Tellurium: A High-Performance Cathode for Magnesium Ion Batteries Based on a Conversion Mechanism.

Magnesium ion batteries (MIBs), due to the low redox potential of Mg, high theoretical capacity, dendrite-free magnesiation, and safe nature, have been recognized as a post-lithium energy storage system. However, an ongoing challenge, sluggish Mg 2+ kinetics in the small number of available cathode materials of MIBs, restricts its further development. The existing cathodes mostly deliver unsatisfactory capacity with poor cycling life based on the traditional ion-intercalation mechanism. Herein, we fabricated a conversion-type Mg∥Te battery based on a reversible two-step conversion reaction (Te to MgTe 2 to MgTe). High discharge capacities (387 mAh g -1 ) and rate capability (165 mAh g -1 at 5 A g -1 ) can be achieved. The diffusivity of Mg 2+ can reach 3.54 × 10 -8 cm 2 s -1 , enabled by the high electrical conductivity of Te and increased surface conversion sites. Subsequently, ab initio molecular dynamics simulation was also carried out to further confirm the conversion mechanism and fast Mg 2+ transportation kinetics.