Initiating Reversible Aqueous Copper-Tellurium Conversion Reaction with High Volumetric Capacity through Electrolyte Engineering.

Pursuing conversion-type cathodes with high volumetric capacity that can be used in aqueous environments remains rewarding and challenging. Tellurium (Te) is a promising alternative electrode due to its intrinsic attractive electronic conductivity and high theoretical volumetric capacity yet still to be explored. Herein, for the first time, the kinetically/thermodynamically co-dominat copper-tellurium (Cu-Te) alloying phase conversion process and corresponding oxidation failure mechanism of tellurium were disclosed using in situ synchrotron X-ray diffraction and comprehensive ex situ characterization techniques. By virtue of the fundamental insights into the tellurium electrode, facile and precise electrolyte engineering (solvated structure modulation or reductive anti-oxidant addition) was implemented to essentially tackle the dramatic capacity loss in tellurium, affording reversible aqueous Cu-Te conversion reaction with an unprecedented ultrahigh volumetric capacity of up to 3927 mAh cm -3 , a flat long discharge plateau (capacity proportion of ∼81%), and an extraordinary level of capacity retention of 80.4% over 2000 cycles at 20 A g -1 of which lifespan thousand-fold longer than Cu-Te conversion using CuSO 4 -H 2 O electrolyte. This work paves a significant avenue for expanding high-performance conversion-type cathodes towards energetic aqueous multivalent-ion batteries. This article is protected by copyright. All rights reserved.