Tellurium: A High-Volumetric-Capacity Potassium-Ion Battery Electrode Material.

: Currently, exploring high-volumetric-capacity electrode materials that allow for reversible (de-)insertion of large-size K+ ions remains challenging. Tellurium (Te) is a promising alternative electrode for storage of K+ ions due to its high volumetric capacity, confirmed in lithium-/sodium-ion batteries, and the intrinsic good electronic conductivity. However, the charge storage capability and mechanism of Te in potassium-ion batteries (KIBs) have not been unveiled until now. Here, a novel K-Te battery is constructed, and the K+ -ion storage mechanism of Te is revealed to be a two-electron conversion-type reaction of 2K + Te ↔ K2 Te, resulting in a high theoretical volumetric capacity of 2619 mAh cm-3 . Consequently, the rationally fabricated tellurium/porous carbon electrodes deliver an ultrahigh reversible volumetric capacity of 2493.13 mAh cm-3 at 0.5 C (based on Te), a high-rate capacity of 783.13 mAh cm-3 at 15 C, and superior long-term cycling stability for 1000 cycles at 5 C. This excellent electrochemical performance proves the feasibility of utilizing Te as a high-volumetric-capacity active material for storage of K+ ions and will advance the practical application of KIBs.