This study presents a novel magnesium (Mg)-tellurium (Te) dual-ion battery by unlocking the reversible four-electron Te⁰/Te⁴⁺ conversion in elemental Te. The key innovation lies in modifying the classic magnesium aluminum chloride complex (MACC) electrolyte by introducing Mg bis(trifluoromethanesulfonyl)imide (Mg(TFSI)₂), which enables the two-step Te⁰/TeCl₄ conversion. This conversion involves Cl⁻ as charge carriers and generates a tellurium subchloride phase as an intermediate. The Te cathode achieves a high specific capacity of 543 mAh g⁻¹ and an outstanding energy density of 850 Wh kg⁻¹, outperforming most previously reported cathodes. The addition of Mg(TFSI)₂ reduces ion-molecule interactions and mitigates ion-solvent aggregation in the MACC electrolyte, facilitating Cl⁻ dissociation and enabling the Te⁰/Te⁴⁺ conversion. Additionally, Mg(TFSI)₂ acts as an effective buffer to mitigate Mg anode corrosion and passivation caused by electrolyte MgCl₂ consumption. The study also demonstrates that the Te cathode undergoes Te/TeCl₄ conversion with Cl⁻ as charge carriers, and the Te electrode exhibits excellent cyclability when combined with a graphite oxide (GO)-coated separator. The Te electrode achieves a high energy density of 850 Wh kg⁻¹, comparable to the best reported conversion-type S cathode, and significantly higher power density. The study provides crucial insights into the development of advanced Mg-based dual-ion batteries, highlighting the importance of anion charge carriers in enhancing conversion kinetics and battery performance. The findings demonstrate that the Te⁰/Te⁴⁺ conversion is a promising approach for high-performance Mg//Te dual-ion batteries.This study presents a novel magnesium (Mg)-tellurium (Te) dual-ion battery by unlocking the reversible four-electron Te⁰/Te⁴⁺ conversion in elemental Te. The key innovation lies in modifying the classic magnesium aluminum chloride complex (MACC) electrolyte by introducing Mg bis(trifluoromethanesulfonyl)imide (Mg(TFSI)₂), which enables the two-step Te⁰/TeCl₄ conversion. This conversion involves Cl⁻ as charge carriers and generates a tellurium subchloride phase as an intermediate. The Te cathode achieves a high specific capacity of 543 mAh g⁻¹ and an outstanding energy density of 850 Wh kg⁻¹, outperforming most previously reported cathodes. The addition of Mg(TFSI)₂ reduces ion-molecule interactions and mitigates ion-solvent aggregation in the MACC electrolyte, facilitating Cl⁻ dissociation and enabling the Te⁰/Te⁴⁺ conversion. Additionally, Mg(TFSI)₂ acts as an effective buffer to mitigate Mg anode corrosion and passivation caused by electrolyte MgCl₂ consumption. The study also demonstrates that the Te cathode undergoes Te/TeCl₄ conversion with Cl⁻ as charge carriers, and the Te electrode exhibits excellent cyclability when combined with a graphite oxide (GO)-coated separator. The Te electrode achieves a high energy density of 850 Wh kg⁻¹, comparable to the best reported conversion-type S cathode, and significantly higher power density. The study provides crucial insights into the development of advanced Mg-based dual-ion batteries, highlighting the importance of anion charge carriers in enhancing conversion kinetics and battery performance. The findings demonstrate that the Te⁰/Te⁴⁺ conversion is a promising approach for high-performance Mg//Te dual-ion batteries.