Halogen-bond chemistry-rectified hypervalent tellurium redox kinetics towards high-energy Zn batteries†

Abstract

Hypervalent Te redox (Te⁰/Te⁴⁺) in ionic liquid electrolytes (ILEs) is promising for energetic Zn batteries. However, the energy contribution of Te⁰/Te⁴⁺ is only one-third of the total redox-amphoteric conversion, so the contribution should be maximized for energy upgradation. The underlying kinetics-limited factor is vital but usually overlooked in previous explorations. Herein, we unlock a halogen-bond chemistry-rectified Te⁰/Te⁴⁺ redox with an almost maximized contribution for 700 W h kg_Te⁻¹ Zn batteries. The Zn–X bond barriers in ZnX₄²⁻ (X = Cl, Br) species from ILEs play crucial roles in rectifying the Te⁰/Te⁴⁺ redox kinetics, especially in localized concentrated ILEs, resulting in sharply different redox conversion depths. When ZnBr₄²⁻ with a weak Zn–Br bond (34.96 kcal mol⁻¹) is used as the activator, the Te⁰/Te⁴⁺ redox contribution can be maximized to ∼90.0% over 5000 cycles at 5 A g⁻¹, 1.8-fold higher than that with the ZnCl₄²⁻ activator via the strong Zn–Cl bond (102.81 kcal mol⁻¹), and surpassing those in most aqueous systems (ca. 33.0%). This work decodes the halogen-bond chemistry-rectified kinetics to maximize the hypervalent redox contribution towards high-energy Zn batteries, which could apply to other chalcogen conversion batteries.