrolyte by introducing Mg bis(trifluoromethanesulfonyl)imide (Mg(TFSI)), which initiates the Te³⁺/Te⁴⁺ conversion through two distinct charge-storage steps. The Te cathode undergoes a Te/TeCl₄ conversion involving Cl⁻ as charge carriers, with a tellurium subchloride phase as an intermediate. This results in a high specific capacity of 543 mAh/gTe⁻¹ and an energy density of 850 Wh/gTe⁻¹, outperforming most previously reported Mg-based cathodes. The addition of Mg(TFSI)₂ reduces ion-molecule interaction and mitigates ion-solvent aggregation, facilitating Cl⁻ dissociation from the electrolyte. Additionally, Mg(TFSI)₂ acts as a buffer to mitigate corrosion and passivation of Mg anodes caused by the consumption of MgCl₂ in the electrolyte. These findings provide crucial insights for the development of advanced Mg-based dual-ion batteries.This study addresses the challenge of developing high-performance cathodes for magnesium (Mg) batteries by unlocking the reversible four-electron Te³⁺/Te⁴⁺ conversion in elemental tellurium (Te). The researchers tailored the classic magnesium aluminum chloride complex (MACC) electrolyte by introducing Mg bis(trifluoromethanesulfonyl)imide (Mg(TFSI)), which initiates the Te³⁺/Te⁴⁺ conversion through two distinct charge-storage steps. The Te cathode undergoes a Te/TeCl₄ conversion involving Cl⁻ as charge carriers, with a tellurium subchloride phase as an intermediate. This results in a high specific capacity of 543 mAh/gTe⁻¹ and an energy density of 850 Wh/gTe⁻¹, outperforming most previously reported Mg-based cathodes. The addition of Mg(TFSI)₂ reduces ion-molecule interaction and mitigates ion-solvent aggregation, facilitating Cl⁻ dissociation from the electrolyte. Additionally, Mg(TFSI)₂ acts as a buffer to mitigate corrosion and passivation of Mg anodes caused by the consumption of MgCl₂ in the electrolyte. These findings provide crucial insights for the development of advanced Mg-based dual-ion batteries.