Origin of Phase Engineering CoTe2 Alloy Toward Kinetics-Reinforced and Dendrite-Free Lithium-Sulfur Batteries.

Abstract

Slow electrochemistry kinetics and dendrite growth are major obstacles for lithium-sulfur (Li-S) batteries. The investigations over the polymorph effect require more endeavors to further access the related catalyst design principles. Herein, the systematic evaluation of CoTe2 alloy with two polymorphs regarding sulfur reduction reaction (SRR) and lithium plating/stripping is reported. As disclosed by theoretical calculations and electrochemical measurements, the orthorhombic (o-) and hexagonal (h-) CoTe2 make a substantial difference. The reactivity origin of the CoTe2 polymorphs is explored. The higher position of d-band centers for the Co atoms on the o-CoTe2 leads to a higher displacement of the antibonding state; the lower antibonding state occupancy, the more effective the interaction with the sulfide moieties and lithium. Hence, o-CoTe2 annihilates h-CoTe2 and exhibits better catalysis and more uniform lithium deposition, consolidated by excellent performance of full cell made of o-CoTe2 . It keeps stable charging/discharging for 800 cycles at 0.5 C with only 0.055% capacity decay per cycle and even achieves an areal capacity of 6.5 mAh cm-2 at lean electrolyte and high sulfur loading of 6.4mg cm-2 . This work establishes the mechanistic perspective about the catalysts in Li-S batteries and provides new insight into the unified solution.